TAB planning begins with design functions, because most of the devices required for adjustments are integral parts of the design and installation. To ensure that proper balance can be achieved, the engineer should show and specify a sufficient number of dampers, valves, flow measuring locations, and flow-balancing devices; these should be properly located in required straight lengths of pipe or duct whenever possible for accurate measurement. Testing depends on system characteristics and layout. Interaction between individual terminals varies with pressures, flow requirements, and control devices.

The design engineer should specify balancing tolerances. Minimum flow tolerances are ±10% for individual terminals and branches in noncritical applications and ±5% for main air ducts. For critical water systems where differential pressures must be maintained, tolerances of ±5% are suggested. For critical air systems, recommendations are the following:

Balancing Devices. Balancing devices should be used to provide maximum flow-limiting ability without causing excessive noise. Flow reduction should be uniform over the entire duct or pipe. Single-blade dampers or butterfly balancing valves are not acceptable for use as balancing devices because of the uneven flow pattern at high pressure drops. Pressure drop across equipment is not an accurate flow measurement but can be used to determine whether the manufacturer design pressure is within specified limits. Liberal use of pressure taps at critical points is recommended.

Normal design minimizes conditions causing air turbulence, to produce the least friction, resistance, and consequent pressure loss. Under some conditions, however, air turbulence is desirable and necessary. For example, two airstreams of different temperatures can stratify in smooth, uninterrupted flow conditions. In this situation, design should promote mixing. Return and outdoor airstreams at the inlet side of the air-handling unit tend to stratify where enlargement of the inlet plenum or casing size decreases air velocity. Without a deliberate effort to mix the two airstreams (e.g., in cold climates, placing the outdoor air entry at the top of the plenum and return air at the bottom of the plenum to allow natural mixing), stratification can be carried throughout the system (e.g., filter, coils, eliminators, fans, ducts). Stratification can freeze coils and rupture tubes, and can affect temperature control in plenums, spaces, or both.

Stratification can also be reduced by adding vanes to break up and mix the airstreams. No solution to stratification problems is guaranteed; each condition must be evaluated by field measurements and experimentation.

Airflow-measuring instruments should be field verified by comparing to pitot tube traverses to establish correction and/or density factors.

Check correction factors given by air diffuser manufacturers by field measurement and comparing them to actual flow measured by pitot tube traverse.

A capture hood is frequently used to measure device airflows. Correction factors should be established by field measurement and comparison to actual flow measured by pitot tube traverse for hood measurements with varying flow and deflection settings.

Rotating vane anemometers are commonly used to measure airflow from sidewall grilles. Effective areas (correction factors) should be established with the face dampers fully open and deflection set uniformly on all grilles. Correction factors are required when measuring airflow in open ducts (i.e., damper openings and fume hoods [Sauer and Howell 1990]).

The preferred method of measuring duct volumetric flow is the pitot tube traverse average as detailed in ASHRAE Standard 111. When using airflow measuring stations, these airflow measurements should be checked against a pitot tube traverse.

Power input to a fan’s driver should be used as only a guide to indicate its delivery; it may also be used to verify performance determined by a reliable method (e.g., pitot tube traverse of system’s main) that considers possible system effects. For some fans, the flow rate is not proportional to the power needed to drive them. In some cases, as with forward-curved-blade fans, the same power is required for two or more flow rates. The backward-curved-blade centrifugal fan is the only type with a flow rate that varies directly with power input.

If an installation has an inadequate straight length of ductwork or no ductwork to allow a pitot tube traverse, follow Sauer and Howell’s (1990) procedure: use a vane anemometer to read air velocities at multiple points across the face of a coil to determine loss coefficient.

Measured air pressures include barometric, static, velocity, total, and differential. For field evaluation of air-handling performance, pressure should be measured per ASHRAE Standard 111 and analyzed together with manufacturers’ fan curves and system effect as predicted by AMCA Standard 210. When measured in the field, pressure readings, air quantity, and power input often do not correlate with manufacturers’ certified performance curves and proper correction is necessary.

Pressure drops through equipment such as coils, dampers, or filters should not be used to measure airflow. Pressure is an acceptable means of establishing flow volumes only where it is required by, and performed in accordance with, the manufacturer certifying the equipment.

Inclined Manometer. The inclined manometer is made of a single tube, inclined (usually 10:1 slope), to enlarge the reading. Alcohol or special oils are normally used in place of water. Such oils have a lower specific gravity than water which serves to further enlarge the reading. Manometers using these fluids have scales calibrated in in. of water corresponding to the pressure indicated on the oil of a known specific gravity. Recommended for use with pitot tubes or static pressure probes.

The combination vertical-inclined manometer is constructed of an inclined fluid column with a scale of 0 to 1.0 or 2.0 in. of water connected to a vertical fluid column with scales of 5 or 10 in. of water. Recommended for use with pitot tubes or static pressure probes.

Limitations:

Pitot Tube. A pitot tube, used in conjunction with a manometer, provides a basic method of determining the air velocity within a duct. The typical pitot tube is of a double concentric tube construction, consisting of an 1/8 in. OD inner tube concentrically located inside a 5/16 in. OD outer tube that measures total pressure. The outer static tube has eight equally spaced 0.04 in. diameter holes around the circumference of the outer tube, located 2.5 in. back from the nose or open end of the pitot tube tip. At the base (tube connection) end, the inner tube is open ended, as is the head. The outer tube has a side outlet tube connector perpendicular to the outer tube, directly parallel with and in the same direction as the head end of the pitot static tube. Recommended for measuring an airstream’s

When used with a manometer or micromanometer, the pitot tube is very reliable and rugged. Its use as a direct measurement tool is preferred over many other methods for the field measurement of air velocity, system total air, outdoor air, return air quantities, fan static pressure, fan total pressure, and fan outlet velocity pressures where such measured quantities may be required and within the range or capabilities of the instrument.

Instruments that may be used with the pitot static tube include the following:

Limitations:

Accuracy of field measurement. Rigorous error analysis shows that flow rate determinations by the pitot static tube and manometer combination method can range from 5 to 10% error. Experience shows that qualified technicians can obtain measurements within 5 and 10% accuracy of actual flow under good field conditions. It has also been determined that suitable traverse conditions do not always exist, and measurements can then exceed a ±10% error rate.

Chronometric Tachometer. The chronometric tachometer is a hand-held instrument that combines an accurate timer and a revolution counter. After the instrument tip is placed on the rotating shaft, pushing the stopwatch button simultaneously activates the counter and the stopwatch. After the timer has run for either 3 or 6 s, the instrument stops counting revolutions even though it is still in contact with the rotating shaft. The scale is calibrated to give readings directly in rpm. Instrument accuracy is within ±0.5% of full scale. Hand tachometers (e.g., dial face [Eddy current], solid-state with digital readout) can produce instantaneous rpm measurement readings, with accuracy within ±1% of full scale. Tachometers are recommended for determining the speed of any shaft having a countersunk end.

Limitations:

Accuracy of field measurements. Accuracy is within one-half of a scale division mark.

Clamp-on Volt-Ammeter. This instrument has trigger-operated, clamp-on transformer jaws that allow current readings without interrupting electrical service. Most volt-ammeters have several scale ranges, in amperes and volts. Two voltage test leads are furnished that may be quick-connected to the bottom of the volt-ammeter opposite the end used for measuring current. Some models have a built-in ohmmeter. Instrument accuracy is within ±3% of full scale. Recommended for measuring operating voltages and currents of electric motors and of electric resistance heating coils.

Limitations:

Accuracy of field measurements. Accuracy is ±3% of full scale.

Anemometers. There are several types of anemometers. The deflecting vane anemometer consists of a pivoted vane enclosed in a case. As it passes through the anemometer, air exerts a pressure on the vane. Movement of the vane is resisted by a hairspring. The instrument gives instantaneous readings of directional velocities on an indicating scale, and can be supplied with various remote- and direct-connected measuring tips (jets). Recommended for measuring air quantities through both supply and return air terminals using the proper air terminal factor A_k (effective area) for airflow calculation, as well as for indicating low velocities (100 to 300 fpm) where the instrument case itself with the appropriate probe attached is placed in the airstream.

Limitations:

Accuracy of field measurements. Accuracy is within ±10% when the instrument is calibrated and used in accordance with the manufacturers’ recommendations. Air inlet and outlet device flow A_k factors are a function of duct and damper conditions, which affect velocity immediately before the device. Use under conditions not identical to the manufacturers’ test conditions produces measurement error. The instrument must be calibrated in the field for correction factor by pitot tube traverse within the limitations of the system.

The revolving vane or propeller anemometer can be either mechanical or direct-reading digital. For the mechanical type, a mechanical propeller or revolving vane anemometer consists of a light wind-driven wheel connected through a gear train to a set of recording dials that read the linear feet of air passing through the wheel in a measured length of time. The instrument is made in various sizes, but 3, 4, and 5 in. are the most common. Each instrument requires individual calibration. The required instrument accuracy of calibration is 1 to 3% of scale (using a corrective chart). Recommended for measuring supply, return, and exhaust air quantities at air inlets and outlets, as well as air quantities at the faces of return air dampers or openings, total air across the filter or coil face areas, etc.

The direct-reading digital type differs from the mechanical type mainly in that it uses a powered electronic circuit to convert a pulse generated by the rotating vane into a small electric current to give a meter reading calibrated directly in air velocity units. Generally, these instruments have microprocessor software to compensate for any nonlinearity. Recommended for measuring supply, return, and exhaust air quantities at air inlets and outlets; air quantities at the faces of return air dampers or openings; total air across the filter or coil face areas, etc.

Limitations:

Accuracy of field measurements:

Operation of the thermal anemometer, which can be either single point or omnidirectional, depends on the fact that the resistance of a heated element changes with its temperature. As airflows over the element in the probe, the temperature of the element changes from its temperature in still air. The resistance change is indicated as a velocity on the indicating scale of the instrument. Instruments are available using a heated thermocouple, heated thermistor, or a heated wire. They have similar characteristics regarding uses, limitations, and accuracy. Some instruments are also provided with temperature scales that can be used by setting the proper selector button. Others can measure static pressure with provided accessories. Recommended uses include measuring the following:

Limitations:

Accuracy of field measurements. Accuracy is ±3% above 100 fpm. The instrument must be calibrated in the field for correction factor by pitot tube traverse within the limitations of the system.

Thermometers. Dial thermometers are of two general types: stem and flexible capillary. Their dial heads can be 1 3/4 to 5 in., with stainless steel encapsulated temperature sensing elements. Hermetically sealed, they are rust-, dust-, and leakproof and are actuated by sensitive bimetallic helix coils. Some can be field calibrated. Sensing elements range in length from 2 1/2 to 24 in. and are available in many temperature ranges with or without thermometer wells.

Small dial thermometers usually use a bimetallic temperature-sensing element in the stem. Temperature changes cause a change in the twist of the element, and this movement is transmitted to the pointer by a mechanical linkage.

The flexible capillary dial thermometer has a rather large temperature-sensing bulb connected to the instrument with a capillary tube. The instrument contains a Bourdon tube, the same as in pressure gages. The temperature sensing system, consisting of the bulb, capillary tube, and Bourdon tube, is charged with either liquid or gas. Temperature changes at the bulb cause the contained liquid or gas to expand or contract, resulting in changes in the pressure exerted within the Bourdon tube. This causes the pointer to move over a graduated scale as in a pressure gage, except that the thermometer dial is graduated in degrees. The advantage of this type is that it can be used to read temperature in a remote location. In using a dial thermometer, the stem or bulb must be immersed a sufficient distance to allow this part of the thermometer to reach the temperature being measured.

Recommended uses include checking both air and water temperature in ducts and pipe thermometer wells.

Limitations:

Accuracy of field measurements. Accuracy is within one-half of a scale division mark.

There are four basic types of digital electronic thermometers: thermocouple, thermistor, resistance temperature detector (RTD), and diode sensors. They consist of a portable, handheld, battery-powered, digital thermometer connected by a short cable to various interchangeable probes that are designed for sensing the temperature of air or other gases, immersion in liquids, or contact with a solid surface. Some instruments have a calibration reference, which allows calibrating out offsets introduced by mechanical shocks, ambient temperature variations, or component drift. Some instruments can switch between I-P and SI units and between resolutions of 0.1 and 1.0. Response times are 1 to 10 s for liquids and solids, and 5 to 50 s for gases. Instrument accuracy is ±0.5°F where the range is below 700°F and ±1.5°F for broader ranges. The lower-range instruments should be used unless the expected measurements will be out of their range.

Recommended uses include all TAB temperature measurements, including air and other gases, liquids, and surfaces of pipes and other components with the appropriate probe. The manufacturers’ directions must be followed regarding proper use of probe and maximum allowable temperature for the probe and or thermometer. Equipment is available to measure from –380 to 2250°F. A common range is +14 to +248°F.

Limitations:

Accuracy of field measurements. When properly used, the instrument accuracy shall be attainable in the field.

Pyrometers. Pyrometers normally used in measurements of surface temperatures in heating and air conditioning applications use a thermocouple as a sensing device and a millivoltmeter (or potentiometer) with a scale calibrated for reading temperatures directly. A variety of types, shapes, and scale ranges are available. The required instrument test accuracy is ±1% of full scale. Recommended uses include

Limitations. In piping applications, remember that the surface temperature of the conduit is not equal to the fluid temperature, and that a relative comparison is more reliable than an absolute dependence on readings at a single circuit or terminal unit.

Accuracy of field measurements. Accuracy is within one-half of a scale division mark.

Calibrated Pressure Gage. Test gages should be at least Grade A quality; have Bourdon tube assemblies made of stainless steel, alloy steel, monel, or bronze; and have a nonreflecting white face with black lettering conforming to ASME Standard B40.1-1985. Test gages are usually 3.5 to 6 in. in diameter, with bottom or back connections. Many dials are available with pressure, vacuum, or compound ranges. Minimum accuracy is within 1% of full scale. Recommended uses are checking pump pressures; coil, chiller, and condenser pressure drops; and pressure drops across orifice plates, venturis, and other flow calibrated devices.

Limitations:

Accuracy of field measurements. Accuracy is within one-half of a scale division mark.

Differential Pressure Gage. This instrument is a dual-inlet, Grade A, dual Bourdon tube pressure gage with a single indicating pointer on the dial face that indicates the pressure differential between two measured pressures. It can be calibrated in psi, in. of water, or in. of mercury. The required instrument accuracy minimum is ±1% of full scale. At lower differential pressure ranges, recommended for use with water hose flexible connectors for water distribution balancing (similar to how a mercury U-tube manometer is used). At higher differential pressure ranges, these instruments can be used in lieu of the two combination high-pressure gages mounted on the mercury U-tube manometer board.

Limitations:

Accuracy of field measurements. Within one-half of a scale division mark.

Differential Pressure Manifold Gage. This is a single-port, Grade A, Bourdon tube, calibrated test gage attached to the bull of a tee. Each branch is fitted with a tight shutoff ball valve and a length of hose, terminating in a union and nipple for attachment to a conventional gage port at each measuring point. Recommended use is to indicate pressure at each point by alternating valve opening and closing. Using a single gage eliminates potential error from using two separate permanently mounted gages, which are subject to possible vibration damage and differences in calibration.

Calibration is required. Readings must be verified with a recently calibrated instrument on each project. If the reading is not within ±2% of the recently calibrated instrument, have the pressure gage recalibrated by a qualified testing lab.

Revolution Counter (Odometer) and Timing Device. The revolution counter is a small handheld counting device that is pressed to the center of a rotating shaft for a period of 30 to 60 s. Reasonable accuracy can be obtained by using a good watch with a sweep second hand or a digital watch if a stopwatch is not available. Recommended use is for determining shaft speed on any shaft having an accessible shaft end with a countersink.

Limitations:

Accuracy of field measurement. Accuracy is ±2%, when used properly.

Electronic Tachometer (Stroboscope and Photoelectric). The stroboscope has a controlled high-speed electronic flashing light whose frequency is electronically controlled and adjustable. When the frequency of the flashing light is adjusted to equal the frequency of the rotating machine, the machine appears to stand still. This unit need not be in contact with the machine during use. Instrument accuracy is generally within 1.5% of the indicated value, and within 1% if a magnetic pickup is used.

The solid-state photoelectric tachometer is an optional instrument that is pointed at the device to be measured and the revolution speed is directly read on the dial face. A reflective paint or material must be spotted on the rotating device; this spot is counted and electronically integrated over time to give an instantaneous reading. The instruments usually have several ranges, and no electrical or physical contact with the device is necessary. Accuracy is within ±1% of the dial scale reading when properly calibrated.

Recommended use is for measuring rotational speeds when instrument contact with the rotating equipment is not feasible.

Limitations:

Accuracy of field measurements. Accuracy is within one-half of a scale division.

Dual-Function Tachometer. This instrument provides both optical and contact measurements of rotation and linear motions. Many allow a choice of ranges, depending on the application. A digital display always indicates the unit of measurement to identify the operating range. A memory button may be used to recall the last, maximum, minimum, and average readings. Compact size and light weight make for easy operation. Recommended use is for measuring rotation speeds by direct contact or by counting the speed of a reflective mark.

Limitations:

Accuracy of field measurements. Accuracy is within one-half of a scale division.

Low-Density Fluid U-Tube Manometer. The manometer is a simple, useful way to measure partial vacuum and pressure. In its simplest form, it consists of a U-shaped glass tube partially filled with liquid; a difference in height of the two fluid columns denotes a pressure difference in the two legs. Recommended uses include measuring pressure drops above 1.0 in. of water across filters, coils, eliminators, fans, grilles, and duct sections; and measuring low manifold gas pressures.

Limitations:

Diaphragm-Type Differential Pressure Gage. A dry diaphragm-operated differential pressure gage that uses a calibrated spring-loaded horseshoe magnet lever operated from the differential pressure on the diaphragm, causing rotation of a highly magnetic permeable helix that positions a pointer on the pressure scale. The pressure gage is operated by magnetic field linkage only, so it is extremely sensitive and accurate; its construction design makes it resistant to shock and vibration. The helix rotates on antishock-mounted sapphire bearings. A zero-calibration screw is located on the plastic cover. Common ranges are 0 to 0.5, 1.0, or 5.0 in. of water. There are approximately 30 available pressure ranges. The minimum accuracy of the instrument is ±2% of full dial range. Recommended for use with pitot tube or with static probe, or with specially constructed induction unit primary air total pressure measuring tip for primary air distribution balancing on high-pressure induction systems.

Limitations:

Smoke Devices. These devices are generally used in special studies of airflow and duct leakage. Candles are available in various sizes and durations of burning time. The chemical element in the smoke is zinc chloride.

Sticks are activated by crushing the end of the device, releasing a smoke stream approximately double that of a cigarette. Guns generally use a chemical that readily combines with atmospheric moisture. A cartridge produces 500 to 1000 puffs of smoke, or releases the same quantity in a steady stream. Borazine guns emit dense white clouds of smoke that tend to remain suspended in air for some time. A valve adjustment regulates the discharge.

Recommended uses include determining the direction and observing the velocity and pattern of airflow in room studies, hoods, filters, etc. Discharge patterns from exhaust systems, driers, hoods, and stacks can be identified.

Limitations:

Flow Capture Hoods. A conical or pyramid shaped hood may be used to collect the airflow from a terminal and guide it over a flow measuring system which reads directly in cubic feet per minute. The instrument can be a swinging vane anemometer, differential pressure air gage (diaphragm type), manometer, or thermal anemometer. The balancing cone should be tailored for the particular job. The large end of the cone should be sized to fit over the complete air inlet or outlet device and should have a seal to eliminate air leakage. The cone should terminate in a straight section with factory designed and calibrated pressure grids, straighteners, and instruments.

Recommended uses include proportionally balancing air distribution devices.

Limitations:

Accuracy of field measurements. If the hood is properly shaped and positioned at the air terminal, accuracy of field measurements will be within the limitations of the flow reading instrument.

Micromanometer (Hook Gage). These instruments are designed to read small differences in air pressure accurately and usually have a wide scale range. Most scales read pressures of 0 to 4 in. of water, in hundredths of an inch of water on the vertical scale, and thousandths of an inch of water on a vernier scale.

Different versions of this instrument exist. The most common type contains two glass vials about 2 to 3 in. in diameter. A pointed needle or hook is positioned by a micrometer adjustment until the point dimples the water surface but does not break the surface tension. The difference in level is determined in micrometer readings.

Another variation of this instrument has a single vial or well and an inclined scale. The well is positioned by a micrometer or vernier adjustment. It is very important that all micromanometers, including the electronic units, be accurately leveled.

The solid-state electronic hook gage will measure positive, negative, or differential pressures to ±0.00025 in. of water over a 0 to 2 in. of water range. It can also be used with pitot tubes for accurate measurement of air velocities as low as 350 fpm. Recommended uses include readings at hoods, perforated ceilings, etc.; calibrating other instruments; and measurements of velocities between 450 and 600 fpm, when used with a standard pitot tube.

Limitations:

Double Reverse Tube. Other names for this device include impact reverse tube, combined reverse tube, and type S tube. It consists of two stainless steel tubes approximately 0.38 in. OD, permanently joined lengthwise. The tubes open facing opposite directions at the probe end with open ends at the base for connection to a manometer. (See Figure 1.) Recommended for use in dirty or wet airstreams where the amount of particulate matter in the airstream impairs the use of a pitot static tube. The instrument can be used to measure total pressure, static pressure, and obtain velocity pressure.

Limitations:

Accuracy of field measurements. Accuracy for field use of the combination of a double reverse tube with manometers is ±10%.

Clamp-On AC Power Meter (Wattmeter). The clamp-on type power meter has trigger-operated, clamp-on transformer jaws, like a voltammeter. This instrument measures true rms voltage and current, in addition to power in single phase or balanced three phase circuits. Compared with mean value measurement, true rms measurement is especially valuable for distorted waves, such as noise and multiplexed signals. Typical ranges are 20 to 600 V rms, 2 to 200 A rms, and 2 to 200 kW; or 20 to 600 V rms, 0.2 to 20 A rms, and 0.2 to 20 kW. Recommended uses include measurement of single, split-phase, and three-phase power sources. Given motor efficiency and power factor, power draw can be related to motor brake horsepower on a fan or pump curve and the operating point determined.

Limitations:

Accuracy of field measurements. Accuracy is within ±1% of reading plus 0.5% of range

Recording Instruments. Recording instruments exist in wide variety, available to record any measurement taken by an instrument, such as dry-bulb temperature, wet-bulb temperature, relative humidity, and operating periods of cycling electrical equipment. The recording charts may be either continuous strip or circular, with chart rotation once every 24 h or 7 days. Some instruments are available with one or more remote bulbs. Recommended for obtaining round-the-clock data on the operation or performance of equipment. They are particularly useful for studying and diagnosing questionable operation in refrigerators, greenhouses, processing rooms, ovens, and comfort air conditioning systems.

Limitations. Some judgment must be used in the application of recording instruments. There are great differences in quality, accuracy, and cost. Care must be used to start the instrument at the correct time of day, and on the right day when a seven-day chart is used. Calibration is required. Readings must be verified with a recently calibrated instrument on each project. If the reading is not within ±2% of the recently calibrated instrument, have the pressure gage recalibrated by a qualified testing lab.

Accuracy of field measurements. Carefully study the manufacturer catalog data for instrument accuracy. It is important to read and observe specific operating instructions to obtain the published accuracy from a given instrument.

Humidity-Measuring Devices. A number of instruments are available to measure the level of moisture in air, including

Calibration is required. Readings must be verified with a recently calibrated instrument on each project. If the reading is not within ±2% of the recently calibrated instrument, have the instrument recalibrated by a qualified testing lab.

Recommended use varies by type; hygrometers give direct, rapid relative humidity readings, and digital psychrometers provide dry- and wet-bulb depression within approximately 30 s.

Accuracy of field measurements. Hygrometers have an accuracy of ±2 to 3% rh in the 20 to 95% rh range. Psychrometer thermometer readings have an accuracy of ±0.5°F.

Barometer. A barometer measures atmospheric pressure, which is required to correct all airflow readings to standard conditions. A Bourdon tube type with accuracy of 1% of full scale should be used.

Barometric pressure information may also be obtained from weather radio stations or airports in the immediate vicinity. Actual pressure at local elevation must be used for air density calculations.

Fluid System Digital Electronic Differential Pressure Meter. This instrument measures the differential pressure across an element in a system when flow is present, providing digital readings in the range of 3.6 to 600 in. of water. Some instruments include a temperature probe for a range of 32 to 248°F, hoses with snap-on fittings, and automatic air purging. A computer is available for calculating the flow in a range of 0.2 to 4750 gpm and computing the hand wheel setting of compatible valves by proportional balancing procedures. Maximum working pressures can be up to 300 psig.

Recommended uses include measurement of fluid flow, temperature, and differential pressure, as well as computing the setting of compatible valves by proportional balancing procedures.

Limitations:

Accuracy of field measurements. Accuracy of differential pressure within 12 in. of water or 2% of valve readout (whichever is greater). This same accuracy is true for measurement of flow, done via the computing feature.

Electronic Differential Pressure Meter. This instrument is a portable device which measures differential pressure and gives a digital readout directly in pressure or velocity. Some instruments are also available with adapters and probes to measure flow and temperature. Typical ranges are 0 to 100 in. of water for low-density fluids, and 0 to 2400 in. of water or 0 to 100 psi for high-density fluids. Temperatures can be measured from –55 to 250°F. Recommended for use with a pitot tube, static probe, flow grid, orifice plate, or special balancing valve. Some instruments can also be combined with a flow-measuring hood. Many instruments have memories, averaging capabilities, and printers.

Limitations:

Accuracy of field measurements. Experience shows that qualified technicians can obtain measurements that range between ±5 and 10% accuracy under good field conditions. However, good field conditions do not always exist, and measurements can easily exceed ±10% error.

Ultrasonic Flowmeters. This is a device that determines flow through the use of acoustic signals, measured in design units (e.g., gallons per minute). The ultrasonic flow metering station is either an integral part of the piping system or a strap-on meter. In either case, there is no intrusion into the pipe or liquid flow that would generate a pressure drop. There are no moving parts in the flow to maintain or service. Two distinct types of ultrasonic flow meters exist: a transit-time device for HVAC or clear water measurement, and a Doppler-effect device for flows containing a required volume of particulate in the liquid. Recommended use includes measurement of flow in full pipes; these devices are excellent when low or nonexistent pressure drop is a requirement. These are best for larger pipes, and most manufacturers’ specifications are based on flows of 1 fps or greater.

Limitations:

Accuracy of field measurements.

Doppler Flowmeters:

Transit-Time Flowmeters:

Turbine Flowmeter. This mechanical device uses a wheel placed in the path of the flow. Liquid causes the wheel to turn at speeds relative to the velocity, generating a signal and providing flow information directly in design units (e.g., gallons per minute) or a milliamp output. Recommended for measurement of flow in pipes with clean fluid flow.

Limitations:

Accuracy of field measurements. Accuracy is within 2%.

Permanently Installed Airflow Measuring Stations. There are two main types of permanent airflow measuring stations. The velocity pressure array comprises a fixed array of velocity pressure measuring devices.

Recommended uses. These stations measure the fan total airflow and distribution of air in branch ducts. Other useful measurements include those of outdoor, return, and relief airflow.

Limitations:

Accuracy of field measurements. Under ideal conditions, a velocity pressure airflow measuring station should produce an accuracy of ±5% plus the error rate of the pressure sensor. Because of sensitivity to disturbances and duct conditions, the manufacturer’s duct placement recommendations or ASHRAE Handbook—Fundamentals requirements for measurement with technologies based on velocity-pressure equalizing principles should be observed.

The thermal dispersion array airflow measuring station obtains velocity measurements directly using independent measurement points in a fixed array before averaging. Communications options allow technicians to download instantaneous point velocity and temperature data independently from the control system. A remote traverse without time lag between samples is possible either using an infrared reading device or over an RS-485 network using BACnet™ or Modbus^® protocols. The independent nature of the sensor data allows for accurate duct area averaging.

Recommended uses:

Limitations:

Accuracy of field measurements. Accuracy should be within ±3% of reading, when placement is within the manufacturer’s guidelines.

Multifunction Portable Instruments. Digital electronic instruments are available with a wide selection of probes that can be fitted into the various channel ports of a single handheld meter with various uses, accuracies, and limitations. These uses can be singular (e.g., thermohygrometers for temperature and relative humidity) or many. Types of measurements include temperature of air, gas, and liquids with a wide choice of sensing elements, such as thermocouples or RTDs; pressure of air, gas, and liquids with manometers or pitot tubes; differential air pressure, static pressure, or barometric pressure; and differential water pressure or gage pressure. Amongst the specific tools used are wind vane, hot wire, or pitot tube anemometers; optical, inductive, and rotational tachometers; and water and air quality attachments for pH, conductivity, salinity, and mV, O₂, and ion concentration.

Some instruments have both battery and plug-in AC power; recording memory for downloading onto computers or transmission over RS-232 or RS-500 interface; hold, alternating, and averaging circuits for applications as traverses; relative humidity calibrating devices; and other features.

Individual manufacturers must be consulted for details of accuracy, limitations, usage, and response times of the individual measurements.

Instruments should be calibrated in accordance with ASHRAE Standard 111 to verify their accuracy and repeatability before use in the field.

Before air system testing, adjusting, and balancing, obtain and verify the following:

Perform the following in accordance with design documents before beginning air system testing, adjusting, and balancing:

Perform the following tests and adjustments before beginning the air system balancing:

The following steps occur after all air terminal devices and related air inlet or outlet devices are balanced:

Sensible Heat

where

ΔT

=

dry-bulb temperature difference between air entering and air leaving the coil. In applications where cfm to conditioned space must be calculated, ΔT is the difference between supply air dry-bulb temperature and room dry-bulb temperature, °F

Total Heat Air-Side

where

4.5	=	conversion factor, 60 min/h × 0.075 lb/ft3
Δhtot	=	change in total heat content of supply air (enthalpy), in Btu/lb (from wet-bulb temperatures and psychrometric chart or table of properties of mixtures of air and saturated water vapor)

Total Heat Water-Side

where

500	=	conversion factor, 60 min/h × 8.33 lb/gallon × 1 Btu/lb · °F
ΔTw	=	temperature difference between the entering and leaving water, °F

Traverse Procedure. After the air system has been prepared, balance by the procedures set forth. Note: When system characteristics prevent design flow rates, balance the system components to equal percentages of design unless otherwise instructed by the design engineer.

Balancing Submain Air Ducts.

Balancing Branch Air Ducts. Balance the airflow in each branch duct by the following procedure:

Balancing Air Terminal Device Flow Rates. After obtaining the required airflow rates in submain and branch ducts, balance each air terminal device by the following procedures:

Final Adjusting and Balancing. Upon completion of the preceding steps, obtain final measurements as follows:

Air-Side Systems. In addition to the applicable procedures already detailed, the following air-side systems require additional balancing procedures as indicated. Note: For systems using fan volume controls, balance at less than 100% volume setting to allow for future pressure loss of wet coils, damper movement, or dirty filter, or simulate pressure losses with volume controls at 100%.

Single-Duct, Pressure-Dependent Systems:

Multizone Systems:

Single-Duct, Fan-Powered Pressure-Systems:

Fan configurations vary among air terminal devices in fan-powered systems. The internal fan may be in series with the primary air for continuous airflow, or it may be in parallel with the primary air for intermittent airflow.

Airflow from these fans is controlled by various methods, such as multiple wiring for three-speed control, silicon-controlled rectifiers (SCR) for multiple-speed control, or manual dampers at the fan discharge. Consult the air terminal device manufacturer for the proper operation and setting of the flow control.

Single-Duct, Fan-Powered Pressure-Independent Systems:

Fan configurations and airflow control for these devices are the same as described in the Single-Duct, Fan-Powered Pressure-Dependent Systems section. Consult the terminal manufacturer for the proper operation and setting of the flow control.

Dual-Duct, Pressure-Independent Systems:

This type of system uses control schemes that supply a varying quantity of heated or cooled air to the space. The hot duct and cold duct each have their own volume controller.

Laboratory Testing and Balancing:

The first three steps are written as for laboratories where room pressure is negative. The exhaust and supply airflow percentages will switch when the laboratories are designed to be positive pressure.

Note in the sketch that all face readings are for reference only. The flow is established by pitot tube traverse. At the present time, there is no way to take the average velocity multiplied by the face area to determine total flow. Each velocity-measuring instrument will require different correction factors, and these corrections are often different for different size hoods of the same type.

If the hood does not pass this requirement a caution tag must be placed on the sash. The caution tag should be a fluorescent orange tag stating that the hood does not meet specified flow requirements, with the date.

Tracking the laboratory control can be done in the following manner by establishing airflows for each air terminal device:

To be of value to the consulting engineer and owner’s maintenance department, the air-handling report should consist of at least the following items:

Many independent firms have developed detailed procedures suitable to their own operations and the area in which they function. These procedures are often available for information and evaluation on request.

The traditional heating-only hydronic terminal (200°F, 20°F Δt) gradually reduces heat output as flow is reduced (Figure 1). Decreasing waterflow to 20% of design reduces heat transfer to 65% of that at full design flow. The control valve must reduce waterflow to 10% to reduce heat output to 50%. This relative insensitivity to changing flow rates is because the governing coefficient for heat transfer is the air-side coefficient; a change in internal or water-side coefficient with flow rate does not materially affect the overall heat transfer coefficient. This means (1) heat transfer for water-to-air terminals is established by the mean air-to-water temperature difference, (2) heat transfer is measurably changed, and (3) a change in mean water temperature requires a greater change in waterflow rate. Figure 1 shows the relationship between water-side design criteria and heat transfer.

The coil was selected for an entering water temperature of 180°F, and design water temperature drops Δt of 20°F and 60°F. The design exit air temperature of the coil is 120°F. Note that with waterflow twice that of design, there is a reasonable amount of temperature difference to indicate overflow. Acceptable industry practice has been to allow for only 10% overflow, and in that case a 20° Δt coil yields a negligible increase in heat transfer (101%) and an equally tough to measure 0.75°F change in departing air temperature. Similarly, the coil with 60°Δt has only 104% of design heat transfer with a 2° increase in leaving air temperature. The designer should not assume that a temperature control system will be able to adequately control any overflows based on sensing the increase in temperature. Though possible if great care is taken to match the control valve to the coil and tune the control loop for proper control, more often than not, this is rarely attained in implementation.

Tests of hydronic coil performance show that when flow is throttled to the coil, the water-side differential temperature of the coil increases with respect to design selection. This applies to both constant-volume and variable-volume air-handling units. In constantly circulated coils that control temperature by changing coil entering water temperature, decreasing source flow to the circuit decreases the water-side differential temperature.

A secondary concern applies to heating terminals. Hot water can be supplied at a wide range of temperatures. Inadequate heating capacity caused by actual conditions varying from design or insufficient flow can sometimes be overcome by raising supply water temperature. Designs below the 250°F limit (ASME Boiler and Pressure Vessel Code) often add enhanced flexibility to make this adjustment if there is adequate source capacity.

Figure 2 shows the flow variation when 90% terminal capacity is acceptable. Note that heating tolerance decreases with temperature and flow rates and that chilled-water terminals are much less tolerant of flow variation than hot-water terminals.

A third concern also needs to be considered when dual-temperature heating/cooling hydronic systems are employed. These systems are sometimes first started during the heating season. Adequate heating ability in the terminals may suggest that the system is balanced. However, when operated in cooling mode, capacity may vary greatly from that required. Figure 2 shows that 40% of design flow through the terminal provides 90% of design heating with 140°F supply water and a 10°F temperature drop. Increased supply water temperature establishes the same heat transfer at terminal flow rates of less than 40% design.

Sometimes, dual-temperature water systems have decreased flow during the cooling season because of chiller pressure drop; this could cause a flow reduction of 25%. For example, during the cooling season, a terminal that heated satisfactorily would only receive 30% of the design flow rate.

Although the example of reduced flow rate at Δt = 20°F only affects heat transfer by 10%, this reduced heat transfer rate may have the following negative effects:

Terminals with lower water temperature drops have greater tolerance for unbalanced conditions. However, larger waterflows are necessary, requiring larger pipes, pumps, and pumping cost.

System balance becomes more important in terminals with a large temperature difference. Less waterflow is required, which reduces the size of pipes, valves, and pumps, as well as pumping costs. A more linear emission curve gives better system control. If flow varies by more than 5% at design flow conditions, heat transfer can fall off rapidly, ultimately causing poorer control of the wet-bulb temperature and potentially decreasing system air quality.

Increasing the flow rate above design in an effort to increase heat transfer requires careful consideration. Figures 1 and 3 both show that increasing the flow to 200% of design only increases heat transfer by 6 to 20%. However, the excess flow increases resistance or pressure drop four times and, more importantly, energy draw by a factor of eight using the cube of the original power (from the pump laws).

Heat transfer for a typical chilled-water coil in an air duct versus waterflow rate is shown in Figure 4. The curves are based on AHRI rating points: 45°F inlet water at a 10°F rise with entering air at 80°F db and 67°F wb. The basic curve applies to catalog ratings for lower dry-bulb temperatures providing a consistent entering-air moisture content (e.g., 75°F db, 65°F wb). Changes in inlet water temperature, temperature rise, air velocity, and dry- and wet-bulb temperatures cause terminal performance to deviate from the curves. Figure 4 is only a general representation and does not apply to all chilled-water terminals. Comparing Figure 4 with Figure 1 indicates the similarity of nonlinear heat transfer and flow for both the heating and cooling terminals.

Table 1 shows that if the coil is selected for the load and flow is reduced to 90% of load, three flow variations can satisfy the reduced load at various sensible and latent combinations. Note that the reduction in flow will not maintain a chilled-water design differential when coil velocity drops below 1.5 fps. This affects chiller loading and unloading.

The coil characteristic shown in Figure 5 is for air that is always recirculated within a space, such as in a fan-coil. Another common (but nonstandard) approach in chilled-water systems is for airflow volume across the coil to vary according to load. Static pressure in the supply duct is controlled by VAV box dampers opening and closing, and some percentage of outdoor air is introduced at entering conditions. With these control modifications, the coil starts to appear more linear, depending on air turndown (determined by load) and variations in dry- and wet-bulb temperatures of the air being introduced. In some cases, as sensible design conditions are approached, reasonable variance in wet-bulb temperature can significantly change heat transfer across the coil. If enthalpy is the control set point, fluid flow may vary by 40% or more of design at the same entering dry-bulb temperature. These common characteristics make fluid flow measurement of a coil (rather than using surrogate indicators such as water-side Δt) important in indicating the system balance.

The design procedure rests on a design flow rate and an allowable flow tolerance. The designer must define both the terminal’s flow rates and feasible flow tolerance, remembering that the cost of balancing rises with tightened flow tolerance. Any overflow increases pumping cost, and any flow decrease reduces the maximum heating or cooling at design conditions.

Minimum Design Requirements for Hydronic System Installation. Given the effect of flow on heat transfer, comfort, and energy efficiency, each coil must have some form of verifiable flow measurement to enable measurement and verification to properly verify system operation (even if no adjustments are planned). Traditionally, this function was performed by balancing valves, and the required performance was communicated in the written specification and in schematic drawings like the one shown in Figure 6.

The example is not meant to endorse any particular method of control or specification. For example, having thermometers entering and leaving the coil is a nice feature, especially when working on large coils and air-handling units. However, most terminal unit coils (e.g., fan-coils, terminal reheat coils) serving a small temperature control zone have flow rates of 0.5 to 10 gpm, and there are many coils. In that instance, the expense of thermometers is not justified. Alternatively, a measurement device could be installed that allows for the insertion and removal of a temperature sensor into the fluid stream to make a measurement. Note that many fittings and devices are shown. It is very common to find specialty devices installed as an alternative to the specification drawing at the request of the installer, with the object of providing functional performance while increasing the installation efficiency. Typically these are called hook-up kits or coil kits and are installed with the TAB device and the control valve.

Figure 7 shows the three most common types of devices applied; note that the market can drive subtle variances of their design. There are a few things that are important in applying these devices:

Balancing Devices. Traditional balancing valves are of two basic styles: static or dynamic. In addition, a simple flow measurement device such as an orifice or venturi could serve the same function, but these are often integrated into the balance valve

Static Balance Valves. Varieties exist for both operation and measurement. This valve is typically set to a position by a technician and does not self-adjust in operation. Typically, the simplest type of valve has a throttling device able to measure pressure entering and exiting the throttling orifice. Manufacturers publish the performance data associated with the valve using a standardized valve test, such as ISA Standard 75.02.01, with adjustment to compensate for the valve design and measurement points. In this manner, the balancing device uses a variable orifice for flow calculation based on the orifice flow coefficient c_V at the operating position. This device generally provides an acceptable flow measurement when wide open, but if care is not exercised to carefully match the differential pressure measurement device range to the flow coefficient of the valve, flow accuracy declines as the valve is closed.

A modified type of static valve uses a fixed orifice for flow calculation combined with a variable orifice for flow adjustment. The fixed orifice may be a simple orifice, venturi profile, or nozzle. Variable orifice measurement requires knowing where the device is set to calculate flow, which may require having to adjust a measurement device each reading. The fixed orifice, on the other hand, does not change each reading, thus giving a direct readout on flow if the measurement device incorporates this calculation and the measurement range is adequate for the measured flow. Remember the square relationship of flow to pressure drop: if 1 gpm is being measured at a pressure drop of 1 psi, then reducing the flow to half gives a measured pressure drop of 0.25 psi. These pressures can become quite small, and finding the proper range sensor is difficult unless care is taken in sizing and design to allow for enough pressure drop to calculate a reasonably accurate flow. Measuring at design flow is important and should be relatively easy to accomplish. However, if the intent is to check the system at part load, especially at flows less than 50% of design, this must be taken into account when selecting the design pressure drop for the measurement device, to make sure the signal is of enough magnitude as to be measurable by the available devices.

The built-in benefit of a static balancing valve is that, when properly field adjusted, all system flow paths have the same head loss (the same as the design head loss calculated for the selection of the pump). This system is therefore proportionally balanced; if flow is too great, all circuits have the same overflow, and if flow is too small, all circuits receive the same percentage of flow. This can be highly advantageous for some system designs. Note that in a system that is properly proportionally balanced, at least one of the balancing valves will be open, providing only the pressure drop required to provide an adequate differential pressure signal for flow calculation. There are no parasitic head losses in the system, because all paths have the same head loss, and maximum flow is limited, reducing flow to only that of design, thus saving pump horsepower and energy.

Dynamic Devices (Automatic Flow Limiters). The process of adjusting the maximum flow in a circuit can be expensive or laborious, but there will be varying differential pressures at each branch that cause excessive flows at design, especially when control valves are selected with little care for required pressure drop at the point of system application. The dynamic device incorporates a system-powered regulator to either vary the open orifice area to keep no more than a specific set point flow, or control the differential pressure across a fixed orifice to accomplish the same function. Like all regulators, these devices rely on machined control areas and engineered springs to set a specific range of operation, and therefore exhibit proportional control of the regulator for the flow, but not proportional regulation of the controlled system (as does the static valve). Typically, these valves operate over a fixed range of differential pressure (e.g., 2 to 32, 2 to 60, or 5 to 60 psid).

A drawback is that these valves do not definitively know the position, and thus the flow coefficient, where the regulator is operating. They also often do not allow for the correct pressures to establish flow. As a result, these devices cannot be used to measure flow at the design condition, and the manufacturer’s statement of flow must be taken at face value. Performance is generally reasonable, but there are occasions when suspended construction material can obstruct the working apparatus, blocking flow and giving no indication that there is an issue. It is recommended that when these types of devices are installed, a properly sized fixed orifice device be installed to allow for positive flow measurement.

Pressure Regulators. Regulators are some of the earliest automatic control devices, using various materials and approaches to control specific processes. For example, the simple bimetallic element, which has two physically bonded strips of metal with different coefficients of expansion and contraction, is harnessed into the thermostat, so that when the element heats or cools, the corresponding physical movement of the element actuates a switch or provides control of air pressure to actuate a damper motor or valve. For TAB, system water pressure is directed to both sides of a diaphragm-operated actuator, to open or close a valve. Using a spring on the actuator, a specific pressure set point can be controlled for either a static or differential pressure; by adding other system-powered devices, this basic function can be turned into a flow regulator or other type of control element. Use of regulators on hydronic systems is returning to popularity, with widespread application of variable-speed pumping and designs that attempt to recreate proportional control. (The application of variable speed pumping will be handled separately.)

A differential pressure regulator is typically used, and it is applied either as an independent device across an individual branch, a temperature control valve, or a multiterminal branch. A subset of ΔP regulators is the pressure-independent control valve, which incorporates the ΔP regulator into the body of the temperature control valve to control the pressure drop across the control orifice. In that specific application, whenever system differential pressure at the point of the controlled valve exceeds the regulator pressure set point, the fixed ΔP set point is kept constant. This mimics the same conditions applied when a TC control valve is given the standard flow capacity test, and consequently the valve characteristic is maintained without deviation, because of system hydraulics.

The regulator ΔP is normally less than the pressure drop across the valve assembly as prescribed by the flow capacity test. Manufacturers normally state the controlled range of flow of the valve and the operating ΔP range, and often of the regulator. If the manufacturer states a specific flow coefficient C_v for the valve, this should imply the entire assembly’s pressure drop per the standard test method. Whether these devices can be used for flow measurement or verification varies with manufacturer. In some cases, manufacturers provide the ability to measure pressure drop across some portion of the valve. It is common to designate three critical pressures: P1 (upstream pressure), P2 (regulator pressure), and P3 (downstream pressure). If only P1 and P3 are measurable, flow verification cannot be performed because the drop around the controlled orifice is unknown. If P2 and P3 are known and the flow coefficient for the applied position is known (published), it may be possible to verify flow. Some manufacturers incorporate fixed-flow orifices specifically for flow verification. Similar to automatic flow limiters, it is recommended that when these types of devices are installed, a properly sized fixed orifice device be installed (if not included in the valve assemblage) to allow positive flow measurement.

Hydronic system measurement tools can be categorized by function: electrical (to deal with pumps), pressure and differential pressure (to establish system settings, pressure losses, and calculate flow rates), temperature (to establish performance levels), and direct-flow instruments (e.g., a strap-on instrument such as a doppler effect type of meter to measure flow directly). In addition, it is useful to apply thermal imagers and vibration analyzers when testing for improper operation and, if the TAB technician is designated to perform alignments, an alignment analyzer.

Electrical Measurements. As a result of the wide application of variable-speed drives to pumps, both a portable oscilloscope and a digital multimeter with required test probes and safety gear and procedures are required to take reasonable and repeatable measurements and establish power use. The oscilloscope is required to measure the voltage and current leaving the drive to the motor and entering the motor and check for imbalance. There are several other measurements that are useful but may not be part of the designated TAB technician’s responsibility.

The majority of motors applied to large commercial systems are three-phase motors, and when attached to a speed drive, the frequency of the drive operation is too fast for a digital multimeter. In addition, both the scope and the digital multimeter (DMM) should incorporate a low-pass filter to filter out high frequencies associated with the drive. Note the instrument manufacturer, model, and whether the device includes a low-pass filter measurement documentation. If readings are taken by other technicians at a later time, using meters without the low-pass filter, there may be substantial difference in the reported measurement when no difference actually exists. Because of the function of the drive, voltage measurements can be significantly greater than the nominal 480 V assumed to being measured. Instruments should be rated for 750 to 1000 V to be safe. Analog meters are unacceptable for making these measurements because they lack the required electrical protections and capability to handle power transients. Note that power analyzers may not be substituted for oscilloscopes. Power analyzers are designed to measure supply power lines, but are incapable of measuring drive output power because of the frequencies encountered. The oscilloscope also allows for checking (1) drive setup for output versus load; (2) whether there are overvoltage reflections on the line, which could cause motor winding damage; (3) motor shaft voltages; (4) bearing currents, which can cause fluting of the bearing raceway leading to excess vibration and noise and ultimately leading to reduced motor life; and (5) if there is motor leakage current, which can interfere with control system data acquisition and communications. The digital multimeter is inadequate for many of these measurements, though there are other measurements for which it is very appropriate. Regardless, it too should have the low pass filter to deal with any high frequencies which could lead to errors in measurement.

Pressure Measurement. A broad variety of gages, transmitters, and digital meters exist for the purposes of pressure and differential pressure measurement. The use of the tube-filled manometers was the traditional standard of care, however the indicating fluid was mercury (now a banned substance), so these should never be seen in field application. Most commonly applied still would appear to be a basic mechanical, diaphragm separated dial gage, the device could also be liquid filled. In some cases these might be advantageous due to the inherent simplicity of the device, but what is important is carefully matching the gage range to the expected range of reading, and to ensuring that overpressurization does not influence or damage the gage. The most common problem of the field application of these types of devices is that a user will apply a gage with a reading of 0 to 100 ft of water (up to 45 psi) on a device providing a signal in the range of 0 to 10 in. (up to 0.4 psi).

Digital manometers are also used. In these units, a semiconductor differential pressure sensor or matched pair of gage pressure sensors is used, with either electronic analog circuitry or an application-specific microprocessor to convert the electrical signal from the sensor into usable data by the technician. In many cases, the manufacturers will apply some user adaptability to enter field data that might display the differential pressure, and convert that sensed value to a calculated flow. In other cases, the applied microprocessor has a far greater set of operations, from device databases to instructional methods on making system adjustments. Most important to the balancing process is that an accurate, precise, and appropriate range sensor is applied to the measurement device, and that it is properly compensated for temperature of the working fluid. All sensing devices rely on some electrical interpretation of the physical movement of an object (e.g., diaphragm) in response to changing pressure. The same technologies that are applied to free-standing sensors used in the control process are also applied in the test instrumentation used by balancers. Digital manometers should minimally offer a capability of zeroing the sensor and electrical signal before measurement of the test specimen, and may also offer connection methods to the test specimen that balance the pressure across the device until reading to prevent sensor damage, and ensure that the physical connection device (e.g., tubes) are filled with liquid and vented of air. Test instruments should be regularly checked against a traceable reference standard; allow for regular calibration as required.

Temperature Measurement. Careful system design should always allow for a sensor to be placed directly into a fluid stream, not externally mounted to the pipe. There are a wide variety of mechanical temperature sensing methodologies, such as the traditional liquid-filled thermometer, and bimetallic or vapor-filled elements with a calibrated dial indicator or electronic sensing through RTD, thermistor, or other type of sensing element. Electronic sensing also implies semiconductor devices and implementations that can be quite small, allowing for the carrying or sheathing element to be equally small: the tube that carries the physical sensing device and wires can be diametrically as small as a hypodermic needle (0.06 in. diameter), or the more traditional instant-read type of dial indicator probe, which is slightly greater than 0.13 in. in diameter. Probe size should be checked to ensure that it can be injected into the fluid stream as far as possible (as this may be restricted by entry point). Temperature instruments should be regularly checked against a traceable reference standard, and allow for regular calibration as required and capable.

Less commonly applied, and appropriate for specific applications, are thermographic imagers, which may be handheld and have digital imaging. Though inappropriate for direct fluid temperature measurement, they are invaluable for extra measurements such as showing the face of a heat transfer coil or to indicate faulty points of insulation. On devices such as pumps, they can provide valuable data on motor and bearing operation.

Flow Sensing. The noninvasive flow sensor typically uses a form of ultrasonic detection to establish flow on the interior of a pipe. This is a nontraditional instrument in balancing for several reasons, including setup time and the data required to translate the signal into waterflow. However, in certain application instances, such as measuring main distribution piping, there can be value in spot checking flow rates.

In all of these device categories, there is a wide variety of other technologies which may be applied, especially when those applications are permanent to system operation. However, it is this permanence that makes them less applicable to field testing for TAB. A fluid flow turbine meter may be very good for getting a flow measurement, but adding and then removing the device to the fluid stream (aside from the piping complications) also substantively changes the system pressure drop and flow rate, making the overall readings and adjustments less accurate. This should be accounted for in design. If there are specific devices that the designer feels are more appropriate to the goals that they wish to accomplish, specific mechanical installation techniques and equipment should be incorporated into the design to accommodate those measurements. For example, a removable section of piping could allow for physical checking of the interior pipe surfaces to ensure accuracy for an ultrasonic device.

Expect sensing errors, and the associated error in rational units (e.g. ΔP into volume-per-unit-time flow). Expect that, when the accounting is complete, a gross reading at one point in the system will not be the same as all the individual unit flows when added. When attempting to establish the validity of the reported numbers, it may be necessary to recheck not only the installed devices but also the pipes and fittings. Expect problems, and provide simple logical points of measurement opportunity that allow the anomaly to be traced until satisfaction can be established with the data.

Anecdotal evidence supports the necessity of these precautions. In a 60 story office tower in Chicago, it was known for years that the chilled-water system did not seem to work right and that, in particular, the pumps did not develop the required system flow. After checking all of the installed devices, the building owners eventually installed extra measurement points that allowed enough data to be taken to track anomalies. Eventually, these measurements led to a specific section of pipe. The system was shut down for maintenance, drained, and the suspect pipe was cut open only to find it stuffed with tubes of conduit. Apparently the electrician thought it was a convenient storage spot during construction, and the pipefitters never recognized that it was a mistake, not some form of flow straightener in the pipe, welding it in. These types of errors can (and do) occur with regularity. Catching errors such as this is not the purpose of TAB, but the principles of TAB measurements can be used to address functional problems, as well as the normal system hydraulics.

Water-side balancing adjustments should be made with a thorough understanding of piping friction loss calculations and measured system pressure losses. It is good practice to show expected losses of pipes, fittings, and terminals, and expected pressures in operation on schematic system drawings (as recommended in ASHRAE Standard 111). Designers often use schematic drawings to provide functional representation of a system design, in addition to the dimensional piping plans associated with the building layout drawings. It is suggested that one of these schematics be drawn in a flat connection or ladder-type diagram, as shown in Figure 8. Conceptually, the schematic allows main distribution paths, branch connections, major devices, and the pump, without any piping lines crossing. The drawing serves several purposes: allowing all paths and various system interactions to be easily seen, evaluating opportunities for reverse or gravity flows, easily translating to a spreadsheet for sizing and analysis calculations, quickly and efficiently establishing the required balance adjustments and identifying differences between installed versus design differences (done by the TAB technician), and establishing and communicating more detailed sequences of operation for the control system.

The power of commonly available spreadsheets allows designers to create a straightforward calculation procedure that is easily verifiable by the firm using it. The spreadsheet approach also allows analysis to be performed while sticking to the basics of a system operating at the intersection of its pump and system curves. The accuracy of these methods is reasonably good, and the implementation complexity can be left to the designer of the spreadsheet. For example, to achieve a higher degree of precision in the calculations for fittings, the spreadsheet can account for the influences of geometric plane interaction (as shown by ASHRAE research and detailed in the 2021 ASHRAE Handbook—Fundamentals). However, if this is of less concern, the spreadsheet can implement something as simple as K factors or fitting TEL. Using Figure 8 as an example, a simple spreadsheet was established to provide design analysis, shown in Figure 9.

The spreadsheet allows calculation of the system flow coefficient (analogous to a valve flow coefficient C_V, and outlined in Chapter 47 of the 2020 ASHRAE Handbook—HVAC Systems and Equipment) for showing how various branches will operate. In any pumped piping system, the system will operate at the intersection of the pump and system curve. The system curve is a composite of many system curves, which represent all of the individual paths of waterflow in the system. Each individual path flow coefficient is an indirect sum of the individual component (pipe, fittings, valves, coils, etc.) flow coefficients which may be either implied from calculation or tested under standard test procedures.

The math of the spreadsheet is expressed through algebraic rearrangement of the basic flow equation:

Given that the system head loss in a closed-loop hydronic system is the total of the single largest path’s head loss of pipe, fittings, etc., the sum of the head losses can be rearranged into the requisite components of flow and flow coefficient as shown. As the flow is the same in all paths, the term drops out and an equation that can be solved for the system flow coefficient from the components is realized.

Each individual segment in a flow path will have a path flow rate equal to the design flow rate of the served heat transfer device, and the unique or shared head loss in a segment for that flow. For instance, Coil Path 3 has a flow rate of 100, but the distribution piping segment A-B has a design flow 800 for all eight circuits (only three are shown in Figure 9) and design head loss of 4.03. Using hydronic design principles, all paths see the bulk head loss, and the pump must provide enough energy to overcome these losses, so calculation of the path flow coefficient is as shown in the equation above. All that is being illustrated is the addition of the head losses in each flow path, but doing so as the X form of the equation, the flow divided by the flow coefficient squared.

Parallel-path flow coefficients are simply additive, and when used to develop a system curve, they can be plotted to a specific pump curve and the intersection point calculated. This allows for the requirements of the first pass of system adjustment to be determined.

Note that there will be differences in actual measured pressures and those calculated. In keeping with the Bernoulli principles, when fittings and devices are fitted to an installed system, they do not always behave in a perfectly theoretical way. Sometimes there are greater or fewer losses of a combined device, influenced by changes in velocity head and velocity head recovery and exhibited in things like the vicinity of a change in flow direction, and changes in the X, Y, and Z planes of the pipe. These losses can only be tested for, and examples of these influences are demonstrated in ASHRAE research project RP-968 (Rahmeyer 1998) (partially published in Tables 3, 4, and 5 and Figures 2 and 3 in Chapter 22 of the 2021 ASHRAE Handbook—Fundamentals). However, this should not be used as a reason not to calculate. The first step should always be to have a more rational quantitative approach by which to direct and decide.

One of the by-products of this type of analysis is the calculation of control valve authority, or the authority of any device used to throttle flow. Simply put, valve authority β is the ratio of control valve pressure drop to the maximum pressure drop of the system that it serves. For a constant-speed pump, ΔP maximum is the pump head, in a variable-speed pumping system, the pressure drop ΔP maximum is the controlled set-point pressure for the pump speed controller The indexing number offers a simple indication of how the valve will perform, but is fairly useless for calculating what the flow would be. However, treated as flow coefficients, the equivalent system flow coefficient is determined as follows.

When the system flow coefficient is calculated for each valve position’s flow coefficients, the deviation of a given valve’s flow control characteristic may be graphically shown. Figure 10 shows the graphical result for a modified equal-percentage valve at various valve authorities. In the field there may be deviations from this, though the deviation has also been seen in operating systems. Through application of this method of analysis, the effects of balancing the system can be demonstrated for relative effect. It has been anecdotally maintained that application of balancing valves degrades control valve performance, and an example shows this to be partially true, with an unbalanced valve having 22% authority, compared to the same circuit balanced, which has 16%. If the control valve completely opens, under the applied pump differential of 66 ft of water, that is higher than that required for the design flow. Though perfect for the most significant path that the pump was selected for, unbalanced and closer to the pump there will be about 15% overflow. This is shown in Figure 10, based on the example. This overflow is very likely not to be recognized by the valves temperature controller, and the beginning result is that there will be excess pump energy used until the controller is able to respond and reduce flow. For the controls technician, adjusting the proportional setting is harder. In the extreme, controller hunting will occur, continuously opening and closing the valve, over and underflowing. Balancing the poorly sized control valve at reduces the maximum opening overflow. Reduced flow at this condition saves pump energy. Tuning the control loop, however, can only be fixed by selecting the temperature control valve with a better valve authority, which means more design pressure drop, and indirectly increases the design pump head.

From the perspective of cost, reducing flow always saves operating expense (relatively). The use of a balancing device will generally save 10 to 15% (more for systems that have paid little or no attention to the hydronic system details, or that have pumps that provide more head than absolutely required) of the pump energy. Poor control valve authority has a larger energy penalty than balancing maximum flow, because the tuning that is possible leads to valves that generally react to disturbances sooner than the load requires (more flow at load), and at each valve position, more flow is delivered than would be indicated by the characteristic. Pumping costs can be significantly reduced by being able to maintain control valve characteristic (on the order of 50%) with even more energy when considering the operation cost of the source energy provider. In that regard, applying hydronic design options, such as properly zoned secondary pumping, zone differential pressure control, or pressure-independent control valves (PICV) for zone pressure control adds operating benefit.

Per CSI Standard 2305.93, TAB specification requires direct section implementation of equipment, procedures, and specialists. In addition, coordination should be noted in sections on controls, pumps, any installation sections, etc.

Hydronic systems should be tested by direct flow measurement. This method is accurate because it deals with system flow as a function of differential pressures, and avoids compounding errors introduced by temperature difference procedures. To achieve this, each circuit should have some form of inexpensive yet accurate producer of differential pressure related to flow, such as the previously outlined static balancing valve, or a small venturi or orifice measuring station. This requirement could also be a direct reading sensor (as these prices reach competitive levels, or the importance of the measured path requires). Measuring flow at each terminal enables verification of the system operation and, where required, proportional balancing. It also allows matching pump head and flow to actual system requirements and reducing excess flows by trimming the pump impeller or reducing pump speed. Often, reducing pump operating cost pays for the cost of water-side balancing.

Proper equipment selection and preplanning are needed to successfully balance hydronic systems. Circumstances sometimes dictate that flow, temperature, and pressure be measured. The designer must specify the waterflow balancing devices and measurement points for installation during construction and use in testing during hydronic system measurement and adjustment. In addition, the designer is well served by specifying the minimum acceptable level for test equipment, which should include full-scale range and accuracy and required calibration. In so specifying, simplicity should be the order of the day. Temperature sensors should be able to fit into the specified measurement ports. Pressure and differential pressure sensing devices should be capable of providing accuracy that, when converted to system flow, falls within the specified tolerance for flow adjustment. Note that (as typical of all HVAC equipment) there is a broad range of implementation for specific instrumentation devices.

Balancing requires accurate record keeping while making field measurements. Dated and signed field test reports help the designer or customer in work approval, and the owner has a valuable reference when documenting future changes.

Flow measurement devices and balancing valves are placed in the system to measure flow and, where required, adjust waterflow to a terminal, branch, zone, riser, or main. These should be located on the leaving side of the hydronic branch, following the temperature control valve and prior to isolation or service valves. General branch layout is from takeoff to entering service valve and strainer, then to the coil, control valve, and balancing/service valve. Pressure is thereby left on the coil, helping keep dissolved air in solution and preventing false balance problems resulting from collected air and improper pressure references.

An improper but commonly applied sizing method is to select the valve or device for line size. These devices should be selected to pass design flows when near or at their fully open position with the differential pressure required to accurately represent flow for the measurement range desired. Although a small pressure drop may allow determination of design flow, it should be remembered that measurements will almost always be taken at reduced flows. The square relationship between flow and head will greatly reduce the available differential pressure for measurement. If a minimum differential pressure of 1 psi is used for sizing, measurement at 50% design flow means measured ΔP will be 0.25 psi; conversely, twice the flow will be a drop of 4 psi. This factors into the practical and available instrumentation used in field measurement. If a manufacturer publishes a minimum accuracy of 0.072 psi 1 gpm with an uncorrected valve flow coefficient of 1, then a 1 psi drop would produce that reading at ±0.28 gpm, or ±30%. If the designer is specifying a flow tolerance of ±10%, then sizing of devices and matching them to instrumentation become very important. A bare minimum 1 psi pressure drop is suggested; more pressure drop for basic measurements is recommended. Many balancing valves and measuring meters give an accuracy of ±5% of range down to a pressure drop of 12 in. of water with the balancing valve wide open. Too large a balancing valve pressure drop affects the performance and flow characteristic of the control valve. Too small a pressure drop affects its flow measurement accuracy as it is closed to balance the system. Equation (5) may be used to determine the flow coefficient C_v for a balancing valve or to size a control valve.

The flow coefficient C_v is defined as the number of gallons of water per minute that flows through a wide-open valve with a pressure drop of 1 psi at 60°F. This is shown as

where

Q	=	design flow for terminal or valve, gpm
SG	=	specific gravity of fluid
ΔP	=	pressure drop, psi

If pressure drop is determined in feet of water Δh, Equation (5) can be shown as:

where Δh is pressure drop in ft of water.

For single-, multiple-, and parallel pump systems, after pump start-up and confirmation of system venting,

This common balancing procedure is based on measuring the water temperature difference between supply and return at the terminal. The designer selects the cooling and/or heating terminal for a calculated design load at full-load conditions. At less than full load, which is true for most operating hours, the temperature drop is proportionately less. Figure 11 demonstrates this relationship for a heating system at a design Δt of 20°F for outdoor design of 10°F and room design of 70°F.

For every outdoor temperature other than design, the balancing technician should construct a similar chart and read off the Δt for balancing. For example, at 50% load, or 30°F outdoor air, the Δt required is 10°F, or 50% of the design drop.

This method is a rough approximation and should not be used where great accuracy is required. It is not accurate enough for cooling systems.

Preset Method. A thorough understanding of the pressure drops in the system riser piping, branches, coils, control valves, and balancing valves is needed. Generally, several pipe and valve sizes are available for designing systems with high or low pressure drops. A flow-limiting or trim device will be required. Knowing system pressure losses in design allows the designer to select a balancing device to absorb excess system pressures in the branch, and to shift pressure drop (which might be absorbed by a balancing device nearly close to achieve balance) to the pipes, coils, and valves so the balancing device merely trims these components’ performance at design flow. It may also indicate where high-head-loss circuits can exist for either relocation in the piping network, or hydraulic isolation through hybrid piping techniques. The installed balancing device should never be closed more than 40 to 50%; below this point flow reading accuracy falls to 20 to 30%. Knowing a starting point for setting the valve (preset) allows the designer to iterate system piping design. This may not always be practical in large systems, but minimizing head and flow saves energy over the life of the facility and allows for proper temperature control. In this method,

Proportional water-side balancing may use design data, but relies most on as-built conditions and measurements and adapts well to design diversity factors. This method works well with multiple-riser systems. When several terminals are connected to the same circuit, any variation of differential pressure at the circuit inlet affects flows in all other units in the same proportion. Circuits are proportionally balanced to each other by a flow quotient:

To balance a branch system proportionally,

Note: When all balancing devices are open, flow will be higher in some circuits than others. In some, flow may be so low that it cannot be accurately measured. The situation is complicated because an initial pressure drop in series with the pump is necessary to limit total flow to 100 to 110% of design; this decreases the available differential pressure for the distribution system. After all other risers are balanced, restart analysis of risers with unmeasurable flow at step (2).

Identify the riser with the highest flow ratio. Begin balancing with this riser, then continue to the next highest flow ratio, and so on. When selecting the branch with the highest flow ratio,

The reference circuit has the lowest quotient and the greatest pressure loss. Adjust all other balancing valves in that branch until they have the same quotient as the reference circuit (at least one valve in the branch should be fully open).

When a second valve is adjusted, the flow quotient in the reference valve also changes; continued adjustment is required to make their flow quotients equal. Once they are equal, they will remain equal or in proportional balance to each other while other valves in the branch are adjusted or until there is a change in pressure or flow.

When all balancing valves are adjusted to their branches’ respective flow quotients, total system waterflow is adjusted to the design by setting the balancing valve at the pump discharge to a flow quotient of 1.

Pressure drop across the balancing valve at pump discharge is produced by the pump that is not required to provide design flow. This excess pressure can be removed by trimming the pump impeller or reducing pump speed. The pump discharge balancing valve must then be reopened fully to provide the design flow.

As in variable-speed pumping, diversity and flow changes are well accommodated by a system that has been proportionately balanced. Because the balancing valves have been balanced to each other at a particular flow (design), any changes in flow are proportionately distributed.

Balancing the water side in a system that uses diversity must be done at full flow. Because components are selected based on heat transfer at full flow, they must be balanced to this point. To accomplish full-flow proportional balance, shut off part of the system while balancing the remaining sections. When a section has been balanced, shut it off and open the section that was open originally to complete full balance of the system. When balancing, care should be taken if the building is occupied or if load is nearly full.

Variable-Speed Pumping. To achieve hydronic balance, full flow through the system is required during balancing, after which the system can be placed on automatic control and the pump speed allowed to change. After the full-flow condition is balanced and the system differential pressure set point is established, to control the variable-speed pumps, observe the flow on the circuit with the greatest resistance as the other circuits are closed one at a time. The flow in the observed circuit should remain equal to, or more than, the previously set flow. Waterflow may become laminar at less than 2 fps, which may alter the heat transfer characteristics of the system.

Flow Balancing by Rated Differential Procedure. This procedure depends on deriving a performance curve for the test coil, comparing water temperature difference Δt_w to entering water temperature t_ew minus entering air temperature t_ea. One point of the desired curve can be determined from manufacturer’s ratings, which are published as (t_ew – t_ea). A second point is established by observing that the heat transfer from air to water is zero when (t_ew – t_ea) is zero (consequently, Δt_w = 0). With these two points, an approximate performance curve can be drawn (Figure 12). Then, for any other (t_ew – t_ea), this curve is used to determine the appropriate Δt_w. The basic curve applies to catalog ratings for lower dry-bulb temperatures, providing consistent entering air moisture content (e.g., 75°F db, 65°F wb). Changes in inlet water temperature, temperature rise, air velocity, and dry- and wet-bulb temperatures cause terminal performance to deviate from the curves. The curve may also be used for cooling coils for sensible transfer (dry coil).

Flow Balancing by Total Heat Transfer. This procedure determines waterflow by running an energy balance around the coil. From field measurements of airflow, wet- and dry-bulb temperatures up- and downstream of the coil, and the difference Δt_w between entering and leaving water temperatures, waterflow can be determined by the following equations:

where

Qw	=	waterflow rate, gpm
q	=	load, Btu/h
qcooling	=	cooling load, Btu/h
qheating	=	heating load, Btu/h
Qa	=	airflow rate, cfm
h	=	enthalpy, Btu/lb
t	=	temperature, °F

The desired waterflow is achieved by successive manual adjustments and recalculations. Note that these temperatures can be greatly influenced by the heat of compression, stratification, bypassing, and duct leakage.

All the variations of balancing hydronic systems cannot be listed; however, the general method should balance the system and minimize operating cost. Excess pump pressure (operating power) can be eliminated by trimming the pump impeller. Allowing excess pressure to be absorbed by throttle valves adds a lifelong operating-cost penalty to the operation.

The following is a general procedure based on setting the balance valves on the site:

Any component (terminal, control valve, or chiller) that has an accurate, factory-certified flow/pressure drop relationship can be used as a flow-indicating device. The flow and pressure drop may be used to establish an equivalent flow coefficient as shown in Equation (3). According to the Bernoulli equation, pressure drop varies as the square of the velocity or flow rate, assuming density is constant:

For example, a chiller has a certified pressure drop of 25 ft of water at 100 gpm. The calculated flow with a field-measured pressure drop of 30 ft is

Flow calculated in this manner is only an estimate. The accuracy of components used as flow indicators depends on the accuracy of (1) cataloged information concerning flow/pressure drop relationships and (2) pressure differential readings. As a rule, the component should be factory-certified flow tested if it is to be used as a flow indicator.

Gages or digital differential pressure manometers are used to read differential pressures. Accurate readout is diminished when two separate devices are used, especially when the two are gages that are permanently mounted. When applying a single pressure gage for differential readout, follow the example of Figure 13. This gage should be alternately valved to the high- and low-pressure side to establish the differential. A single gage needs no static height correction, and excess coordinated errors caused by disparate gage calibration are eliminated.

Differential pressure can also be read from differential gages, thus eliminating the need to subtract outlet from inlet pressures to establish differential pressure. Differential pressure gages are usually dual gages mechanically linked to read differential pressure. The differential pressure gage readout can be stated in terms of psi or in feet of head of 60°F water.

Pressure gage readings can be restated to fluid head, which is a function of fluid density. The common hydronic system conversion factor is related to water density at about 60°F; 1 psi equals 2.31 ft. Pressure gages can be calibrated to feet of water head using this conversion. Because the calibration only applies to water at 60°F, the readout may require correction when the gage is applied to water at a significantly higher temperature.

Pressure gage conversion and correction factors for various fluid specific gravities (in relation to water at 60°F) are shown in Table 2. The differential gage readout should only be defined in terms of the head of the fluid actually causing the flow pressure differential. When this is done, the resultant fluid head can be applied to the C_v to determine actual flow through any flow device, provided the manufacturer has correctly stated the flow to fluid head relationship.

For example, a manufacturer may test a boiler or control valve with 100°F water. If the test differential pressure is converted to head at 100°F, a C_v independent of test temperature and density may be calculated. Differential pressures from another test made in the field at 250°F may be converted to head at 250°F. The C_v calculated with this head is also independent of temperature. The manufacturer’s data can then be directly correlated with the field test to establish flow rate at 250°F.

A density correction must be made to the gage reading when differential heads are used to estimate pump flows as in Figure 14. This is because of the shape of the pump curve. An incorrect head difference entry into the curve caused by an uncorrected gage reading can cause a major error in the estimated pumped flow. In this case, the gage reading for a pumped liquid that has a specific gravity of 0.9 (2.57 ft liquid/psi) was not corrected; the gage conversion is assumed to be 2.31 ft liquid/psi. A 50% error in flow estimation is shown.

Manometers are used for differential pressure readout, especially when very low differentials, great precision, or both, are required. But manometers must be handled with care; they should not be used for field testing because fluid could blow out into the water and rapidly deteriorate the components. A proposed manometer arrangement is shown in Figure 15.

Figure 15 and the following instructions provide accurate manometer readings with minimum risk of blowout.

An error is often introduced when converting inches of gage fluid to feet of test fluid. The conversion factor changes with test fluid temperature, density, or both. Conversion factors shown in Table 2 are to a water base, and the counterbalancing water height H (Figure 15) is at room temperature.

Manufacturers provide flow information for several devices used in hydronic system balance. In general, the devices can be classified as (1) orifice flowmeters, (2) venturi flowmeters, (3) velocity impact meters, (4) pitot-tube flowmeters, (5) bypass spring impact flowmeters, (6) calibrated balance valves, (7) turbine flowmeters, and (8) ultrasonic flowmeters.

The orifice flowmeter is widely used and is extremely accurate. The meter is calibrated and shows differential pressure versus flow. Accuracy generally increases as the pressure differential across the meter increases. The differential pressure readout instrument may be a manometer, differential gage, or single gage.

The venturi flowmeter has lower pressure loss than the orifice plate meter because a carefully formed flow path increases velocity head recovery. The venturi flowmeter is placed in a main flow line where it can be read continuously.

Velocity impact meters have precise construction and calibration. The meters are generally made of specially contoured glass or plastic, which allows observation of a flow float. As flow increases, the flow float rises in the calibrated tube to indicate flow rate. Velocity impact meters generally have high accuracy.

A special version of the velocity impact meter is applied to hydronic systems. This version operates on the velocity head difference between the pipe side wall and the pipe center, which causes fluid to flow through a small flowmeter. Accuracy depends on the location of the impact tube and on a velocity profile that corresponds to theory and the laboratory test calibration base. Generally, the accuracy of this bypass flow impact or differential velocity head flowmeter is less than a flow-through meter, which can operate without creating a pressure loss in the hydronic system.

The pitot-tube flowmeter is also used for pipe flow measurement. Manometers are generally used to measure velocity head differences because these differences are low.

The bypass spring impact flowmeter uses a defined piping pressure drop to cause a correlated bypass side branch flow. The side branch flow pushes against a spring that increases in length with increased flow. Each individual flowmeter is calibrated to relate extended spring length position to main flow. The bypass spring impact flowmeter has, as its principal merit, a direct readout. However, dirt on the spring reduces accuracy. The bypass is opened only when a reading is made. Flow readings can be taken at any time.

The calibrated balance valve is an adjustable orifice flowmeter. Balance valves can be calibrated so that a flow/pressure drop relationship can be obtained for each incremental setting of the valve. A ball, rotating plug, or butterfly valve may have its setting expressed in percent open or degree open; a globe valve, in percent open or number of turns. The calibrated balance valve must be manufactured with precision and care to ensure that each valve of a particular size has the same calibration characteristics.

The turbine flowmeter is a mechanical device. The velocity of the liquid spins a wheel in the meter, which generates a 4 to 20 mA output that may be calibrated in units of flow. The meter must be well maintained, because wear or water impurities on the bearing may slow the wheel, and debris may clog or break the wheel.

The ultrasonic flowmeter senses sound signals, which are calibrated in units of flow. The ultrasonic metering station may be installed as part of the piping, or it may be a strap-on meter. In either case, the meter has no moving parts to maintain, nor does it intrude into the pipe and cause a pressure drop. Two distinct types of ultrasonic meter are available: (1) the transit time meter for HVAC or clear-water systems and (2) the Doppler meter for systems handling sewage or large amounts of particulate matter.

If any of the above meters are to be useful, the minimum distance of straight pipe upstream and downstream, as recommended by the meter manufacturer and flow measurement handbooks, must be adhered to. Figure 16 presents minimum installation suggestions.

Although the pump is not a meter, it can be used as an indicator of flow together with the other system components. Differential pressure readings across a pump can be correlated with the pump curve to establish the pump flow rate. Accuracy depends on (1) accuracy of readout, (2) pump curve shape, (3) actual conformance of the pump to its published curve, (4) pump operation without cavitation, (5) air-free operation, and (6) velocity head correction.

When a differential pressure reading must be taken, a single gage with manifold provides the greatest accuracy (Figure 17). The pump suction to discharge differential can be used to establish pump differential pressure and, consequently, pump flow rate. The single gage and manifold may also be used to check for strainer clogging by measuring the pressure differential across the strainer.

If the pump curve is based on fluid head, pressure differential, as obtained from the gage reading, needs to be converted to head, which is pressure divided by the fluid weight per cubic foot. The pump differential head is then used to determine pump flow rate (Figure 18). As long as the differential head used to enter the pump curve is expressed as head of the fluid being pumped, the pump curve shown by the manufacturer should be used as described. The pump curve may state that it was defined by test with 85°F water. This is unimportant, because the same curve applies from 60 to 250°F water, or to any fluid within a broad viscosity range.

Generally, pump-derived flow information, as established by the performance curve, is questionable unless the following precautions are observed:

Power draw should be measured in watts. Ampere readings cannot be trusted because of voltage and power factor problems. If motor efficiency is known, the wattage drawn can be related to pump brake power (as described on the pump curve) and the operating point determined.

For existing installations, establishing accurate thermal load profiles is of prime importance because it establishes proper primary chilled-water supply temperature and flow. In new installations, actual load profiles can be compared with design load profiles to obtain valid operating data.

To perform proper testing and balancing, all interconnecting points between the primary and secondary systems must be designed with sufficient temperature, pressure, and flow connections so that adequate data may be indicated and/or recorded.

As indicated previously, proper location and use of instruments is vital to accurate balancing. Instruments for testing temperature and pressure at various locations are listed in Table 3. Flow-indicating devices should be placed in water systems as follows:

Steam distribution cannot be balanced by adjustable flow-regulating devices. Instead, fixed restrictions built into the piping in accordance with carefully designed pipe and orifice sizes are used to regulate flow.

It is important to have a balanced distribution of steam to all portions of the steam piping at all loads. This is best accomplished by properly designing the steam distribution piping, which includes carefully considering steam pressure, steam quantities required by each branch circuit, pressure drops, steam velocities, and pipe sizes. Just as other flow systems are balanced, steam distribution systems are balanced by ensuring that the pressure drops are equalized at design flow rates for all portions of the piping. Only marginal balancing can be done by pipe sizing. Therefore, additional steps must be taken to achieve a balanced performance.

Steam flow balance can be improved by using spring-type packless supply valves equipped with precalibrated orifices. The valves should have a tight shutoff between 25 in. of Hg and 60 psig. These valves have a nonrising stem, are available with a lockshield, and have a replaceable disk. Orifice flanges can also be used to regulate and measure steam flow at appropriate locations throughout the system. The orifice sizes are determined by the pressure drop required for a given flow rate at a given location. A schedule should be prepared showing (1) orifice sizes, (2) valve or pipe sizes, (3) required flow rates, and (4) corresponding pressure differentials for each flow rate. It may be useful to calculate pressure differentials for several flow rates for each orifice size. Such a schedule should be maintained for future reference.

After the appropriate regulating orifices are installed in the proper locations, the system should be tested for tightness by sealing all openings in the system and applying a vacuum of 20 in. of Hg, held for 2 hours. Next, the system should be readied for warm-up and pressurizing with steam following the procedures outlined in Section VI of the ASME Boiler and Pressure Vessel Code. After the initial warm-up and system pressurization, evaluate system steam flow, and compare it to system requirements. The orifice schedule calculated earlier will now be of value should any of the orifices need to be changed.

Many devices are available for measuring flow in steam piping: (1) steam meters, (2) condensate meters, (3) orifice plates, (4) venturi fittings, (5) steam recorders, and (6) manometers for reading differential pressures across orifice plates and venturi fittings. Some of these devices are permanently affixed to the piping system to facilitate taking instantaneous readings that may be necessary for proper operation and control. A surface pyrometer used in conjunction with a pressure gage is a convenient way to determine steam saturation temperature and the degree of superheat at various locations in the system. This information can be used to evaluate performance characteristics.

Many large steam systems generate steam at higher pressures (for distribution efficiencies) than what is required by the building systems, and then modulate the pressure using pressure-reducing valves (PRVs). To aid in stable pressure control at low loads, many engineers install two PRVs sized for 1/3 and 2/3 of the design flow rate. To aid in stable pressure control during moderate loads, verify that the 2/3 PRV does not open until the 1/3 PRV is full open.

Calculations and Verification

The following verification procedures may be used with either pneumatic or electrical controls:

Pneumatic System Modifications

Electronic Systems Modifications

Direct Digital Controllers

Direct digital control (DDC) offers nontraditional challenges to the balancing technician. Many control devices, such as sensors and actuators, are the same as those in electronic and pneumatic systems. Currently DDC is dominated by two types of controllers: fully programmable or application-specific. Fully programmable controllers offer a group of functions linked together in an applications program to control a system such as an air-handling unit. Application-specific controllers are functionally defined with the programming necessary to carry out the functions required for a system, but not all adjustments and settings are defined. Both types of controllers and their functions have some variations. One of the functions is adaptive control, which includes control algorithms that automatically adjust settings of various controller functions.

The balancing technician must understand controller functions so that they do not interfere with the test and balance functions. Literacy in computer programming is not necessary, although it does help. When testing the DDC,

In cases where the balancing agency is required to test discrete points in the control system,

Refer to ASHRAE Standard 111 for further details on HVAC TAB.

Present technology does not test whether equipment is operating within rated sound levels; field tests can only determine sound pressure levels, and equipment ratings are almost always in terms of sound power levels. Until new techniques are developed, the testing engineer can only determine (1) whether sound pressure levels are within desired limits and (2) which equipment, systems, or components are the source of excessive or disturbing transmission.

Sound-Measuring Instruments. Although an experienced listener can often determine whether systems are operating in an acceptably quiet manner, sound-measuring instruments are necessary to determine whether system noise levels are in compliance with specified criteria, and if not, to obtain and report detailed information to evaluate the cause of noncompliance. Instruments normally used in field testing are as follows.

The precision sound level meter is used to measure sound pressure level. The most basic sound level meters measure overall sound pressure level and have up to three weighted scales that provide limited filtering capability. The instrument is useful in assessing outdoor noise levels in certain situations and can provide limited information on the low-frequency content of overall noise levels, but it provides insufficient information for problem diagnosis and solution. Its usefulness in evaluating indoor HVAC sound sources is thus limited.

Proper evaluation of HVAC sound sources requires a sound level meter capable of filtering overall sound levels into frequency increments of one octave or less.

Sound analyzers provide detailed information about sound pressure levels at various frequencies through filtering networks. The most popular sound analyzers are the octave band and one third octave band center frequency analyzers, which break the sound into the eight octave bands or twenty-four third octave bands of audible sound. Octave band or narrower sound analyzers are required where specifications are based on noise criteria (NC) and room criteria (RC) curves or similar frequency criteria and for problem jobs where knowledge of frequency is necessary to determine proper corrective action.

Personal computers are a versatile sound-measuring tool. Software used on portable computers has all the functional capabilities described previously, plus many that previously required a fully equipped acoustical laboratory. This type of sound-measuring system is many times faster and much more versatile than conventional sound level meters. With suitable accessories, it can also be used to evaluate vibration levels. Accuracy and calibration to applicable standards are of concern for software.

Regardless of which sound-measuring system is used, it should be calibrated before each use. Some systems have built-in calibration, while others use external calibrators. Much information is available on the proper application and use of sound-measuring instruments.

Air noise, caused by air flowing at a velocity of over 1000 fpm or by winds over 12 mph, can cause substantial error in sound measurements because of wind effect on the microphone. For outdoor measurements or in drafty places, either a wind screen for the microphone or a special microphone is required. When in doubt, use a wind screen on standard microphones.

Sound Level Criteria. Without specified values, the testing engineer must determine whether sound levels are within acceptable limits (Table 1 in Chapter 49 Note that a complete absence of noise is seldom a design criterion, except for certain critical locations such as sound and recording studios. In most locations, a certain amount of noise is desirable to mask other noises and provide speech privacy; it also provides an acoustically pleasing environment, because few people can function effectively in extreme quiet. Table 1 in Chapter 8 of the 2021 ASHRAE Handbook—Fundamentals lists typical sound pressure levels. Most field sound-measuring instruments and techniques yield an accuracy of ±3 dB, the smallest difference in sound pressure level that the average person can discern. A reasonable tolerance for sound criteria is 5 dB.

The measured sound level of any location is a combination of all sound sources present, including sound generated by HVAC equipment, as well as sound from other sources such as plumbing systems and fixtures, elevators, light ballasts, and outdoor noises. In testing for sound, all sources from other than HVAC equipment are considered background or ambient noise.

Background sound measurements generally have to be made (1) when the specification requires that the sound levels from HVAC equipment only, as opposed to the sound level in a space, not exceed a certain specified level; (2) when the sound level in the space exceeds a desirable level, in which case the noise contributed by the HVAC system must be determined; and (3) in residential locations where little significant background noise is generated during the evening hours and where generally low allowable noise levels are specified or desired. Because background noise from outdoor sources such as vehicular traffic can fluctuate widely, sound measurements for residential locations are best made in the normally quiet evening hours. Procedures for residential sound measurements can be found in ASTM Standard E1574, Measurement of Sound in Residential Spaces.

Sound Testing. Ideally, a building should be completed and ready for occupancy before sound level tests are taken. All spaces in which readings will be taken should be furnished with whatever drapes, carpeting, and furniture are typical because these affect the room absorption, which can affect sound levels and the subjective quality of the sound. In actual practice, because most tests must be conducted before the space is completely finished and furnished for final occupancy, the testing engineer must make some allowances. Because furnishings increase the absorption coefficient and reduce by about 4 dB the sound pressure level that can be expected between most live and dead spaces, the following guidelines should suffice for measurements made in unfurnished spaces. If the sound pressure level is 5 dB or more over the specified or desired criterion, it can be assumed that the criterion will not be met, even with the increased absorption provided by furnishings. If the sound pressure level is under 4 dB greater than the specified or desired criterion, recheck when the room is furnished to determine compliance.

Follow this general procedure:

Noise Transmission Problems. Regardless of precautions taken by the specifying engineer and installing contractors, situations can occur where the sound level exceeds specified or desired levels, and there will be occasional complaints of noise in completed installations. A thorough understanding of Chapter 49 and the section on Testing for Vibration in this chapter is desirable before attempting to resolve any noise and vibration transmission problems. The following is intended as an overall guide rather than a detailed problem-solving procedure.

All noise transmission problems can be evaluated in terms of the source-path-receiver concept. Objectionable transmission can be resolved by (1) reducing noise at the source by replacing defective equipment, repairing improper operation, proper balancing and adjusting, and replacing with quieter equipment; (2) attenuating paths of transmission with silencers, vibration isolators, and wall treatment to increase transmission loss; and (3) reducing or masking objectionable noise at the receiver by increasing room absorption or introducing a nonobjectionable masking sound. The following discussion includes ways to identify actual noise sources using simple instruments or no instruments and possible corrections.

When troubleshooting in the field, the engineer should listen to the offending sound. The best instruments are no substitute for careful listening, because the human ear has the remarkable ability to identify certain familiar sounds such as bearing squeak or duct leaks and can discern small changes in frequency or sound character that might not be apparent from meter readings only. The ear is also a good direction and range finder; noise generally gets louder as one approaches the source, and direction can often be determined by turning the head. Hands can also identify noise sources. Air jets from duct leaks can often be felt, and the sound of rattling or vibrating panels or parts often changes or stops when these parts are touched.

In trying to locate noise sources and transmission paths, the engineer should consider the location of the affected area. In areas remote from equipment rooms containing significant noise producers but adjacent to shafts, noise is usually the result of structure-borne transmission through pipe and duct supports and anchors. In areas adjoining, above, or below equipment rooms, noise is usually caused by openings (acoustical leaks) in the separating floor or wall or by improper, ineffective, or maladjusted vibration isolation systems.

Unless the noise source or path of transmission is quite obvious, the best way to identify it is by eliminating all sources systematically as follows:

Vibration testing is necessary to ensure that (1) equipment is operating within satisfactory vibration levels and (2) objectionable vibration and noise are not transmitted to the building structure. Although these two factors are interrelated, they are not necessarily interdependent. A different solution is required for each, and it is essential to test both the isolation and vibration levels of equipment. When measured routinely at the same location, vibration can be used for predictive maintenance.

General Procedure.

Instruments. Although instruments are not required to test vibration isolation systems, they are essential to test equipment vibration properly.

Sound-level meters and computer-driven sound-measuring systems are the most useful instruments for measuring and evaluating vibration. Usually, they are fitted with accelerometers or vibration pickups for a full range of vibration measurement and analysis. Other instruments used for testing vibration in the field are described as follows.

Reed vibrometers are relatively inexpensive and are often used for testing vibration, but their relative inaccuracy limits their usefulness.

Vibrometers are moderately priced and measure vibration amplitude by means of a light beam projected on a graduated scale.

Vibrographs are moderately priced mechanical instruments that measure both amplitude and frequency. They provide a chart recording amplitude, frequency, and actual wave form of vibration. They can be used for simple, accurate determination of the natural frequency of shafts, components, and systems by a bump test.

Reed vibrometers, vibrometers, and vibrographs have largely been supplanted by electronic meters that are more accurate and have become much more affordable.

Vibration meters are moderately priced, relatively simple-to-use modern electronic instruments that measure the vibration amplitude. They provide a single broadband (summation of all frequencies) number identifying the magnitude of the vibration level. Both analog and digital readouts are common.

Vibration analyzers are relatively expensive electronic instruments that measure amplitude and frequency, usually incorporating a variable filter.

Strobe lights are often used with many of the other instruments for analyzing and balancing rotating equipment.

Stethoscopes are available as inexpensive mechanic’s type (basically, a standard stethoscope with a probe attachment), relatively inexpensive models incorporating a tunable filter, and moderately priced powered types that electronically amplify sound and provide some type of meter and/or chart recording.

The choice of instruments depends on the test. Vibrometers and vibration meters can be used to measure vibration amplitude as an acceptance check. Because they cannot measure frequency, they cannot be used for analysis and primarily function as a go/no-go instrument. The best acceptance criteria consider both amplitude and frequency. Anyone seriously concerned with vibration testing should use an instrument that can determine frequency as well as amplitude, such as a vibrograph or vibration analyzer.

Vibration measurement instruments (both meters and analyzers) made specifically for measuring machinery vibration typically use moving coil velocity transducers, which are sizable and rugged. These are typically limited to a lower frequency of 500 cycles per minute (cpm) [8.33 Hz] with normal calibration. If measuring very-low-speed machinery such as large fans, cooling towers, or compressors operating below this limit, use an adjustment factor provided by the instrument manufacturer or use an instrument with a lower low-frequency limit, which typically uses a smaller accelerometer as the vibration pickup transducer.

Testing Vibration Isolation.

The only accurate check of isolation efficiencies is to compare vibration measurements of equipment operating with isolators to measurements of equipment operating without isolators. Because this is usually impractical, it is better to check whether the isolator’s deflection is as specified and whether the specified or desired isolation efficiency is being provided. Figure 21 shows natural frequency of isolators as a function of deflection and indicates the theoretical isolation efficiencies for various frequencies at which the equipment operates.

Although it is easy to determine the deflection of spring mounts by measuring the difference between the free heights with a ruler (information as shown on submittal drawings or available from a manufacturer), these measurements are difficult with most pad or rubber mounts. Further, most pad and rubber mounts do not lend themselves to accurate determination of natural frequency as a function of deflection. For these mounts, the most practical approach is to check that there is no excessive vibration of the base and no noticeable or objectionable vibration transmission to the building structure.

If isolators are in the 90% efficiency range and there is transmission to the building structure, either the equipment is operating roughly or there is a flanking path of transmission, such as connecting piping or obstruction, under the base.

Testing Equipment Vibration. Testing equipment vibration is necessary as an acceptance check to determine whether equipment is functioning properly and to ensure that objectionable vibration and noise are not transmitted. Although a person familiar with equipment can determine when it is operating roughly, instruments are usually required to determine accurately whether vibration levels are satisfactory.

Vibration Tolerances. Vibration tolerance criteria are listed in Table 45 of Chapter 49. These criteria are based on equipment installed on vibration isolators and can be met by any reasonably smoothly running equipment. Note that values in Chapter 49 are based on root-mean-square (RMS) values; other sources often use peak-to-peak or peak values, especially for displacements. For sinusoid responses, it is simple to obtain peak from RMS values, but in application the relationship may not be so straightforward. The main advantage of RMS is that the same instrumentation can be used for both sound and vibration measurements by simply changing the transducer. Also, there is only one recognized reference level for the decibel used for sound-pressure levels, but for vibration levels there are several recognized ones but no single standard. A common mistake in interpreting vibration data is misunderstanding the reference level and whether the vibration data are RMS, peak-to-peak, or peak values. Use great care in publishing and interpreting vibration data and converting to and from linear absolute values and levels in decibels.

Procedure for Testing Equipment Vibration.

Evaluating Vibration Measurements.

Amplitude Measurement. When specification for acceptable equipment vibration is based on amplitude measurements only, measurements can be made with an instrument that measures only amplitude (e.g., a vibration meter or vibrometer),

Amplitude and Frequency Measurement. When specification for acceptable equipment vibration is based on both amplitude and frequency measurements must be made with instruments that measure both amplitude and frequency (e.g., a vibrograph or vibration analyzer),

Vibration Analysis. The following guide covers most vibration problems that may be encountered.

Axial Vibration Exceeds Radial Vibration. When the amplitude of axial vibration (parallel with shaft) at any bearing exceeds radial vibration (perpendicular to shaft, vertical or horizontal), it usually indicates misalignment, most common on direct-driven equipment because flexible couplings accommodate parallel and angular misalignment of shafts. This misalignment can generate forces that cause axial vibration, which can cause premature bearing failure, so misalignment should be checked carefully and corrected promptly. Other possible causes of large-amplitude axial vibration are resonance, defective bearings, insufficient rigidity of bearing supports or equipment, and loose hold-down bolts.

Vibration Amplitude Exceeds Allowable Tolerance at Rotational Speed. The allowable vibration limits established by Table 41 of Chapter 49 are based on vibration caused by rotor imbalance, which results in vibration at rotational frequency. Although vibration caused by imbalance must be at the frequency at which the part is rotating, a vibration at rotational frequency does not have to be caused by imbalance. An unbalanced rotating part develops centrifugal force, which causes it to vibrate at rotational frequency. Vibration at rotational frequency can also result from other conditions such as a bent shaft, an eccentric sheave, misalignment, and resonance. If vibration amplitude exceeds allowable tolerance at rotational frequency, the following steps should be taken before performing field balancing of rotating parts:

Vibration at Other than Rotational Frequency. Vibration at frequencies other than driving and driven speeds is generally considered unacceptable. Table 4 shows some common conditions that can cause vibration at other than rotational frequency.

Resonance. If resonance is suspected, determine which part of the system is in resonance.

Isolation Mounts. The natural frequency of the most commonly used spring mounts is a function of spring deflection, as shown in Figure 25, and it is relatively easy to calculate by determining the difference between the free and operating height of the mount, as explained in the section on Testing Vibration Isolation. This technique cannot be applied to rubber, pad, or fiberglass mounts, which have a natural frequency in the 300 to 3000 cpm (5 to 50 Hz) range. Natural frequency for such mounts is determined by a bump test. Any resonance with isolators should be immediately corrected because it results in excessive movement of equipment and more transmission to the building structure than if equipment were attached solidly to the building (installed without isolators).

Components. Resonance can occur with any shaft, structural base, casing, and connected piping. The easiest way to determine natural frequency is to perform a bump test with a vibration spectrum analyzer.

Checking for Vibration Transmission. The source of vibration transmission can be checked by determining frequency with a vibration analyzer and tracing back to equipment operating at this speed. However, the easiest and usually best method (even if test equipment is being used) is to shut off components one at a time until the source of transmission is located. Most transmission problems cause disturbing noise; listening is the most practical approach to determine a noise source because the ear is usually better than instruments at distinguishing small differences and changes in character and amount of noise. Where disturbing transmission consists solely of vibration, an instrument will probably be helpful, unless vibration is significantly above the sensory level of perception. Vibration below sensory perception is generally not objectionable.

If equipment is located near the affected area, check isolation mounts and equipment vibration. If vibration is not being transmitted through the base, or if the area is remote from equipment, the probable cause is transmission through connected piping and/or ducts. Ducts can usually be isolated by isolation hangers. However, transmission through connected piping is very common and presents many problems that should be understood before attempting to correct them (see the following section).

Vibration and Noise Transmission in Piping. Vibration and noise in connected piping can be generated by either equipment (e.g., pump or compressor) or flow (velocity). Mechanical vibration from equipment can be transmitted through the walls of pipes or by a water column. Flexible pipe connectors, which provide system flexibility to permit isolators to function properly and protect equipment from stress caused by misalignment and thermal expansion, can be useful in attenuating mechanical vibration transmitted through a pipe wall. However, they rarely suppress flow vibration and noise and only slightly attenuate mechanical vibration as transmitted through a water column.

Tie rods are often used with flexible rubber hose and rubber expansion joints (Figure 26). Although they accommodate thermal movements, they hinder vibration and noise isolation. This is because pressure in the system causes the hose or joint to expand until resilient washers under tie rods are virtually rigid. To isolate noise adequately with a flexible rubber connector, tie rods and anchor piping should not be used. However, this technique generally cannot be used with pumps on spring mounts, which would still permit the hose to elongate. Flexible metal hose can be used with spring-isolated pumps because wire braid serves as tie rods; metal hose controls vibration but not noise.

Problems of transmission through connected piping are best resolved by changes in the system to reduce noise (improve flow characteristics, reduce impeller size) or by completely isolating piping from the building structure. Note, however, that it is almost impossible to isolate piping completely from the structure, because the required resiliency is inconsistent with rigidity requirements of pipe anchors and guides. Chapter 49 contains information on flexible pipe connectors and resilient pipe supports, anchors, and guides, which should help resolve any piping noise transmission problems.

To determine a building’s energy use characteristics, existing conditions must be accurately measured with proper instruments. Accurate measurements point out opportunities to reduce waste and provide a record of the actual conditions in the building before energy conservation measures were taken. They provide a compilation of installed equipment data and a record of equipment performance before changes. Judgments will be made based on the information gathered during the field survey; that which is not accurately measured cannot be properly evaluated.

Generally, instruments used for testing, adjusting, and balancing are sufficient for energy conservation surveying. Possible additional instruments include a power factor meter, light meter, combustion testing equipment, refrigeration gages, and equipment for recording temperatures, fluid flow rates, and energy use over time. Only high-quality instruments should be used.

Observation of system operation and any information the technician can obtain from the operating personnel pertaining to the operation should be included in the report.

Organized record keeping is extremely important. A camera is also helpful. Photographs of building components and mechanical and electrical equipment can be reviewed later when the data are analyzed.

Data sheets for energy conservation field surveys contain different and, in some cases, more comprehensive information than those used for testing, adjusting, and balancing. Generally, the energy engineer determines the degree of fieldwork to be performed; data sheets should be compatible with the instructions received.

The most effective way to reduce building energy waste is to identify, define, and tabulate the energy load by building system. For this purpose, load is defined as the quantity of energy used in a building, or by one of its subsystems, for a given period. By following this procedure, the most effective energy conservation opportunities can be achieved more quickly because high priorities can be assigned to systems that consume the most energy.

A building can be divided into nonenergized and energized systems. Nonenergized systems do not require external energy sources such as electricity and fuel. Energized systems (e.g., mechanical and electrical systems) require external energy. Energized and nonenergized systems can be divided into subsystems defined by function.

Nonenergized Systems. Nonenergized subsystems include building site, envelope, and interior; building use; and building operation.

Building Site, Envelope, and Interior. These subsystems should be surveyed to determine how they can be modified to reduce the building load that the mechanical and electrical systems must meet (without adversely affecting the building’s appearance). It is important to compare actual conditions with conditions assumed by the designer, so that mechanical and electrical systems can be adjusted to balance their capacities to satisfy actual needs.

Building Use. These loads can be classified as people occupancy or operation loads. People occupancy loads are related to schedule, density, and mixing of occupancy types (e.g., process and office). People operation loads are varied and include operation of manual window shading devices; setting of room thermostats; and conservation-related habits such as turning off lights, closing doors and windows, turning off energized equipment when not in use, and not wasting domestic hot or chilled water.

Building Operation. This subsystem consists of the operation and maintenance of all the building subsystems. The load on the building operation subsystem is affected by factors such as the time at which janitorial services are performed, janitorial crew size and time required to clean, amount of lighting used to perform janitorial functions, quality of equipment maintenance program, system operational practices, and equipment efficiencies.

Energized Systems. Energized subsystems of a building generally include plumbing, heating, ventilating, cooling, space conditioning, control, electrical, and food service. Although these systems are interrelated and often use common components, logical organization of data requires evaluating the energy use of each subsystem as independently as possible. In this way, proper energy conservation measures for each subsystem can be developed.

In addition to building subsystem loads, the process load in most buildings must be evaluated by the energy field auditor. Most tasks not only require energy for performance, but also affect the energy consumption of other building subsystems. For example, if a process releases large amounts of heat to the space, the process consumes energy and also imposes a large load on the cooling system.

The following checklist outlines requirements for a field study form, needed to conduct an energy audit.

Inspection and Observation of All Systems. Record physical and mechanical condition of the following:

Interview of Physical Plant Supervisor. Record answers to the following survey questions:

Recording System Information. Record the following system/equipment identification:

Recording Test Data. Record the following test data:

The report should contain the following, as applicable:

Title page:

Summary of comments:

Nomenclature sheet:

Test conditions (to be stated on the fan or pump performance form):

A single line diagram for schematic layout of air distribution systems and hydronic systems is highly recommended to ensure systematic and efficient procedures. Quantities of outdoor air, return air, relief air; sizes and airflow rates for main ducts; sizes and airflow rates for all air terminal devices, dampers, and other regulating devices should be shown. All air terminals should be numbered before filling out the air terminal device report. Though diagrams are suggested, the use of this form is not mandatory.

The performance of air handling apparatus with coils is to be reported. Motor voltage and amperage for three-phase motors should be reported for all three legs (T1, T2, and T3). If the design engineer did not specify a design quantity for any item in the test data section, place an X in the space for the design quantity and record the actual quantity. If available, include equipment manufacturer ratings in the design columns when design quantity is unknown. If motor ratings differ from design, provide an explanation at the bottom of the page. If there are split coils, record data for each airstream.

Apparatus Coil Test Report:

The performance of chilled water, hot water, steam, or DX coils, and for runaround heat recovery systems is to be reported.

Data for gas- or oil-fired devices, (e.g., unit heaters, duct furnaces, etc.) will be recorded. This report is not intended to be used in lieu of a factory startup equipment report, but could be used as a supplement. All available design data should be reported. Some information could apply to the burner motor, burner fan motor, unit air fan motor, etc., depending on the application or equipment. Therefore, designate the motor of the recorded data.

Data for electric furnaces or for electric coils installed in built-up units or ducts will be recorded. “Minimum air velocity” is as recommended by manufacturers.

The performance of all supply, return, and exhaust fans should be recorded.

The results of a pitot tube traverse in all rectangular, round, and oval ducts shall be recorded. For rectangular duct traverses, make a grid representing the duct cross section with a box for each test point and its distance from sides of duct. It is recommended that the velocity pressures be recorded in one half of each box provided and then converted to velocities in the other half of the box at a later time. The velocities should be averaged, but do not average the velocity pressures. For round duct traverses, make a circle representing the duct cross section. Make columns with a number for each test point, along with its distance from sides of duct, and for velocity pressures or velocities taken at points across three diameters at a 60° angles to each other. For oval duct traverses, make columns with a number for each test point, its dimension along the major and minor axis, and velocity pressures or velocities taken at points across the two axes of the duct, or show on a traverse sheet the horizontal reading.

The flow rate of all air terminal devices should be recorded. If the final adjusted flow rate of any air terminal device deviates from design by more than ±10%, a note indicating the amount of variance shall be recorded in the “remarks” section of the report to provide known or potential reasons for such deviation. All correction factors should be shown in the remarks column for all velocity measurement instruments.

The performance of reheat coils or the water coil on terminal units should be recorded.

The control settings and the entering and leaving conditions at the chiller should be recorded. This data should be substantially completed and verified by the manufacturers’ representatives and/or the equipment owner or installing contractor before the HVAC distribution systems are balanced. Temperature and pressure differential readings of the chiller unit evaporator and condenser should be recorded during the TAB procedures. Describe the flow measuring device when used.

(List design and actual quantities where appropriate.)

Test data from package units of all types shall be recorded. If the unit has components other than the evaporator fan, DX coil, and compressor and condenser fan(s), use the appropriate report forms for: water or steam coils, direct fired heaters, electric coils, or return air fans.

Control settings, as well as entering and leaving conditions at the compressor and/or condenser, should be recorded. Because the balancing firm is not necessarily responsible for startup or the proper operation of the machine, this form does not attempt to indicate the performance or efficiency of the machine except as may be determined by the design engineer from the data contained therein.

These data should be substantially completed and verified by the manufacturers’ representatives and/or the equipment owner or installing contractor before the HVAC distribution systems are balanced. Temperature and pressure differential readings of the unit should be recorded during the TAB procedures.

This report may also be used to record data for the refrigerant side of unitary systems, bare compressors, separate air-cooled condensers, or separate water-cooled condensers.

This data should be substantially completed and verified before the system is balanced. The pump data section is to be used for the recirculating pump in evaporative condensers, not the system used with cooling towers.

The record final conditions for steam or hot water heat exchangers should be recorded.

The final data on each pump is to be recorded. The actual impeller diameter entry is that indicated by plotting the head curve based on a no-flow head test or by actual field measurement where possible.

Net positive suction head (NPSH) is important for pumps in open circuits and for pumps handling fluids at elevated temperatures.

The control settings and the entering and leaving conditions at the boiler should be recorded. Because the balancing firm is not necessarily responsible for start-up or the proper operation of the machine, these data do not attempt to indicate the performance or efficiency of the boiler except as may be determined by the design engineer from the data contained therein.

This report should be substantially completed and verified by the manufacturers’ representatives and/or the installing contractor before the HVAC distribution systems are balanced. Temperature and/or pressure readings of the boiler should be entered during TAB procedures.

A flue gas analysis normally is not in the scope of TAB procedures, but data could be added in a commentary section if available and required by the engineer/owner.

This report is to document the application and date of the most recent calibration test or calibration for each instrument used in the testing, adjusting, and balancing work.

This report is intended to provide sufficient information to determine cause of failure and provide feedback to the manufacturer, designer, or installer. This report should be used as soon as a problem has occurred, and its inclusion in the final report is at the discretion of the balancer. It should be noted on the report, if appropriate, that the analysis and recommendations are not to be considered final or expert.

Reports should comply with ASHRAE Standard 111, be complete, and include the location of test drawings. An instrument list including serial numbers and current and future calibration dates should also be provided.