ASHRAE HVAC APPLICATIONS IP CH 38-2015 TESTING ADJUSTING AND BALANCING.pdf

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1、38.1CHAPTER 38TESTING, ADJUSTING, AND BALANCINGTerminology . 38.1General Criteria. 38.1Air Volumetric Measurement Methods. 38.2Balancing Procedures for Air Distribution 38.3Variable-Volume Systems . 38.4Principles and Procedures for Balancing Hydronic Systems . 38.6Water-Side Balancing. 38.8Hydronic

2、 Balancing Methods. 38.9Fluid Flow Measurement . 38.12Steam Distribution 38.15Cooling Towers. 38.15Temperature Control Verification. 38.16Field Survey for Energy Audit 38.17Reports . 38.18Testing for Sound and Vibration. 38.19YSTEMS that control the environment in a building changeSwith time and use

3、, and must be rebalanced accordingly. Thedesigner must consider initial and supplementary testing and balanc-ing requirements for commissioning. Complete and accurate operat-ing and maintenance instructions that include intent of design andhow to test, adjust, and balance the building systems are es

4、sential.Building operating personnel must be well-trained, or qualified oper-ating service organizations must be employed to ensure optimumcomfort, proper process operations, and economical operation.This chapter does not suggest which groups or individuals shouldperform a complete testing, adjustin

5、g, and balancing procedure. How-ever, the procedure must produce repeatable results that meet thedesign intent and the owners requirements. Overall, one source mustbe responsible for testing, adjusting, and balancing all systems. Aspart of this responsibility, the testing organization should check a

6、llequipment under field conditions to ensure compliance.Testing and balancing should be repeated as systems are reno-vated and changed. Testing boilers and other pressure vessels forcompliance with safety codes is not the primary function of the test-ing and balancing firm; rather, it is to verify a

7、nd adjust operatingconditions in relation to design conditions for flow, temperature,pressure drop, noise, and vibration. ASHRAE Standard 111 detailsprocedures not covered in this chapter.1. TERMINOLOGYTesting, adjusting, and balancing (TAB) is the process of check-ing and adjusting all environmenta

8、l systems in a building to producethe design objectives. This process includes (1) balancing air andwater distribution systems, (2) adjusting the total system to providedesign quantities, (3) electrical measurement, (4) establishing quan-titative performance of all equipment, (5) verifying automatic

9、 con-trol system operation and sequences of operation, and (6) sound andvibration measurement. These procedures are accomplished bychecking installations for conformity to design, measuring andestablishing the fluid quantities of the system as required to meetdesign specifications, and recording and

10、 reporting the results.The following definitions are used in this chapter. Refer to ASH-RAE Terminology (https:/www.ashrae.org/resources-publications/free-resources/ashrae-terminology) for additional definitions.Test. Determine quantitative performance of equipment.Adjust. Regulate the specified flu

11、id flow rate and air patterns atterminal equipment (e.g., reduce fan speed, adjust a damper).Balance. Proportion flows in the distribution system (submains,branches, and terminals) according to specified design quantities.Balanced System. A system designed to deliver heat transferrequired for occupa

12、nt comfort or process load at design conditions.A minimum heat transfer of 97% should be provided to the space orload served at design flow. The flow required for minimum heattransfer establishes the systems flow tolerance. The fluid distribu-tion system should be designed to allow flow to maintain

13、therequired tolerance and verify its performance.Procedure. An approach to and execution of a sequence of workoperations to yield repeatable results.Report forms. Test data sheets arranged in logical order for sub-mission and review. They should also form the permanent record tobe used as the basis

14、for any future TAB work.Terminal. A point where the controlled medium (fluid or energy)enters or leaves the distribution system. In air systems, these may bevariable- or constant-volume boxes, registers, grilles, diffusers, lou-vers, and hoods. In water systems, these may be heat transfer coils,fan-

15、coil units, convectors, or finned-tube radiation or radiant panels.2. GENERAL CRITERIAEffective and efficient TAB requires a systematic, thoroughlyplanned procedure implemented by experienced and qualified staff.All activities, including organization, calibration of instruments, andexecution of the

16、work, should be scheduled. Air-side work must becoordinated with water-side and control work. Preparation includesplanning and scheduling all procedures, collecting necessary data(including all change orders), reviewing data, studying the system tobe worked on, preparing forms, and making preliminar

17、y field in-spections.Air leakage in a conduit (duct) system can significantly reduceperformance, so conduits (ducts) must be designed, constructed, andinstalled to minimize and control leakage. During construction, allduct systems should be sealed and tested for air leakage. Water,steam, and pneumat

18、ic piping should be tested for leakage, which canharm people and equipment.Design ConsiderationsTAB begins as design functions, with most of the devicesrequired for adjustments being integral parts of the design and instal-lation. To ensure that proper balance can be achieved, the engineershould sho

19、w and specify a sufficient number of dampers, valves,flow measuring locations, and flow-balancing devices; these must beproperly located in required straight lengths of pipe or duct for accu-rate measurement. Testing depends on system characteristics andlayout. Interaction between individual termina

20、ls varies with pres-sures, flow requirements, and control devices.The design engineer should specify balancing tolerances. Mini-mum flow tolerances are 10% for individual terminals andbranches in noncritical applications and 5% for main air ducts. Forcritical water systems where differential pressur

21、es must be main-tained, tolerances of 5% are suggested. For critical air systems, rec-ommendations are the following:The preparation of this chapter is assigned to TC 7.7, Testing and Balancing.38.2 2015 ASHRAE HandbookHVAC ApplicationsPositive zones:Supply air 0 to +10%Exhaust and return air 0 to 1

22、0%Negative zones:Supply air 0 to 10%Exhaust and return air 0 to +10%Balancing Devices. Balancing devices should be used to providemaximum flow-limiting ability without causing excessive noise.Flow reduction should be uniform over the entire duct or pipe. Sin-gle-blade dampers or butterfly balancing

23、valves are not good bal-ancing valves because of the uneven flow pattern at high pressuredrops. Pressure drop across equipment is not an accurate flow mea-surement but can be used to determine whether the manufacturerdesign pressure is within specified limits. Liberal use of pressuretaps at critical

24、 points is recommended.3. AIR VOLUMETRIC MEASUREMENT METHODSGeneralThe pitot-tube traverse is the generally accepted method of mea-suring airflow in ducts; ways to measure airflow at individual ter-minals are described by manufacturers. The primary objective is toestablish repeatable measurement pro

25、cedures that correlate with thepitot-tube traverse.Laboratory tests, data, and techniques prescribed by equipmentand air terminal manufacturers must be reviewed and checked foraccuracy, applicability, and repeatability of results. Conversion fac-tors that correlate field data with laboratory results

26、 must be devel-oped to predict the equipments actual field performance.Air DevicesAll flow-measuring instruments should be field verified by com-paring to pitot-tube traverses to establish correction and/or densityfactors.Generally, correction factors given by air diffuser manufacturersshould be che

27、cked for accuracy by field measurement and bycomparing actual flow measured by pitot-tube traverse to actualmeasured velocity. Air diffuser manufacturers usually base theirvolumetric test measurements on a deflecting vane anemometer.The velocity is multiplied by an empirical effective area to obtain

28、the air diffusers delivery. Accurate results are obtained by measur-ing at the vena contracta with the probe of the deflecting vane ane-mometer. Methods advocated for measuring airflow of troffer-typeterminals are similar to those for air diffusers. A capture hood is frequently used to measure devic

29、e airflows,primarily of diffusers and slots. Loss coefficients should be estab-lished for hood measurements with varying flow and deflection set-tings. If the air does not fill the measurement grid, the readings willrequire a correction factor. Rotating vane anemometers are commonly used to measure

30、air-flow from sidewall grilles. Effective areas (correction factors)should be established with the face dampers fully open and deflec-tion set uniformly on all grilles. Correction factors are requiredwhen measuring airflow in open ducts i.e., damper openings andfume hoods (Sauer and Howell 1990).Duc

31、t FlowThe preferred method of measuring duct volumetric flow is thepitot-tube traverse average. The maximum straight run should beobtained before and after the traverse station. To obtain the bestduct velocity profile, measuring points should be located as shownin Chapter 36 of the 2013 ASHRAE Handb

32、ookFundamentals andASHRAE Standard 111. When using factory-fabricated volume-measuring stations, the measurements should be checked against apitot-tube traverse.Power input to a fans driver should be used as only a guide to indi-cate its delivery; it may also be used to verify performance determined

33、by a reliable method (e.g., pitot-tube traverse of systems main) thatconsiders possible system effects. For some fans, the flow rate is notproportional to the power needed to drive them. In some cases, as withforward-curved-blade fans, the same power is required for two ormore flow rates. The backwa

34、rd-curved-blade centrifugal fan is theonly type with a flow rate that varies directly with power input.If an installation has an inadequate straight length of ductwork orno ductwork to allow a pitot-tube traverse, the procedure from Sauerand Howell (1990) can be followed: a vane anemometer reads air

35、velocities at multiple points across the face of a coil to determine aloss coefficient.Mixture PlenumsApproach conditions are often so unfavorable that the air quan-tities comprising a mixture (e.g., outdoor and return air) cannot bedetermined accurately by volumetric measurements. In such cases,the

36、 mixtures temperature indicates the balance (proportions)between the component airstreams. Temperatures must be mea-sured carefully to account for stratification, and the differencebetween outdoor and return temperatures must be greater than 20F.The temperature of the mixture can be calculated as fo

37、llows:Qttm= Qoto+ Qrtr(1)whereQt= total measured air quantity, %Qo= outdoor air quantity, %Qr= return air quantity, %tm= temperature of outdoor and return mixture, Fto= outdoor temperature, Ftr= return temperature, FPressure MeasurementAir pressures measured include barometric, static, velocity, tot

38、al,and differential. For field evaluation of air-handling performance,pressure should be measured per ASHRAE Standard 111 and ana-lyzed together with manufacturers fan curves and system effect aspredicted by AMCA Standard 210. When measured in the field,pressure readings, air quantity, and power inp

39、ut often do not corre-late with manufacturers certified performance curves unless propercorrection is made.Pressure drops through equipment such as coils, dampers, or fil-ters should not be used to measure airflow. Pressure is an acceptablemeans of establishing flow volumes only where it is required

40、 by, andperformed in accordance with, the manufacturer certifying theequipment.StratificationNormal design minimizes conditions causing air turbulence, toproduce the least friction, resistance, and consequent pressure loss.Under some conditions, however, air turbulence is desirable andnecessary. For

41、 example, two airstreams of different temperaturescan stratify in smooth, uninterrupted flow conditions. In this situa-tion, design should promote mixing. Return and outdoor airstreamsat the inlet side of the air-handling unit tend to stratify whereenlargement of the inlet plenum or casing size decr

42、eases air veloc-ity. Without a deliberate effort to mix the two airstreams (e.g., incold climates, placing the outdoor air entry at the top of the plenumand return air at the bottom of the plenum to allow natural mixing),stratification can be carried throughout the system (e.g., filter, coils,elimin

43、ators, fans, ducts). Stratification can freeze coils and rupturetubes, and can affect temperature control in plenums, spaces, orboth.Stratification can also be reduced by adding vanes to break upand mix the airstreams. No solution to stratification problems isTesting, Adjusting, and Balancing 38.3gu

44、aranteed; each condition must be evaluated by field measure-ments and experimentation.4. BALANCING PROCEDURES FOR AIR DISTRIBUTIONNo one established procedure is applicable to all systems. Thebibliography lists sources of additional information.Instruments for Testing and BalancingThe minimum instru

45、ments necessary for air balance areManometer calibrated in 0.005 in. of water divisionsCombination inclined/vertical manometer (0 to 10 in. of water)Pitot tubes in various lengths, as requiredTachometer (direct-contact, self-timing) or strobe lightClamp-on ammeter with voltage scales root-mean-squar

46、e (RMS)typeRotating vane anemometerDeflecting vane anemometerThermal anemometerCapture hoodDigital thermometers (0.1F increments as a minimum) and glassstem thermometers (0.1F graduations minimum)Sound level meter with octave band filter set, calibrator, andmicrophoneVibration analyzer capable of me

47、asuring displacement velocityand accelerationWater flowmeters (0 to 50 in. of water and 0 to 400 in. of waterranges)Compound gageTest gages (100 psi and 300 psi)Sling psychrometerEtched-stem thermometer (30 to 120F in 0.1F increments)HygrometersRelative humidity and dew-point instrumentsInstruments

48、must be calibrated periodically to verify their accu-racy and repeatability before use in the field.Preliminary Procedure for Air Balancing1. Before balancing, all pressure tests (duct leakage) of duct andpiping systems must be complete and acceptable.2. Obtain as-built design drawings and specifica

49、tions, andbecome thoroughly acquainted with the design intent.3. Obtain copies of approved shop drawings of all air-handlingequipment, outlets (supply, return, and exhaust), and tempera-ture control diagrams, including performance curves. Comparedesign requirements with shop drawing capacities.4. Compare design to installed equipment and field installation.5. Walk the system from air-handling equipment to terminal unitsto determine variations of installation from design.6. Check dampers (both volume and fire) for correct and lockedposition and temperature control