ASHRAE 90138-2010 DAMPERS AND AIRFLOW CONTROL.pdf

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1、 Dampers and Airflow Control American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. Laur

2、ence G. Felker, a mechanical engineer, has worked as an electrician, HVACservice technician, and mechanical system designer. He has 19 years of experiencedesigning pneumatic, analog electronic, and direct digital control systems. Since 1991he has specialized in actuated damper and valve applications

3、 for Belimo Americas. Hehas been a member of the American Society of Heating, Refrigerating and Air-Condi-tioning Engineers, Inc. (ASHRAE) since 1978 and is a member of the InternationalCode Council (ICC) and the National Fire Protection Association (NFPA). His previ-ously published work includes Ev

4、ans Equations of Unified Field Theory (arima publish-ing), a theoretical physics book.Travis L. Felker earned a bachelor of science degree in mathematics and worked forBelimo Americas for two years. Presently, he is working on his masters degree ineducation and teaching junior college.Updates and er

5、rata to this publication will be posted on the ASHRAE website at www.ashrae.org/publicationupdates.“CPVUUIF“VUIPST American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either

6、 print or digital form is not permitted without ASHRAEs prior written permission. Dampers and Airflow ControlLaurence G. FelkerTravis L. FelkerAmerican Society of Heating, Refrigerating andAir-Conditioning Engineers, Inc.Atlanta American Society of Heating, Refrigerating and Air-Conditioning Enginee

7、rs, Inc. (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ISBN 978-1-933742-53-32009 American Society of Heating, Refrigeratingand Air-Conditioning Engineers, Inc

8、.1791 Tullie Circle, NEAtlanta, GA 30329www.ashrae.orgAll rights reserved.Printed in the United States of America on 30% post-consumer waste using soy-based inks.ASHRAE has compiled this publication with care, but ASHRAE has not investigated, and ASHRAE expressly disclaimsany duty to investigate, an

9、y product, service, process, procedure, design, or the like that may be described herein. Theappearance of any technical data or editorial material in this publication does not constitute endorsement, warranty, orguaranty by ASHRAE of any product, service, process, procedure, design, or the like. AS

10、HRAE does not warrant thatthe information in the publication is free of errors, and ASHRAE does not necessarily agree with any statement or opin-ion in this publication. The entire risk of the use of any information in this publication is assumed by the user.No part of this book may be reproduced wi

11、thout permission in writing from ASHRAE, except by a reviewer who mayquote brief passages or reproduce illustrations in a review with appropriate credit; nor may any part of this book be repro-duced, stored in a retrieval system, or transmitted in any way or by any meanselectronic, photocopying, rec

12、ording,or otherwithout permission in writing from ASHRAE. Requests for permission should be submitted atwww.ashrae.org/permissions._Library of Congress Cataloging-in-Publication DataFelker, Laurence G., 1946Dampers and Airflow Control / Laurence G. Felker, Travis L. Felker.p. cm.Includes bibliograph

13、ical references and index.ISBN 978-1-933742-53-31. Air ducts 2. Airflow 3. Damping (Mechanics) I. Felker, Travis L. II. Title. TH7683.L7F45 2009697dc222009012084“4)3“ mechanical and control contractors; and testing, adjusting, and balancing(TAB) contractors are the target audience of this book. Each

14、 specializes in a different partof the heating, ventilating, and air-conditioning (HVAC) system. Some material presentedhere is already familiar to each of these groups, and some material falls outside their normalareas of concern. For example, the information on loss coefficients and pressure loss

15、is basicto the mechanical engineer; however, it is unfamiliar to most control contractors. Much ofthe subject material bridges gaps that exist between disciplines. The gaps observed in airsystems are as follows:Lack of understanding of the final control elementthe damperLack of understanding of the

16、detailed methods of the other trades on a projectLack of understanding of the complexity of airflowsThere are many articles published regarding, for example, indoor air quality (IAQ) thatsay what actions to take. However, there are few suggestions for how they should be taken.This book addresses how

17、 to apply dampers within systems to achieve clearly defined goals.The control of airflow in any commercial building is necessary for a variety of functions:Temperature controlIAQ (ventilation)Envelope pressure control (mold and infiltration control) Elevator door operationExterior door operationExha

18、ustMakeup airPressure cascade from one zone to anotherMitigation/control of chemical, biological, and radiological (CBR) releaseSmoke containment using shaft and wall dampersSmoke control using pressure differentialsAtria and large-space smoke extractionStairwell pressurizationEgress corridor smoke

19、control Zone smoke control American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. %BNQFS

20、TBOE“JSGMPX$POUSPMFans and dampers are the primary control devices for airflow management. Fans areadequately covered in many available technical publications, such as those published by theAir Movement and Control Association (AMCA 2002). However, this is the first book writ-ten about dampers. Many

21、 articles and manufacturer bulletins exist, and product informationis available from manufacturers, but nothing is comprehensive. The principles explained are applicable to all damper applications. Fire and smokecontrol texts offer good insight into airflow strategy and tactics and are sources of in

22、forma-tion not available elsewhere. For more information, see Chapter 16.130#- NIOSH 2007). While people do not complain on a daily basis about IAQ, theydo complain about temperature. A system not controlling temperature well is almost inev-itably not controlling ventilation adequately to protect te

23、nants from health problems. Nor arethe owner, architect, and mechanical consultant protected from lawsuits (Katz and Portner1993).ANSI/ASHRAE Standard 62.1-2007, Ventilation for Acceptable Indoor Air Quality(ASHRAE 2007a), focuses on ventilation. ANSI/IESNA/ASHRAE Standard 90.1-2007,Energy Standard

24、for Buildings Except Low-Rise Residential Buildings (ASHRAE 2007b),provides guidance on energy use. Application of each standard depends on airflow. Whenapplying ASHRAE Standard 62.1, particularly in sophisticated applications like dynamicreset (Stanke 2006), it is necessary to ensure the dampers ca

25、n perform correctly.Seventy percent of the total number of commercial buildings are owner occupied. Theowner and occupants directly benefit from IAQ; however, building owners have limitedfinances, and it is normal to consider first cost as a primary concern, meet minimal coderequirements, and ignore

26、 life-cycle costs. An engineer typically works with time, financial,code, and standard constraints, and the mechanical designer has to do more work at the samepay to meet a high level of standards. Efforts by the U.S. Green Building Council (USGBC2007) are a step in the right direction toward bridgi

27、ng the gap between building costs andgood IAQ. Knowledge of dampers also helps engineers and mechanical designers avoidproblems and contributes to optimal design and cost efficiency.Poor temperature control causes lost productivity and wasted energy. Inclusive formalsurveys are not available on buil

28、t-up systems; however, performance of most packagedequipment is suspect. For example, according to the California Energy Commission “SmallSystem Design Guide” study,Economizers show a high rate of failure in the study. Of the units equipped with econ-omizers, 64% were not operating correctly. Failur

29、e modes included dampers that werestuck or inoperable (38%), sensor or control failure (46%), or poor operation (16%). Theaverage energy impact of inoperable economizers is about 37% of the annual coolingenergy (Jacobs et al. 2003). In the authors experience, about 15% of buildings have airflow prob

30、lems that lead tobad temperature control, IAQ deterioration, space pressurization irregularities, and wastedenergy. Another 20% can limp along for years with moderate troubles and property ownerindifference. Seasonal difficulties are common. There are no airflow or pressure control contractors. The

31、temperature control and TABcontractors are responsible for airflow and pressure control, but first they require a solidmechanical engineering design. The control contractor tends to think first of the sensor andlogic portion of his system and last about the final control element. There is little inf

32、ormationavailable on how and why to size dampers. Both valves and dampers are fluid-flow controldevices, and proper sizing requires a mechanical engineering approach.It is not atypical for engineers to design the mechanical system and then overlay thecontrol system. The two must be designed together

33、. The controls can fine-tune a good American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permissio

34、n. *OUSPEVDUJPO mechanical design; however, they must be included as a part of the design for maximumeffectiveness. Controls cannot compensate for many mechanical design problems.Since each building is unique, and the mechanical system must work the first time,design is critical. Of course, the spac

35、e, money, and time constraints placed on the mechanicaldesigner are sometimes severe and shortsighted on the part of the architect and owner if long-term quality is a goal. *.1035“/$ accuracy is not an important issue. A controller cannot compensate for incorrectdamper or actuator sizing. The TAB co

36、ntractor or commissioning authority can only some-times set airflows to correct for problems. Concentration on the final control elements in the design process can solve most of theseproblems. Equipment sizing is very rarely a problem. The airflow system delivering most ofthe conditioned air to the

37、occupants causes the difficulties. Factory-built mixing boxescontrol flow with difficulty due to space constraints. The willingness of design engineers todesign around some space constraints leads to systems that work only part time. “*3-084*/“#6*-%*/(“/%4:45 this can result in irregular flow patter

38、ns)Leakage paths through ceilings and floorsLeakage paths through pipes, chases, shafts, and any penetrationsUnknown variables and factors, although, possibly, exhaust should be a term reserved for localexhaust or powered exhausts. Clarity in terminology is necessary for clear thinking. The term rec

39、irculation and exhaust air could be used instead of return air. It diverts atthe return plenum into relief air and recirculation air. In this book, each term is used to reflectactual practices. AHU Air-handling unitDA Discharge airdischarge from air handler going to supply diffusers or VAV boxesEA E

40、xhaust airIGV Inlet guide vaneMA Mixed airpart outdoor and part recirculated from the spaceOA Outdoor air RA Recirculation air or, alternately, return airRAD Return-air damperRAF Return-air fan REA Recirculation and exhaust airpart goes back to the AHU, and part is relieved.REF Relief-exhaust fanRFA

41、 Relief airRP Return-relief plenumdiverting tee in the return-air path SA Supply air to space SAF Supply-air fanVAV Variable air volumeVFD Variable-frequency drive5:1*$“-13 however, the system overall is adapted for neithereconomizer operation nor space pressure control.When there is both an SAF and

42、 an RAF, the RP is positive in all damper positions (unlessthe supply overpowers the RAF in error). The MA is negative; the value varies with thedamper positions. When the OA damper is fully open, there is little pressure loss in that path.When the RAD is fully open (and the OA damper is closed), th

43、e RAF pushes air into the MAduct in some cases. The MA could go positive if the fans are unbalanced. Typically, the MA is negative and the RP is positive. The balance or neutral pressurepoint where the static pressure is zero is often inside the RAD itself. The velocity pressureis always positive, s

44、ince air is moving. The pressures at various points vary as the economizerdampers and VAV dampers proportion.With an REF, there is no neutral pressure point when the REF is OFF. The SAF pulls theplenum negative. When the REF is ON, both the SAF and REF pull the duct negative untilthe RAD is closed.

45、The balance point is within the RAD when it is closing; however, theneutral pressure point floats around in some cases. This is a difficult system to control.The exact location of the neutral pressure point is not critical as long as the rest of thesystem is operating correctly. Designing the fans s

46、tatic pressures with respect to the duct and damper pressure lossesat the various velocities is necessary. Given the unknowns, it is necessary to provide methodsto balance the system. Balancing dampers and the use of VFDs help control airflow.JHVSF*1SFTTVSFQPJOUTJOBUZQJDBMBJSIBOEMJOHVOJU “)6 America

47、n Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. %BNQFSTBOE“JSGMPX$POUSPMA hydraulic analysis is always necess