ASHRAE UFAD GUIDE-2013 UFAD Guide Design Construction and Operation of Underfloor Air Distribution Systems.pdf

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1、AIR-CONDITIONING SYSTEM DESIGN MANUALSECOND EDITIONAIR-CONDITIONING SYSTEM DESIGN MANUALSECOND EDITIONWalter T. Grondzik, EditorProduct code: 90338 4/13Errata noted in the list dated 01/04/2010 have been corrected.UFAD GUIDEDesign, Construction and Operation of Underfloor Air Distribution SystemsFor

2、 Use in Construction, Commissioning, Operations and MaintenanceReferences Standards, Codes, and RatingsProvides Cost and Energy ConsiderationsContains Information for Every Stage of Building and Maintaining UFAD Systems UFAD GUIDEDesign, Construction and Operation of Underfloor Air Distribution Syst

3、ems1791 Tullie Circle NEAtlanta, GA 30329-2305www.ashrae.orgThe Comprehensive Guide to Underfloor Air DistributionThe use of underfloor air distribution (UFAD) is increasing in North America as a solution to space conditioning concerns. This design guide provides assistance in the planning, construc

4、tion, and operation of UFAD systems, while carefully detailing the major differences between UFAD and more traditional forms of space conditioning. UFAD GUIDE: Design, Construction, and Operation of Underfloor Air Distribution Systems incorporates updated results from laboratory and field experiment

5、s. Also in-cluded are simulation studies, manufacturers literature, design experiences from practicing engineers, as well as other relevant guidelines from users of UFAD. For those in the construction, building commissioning, and operations and maintenance industries, this design guide provides a we

6、alth of information on an emerging technology, all while keeping in mind the typical flow of decision making.Product code: 90452 6/139 781936 504497UFAD GUIDE 2013 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form i

7、s not permitted without ASHRAEs prior written permission. * Denotes members of voting status when the document was approved for publication.ASHRAE Technical Resource Group onUnderfloor Air Design (TRG7.UFAD)James E. Megerson, Chair*Building Systems and DiagnosticsDavid Marciniak*General Services Adm

8、inistrationDaniel Int-Hout III, Vice Chair*KruegerMichael Joseph McQueeny*AirFixture, LLCWilliam Reynolds, Secretary*Tate Access FloorsR. Gaylon Richardson*Engineered Air BalanceJames K. Vallort, Programs*Environmental Systems Design, Inc.Julian Rimmer*EH Price Ltd.Fred Bauman, Research*Center for t

9、he Built EnvironmentPaul Turnbull*Siemens Building Technologies Inc.Kevin J. Gebke, Webmaster*DuctSox CorporationGary L. Wingfield*Francis A. Mills*Sinclair Knight MerzJerry M. SipesPrice Industries Inc.Harvey Brickman*Tishman Reality however, itsuse in commercial and institutional buildings is incr

10、easing in North America.The purpose of this Guide is to provide assistance in the design, con-struction, and operation of UFAD systems. The Guide also incorporatesimportant research results to support the UFAD design recommendationspresented, and includes an extensive annotated bibliography for thos

11、e seek-ing additional detailed information. This Guide does not cover alternate airdistribution system design procedures in detail; however; reference to morecommon systems is used to explain or contrast the methods used to designUFAD systems. It is not the intent of this Guide to promote one system

12、 overanother but to merely point out the major differences between UFAD andconventional system design. For more information on standard heating, ven-tilating, and air-conditioning design, please refer to other publications fur-nished by ASHRAE, including ASHRAE Handbook (ASHRAE 2009,2010d, 2011, 201

13、2), Air-Conditioning Systems Design Manual (Grondzik2007), and A Designers Guide to Conventional Ceiling-Based Room AirDiffusion (Rock and Zhu 2001).The development of this Guide is based on a compilation of availableinformation, including research results from laboratory and field experi-ments, sim

14、ulation studies, manufacturers literature, design experience ofpracticing engineers, and other relevant guidelines from users of the technol-ogy. Despite recent growth in the UFAD market, widespread experiencewith these systems is still at an early stage. The guidelines presented here arebased on th

15、e most current and best available data and information. It is notthe intent of the authors to cover every possible design scenario. It is up tothe reader to use good engineering judgment and common sense when 2013 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution,

16、 or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. UFAD GUIDE2applying methodologies described herein. The Guide is intended for use bydesign engineers, architects, building owners, facility managers, equipmentmanufacturers, installers, utilit

17、y engineers, researchers, and other users ofUFAD technology.1.2 Organization of the GuideThe Guide is organized to follow the typical flow of decision making andneed for information, from system inception through design, construction,and operation of the system.1.3 Basic UFAD System DescriptionA UFA

18、D system uses the open space (underfloor supply plenum) between astructural slab and the underside of a raised floor system to deliver condi-tioned air to supply outlets located at or near floor level within the occupiedzone (up to 6 ft 1.8 m height) of the space. Floor diffusers make up thelarge ma

19、jority of installed UFAD supply outlets, and throughout this Guide,unless otherwise noted, use of the term UFAD system will refer primarily tothis configuration.Figure 1.1 presents a schematic diagram of a UFAD system for a cool-ing application in an interior zone of an open-plan office building. So

20、me ofthe most significant differences between UFAD systems as compared toconventional ceiling-based systems is the use of the RAF in lieu of air distri-bution ductwork.The major features of a UFAD system are described in greater detailbriefly in this chapter, and throughout the Guide.With some excep

21、tions, UFAD systems use many of the same types ofcentral heating and cooling equipment and primary air-handling units(AHU) as conventional air distribution design. One common exception is theFigure 1.1 Underfloor Air Distribution System 2013 ASHRAE (www.ashrae.org). For personal use only. Additional

22、 reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 1 Introduction3means for dehumidification and reheating the supply air to deliver the airproperties needed (dehumidified 65F 18C air). Supply air containing atleast

23、 the minimum volume of outdoor air is filtered and conditioned to therequired temperature and humidity at the central AHU or, in some cases, incombination with floor-by-floor or zonal AHUs. It is delivered via somecombination of shafts, trunk ductwork, and, if needed, plenum distributionductwork int

24、o the underfloor plenum.The underfloor plenum is formed by installation of a raised floor sys-tem, typically consisting of22ft(0.6 0.6 m) concrete-filled steel(or other construction) floor panels. Raised floors used with UFAD sys-tems are most commonly installed at heights of 1218 in. (0.30.46 m)abo

25、ve the concrete structural slab of the building, although lowerheights are possible. A raised floor system has traditionally been used todistribute all power/voice/data (PVD) cabling through the underfloorplenum. When combined with a UFAD system, the raised floor cavitycreates an integrated service

26、distribution plenum, which can containcabling, ductwork, plumbing, and other building system infrastructure.When configuring an underfloor air supply plenum, there are threebasic approaches that are outlined in general below. In practice, finalplenum designs often contain elements from all three.By

27、far the most common practice, and the focus of this Guide, is apressurized plenum using primary air-handling equipment tomaintain a slight positive pressure in relation to the conditionedspace (typical design pressures are 0.050.08 in. wc (12.520 Pa).This pressure differential allows air to be distr

28、ibuted through theplenum and into the space through manual and/or variable-air-volume (VAV) grilles/diffusers and fan powered terminal units,either used alone or in combination with one another. Evidence fromcompleted projects indicates that uncontrolled air leakage frompressurized supply plenums ca

29、n impair system performance andoccupant comfort. As discussed later, great care and attention mustbe paid during design and construction to ensure a well-sealedunderfloor plenum.Zero-pressure plenums use primary air handlers and local fan-powered outlets, or underfloor fan terminals in combination w

30、ithducted outlets, to deliver air into the conditioned space. Since thesupply plenum and conditioned space are at the same pressure,zero-pressure plenums pose no risk of uncontrolled air leakage tothe space, adjacent zones, or the outdoors. However, to date, thisapproach has seen only limited applic

31、ation due to lack ofknowledge, perceived higher costs, and system complexity.In rare cases, fully-ducted air supply through the plenum toterminal devices and/or supply outlets has been used to avoid airleakage as well as temperature gain in the underfloor plenum (see 2013 ASHRAE (www.ashrae.org). Fo

32、r personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. UFAD GUIDE4below). This approach, however, reduces the flexibility forreconfiguration provided by the raised floor system and alsoimp

33、acts the required fan power for air distribution. Higher initialand operational costs are again a consideration for this approach.On a given building floor, the underfloor plenum provides the primarymeans for horizontal distribution of conditioned air across the floorplate. Vertical partitions (plen

34、um dividers) can be used to limit the max-imum size of any single plenum zone to that allowed by applicablebuilding codes, tenant requirements, or as selected by the systemdesigner. Typically, especially in larger buildings, some amount of duc-twork (rigid or flexible) or air highways (fabricated ai

35、r channels that useraised floor panels and the slab as top and bottom, respectively) are usedto partially distribute supply air across the floor plate as a means ofreducing temperature gain to the supply plenum.Once the supply air enters the underfloor plenum, it flows freely indirect contact with t

36、he thermally massive slab (unless insulation is used)and floor panels, and enters the workspace through diffusers at or nearfloor level. Because the air is supplied directly into the occupied zone,floor supply outlet temperatures should be maintained no lower than inthe range of 61F65F (16F18C) to a

37、void uncomfortably cool con-ditions for the nearby occupants.Cool supply air flowing through the plenum is exposed to heat gainfrom both the slab (in a multistory building) and the raised floor panels.The magnitude of this heat gain is related to several factors. If notaddressed properly, this heat

38、gain can be significant, resulting in unde-sirable temperature rise to the supply air in the plenum. Supply air tem-perature rise has proven to be an important consideration in the designand operation of UFAD systems, impacting the required supply air tem-perature leaving the air handler, the airflo

39、w quantity to the space, andthe resulting energy use of the system.There are a number of diffuser types that are suitable for UFAD sys-tems. As with overhead diffusers, they are designated by their control andflow characteristics, each designed to accomplish different tasks. Thesecharacteristics wil

40、l determine the application for which they are used. Referto Section 6.2 for additional information on diffuser type. 2013 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior wri

41、tten permission. Room AirDistributionPrinciples25Room air distribution systems, like other HVAC systems, are intended toachieve required thermal comfort and ventilation for space occupants andprocesses. Room air distribution systems can be classified by their primaryobjective and the method by which

42、 they attempt to accomplish that objec-tive. The objective of any air distribution system can be classified as one ofthe following:Conditioning and/or ventilation of the space for occupant thermal com-fortConditioning and/or ventilation to support processes within the spaceA combination of theseASHR

43、AE HandbookHVAC Applications (2011) categorizes room airdistribution systems as follows:Mixed systems, which have little or no thermal stratification of airwithin the occupied and/or process space.Full thermal stratification systems (e.g., thermal displacement ventila-tion), which have little or no

44、air mixing in the occupied and/or processspace.Partially mixed systems, which provide limited air mixing in the occu-pied and/or process space.Task/ambient air distribution, which focus on conditioning only part ofthe space for thermal comfort and/or process control.UFAD systems may exhibit room air

45、 distribution characteristics similarto any of the aforementioned methods. The primary differentiator betweenthe methods is the type of diffuser used. This chapter will discuss all fourapproaches to room air distribution and how they relate to the thermal com-fort and indoor air quality of the space

46、 served by the UFAD system.2.1 Mixed-Air Distribution SystemsHistorically, the approach to HVAC design in commercial buildings hasbeen to both supply and remove air at or near the ceiling level (Figure 2.1).Overhead diffusers discharge conditioned air at velocities higher than thoseacceptable for oc

47、cupant comfort. The supply air temperature may be lower,higher, or equal to the room air temperature setpoint, depending on the space 2013 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without A

48、SHRAEs prior written permission. UFAD GUIDE6cooling/heating load. Turbulent supply air jet create rapid mixing with roomair so that the supply jets temperature quickly approaches that of theentrained room air. As the jet proceeds into the room, it entrains room (sec-ondary) air into the primary air jet, causing it to grow and spread in size, andtherefore to reduce in air speed. A syst