UFAD guide : design, construction, and operation of underfloor air distribution systems

324 Pages·2013·14.16 MB·English

UFAD GUIDE
Design, Construction and Operation
of Underfloor Air Distribution Systems
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Includesbibliographicalreferencesandindex.
Summary:“GuideprovidesassistanceinthedesignofUFADsystemsthatareenergyefficient,
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Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Purpose of This Guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Organization of the Guide . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Basic UFAD System Description. . . . . . . . . . . . . . . . . . . . . 2
Chapter 2 Room Air Distribution Principles. . . . . . . . . . . . . . . . . . . . 5
2.1 Mixed-Air Distribution Systems . . . . . . . . . . . . . . . . . . . . . 5
2.2 Thermal Displacement Ventilation (TDV) Systems . . . . . . 6
2.3 UFAD Systems—Cooling Operation. . . . . . . . . . . . . . . . . 11
2.4 Controlling Stratification. . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5 Cooling Load Characteristics of UFAD Systems . . . . . . . 17
2.6 Heating in UFAD Systems . . . . . . . . . . . . . . . . . . . . . . . . . 18
Chapter 3 Underfloor Air Supply Plenum Principles. . . . . . . . . . . . 19
3.1 Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 Airflow Performance in Pressurized Plenums . . . . . . . . 26
3.3 Air Leakage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.4 Thermal Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.5 Moisture and Condensation. . . . . . . . . . . . . . . . . . . . . . . 55
3.6 Underfloor Zoning—Plenum Dividers. . . . . . . . . . . . . . . 55
Chapter 4 Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.1 Building Structure Considerations. . . . . . . . . . . . . . . . . . 59
4.2 Buildings Planned with Raised Access Floor (RAF) . . . . . 61
4.3 Special Functions and Considerations for
UFAD Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.4 Applications where UFAD Systems Are
Not Recommended. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.5 Specific Space Considerations and Cautions with
UFAD Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.6 UFAD Use in Combination with Other HVAC Systems . . 65
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UFAD GUIDE
Chapter 5 UFAD System Configurations. . . . . . . . . . . . . . . . . . . . . . 67
5.1 Air-Handling System Configurations for UFAD . . . . . . . . 67
5.2 Perimeter System Options . . . . . . . . . . . . . . . . . . . . . . . . 72
Chapter 6 Diffusers and Terminal Units for UFAD. . . . . . . . . . . . . . 93
6.1 Diffusers for UFAD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.2 Terminal Units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Chapter 7 Indoor Environmental Quality. . . . . . . . . . . . . . . . . . . . 103
7.1 Thermal Acceptability . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.2 Ventilation and IAQ Performance . . . . . . . . . . . . . . . . . 109
7.3 Acoustics and Speech Privacy. . . . . . . . . . . . . . . . . . . . . 109
Chapter 8 Energy Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.1 Definition of Parameters for
Energy Performance Assessment. . . . . . . . . . . . . . . . . . 113
8.2 Energy Performance Overview. . . . . . . . . . . . . . . . . . . . 113
8.3 Air Distribution Energy . . . . . . . . . . . . . . . . . . . . . . . . . . 114
8.4 Air-Side Economizers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
8.5 Cooling-System Efficiency. . . . . . . . . . . . . . . . . . . . . . . . 121
8.6 Heating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.7 Using Energy Simulations to Optimize Design . . . . . . . 122
8.8 Verification of Energy Performance. . . . . . . . . . . . . . . . 135
Chapter 9 Standards, Codes and Ratings. . . . . . . . . . . . . . . . . . . . 137
9.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
9.2 ASHRAE Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
9.3 Building Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
9.4 National Fire Protection Association
(NFPA) Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
9.5 Other Standards and Rating Systems . . . . . . . . . . . . . . 152
Chapter 10 Cost Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
10.1 Standard First-Cost Components. . . . . . . . . . . . . . . . . . 156
10.2 Design-Dependent First-Cost Components. . . . . . . . . . 157
10.3 Life-Cycle-Cost Components. . . . . . . . . . . . . . . . . . . . . . 163
Chapter 11 Guidance for System Design . . . . . . . . . . . . . . . . . . . . 167
11.1 Design Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
11.2 Space Planning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
11.3 Architectural and Structural Considerations
(Principles and Criteria). . . . . . . . . . . . . . . . . . . . . . . . . . 168
11.4 Determination of Space Cooling and Heating Loads . . 175
11.5 Zoning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 222
11.6 Air Distribution System Configuration. . . . . . . . . . . . . . 224
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Contents
11.7 Determining Zone Supply Air Temperature and
Airflow Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . 230
11.8 Supply Outlet Selection and Location . . . . . . . . . . . . . . 231
11.9 Determining Return Air Configuration . . . . . . . . . . . . . 232
Chapter12 Controls for UFAD Systems . . . . . . . . . . . . . . . . . . . . . 235
12.1 Control System Components . . . . . . . . . . . . . . . . . . . . . 235
12.2 Control Strategies for UFAD . . . . . . . . . . . . . . . . . . . . . . 239
12.3 Space Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
12.4 Air-Handler-Unit Control. . . . . . . . . . . . . . . . . . . . . . . . . 244
Chapter 13 Guidance for Construction. . . . . . . . . . . . . . . . . . . . . . 255
13.1 Prebid Meetings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
13.2 Preconstruction Meetings. . . . . . . . . . . . . . . . . . . . . . . . 256
13.3 Shop Drawing and Submittal Review. . . . . . . . . . . . . . . 256
13.4 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
13.5 Construction Sequencing . . . . . . . . . . . . . . . . . . . . . . . . 258
13.6 Documentation of Site Observations
during Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
13.7 As-Built Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
13.8 Carpet and Furniture Installation . . . . . . . . . . . . . . . . . 261
13.9 Furniture Coordination. . . . . . . . . . . . . . . . . . . . . . . . . . 262
Chapter 14 Guidance for Building Commissioning. . . . . . . . . . . . 263
14.1 Whole-Building Commissioning. . . . . . . . . . . . . . . . . . . 263
14.2 Commissioning through All Phases of the Project. . . . 263
14.3 Special Commissioning Considerations for UFAD . . . . 263
14.4 Plenum Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . 273
Chapter 15 Guidance for Operation and Maintenance. . . . . . . . . 293
15.1 Maintainability, Accessibility, Serviceability . . . . . . . . . 293
15.2 Maintaining Plenum Integrity . . . . . . . . . . . . . . . . . . . . 294
15.3 Cleanliness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
15.4 Operations Monitoring and Documentation. . . . . . . . . 295
15.5 Flexibility and Change—
Requirements and Documentation . . . . . . . . . . . . . . . . 296
15.6 Occupant Satisfaction. . . . . . . . . . . . . . . . . . . . . . . . . . . 296
15.7 Acoustic Performance (from CBE) . . . . . . . . . . . . . . . . . 297
15.8 System Adjustments after Occupancy . . . . . . . . . . . . . 297
15.9 UFAD Performance Considerations. . . . . . . . . . . . . . . . 299
Chapter 16 References and Bibliography. . . . . . . . . . . . . . . . . . . . 301
Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
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1
Introduction
1.1 Purpose of This Guide
Underfloorairdistribution(UFAD)isamethodofdeliveringairtobuilding
spaces for the purpose of conditioning the space for occupant comfort. This
typeofairdistributionmaybeappropriateforanumberofdifferentbuilding
types, including but not limited to schools, churches, offices, and libraries.
Underfloorairdistributionderivesitsnamefromtheuseoftheareabelowa
raised access floor (RAF) system as an air supply plenum to deliver condi-
tioned air throughout the space to floor-mounted diffusers. This technology
has traditionally been common in the computer-room industry; however, its
useincommercialandinstitutionalbuildingsisincreasinginNorthAmerica.
The purpose of this Guide is to provide assistance in the design, con-
struction, and operation of UFAD systems. The Guide also incorporates
important research results to support the UFAD design recommendations
presented,andincludesanextensiveannotatedbibliographyforthoseseek-
ing additional detailed information. This Guide does not cover alternate air
distributionsystemdesignproceduresindetail;however;referencetomore
common systems is used to explain or contrast the methods used to design
UFADsystems.ItisnottheintentofthisGuidetopromoteonesystemover
another but to merely point out the major differences between UFAD and
conventionalsystemdesign.Formoreinformationonstandardheating,ven-
tilating, and air-conditioning design, please refer to other publications fur-
nished by ASHRAE, including ASHRAE Handbook (ASHRAE 2009,
2010d, 2011, 2012), Air-Conditioning Systems Design Manual (Grondzik
2007), and A Designer’s Guide to Conventional Ceiling-Based Room Air
Diffusion(RockandZhu2001).
The development of this Guide is based on a compilation of available
information, including research results from laboratory and field experi-
ments, simulation studies, manufacturers’ literature, design experience of
practicingengineers,andotherrelevantguidelinesfromusersofthetechnol-
ogy. Despite recent growth in the UFAD market, widespread experience
withthesesystemsisstillatanearlystage.Theguidelinespresentedhereare
based on the most current and best available data and information. It is not
the intent of the authors to cover every possible design scenario. It is up to
the reader to use good engineering judgment and common sense when
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UFAD GUIDE
Figure 1.1 Underfloor Air Distribution System
applying methodologies described herein. The Guide is intended for use by
design engineers, architects, building owners, facility managers, equipment
manufacturers, installers, utility engineers, researchers, and other users of
UFADtechnology.
1.2 Organization of the Guide
The Guide is organized to follow the typical flow of decision making and
need for information, from system inception through design, construction,
andoperationofthesystem.
1.3 Basic UFAD System Description
AUFADsystemusestheopenspace(underfloorsupplyplenum)betweena
structural slab and the underside of a raised floor system to deliver condi-
tionedairtosupplyoutletslocatedatornearfloorlevelwithintheoccupied
zone (up to 6 ft [1.8 m] height) of the space. Floor diffusers make up the
largemajorityofinstalledUFADsupplyoutlets,andthroughoutthisGuide,
unlessotherwisenoted,useofthetermUFADsystemwillreferprimarilyto
thisconfiguration.
Figure1.1presentsaschematicdiagramofaUFADsystemforacool-
ingapplicationinaninteriorzoneofanopen-planofficebuilding.Someof
the most significant differences between UFAD systems as compared to
conventionalceiling-basedsystemsistheuseoftheRAFinlieuofairdistri-
butionductwork.
The major features of a UFAD system are described in greater detail
brieflyinthischapter,andthroughouttheGuide.
With some exceptions, UFAD systems use many of the same types of
central heating and cooling equipment and primary air-handling units
(AHU)asconventionalairdistributiondesign.Onecommonexceptionisthe
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1 · Introduction
means for dehumidification and reheating the supply air to deliver the air
propertiesneeded(dehumidified±65°F[18°C]air).Supplyaircontainingat
least the minimum volume of outdoor air is filtered and conditioned to the
requiredtemperatureandhumidityatthecentralAHUor,insomecases,in
combination with floor-by-floor or zonal AHUs. It is delivered via some
combination of shafts, trunk ductwork, and, if needed, plenum distribution
ductworkintotheunderfloorplenum.
• The underfloor plenum is formed by installation of a raised floor sys-
tem, typically consisting of 2 × 2 ft(0.6 × 0.6 m) concrete-filled steel
(orotherconstruction)floorpanels.RaisedfloorsusedwithUFADsys-
temsaremostcommonlyinstalledatheightsof12–18in.(0.3–0.46m)
above the concrete structural slab of the building, although lower
heightsarepossible.Araisedfloorsystemhastraditionallybeenusedto
distribute all power/voice/data (PVD) cabling through the underfloor
plenum. When combined with a UFAD system, the raised floor cavity
creates an integrated service distribution plenum, which can contain
cabling,ductwork,plumbing,andotherbuildingsysteminfrastructure.
• When configuring an underfloor air supply plenum, there are three
basic approaches that are outlined in general below. In practice, final
plenumdesignsoftencontainelementsfromallthree.
• By far the most common practice, and the focus of this Guide, is a
pressurized plenum using primary air-handling equipment to
maintain a slight positive pressure in relation to the conditioned
space (typical design pressures are 0.05–0.08 in. wc (12.5–20 Pa).
This pressure differential allows air to be distributed through the
plenum and into the space through manual and/or variable-air-
volume (VAV) grilles/diffusers and fan powered terminal units,
eitherusedaloneorincombinationwithoneanother.Evidencefrom
completed projects indicates that uncontrolled air leakage from
pressurized supply plenums can impair system performance and
occupant comfort. As discussed later, great care and attention must
be paid during design and construction to ensure a well-sealed
underfloorplenum.
• Zero-pressure plenums use primary air handlers and local fan-
powered outlets, or underfloor fan terminals in combination with
ducted outlets, to deliver air into the conditioned space. Since the
supply plenum and conditioned space are at the same pressure,
zero-pressure plenums pose no risk of uncontrolled air leakage to
the space, adjacent zones, or the outdoors. However, to date, this
approach has seen only limited application due to lack of
knowledge,perceivedhighercosts,andsystemcomplexity.
• In rare cases, fully-ducted air supply through the plenum to
terminal devices and/or supply outlets has been used to avoid air
leakage as well as temperature gain in the underfloor plenum (see
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UFAD GUIDE
below). This approach, however, reduces the flexibility for
reconfiguration provided by the raised floor system and also
impacts the required fan power for air distribution. Higher initial
andoperationalcostsareagainaconsiderationforthisapproach.
• On a given building floor, the underfloor plenum provides the primary
means for horizontal distribution of conditioned air across the floor
plate.Verticalpartitions(plenumdividers)canbeusedtolimitthemax-
imum size of any single plenum zone to that allowed by applicable
building codes, tenant requirements, or as selected by the system
designer.Typically,especiallyinlargerbuildings,someamountofduc-
twork(rigidorflexible)orairhighways(fabricatedairchannelsthatuse
raisedfloorpanelsandtheslabastopandbottom,respectively)areused
to partially distribute supply air across the floor plate as a means of
reducingtemperaturegaintothesupplyplenum.
• Once the supply air enters the underfloor plenum, it flows freely in
directcontactwiththethermallymassiveslab(unlessinsulationisused)
and floor panels, and enters the workspace through diffusers at or near
floor level. Because the air is supplied directly into the occupied zone,
floorsupplyoutlettemperaturesshouldbemaintainednolowerthanin
therangeof61°F–65°F(16°F–18°C)toavoiduncomfortablycoolcon-
ditionsforthenearbyoccupants.
• Cool supply air flowing through the plenum is exposed to heat gain
fromboththeslab(inamultistorybuilding)andtheraisedfloorpanels.
The magnitude of this heat gain is related to several factors. If not
addressed properly, this heat gain can be significant, resulting in unde-
sirabletemperaturerisetothesupplyairintheplenum.Supplyairtem-
perature rise has proven to be an important consideration in the design
andoperationofUFADsystems,impactingtherequiredsupplyairtem-
perature leaving the air handler, the airflow quantity to the space, and
theresultingenergyuseofthesystem.
There are a number of diffuser types that are suitable for UFAD sys-
tems. As with overhead diffusers, they are designated by their control and
flow characteristics, each designed to accomplish different tasks. These
characteristicswilldeterminetheapplicationforwhichtheyareused.Refer
toSection6.2foradditionalinformationondiffusertype.
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Room Air
2
Distribution
Principles
Room air distribution systems, like other HVAC systems, areintended to
achieve required thermal comfort and ventilation for space occupants and
processes. Room air distribution systems can be classified by their primary
objective and the method by which they attempt to accomplish that objec-
tive.Theobjectiveofanyairdistributionsystemcanbeclassifiedasoneof
thefollowing:
• Conditioningand/orventilationofthespaceforoccupantthermalcom-
fort
• Conditioningand/orventilationtosupportprocesseswithinthespace
• Acombinationofthese
ASHRAE Handbook—HVAC Applications (2011) categorizes room air
distributionsystemsasfollows:
• Mixed systems, which have little or no thermal stratification of air
withintheoccupiedand/orprocessspace.
• Full thermal stratification systems (e.g., thermal displacement ventila-
tion),whichhavelittleornoairmixingintheoccupiedand/orprocess
space.
• Partially mixed systems, which provide limited air mixing in the occu-
piedand/orprocessspace.
• Task/ambientairdistribution,whichfocusonconditioningonlypartof
thespaceforthermalcomfortand/orprocesscontrol.
UFADsystemsmayexhibitroomairdistributioncharacteristicssimilar
to any of the aforementioned methods. The primary differentiator between
the methods is the type of diffuser used. This chapter will discuss all four
approachestoroomairdistributionandhowtheyrelatetothethermalcom-
fortandindoorairqualityofthespaceservedbytheUFADsystem.
2.1 Mixed-Air Distribution Systems
Historically, the approach to HVAC design in commercial buildings has
beentobothsupplyandremoveairatorneartheceilinglevel(Figure2.1).
Overheaddiffusersdischargeconditionedairatvelocitieshigherthanthose
acceptableforoccupantcomfort.Thesupplyairtemperaturemaybelower,
higher,orequaltotheroomairtemperaturesetpoint,dependingonthespace
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