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Under Floor Air Distribution (UFAD) Course No: M01-011
Credit: 1 PDH
Elie Tawil, P.E., LEED AP
Continuing Education and Development, Inc. 9 Greyridge Farm Court Stony Point, NY 10980 P: (877) 322-5800 F: (877) 322-4774 [email protected]
Leading by example,saving energy andtaxpayer dollarsin federal facilities
DOE/EE-0295
Internet: www.eere.energy.gov/femp/
No portion of this publication may be altered in any form withoutprior written consent from the U.S. Department of Energy, EnergyEfficiency and Renewable Energy, and the authoring national laboratory.
Alternative Air Conditioning Technologies:Underfloor Air Distribution (UFAD)An overview of UFAD technology and its potential in federal facilities
Introduction and BackgroundRecent trends in today’s office environment make it increasingly more difficult for conventional central-ized HVAC systems to satisfy the environmental preferences of individual office workers using thestandardized approach of providing a single uniform thermal and ventilation environment. Since itsoriginal introduction in West Germany during the 1950s, the open plan office containing modularworkstation furniture and partitions is now the norm. Thermostatically controlled zones in openplan offices typically encompass relatively large numbers of workstations in which a diverse workpopulation having a wide range of preferred temperatures must be accommodated. Modern office
buildings are also being impacted by a large influx of heat-generating equipment (computers, printers, etc.) whoseloads may vary considerably from workstation to worksta-tion. Offices are often reconfigured during the building’slifetime to respond to changing tenant needs, affectingthe distribution of within-space loads and the ventilationpathways among and over office partitions. Compound-ing this problem, there has been a growing awareness ofthe importance of the comfort, health, and productivityof individual office workers, giving rise to an increaseddemand among employers and employees for a high-qualitywork environment.
Task Ambient Conditioning
During recent years an increasing amount of attention has been paid to air distribution systems thatindividually condition the immediate environments of office workers within their workstations toaddress the issues outlined above. As with task/ambient lighting systems, the controls for the “task”components of these systems are partially or entirely decentralized and under the control of the occu-pants. Typically, the occupant has control over the speed and direction, and in some cases the tem-perature, of the incoming air supply. Variously called “task/ambient conditioning,” “localized thermaldistribution,” and “personalized air conditioning” systems, these systems have been most commonlyinstalled in open-plan office buildings in which they provide supply air and (in some cases) radiantheating directly into workstations. TAC systems can be classified into the following two major categories:1) furniture-based, and 2) floor-based, underfloor air distribution (UFAD). A majority of these sys-tems include a raised floor system with which underfloor plenums are used to deliver conditioned airto the space through floor grills, or in conjunction with the workstation furniture and partitions.
Illustration of typicalswirl diffuser used inUFAD systems.
Underfloor Air Distribution
In the 1970s, underfloor air distributionwas introduced into office buildings inWest Germany as a solution to cablemanagement and heat load removalissues caused by the proliferation ofelectronic equipment throughout theoffice [1]. In these buildings, the com-fort of the office workers had to be con-sidered, giving rise to the developmentof occupant-controlled localized supplydiffusers to provide task condition-ing. Some of the first UFAD systemsin Europe used a combination of desk-top outlets for personal comfort con-trol and floor diffusers for ambientspace control [2].
Prior to the 1990s, office installationsusing underfloor systems had beenfound primarily in South Africa,Germany, and other parts of Europe.The technology was not commonlyused in North America prior to about1995, in part due to the downturn inoffice building construction beginningin the mid-1980s. Japan did not experi-ence this same downturn, and as a result,significant growth in UFAD technologywas observed during this period. Between1987 and 1995, more than 250,000 m2
(2.7 million ft2) of office space in morethan 90 buildings were installed withUFAD systems in Japan [3].
However, in the late 1990s growthfor raised floor installations in theUS was dramatic and designers andmanufacturers predicted that 35%of new offices would use raised floorsby 2004. Half of these installationswere expected to incorporate UFADtechnology. This rate of increase hasslowed now (2003) due to the eco-nomic downturn and much reducedoffice construction.
The purpose of this technology reviewis to provide federal facilities managersan overview of the principles, features,
benefits, and limitations of this impor-tant innovation in building condition-ing technology.
Technology Description
A task/ambient conditioning system isdefined as any space conditioning sys-tem that allows thermal conditions insmall, localized zones (e.g., regularlyoccupied work locations) to be individu-ally controlled by building occupants,while still automatically maintainingacceptable environmental conditionsin the ambient space of the building(e.g., corridors, open-use space, andother areas outside of regularly occu-pied work space).
UFAD systems are uniquely character-ized by their ability to allow individualsto have some degree of control over theirlocal environment, without adverselyaffecting that of other nearby occupants.1
Depending on the UFAD system design,ambient environmental control innon-work areas may be provided byadditional local supply outlets, or by aseparate space conditioning system, butin either case under automatic control.
The types of diffusers supported,active or passive, further distinguishUFAD systems from furniture-basedTAC systems. Active diffusers (forpurposes of this report) are definedas those with local means of volumeadjustment (such as an integral variablespeed fan or damper) that is amenableto automatic zone control (in additionto means for occupant control). Passivediffusers, although they may have meansfor occupant adjustment, are combinedwith terminal or system elements toachieve zone control. Systems designedwith all fan-assisted active diffuserstypically utilize zero-pressure plenums.Passive diffusers require pressurizedplenums. The majority of UFADsystems currently being deployed
have pressurized plenums with eitheractive or passive diffusers.
Principles of Operation
Figures 1 and 2 illustrate the funda-mental differences between traditionaloverhead and furniture-based TAC andUFAD systems, respectively. As shownin Figure 1, overhead systems (in officebuildings, these are predominately vari-able air volume [VAV] all-air distribu-tion systems) employ an extensive arrayof ductwork and terminal devices toprovide supply air through the ceiling-mounted diffusers. Often referred to asmixing ventilation systems, these sys-tems are designed to promote completemixing of supply air with room air,thereby maintaining the entire volumeof air in the space at the desired tem-perature setpoint. Space air is typicallyreturned to the AHU via an open ceil-ing plenum that also contains variousother systems for lighting, electrical,communications, and fire protection.UFAD systems turn this conceptupside down and have in commonthe following characteristics:
• Supply air, including at least theminimum required volume of out-side air, is filtered and conditionedto the required temperature andhumidity by a conventional AHUand passed through a minimumamount of ductwork to an under-floor plenum. The underfloor ple-num is formed by installation of araised floor system, typically con-sisting of 0.6 m x 0.6 m (2 ft x 2 ft)concrete-filled steel floor panelspositioned 0.3–0.46 m (12–18 in.)above the concrete structural slabof the building. The raised floorsystem also allows all cable services,such as power and communication,to be located in the plenum andprovides easy access for modifica-tions and maintenance.
1 In open plan settings there is less control due to airflow rate change associated with opening and closing floor diffusers than in private offices. Betteroccupant control is achieved by designs that allow the airflow to be directed toward the occupant.
2 — FEDERAL ENERGY MANAGEMENT PROGRAM
personal comfort preferences. Differ-ent supply outlet configurationsmay be used depending on theconditioning requirements for aparticular zone of the building, asdiscussed below.
• UFAD systems benefit from a floor-to-ceiling airflow pattern that takesadvantage of the natural buoyancyproduced by heat sources in theoffice to efficiently remove heatloads and contaminants from thespace. Air is returned from the roomat ceiling level through recessedlighting fixtures and return grillesvia a conventional ceiling returnplenum or return grilles locatedhigh in the space when a returnplenum is not used.
• Because the air is supplied directlyinto the occupied zone (up to 6 ft(1.8 m) height), supply outlet tem-peratures are generally maintainedabove 17 to 18°C (63 to 64°F) toavoid uncomfortably cool condi-tions for the nearby occupants andto minimize cool temperatures nearthe floor.
There are a wide variety of approachesbeing used to provide a combination ofindividual and automatic zone controlfor UFAD systems.2 (See reference [4]).Typically, these systems use variable-air-volume (VAV) or constant-air-volume(CAV) methods for general zone con-trol (i.e., overall zone control otherthan local occupant control).
• Six types of diffusers are currentlybeing offered;
1. Fan-assisted, active
2. Variable area, active
3. Swirl, passive
4. Swirl, active
5. Linear bar grille, passive
6. Linear bar grille, active
Figure 1. Overhead system.
Figure 2. TAC system.
2 The author has identified over a dozen variations of these systems.
• Individual office workers can controltheir local thermal environment overa relatively wide range (typicallyby adjusting the volume and/or
trajectory of the supply air enteringthe space), giving them the oppor-tunity to fine-tune the thermal con-ditions in their workstation to their
FEDERAL ENERGY MANAGEMENT PROGRAM — 3
• The heating and cooling loads ofperimeter zones are handled by fan-powered constant volume or variablevolume terminal reheat units locatedin the underfloor plenum (similarto those shown in Figure 3). Passiveor active diffusers are located inoccupied areas of the zone normallywithin about 4.5 m (15 ft) from theexterior walls. Passive diffusers aregenerally supplied by a (series) fan
can accommodate individual differences.In today’s work environment, there canbe significant variations in individualcomfort preferences due to differencesin clothing and activity level (meta-bolic rate) as well as differences in thelocal heat gains and losses. By allowingpersonal control of the local thermalenvironment, UFAD systems couldsatisfy virtually all occupants, includ-ing those out of thermal equilibriumwith their surrounding ambient envi-ronment, as compared to the 80% sat-isfaction quota targeted in practice byexisting thermal comfort standards [5].
Improved air movement and ventilationeffectiveness; cleaner environment – Someamount of improvement over conven-tional uniformly-mixed systems isexpected by delivering the fresh supplyair near the occupant and at the floor.
Improved occupant satisfaction andincreased worker productivity – UFADsystems have the potential to increasethe satisfaction and productivity ofoccupants as a result of their havingthe ability to individually control theirworkspace environments. The financialimplications of such improvements canbe extremely large as salary costs typi-cally make up at least 90% of all costs(including construction, operation,and maintenance) over the lifetimeof a building.
Energy Savings – Energy savings overconventional overhead systems arepredominately associated with twofactors: cooling energy savings fromeconomizer operation and increasedchiller COP, and fan energy savings.Details of how these savings areachieved can be found in [6].
Limitations
Among the items that limit the wide-spread acceptance and application ofUFAD technology are the following:
New and unfamiliar technology – Forthe majority of U.S. building owners,
Figure 3. Pressurized plenum UFAD system.
Figure 4. Typical interior swirl diffuser layout.
powered mixing box or fan coil unit,or a VAV box either connected to thediffuser by ducting or by supplyingair to a partitioned area of the ple-num where the diffusers are located.
• Interior zones are generally largezones each controlled by one ther-mostat, but with diffusers locatednear the occupants within or closeto their workstations.
Figure 3 shows a schematic diagram andFigure 4 a typical diffuser layout for apressurized plenum UFAD system. Thissystem is being commonly applied tooffice buildings due to its simplicity andcost savings. Although this floor-basedair distribution system provides some-what limited individual comfort controlfor occupants, it still affords many ofthe same flexibility and energy-savingbenefits associated with the others.
Potential of UFADApplications
Benefits
Improved thermal comfort for individualoccupants – Occupant thermal comfortis perhaps the area of greatest potentialimprovement in that UFAD systems
4 — FEDERAL ENERGY MANAGEMENT PROGRAM
developers, architects, engineers, andequipment manufacturers, UFAD sys-tems still represent a relatively new andunfamiliar technology. The decisionto select a UFAD system will initiallyrequire changes in common practice,including new procedures and skills inthe design, construction, and operationof such systems as well as changes inresponsibilities of the various installa-tion trades. This situation creates someamount of perceived risk to designersand building owners.
Perceived higher costs – An industry sur-vey found the perceived higher cost ofUFAD systems to be one of the two topreasons that UFAD technology is notused more widely by the industry today.
Many designers immediately eliminateunderfloor UFAD systems from consid-eration out of concern for higher firstcosts of the raised flooring. However, asdescribed above, there are many factorsassociated with raised floor systems thatcontribute to reduced life-cycle costs incomparison to traditional air distribu-tion systems. In UFAD systems usingfan-powered supply diffusers, the addi-tional cost of installing and maintain-ing many small units must be balancedagainst the benefits of providing per-sonal environmental control (reducedoccupant complaints) and reducingthe size of other system components(e.g., central fan).
Limited applicability to retrofits andcertain building types/areas – The installa-tion of UFAD systems and the advan-tages that they offer are most easilyachieved in new construction. Someof the key system features are not alwayssuitable for retrofit applications (e.g.,access floors cannot be installed in exist-ing buildings with limited floor-to-floorheights). Although widely applicable,there are building types and areaswithin buildings where access floorsand underfloor air distribution are not
appropriate. These areas are generallythose in which spillage has the poten-tial to occur, including bathrooms,laboratories, cafeterias, and shop areas.
Lack of information, design guidelines,and evaluation methods – Althoughin recent years there have been anincreased number of publications onUFAD technology (see References),there is still not a complete under-standing of some fundamental fluidmechanics and thermal issues and nostandardized design methods existyet. System operating sequences andcontrol techniques are likewise areunder development.
Earlier versions of ASHRAE Standard55 [7] were based on the assumptionof a well-mixed and uniformly condi-tioned environment. UFAD systems,however, usually involve greater vari-ability of thermal conditions over bothspace and time. The effect of providingoccupant-control has not been fullytaken into account, although it is wellestablished that occupants will tolerategreater fluctuations in environmentalconditions if they have control overthem. The current version of the stan-dard (55-92) was revised (see Figure 3of the standard) to allow higher airvelocities than the previous version, ifthe occupant has control over the localair speed.
ASHRAE Standard 113-90 [8] is theonly currently available building stan-dard for evaluating the air diffusion per-formance of an air distribution system.The current version of Standard 113,however, is based on the assumption ofa single uniformly mixed indoor envi-ronment, as provided by a conventionaloverhead air distribution system. Thisassumption is not necessarily appropri-ate for evaluating the performance ofUFAD systems that deliver conditionedair directly into the occupied zone of thebuilding through supply outlets that are
in close proximity to and under thecontrol of the building occupants.
Potential for higher building energy use –As with any space conditioning system,a poorly designed and operated UFADsystem has the potential to use moreenergy than that used by a well-designedconventional system. For example, theenergy use of UFAD systems usinglarge numbers of small local fans3 mayincrease due to the relatively poor fanand motor efficiencies in these units.
Thermal discomfort – UFAD systemsare perceived by some to produce acold floor, and because of the closeproximity of supply outlets to the occu-pants, the increased possibility of exces-sive draft exists. Some systems appearto be designed and operated in such amanner that they produce hot and coldcomplaints similar to existing conven-tional systems despite the potential toachieve better comfort performance.
Problems unique to underfloor plenums –In UFAD systems, concern is some-times expressed about the increasedprobability of spillage and dirt enter-ing directly into the underfloor supplyair stream, and therefore being morewidely distributed throughout theoccupied space. There is also someconcern about improperly dehumidi-fied air being delivered to the plenumwhere condensation could occur oncool structural slab surfaces.
Virtually all of the issues listed aboveare actively being researched [9] oraddressed by design and constructionprofessionals and equipment vendorsin response to market demand. Someof these issues (e.g., plenum dirt andmoisture) have not been shown to beproblems in projects installed to date.Many of the problems that do occurcan be traced to inadequate design andoperating strategies that have resultedfrom lack of knowledge and experience
3 Either integral to the floor diffuser or in terminal units.
FEDERAL ENERGY MANAGEMENT PROGRAM — 5
typically associated with early installa-tions of any nascent technology.
Cost-Effectiveness
Cost considerations will be differentdepending on whether the installationrepresents new or retrofit construction.Total first costs (shell and core plus ten-ant improvement) for UFAD systemsutilizing raised flooring will likely besomewhat higher than those for a con-ventional system. Preliminary resultsfrom research studies [9] have showntotal building first costs of pressurizedUFAD systems in new construction(including raised floor and structuraldifferences) to be about 4-6% greaterthan conventional. However, if a raisedfloor system has already been justifiedfor other reasons, such as improved cablemanagement, the cost differential isoften eliminated altogether. In new con-struction, UFAD can lead to reducedfloor-to-floor heights thus reducingstructural costs. Furniture-based andactive diffuser based systems will gen-erally cost more than other solutions.
Operating costs can be reduced in accor-dance with the energy-saving strategiesdiscussed above. With the improvedthermal comfort and individual controlprovided by UFAD systems, occupantcomplaints requiring response by facilitystaff can be minimized. UFAD systemsusing raised flooring provide maximumflexibility and significantly lower costsassociated with reconfiguring buildingservices (when changes are being madein the office layout) due to churn—andthus reduce life-cycle costs substantially.
First cost for retrofits, generally the bulkof construction activity is most likelygreater than those for new construc-tion. And as indicated previously, somefacilities are not amenable to retrofitby UFAD systems.
To determine total life cycle cost dif-ferences between UFAD systems andconventional designs the followingfactors must be considered in additionto first cost:
Churn – This is the cost associated withrelocating personnel and is defined asthe ratio of total workplace moves ina year to the total number of buildingoccupants. These figures vary widelyby industry type and building activi-ties. Results of a study by IFMA [10]are shown in Table 1.
As shown government facilities havesignificantly lower churn than otherindustries, which is also reflected in themuch lower percentage of open planspace. This indicates that the benefitsof reduced churn costs in federal facili-ties may be limited. It should be notedthat the cost of churn can vary consid-erably depending on the extent of thereconfiguration; i.e., simply movingto a new cubicle is much different thatreconfiguring the layout of cubicles and/or offices. The high proportion of officesin government facilities could drive thesecosts significantly if the reconfigurationinvolves more than office to office moves.
O&M – This item includes the costs offacility management and energy. Whileenergy savings estimates are limited dueto the lack of appropriate capabilities inenergy simulation programs and data
from monitored projects, indicationsare that savings in annual HVAC sys-tem energy can be in the range of 10-20% depending on system design andweather conditions. Maintenance costsare expected to be less than conven-tional systems due to the ease of accessto the distribution system. However,commissioning/startup costs may begreater since the location and opera-tion of the diffusers may requirefine-tuning to optimize the occupantinteraction benefits.
Productivity and health – The savingsassociated with productivity and healthbenefits are difficult to measure andrequire considerably more research. How-ever, recent studies [11] indicate thatwork performance improvements of 0.5to 5% may be possible when the indoorenvironmental quality is improved.
Federal-Sector Potential
The potential for deployment of UFADtechnology in the federal sector willdepend on cost-effectiveness andavailability of suitable buildings. Eachproject must be considered on its ownmerits. Overall the federal governmentowns and operates over 500,0005 resi-dential and non-residential buildingstotaling about 3 billion ft2 [12]. Thefloor space is broken down betweenagencies as shown in Table 2.
4 This study did not distinguish between various types of government facilities (i.e., state, local, federal) so it is unclear as to how representative these fig-ures are for federal facilities.5 About 85% of these buildings are military housing.
Table 1. Churn rates.
Office planChurn (% office/
Group % open/bullpen)
Services 37 35/55/10
Manufacturing 40 34/58/8
Institutional/Government4 23 67/20/13
Table 2. Federal building floorspace.
Agency % of Floor space
Defense 65.4
Postal 10.7
GSA 6.1
VA 5.0
DOE 2.6
Other 10.2
6 — FEDERAL ENERGY MANAGEMENT PROGRAM
There are roughly 76,000 existing non-residential federal buildings [13] com-prising 1.7 billion ft2 of floor space. Ofthis floor space, 51% (7% health care,23% mercantile services, and 21%offices) is suitable for the applicationof UFAD. Assuming a rate of growthin federal floor space roughly equiva-lent to the private sector at 2%6 peryear, and assuming that the ultimatepenetration of UFAD technologycould reach that of VAV systems innew construction (i.e., 75%) thenabout 13 million ft2 per year of newconstruction could be considered fora UFAD solution. Likewise, using thesame criteria, about 650 million ft2 ofexisting facilities could be consideredfor UFAD retrofits.
Summary and Conclusions
UFAD systems have significant poten-tial advantages compared with tradi-tional VAV systems. Rarely has therebeen a space conditioning technologythat promises the combined benefitsof improved thermal comfort, energyefficiency, and productivity and healthimprovement. While this technologyhas seen significant adoption in othercountries, its use in the United Stateshas only been notable since 1995.UFAD technology, like all nascenttechnologies, is being advanced bothin theory and practice by researchers,designers, manufacturers, and “earlyadopter” owners who are working tobring the design, operation, and costs
to the point where it can be more easilyand reliably applied. UFAD technol-ogy may someday displace overheadVAV as the “system of choice” forspace conditioning.
While the use of UFAD systems in par-ticular is becoming more common inthe private commercial sector, the over-all potential for UFAD in federal facili-ties may be limited by low churn thatreduces life-cycle cost benefits. In addi-tion, the overall federal building stockis not as amenable to UFAD installa-tions as the private sector due to thehigher cost of retrofits (i.e., a greaterratio of fixed private offices) and lessoverall applicable building types (51%of the federal building floor spaceversus 62% for private commercial).
However, in those situations where itis appropriate there are many compel-ling reasons to consider UFAD for thespace conditioning solution.
Acknowledgment
Much of the material for this report hasbeen derived from the work of FredBauman at the Center for the BuiltEnvironment (CBE) at the Universityof California, Berkeley. The authorwould like to gratefully acknowledgethe support of Mr. Bauman, CBEand its industry partners, CBE spon-sor the National Science Foundation(NSF), and the Regents of the Univer-sity of California.
Manufacturers
Greenheck(Fan-powered terminals)P.O. Box 410,Schofield, WI 54476-0410(715) 359-6171www.greenheck.com
Krantz(Swirl diffusers)Eurotech Products Inc.3835 Deer RunDenver, NC 28037(704) 483-2050
Titus(Swirl diffusers andfan-powered terminals)990 Security rowRichardson, TX 75801(972) 699-1030www.titus-hvac.com
Trox USA(Swirl diffusers andfan-powered terminals)1005 Alderman Drive, Suite 103Alpharetta, GA 30202www.troxusa.com
Nailor Industries(Swirl diffusers andfan-powered terminals)4714 Winfield Rd.Houston, Texas 77039(281) 590-1172www.nailor.com
York International Corp.(Complete product line forpressurized plenum systems)P.O. Box 1592York, PA 17405(717) 771-6878www.york.com
6 This also assumes that the rate of growth in the three most applicable building types is equal to the nominal rate.
FEDERAL ENERGY MANAGEMENT PROGRAM — 7
Produced for the U.S. Departmentof Energy, Energy Efficiency andRenewable Energy, by the LawrenceBerkeley National Laboratory
DOE/EE-0295
March 2004
For More Information
EERE Information Center
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General Program Contacts
Ted Collins
New Technology Demonstration
Program Manager
Federal Energy Management
Program
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Washington, D.C. 20585
Phone: (202) 586-8017
Fax: (202) 586-3000
Steven A. Parker
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Laboratory
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Fax: (509) 375-3614
Bill Carroll
Lawrence Berkeley National
Laboratory
One Cyclotron Road
Berkeley, CA 94720
Phone: (510) 486-4890
Fax: (510) 486-5454
Technical Contact and Author
Tom Webster, P.E.
Center for the Built Environment
University of California
Lawrence Berkeley National
Laboratory
Berkeley, CA 94720
Phone: (510) 643-6915
Fax: (510) 643-5571
Disclaimer
This report was sponsored by the United States Department of Energy, Energy Efficiency and
Renewable Energy, Federal Energy Management Program. Neither the United States Govern-
ment nor any agency or contractor thereof, nor any of their employees, makes any warranty,
express or implied, or assumes any legal liability or responsibility for the accuracy, complete-
ness, or usefulness of any information, apparatus, product, or process disclosed, or represents
that its use would not infringe privately owned rights. Reference herein to any specific commer-
cial product, process, or service by trade name, trademark, manufacturer, or otherwise does not
necessarily constitute or imply its endorsement, recommendation, or favoring by the United
States Government or any agency or contractor thereof. The views and opinions of authors
expressed herein do not necessarily state or reflect those of the United States Government or
any agency or contractor thereof.
References
[1] Sodec, F., and R. Craig., “The underfloor air supply system—the European experience,”ASHRAE Transactions, vol. 96, No. Part 2. 1990.
[2] Sodec, F., “Air distribution systems report no. 3554A,” Krantz GmbH & Co, September 19,1984.
[3] Tanabe, S., “Task/ambient conditioning systems in Japan,” presented at Workshop on task/ambient conditioning systems in commercial buildings, San Francisco, May 4–5 1995.
[4] Bauman, F. Underfloor Technology [Website]. Center for the Built Enviornment. Available from:www.cbe.berkeley.edu/underfloorair.
[5] ASHRAE, “Thermal environmental conditions for human occupancy,” ANSI/ASHRAE Stan-dard 55-1992, American Society of Heating, Refrigerating, and Air-Conditioning Engineers,Inc., 1992.
[6] Bauman, F., “Outlook for Underfloor Air Distribution,” ASHRAE Journal, June 2001, p. 18.[7] ASHRAE, “ANSI/ASHRAE Standard 55-1992: Thermal Environmental Conditions for Human
Occupancy,” American Society of Heating, Refrigerating, and Air-Conditioning Engineers,Inc., 1992.
[8] ASHRAE, “ANSI/ASHRAE Standard 113-1990: Method of testing for room air diffusion,”American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1990.
[9] CBE. [Website]. Center for the Built Enviornment (CBE), 2001. Available from:www.cbe.berkeley.edu.
[10] IFMA, “Benchmarking,” International Facilities Management Association, 1997.[11] Fisk, W. J., “Health and Productivity Gains from Better Indoor Environments and Their
Relationship with Building Energy Efficiency,” LBNL-45484, Lawrence Berkeley NationalLaboratory, July 31, 2000.
[12] DOE/BTS. 2001 BTS Core Databook: Table 2.3, Federal Buildings and Facilities Characteristics[Website]. DOE/Office of Building Technology, State and Community Programs (BTS),July 31, 2001. Available from: http://btscoredatabook.eren.doe.gov/frame.asp?p=chapterdisplaymain.asp?ChapterID=2.
[13] EIA, “CBECS: Commercial Buildings Characteristics 1995,” DOE/EIA-E-0109, Energy Infor-mation Administration (EIA), U.S. Department of Energy, August 1997.
