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Current UFAD Research Areas at CBE

With the growing awareness of the advantages of underfloor air distribution in the building industry, many more UFAD installations will be completed in the coming years. As this occurs, it will be important to quantify the installation and operating costs, as well as the energy, environmental, and productivity benefits using underfloor air technology. Building owners, developers, and other technology users need this kind of proof of performance cost-effectiveness (reduced life-cycle building costs) to overcome the barrier of higher first costs often associated with this and other intelligent building technologies. In addition, as building occupants and tenants understand more about comfort and indoor air quality issues, they will not only demand higher quality work environments, but will be willing to pay more for them.

The Center for the Built Environment is now engaged in a large research program focusing on underfloor air distribution. Ongoing CBE research projects are summarized below, along with related efforts currently supported by other organizations, including ASHRAE and ARTI. Results of ongoing CBE research are available to our current CBE sponsors. As projects are completed, results will become publicly available through CBE reports, conference proceedings, journal publications, and this website. Efforts are now underway in the following areas to provide more information and support to the building industry on underfloor air distribution technology.

Energy Performance Modeling of Underfloor Air Distribution (UFAD) Systems
The goal of this project is to develop simulation software to model the energy performance of UFAD systems and to compare it with that of conventional systems. This project is a multi-institutional effort that will culminate with validated UFAD modeling capability for EnergyPlus, the whole-building software developed by the U.S. Department of Energy. CBE is involved in full-scale testing of UFAD plenum performance and room air stratification, as described below. Details on this research

Performance of Underfloor Air Supply Plenums
In the first phase of this project, a full-scale underfloor air supply plenum test facility was used to determine the minimum effective plenum height that allowed acceptable air flow performance from an array of floor grills in a pressurized underfloor air supply plenum [1]. In the current phases of this project CBE is conducting full-scale tests in to support the UFAD modeling capability for EnergyPlus. Details on this research

Room Air Stratification Testing
As part of the development of UFAD capability for EnergyPlus, CBE is now in the process of conducting full-scale tests to document temperature stratification in UFAD buildings. This research will allow the designers and operators of UFAD systems to optimize the performance of UFAD systems in terms of occupant comfort and energy performance. Details on this research

Underfloor Systems Case Studies and Project Database
The purpose of this project is to develop a better understanding of successful designs as well as barriers to implementation of UFAD systems. CBE is compiling a database (currently more than 180) of North American UFAD projects and is preparing brief project profiles on several of these installations. To date, 6 project profiles have been completed and are currently posted on this website. In addition, two detailed case studies have been written to provide in-depth analysis of selected projects, including design details, system performance, and occupant satisfaction. CBE plans to conduct case studies of more underfloor air installations in the coming years. Details on this research

Field Study of Capitol Area East End Complex
CBE is studying and comparing the performance of two office buildings, currently under design and construction by the California State Department of General Services (DGS) in a large five-square block area directly south and east of Capitol Park in Sacramento, California, known as the Capitol Area East End Complex.  The primary building of interest is a 6-story, 28,000-m2 (300,000-ft2) building on Block 225 that will use underfloor air distribution (UFAD) exclusively on the top five stories of the building.  The ground floor will use conventional overhead air distribution.  A second office building within the Capitol Area East End Complex, Block 172, will use a conventional overhead air distribution system throughout and was selected for comparison.  This project will provide detailed data quantifying the relative impacts of UFAD technology in the form of energy use, indoor environmental quality, occupant satisfaction, comfort, and performance, and first and life-cycle (operating) costs. Details on this research

UFAD Cost Analysis Study
Under sponsorship by the U.S. General Services Administration (GSA), CBE is developing a detailed UFAD cost model to allow comparison between UFAD and conventional systems, as well as evaluation of alternative UFAD system designs. The cost model incorporates integrated design principles, allowing decisions on one or more variables to be traded off against their cost impacts on other ones. All assumptions, detailed cost estimating algorithms, as well as actual material and labor costs, have been developed and entered into the model based on an extensive collaboration and exchange of information with knowledgeable and experienced designers, contractors, and manufacturers. The model will ultimately contain both first and life-cycle cost calculations, but at this point we are nearing the end of the first phase -- Development of the First Cost Model. Details on this research

ASHRAE UFAD Design Guide
Beginning in 1999, under sponsorship by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), CBE developed the ASHRAE Underfloor Air Distribution (UFAD) Design Guide (1064-RP). The design guide was completed and published by ASHRAE in December 2003. The guide covers a wide range of topics, selected because they represent areas in which important differences exist between conventional systems and UFAD design.  Where available, preliminary design guidance is also provided for the closely related task/ambient conditioning (TAC) systems. Details on this research

Underfloor Plenum Fan Power
Using simplified energy analysis, CBE investigated the impact of various design assumptions on the supply fan energy consumption of pressurized underfloor plenum systems compared to that of traditional overhead systems [2]. Download a PDF version of this report (280K)

ARTI White Paper 
Under sponsorship by the Air-Conditioning and Refrigeration Technology Institute (ARTI), Carnegie Mellon University completed a state-of-the-art review of "Flexible and Adaptive HVAC Distribution Systems for Office Buildings." The final report, published in 2002, documents the performance of recent developments in flexible and adaptive distribution systems in office buildings, and also documents the barriers and opportunities for both industry and professional practice in the development of innovative, flexible and adaptive HVAC distribution systems. The final report [3] is available at www.arti-21cr.org/research/completed/index.html.

ASHRAE Standards Revision
ASHRAE Standard 55-2004 -- Thermal Environmental Conditions for Human Occupancy [4] has recently been revised and approved for publication. The revised Standard includes a new adaptive standard for naturally ventilated buildings (i.e., buildings in which occupants have some amount of control over their thermal environment) that takes into account people's adaptive thermal expectations. 
ASHRAE Standard 113-1990 -- Method of Testing for Room Air Diffusion [5] is currently being revised to include a new standardized test and analysis method for evaluating the performance of TAC and underfloor air distribution systems.

Underfloor Air Technology Website
CBE is continuously updating this website dedicated to providing a complete and unbiased description of underfloor air distribution technology.

[1] Bauman, F., P. Pecora, and T. Webster. 1999 "How low can you go? Air flow performance of underfloor plenums." Center for the Built Environment, University of California, Berkeley, October.

[2] Webster, T., E. Ring, and F. Bauman, 2000 "Supply fan energy use in pressurized underfloor plenum systems." Center for the Built Environment, University of California, Berkeley, October. 

[3] Loftness, V., R. Brahme, M. Mondazzi, E. Vineyard, and M. MacDonald. 2002. “Energy savings potential of flexible and adaptive HVAC distribution systems for office buildings – Final report.” Air Conditioning and Refrigeration Technology Institute 21-CR Research Project 605-30030, June.

[4] ASHRAE. 2004. ANSI/ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. 

5] ASHRAE. 1990. ANSI/ASHRAE Standard 113-1990, Method of Testing for Room Air Diffusion. Atlanta: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.

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