Project Title:

Energy Performance Modeling of Underfloor Air Distribution Systems

Development of the first tool to provide accurate whole-building modeling of the energy performance of underfloor systems.

Status (updated 7/18/2007): Complete

Funding sources: CBE Industry Consortium, Research Grants


Project Objective

Develop underfloor air distribution (UFAD) system simulation software that can be used by design practitioners to model the energy performance of UFAD systems, optimize UFAD systems design, and to make accurate comparisons with conventional systems.

Significance to Industry

Despite the growth of UFAD applications in North America, the technology is still in its infancy. There are few standardized methods and guidelines for designing and optimizing these systems, and whole-building energy calculation software now available does not allow for their accurate modeling. This slows the adoption of UFAD systems, and results in buildings that may not fully optimize the potential benefits of these systems. The availability of a whole-building energy modeling tool will help UFAD technology achieve its full potential by enabling the design of UFAD systems that are energy efficient, and effective in their performance.

Research Approach

This project is a three-year, multi-institutional effort that will culminate with a validated UFAD modeling capability for EnergyPlus, the next-generation whole-building energy simulation program developed by the U.S. Department of Energy to supercede DOE-2. The new UFAD capability will be suitable for designing and analyzing UFAD system performance.

For this project CBE is collaborating with UC San Diego, Lawrence Berkeley National Laboratory, and York International. This work is being jointly funded by CBE, The California Energy Commission, the U.S. Department of Energy, and York International. This project has been developed in three phases:

1. The development of a sound theoretical understanding of the behavior of UFAD systems by conducting laboratory bench and full-scale experiments. This work will be conducted at three test facilities: CBE's full scale UFAD plenum test bed at UC Berkeley, the full scale room air stratification test chamber operated by York International, and the small-scale salt tank laboratory at UCSD.

2. Development of a validated mathematical models of the room air stratification (RAS) phenomenon and the thermal performance of UFAD supply plenums.

3. Integration of the RAS and plenum models along with system upgrades into the EnergyPlus whole-building energy simulation program. The final product will be a version called EnergyPlus/UFAD that can be used by design professionals and others to simulate UFAD system performance.

When the software development is complete, the project team will develop a technology transfer program to promote the adoption of the tool by industry.

Final Report

"Energy Performance of Underfloor Air Distribution Systems." Final Project Report submitted to California Energy Commission (CEC) Public Interest Energy Research (PIER) Program. Center for the Built Environment, University of California, Berkeley, CA, April 2007.

Part I: Project Summary (final draft)

Part II: Room Air Stratification Full Scale Testing

Part III: The Fluid Dynamics of a UFAD System

Part IV: Underfloor Plenum Testing and Modeling

Part V: EnergyPlus Development

Publications and Reports

Webster, T., F. Bauman, K. Lee, S. Schiavon, A. Daly and T. Hoyt. 2013. CBE EnergyPlus modeling methods for UFAD systems. CBE Summary Report. August.

Webster, T., T. Hoyt, E. Lee, A. DAly, J. Feng, F. Bauman, S. Schiavon, K.H. Lee, W. Pasut and D. Fisher. 2012. Influence of design and operating conditions on underfloor air distribution (UFAD) system performance. Proceedings of SimBuild 2012. Madison, WI. August 1-3.

Lee, K.H., S. Schiavon, T. Webster, F. Bauman, J. Feng and T. Hoyt. 2011. Lessons learned in modeling underfloor air distribution system. Proceedings of SimBuild 2011.

Webster, T., K.H. Lee, F. Bauman, S. Schiavon, T. Hoyt, J. Feng and A. Daly. 2010. Influence of supply air temperature on underfloor air distribution (UFAD) system energy performance. Proceedings of SimBuild 2010.

Webster, T., F. Bauman and A. Daly. 2008. Modeling underfloor air distribution systems. Proceedings of SimBuild 2008.

Bauman, F. and T. Webster, 2005. Research Overview of the UFAD EnergyPlus Model: Plenum and RAS Testing and Modeling. Berkeley, CA. October. (PDF 3MB)

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CBE UFAD Test Facility

Project chart of project roles and institutions involved in EnergyPlus/UFAD development.

CBE UFAD Test Floor

Example of salt tank testing being conducted by UCSD.

CFD Model of UFAD Plenum

The EnergyPlus/UFAD tool will allow users to model the unique aspects of UFAD systems.