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Trick or Treat: A Solution to "Tricking the Software" for Modeling Chilled Beams in Laboratories

Paul Erickson and Bob Sherman, P.E., LEED AP, Affiliated Engineers, Inc.

In the past several years, chilled beam technology has emerged in the United States as one HVAC energy saving alternative to historically conventional all air systems such as variable air volume (VAV). All chilled beams have a radiator element which provides radiant cooling via circulated cool water. There are passive beams and active beams. The primary distinction between the two is based on the mechanism by which air flow is promoted and how fresh air is introduced in the occupied space.

This technology is most applicable to interior environments where heat gain in the space (solar radiation, equipment heat, etc.) is the primary impetus for determining air flow quantities. Chilled beams have been used successfully in office environments for years and now they are starting to be introduced into laboratories. One challenge to incorporating them into modern laboratory spaces is that conventional energy modeling does not include solutions for chilled beams.

Affiliated Engineers, Inc. (AEI) is designing laboratory spaces utilizing chilled beam technology in conjunction with several different clients and architectural partners. In order to make the case to incorporate and design them correctly, the authors needed to model the performance of chilled beams. The key issue with modeling chilled beams has been current software’s inability to accurately model the specific thermodynamics of chilled beams. The primary methodology for modeling this technology has been to use an induction unit and subtract any fan energy used in the system from the overall model, in essence, by "tricking" the software. This is done in modeling programs such as Visual DOE and eQuest. This has led to widely varying results.

Looking to produce more accurate results, AEI hired Thermal Energy System Specialists (TESS) to develop TRNSYS "modules" for use in simulating chilled beams in buildings. Specifically, TESS developed descriptive TRNSYS modules from performance data using the Trox chilled beam data. TESS developed a module for both active chilled beams and passive chilled beams. With these modules, TRNSYS can be used to accurately model chilled beams in any building setting, including laboratories.

Using a front-end user interface called TRNSed, AEI has the capability to quickly do basic comparisons between VAV systems and chilled beam systems in a laboratory building to assist in building concept evolution early in project design phases. These comparisons allow various modifications, such as geographic location, internal set points, internal loads, and method of primary chilled water supply (dedicated chiller for chilled beams, or combined chiller for all loads).

Biography:

Bob Sherman, P.E., LEED AP, is a project manager and lead mechanical engineer at Affiliated Engineers, Inc. Mr. Sherman’s experience includes all phases of HVAC engineering, from initial design concepts and optimization comparisons through construction documentation, specifications, quality control and construction administration. Project experience includes corporate, public health, and higher education laboratories. Mr. Sherman is an integral part of AEI’s sustainable group. Current projects include a LEED-certified building in construction and two major laboratory buildings in design that are equivalent to the LEED Silver rating, one of which is utilizing chilled beams.

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