Trick or Treat: A Solution
to "Tricking the Software" for Modeling Chilled Beams
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
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 softwares 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
P.E., LEED AP, is a project manager and lead mechanical engineer
at Affiliated Engineers, Inc. Mr. Shermans 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 AEIs 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.
Back to Agenda