[Bldg-sim] Direct Evaporative Coolers & the eQUEST Games

Kearns, Patrick pkearns at nexant.com
Mon Jan 21 14:17:14 PST 2008

Help!  I have been modeling a car dealership which uses several
disparate systems in combination to condition spaces.
The baseline HVAC system is Packaged Single Zone with Gas Heat.
The actual design for many of the service bays is:
Direct Evaporative Cooler
Unit Heater(s)
Exhaust Fans
For purposes of modeling the actual design, it seemed appropriate to
model the system as "Evaporative Cool' with "Furnace" selected for heat.
The OA fraction was set to 1.0 (more on this later).  Actual design
capacities were input into the model.  The unfortunate by-product of
this (as is often the case) was that there were a bunch of unmet hours
(76), mostly cooling.
So after playing around with several settings, the only way to get the
unmet cooling hours down seemed to be to change the system type back to
"Package Single Zone" and set the unitary power to 0 for the
'compressor' which really does not exist.  This makes the unmet hours go
away, but seems to create a higher heating load, despite the fact that
the actual design has higher thermal efficiency than the baseline.  The
space heating almost doubles from the baseline to the proposed.
My suspicion has been that eQUEST does not realize that the evap.
coolers only run during the summer, and thinks it has to heat 100% OA
year-round.  Appendix G says that the minimum outdoor ventilation rates
should be the same (right or wrong) for the proposed and baseline
designs.  So...my solution was to set a minimum OA schedule, with the
summer being 1 and the winter at 0.  Well...this may be closer to
reality, but now the unmet hours spike to 423!
So...it seems to be the recurring problem of fixing one problem, only to
create another one.  Any ideas on how better to simulate this?
Thanks for any tips in advance.
Patrick A. Kearns, P.E.
Nexant, Inc.
www.nexant.com <http://www.nexant.com/> 
303-998-2479 Office
303-918-8731 Mobile
pkearns at nexant.com <mailto:pkearns at nexant.com> 
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