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

[Michael Tillou]

Two approaches to consider.
 
1.  Ask yourself is whether the evaporative cooler is even capable of
providing the level of cooling you tell it (ie: satisfying your cooling
setpoint)?  Typically direct evaporative coolers are not intended to provide
full cooling capability just cooling relief.  Address the problem by raising
your cooling setpoint in the spaces being served by the evap coolers.  Make
sure to use the same cooling schedule for your baseline model.
 
2.  Simulate the HVAC systems in the proposed design with mechanical cooling
that has the same performance as the baseline but use the direct evap cooler
add-on feature as the first stage of cooling.  While your proposed design
technically doesn't have mechanical cooling I believe the intent of Appendix
G would require you to simulate it in order to satisfy your unmet cooling
hours.  The add-on evap cooling feature in eQuest is able to deal with the
changes in ventilation air required for direct evap cooling so you can get
rid of the crazy MIN-OA-SCH.  The user manuals should give you all the info
you need about the evap cooling keywords you will want to use.  I think
there is even a diagram showing how the evap cooling add-on ties into the
HVAC system.
   
As far as your comment about fixing one problem to create another....welcome
to energy modeling in DOE2.2.  
 
good luck
 
Mike
 
Michael Tillou, PE, LEED
Tillou Engineering, LLC
Williamstown, MA 01267
P: 413-458-9870 C: 413-652-1087
 
  _____  

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Kearns, Patrick
Sent: Monday, January 21, 2008 5:17 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Direct Evaporative Coolers & the eQUEST Games


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.
 
Regard,
 
Patrick A. Kearns, P.E.
Nexant, Inc.
 <http://www.nexant.com/> www.nexant.com
303-998-2479 Office
303-918-8731 Mobile
 <mailto:pkearns at nexant.com> pkearns at nexant.com
 
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