[Bldg-sim] Multiple HVAC systems serving one zone

Andrew Sheaffer asheaffer at environcorp.com
Mon Nov 26 13:42:24 PST 2012

I am having some difficulty setting up multiple HVAC systems serving one zone.
The situation is that I am modeling a building with packaged rooftop units as
well as exhaust fans. However, I can't model the exhaust fans using the exhaust
fan object because the exhaust fans are controlled based on enthalpy
differential with outdoor air (as I understand it, exhaust fan availability
managers only allow temperature differential).

So I thought I would set up another HVAC system in addition to the RTUs that
would function like the exhaust fans (with a supply fan, rather than exhaust, no
heating or cooling coils). I could then use an outside air controller to
specify the enthapy differential control. The issue I am having is setting up
both systems to serve one zone. Do I connect the second system (exhaust
system)to the zone inlet node, or upstream of the zone splitter associated with
the RTUs? Where do I connect downstream of the zone?

Any help would be much appreciated. Of course, if anyone has a way of getting
the exhaust fan object to run on differential enthalpy, I would take suggestions
there too!!


[cid:image003.jpg at 01CDCBEC.967765A0]<http://www.environcorp.com/>
Andrew Sheaffer, PE, CPEnMS, CEM | Manager, Carbon and Energy
ENVIRON International Corporation
333 W. Wacker | Suite 2700 | Chicago, IL 60606
T: +1 312 288 3897 | F: +1 312 288 3801 | M: +1 312 731 7096
asheaffer at environcorp.com<mailto:asheaffer at environcorp.com>

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