[Bldg-sim] Large Unmet Heating/Cooling in Baseline

Lynn Qualmann LQualmann at sbwConsulting.com
Fri Mar 14 17:29:44 PDT 2008


Rob -

 

I ran into the same problem, only with a much more complex building.
Mike's approach should work fine for the number of zones you have.
However, I don't think Appendix G precludes reheat for a PSZ-AC baseline
system. For System type 3, heat source is specified as fossil fuel
furnace in Table G3.1.1B (furnaces can serve individual zones), but I
don't see where it says you can't use reheat. Section G3.1.3 addresses
system specific baseline system requirements, but none of the
subsections therein say anything about System type 3. I don't see it
address in G3.1.2, either. In reality, PSZ's are known to be pretty
lousy at maintaining space temperature setpoints even with reheat.

 

-Lynn

 

: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Rob
Bialobrzeski
Sent: Friday, March 14, 2008 12:30 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Large Unmet Heating/Cooling in Baseline

 

I am modeling a school gymnasium building that has two gyms and a two
story office/locker room wing.  The office/locker room wing has several
zones that have very different loads, but are designed to all be served
by the same packaged, constant volume, 100% outside air ERV.  In the
design case model, heating is supplied to these zones primarily by HW
baseboards, while cooling loads are satisfied by the supply air.

Appendix G dictates that the baseline HVAC system be Type 3, PSZ-AC with
constant volume DX cooling and furnace heating (no reheat).  When
modeling this system type, I am getting a large amount of unmet heating
and cooling hours (as many as 1,500 hours for a given zone) in the
office/locker room zones.  My guess is that this is happening because
the baseline HVAC system has no heat source at the zone level (where the
proposed case has baseboards), and many of the slave zones have very
different heating/cooling loads than the control zone.  I am not sure
how I can adjust the model to eliminate these unmet hours while still
being consistent with Appendix G.  The only method that has worked for
me so far is to drastically increase the system supply flow, but this
creates large fan savings that may not be reasonable.  Is it appropriate
to add zone reheat even though it is not called for in Appendix G? 

 

Hopefully I've presented my problem clearly enough.  Any help would be
much appreciated!

 

Thanks,

 

Rob Bialobrzeski

 

DMI

35 Walnut Street

Wellesley, MA 02481

Phone: 781-431-1100 x17

Fax: 781-431-1109

 

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