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
Rob,
You should be modeling one PSZ for each thermal zone.
Michael Rosenberg
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