[Equest-users] Plenums and PSZ systems

[ron lamarre]

Hi to all:

We're designing a new 22K SF LEED office building with a baseline HVAC system = PSZ RTUs.  Two issues have come up with the final parametric runs.

1.  The design incorporates plenum returns; which result in e-Quest warning messages regarding the lack of floors and ceilings in the plenum spaces.  We have been ignoring these given that the plenums are "unconditioned" spaces and are without thermostats - is this the correct method?  We are not providing any ductwork and the returns will not be directly into the units.

2.  The electrical loads are huge.  When the simulation is run with just the ASHRAE baseline, the only equipment that can be elevating the power to this extreme is the electric DX cooling from the PSZ RTUs.  All lighting is around 1.0 W/SF and there are no process loads yet added.
The ASHRAE User Manual suggests that when a PSZ system is used, a "system for each zone" is provided; which is the case in the current model.  We have 24 seperate zones/thermal blocks with dedicated RTUs).  When the HVAC is zoned as designed for the PVVT design case, there are 9 RTUs; however, the unmet heating and cooling hours are off the charts. - Are PSZ systems supposed to have one RTU per thermal block, and if so how does one control the hours out of the throttling zone?

Any help would be greatly appreciated.  Thanks.


Ron Lamarre, AIA, NCARB
Architect - LEED AP

L A M A R R E  A R C H I T E C T S 
3 Hoyt Circle 
Atkinson NH 03811 
t: 603.362.9514 
f: 603.362.9520 
e: lamarre_arch at yahoo.com


      
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