[Equest-users] Fw: Plenums and PSZ systems

[ron lamarre]

Thanks for the help, here's what I've been able to figure out so far:


1.  The plenum warning is normal since eQuest assigns a "U-value" for the ceilings (plenum floor) and not a "layered" construction; therefore, eQuest assigns a default plenum floor weight.  Its unconditioned interior space so there no negative modeling effect.

2.  The electrical loads were adjusted by correcting the elevator process load schedule.

The only remaining issue is the modeling of a PVVT system.  How does one model zones using plenums with a PVVT system in eQuest 3.6 ?  Some options already considered (all in the detailed interface):
a.  making all the plenum walls into air walls did not work.
b.  increasing the sizing ratio did not work (even making the ratio more than 10 did not signifcantly reduce the out-of-throttling-zone hours)
c.  adjusting the CFMs and outdoor air did not help reduce the out-of-throttling-zone hours
d.  adjusting the control zone (switching the slave zones) adjusts the hours from one zone to another; but does not solve the out-of-throttling-zone hours

LEED Simulation Question: Does the proposed model need to include the exact construction document CFMs and zones or can the CFMs be adjusted (while remaining the same within the models) to make the baseline and proposed simuations work?

Note: since a PSZ system and a PVVT system is heated and cooled by supply air, it may be that the only way this works is to have difference CFMs between models.

Any help would be great.  Thanks.


Ron Lamarre, AIA, NCARB
Architect - LEED AP

 

________________________________
From: ron lamarre <lamarre_arch at yahoo.com>
To: equest-users at lists.onebuilding.org
Cc: equest-users at lists.onebuilding.org
Sent: Saturday, June 13, 2009 8:57:22 AM
Subject: Re: [Equest-users] Plenums and PSZ systems



________________________________
From: ron lamarre <lamarre_arch at yahoo.com>
To: equest-users at lists.onebuilding.org
Sent: Tuesday, June 2, 2009 5:44:14 PM
Subject: Plenums and PSZ systems


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


      
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