[Equest-users] Fw: Plenums and PSZ systems

[Dakota Kelley]

Ron,

 

You are correct about 1) below.  I would imagine you have acoustic tile
for your ceiling construction, and eQUEST converts this material to a
simple U-value rather than a layered construction with thermal lag.  The
main problem resulting from using simple vs. layered constructions is
when the method differs between the baseline and proposed models.  For
example, it would be inaccurate to model the baseline's exterior walls
with the U-value method while modeling the proposed with a layered
construction.  The baseline would not have thermal lag accounted for
when the loads are simulated.  

 

Problems with hours outside throttling range are usually system control
issues rather than capacity issues, especially if you're letting eQUEST
auto-size.  For example, a system that is twice as large as it needs to
be for peak loads will probably still have trouble increasing space
temperature by 15 degrees in one hour.  You'll need to coordinate your
design temps, thermostat schedule (pay attention to night setback temps
and morning warm-up), and OA schedule to ensure the system is properly
controlled.  I recommend locking out OA during morning warm-up.  The
detailed reports will help you research problem zones (SS-F and SS-O).
Find out where the problems are occurring and adjust your system control
accordingly. 

 

Regarding CFM between baseline and proposed, I would be suspicious if
they matched.  In fact, I've never submitted to LEED with matching flow
rates.  The proposed system should match construction drawings, and I
assume the mechanical engineer did not use eQUEST for sizing.  ASHRAE
90.1-2004 G.3.1.2.8 says the baseline's supply needs to be determined
from a 20 degree dT.  eQUEST can then auto-size the baseline flows
during sizing runs, and you can use those flows with G3.1.2.9 to
determine your baseline fan power.  Even if a 20 degree dT for the
proposed case was used with eQUEST auto-sizing, the resulting flow rates
should be different because the space loads are different (i.e.
different skin loads).

 

Please feel free to contact me directly if you need further
clarification.

 

Thanks,

 

  Dakota Kelley

     Modeling Services

 

 

 

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From: ron lamarre [mailto:lamarre_arch at yahoo.com] 
Sent: Sunday, June 14, 2009 9:16 AM
To: equest-users at lists.onebuilding.org
Cc: equest-users at lists.onebuilding.org
Subject: [Equest-users] Fw: Plenums and PSZ systems

 

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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