[BLDG-SIM] Appendix G Baseline HVAC system and modeling packaged VAV with gas heat

Aulbach, John jaulbach at nexant.com
Wed Oct 3 14:13:39 PDT 2007


Andrew:
 
I don't know what your climatic area is, but why should ANY heating show
up at the central unit? A VAV w/reheat, in my meager experience, is
controlling the central cooling coil to 55 DegF and adjusting reheat
coils (and VAV airflows) from there. When winter shows up, your cooling
coil is REALLY backed off (or off) and the VAV still flies, with heat
added at the space (terminal) level.
 
The only purpose you may have for a central heating coil is to preheat
outside air to, say, 40 DegF. Depending on where your climate is, this
may RARELY happen?
 
Does this sound right, folks?

________________________________

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Andrew
Craig
Sent: Wednesday, October 03, 2007 1:35 PM
To: BLDG-SIM at gard.com
Cc: Andy Frichtl
Subject: [BLDG-SIM] Appendix G Baseline HVAC system and modeling
packaged VAV with gas heat



I have two questions that have come up recently...

 

1.	If the a proposed building pursuing LEED is going to use a
Packaged VAV system with a gas furnace in the unit and electric reheat
in the boxes, would the baseline building (according to ASHRAE Appendix
G) fall under the Fossil/Electric Hybrid category or the Electric
category since that is the predominant heating source? 
2.	Secondly, what is the best way to model this type of system in
eQUEST?  I have experimented with first defining a packaged VAV unit in
the wizard with hot water coils as the heating source.  Then in the
detailed edit mode, I changed the system "Heat Source" to furnace and
"Zone Heat Source" to electric and deleted the boiler and hot water
loop.  When I simulated this model, no natural gas usage showed up in
the BEPS report under Space Heating, however, there was a tiny amount
(~2% of total heating energy) that appeared in the Pumps & Aux category.
Can anyone explain what's happening and/or suggest the best way to model
this kind of system?  As a side note, from projects we have monitored
here in Oregon, we would expect to see about 30% of the total heating
energy use go to natural gas for this type of system, primarily from
morning warm-up. 

 

Thanks for your input.

 

Regards,

 

Andrew Craig, EIT, LEED(r) AP | Mechanical Designer

INTERFACE ENGINEERING 
708 SW Third Avenue | Suite 400 | Portland, OR 97204 

direct: 503.382.2696
office: 503.382.2266
fax: 503.382.2262
email: Andrew_C at ieice.com
web: www.ieice.com 

Consultants of Choice to the Built Environment for over 35 years
Kirkland, WA | Portland, OR | Sacramento, CA | Salem, OR | SanFrancisco,
CA

 


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