[Equest-users] Heat Pump Heating Undersized

Brian Goldsmith Brian.Goldsmith at atce.com
Fri Apr 8 10:00:59 PDT 2011


So if I force the cfm/sqft to 2, it brings the unmet load hours down to about 80, which is good. But of course the fan energy spikes. Each zone has its own unit. Is it good practice to force the cfm/sqft? Especially considering what this does to the fan energy?

Brian Goldsmith
Brian.Goldsmith at atce.com<mailto:Brian.Goldsmith at atce.com>
direct  408.487.1217

________________________________
From: Joe Fleming [mailto:joe at thespinnakergroupinc.com]
Sent: Thursday, April 07, 2011 1:55 PM
To: Brian Goldsmith; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Heat Pump Heating Undersized

Check the minimum flow ratio and the minimum design flow cfm/sqft for the trouble zones.
In the VAV system equest distributes a percentage of the supply airflow to each zone.  But cfm/sqft is a priority in the hierarchy and if you bump it up for the trouble zones you will get higher cooling and heating airflows at your given SAT.  The energy you provide to the room is equal to CFM*(Tsupply-Troom)*(1.085 or another conversion factor depending on units and air density).  So if your schedules and equipment are set up correctly you should override the equest defaults for airflows or SAT.


Joe Fleming, E.I., LEED AP BD+C, BEMP
Commissioning Agent
561-602-3132

The Spinnaker Group
www.thespinnakergroupinc.com

From: Brian Goldsmith [mailto:Brian.Goldsmith at atce.com]
Sent: Thursday, April 07, 2011 4:36 PM
To: Joe Fleming; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Heat Pump Heating Undersized

Ya I looked at all that, seemed to be fine. It seems like whenever I change my system from single zone package to variable air volume this problem comes up. I just changed the system type and left everything else the same.

Brian Goldsmith
Brian.Goldsmith at atce.com<mailto:Brian.Goldsmith at atce.com>
direct  408.487.1217

________________________________
From: Joe Fleming [mailto:joe at thespinnakergroupinc.com]
Sent: Thursday, April 07, 2011 12:14 PM
To: Brian Goldsmith; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Heat Pump Heating Undersized

Usually scheduling (fan, available heating and t-stat don't coincide every hour of every day), airflow (too low), SAT (too low), or multiple zones on one unit.
Usually...

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Brian Goldsmith
Sent: Thursday, April 07, 2011 2:24 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Heat Pump Heating Undersized

I'm having trouble with the heating in my heat pump. I modeled a Packaged VAV (PVAVS) with HEAT-SOURCE= Heat Pump and ZONE-HEAT-SOURCE= Not Installed. Set HEAT-SET-T to 120F, DESIGN-HEAT-T to 70F, and did not specify auxiliary heat. I get the message that my zone has insufficient heating capability. Looking at SS-A, is says the maximum heating load is only -10.1 KBTU/HR. Looking at SS-P, the report says my heating capacity is -47.8 KBTU/HR. So why do I have 563 underheated hours? Does it have something to do with the system type? I tried ZONE-HEAT-SOURCE= Heat pump and tried HEAT-SIZING-RATIO= 5, just to see if either one would do anything, although I didn't really expect them to. Also tried electric supplemental heat, which comes out to -31.715 KBTU/HR. My design supply flow is 1913 CFM, and the outside air flow is 252 CFM. The design supply flow is the same for both the heating and cooling performance summaries. Should this be the case? Thanks for any help.

Brian Goldsmith, LEED(r) AP
Design Engineer
[cid:image001.jpg at 01CBF5D3.DC7BB330]
97 E. Brokaw Road, No 300
San Jose, CA 95112
main    408.487.1200
direct  408.487.1217
www.atce.com<http://www.atce.com/>

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