[Equest-users] Heat Pump Heating Undersized

[Joe Fleming]

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

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, LEEDR AP

Design Engineer



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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