[Equest-users] Heat Pump Heating Undersized

[Carol Gardner]

Brian,

Hard to say without knowing more e.g. building type, internal loads, etc.,
but in general, although Paul may disagree, that's pretty high. I do not
disagree with using that methodology, as long as the cfm/sf stays within
reason.

If I were you I would start with looking at the internal loads, like w/sf
for equipment and process, etc. If they can be raised or lowered reasonable,
do so. The rule is, in general, that they be the same in both cases, so make
sure you pick the changes up in your other model. Also look at your
temperatures entered in the zones/systems and associated schedules.

Otherwise, you can always send the .pd2 and .inp files to us.

Carol

On Fri, Apr 8, 2011 at 10:00 AM, Brian Goldsmith
<Brian.Goldsmith at atce.com>wrote:

>  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***
>
> *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***
>
> *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**® AP*
>
> Design Engineer
>
> 97 E. Brokaw Road, No 300
>
> San Jose, CA 95112
>
> *main    *408.487.1200
>
> *direct*  408.487.1217
>
> www.atce.com
>
>
>
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-- 
Carol Gardner PE
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