[Equest-users] Heat Pump Heating Undersized

Shuichi Hendrickson Shuichi.Hendrickson at erm.com
Sun Apr 10 20:15:31 PDT 2011


Brian,

A few additional thoughts.


  1.  If you haven't already, set NIGHT-CYCLE-CTRL = CYCLE-ON-ANY. If you don't do this or schedule a warm up, you will likely have unlet load hours in the morning. You can check this in the SS-O.
  2.  I've found that perimeter zones are usually the most troublesome and have employed specifying cfm/ft2 at zone level in the past, though I agree with others that 2cfm/ft2 seems high.
  3.  Consider setting your Tstat control to REVERSE ACTION if you have low min flow ratio (i.e. < 0.4). This will allow the boxes to open beyond MIN-DES-FLOW during heating.
  4.  Don't know anything about your project, but if this is a LEED ASHRAE90.1 baseline and you are modelling one system floor, take a look at your peak loads by zone. If your problem zone loads differ by more than what is specified in Section G3.1.1 b. of the Performance Rating Method, you may be able to create a separate system. DOE2 has difficulty with systems where loads vary a lot between zones. I doubt any energy model can handle this that well.

Good luck,

Shuichi Hendrickson
Environmental Engineer, LEED AP

ERM Japan
The Landmark Tower
Yokohama 19F
2-2-1-1, Minatomirai, Nishi-ku
Yokohama, 220-8119, Japan

T:+81(0)45-640-3780
F:+81(0)45-640-3781
shuichi.hendrickson at erm.com<mailto:shuichi.hendrickson at erm.com>
www.erm.com<http://www.erm.com/>
Ranked No1 All-Environmental Firm: ENR Magazine (2004, 2005, 2006, 2007)
Environmental Adviser of the Year: Acquisitions Monthly (2005, 2006, 2008)
P Please consider the environment before printing this email

________________________________
From: joe at thespinnakergroupinc.com [mailto:joe at thespinnakergroupinc.com]
Sent: Sunday, April 10, 2011 4:22 AM
To: Bruce Easterbrook; Carol Gardner
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Heat Pump Heating Undersized

"...as your time averaged outside air requirements also come into play and may not allow the VAV system to put enough flow into a zone due to OA requirements of other zones."

Very good point.


Sent from myTouch 4G
----- Reply message -----
From: "Bruce Easterbrook" <bruce5 at bellnet.ca>
To: "Carol Gardner" <cmg750 at gmail.com>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Subject: [Equest-users] Heat Pump Heating Undersized
Date: Sat, Apr 9, 2011 10:46 am

I agree with Carol and Joe.  In almost all cases you shouldn't need to have the cfm/SF 400% higher than the eQuest set point.  If you do, it is likely going to be a process load that causes this.  I have found the 0.5 cfm/SF eQuest default too low in most cases but leave it for my first run because what you really want are the heat/cool loads of the zones.  Joe's tip, CFM*(Tsupply-Troom)*(1.085) = BTU/h provides your tool.  Your equipment provides the delta T of your air heating and cooling flows, the only variable is CFM.  Use your loads required by the building to determine your CFM.  The old rule of thumb was around 1 CFM/SF but in most cases this is too generous.  I think the reason eQuest uses a low default is to help you keep the fan energy to a minimum and maximize the efficiency of your system.  You want just enough CFM to do the job, more is a waste, too little gives lots of unmet load hours.  This is where I start when tweaking a system.  Your cooling flow normally sets the flow as it has the smallest delta T.  Heat pumps have a lower heating delta T than a furnace.  VAV further complicates as your time averaged outside air requirements also come into play and may not allow the VAV system to put enough flow into a zone due to OA requirements of other zones.  OA is also quite dominate when it comes to energy consumption.  One other area to consider it where your controlling zone is for your temperature control.  Selecting the proper zone can have a large effect on unmet load hours.
eQuest is a tool and will never give you the perfect system with the first press of the sim button.  If you are just starting with eQuest consider yourself lucky if it even runs through.  Your detailed reports give you the clues you need to refine your model.  Start with the coarse variables, CFM, delta T's, note I didn't mention throttling range.  Allowing your system to run loose too early will hide problems in your design.  A 2 degree throttling range is tight in my opinion but again eQuest is trying to help with getting an efficient system.  Look for errors in input, incorrect assumptions and numbers which don't seem right.  Slow and plodding, one change at a time, check the effect and ALWAYS have a backup file.
Bruce Easterbrook P.Eng.
Abode Engineering

On 08/04/2011 01:32 PM, Carol Gardner wrote:
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<mailto: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<mailto:Brian.Goldsmith at atce.com>
direct  408.487.1217<tel:408.487.1217>

________________________________
From: Joe Fleming [mailto:joe at thespinnakergroupinc.com<mailto:joe at thespinnakergroupinc.com>]
Sent: Thursday, April 07, 2011 1:55 PM

To: Brian Goldsmith; equest-users at lists.onebuilding.org<mailto: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<tel:561-602-3132>

The Spinnaker Group
www.thespinnakergroupinc.com<http://www.thespinnakergroupinc.com>

From: Brian Goldsmith [mailto:Brian.Goldsmith at atce.com<mailto:Brian.Goldsmith at atce.com>]
Sent: Thursday, April 07, 2011 4:36 PM
To: Joe Fleming; equest-users at lists.onebuilding.org<mailto: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<tel:408.487.1217>

________________________________
From: Joe Fleming [mailto:joe at thespinnakergroupinc.com<mailto:joe at thespinnakergroupinc.com>]
Sent: Thursday, April 07, 2011 12:14 PM
To: Brian Goldsmith; equest-users at lists.onebuilding.org<mailto: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> [mailto: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<mailto: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
[%20]
97 E. Brokaw Road, No 300
San Jose, CA 95112
main    408.487.1200<tel:408.487.1200>
direct  408.487.1217<tel:408.487.1217>
www.atce.com<http://www.atce.com/>


_______________________________________________
Equest-users mailing list
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>



--
Carol Gardner PE






_______________________________________________

Equest-users mailing list

http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>

________________________________

This electronic mail message may contain information which is (a) LEGALLY PRIVILEGED, PROPRIETARY IN NATURE, OR OTHERWISE PROTECTED BY LAW FROM DISCLOSURE, and (b) intended only for the use of the Addressee (s) names herein. If you are not the Addressee (s), or the person responsible for delivering this to the Addressee (s), you are hereby notified that reading, copying, or distributing this message is prohibited. If you have received this electronic mail message in error, please contact us immediately and take the steps necessary to delete the message completely from your computer system. Thank you.

Please visit ERM's web site: http://www.erm.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20110411/92923834/attachment-0002.htm>


More information about the Equest-users mailing list