[Equest-users] Heat Recovery Increases Cooling load

[Chris Baker]

I had a similar problem on my first energy model in equest.  In my case it was associated with one particular “problem child” zone.

The heating and cooling loads of this one zone were extreme – Particularly, in Alaska’s coldest winter months (December, January) and I struggled with it for about half a day trying to figure it why.  It was a VAV system calling for heating AND cooling in the middle of Winter in Alaska?
The cause of the drama ended up being an exhaust fan (hood) in the kitchen/cooking zone.

The fan energy and flow of the exhaust fan was fine and schedules were fine.  But while operating it caused the VAV system to operate excessively in response. So much that it overheated the space, it would then cool the space excessively, it would then heat the space again (total madness).

Not only that but it was pulling the same OSA ratio as the rest of the zones in the system - Alaskan OSA in December/January no less!  Here-in lied the problem.

Once I was able to put this together I was able to apply an easy fix.

I set up a new OSA ratio schedule for this VAV system that directly corresponded to the exhaust fan schedule.  When exhaust fan was on it would pull recirculated/return-air only and OSA dampers would be shut.  Instantly fixed the problem.

I would definitely check the heating/cooling loads throughout to make sure nothing is throwing the system too off-kilter.

Also, I highly recommend using the mixed air reset as mentioned in the previous post.

-Chris Baker

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Brian Fountain
Sent: Friday, December 18, 2015 5:04 AM
To: Nufal, Maye; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Heat Recovery Increases Cooling load

The default settings for heat recovery control is'float' which always maximizes heat recovery, even if it reduces free cooling. Changing this to 'mixed air reset' will help.

Also, on the 2nd heat recovery tab, the default is 1" of static added to the supply fan (on top of whatever you have on the fan tab) to account for the added fan power to push the air through the heat recovery device.

From: Nufal, Maye
Sent: Friday, December 18, 2015 8:58 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Heat Recovery Increases Cooling load


Hi,

We’ve been facing the same issue in multiple projects ;  using heat recovery somehow increases our cooling load.

This was evident in a VAV system as well as Central Plant Systems .

We’ve tried using both Sensible HX/Enthalpy wheel with same results.

Has anyone been able to tackle this issue ?

Help/workaround ideas is appreciated.

THANKS ☺

MN






Maye Nufal , LEED BD+C
Sustainable Buildings Consultant
Stantec
100-401 Wellington Street West Toronto ON M5V 1E7
Phone: (416) 598-7157
Fax: (416) 596-7892
Maye.Nufal at stantec.com<mailto:Maye.Nufal at stantec.com>

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