[Equest-users] Dedicated Outside Air Unit

[James Hess]

We had this same situation on our projects, and one in particular that used chilled water FCU's, but with an ERU DOAS doing the outside air.

We modeled the ERU DOAS separately in a detailed model/custom spreadsheet workbook we created (with help of VBA code) that could run hourly calcs on a full set of TMY3 weather data.

We will be submitting this soon as exceptional calc as part of LEED submission.

As far as exhaust air conditions, I just assumed exhaust air conditions typically found in facilities (i.e. 75 F, 50% RH in summer, 70 F, 40% RH in winter).  I think that is a very reasonable assumption.

I think this is the approach we will have to take until the DOAS ERU model arrives in eQuest, which I hope is soon.

The spreadsheet developed will serve us well because I'm also using it to quantify electrical demand savings for a local utility energy efficiency incentive program (i.e. peak demand reduction during summer months).

My challenge is modifying the spreadsheet to accommodate more complex ERU arrangements such as the Trane CDQ unit or the Semco Pinnacle unit, both with low temp dessicants that deliver low dewpoint area to building.  Currently scratching my head over how to model these, which wouldn't be a problem, except that they are showing up on our projects ...  :)

Thanks!

Regards,

JAH


James A.  Hess, PE, CEM
Senior Energy Engineer
TME, Inc.
Little Rock, AR
ph   501-666-6776
cell  501-351-4667
jhess at tmecorp.com<mailto:email at tmecorp.com>

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Eric O'Neill
Sent: Wednesday, February 24, 2010 10:52 AM
To: David Everhart; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Dedicated Outside Air Unit

Hi David,

I've been looking for a solution to this for a while. Modeling a DOAS using the dummy zone (set all walls to adiabatic, or with a u-value of 0.00001) is one thing, and can be done pretty easily. All your zones can get their OA from that zone. There's plenty of posts in the archive<http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/> for this (search for dummy zones), so I'll leave it there.

The trouble is, unless I'm missing something, you can't route the exhaust air back to the DOAS, so your ERV won't model correctly. I've resorted to creating an hourly report and calculating the additional ERV savings, minus additional fan and motor losses. It's certainly not ideal, and I haven't tried it on a LEED project yet, so I can't speak to the acceptability to the USGBC.

I had taken an eQuest training class, maybe 1.5 years ago, and the instructor had mentioned the developers were currently working on developing a DOAS system for eQuest and they hoped to release it within a few months, but nothing yet.

If anyone has found a way to get this working properly, or has any updates on the development in eQuest (is it in the forthcoming 3.64?), that would be great to know. It's frustrating, because it is certainly only going to be more prevalent in the future.

Eric

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of David Everhart
Sent: Wednesday, February 24, 2010 10:14 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Dedicated Outside Air Unit

I have a school which will be served by ground source heat pumps.  Outside air will be provided to the classrooms with a Dedicated Outside Air Unit/ ERV with a VAV fan which operates based on CO2 sensors within the spaces.  The heat pumps won't have any outside air provided to them.

My question is what's the best way to model this?  Since you can't apply more than one HVAC system to a particular space, do I create a fake space and apply the outside air unit/ERV to that?  If so, how do I model the fake space such that there is no heat loss and only people to require outside air?

I tried to just model the dedicated outside air system by way of the heat pumps, but I run into problems when trying to specify when the dedicated outside air unit would operate.  I would want it to operate independently from just when the heat pump is operating and I can't find a way to do this.

Has anyone had any luck modeling something similar to this?

Thanks.

David B. Everhart, P.E. LEED AP
Latimer, Sommers and Associates, P.A.
3639 SW Summerfield Dr., Suite A
Topeka, KS 66614
p.  785.233.3232
f.  785.233.0647
deverhart at lsapa.com<mailto:deverhart at lsapa.com>

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