[Equest-users] Residential Baseline HVAC System Type (Not Again)

[Riley Beise]

Robert,

I've recently dealt with a similar situation with a third party reviewer, and the conclusion was that the baseline would be System 2 (PTHP) for the apartments, with a DOAS supplying ventilation.  The reviewer provided an unofficial interpretation response from ASHRAE from when this question was asked in the past.  Technically then, you indeed may end up with heat recovery on your baseline DOAS, although since common practice (at least in my region and limited experience) is to exhaust from the suites directly, you may be successful in arguing that the baseline should be considered to exhaust at the suite level as to not penalize your design for ducting exhaust back to the DOAS for energy recovery.  In that case you could claim exemption h, the largest exhaust source is less than 75% of the supply flow.

Good luck!

Riley Beise, P.Eng., BEMP, LEED Green Associate
Energy Analyst

AME Consulting Group
721 Johnson Street
Victoria, BC, V8W 1M8
p.  250-382-5999

From: Robert Stephenson [mailto:rstephenson at veic.org]
Sent: Tuesday, July 02, 2013 12:47 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Residential Baseline HVAC System Type (Not Again)

I have reviewed the list archives on this issue and found some conflicting opinions for residential buildings. To give some background, I am working on a model for a large adaptive reuse project that includes the conversion of a warehouse building to residential apartments. The proposed design includes split system heat pumps in the units (Electric Heat) and several RTUs (fossil fuel heat) serving as DOASs w/ energy recovery conditioning the corridor spaces and supplying/exhausting air from the residential apartment spaces. The corridor spaces exceed 25,000 square feet and 5 floors. I have the proposed design squared away, but I was hoping for an endorsement of my approach to the baseline before reconfiguring almost everything under my air-side HVAC tab.

For the baseline systems my strict reading of Table G3.1.1A along with the exceptions under G3.1.1 would indicate that for my baseline design I would do the following:

-Apartment spaces: System 2 PTHP.
-Corridor spaces: System 7 VAV w/ Reheat.

I am hesitant to plunge forward, as System 7 seems an unrealistic baseline for this application. I am also a bit confused as to how I should model the outside air delivery in my baseline. I believe I should deliver outside air via the central systems as I did in the proposed design rather than directly at the PTHP in each unit. Since the building is in Climate Zone 3A, I would not include an economizer, but I might have to include exhaust air heat recovery for cooling if the design supply air capacity for these systems exceeds 5,000 CFM, per G3.1.2.10. Am I interpreting that correctly?

To top it off, there was also a school of thought within the archives that one should model the whole baseline building with System 2 for this situation. It would certainly be less complicated, but create issues around fuel use type and fan power.

Any feedback is much appreciated.

Robert Stephenson
Technical Energy Analyst
Evaluation, Measurement & Verification Services
Vermont Energy Investment Corporation
rstephenson at veic.org<mailto:rstephenson at veic.org>
(802) 540-7886

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