exhaust heat recovery system with PTAC in eQUEST

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As per ASHRAE 90.1-2013, exhaust air energy recovery is required for
ventilation systems operating greater than 8000 hours per year. I am
working on a baseline model of 6 storeys apartment building in climate zone
5A. As per ASHRAE 90.1-2013 Appendix G, apartments units are required to
have PTAC systems with heat recovery. I am wondering, how to model PTAC
with heat recovery in eQUEST. PTAC system cannot take heat recovery in
eQUEST.

Also, ASHRAE does not have any information on fan power for energy recovery
systems. Should the ERV fan be a part of allowable 0.0003 kW/cfm fan power?

Any suggestions will be appreciated.

Thanks,

Sunayana Jain

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Hi Sunayana,
Use Pkgd Single Zone (PSZ) systems to model Appendix G PTACs. You will need to create one PSZ system per zone which might mean 100+ systems for your 6-story apartment building. Floor multipliers are probably in order.
The PTAC fan power of 0.0003 kW/cfm includes ERVs. I?m not aware of an exception to Appendix G that would apply.
There are a few possibilities for justifying no ERV in the baseline:

- Ventilation system runs <8000 hrs/year (hard to justify for apartments?)

- The building is a multipurpose use and you can model additional system types in the nonresidential areas

- 6.5.6.1 exception (8.), ?where the largest source of air exhausted at a single location at the building exterior is less than 75% of the design outdoor airflow rate?. This would seem to apply, since each PTAC handles the ventilation load for one zone, and the baseline would have no large common exhaust location.
Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
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Hi Bill,
We have been around that exception a number of times. The conclusion reached is that exception 8 does not apply if each suite has an ERV responsible for the outdoor air and exhaust of that suite.

If the building has a central make-up air system dumping air into the corridors, through the carpet filter under the doors into the suites, then locally exhausted, then exception 8 does apply.

Here in Ontario we model the baseline as per Section 11, ECB. Most new apartment buildings have insuite ERVs and fan coils. Therefore the baseline suite systems also have heat recovery.

Christopher R. Jones, P.Eng.
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Bill,
The great majority of high rise multi-family buildings are condominiums (like your co-ops). Each suite is metered for electricity directly by the utility so the designs try to get as much electricity into the suites. Then there is the all glazing fad that isn?t fading. In order to meet the local code, you need condensing boilers for heating and air side heat recovery therefore the insuite ERVs.

Note, all designs also include a makeup air system for corridor pressurization (mostly for odor control) and there is no return to these make-up air systems. 50 cfm per suite is the typical amount dumped into the corridors. As well, most of these buildings pursue LEED therefore have weather stripping on the suite doors for the tobacco prerequisite. I don?t know where all that corridor pressurization makeup air goes.

Christopher R. Jones, P.Eng.
Technical Specialist
Sustainability & Energy

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