# FW: Residential or Nonresidental? And sizing for PTAC units.

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Loren,

One of the notes under Table G3.1.1A of ASHRAE 90.1-2004 states,
"Residential building types include dormitory, hotel, motel, and
multifamily. Residential space types include guest rooms, living
quarters, private living space, and sleeping quarters. Other building
and space types are considered nonresidential." The User's Manual also
says, "If a building has both residential and nonresidential spaces, for
instance a residential tower with retail and restaurants at the base,
then the HVAC system type is determined separately for the residential
and nonresidential portions."

I recently did an energy model for a motel that had first floor retail
spaces, a swimming pool, an indoor parking garage, and a fairly large
lobby. I used realistic systems for these spaces instead of PTACs or
PTHPs. For a different motel I modeled, the nonresidential spaces were
rather insignificant, so I used PTHPs throughout.

Regarding which capacity to use for the EER calculation, I would use
realistic capacities. For example, for the space that needs 40 kBTU/h, I
would assume that there would be two 20 kBTU/h units and use 20 kBTU/h
for the capacity in the EER equation.

I think the decision to use an average EER for all the units is a
judgment call depending on how complex you want your model to be. It's
the usual trade-off between making assumptions to simplify the model or
adding complexity to get more accuracy (presumably).

Sincerely,

Keith Swartz, PE, LEED(r) AP

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Thank you both Andrew and Keith,

Understanding the exceptions, and also correct calculations for the EER
(didn't realize there was a limit of 15,000 BTU for the calculation until I
read the small print!) are very helpful. It brings up another question,
now, though:

When modeling a PTAC unit, and taking this EER value, would you use this to
include the supply fan energy? G.3.1.2.1 states that you should separate it
into various components, which confuses me a bit. I know this is getting
down to minutia, however, just trying to make sure I'm doing this
correctly. If this is something that is common practice to look over, and
just make sure to include the supply fan efficiencies within the EER for
entire unit (something that would make sense to me as it is a packaged
unit), also let me know.

Thanks again,

Loren

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Joined: 2011-10-02
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Loren,

I haven't had to get into that much detail for my energy models (not
LEED), so I won't be much help on this. I suggest finding out from the
manufacturer if the published EER includes fan power or not.

Sincerely,

Keith Swartz, PE, LEED(r) AP

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Joined: 2011-09-30
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For an 90.1, it asks you to separate the fan from the compressor. This is because the standard will ask for fans to run constantly, however if you have a combined EER (entered as cooling-EIR) the fan power will not be calculated when the compressor cycles off.

That may be okay for non-App G analysis, particularly if your project will cycle with the compressor.

David

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