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

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

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

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