ASHP for PGH in Climate Zone 6
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We live in a recently built house (not passive certified but following PGH principles). The house has three floors with radiant floor heating installed in the basement and main floor. We’d like to retrofit ASHPs for AC and additional heating on the second floor.
After substantial reading and research (thanks to this forum) I was considering hiring a professional firm to do perform the Manual J and system design but the consulting costs for the firm I spoke to were very high for a relatively small project.
Rather than spend a lot on Manual J software and after seeing https://www.greenbuildingadvisor.com/question/chatgpt-4-0-and-manual-j I thought I’d see if ChatGPT could provide some rough load
calculations (which I’ve attached here). It was very seamless to upload the
architectural plans and prompt it to use the included window and door schedule. As I don’t have any HVAC background, my first question is if these numbers seem reasonable?
Based on these calculations I would consider a Fujitsu ARU12RGLX with ducting for the basement and the main floor (installed in the mechanical room) and a Fujitsu ARU9RGLX for the second floor installed in a closet with short duct runs to 2 bedrooms and the main hallway.
Just trying to get a sense if this approach seems reasonable from a sizing
perspective? The main goal is have more continuous running for humidity control (which can be problematic during our summers).
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Replies
Interesting approach. Very efficient way to get a diy ballpark load. And those manual j numbers look reasonable to me for a pgh in your climate zone.
If dehumidification is a consideration I’d have a look at the spec sheets for what ever heat pump units you are looking at. Some high performing models have great SEER numbers but pretty low pints/hr numbers. I don’t know much about Fujitsu. I do know the next gen A2L refrigerant Mitsubishi hyper heats are supposed to have double the moisture removal capacity of the current line. So there may be some benefit in waiting for the a2l equipment.
The models you list are previous gen r410a and show up as “retired” when I google for what that’s worth. Anyway, good luck on your project.
I'm kind of surprised that with cold winters and mild summers that you would have a higher cooling load than your heating load. I would expect your heating load to be higher than your cooling load.
There is a free energy modeling software available eQuest you could try. It isn't super hard to use. It uses the same energy plus backbone created by the DOE that most do.
This sizing for the equipment does look about like what you'd expect from a very well insulated home though.