Need help finding an efficient heat pump (with “Hyper-heat”) for a small house
I’m an architect (learning a bit about things like the STRETCH Code and HERS) involved in designing a carriage house on Martha’s Vineyard. The town requires meeting a HERS index of 55. The project is pretty small with only 1,2oo square feet of conditioned space and two bedrooms.
Our initial thought was to use a Mitsubishi multi-zone mini-split system with Hyper heat. But we’ve found that the units with 4 or 5 zones are too big for our needs….only 18,000 BTU/hr at a design temperature of 10 degrees.
Then we thought about doing a single zone ducted system, but Mitsubshi says that their air handlers with Hyper-heat need a larger ODU. One compromise is a two zone 22K BTU/h system with an 18K BTU/h ducted air handler and a 6K BTU/hr wall unit…But using Mitsubishi, the unit would only have a SEER of 16 and HSPF of 9.65. Our original rating calcs assumed a SEER of 20 and a HSPF of 11….. we would like to get as close to that as possible.
Any suggestions would be appreciated. Another manufacturer? Work-arounds, whatever. Basically, we prefer not to oversize the 18K Btu/h heating, and need that at 10 degrees or less, and we’re agnostic regarding a single zone or five zones.
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