Packaged unit heat pump replacement
I’m investigating the replacement of the 10 year old 3 ton (undersized!) Frigidaire packaged heat pump that came with our house with something newer, more efficient, with good reliability, and much quieter than the rated 74 dB we have now. Packaged units (I’ll use “PU”) seem to get zero to little attention by manufacturers as far as making newer, higher efficiency designs. At best I find variable speed blowers and 2 stage compressors that yield HSPF 8-8.5. We have 10 kW strip heaters for backup. The only power source we have is electricity.
We live in the Northwest where design temp is 17F. In my experience it is common to have cold winter nights in the mid-20’s, so strip heaters (or the wood fireplace insert!) come on routinely. Our house is a 3750 SF rambler roughly 40 ft wide x 80 ft long, and the PU is at the very end of the house along a 40 ft wall, just outside our bedroom. The duct work is in the crawl space and has been upgraded by me to all metal, insulated, with the main line running the 80 ft length of the house, with side branch runs as needed. There is one return air vent in the hallway 20 feet from the PU, so a short run. Measured static across the PU supply-return is 0.24, however 0.12 of that was separately measured across the new 4″ air filter, so duct system should be 0.12 as well.
Based on the existing Frigidaire spec and real world performance of seeing a 30F balance point, I’ve made a straight-line plot of our passive heat loss at any temperature: At 17F we lose 37,500 BTU, at 25F it’s 31,000 BTU, etc.
I’m looking at (so far) a Mits PVA-A36AA7 with PUZ-HA36NHA5 heat pump. This unit has a max capacity of 38 MBTU at 17F. The problem is that the air handler is intended to go indoors. I’m trying hard to avoid massive duct work re-routing and would like to consider installing the air handler outside. We have 4 foot eaves, so it would be well protected outside. I can build a “dog house” onto the house for further protection. The PVA comes with R4.2 insulation, but I could enhance that if needed to prevent condensation. Would need creative ductwork to adapt the existing side-by-side supply/return ducts (where PU interfaces) to the PVA-type flow.
Q1: Does anyone have other ideas about replacing a packaged unit with a more conventional (and common) heat pump design without getting crazy on cost?
Q2: Any issues with installing the indoor air handler in an outdoor dog house?
Q3: I can still consider a replacement PU but it would need to be 4 ton minimum due to the performance drop at low temps, and that would give me a BP of about 25F using Goodman and similar online specs. 5 ton only 22F so not much extra bang for the buck, plus air flow requirements go up.
I would appreciate your thoughts and suggestions. Thank you!
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