Choosing an HVAC System
Hey y’all, looking to crowdsource some opinions on HVAC for my renovation. Just got Manual J load calcs done by Energy Vanguard, but had them hold off on equipment selection / duct design because I have a few options that I want to consider — but now I can’t make up my mind!
The house is 2-story with full basement, and I’m doing extensive work on the first and second floors; the basement sucks but fixing it is a later phase of this project (read: probably a couple years down the road). 2nd floor has 2 bedrooms, laundry room, bathroom, and an open hallway / study / staircase area — heating load 10k BTU/h, cooling load 5k BTU/h; interior completely gutted. 1st floor has 2 bedrooms, bathroom, and an open-ish living / dining / kitchen/ traffic circulation area, also open to the 2nd floor staircase — heating load 16k BTU/h, cooling load 10k BTU/h. Basement adds another 10k BTU/h heating load and no cooling load.
Plan 1: My initial idea was a ducted mini-split serving the second floor; based on these calcs it could be probably be the smallest (9k) Fujitsu Halcyon unit. A second ducted unit located in the basement could serve the basement and first floor — though I’m not sure of the implcations of either (a) sizing it for the full current load, but then insulating the basement later, or (b) undersizing it and just letting the basement be cold.
Plan 2: The 1st floor bedrooms, bathroom, and hallway sum to ~3.5k BTU/h heating load. The remainder of the first floor would then be close to 12k BTU/h heating load. That tempts me to (a) make the 2nd floor ducted unit a Fujitsu 12k unit and also serve the two first floor bedrooms (BUT the ductwork would be quite challenging if even possible) and (b) use a 12k ductless unit for the remainder of the first floor, centrally located in the basically open area. The basement gets neglected in this plan, and the ductwork for the 1st floor bedrooms might not be possible, but it is semi-tempting.
Plan 3: The wildcard here is that I have a 2.5-ton-ish water-source heat pump unit in my garage. It’s a Climatemaster Tranquility single-stage unit that I got new but super cheap at a surplus place — BUT it’s a commercial 480V 3-phase unit that I got running with a transformer and a VFD from the same industrial surplus place 😉 (the VFD *might* let me fake multi-stage or continuously variable capacity — but I’m not sure if its specific compressor would be OK with that). Anyway, unlike most geothermal installs, I already have the unit and would DIY most of it, but I’d still need to have the outdoor part installed — due to not wanting to kill all my trees, I’d either need to go vertical wells or directional boring.
So, I have three (or more?) potential plans, all of which will cost several thousand dollars (either buying air source heat pumps, or paying for the ground-source wells / directional boring install), and all of which are complex in varying ways. I think my original plan has overall the most straightforward ducting, but plan 2 is tantalizingly elegant. Plan 3 mostly justifies my impulse buy of a commercial surplus heat pump 😉
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