I am getting ready to set up an office in a 10'x16' (160 SF) "shed" building, and am trying to decide whether I should attempt to (primarily) heat it with an EG4 9K BTU mini-split, in midcoast Maine (zone 6). Thoughts and ideas welcome. Here are the relevant details:
Building will have 3" closed cell spray foam in ceiling (including gable ends) and under floor, so about R20 there. Ceiling will then get another 6" of mineral wool, taking that to R40 - about the most I can pack in. Walls will be 2x6 with mineral wool insulation, so about R21. Fiberglass "builder grade" 9-lite door typical of most home's "back" doors. Two 30x48" "builder grade", double hung windows (u-factor about .26 as I recall, so about R3.8).
Mini-split has Seer2 of 29.5, HSPF2 of 10.7. This equates to 13.38 BTU per watt. My semi-educated guess is that for 50-70% of winter I can get by with the building needing only about 3,000 BTU/hour. so just over 5,200 watts per day.
Batteries are three 24V, 100ah LiFePO4 in parallel, so about 7, 500 available watts per day, max. 1260 watts of PV feeding Victron MPPT SCC and 3000 KVA Mulitplus inverter. 120 V only (no 240V available). Inverter can automatically connect AC ("shore power") as needed, and all other loads max out at about 150 watts, with winter daily draw around 800-1200 watts total (includes inverter), other than the mini-split.
If my guess is correct, my usage will be about 6400 watts/day, so the AC will be kicking in often (every day). And, I can install an inexpensive direct vent propane heater for backup heat when needed.
I'm leaning toward doing this IF MY GUESSTIMATE OF ABOUT 5,200 WATTS/DAY SEEMS REASONABLE for much of winter, but thought I'd get everyone's thoughts. The alternative is to install a better propane heater (Rinnai) snd a small window AC for cooling, at a modestly lower capital cost but that will require more propane. Summer will provide ample sun for powering cooling no matter what I choose.
Building will have 3" closed cell spray foam in ceiling (including gable ends) and under floor, so about R20 there. Ceiling will then get another 6" of mineral wool, taking that to R40 - about the most I can pack in. Walls will be 2x6 with mineral wool insulation, so about R21. Fiberglass "builder grade" 9-lite door typical of most home's "back" doors. Two 30x48" "builder grade", double hung windows (u-factor about .26 as I recall, so about R3.8).
Mini-split has Seer2 of 29.5, HSPF2 of 10.7. This equates to 13.38 BTU per watt. My semi-educated guess is that for 50-70% of winter I can get by with the building needing only about 3,000 BTU/hour. so just over 5,200 watts per day.
Batteries are three 24V, 100ah LiFePO4 in parallel, so about 7, 500 available watts per day, max. 1260 watts of PV feeding Victron MPPT SCC and 3000 KVA Mulitplus inverter. 120 V only (no 240V available). Inverter can automatically connect AC ("shore power") as needed, and all other loads max out at about 150 watts, with winter daily draw around 800-1200 watts total (includes inverter), other than the mini-split.
If my guess is correct, my usage will be about 6400 watts/day, so the AC will be kicking in often (every day). And, I can install an inexpensive direct vent propane heater for backup heat when needed.
I'm leaning toward doing this IF MY GUESSTIMATE OF ABOUT 5,200 WATTS/DAY SEEMS REASONABLE for much of winter, but thought I'd get everyone's thoughts. The alternative is to install a better propane heater (Rinnai) snd a small window AC for cooling, at a modestly lower capital cost but that will require more propane. Summer will provide ample sun for powering cooling no matter what I choose.