9K BTU EG4 mini-split to heat insulated "shed" in Maine?

[Madcodger]

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.

 

[JeffR]

I'm currently living in a 160ft² shed house in Montana with far less insulation than you're describing. Overnight temperatures are starting to drop. I have three 100Ah 48v EG4 batteries. The 9k doesn't use a lot of power. I wake up in the morning with 70% battery remaining so far here in mid-late September.

 

[SCmountainman]

My experience
320 sq ft tiny home/2.5” closed cell foam insulation running a 21 SEER Gree 12kbtu mini split heat pump. Winter temps down to 4F last winter. Indoor set point of 70F. During single digit weather the Gree pulls around 800 watts unless coming out of a defrost cycle. Throwing out 90F air even in single digit outdoor temps. When temps outside are more moderate 30F to 40F it pulls 500 watts+/-.
Cooling in summer with outdoor temps of 95F and indoor set point of 70F it only pulls around 250-350 watts.
Of course these wattage numbers are average, the VFD compressor will ramp up and down some but these are my real world measurements.
Propane is not fun in a tiny home. CO and CO2 levels go nuts. A 10kbtu propane heater will need almost 50 CFM of makeup/fresh air. Not including the fresh air YOU need as well. Plus it adds moisture to the living space. So propane was a no go for me. Still have the propane as backup though. Hope this helps. ?

 

[pvgirl]

A tool like pvwatts can show how much solar you can expect by month, so you can see how much average production you will get in the winter months. In addition to insulation, air sealing the building during construction will also help reduce demand for heat. Use a site like http://ashrae-meteo.info/v2.0/ to determine what the design temps are for your location, to confirm what type of weather you will need design for.

More then likely solar and a heat pump will meet much of your heating and cooling needs, what to do when the sun doesn't shine is problem. If this cabin is truly off grid a propane Direct-Vent Wall Furnace that doesn't require electricity would be a good choice, and direct vent eliminates the need for any makeup air and most worries about CO. If grid power is available this can run the heat pump until solar is available again, and if necessary a small electric resistance heater if extra heat is needed.

 

[Madcodger]

Thanks, all. Exactly the info I needed, @JeffR and @SCmountainman as it's real world experience. I have three mini-splits in three different buildings, each with an Emporia Vue monitoring it, but nothing as small as what I need in this little shed so your numbers give me something to use for planning.

Re : direct vent wall furnaces that don't require electricity, I can't find any that have efficiency better than about 65%. You can beat that without direct venting, but as noted I don't want the moisture or gasses. A Rinnai direct vent can do 82% efficiency, which i think is as good as it gets but costs the same as the heat pump. I suspect I may end up spending like a mad man and putting in the heat pump first, then a small, not-Rinnai direct vent propane heater to handle the really cold nights. Will report back......

 

[NEHP]

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.

I'm in Brewer Maine and I am heating a 12x24 building (2x4 construction, insulated) with a 9K Fujitsu no problem. I just this year added the EG4 Hybrid 12K heat pump and so far so good. I have 3 300w panels (recoment 4 400w) connected directly to the heat pump and the ac power is coming from my batteries.

 

[Madcodger]

Thanks, @NEHP - great info, and welcome to the forum.

I ended up putting in a small (8K BTU) Rinnai propane direct vent wall furnace as I really needed to get the building heated quickly and was concerned about having enough solar to use a heat pump from Nov- Feb. But I wired in a circuit and outside electric disconnect box for one as I finished the shed office, and plan to install one in April, primarily for air conditioning and shoulder season heating.

My 1260 watts of solar are set at about a 26 degree pitch (angle of shed roof) and also lose sun to trees in the afternoon. It's not a problem in the summer, but it's a big deal come November. So, I'll use the heat pump as much as I can, and then switch to propane as required.