Mini Split Info

[Todd]

I went to a home show up in Duluth yesterday and setup an appointment to see about installing a 12,000 BTU Mitsubishi mini split. I’m off grid and have a on the small side 10kw solar system. On a good sunny day I have 1200 watts coming into my charge controller/ inverter. I’m researching how many watts these mini splits use and see anywhere from 600-1200 watts. I suppose it depends on a lot of factors but I’d like to know if I’m running this thing on a full sun day will I be able to run the A/C mode full blast and still have a little left over to charge my batteries or will it just be a steady drain? Any info on personal experience or wattage drain would be helpful. Thanks

 

[Whitenuckler]

Any good heat pump will be 240V (or usa voltage) with a compressor. I would not run it on anything but utility as you could damage the heat pump and your inverter. Get a cheap small 120V window unitto get by but you will be shocked at how much even those use for power and huge startup surge

 

[Todd]

Any good heat pump will be 240V (or usa voltage) with a compressor. I would not run it on anything but utility as you could damage the heat pump and your inverter. Get a cheap small 120V window unitto get by but you will be shocked at how much even those use for power and huge startup surge

I have a portable 10,000 BTU a/c unit I’ve been using for the past few years and yes it draws a good 1500 watts on high. My system can run that for a good 6 hours or a little more if I want to drain my batteries down below 50% but I usually will just switch it over to a generator at that time and let the batteries recharge.

I have two ea 24v 200ah 5000w lithium batteries in parallel from Signature Solar. They actually sell a mini split for cheap so I think they should be safe for solar systems. Also heard and seen others doing this on their systems so not sure it would damage mine? Im also looking at the 110v verses the 220v that I don’t have.

 

[Whitenuckler]

I have a portable 10,000 BTU a/c unit I’ve been using for the past few years and yes it draws a good 1500 watts on high. My system can run that for a good 6 hours or a little more if I want to drain my batteries down below 50% but I usually will just switch it over to a generator at that time and let the batteries recharge.

I have two ea 24v 200ah 5000w lithium batteries in parallel from Signature Solar. They actually sell a mini split for cheap so I think they should be safe for solar systems. Also heard and seen others doing this on their systems so not sure it would damage mine? Im also looking at the 110v verses the 220v that I don’t have.

I like that idea. If you can get a system proven to work and has the backing and approval of the same supplier. Just be sure you get them to install it. I would also ask if the line set will be cut to length. Some systems are selling fixed length line sets pre-charged.

 

[EbS-P]

I would be looking at a hybrid AC/DC mini split. Somewhere, but I can’t find it now you could set the max AC current draw. Not sure if that’s helpful. Basically you need a cool on excess solar function. Tesla has this for their new cars. It will match charging rate up to the 32/40 amp maximum to minimize what you send to the grid. Or just waist in your case.

EG4® 12K Hybrid Solar Powered Mini-Split 12000 BTU AC/DC

EG4® 12K Hybrid Solar Powered Mini-Split: Eco-friendly, ENERGY STAR certified AC/heat pump with hassle-free installation & solar integration.

eg4electronics.com

States max 1100w

 

[DBoon]

Hi Todd,

If you dropped down to 9000 BTU their might be some manufacturers who offer size unit with 115V input, and then you could be a little more assured that it wouldn't draw more than 1800 watts, worst case. Getting any unit that never draws more than 1200 watts is probably impossible (unless there is something that is intelligently tied to your solar PV inverter or charge controller to only use excess solar PV production). The idea to get one that runs off solar PV DC is a great idea (if something like that exists for heat and not just AC).

BUT if you can locate an installation manual for the unit you are looking at, there should be a table that specifies maximum output BTUs and maximum input power for a given indoor temperature and outdoor temperature. My 15,000 BTU Fujitsu low-temp heating unit with an outdoor (dry bulb) temperature of 32 degrees F and an indoor temperature of 70 degrees F would consume 2.73 kW to output 20,700 BTUs. At -15 degrees F and 70 degrees F indoor, it would consume 2.32 kW and output 15,000 BTUs (yes - less input power, but a lot less BTUs also). At warmer outdoor temperatures, input power slipped to 2.02 kW.

That's one manufacturer and one size rating, but you can see how this works.

What isn't clear from these ratings is what would happen once the indoor room temperature was established and the call for heat was a lot less than the max BTU output of the unit. Of course, what we know is that it would modulate down, probably by a lot, and you would see only 20-40% of those max input power ratings (and less output BTUs as well).

 

[Todd]

I may be able to get away with a 9000 btu unit but I’m trying to heat and cool approx 600 sq ft and that the max rating for a 12,000 btu unit.

I watch an off grid guy on YouTube and he installed a 12,000 btu Mr Cool on his solar system and said cooling it uses 700 watts full bore and 600 watts heating.

These things cycle on and off correct? Or do they continue to run and just adjust the wattage up and down? I guess I’m not really sure how they operate.

 

[Whitenuckler]

Do you have any places you can insulate better? That is one way to beat the cold and heat and use less kW.
Attics, walls, floors, windows, doors ect.

 

[Todd]

Do you have any places you can insulate better? That is one way to beat the cold and heat and use less kW.
Attics, walls, floors, windows, doors ect.

It’s a log cabin, I chase leaks every winter with caulk gun lol. My wood stove has no problem heating the place I just like the idea of a supplemental mini split for take the chill off heat and occasional cooling. Even if the mini split sucks too much juice I still have a generator to help charge the batteries as needed. Many times i switch back and forth powering the portable ac with the solar and generator. I’d like to get away from the genny as much as I can.

 

[EbS-P]

It’s a log cabin, I chase leaks every winter with caulk gun lol. My wood stove has no problem heating the place I just like the idea of a supplemental mini split for take the chill off heat and occasional cooling. Even if the mini split sucks too much juice I still have a generator to help charge the batteries as needed. Many times i switch back and forth powering the portable ac with the solar and generator. I’d like to get away from the genny as much as I can.

Adding two or three panels paired to the mini split (or not I guess) then running the hybrid option to the inverter probably covers most of the extra demand

 

[Whitenuckler]

It’s a log cabin, I chase leaks every winter with caulk gun lol. My wood stove has no problem heating the place I just like the idea of a supplemental mini split for take the chill off heat and occasional cooling. Even if the mini split sucks too much juice I still have a generator to help charge the batteries as needed. Many times i switch back and forth powering the portable ac with the solar and generator. I’d like to get away from the genny as much as I can.

Sounds nice. Was there an option for hook-up or none around? For sure you should focus on cooling. You could look at one of those buried coil heat pump systems. A nice pellet stove would add that heat part no problem. It's like a furnace.

 

[DBoon]

I may be able to get away with a 9000 btu unit but I’m trying to heat and cool approx 600 sq ft and that the max rating for a 12,000 btu unit.

600 square feet with a 9000 btu demand is 15 btu/ft2 - which is what a really well insulated house might be, but you don't have that. Having said that, the ratings can be deceiving. The BTU rating is usually for the cold temperature rating and it can put out a lot more BTUs at higher temperatures. You really need to get the detailed charts from the installation manual, like I did with my Fujitsu (see image) which puts out 30% more heat at 32 degrees than it does at -15 degrees F.

These things cycle on and off correct? Or do they continue to run and just adjust the wattage up and down? I guess I’m not really sure how they operate.

Ideally, they never go completely off, they just keep turning down and "modulating" their output. Some cold-climate units provide rated heat down to really cold temperatures (like mine) and modulate over a wider range (e.g., 10-100% instead of 30-100%). They all use variable speed motor drives to slow the motor down, so as they modulate down in heat output (and power input), they get disproportionately efficient, so running at 50% speed/output will use less than half the max input power (maybe only a quarter of the max input power) compared to when running at 100%. So the max input power is real - it could happen - but you are probably never running at that provided the unit is running all the time OR when you turn it on the house is already warmed up and now it just has to keep the house warm. That's probably why your friend measures 700 watts on his Mr. Cool unit all the time - it's not really running at 100% so its not drawing anywhere near 100% rated input power.

 

[Todd]

Sounds nice. Was there an option for hook-up or none around? For sure you should focus on cooling. You could look at one of those buried coil heat pump systems. A nice pellet stove would add that heat part no problem. It's like a furnace.

It would have cost $30k to run electric in here. Solar was around $10k.

 

[Todd]

Adding two or three panels paired to the mini split (or not I guess) then running the hybrid option to the inverter probably covers most of the extra demand

I was hoping I could get away with the panels I have but yeah there is a system I’m looking at that runs straight from panels on dc and automatically converts over to ac when needed.

 

[Whitenuckler]

It would have cost $30k to run electric in here. Solar was around $10k.

Geo Thermal systems are not cheap either. I saw a news article that said in the future there will be solar systems and cars that are compatible so you can use your car battery as storage. With the advances they are making in battery technology I can see that coming fast.
Having only 120VAC is probably a limitation as well, but in the end in comes down to panels, sun and batteries to produce kwh of energy.

 

[Todd]

600 square feet with a 9000 btu demand is 15 btu/ft2 - which is what a really well insulated house might be, but you don't have that. Having said that, the ratings can be deceiving. The BTU rating is usually for the cold temperature rating and it can put out a lot more BTUs at higher temperatures. You really need to get the detailed charts from the installation manual, like I did with my Fujitsu (see image) which puts out 30% more heat at 32 degrees than it does at -15 degrees F.


Ideally, they never go completely off, they just keep turning down and "modulating" their output. Some cold-climate units provide rated heat down to really cold temperatures (like mine) and modulate over a wider range (e.g., 10-100% instead of 30-100%). They all use variable speed motor drives to slow the motor down, so as they modulate down in heat output (and power input), they get disproportionately efficient, so running at 50% speed/output will use less than half the max input power (maybe only a quarter of the max input power) compared to when running at 100%. So the max input power is real - it could happen - but you are probably never running at that provided the unit is running all the time OR when you turn it on the house is already warmed up and now it just has to keep the house warm. That's probably why your friend measures 700 watts on his Mr. Cool unit all the time - it's not really running at 100% so its not drawing anywhere near 100% rated input power.

Yeah the guy I talked to at the home show said the Mitsubishi could deliver heat all the way down to -25 outdoor temps but I’d have my wood stove going on those days. Also really not enough sun that time of year to take advantage of that.

So it sounds like turning on the unit on a couple hours ahead of when you think your going to need it will keep the wattage down.

 

[DBoon]

The best thing is to probably never turn it off, but if that is not possible (e.g., you only want to run it when the sun is shining), then when you first turn it on you simply have the thermostat set a little low (at current house temperature, perhaps), and gradually raise the thermostat over the course of a couple of hours. If you had a power monitoring system installed in your circuit board panel (e.g., something like Sense) then you could see what the wattage draw is for the breaker that feeds your minisplit and act appropriately with the thermostat. Also, most of these mini-splits have a short-term "Powerful" mode to provide a burst of extra heat for maybe a half hour or so, and the max input power ratings might also be based on that mode.

I think you definitely want to consider three things when you look at what mini-split you would install:

1. What the modulating range is - getting something that can operate over a wide range (e.g., 10 or 20 % on lowest setting vs. 30 or 40% on lowest setting) is better so that you unit operates more in "low and slow and efficient" mode. The cheapest units usually have a narrower modulating range.
2. Not chasing low-temperature performance as much. Extra low-temperature units will provide heat and/or more heat at very low temperatures (-17 degrees F, -25 degrees F, etc.) but their efficiencies are not as high when temperatures are warmer (which is most of the heating season). They also cost more. What you really want is best efficiency in the temperature ranges you think you'll be using it in. I think I remember that you have two woodstoves in your house, so you don't need the minisplit to help out when it is really cold.
3. Maybe going one size higher (15 kBTU) IF the modulating range goes pretty low (down to 10%, let's say). The max input power requirements are probably not that much more and the cost difference might be minimal, but the unit will be operating low and slow more often and therefore in a highly efficient mode more often while still meeting your heat requirements. Essentially, it will use less electricity (probably) for a 15 kBTU to deliver 12 kBTUs to your house than a 12 kBTU unit to deliver 12 kBTUs to your house. Again, this all depends on the particular manufacturer and their particular model - you need to get the detailed performance curves like I attached earlier for my unit.

BTW, been meaning to tell you that the rebuild of the Woodstock stove really came out nice - very nice work!

 

[Todd]

The best thing is to probably never turn it off, but if that is not possible (e.g., you only want to run it when the sun is shining), then when you first turn it on you simply have the thermostat set a little low (at current house temperature, perhaps), and gradually raise the thermostat over the course of a couple of hours. If you had a power monitoring system installed in your circuit board panel (e.g., something like Sense) then you could see what the wattage draw is for the breaker that feeds your minisplit and act appropriately with the thermostat. Also, most of these mini-splits have a short-term "Powerful" mode to provide a burst of extra heat for maybe a half hour or so, and the max input power ratings might also be based on that mode.

I think you definitely want to consider three things when you look at what mini-split you would install:

1. What the modulating range is - getting something that can operate over a wide range (e.g., 10 or 20 % on lowest setting vs. 30 or 40% on lowest setting) is better so that you unit operates more in "low and slow and efficient" mode. The cheapest units usually have a narrower modulating range.
2. Not chasing low-temperature performance as much. Extra low-temperature units will provide heat and/or more heat at very low temperatures (-17 degrees F, -25 degrees F, etc.) but their efficiencies are not as high when temperatures are warmer (which is most of the heating season). They also cost more. What you really want is best efficiency in the temperature ranges you think you'll be using it in. I think I remember that you have two woodstoves in your house, so you don't need the minisplit to help out when it is really cold.
3. Maybe going one size higher (15 kBTU) IF the modulating range goes pretty low (down to 10%, let's say). The max input power requirements are probably not that much more and the cost difference might be minimal, but the unit will be operating low and slow more often and therefore in a highly efficient mode more often while still meeting your heat requirements. Essentially, it will use less electricity (probably) for a 15 kBTU to deliver 12 kBTUs to your house than a 12 kBTU unit to deliver 12 kBTUs to your house. Again, this all depends on the particular manufacturer and their particular model - you need to get the detailed performance curves like I attached earlier for my unit.

BTW, been meaning to tell you that the rebuild of the Woodstock stove really came out nice - very nice work!

Good info thanks. I will ask the dealer about the low and slow ranges.

Just one wood stove (Fireview) in my cabin but I also have a Jotul 602 in my small workshop and a sauna stove in my bath house.

 

[EbS-P]

I was hoping I could get away with the panels I have but yeah there is a system I’m looking at that runs straight from panels on dc and automatically converts over to ac when needed.

My issue is if you have solar just add more panels and get a cheap 120v AV 12k btu unit. Otherwise those extra panels will probably not be utilized 50% of the time. (Just a guess). But adding more panels to my system is not a diy job. (I’m not opening my powerwall)

So…. What you you get is you added another 2k in batteries??

 

[Todd]

My issue is if you have solar just add more panels and get a cheap 120v AV 12k btu unit. Otherwise those extra panels will probably not be utilized 50% of the time. (Just a guess). But adding more panels to my system is not a diy job. (I’m not opening my powerwall)

So…. What you you get is you added another 2k in batteries??

Eventually I will add more panels but I will have to hire that out since they are all on a steep metal roof. Also thinking of adding an additional battery or two. Not sure if I can justify the extra cost right now just to run a mini split occasionally.

 

[Highbeam]

These things definitely cycle. They just don’t mix the air well enough not to so when they hit setpoint and the fan idles down , the air in the room stratifies and triggers another cycle. This is especially apparent in heating mode and if your desired setpoint is much higher than room temperature. Puff puff puff.

In cooling mode I notice much less cycling and a more constant level of noise and wattage draw. I wonder if the standard mounting height of standard indoor heads is the reason.

These things sip power. Unless you are at the design limits I think you will be amazed at the low draw. Both surge and constant.

Don’t be afraid of 120 volt units. Your solar system may even make better power than the utility. I do not regret saving many thousand dollars by self installing a mrcool. Super easy and the thing has worked perfectly over the years.

On edit... These things do all kinds of weird stuff. Modulating, cycling, sampling outside temps, coil temps, inside, temps, pressure temps etc. The inside unit blower will go up and down to near nothing, sometimes stop completely, the outside unit has a compressor and fan that are independent and will run or not and at different speeds seemingly independent of the inside fan. Like an automatic transmission, there is magic inside and I find it best to just let it work.

 

[Whitenuckler]

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

This guy seems to have something going

 

[Todd]

Local heating and cooling guys want $8-9k to install one 12,000 btu Mitsubishi 25 seer mini split! No way can I justify that for supplemental heating and cooling!

 

[Pinesmoke]

Todd check out
www.hvacdirect.com

These guys are local to me and are the real deal and they sell to the public. I think rusty bought from them last year. Hardware is waaaay under that quote you got.

Just a fast look a 22 sear DIY kit is under 2k.

Might be an option.

 

[Whitenuckler]

Local heating and cooling guys want $8-9k to install one 12,000 btu Mitsubishi 25 seer mini split! No way can I justify that for supplemental heating and cooling!

Good time to price out the cheapest option