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Minisplit equivalent of 10kW resistive heater?

rhino

Solar Wizard
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Jun 6, 2020
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3,190
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Minnesota
I'm having trouble figuring out what would be the equivalent of a 10kW resistive electric heater when it is 0°F outdoor air temp in the form of a mini split and how many watts would it use while running?
 
10 kw will give you about 34000 btu's. You will need to do a little research to figure out which units will give you that output.
I would first get a heat load calculation done to see what is really required.
 
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Roughly that looks correct to me. That would give you a COP of 1.6. You loose efficiency and capacity as the outside air temperature drops.
 
Roughly that looks correct to me. That would give you a COP of 1.6. You loose efficiency and capacity as the outside air temperature drops.
Is there something on the market better then that for same scenario? I was expecting at least 2x savings before I'd consider it.
 
I don't know but doubt it. I'm sure there's something. The issue is what it would cost and the associated ROI.

Unless you live in an extreme north area/climate it won't pay back. This statement doesn't take into account if you're trying to run from batteries overnight or through lack of sunshine. If that is a consideration.
 
There are more efficient units than the DIY ones. A few sites to peruse options, and you can check out manufacturer websites such as GREE, Mitsubishi, etc. As others said, COP will go down as temperatures lower.


No affiliation, direct links.
 
Looking at an efficient Mitsubishi Mini Split MSZ-FS06NA & MUZ-FS06NA that lists a COP of 2.26 at -5F: https://www.ecomfort.com/manuals/940b1fb751fae0ba3df1b3f2d50c3734.pdf
It lists 10500 btus at 5f using a max of 1250Watts. So you would probably need 4 units to get you to the equivalent of 10kw heating element. It would use half at 5kw.
I switched my central A/C to these mini splits (I have 5 units) and they keep us warn/cool in NC.
 
I want to vouch for the Mitsubishi Mr Slim reliability. I installed 3 units in 2011 and they are still going, now on their 14th year.
 
If you are trying to heat multiple rooms, or even a single large space, it might also be useful to consider multiple heat pumps instead of a single unit with multiple indoor heads, or even a very large unit with a single head. Single head units tend to be more efficient, smaller heat pumps tend to be more efficient than larger ones, and it also creates redundancy.
 
I would look at how much per hour your strip heaters are running at your target outdoor temperature to get an idea of your heat load, to help size the mini-split. If your 10kW strip heaters only run for 30 minutes out of the hour than you may only need a 18kBTU. The price difference between 18kBTU and 24kBTUs may only be a couple hundred $$ so may be worth oversizing and being able to carry you to a lower outdoor temperature.

Make sure you look at the dimensions, the size of the indoor and outdoor units on the 18kBTU and larger units may surprise you if you're not already familiar.
 
You're in MN, you want to look for ones that are good down to subzero typically they'll have Hyper Heat in the name. Mistubishi, I personally have a Pioneer Hyperformance that's rated to -22ºF. It's going to do better at 0º than one rated down to 0º will do. My 18K BTU I see between 900-1,900watts depending on how cold it is outside. Below about 27º it's got a constant 300-400watt load to keep the compressor oil warm even if it's not "running" but on.
 
You're in MN, you want to look for ones that are good down to subzero typically they'll have Hyper Heat in the name. Mistubishi, I personally have a Pioneer Hyperformance that's rated to -22ºF. It's going to do better at 0º than one rated down to 0º will do. My 18K BTU I see between 900-1,900watts depending on how cold it is outside. Below about 27º it's got a constant 300-400watt load to keep the compressor oil warm even if it's not "running" but on.
That GREE one I mentioned above says it is rated to -31°F which I've never seen for any other one? https://www.greecomfort.com/our-products/vireo-plus-ultra/
 
Minnesooda eh? Do you have a large enough yard for geothermal? I have a home up there and have looked into this before, Air to Air heat pump heating not practical IMHO. Sticking to gas heating.
 
That GREE one I mentioned above says it is rated to -31°F which I've never seen for any other one? https://www.greecomfort.com/our-products/vireo-plus-ultra/
1738070600731.png

For R32 refrigerant, -31°F outside temp with about -10 °F required lower outside coil temp to absorb any significant heat from outside air would have outside evaporator coil saturation temp pressure for R32 of 17.4 psig.

Inside coil for 72 °F inside air temp requires about 15 °F higher inside condenser coil temp to yield much inside air heating. For R32, this is 87 °F inside condenser coil saturation temp. For R32 this has high side pressure of 269 psig.

For these inside to outside temp deltas, the required compressor compression ratio is (269-14.7 psia) / (17.4-14.7 psia) = 254 psia / 2.7 psia = compression ratio of 94.

I call BS!. No air conditioner compressor is going to survive very long at a compression ratio of 94, if it could achieve that compression ratio at all.

Not to mention, at that compression ratio there will be little refrigerant mass flow pumping, meaning very little actual BTU's will be generated.

Hyper-heat models run their compressor rpm's higher to achieve higher mass flow to maintain BTU yield, but their compression ratio is not much greater than about 10. Normal summertime cooling mode compression ratio is about 3.

Hyper-heat VFD drive inverter runs its output frequency up to 144 Hz which translates to compressor rpm's of up to 8,500 rpm's maximum versus non-hyper-heat models limit to about 75 Hz which translates to compressor rpm's of 4,500 rpm's maximum. The higher rpm's allows the compressor to maintain refrigerant mass flow pumping rate. Refrigerant mass flow rate translates to BTU's transferred.

You can tell hyper-heat models by their sound at cold outside temperatures. The high rpm compressor sounds like a jet engine.
 
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I run a Senville 18K Aura in the kitchen on days below 0°F and it worked just fine. But it does like energy at that temp as the fan speed and compressor speed are greatly increased. It is the Arctic compressor version.

Northern MN, I'd use a Senville Aura for the shoulder seasons and occasional warm day during winter. Any temp above 0°F will be efficient use of energy, after that it starts declining quickly. I only run during the day when ambient temps are low and usually at night only during shoulder seasons.

Instead of one large unit, consider a pair or more of units. You could get by with a pair of 18K units that are higher SEER2/HSPF2 rated than a single 30+K unit. This also allows for more even heating/cooling/zoning and ability to only use one unit if desired.
 

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