Winter use of Mini Splits - Fujitsu - Crazy Idea

ColdHouse · January 30

So I have a three indoor head and one outside Fujitsu mini split system, that was primarily purchased to provide AC into our 100% radiant floor heated house. The system is seven or eight years old and struggles to provide any heat as the temps drop into the teens or below. It is -16*f at my home this morning as I type and I began thinking how nice it would be to have hyper heat Mitsubishis ”that work down to -22 ”from my understanding” to supplement some BTU’s on mornings like this or as a back-up heat source if the boiler went down. Here’s the crazy thought : What if I added a electric heater to the outside unit “if room allowed” and have it on a separate switch that I could turn on on days like this to get it to possible provide the extra BTU’s throughout my three head system. Has anyone done such or what are the thoughts on possibly doing so? My thought was a battery type heating pad or such in the 5-10KW range.

ethicalpaul · January 30

you’d just put an electric heater in your house, or three of them, one in each room with a head unit

ChrisJ · January 30

Heat pumps are generally cheaper to run than resistive electric heat simply because you're not making heat, you're relocating it. Even though it seems cold, there's still plenty of heat out there to bring inside.

Your idea doesn't make sense because why would you use energy to transfer heat you're creating in the first place using a heater from outside, to inside when you can just produce that heat inside to begin with?

GGross · January 30

Part of the shutdown is the air temp around the unit and how the defrost cycle works. At -16f, lets say you need to raise the air temperature all around the unit, including entering air, constantly, up to 0f to get a COP over 1, you are still using all that heat energy to raise the outdoor temp, and then using a little less again to get a little heat added to the house, meanwhile if you had just used the same KW of heat energy as resistance heating direct to the house you would still be ahead in terms of cost. And both of those options are almost certainly less cost effective than using the gas.

pecmsg · January 30

A heap pump will always have a 1:1 ratio kw to heat.

Resistance is 1:0

GGross · January 30

https://forum.heatinghelp.com/discussion/comment/1885264#Comment_1885264

This is not true. resistance is 1:1 1 KW heat energy out (3412 btu/hr) for every 1KW you use

Heat pumps currently can operate at over a 5:1 ratio, 5 KW of heat out, for every 1 kw energy in that is what the COP value is showing you, so a COP of 3 mean its operating at 3:1 300% efficient

ColdHouse · January 30

Ok, so a bad idea! LOL.

My concept was thinking raising the Freon temp was the issue and maybe a added heat inside the unit may help and then use the three head to distribute the heat throughout the house.

GGross · January 30

https://forum.heatinghelp.com/discussion/comment/1885270#Comment_1885270

Yes its a bad idea. But what you describe is sort of accurate, its just that you will use at a minimum double the fuel to accomplish the same thing your gas heating is already doing, and you will run the risk of hurting the outdoor unit. Remember space heaters (basically what you are describing using) are not free heat, and heat pumps are in essence sucking the heat from the environment around them, they work because the average air temp has enough latent heat energy that they can extract from it, think of the outside world as a massive heatsink your ODU uses. You would need a space heater to keep the entire area around your unit heated, and the heat pump would be constantly pulling that heat out, it would be a massive heater you would need, and cost an incredible amount of money.

pecmsg · January 30

A heap pump is always more effici8ent then straight electric. At negative temperatures the heat output drops to just above 1:1

ratio · January 30

It would, technically, but not all of the heat produced by the heat strips in the heat pump would be captured by the heat pump, some would escape to the outdoors. You would get less heat out than you would with the electric heat inside the house, which would put 100% of the heat towards heating the house.

ethicalpaul · January 30

At cold enough temperatures the heat loss of the lineset must start to become significant too

ColdHouse · January 31

thanks all for brining the concept into the proper perspective. I will not be adding a heater to my mini’s.

gpjazz · January 31

Yeah,, trying to warm up the outside air around the unit is not likely gonna work too well..

For reference, the sun has a hard time heating up the earth and surrounding air. So I don't think an electric heating pad is gonna cut it

Winter use of Mini Splits - Fujitsu - Crazy Idea

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