Mini split efficiency - heating vs cooling?

[Getyourbone]

Right or wrong, I’m used to thinking of mini splits as primarily cooling units

I find my self in an environment again where heating is far more important than cooling...living in a house that Is all electric heating and also does not have any air conditioning.

It would be nice to have air in the summer but main concern is winter... quickly warm up the house in the morning and when coming home in the evening less expensively than cranking up the baseboard.

The house is not off grid but would like to move it that direction at least partially.

So the question is...Do the highly efficient mini split systems heat just as effectively and effieciently as they do cooling? More efficiently/ less expensively than baseboard electric?

FYI, Rural Western Wisconsin so possible to have close to -40 f in winter and upwards of 100 f in the summer...

 

[gnubie]

They are a very efficient way to heat. I have a Fujitsu reverse cycle split in my bedroom. Cooling rating (not power consumption!) is 2.5kW, heating rating is 3.5kW. Any sort of heat pump based heating is going to be more efficient than a radiant heater as they are over unity, more heat (in watts) out than power in (in watts), while a radiant heater is watts in = watts out.

One thing to consider though, since it is a heat pump it relies on being able to pull heat from the outside unit. Very cold temperatures on the outside will hinder their operation. You should check with the manufacturer to see if there is any point in their model heat pump at -40.

 

[svetz]

Solar's doable for heating (and cooling), but you need batteries for night and those are expensive. Has anyone checked into alternative heat storage (e.g., liquid crystals, salts)?

 

[somewhereinusa]

I have two mini splits in my RV and, while they are very efficient at cooling, they don't produce much heat at anything below freezing. The colder it gets the more time they spend thawing the outside unit. I've seen units that advertise that they produce heat at lower temperatures but, there isn't much heat to be had at anything below 0° F.

 

[monty]

Heat pumps quickly go from a COP of 3+ to much less than 1 as the temperatures approach freezing and go way below as in -40... then it's most likely just emergency heat which is crazy and totally inefficient.

 

[mtt04]

I'm in Canada. I have tons of them in rentals and in my home.
I've converted from heating oil and use electric baseboard as backup which is CRITICAL!
You must have a backup heat source.

They are awesome until -25celsius.
The new ones go down to -30 celsius or better.

I install Senvilles as they are Dirt cheap and work great.
I've installed many and the senvilles are Fujitsu and Midea knockoffs

I've opened them up. Pretty much identical.

The newer generations of Fujitsu are apparently excellent. These mini splits are all made in One monster sized factory in china.
They pump out different models out of each door.

Highly recommended technology.

You need at least 23 SEER in winter climates
Heating Rating should be at least 10 hspf

 

[gnubie]

My recently released model Fujitsu works great but it has a behaviour that is annoying to me. When it is heating mode, be it full auto or specifically set to heat, it won't let me control the fan speed. The intention is that it's better to not have the fan running in the cold as that makes the apparent temperature lower.

When in heating mode it will fiddle around with the vent position and when it decides that it needs to push a lot of heat into the room it quickly run the fan up from almost nothing to a quite fast speed for a short time then drop it back down again. That constant change in noise (it's not noisy per se) and air direction actually disturbs my sleep. I'd rather be able to manually set the fan and vent for heat mode and have it not to be able to change that, which is how it works in cooling mode.

 

[mtt04]

My recently released model Fujitsu works great but it has a behaviour that is annoying to me. When it is heating mode, be it full auto or specifically set to heat, it won't let me control the fan speed. The intention is that it's better to not have the fan running in the cold as that makes the apparent temperature lower.

When in heating mode it will fiddle around with the vent position and when it decides that it needs to push a lot of heat into the room it quickly run the fan up from almost nothing to a quite fast speed for a short time then drop it back down again. That constant change in noise (it's not noisy per se) and air direction actually disturbs my sleep. I'd rather be able to manually set the fan and vent for heat mode and have it not to be able to change that, which is how it works in cooling mode.

That is not uncommon. Most of the fancy ones do this from what I've seen.

I noticed that in one of my old Fujitsu's. Auto never worked at all really. I was able to set the fan speed manually when not in Auto mode. It calved after 5 years and I replaced it with a Senville which has far better manual mode. You can adjust fan speed etc.
It also has Follow Me. It is like auto mode but I can change the fan speed slightly.

 

[mtt04]

Getourbone you asked about efficiency.

The 12K BTU ones i use use 1000 watts in heating or cooling
That will also heat 600 sq feet versus a baseboard.

 

[Supervstech]

Mostly, Heatpump’s are sized for the cooling load.
In a heat need area, with variable speed compressors, sizing for the heating load is ok... but can result in high moisture during the cooling season, so be cautious doing this.
Be aware with mini splits, the outdoor unit will need to defrost itself occasionally .
When it does, there will be a BLAST of very cold air.

 

[Supervstech]

I have two mini splits in my RV and, while they are very efficient at cooling, they don't produce much heat at anything below freezing. The colder it gets the more time they spend thawing the outside unit. I've seen units that advertise that they produce heat at lower temperatures but, there isn't much heat to be had at anything below 0° F.

How old are your minis? What brand? They should heat well down to -5 or so... more if sized large for the heat load.

keep this in mind.
The average cooling load for an rv is 18000btus, the average heating load is 60,000... or more in very cold areas of the country.
so a mini sized for cooling, at BEST can only put out 18K... and cold air limits that to around 12 or so K... when ya need 45 or more... as the room temp drops so does the vent temp output...

 

[somewhereinusa]

How old are your minis? What brand? They should heat well down to -5 or so... more if sized large for the heat load.

keep this in mind.
The average cooling load for an rv is 18000btus, the average heating load is 60,000... or more in very cold areas of the country.
so a mini sized for cooling, at BEST can only put out 18K... and cold air limits that to around 12 or so K... when ya need 45 or more... as the room temp drops so does the vent temp output...

Mine are 5 years old, I may have been quoting some old info. To tell you the truth I haven't really tried mine much below freezing, I just fire up the boiler and have nice toasty feet from the in floor radiant heat at that point.

 

[offgriddle]

For 23 people on Oith that are truly off grid, how many watts would they be required to generate to operate a heat pump sufficient to heat a 1,200 square foot, properly insulated cabin when the temperatures were in the range of frosty and freezing? https://www.energygroove.net/heat-pump-calculator/

 

[mtt04]

Those energy calculators are waste of time. Built by a bunch of engineers who couldn't screw in a lightbulb.
Take your space, Sqft, wall height, # of floors. Sqft on each floor.

I tried to use these calculators and imho they are pointless.
Here is true blue sizing I do.

These are senville Leto and Aura models.
These are all I use.

So other manufacturers may be slightly different. But I'm telling ya. I've cracked them open. All Japanese parts mostly assembled in China.
And I"m not arguing with anyone so don't bother.

I've got 17 of them now.
These are senville Leto and Aura models.
These are all I use. They are very high quality for the money.
Get a hvac guy to install if you wish or do it yourself.
Buy the vacumm on ebay and the wiring bits.
I''ve installed 17 myself with only 2 requiring a HVAC tech becuase I couldn;t get to -76 on teh gauge.
Techs use vacuum gauges to 500 microns is their preferred vacuum. No idea what that is ont eh ebay pump gauges.
Don't really care about that number as I vacumm them to the bottom of the r410a gauge and rarely have a problem

I top up a few with r410a every couple years as they sometimes loose some gas.

9000 Btu - 110V - 300sqft
9000 Btu - 220v - 350 sqft - They seem to run for efficiently with more fan power.
12000 BTU - 110v - 450sqft
12000 Btu - 220v - 600 sqft
18000 Btu - 220v - 800 sqft

Go to senville.com and look at the specs of each.
They range in cooling watts and heating watts.
The number is right there.
That spec is at full speed. They percolate at roughly 300-400 watts in standby.
In freezing temps they will run at full tilt mroe often. So use the spec for heating anf add 20% for good measure.
That will be your heating wattage.

BTW my house has 12 foot ceilings at 600sqft. I put in a 18000 BTU to fill the larger space. becuase a 12000 BTU heating in winter doesn;t produce the volume for that high a ceiling.

That s area and wall size matters
This is the KEY PART!
Never oversize thinking its better. Most of mine 12000BTU working full tilt. They are vastly more efficient working hard than an 18000 percolating. It'll also kill the unit faster. They hate to percolate.

I had one die in a year because I oversized.

If you think you need 13000 btus, consider the 12000 as its power usage is hugely less than an 18000
but factor in the heating BTU's.

18k's have far mroe heating capacity than a 12k

If i was going off grid I'd use a 110v 9000Btu and a 110v 12000Btu as required. They hardly use any power.
Their only issue is they only heat to -5 celsius (Leto series Senvilles)


cheers

 

[offgriddle]

Those energy calculators are waste of time. Built by a bunch of engineers who couldn't screw in a lightbulb.
Take your space, Sqft, wall height, # of floors. Sqft on each floor.

I tried to use these calculators and imho they are pointless.
Here is true blue sizing I do.

These are senville Leto and Aura models.
These are all I use.

So other manufacturers may be slightly different. But I'm telling ya. I've cracked them open. All Japanese parts mostly assembled in China.
And I"m not arguing with anyone so don't bother.

I've got 17 of them now.
These are senville Leto and Aura models.
These are all I use. They are very high quality for the money.
Get a hvac guy to install if you wish or do it yourself.
Buy the vacumm on ebay and the wiring bits.
I''ve installed 17 myself with only 2 requiring a HVAC tech becuase I couldn;t get to -76 on teh gauge.
Techs use vacuum gauges to 500 microns is their preferred vacuum. No idea what that is ont eh ebay pump gauges.
Don't really care about that number as I vacumm them to the bottom of the r410a gauge and rarely have a problem

I top up a few with r410a every couple years as they sometimes loose some gas.

9000 Btu - 110V - 300sqft
9000 Btu - 220v - 350 sqft - They seem to run for efficiently with more fan power.
12000 BTU - 110v - 450sqft
12000 Btu - 220v - 600 sqft
18000 Btu - 220v - 800 sqft

Go to senville.com and look at the specs of each.
They range in cooling watts and heating watts.
The number is right there.
That spec is at full speed. They percolate at roughly 300-400 watts in standby.
In freezing temps they will run at full tilt mroe often. So use the spec for heating anf add 20% for good measure.
That will be your heating wattage.

BTW my house has 12 foot ceilings at 600sqft. I put in a 18000 BTU to fill the larger space. becuase a 12000 BTU heating in winter doesn;t produce the volume for that high a ceiling.

That s area and wall size matters
This is the KEY PART!
Never oversize thinking its better. Most of mine 12000BTU working full tilt. They are vastly more efficient working hard than an 18000 percolating. It'll also kill the unit faster. They hate to percolate.

I had one die in a year because I oversized.

If you think you need 13000 btus, consider the 12000 as its power usage is hugely less than an 18000
but factor in the heating BTU's.

18k's have far mroe heating capacity than a 12k

If i was going off grid I'd use a 110v 9000Btu and a 110v 12000Btu as required. They hardly use any power.
Their only issue is they only heat to -5 celsius (Leto series Senvilles)


cheers

Really great information, well written too. Thank you for sharing your hard earned knowledge.

 

[Bob B]

I didn't work with Mini-split systems, but worked on the electronic control of HVAC systems ..... He is exactly right about oversizing. Oversize = "short cycling" of equipment = excessive equipment failures.

 

[Supervstech]

For 23 people on Oith that are truly off grid, how many watts would they be required to generate to operate a heat pump sufficient to heat a 1,200 square foot, properly insulated cabin when the temperatures were in the range of frosty and freezing? https://www.energygroove.net/heat-pump-calculator/

First thing you want to do is calculate your heating and cooling loads... https://www.loadcalc.net/

This will help if you are in he USA...

 

[offgriddle]

First thing you want to do is calculate your heating and cooling loads... https://www.loadcalc.net/

This will help if you are in he USA...

Thanks Superv for the tips and calculator, I book marked it for future use. Peace.

 

[mtt04]

Thats the best load calculator I''ve seen. Very accurate.
Good for those who need help in estimation.