Wintertime Minisplit use article

[Brian26]

https://www.centralmaine.com/2018/10/28/hot-and-cold-on-heat-pumps-in-maine/

Interesting article I will look forward to the study conclusions. I am somewhere in between and my normal choice of fuel is electric or wood with oil as backup if all else fails. I just have one minisplit on my main floor and need to heat my office in the second floor by convection up a stairwell. I find it works well down to about 30 F but unless the sun is out the heat coming up the stairs just doesn't offset the heat loss. Its not a great setup but hard to justify switching my older office cooling only mini split until it dies. I also run the minisplit off of banked "free" solar power so I don't want to burn my surplus up to early in the season.

I do agree that the way to go in cold conditions with a mini split is set it and forget it. Its definitely takes several hours to warm up a cold house when I am out of town on business for few days. My normal approach is heat up the wood boiler storage before I head out and set back the thermostats to 60 F and then set the minisplit to 64F. That will carry the house for several days unless its really cold (below zero). When I get home I crank up the boiler to reheat the house as the minisplit may take 12 plus hours.

The other issue is if its damp or snowing in cold conditions the coils frost up quicker and that means more defrost cycles which are noisy. Mine is situated on the downwind side of the house well off the ground with roof over it to deflect snow but it its blowing snow it can get frosted up.

I did a recent posting that a family friend that does vented kerosene heaters is getting a lot of calls from folks with minisplits to get their old Monitors repaired or new ones installed for cold weather heating. A minisplit just doesn't put out very warm air in cold conditions and along with the fan running full bore it can get drafty. A Monitor puts out a lot warmer air and can put out more of it when needed.

Not sure if you saw this article with the linked evaulation. Its a good read about mini splits in Mass and Rhode Island.


https://blog.greenenergyconsumers.org/blog/we-need-a-plan-for-ductless-mini-split-heat-pumps

Given that our organization works in both Massachusetts and Rhode Island, we were anxious to read a major evaluation study conducted for utilities in those states by the Cadmus Group. The study cost several hundred thousand dollars, took over two years, and analyzed data from over 150 homes. Here is a summary of some of the findings highlighted in the report

Interesting section from the study.

The figure also shows a temperature balance point about 32°F for an oil‐fired system in 2016 and 12°F
in 2015. Both winters indicate a propane balance point of ‐15°F, meaning a DMSHP would always be less
expensive than the propane option.
Figure ES‐7 shows the same analysis, but addresses units listed as cold climate. These units operate
somewhat more efficiently, and the economic balance points shift to colder temperatures, where gas
balance points were at or above 58°F for both winters. Oil‐fired systems’ balance points were 26°F for
2016 and 8°F for 2015. These values do not account for zonal savings. For example, if a homeowner
could use a DMSHP to heat 30% less of their home, that temperature balance point would drop by 20°F
or more.

 

[georgepds]

Good points,but do any of them address the fact that I'd freeze my but off if I relied on the mini split in the dead of winter

They work fine in the shoulder season , but will only keep my house in the 60s this time of year.( northeast ma)

Yes, I know, my installer probably did not do a proper manual j calculation. That said, two fujitsu rls 2 12 kbtu/hr units should do better in a 1500 ft^2 house

Lord help the people who believe these studies and don't have adequate (I'm talking wood stove here)backup

 

[georgepds]

Ok... you do warn people

"Consumers need education on how to operate a mini-split. At very cold temperatures, if oil prices are low, a consumer is better off running the central heating system. But most of the time, the mini-split would be preferred."

But this is misleading

"If your house is zoned appropriately and you have 800 or so square feet that a heat pump can serve, you can shut off the central system to that area and save on fuel"

You can save during the shoulder season, when it's not so cold

 

[georgepds]

Re"While some of the group’s members sell and install heat pumps, the association considers them to be best used as air conditioners in summer and heaters in spring and fall. In winter, it says, nothing beats a central heating system."

Can I hear an amen?

https://www.centralmaine.com/2018/10/28/hot-and-cold-on-heat-pumps-in-maine/

 

[maple1]

Good points,but do any of them address the fact that I'd freeze my but off if I relied on the mini split in the dead of winter

They work fine in the shoulder season , but will only keep my house in the 60s this time of year.( northeast ma)

Yes, I know, my installer probably did not do a proper manual j calculation. That said, two fujitsu rls 2 12 kbtu/hr units should do better in a 1500 ft^2 house

Lord help the people who believe these studies and don't have adequate (I'm talking wood stove here)backup

How cold is it outside there this time of year? Likely colder than here.

We have two 12ks, in a 2700 sq.ft. two story. They don't cover the whole house, there is one end of the downstairs that will chill off without burning some wood. Far end of the kitchen. That has lots of windows. But so far this winter I'd say they could carry 3/4 of the load. It hasn't quite hit -20c yet, but we've had a bit between -15 & -20, and quite a bit between -5 & -15. I am sure if we put another unit in that problem spot, we could get through the winter totally on the splits, at less operating cost than anything else except wood. As long as the power didn't go out.

(I would still have a wood burner though for some supplementing when I felt like it, or 'just in case').

 

[rowan_cb]

We had 2 Mistubishi MSZ-GL's installed on Wednesday. An 18,000 btu unit downstairs, and a 12,000 btu upstairs.

House is just under 2,000 sq. ft., and the downstairs, around ~1,300 sq. ft., is fairly open (kitchen and living room (where the heat pump is) are fully opened up, and a straight shot, and the dining room opens off this space with a much wider than average opening.

So far it's been a lot of trial and error with fan speed and vent angle to see what works, but I think we're figuring it out. I've found the temperature needs to be set quite high (around 75) on the downstairs unit to keep the temperatures we're looking for, but the literature I've read from both Efficiency Maine and Efficiency Vermont (where I live) suggests this is not abnormal, and it's kept the main living area quite comfortable, even during the peak of Vermont winter.

I was very concerned at first that, even with the heat pump at 75, the oil furnace was kicking on with the thermostat (which is on a dining room wall just inside the opening off the living room/kitchen space) set to 65. Despite the wide opening into the dining room, it seemed that the warm air from the heat pump was not getting there at all. While we spend most of our time in the kitchen/living room, the current location of the thermostat in the dining room made this problematic!

However, this was on the first night we had the units, and the temperature was right on the borderline of where (given the advice of peakbagger and maple1 in this thread) I will consider shutting the units off (got down to around 15 F). Last night, it was warmer (upper 20's) and I turned the fan up and angled the vents a little differently, and it maintained the dining room at between 64-66, meaning the oil furnace (set at 60) did not kick on at all, which I'm happy about.

The upstairs unit has kept our bedroom, which was previously pretty frigid (oil furnace is forced hot air, and the only way the heat came upstairs, was literally by coming upstairs), very comfortable, and has done a fine job heating the hallway as well when we've left our door open.

Of course, now I will have to monitor my electricity bill and make sure it is actually saving us money to run these things and keep the furnace from kicking on. In the long run, the answer should definitely be yes, as we've has a 7.98 Kwh PV system installed, but this winter may be a little rough, because the solar wasn't up and running until the beginning of December, and our PV generation has obviously been pretty dismal so far.

 

[maple1]

I turn the fan speed up on ours during periods where the room they are in aren't occupied. Which means nights for downstairs unit & days for upstairs unit. It really does send the heat out further.

BTW don't take my word for anything, we haven't had ours for 2 months yet, quite - so still learning.

 

[Connecticut Yankee]

These mini-splits you are all talking about---are they geothermal heat pumps? I'm really out of touch with this stuff, forgive my ignorance. My impression was that in New England and points north, the climate required a geothermal installation.

 

[maple1]

These mini-splits you are all talking about---are they geothermal heat pumps? I'm really out of touch with this stuff, forgive my ignorance. My impression was that in New England and points north, the climate required a geothermal installation.

No. They are air to air heat pumps. Google them up, all kinds of info on them.

 

[Connecticut Yankee]

Thanks, Maple, will do.

 

[Brian26]

I think the best use of mini splits are for those with solar panels. Essentially free heat at 380% efficiency with the use of no fossil fuels. Yeah they don't stand up to the quick fast heat of a wood stove or oil furnace but their efficiency blows away any other form of heating. You simply keep your main furnace/boiler in place and only use it for those very cold nights if your unit can't keep up. Not hard to figure out when to switch by just monitoring your system and temperatures.

Here on the CT shoreline where we don't really get crazy cold temperatures they can work as a full time heating source. My neighbor who has the exact same house was using baseboard electric and reports the electrical savings is mind blowing in comparison to his old baseboards. He said its hundreds of dollars a month. CT has the most expensive electricity in the lower 48 and he will save thousands of dollars in just a few years. He still has his electric baseboards as backup but has never needed to turn them on yet in 2 years.

 

[georgepds]

I think the best use of mini splits are for those with solar panels. Essentially free heat at 380% efficiency with the use of no fossil fuels. Yeah they don't stand up to the quick fast heat of a wood stove or oil furnace but their efficiency blows away any other form of heating. You simply keep your main furnace/boiler in place and only use it for those very cold nights if your unit can't keep up. Not hard to figure out when to switch by just monitoring your system and temperatures.

Here on the CT shoreline where we don't really get crazy cold temperatures they can work as a full time heating source. My neighbor who has the exact same house was using baseboard electric and reports the electrical savings is mind blowing in comparison to his old baseboards. He said its hundreds of dollars a month. CT has the most expensive electricity in the lower 48 and he will save thousands of dollars in just a few years. He still has his electric baseboards as backup but has never needed to turn them on yet in 2 years.

That's what I do.. solar + heat pump

Basic problem is I sized the units using the rule 12kbtu/hr for every 600 ft^2. Should have used bigger for the dead of winter. A proper manual J calc would show that

They work, but set at 72, they deliver 66, less if I'm away

At the time I was concerned about oversized AC, the bang bang compressor problem. Turns out modern high efficiency heat pumps do not have that problem, they use variable speed compressors, and do not on/off cycle


BTW, I grew up on the Connecticut shore ( cove pond). Like you say, it's a lot warmer than northeast Massachusetts shore, but not so cold as Vermont

 

[maple1]

Mine hold heat right at setpoint. Lower level set at 21c, upper level at 20c. Or 19c. Depending what someone finds comfy for sleeping on a particular night.

As with any heating system, a heat loss calc should be done if the system is desired to cover all the heat loss. Square footage vs square footage can vary wildly depending on all kinds of things.

 

[ryanwc]

I'm pretty sure this is a lame question. I'm at the forum because of my new fireplace insert, but also interested in energy efficiency. In reading this thread it suddenly occurred to me that the air conditioner we inherited from the previous owners is a mini-split - a Mitsubishi electric MSY-GE24NA.

In doing some reading, I've realized there is or was a twin system, the MSZ-GE24NA, that would have provided air conditioning and heating. Could the system I have be upgraded in some way to be 2-way? Or would I have to replace both ends of the system?

Currently, on the newer GL systems, the difference between the air conditioner and the all-season heat pump is $300 on $2,000 of equipment, that they probably paid to install as well. Wish they'd sprung for the extra $300.

But if it's just a matter of different controls, rather than different machinery, I wonder if it could be upgraded.

 

[georgepds]

I'm pretty sure this is a lame question. I'm at the forum because of my new fireplace insert, but also interested in energy efficiency. In reading this thread it suddenly occurred to me that the air conditioner we inherited from the previous owners is a mini-split - a Mitsubishi electric MSY-GE24NA.

In doing some reading, I've realized there is or was a twin system, the MSZ-GE24NA, that would have provided air conditioning and heating. Could the system I have be upgraded in some way to be 2-way? Or would I have to replace both ends of the system?

Currently, on the newer GL systems, the difference between the air conditioner and the all-season heat pump is $300 on $2,000 of equipment, that they probably paid to install as well. Wish they'd sprung for the extra $300.

But if it's just a matter of different controls, rather than different machinery, I wonder if it could be upgraded.

I don't know your equipment, but from what little I know of air conditioning and heating, the equipment is different in the outside unit

You'd have a simpler time with a window air conditioner.. turning it around in the winter to get the hot side on the inside

 

[peakbagger]

Not a lame question, I am in the same situation. I had asked the question of a tech several years ago and was told they might be able to salvage the tubing and the condensate drain run as long as the refrigerant is compatible. The installed cost for a new one should be less although the tech may differ as the refrigerant is supposed to be recycled from the older unit. The guts of the outdoor unit are far more complicated with a cold source unit.

 

[ryanwc]

Not a lame question, I am in the same situation. I had asked the question of a tech several years ago and was told they might be able to salvage the tubing and the condensate drain run as long as the refrigerant is compatible. The installed cost for a new one should be less although the tech may differ as the refrigerant is supposed to be recycled from the older unit. The guts of the outdoor unit are far more complicated with a cold source unit.

Thanks for the replies.

 

[georgepds]

For another point of view, the folks at GBA think air source heat pumps can work well in New England if the house is properly air sealed and insulated

https://www.greenbuildingadvisor.com/article/ground-source-heat-pump-right-choice

 

[begreen]

I suspect they are correct. My BIL's house in southern New England is tight and very well insulated. It uses remarkably little fuel to heat in comparison to a conventional stick built house of the same size.

 

[peakbagger]

It really comes down to that 90th percentile day where the outdoor temp is down below zero, the wind is blowing and its snowing. Even though a cold source heat pump is putting out some heat at that temp, the COP is dropping close to one and its output is going down. No matter if there are snow baffles around the outdoor unit, fine wind driven snow will get up inside the coil causing frequent defrost cycles. I know this from practical experience when I intentionally tried to run down subzero in during a snowstorm. I expect it would have kept the pipes from freezing but sure wasn't maintaining setpoint.

Still a lot to be said for having a backup heating source for very cold weather be it woodstove, electric baseboard or vented kerosene heater. I like the wood as all the other options are not very useful without power.

 

[begreen]

Still a lot to be said for having a backup heating source for very cold weather be it woodstove, electric baseboard or vented kerosene heater. I like the wood as all the other options are not very useful without power.

Definitely right for a northern cold climate. Out here the coldest I have seen is 8ºF and that was in the 70's. I stopped by at a house with a Fujitsu Halcyon unit several years ago when it was 14º out. They were snug and warm and the unit was humming along quietly. Our current heat pump system however will only heat down to about 25º so we have resistance electric and the wood stove to fall back on.

 

[SpaceBus]

@begreen Thanks for letting me know this had updates. I was keeping an eye on this thread back in Nov when we first moved into our house. When I was in Afghanistan most of the "housing" for soldiers was just shipping containers made into little shacks. We kept warm with these ductless pumps, but not the nice ones being used in this thread. Ours were usually Chinese knockoffs of the Fujitso and Mitsubishi pumps. They did work, but tiny metal cans are tough to keep above 65 when it's around 0f outside and windy. My particular pump didn't like to defrost, so in the middle of the night when the compressor was covered in ice I had to go out out with a knife and carve the ice out!

I am thinking about putting in two 12-15k btu mini splits in my 1200 sqft well insulated two story salt box, one on each floor to make winter a little easier. Our electric baseboard heaters are working this winter, but they are expensive. The first floor is almost entirely open and has the wood stove. Upstairs has two bedrooms and a bathroom and is a little more cut up. There are however two registers in the walls allowing heat to pass between the bedrooms, which is a huge help. It's just myself and my wife with no kids, so heating the other bedroom isn't crucial anyway. What's the recommendation on make and model for living on the most Northeastern part of the US right on the coast?

 

[maple1]

I am partial to my Daikins.

Also Mitsubishi or Fujitsu, those 3 IMO are the top 3. Might come down local installers/dealers. That are good.

 

[maple1]

I will add my models when in front of my computer again...

 

[DBoon]

For Maine climates, look for Fujitsu RLS models or Mitsubishi HyperHeat - these are good down to -18 degrees F (or so) and still generate rated output at these temperatures. My Fujitsu RLS pushed lots of warm heat out at below zero temperatures - it's not the cold register heat you might know/remember from an old-style ducted heat pump.

If you are running electric resistance heat right now, these types of units will cut your heating bill to a third of what it was, maybe a fourth.