Cold climate air-sourced mini split heat pumps

5 years ago

I suspect that my decision to not include air conditioning in my new build in northern NY was a mistake. I'm thinking a mini-split heat pump might be just the thing. Most of the main floor is open, and there is a loft above it through I could run the piping. A bonus for something like this is that for heating: I currently have resistance-heated hydronic in-floor radiant heating, but the heat pump would provide some heat at a lower cost of electricity. Can a specific brand be recommended by someone out there?

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Comments (8)

tigerdunes
5 years ago
There have been several different threads on this forum over the past several weeks concerning mini split heat pumps. I suggest you check these out and review them and then come back for questions.

TD
ionized_gw
5 years ago
I don't have great heating demands so I don't have the Mitsubishi hyper heat system, but it is very neat technology. I think that they have patent protection for their flash injection scheme.
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First off, 4 stories sounds like a big vertical head for residential mini-split equipment just from my casual notice of those requirements. I would check that out first. I am testing a whole-house mini-split installation right now (Mitsubishi, 7 in, 3 out). I will let you know in a year or so if I like it ;-) On paper they are more efficient due to inherent efficiency and the inherent zoned nature. We have been having pretty hot weather and with my wife out of town this week, I have been pretty much been cooling the bedroom and the kitchen with some intermittent cooling in the utility room where the exercise machine lives. Note that I am not much of a sit and watch TV type. You are really a leg-up over lots of others on this decision as you have experienced mini-splits. One thing to think about is that, IIRC, most of them don't have back-up heat so you will not have any heat while they are defrosting. (Maybe none of them have electric resistance back-up, but I think I ran across at least one brand that does.) You also have to pay close attention to cold weather performance for the mid-Atlantic region. I know that with Mitsubishi's current residential equipment, the 1:1 systems have better low temp performance than the multi-splits. They are more efficient too. Even if they do have back-up heat, you can kill the efficiency pretty fast if you need back-up very often. Keep in mind that there are lots of options to the wall-hung indoor units. They cost more, but there are units that can be dropped into ceilings and others that sit on the floor. There are also short, ducted units that would solve that big room problem by splitting the supply and return. (You could also install more than one indoor unit/room.) Condensate needs to be dealt with using pumps. I am not an HVAC or building pro, so take my observations with a grain of salt. After replacing a ducted system with mini-splits, and talking to my install guys a lot, here are some observations and conclusions. Installing a mini-split through outside walls, as is it usually promoted, is pretty quick and straightforward (read fast and cheap) compared to installing a new duct system in an existing house with no central AC. My install was done through interior walls running the lines/cables under the raised house and out to the side which was much more complicated. If I were doing this over and I had a good duct system within a house envelope, I would stick with it. The trouble is, what is a good duct system? More often than not, they are outside of the living space. In addition, they are considered good when they leak 5% of the air and they only get worse as they age. My system was in the attic with parts of the duct system in the attic and partly in a furred-down space over the hallway. The worst part was one duct that started at the AH in the attic, dropped down under the house in a chase and ran for about 30 feet before it reached the first floor register in an addition with a flat roof (thus no attic). It then reduced in size and ran another 25 feet under the house. That part might have been mini-splitted even if the rest of the house retained a ducted system. By your description, your duct system was not installed very well, but if the design is sound, it could be revamped less expensively than installing minis. In general, I think that ducted systems are trickier to design and install than mini-splits so there is more tolerance for less than careful and knowledgeable installers with mini-splits. Due to their ability to handle variable loads, choosing the right size is not as critical either. (I had 4 tons cooling plus a gas furnace before, now I have about 106% of the cooling and 60% of the heating. The heating was way oversized.) My system will handle cooling fine with the house the way it is, but I should not have trouble after I make improvements to limit infiltration and add insulation. My installer is knowledgeable, smart, very workmanlike, and experienced (he has taught the trade for 30 years). He would have installed new ducts and a two-speed system for a slightly lower price than the chosen mini-split equipment. I doubt that he would do it for the same price if doing it on a similar home going through interior walls. He did not have much mini-split experience and brought in a collaborator that does, on this project because he was looking forward to a learning experience. I don't think that he lost his shirt, but I don't think he made as much as he usually does.
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sktn77a
5 years ago
last modified: 5 years ago
I guess anything would be better than a resistance-heated electric boiler in your climate! Mitsubishi make what looks to be a nice DIY minisplit system.
mtvhike
Original Author
5 years ago
I looked on the web for recommended installers in my county; there were none, but four in the adjacent county. I went to one of them, and they recommend a Fujitsu model which works down to -15°. Even though they usually only do commercial installations, they are willing to consider my project. There are two other HVAC contractors I can contact and I will check with them (the fourth was clearly a handyman).
tigerdunes
5 years ago
works down to -15 degrees...humm...interesting to ask what size system and how many BTUs produced at -15 degrees.....any electric backup strips?...

IMO
fsq4cw
5 years ago
last modified: 5 years ago
I would suggest ‘correcting’ your existing situation by having your electric boiler supplement an air source hydronic heat pump that would use your existing electric hydronic boiler only as a backup. This way, you would have very efficient in-floor hydronic heating and hydronic cooling. All with one well-integrated, efficient system.

The first link contains a video explanation of the system. The second link takes you right into the technical weeds but what is of interest is that same system can be used for every conceivable heating and cooling application – including, zoning, DHW, pool, spa or snow melt!

See page 26 of the 2nd link.

Links 3 & 4 illustrate the type of fan coil units for both heating and cooling that would provide zoned hydronic cooling and heating, that in heating mode would work with your existing boiler as well as the heat pump, to provide a quick boast in indoor temperature when needed as in-floor heating is rather slow to react.

That’s a whole lot to chew on but technically the best single, integrated system for your existing situation other than geothermal.

https://www.nordicghp.com/product/nordic-products/air-source-heat-pump/air-to-water/

https://www.nordicghp.com/wp-content/uploads/2018/03/001970MAN-02-ISSUE-02-ATW-Series-Two-Stage-R410a.pdf

http://www.multiaqua.com/index.php/water-fan-coils/cffwa-universal-2p

http://www.multiaqua.com/index.php/water-fan-coils/cffwa-universal-2p

IMPO

SR
mtvhike
Original Author
5 years ago
Thank you, fsq--- These Nordic systems seem to be overkill, and there are no US installers in the NE (there are several in the Montreal area, and they might be possible).

I got a telephone estimate from the one installer I mention above, for a Fujitsu system. By referring to some of his recent installations, he thinks my cost might be about $7500 (for a 24000 Btu system). Between his and my busy schedule, I cannot get a visit from him this month but we have a tentative meeting in August.

He is quite familiar with my type of situation, but he thinks that, since I already have an existing heating system with which I am very satisfied, I needn't get a system which needs to work as low as -15°F. My primary interest is in cooling, so the system would be sized for that.
ionized_gw
5 years ago
I guess you are deciding whether you want heat pump or cooling only, and if heat pump, what low temperature you want to be able to use them to. My memory tells me that the cost of heat pumps was not much higher than cool-only when mine went in. The lower temperature heat pumps are going to cost more, but you may very well find that they will return more than that cost with a little calculation. The trouble with that calculation using fuel cost only is that it is significantly more expensive to operate a heat pump than resistance heaters. You'll have to be more creative to factor that in.

IMO, mvthike's situation is what mini splits are made for, adding (a little) cooling to a home with established heating without ducts. There are a lot of heat only homes in climes with low cooling needs. ( A lot of them have window units running for a few weeks.) That is, of course, why the installer mentioned is "quite familiar" with that situation in the 'daks and far outside. This particular situation is complicated by the fact that the most economical heating fuel choice, for many, is not available. (Outdoor wood-fired boilers are not unheard of in that area. I bet there are dealers for those a lot closer than for the air-water heat pumps.)

My memory of earlier posts combined with this one says mvthike's "overkill" response is partly due to the fact that this home is unoccupied more than it is occupied so payback with higher cost, highest efficiency, methods is going to be long at best and may reach never.

Tigerdunes, I think that there used to be high wall mini splits with resistance heat. I think I saw info about them when I first started looking at them but they disappeared shortly afterwards. My understanding is that someone decided that heaters of that type with plastic cases were not a good idea. I could be all wrong about this. I do think that is available with their mini ducted equipment.

Cold climate air-sourced mini split heat pumps

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Cold climate air-sourced mini split heat pumps

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