Mitsubishi Heat Pump?

[DianeB]

Elderly neighbor decided to install one of these. He has been heating with wood for 30 years and has back up electric baseboard which he would use if he was under the weather with cold/flu etc. His new son in law is an HVAC guy and is recommending the heat pump to him - says they now are able to heat down to zero degrees - thought I would throw this out to the group...are they really as good as this now? We get perhaps 5 days below zero per year and his electric could potentially be a back up to the heat pump. Neighbor said he will always keep some wood on hand for the stove, but can't do the hauling into the house any longer. We offered to help him stack every year his 4 cord wood delivery, but he does not want to impose. We will definitely make sure he always has a cord on hand for power outages etc.

 

[woodgeek]

Seems like an ideal situation....the minisplit HP will provide a lot of heat, and the baseboards will work like backup, and he already has those. Its an unknown how low the unit will carry the load, but my guess would be that it would carry well more than half if he only burns 4 cords. And cost him ~1/3rd of the kWh per BTU, compared to the baseboard. And the son in law is unlikely to take him for a ride.

 

[DianeB]

Seems like an ideal situation....the minisplit HP will provide a lot of heat, and the baseboards will work like backup, and he already has those. Its an unknown how low the unit will carry the load, but my guess would be that it would carry well more than half if he only burns 4 cords. And cost him ~1/3rd of the kWh per BTU, compared to the baseboard. And the son in law is unlikely to take him for a ride.

carry the load? wish I understood, could you explain? sorry

 

[woodgeek]

Sorry. Heating load. As it gets colder outside, more heat is needed. The mitsu will put out less and less heat as it gets colder, so there will be some outside temp where the mitsu can't keep up...then the backup (baseboards) will help by cycling some. Not a problem, the mitsu will do provide most of the heat needed, and do it cheaply.

 

[fbelec]

i've wired a few different brands of heat pump like that mitsu. (ductless splits) they definitely work at low temps i fired one off at 15 degrees in a second floor attic play room above a garage it worked great and just about noiseless.

 

[begreen]

Good for you covering your neighbor's back. The right Mistsi unit will do a pretty good job down to 0F, but I agree that you want a fall back solution, particularly during power outages.

 

[peakbagger]

The electric utility in Bangor Maine is giving big rebates for split heat pumps that are desinged for heating. They dont recomend them as primary heat but many folks are cutting way back on their backup. Do note that certain models are optimized for heat and they may cost a few bucks more.The biggest issues with them appears to be poor installation. They need to be leak checked and "pumped" down by a pro plus they need to be elevated up off the ground so that they dont get blocked with snow in the winter. Even some so caled "pros" take the easy way out and do a poor job installing them. The other issueis that the outdoor unit should be installed where its warm for winter which is the exact opposite for summer so its worth trying to come up with some sort of shading like a bush that loses its leaves.

 

[woodgeek]

The outdoor unit should be installed where it is sheltered from winter winds (e.g. lee side of house), and either exterior wall mounted or on a raised platform so it won't get buried by snow drifts.

 

[Floydian]

Diane,

I have done a lot of reading on mini splits and I agree with the above posts-sounds like a great choice for your neighbor.

With the Mitsubishi's, the Hyper Heat units models are their best performers. They deliver rated output down to 5, and still put out some heat down to -13. At 5, I believe they operate at a COP 1.8, meaning 1.8 parts air source energy to 1 part grid energy-not bad at all! And any time it is above 5 performance is only going to be better. Another plus is some summertime AC/dehumidification.

Noah

 

[DianeB]

we will see our neighbor this coming weekend and perhaps his SIL will be around as well. His SIL has been doing HVAC for 10 years. I will be very interested in where he puts the outdoor unit and if elevated etc. We do get a lot of drifting in our neighborhood.
thanks everyone for elaborating and explaining things

 

[Retired Guy]

Neighbor used to heat with pellets and has switched over to a Mini Split, he is very happy with it.

 

[maple1]

How big & well insulated is his house?

One mini-split will only heat so much area, and generate so much heat - he may need more than one.

 

[moey]

Fujitsu and Mitsubishi make some that go to 0 even -5. I think if I had a small ranch that currently had oil or propane I would be ripped it out and put in electrical baseboard with a mini split on each end.

You could power them with a 240v generator pretty easily they are about 20 amps although startup could be tough. I dont have any experience just speculating.

Heres a page on the Fujitsu ones

http://www.fujitsugeneral.com/wallmountedRLS2.htm

 

[pen]

My mitsu unit with hyper heat is rated to -13F. Didn't get quite that cold here this winter but at -5F I cranked it up as a test and it still worked great.

I've used it WAY more this winter than I ever used to use the single 6 foot electric baseboard and the electric bill is no higher than it ever has been even with the greater usage.

Very happy but I'm still on my first year. My unit is rated to about 22k btu heating I believe.

pen

 

[fbelec]

if using a ductless split as backup you just might be able to run it on a generator that is big enough like 7500 watt or bigger but if you have a gas powered inverter i don't think you would be able to get it started because of the way inverters run the speed of the engine. at least with a generator the engine is running at speed and with the speed that the ductless splits start there might be enough cushion to get it going. it's definitely less power to heat the same area as electric baseboard. a 24 x 24 room would need 5760 watts of heat on electric baseboard but would heat with a ductless split at around 16000 btu. 1.5 ton unit (18000 btu) would run about12 to 13 amps about 3000 watts. tops.

 

[DianeB]

He does have a small 3 bedroom ranch with a full basement. I think he was planning on on one mini split in his kitchen, living room dining room area which is all open space and use the baseboard in his bedroom if needed. He no longer has kids at home so those bedrooms can stay cool. I think he has a small baseboard heater int he bathroom, but that may just get warm enought from the main area of the house. I hope it works for him and I will be watching closely. Thanks for all the info

 

[pen]

He does have a small 3 bedroom ranch with a full basement. I think he was planning on on one mini split in his kitchen, living room dining room area which is all open space and use the baseboard in his bedroom if needed. He no longer has kids at home so those bedrooms can stay cool. I think he has a small baseboard heater int he bathroom, but that may just get warm enought from the main area of the house. I hope it works for him and I will be watching closely. Thanks for all the info

I have the same setup. I placed the mini split so that I can direction it's air towards the hallway leading to the bedrooms and am extremely impressed at how well it keeps their temperature up (with the doors open of course).

Is the basement used for much? Is it a full basement or a walk-out with studded walls part way up? In hindsight, I wish I had bought a mitsu unit that could carry two head units, and placed the other in my basement to help with dehumidifying in the summer and heating in the winter if I didn't want to run the wood stove.

pen

 

[Floydian]

In hindsight, I wish I had bought a mitsu unit that could carry two head units...

I see the appeal in that but I think you made a good choice as the performance of the hyper heat/single head units is definitely better than the multi head units. The output really starts to drop off at the cooler temps with the multi head units.

Noah

 

[maple1]

Anybody making one of these things yet that, in the summer, would take the heat from your room air & put it into your hot water tank rather than just dumping it outdoors?

 

[moey]

Anybody making one of these things yet that, in the summer, would take the heat from your room air & put it into your hot water tank rather than just dumping it outdoors?

Its called a desuperheater its used in ground source geothermal systems not sure if there are any for air source systems.

 

[maple1]

Yes, there are those. Then there are Heat Pump Water Heaters too.

Just doesn't seem to me like it would be a huge technological step to make one of these mini-split untis have an option to hook it up to a hot water tank so the heat that is dumped during cooling seasons could be dumped into a hot water tank rather than just the great outdoors.

 

[Floydian]

It's coming, Maple1, though not exactly what you're describing. Apparently in Europe the "magic box" approach is available. Air source heating/cooling, potentially tied into the dedicated HRV/ERV ducting for distribution(assuming very LOW heat loads, i.e. Passivhaus) as well as air source DHW. Pretty slick and very spendy. http://www.greenbuildingadvisor.com/blogs/dept/musings/magic-box-your-passivhaus

Noah

 

[woodgeek]

I'm personally skeptical of the 'one air source heat pump to rule them all' that does AC, space heat and water heating. I know they exist, but it is not clearly the most eff approach...a HPWH needs to push (sometimes low temp) space heat into a tank that might be 120°F, something that an AC never needs to do. In cold climates, its performance under these conditions is more important than its summer-time performance (which is great). My ASHP and HPWH use two different refrigerants to do their different jobs.

 

[maple1]

Maybe I'm looking at it too simplistically.

I think I read that a Geyser HPWH can provide the equivalent of a 9000btu window AC unit while heating water in the summer. So upsize that capacity, control it so in the summer it will dump excess heat (beyond what it takes to maintain 140 or so hot water) to the outdoors, then reverse the HP & air duct flows for inside heat in the winter from outside air?

Easy peasy, right?

 

[woodgeek]

With engineering, the devil is in the details, and those are eff and cost.

For example, my HPWH (an AO Smith) has a much bigger fan than the others, meaning it does more air cooling (sensible heat) and less dehumidification (latent heat), but in the end, it does its job (heating water) slightly more efficiently than the competition, because its cold sink is a little warmer. This also allows it to run in ~5 degrees colder ambient temps before it has to shut down b/c of frost. This means it runs in my 48°F garage in January, while a GE model would have switched to conventional a month earlier.

So, maybe there is no problem, they will go on the market any day now, and I will eat a hat. Or maybe us armchair designers don't know a thing about the design constraints, and whether a 'magic box' can compete with minis.

The switchover also has to be fully automatic (most users won't want to deal), the added complexity might add to an install price (by more than it will ever save on those few AC days), the market will be smaller than otherwise (heavy AC climates only) limiting profitability, etc.