Air Source Heat Pump

[leoaarons]

Anybody got an air source heat pump? Are they worthwhile and what's the level of heating like?

[bcroe]

Anybody got an air source heat pump? Are they worthwhile and what's the level of heating like?

There are a lot of posts on them here if you do a search. I have a 3 ton
14.5 SEER since Sept; you can find some description of cold weather
operation in my posts since then. I expect summer cooling will be easy
compared to that. Its powered by my grid tied PV solar. Bruce Roe

[Sunking]

Had them for years. Great in warmer climates, but not so great in the north where you have winter temps dipping to single digits or less. In that cae Dula Fuel source is the way to go so when it does get really cold you can use NG or LPG as emergency heat vs heat strips.

[LucMan]

It all depends on where you live and what you want to heat & cool.
Have one, and have been installing them for over 35 years.Standard US ducted systems are ok in mild climates, but not as efficient as the Japanese designed systems. Fujitsu and Mitsubishi have small units designed for area heating that will operate to -5 F. They also make multiple head systems for an entire house or small commercial applications. They manufacture VRF systems (3 phase only) for large commercial buildings that can reclaim energy from one area and use it in another.
They perform the best in 20 - 47 F range where the COP is around 3, after that the COP starts to drop off. Daikin (Altherma) has an interesting system that is air to water that also heats domestic water and can be used in conjunction with solar thermal. Fujitsu, Mitsubishi, Panasonic, etc also produce a similar unit but they are not available in the US.
Depending on your winter temps you may need supplimental heating to maintain your comfort level.

[bcroe]

It all depends on where you live and what you want to heat
& cool. Have one, and have been installing them for over 35 years.Standard US ducted
systems are ok in mild climates, but not as efficient as the Japanese designed systems.
Fujitsu and Mitsubishi have small units designed for area heating that will operate to -5 F.

Depending on your winter temps you may need supplimental heating to maintain your comfort level.

My 3 ton SEER 14.5 air to air isn't the ultimate, but I'm pretty sure it only uses half as
much power as the 1978 unit it replaced. The ultimate would be buried and big $, and
would make quite a mess here installing. The -5F unit(s) are under consideration for
keeping the shop at 38 F; will need to see how my KWH reserve plays out this year.

i set the winter thermostat to 74F. I know the conservers would like it cranked down to
the threshold of pain, but I'd rather buy more panels. I am not in the "10% camp" which
says to make incremental changes up to the point of failure. As I see it the energy
depends on the temp differential between inside and outside; why should I give up the
couple degrees to comfort when the outside is varying over a 90 degree range?
Bruce Roe

[Sunking]

why should I give up the
couple degrees to comfort when the outside is varying over a 90 degree range?

You wussy, move to TX with 105 degree variance. 100 days at at 100 Plus degrees and one cold day at 0 once a year.

But I like where I am at now with no more than 40 degree extreme variance. Spring year round round with night lows on a cold as heck day of 50 degrees, and rarely ever see 90. Pretty much 60 at night and 80 during the day year round with a fair bit of rain.

[Ben25]

I have a mitsubishi mini split heat pump that heats my house (not including unfinished basement) down to about zero degrees outside temp. The heat pump is good down to -15, but it just can't keep up, partially due to a severe lack of insulation, but that's this years project...

Right now it's using about 15 kWh/day but in colder months it was using close to 50.

Ben

[peakbagger]

I have a 12,000 btu Mitsubishi hyper heat mini split in a very northern climate. It can get to -30 F (-34 C) on occasion. It works well down to about 0 F (-17C). It still puts heat out down to -10 F(-23 C0, but the output is reduced. If you are in snowy climate, its important that you have place to install the outdoor unit that is out of the path of any snow as snow on the coils really ruins the efficiency. I am heating a full first floor and a second floor office but its really a space heater intended to heat or cool one space. The point where you can heat your house is depending on heat loss, a tight house will have a lower heating load and therefore the minisplit can supply the demand. If you have a loose house your breakeven temp will be higher.

Be aware that the hyper heat or cold weather style heat pumps are a special design, regular air source heat pumps may put out heat but usually switch to electric backup when the temp goes below freezing. Mitsubishi has just come out with multizone system but I am not aware of any other standard house sized units that are set up for the cold temps like the mini splits do.

[Ben25]

Also, the hyper heat units need to be mounted at least a foot off the ground. We usually go 18". When they go through the defrost cycle, ice will build up underneath them. I've seen a solid column of ice from the ground to the unit on one that wasn't mounted high enough.

I just installed 2 of those new multi head hyper heat units last week. It's about time they made those, they've been hinting at it for years.

Ben

[peakbagger]

I have my minisplit 4' up off the ground. Luckily the location isn't subject to drifting as with winters snow I could have been in trouble. I have never seen any significant icing.

[LucMan]

The new low temp mini splits come with a resistance base pan heater to keep the base free of ice. Just a heads up up for the people that want to use these off grid as the standby loss is increased.

[gregvet]

Also, the hyper heat units need to be mounted at least a foot off the ground. We usually go 18". When they go through the defrost cycle, ice will build up underneath them. I've seen a solid column of ice from the ground to the unit on one that wasn't mounted high enough.

I just installed 2 of those new multi head hyper heat units last week. It's about time they made those, they've been hinting at it for years.

Ben

Hi Ben,
What are these hyper heat units? Are they designed for cold climates? Are they specifically for space heating or can they be used to supply heat to a radiant floor system?

[peakbagger]

Hyper Heat mini splits are air to air units for space heating. I am not aware of any heat pumps designed for cold conditions that heat up water for radiant heating. The problem is that mini splits don't put out real hot air, they are far better at putting out lots of warm air.

The owner of American Solar Technics in Maine is trialing one this winter, I think he has made comments that it hasn't been impressive but will await for his final report.

[J.P.M.]

One thing to perhaps keep in mind, as another poster have written, insulation will lower the heat load. The remaining load can then be supplied by a smaller unit, or a shorter duty cycle. Smaller is better.

The exterior temp. below which a heat pump becomes equal to resistance heating will be the same, but because the load is less, the energy cost will less.

Always reduce the load before equipment additions/modifications. The other way around flies in the face of common sense. That other way around is sort of a corollary to the "ready, fire, aim" way of doing things.

[Ben25]

^ What they said. There are a few air to water heat pumps on the market, but I haven't used any of them. I believe both Daikin and Fujitsu have one.