Do the window AC & Heat units actually work?

[haugy]

I'm looking at some AC/Heat combo window units as I have two windows in my shop that are in perfect locations for them. In fact I planned on putting in window units.

I've got a 220V plug next to one just for the unit so I can really power something. I've come across some 24,000 BTU units but will those really do much?

I know the AC unit will do alright for my shop. But what about the heat?

It's a 30x40x14' shop. 1" closed cell foam on walls, R19 batts on walls, the drywalled. Ceiling is steel with R30 on top. Two big *** garage doors though.

I know I can always add another 24,000 BTU AC unit next to the other one to really cool down the shop. But I'm also thinking about keeping it at least moderately warm in the winter. Not 60-70 degrees. But in the 50's would be good.

Anyone have any real world experience with a BIG combo unit? Pros/Cons?

 

[MikeLawrence]

The limiting factor here is not that it's a "window unit"; it's that it's an electric heater. This is why ALL 110V space heaters, window units, ptacs, or anything else produce the exact same BTU as a hair dryer: 110V * 20Amp breaker = 2.2kW and since you typically assume you don't have the circuit all to yourself (fan motor for instance) you scale it back and they all end up at around 1.8kW which is around 6K heat btu.

That said, you aren't on 110V, you're talking 208/230V and if you can support a 30 amp cord then you can go with a 5.0kw and put out around 17k heat BTU maximally. Depending on where you live this 'could' be enough but I wouldn't go for it til I did a real heat calc on it because there are a LOT of places where it will be undersized for the space. As for "just putting 2 units in" your limiting factor is likely going to be powering both, not providing enough holes.

Long story short, if you care more about the heat you aren't looking for a "BTU number" at all. You want to know if it's a 1.8, 3.6, or 5.0kW heater.

Michael Lawrence, LISSCO
www.thruwalls.com

p.s. You aren't gonna circumvent the energy conversion issue with a window/wall heat pump... but mini-splits DO scale up to 3.5-4 ton--something to think about anyways.

 

[redsky49]

[QUOTE=MikeLawrence;1147525]The limiting factor here is not that it's a "window unit"; it's that it's an electric heater. This is why ALL 110V space heaters, window units, ptacs, or anything else produce the exact same BTU as a hair dryer....

p.s. You aren't gonna circumvent the energy conversion issue with a window/wall heat pump... but mini-splits DO scale up to 3.5-4 ton--something to think about anyways.[/QUOTE]

Au contraire. You will indeed improve your energy performance with a heat pump.

Quoting the first unit that came up from a Google search

http://www.ajmadison.com/cgi-bin/ajmadison/AH183A35MA.html

reveals the following:

Heat performance utilizing resistance heating element:
11,000 btuh @3555 watts, or 3.1 btu/watt

Heat performance utilizing reverse cycle heat pump:
16,000 btuh @1840 watts, or 8.7 btu/watt

All data taken from the above linked window mounted heat pump.

Bear in mind that the typical air-to-air heat pump begins to lose efficiency as temperatures drop below 40 degrees F, and that many of them will revert to resistance heat at 20 degrees F or so. Mitsubishi, among others, claim superior performance down to 0 degrees F for some of their heat pumps.

In a moderate heating climate, an air-to-air heat pump is an excellent choice, particularly when compared to resistance heat. In colder climes, earth coupled heat pumps are generally the better choice.

In any case, a proper load calculation should be performed prior to the purchase of any equipment.

As always, offered only as opinion

 

[haugy]

That said, you aren't on 110V, you're talking 208/230V and if you can support a 30 amp cord then you can go with a 5.0kw and put out around 17k heat BTU maximally. Depending on where you live this 'could' be enough but I wouldn't go for it til I did a real heat calc on it because there are a LOT of places where it will be undersized for the space. As for "just putting 2 units in" your limiting factor is likely going to be powering both, not providing enough holes.

Long story short, if you care more about the heat you aren't looking for a "BTU number" at all. You want to know if it's a 1.8, 3.6, or 5.0kW heater.

Yeah, I've got the power for one big one. And then have another 110v for another A/C. That's info does help on what I need to look for, for the one unit that will be a dual system.

p.s. You aren't gonna circumvent the energy conversion issue with a window/wall heat pump... but mini-splits DO scale up to 3.5-4 ton--something to think about anyways.

Mini-splits? You lost me on the last sentence.

And I'm in TN. Not the coldest place, but we spent two months last year at 10-20 degrees, so I'm not sure a heat pump will really put out the heat I need to sustain a 50 degree temp.

 

[MikeLawrence]

[QUOTE=MikeLawrence;1147525]The limiting factor here is not that it's a "window unit"; it's that it's an electric heater. This is why ALL 110V space heaters, window units, ptacs, or anything else produce the exact same BTU as a hair dryer....

p.s. You aren't gonna circumvent the energy conversion issue with a window/wall heat pump... but mini-splits DO scale up to 3.5-4 ton--something to think about anyways.[/QUOTE]

Au contraire. You will indeed improve your energy performance with a heat pump.

Quoting the first unit that came up from a Google search

http://www.ajmadison.com/cgi-bin/ajmadison/AH183A35MA.html

reveals the following:

Heat performance utilizing resistance heating element:
11,000 btuh @3555 watts, or 3.1 btu/watt

Heat performance utilizing reverse cycle heat pump:
16,000 btuh @1840 watts, or 8.7 btu/watt

All data taken from the above linked window mounted heat pump.

Bear in mind that the typical air-to-air heat pump begins to lose efficiency as temperatures drop below 40 degrees F, and that many of them will revert to resistance heat at 20 degrees F or so. Mitsubishi, among others, claim superior performance down to 0 degrees F for some of their heat pumps.

In a moderate heating climate, an air-to-air heat pump is an excellent choice, particularly when compared to resistance heat. In colder climes, earth coupled heat pumps are generally the better choice.

In any case, a proper load calculation should be performed prior to the purchase of any equipment.

As always, offered only as opinion

See, and I was trying to avoid the "you can't create heat" argument by being super careful in how I wrote the discussion of strip heat and then I get nailed for heat pump inaccuracy. Not your fault though, I should have been more clear. [And btw, I always enjoy reading your posts =) ]

Heat pumps are a very efficient way to heat a space because instead of "creating" heat they move it around--essentially they air condition the outside and exhaust into your house. If you live in a temperate zone you want a heat pump because it will save you money: plain and simple.

If you are restricted on your power consumption OR have a very large packaged system it may even be that your heat pump can over perform (btu wise) a strip heat due to this efficiency discrepancy. (This is exactly what Redsky showed an example of.)

The reason I said that a packaged unit's heat pump wouldn't help you but a mini-split's might is that I made the assumption that if you needed the outside limit of a unit's rated BTU in the winter it is likely NOT because you want the room 120 degrees but rather that the outside temperature has become very cold which is when most heat pumps switch to resistance heat. That is to say, when you need the heat BTU the most is exactly when it's going to reduce the heat BTU available to you. That said Redsky does have a very valid point when it comes to bringing the room up to temp during "normal winter weather".

The reason I made the odd comment about mini-splits is because that's where Fujitsu (at least... maybe some others) has been advancing the limits of what is possible in heat/air recently: the newer 9k-12k systems are 26 seer when 13 seer was long considered "great". Anyways, to cut this short these super high-efficiency units exploit the high pressure and low temperature of the new R-410a to make their heat pumps work at ridiculously low temperatures which greatly mitigates the number of times you'll observe a "ramp down" in your heat pump. As far as I know packaged systems have not "caught up" yet and exploited this like the mini-splits have.

TL;DR sum up
ALL heat pumps are more efficient than strip heat and therefor allow you to create more heat btu per watt available BUT a packaged system's heat pump will likely ramp down your available heat BTU when you need it most (iff strip heat hbtu < heat pump hbtu) where some newer mini-splits have been extensively tested to show that they won't.

Michael Lawrence, LISSCO
www.thruwalls.com

 

[MikeLawrence]

Yeah, I've got the power for one big one. And then have another 110v for another A/C. That's info does help on what I need to look for, for the one unit that will be a dual system.




Mini-splits? You lost me on the last sentence.

And I'm in TN. Not the coldest place, but we spent two months last year at 10-20 degrees, so I'm not sure a heat pump will really put out the heat I need to sustain a 50 degree temp.

A ductless mini-split takes the window unit that you are familiar with and splits it into two packages the condenser and the evaporator (same as central heat and air basically). The condenser is just a box that would sit on the ground outside of the garage, be mounted to the wall of the garage (much like a window unit then), or be put anywhere that's convenient really. The evaporator usually (there are other options but this is the most common) hangs on the inside wall. Most people (I'd say everyone, but who knows) would consider them smaller, (WAY) quieter, and nicer looking than a window unit. A small 3" hole in the wall allows you to connect the two.

As to your other comment: We are in TN as well (Knoxville) so I definitely know the area's climate--heat pump all the way every time.

 

[haugy]

A ductless mini-split takes the window unit that you are familiar with and splits it into two packages the condenser and the evaporator (same as central heat and air basically). The condenser is just a box that would sit on the ground outside of the garage, be mounted to the wall of the garage (much like a window unit then), or be put anywhere that's convenient really. The evaporator usually (there are other options but this is the most common) hangs on the inside wall. Most people (I'd say everyone, but who knows) would consider them smaller, (WAY) quieter, and nicer looking than a window unit. A small 3" hole in the wall allows you to connect the two.

As to your other comment: We are in TN as well (Knoxville) so I definitely know the area's climate--heat pump all the way every time.

Okay, I'm familiar with the mini-splits, I've just never haard them called that before. Can they do heat as well?

Or would I be better off putting an A/C unit, and heat pump seperate. I'm not really worried about the window thing as they are 6' off the ground, and that's pretty much the only reason I put them in other than occasional daylight.

Thanks for the help, even though some of your jargon is flying right over my head.


EDIT: For example I found this, and these SEEM to look like what would work really well for my shop. Run a dual wall mounted 24RLF system. One on each end of the shop. What do you think? And how do you find pricing info on these. I know they'll be expensive.

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

 

[MikeLawrence]

Okay, I'm familiar with the mini-splits, I've just never haard them called that before. Can they do heat as well?

Or would I be better off putting an A/C unit, and heat pump seperate. I'm not really worried about the window thing as they are 6' off the ground, and that's pretty much the only reason I put them in other than occasional daylight.

Thanks for the help, even though some of your jargon is flying right over my head.

Yes sir, many of them (maybe even "all" over 24k btu) are heat pumps.

Michael Lawrence

EDIT: Response to edit.

Yeah those are the super high efficiency units I was talking about. As far as I know that would be the single most efficient possible way to heat/cool the space. They are definitely a little pricey but depending on how often you'd be heating/cooling the space they could save you some money in the long run.

I can't legally discuss pricing on those over the internet (no one can) but if you give me or Ron a call at the office (1-800-454-7726) we'd be happy to let you know.

Michael Lawrence, LISSCO

 

[haugy]

Thanks for the info, I'll try and give you guys a ring tomorrow. See how much I'm overdoing it.

 

[ixlr8]

There are several online places that have various mini-splits for sale, google is your friend. I just installed a Mitsubishi mini-split heat pump for my home, 15K BTU. Online price was half local installed price. So far plenty of heat with outside temp at 20dF, suppose to be able to provide heat down to 5dF outside.