Using a window A/C in reverse?

[Number21]

I have a cinderblock shop with a wood "barn" in the back. I have a wood stove for heating but I also like electric for supplimental use. I don't always want to start a fire. Problem is electricity is freakin' expensive! My electric bill for the shop alone is going north of $100...

What if I install a 10,000 BTU window air conditioner through the wall between the shop and the barn, as if I was trying to cool the barn? The barn is mostly open to the air but stays a few degrees warmer than outside.

Would the hot side of the air conditioner put 10,000 BTU of heat into my shop, like a miniature heat pump? This time of year air conditioners are cheap on craigslist. And in the summer I could flip it around to cool!

Will this work? Shop is generally around 40-50 degrees, with the barn around 30-40. Obviously the original thermostat would have to be modified/replaced.

10,000 BTU electric heat = roughly 3,000 watts.
10,000 BTU A/C = roughly 1,000 watts.

 

[sneezer41]

Problem is operating temp. it will be too cold on the cold side to turn the ac on. You could probably mess with it, but............

 

[ghnl]

I have seen window mount reversable heat pump units. Can be used for either heat or cooling. i think that would be a better option than a backwards A/C unit.

 

[pseudorealityx]

Agreed with ghnl. If you want to go window unit, get a window heat pump.

 

[Pappa Ugg]

Using the condenser to heat the space won't work very well if the outside temp is low.. remember all an ac unit does is transfer the heat from one location to another....

 

[knipdm01]

youd have to reverse the fan speed too. and you dont have low ambient controls on a regular a/c

 

[z28snksknr]

Running an A/C unit at <60°F or so will damage the unit. If it's cold enough, the refrigerant will not evaporate after expansion in the evaporator and you will send liquid to back to the compressor. Liquids are non-compressible, which means the compressor is going to give before the liquid starts to squish.

Besides, it would be very inneficient to run an A/C system for heat output since you are running a compressor and fan that have MAYBE a 70% efficiency and require the majority of the electric load but put out little heat. You'd be better off with an electric element heater with a fan.

 

[z28snksknr]

One last point, you will not be able to exchange any heat on the cold side of the A/C unit if the temp is <40°F or so. In fact, you will actually COOL DOWN the evaporator further, and the system will actually pull heat from the condenser side (your shop) since you have just inverted the temperature driving force (if that makes sense).

 

[knipdm01]

Agree with the first portion completely.

But a heat pump is has a coefficient of performance of 1 at 0 degrees Fahrenheit. and up to 4 at 55 degrees outside. So at say 30 degrees a heat pump has a COP of 3. Its 1/3 less expensive to heat than with electric resistance heat. So for a house in a somewhat mild climate like TN WV GA? A air source heat pump works great. Colder climates you get too many cold spells where heat pump performance lacks and its an uncomfortable heat with low heat recovery. now water source heat pumps are king!

 

[pseudorealityx]

A heat pump running in those low (~0 F) outdoor temperature ranges are going to have to switch over to defrost mode fairly often and engage the electric resistance heat strip. If that's the case, gas heating equipment is much preferred. Where I live, the HP is the way to go. In Minnesota, it'd be a waste of money.

 

[burleymike]

Won't work, at that low of temps you will be sending liquid refrigerant to the compressor which will dilute the oil and it will die shortly after. Those window shakers also don't have a defrost system on the evaporator so it will turn to a big block of ice and all air flow will stop.

You would be better off trying to find a used heat pump and air handler. There are plenty of good working systems that get scrapped because customers want a shiny new high efficiency system. If you can find a heating and cooling contractor that would sell you a used heat pump cheap that would be the best thing.

Your other option is a PTAC heat pump if you don't have the money to deal with installation costs.
http://www.google.com/products/cata...ct=result&resnum=3&ved=0CBwQ8wIwAg#ps-sellers