Using an air conditioner as a heat pump


I have a friend who has a cottage that has gas fireplace for heat. The cottage was built as a beach house and probably is not well insulated. The gas available is propane and propane now costs more than resistive electric heating in the Pacific Northwest. And that is without considering the efficiency of the gas fireplace. One solution for her would be to replace the gas fireplace with a wood or pellet stove. And that is probably her best choice, even though it would require installing a new chimney ( the gas fireplace is vented through the wall and the height is considerably below the roof top). But she has decided against that.
If anyone built a heat pump that was just intended for heating ( that is no way to use it for air conditioning ) that would work well. There is no great need for air conditioning for a beach house on Puget Sound. But I do not know of any.
So the question is what are the major differences between a window heat pump and a window air conditioner? Besides the obvious things as the reversing valves.
Could one buy a used window air conditioner and installing it backwards be at all feasible. One would have to short out the thermostat in the air conditioner and install a thermostat inside the cottage wired to an outlet. And one might have to use a timer so it would not run long enough to ice up the evaporator. And it would not be useful when it was really cold. But there is a large portion of the year where the temperature is about 50 to 55 F. Not comfortable without some heat, but not a lot of heat needed.
Used air conditioners in the PNW are very cheap. In the range of $30 to $50 for a almost new 5000 btu to 10,000 btu window unit. Almost as cheap as an electric resistance heater. So there is no concern about having a guarantee.
Dan
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Do you want it cheap?? or do you want it right??
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Actually I want to increase my knowledge in how air conditioners differ from heat pumps. Could a heat pump be produced at roughly the same cost of a air conditioner if it were made only to heat the building? Or are there differences that require additional costs? Would a capillary tube work for a heat pump or is a expansion valve necessary? Does the evaporator coil need to be much bigger?
Inquiring minds want to know
Dan
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Actually I want to increase my knowledge in how air conditioners differ from heat pumps. Could a heat pump be produced at roughly the same cost of a air conditioner if it were made only to heat the building? Or are there differences that require additional costs? Would a capillary tube work for a heat pump or is a expansion valve necessary? Does the evaporator coil need to be much bigger?
Inquiring minds want to know
Dan
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The difference is the reversing valve, and accumulator.... other than that they are the same..... Size it for heating in your area... Do a Manual J calculation to correctly size it, and a Manual D for designing the ductwork for correct airflow to each room.
FWIW, all the new equipment has expansion valves in it. Stay as far away from R-22 as possible, use equipment that takes R-410a refrigerant.
If inquiring minds *REALLY* want to know, they should be calling their local, competent, licensed, insured, professionally trained, HVAC technician to do the calculations, and explain the best options for a properly sized, and correctly installed comfort system.
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Just read some books. The books all have lots of information on capillary tubes and I figured that window units would use the least expensive thing.
Dan
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The window units I've seen all use cap tubes. And R-22. There may be some window units with other gasses, but I've not yet worked on one.
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Christopher A. Young
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On Mon, 6 Oct 2008 08:51:39 -0700 (PDT), snipped-for-privacy@krl.org wrote:

Besides the fact that just physical design is going to be a limitation, how do you propose to handle any defrost cycle and the water it contains? Bubba
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Good point.
I used a dehumidifier that was not rated for use in cool areas by using a timer that would allow it to run for half an hour and then not run for half an hour. Since it was in a cool area, the basement, the fact that it cycled every hour did not cause the start winding to overheat.
The water would need to be directed outside. Would have to look at a specific air conditioner to see if this is easy to do. It should not be too difficult to buy some galvanized sheet metal and make a pan. A few pop rivets to prevent movement and some solder ought to work for the corners.
I have not owned a heat pump for the last thirty something years, and had forgotten that they have a defrost cycle. I assume heat pumps reverse to defrost. For a inexpensive system, I suppose one could just stop running the compressor and keep the fan blowing air over the evaporator. That would require a little rewiring so the timer just stopped the compressor.
Dan
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Spray it with gasoline and ignite...
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On Mon, 6 Oct 2008 08:51:39 -0700 (PDT), snipped-for-privacy@krl.org wrote:

Dumbass alert, dumbass alert, dumbass alert!!!!
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On Oct 6, 2:03pm, What a maroon wrote:

Ah but who is the dumbass? One that asks questions or one that responds with nothing related to the question?
Dan
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Thank you, thank you very much.
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Ought to be possible to change out the thermostat. Change it to a much lower temp range, like 35F. Run the AC so that when the evaporator gets to 35F, that the compressor kicks off. Keep the fan running. Should ought to provide SOME heat, and take some of the strain off the electric bill.
You'd have to make the condensate pan that you mentioned. Might work, better than just filament heaters.
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