(besides using things like fuel cells or engines)
There are propane powered freezers that use the combustion to drive the refrigeration cycle directly without a compressor. As I understand it they work well and make good use of it’s energy to drive the cycle. So can this be made into a heat pump to heat a home? Hoping for a way to get more energy than simply burning it in a furnace with efficiencies over 100% and hopefully in the range of electric heat pumps.
It is not the case that the burning of propane generates electricity to power the fridges, but it sets in motion a cycle of evaporation and condensation of ammonia. Here is a nice explanation. It is not electric, it is mechanical or chemical, depending on how you see it.
I guess you could use the other end of the cycle to generate heat instead of cold, but I am not sure I would call that a heat pump*, I doubt the efficiency would be over 100%. But perhaps it would if you desing it cleverly, and if you have some use for the fridge on top of the heating that would be a net gain.
* I wonder now where a heat exchanger ends and a heat pump starts.
The term there is “absorption” chillers, per Pardel-Lux’s link. I think they can even have no moving parts. However, they depend on a heat source and thus are usually only viable where there’s some sort of waste heat to use. So it doesn’t seem reversible on the face of it, but I’d need to look back through those diagrams.
Some 20 years ago I remember a This Old House episode from Arizona where they trialled a natural gas heat pump. It used the gas combustion to run the compressor, basically a natural gas engine instead of an electric motor. The waste heat could then be used to improve heating efficiency and/or provide hot water. I think they ended up having big reliability problems, and maybe the economics don’t work out, because it’s not a technology I’ve heard of recently.
The Einstein Refrigerator is an example of refrigeration using heat. A variation was used to cool breeder reactors. A simpler form of refrigeration using heat in any form is the Icy Ball, once common as a portable refrigerator used in the early days of auto road trips.
I have one in my caravan. There is a small flame Propane) or an electric element (240 V AC or 12 V DC) that evaporates the ammonia. Waste heat is vented outside through a grill. There are no moving parts.
Yes, my friends’ parents had one at their cottage. Brand name Servel, I think.
It seems you can get industrial sized absorption chillers. Good for cooling sizeable buildings. Compared to electrically driven heat pumps of similar capacity their COP is terrible. 0.7 to 1.4, versus of the order of 6.0. But given they can be run off waste heat from other processes or directly heated with propane which is generally a lot cheaper than the equivalent energy in electricity, they are still useful.
So for the OP, the question would be, if I use propane to heat my house, could I add an absorption chiller configured to cool the outside and dump heat inside? I think the answer is a qualified yes. If say you had a propane furnace heating your home, and you ran the adsorption chiller on the flue heat of the furnace, you could probably move some heat inwards. It might not be fabulous. You would need to work through the temperature differences involved to work out the effective COP. Home heating doesn’t need huge differences so the COP might be quite reasonable.
Whether such a system would be cost effective given its complexity is another matter. But I suspect the idea is sound.
Absorbers have notoriously low efficiencies. Their advantage comes being able to use waste heat. I do not remember the exact pressure differences between the high pressure side and the low pressure side but it is around 1 pound or less. Even though the refrigerants used have a very high btu rating for the change of state. NH3 is around 700 BTUs per pound and water is 970 BTUs per pound.
And you could not recover all the heat in the operation. Either you would need electric or if using propane you could not vent the from the primary heat exchanger into the living space.
It would use less power to use an ICE connected to a compressor than run an absorber.
A Stirling cycle engine is a sort of heat pump. I don’t know how it could be used effectively for that purpose when being run from a heat source but reversing the cycle to mechanical operation is used in some cryocoolers.