I would like to do this on a residential unit just on a smaller scale. But I cant think of what to put in the refrigerant line to act as a generator. I could do this is since I have all the tools.
I think you could use air-conditioning refrigerant, like 410r that is non aggressive to ozone...
In order to make that you are also going to need a vacuum pump
pressure gauges, tubes, flanges and copper tubing
and probably an air conditioning pump to get the gas in....
the idea is indeed very smart... because you can extract more power from the lower temperature side this way...
It could be used to generate energy from solar water panels too! as long as you have cool water to use.
You just need a heat sync and a cold sync