Are you talking about absorption refrigerators? That's another name for them. I thought they were not efficient at all, and used a different principle compare

Are you talking about absorption refrigerators? That's another name for them. I thought they were not efficient at all, and used a different principle compared to a heat pump. The principle is different but very similar: a continuous cycle of pressurisation, followed by expansion where that part of the system takes in heat from the surroundings and making them cooler. Kerosene has an efficiency approx 90%, according to one site I read. Using gas lowers that efficiency to about 70%. (I don't know why the difference in efficiencies, I would have thought it would be the same, no matter the heat source.)