Absorption coolers use heat to regenerate their refrigerant. Two common types are a water vapour-LiBr chiller, and an ammonia-water chiller (in fact Einstein patented a mini bar chiller design still used today that has no moving parts, using just helium or hydrogen and gas absorption/evaporation to move refrigerating gasses around)

Single effect chillers have a low Coefficient of Performance (CoP) roughly around 0.4-0.6, meaning for every watt of heat you apply to a single effect chillers, you move 0.4-0.6W of heat, but they only need a minimum of 90⁰C in heat to power them.

Double effect chillers can reach 0.9-1.2 CoP.

Flue gasses are typically hotter than 90⁰C, so you’ll often see absorbers part of combined heat and power systems. Cooling in the summer, heating in the winter. All using waste heat from power generation.

What I find the most fascinating about them is they work using heat. The only power you need to apply is for a few pumps to move fluids around at low pressures, otherwise the primary refrigeration energy comes from heat regenerating the refrigerant.

I’ve often wondered what a district cooling system using these would get for efficiency if you colocated it with something energy hungry like a cement kiln or glass kiln.

Video of how a double effect chillers works

District cooling video

Edit: these are used already for district cooling, just usually for a campus like a university or government complex. The big benefit is you can run them on marginal heat sources, even off of low grade geothermal.