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
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.
Because waste heat is free.
It is never free to actually capture it, and it usually reduces the efficiency of the process you capture it from. Compare for: turbos use “wasted” positive pressure exhausted from the engine. Sure, but in the process they make it harder for the engine to expel exhaust gases. They can only improve efficiency when done well and at the cost of greatly increased complexity and maintenance needs.
If you install heat capturing, 1) you need to adjust the design of the system to adapt it; 2) you impede the heat dissipation efficiency of the system, which you then need to address with additional engineering. It can be done, but it’s not free, and the math on the costs and benefits doesn’t necessarily come out positive. If there is one thing I trust the industry about: if it can be done to save a buck, they are doing it.
I’m going to have to fundamentally disagree with you here. Waste heat recovery boilers have existed for generations, are extremely well understood, and are extremely common. They’re one of the most efficient designs out there for power generation and they can be adapted to work as combined heat and power stations with no loss to the power generating efficiency of the primary boiler or gas turbine.
District heating water at 105⁰C can provide both heat and the energy needed for absorber chillers. Adding the district heating/cooling water tubes after the HRSG isn’t free, yes, but it’s almost free from a capital perspective compared to building a new plant or the cost of a pipeline network + furnaces and ACs in every single home. Especially when you already need to burn energy anyways… 50% of the cost of power is fuel, so if you can reuse waste heat for heating and cooling you reduce electrical demand and make low enthalpy heat into something useful.
Look up combined heat and power plants if you want a reference for what that setup can look like.