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 if you can find a free or cheap heat source that you’re going to vent to atmosphere up a flue, or dump into a river/lake/evaporation you can make cooling with it for almost no marginal cost once you’ve made the capital investment, plus with very little moving parts. An absorption chiller can be the last useful process on your exhaust heat before venting to the environment and all it costs is maintenance and a few small electric pumps.
You use the kiln exhaust gasses which are waste heat. You don’t need to ask the kiln to burn hotter or with more flue gas mass flow. The absorption chillers are already used in district cooling systems on university campuses and government offices. Usually where you have a combined heat and power unit, so you have your own heat source.
Theres nothing stopping you from using any viable heat source though… Plus single effect chillers run on 90°C. For waste heat that’s literally free heat why not as opposed to paying for power? Double effect chillers need 170⁰C heat for their generators, so a cement kiln could provide the heat needed to run the chillers using their exhaust gasses.
A district heating/cooling setup using low grade waste heat around ~150⁰C, plus a soapstone battery (resistively heats soapstone sand when renewables are over producing and need to either sell at any price or shut down) could provide both heating and cooling with nothing but waste heat and a thermal battery that tops up using over productive renewables.
For the same sized electric chiller, you can use 99% less electricity (you just need low pressure low velocity pumps for moving liquids around the absorption chiller) and the heat can come for free or cheap elsewhere.
Most large heat consumers try to reuse their own heat, and if they can’t they pay to discharge it into lakes, rivers, or evaporate water. If instead a district cooling company paid them for their heat they can turn a cost center into a profit center?
I’m summary, absorption chillers work on heat that’s so low temperature it’s almost useless for anything except boiler economization. That’s the value proposition.
Edit: I keep adding more to this comment as ideas flow. Sorry for the rapid edits.
Heat isn’t free because heat is essentially energy transfer, and energy cannot be destroyed or created, thus it always has a cost.
You might be able to try to somehow “recycle” it by piggybacking off of some heat generator such as nuclear power plant cooling water (which is not likely to be hot enough for any level of efficiency (30-40C only, usually), and also unsure of the ramifications it could have with reduced water flow and increases to flow back pressure), but it is much less likely you will find enough sustainable heat that is a byproduct of something else like that compared to just building a heat generator specifically for that. At that point, why not continue to use the technology already in place?
Not to mention building something to house that can damage the local environment, in the same way data centers do. Resources funneled to it, water diversions, noise pollution, etc. Would the pollution cost of this kind of facility be worth the pay off? Would it be less than the already pretty efficient refrigerators already in use with at least equal performance?
In reality, human existence is pollution. It is not possible for humans to live without some level of environment pollution, because humans don’t really provide anything back to the environment it wasn’t already getting from somewhere else. Humans are perhaps the only creature on Earth that could be deleted and there would not likely be any negative effects of the environment. Earth can take care of itself pretty well without human intervention.
There is currently so much waste heat produced by energy production and industrial processes, that for most of what the OP is talking about, the heat may as well be “free” since it was waste heat that has to be vented. Waste heat needs to be used to mitigate climate change, because waste heat is going to become an issue sooner than later.
So my background is in instrumentation and process control as an engineering technologist. In my country that means I can do limited engineering within my scope of practice, part of which extends into thermodynamics, balance of plant, steam enthalpy calculations, sizing and speccing heat exchangers, boilers, condensers, compressors, turbines, valves, and the controls for all of it.
I’m very familiar with all of this, so I can tell you from experience that these absorber plants can be bolted on after an economizer (in the case of a single effect) or you can supply higher grade heat if you’re willing to sacrifice part of your economizer capacity in exchange for cooling in order to get high enough generator temperatures in a dual effect absorber.
Otherwise you have to trim with electrical resistors to get your preheated water up to the generator temp to run the absorber plant (also viable. Bolt on after the economizer and use a small amount of electrical heat to finish the missing heat to run the generator)
The 30-40⁰C you’re referencing is the condenser temperature at an electrical plant. That’s not the flue gas temperature which can still be quite high depending on the plant, in the range of 80-170⁰C depending on how efficient their design is.
Other processes like cement kilns, glass making, garbage incineration all can produce the temperatures you need for dual effect absorbers.
This isn’t theoretical, you can find these absorbers already in use at combined heat and power (CHP) plants running university campuses and government/company campuses. They are already used for limited district cooling for these places to accompany heating.
The overall benefit is they are extremely low impact on the environment since LiBr is non toxic, isn’t poisonous, doesn’t deplete the ozone layer, doesn’t contribute to GHG emissions like released butane or isobutane emissions would. It doesn’t produce toxic gasses or use high pressure or exotic temperatures or materials.
It also reduces electricity demand for cooling massively. An absorber chiller runs on practically unusable waste heat that’s too low enthalpy for any other use. You get free cooling and the plant is very low maintenance, ingests waste heat that would have gone up your chimney or flue, and spits out cold water. What’s not to like?
The best part is they also work extremely well with renewables making them natural partners if you have a thermal sand battery paired with it. District heating and cooling can run from one very simple plant, which is going to be more and more important as our climate gets more hectic from global warming.