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.
Compressor chillers with gases like in typical AC have a cop over 3. Why would anyone design district chilling with 3-5 times lower efficiency than that? All that matters is how much energy you spend. Heating that kiln would take more energy if you steal some of the heat for another job, there’s no free energy.
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.
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.
I had an ammonia type fridge in my trailer I lived in, that ran off propane that was pretty great. I had 2 30lb bottles for my trailer and they would get me a month each of refrigeration and stove use for most meals. Filling a bottle cost around 30 dollars. So maybe there was more energy used compared to a compressor type fridge, but the dollar cost to run as well as convince was well worth it since our solar system was able to sustain us year round without a fridge drawing on it.
Yeah that’s the big thing. Absorption chillers can work on marginal heat that isn’t useful for much else except maybe boiler economization. They run at low temperatures but aren’t efficient.
If you have a neighboring cement kiln that exhausts at 300⁰C, that’s perfect for use in district heating or cooling?
It’s basically a heat recycler for trash heat you might throw out anyways.
Let’s assume we need 100MWth of cooling capacity. At a CoP of 5 (generous case) we need 20MWe of power to move 100MWth (120MWth total with our electrical input converted into heat eventually as well)
Comparing that to absorber chillers: A single effect absorber at a CoP of 0.4 needs 250 MWth of heat energy at or above 90⁰C. If you go dual effect you can get 0.9-1.2, but need higher grade heat. I’ll do the worst case for now.
For reference, 250MWth is roughly what goes up the stack in a 125 MWe plant (hilariously tiny plant. Might run a remote community and be a portable turbine generator or two on a trailer? I’ve worked on gas compressors with higher nameplate capacities than that by miles)
A 1GWe coal plant at 33% efficiency burns 3GWth of heat energy and discharges 2GWth up their stack. That’s 2 GWth you have available as waste heat. By definition it has to be vented to atmosphere or to water at the condenser. That’s a lot of already-paid-for heat being literally thrown out.
If you count cooling efficiency using just the thermal watts you have to burn at the powerplant for the electric cooler to move 100MW of heat:
20MWe / .33 = 60 MWth needed to generate it.
If your electric chiller is a more reasonable CoP of 4:
100MWth heat moved, takes 25MWe.
25MWe at 33% efficiency, is 75.75 MWth of heat energy burned at the power plant to make 25MW of electricity.
If you used a dual effect absorber at 1.2 CoP:
100MWth cooling with 83MWth of heat energy at 170⁰C.
What these two numbers show is we can move 100 MW of thermal energy with an electric chiller by burning 60MW (or 75.8MW) of heat we then turn into electricity from a power plant, or 83MW of heat that already was burned, if we steal heat from the flue gasses and use an absorber chiller. The raw energy input to do 100MW of cooling differs by only 23 MW, so an absorber is in the same order ballpark still.
What’s important to note here is the energy needed to run an electric cooler is $money$ while the energy to run an absorber is waste heat going up the stack… These are used on earth already BTW just typically as a combined heat and power plant for universities or government/company campus. There’s no reason you can’t also apply that to an entire city.
For example, Aarhus University Hospital, Denmark uses a 3 MW absorption chiller powered by 105 °C district heating water. It consumes about 4.3 MW of heat to produce 3 MW of cooling, while simultaneously returning useful heat to the district heating network. It’s operated alongside electric chillers so the most economical option can be chosen depending on electricity prices
Crucially you don’t need to oversize your power grid for a summer heatwave peak, when your power lines are hottest (highest resistance, expand, droop lower and maybe short out on trees) so you can instead use literal waste to cool a city instead. Cooling tends to be ⅓ the amount needed for heating roughly, so you a home that needs 12kW of heating roughly needs 4kW of cooling.
2GWth of cooling capacity at 4kW per home is 500 000 homes cooled with waste heat. Of course this is assuming perfect efficiency, but it illustrates my point. District cooling typically uses 1-3% of the cooling nameplate in electrical demand for pumps afaik, so a 2GWth cooling system needs 60 MWe of pumping. To achieve the same cooling with electric chillers you need 571 MWe (assumed 3.5 CoP) just for chilling, consuming more than half of the power output of our 1GWe plant.
Whoah dude, I don’t know, you’re rapidly saying many numbers without connecting the sentences, what is your point? So either you can get the required chilling capacity using a relatively low amount of electricity, or using a shit ton of captured waste heat. Building a big plant just so you can run a chiller on the waste heat is probably not the most logical path. And now you’re also capturing the heat from power lines or what?
I guess the technology you mention makes sense where a lot of waste heat is consistently available for cheap, thanks for sharing the YSK, moving on.
Oh yeah I forget most people have no idea… Sorry about that.
What I’m saying is we’re throwing out fuck tons of free cooling and heating that we could otherwise use. Every house in North America could be cooled and heated with no extra fuel burned from the same power plants and industrial processes that supply them? Roughly speaking?
Why would you pay for electricity for cooling when a capital expense can get you that for essentially free? You don’t have to make the plant burn more fuel, you don’t have to interfere with how the plant runs, you can just tap off low grade heat and make chilled water to supply a town or city (Dubai uses district cooling if you want an example, although they use electric chillers)
This isn’t theoretical. It’s already used on earth and it works really well.
What I was trying to show with my numbers is the heat energy you need to burn for an equivalent amount of cooling isn’t that different compared to a electrical compressor chiller with a CoP of 3.5. 83MW of heat energy burned vs 60MW of heat energy for electric chillers. The difference is you don’t need to buy 83 MW of heat, whereas you need to buy the 20MW of electrical power (which took 60MW of heat) to run your chillers.
My other numbers were to demonstrate the eye watering amount of energy we discharge out of flue stacks and out of heat exchangers into rivers or lakes… If it’s hot enough, that energy can be used for heating and cooling but currently it goes up a stack.
Not saying this whole idea isn’t bad, but there are plenty of processes with waste heat.
It’s not a bad idea it’s been used repeatedly on earth, its just the incentives never lined up to make district heating and cooling a thing everywhere. Sweden and old Soviet cities use district heating since it’s really cheap at scale. Dubai uses district cooling (with electric chillers though) to cool pretty much the whole city for far cheaper than every building having its own rooftop system.
In North America we take the most insane approach of every home having its own miniature thermal plant (furnace) and electric air conditioner. District heating and cooling is a hard sell because trenching in new insulated pipes would be extremely disruptive and expensive compared to if they were already in the ground prior to this. If you could somehow convince everyone to be ok with the disruption and also to have 80% or more of the city hook into the system as subscribers, it would be vastly cheaper than natural gas heat or electrical cooling.
Parts of Ontario use great lake water for cooling, so district cooling is a thing in parts of Canada.
There still are district systems in north America though they just tend to be university campuses, where all of the buildings and dorms are cooled or heated with one central combined heat and power plant.
One of the biggest benefits of district cooling is elimination of one of the biggest drivers of the urban heat island effect: AC exhaust. Every working AC unit makes every other AC unit near it work harder. A district cooling system pipes everything back to one plant where that heat is rejected out the top of a stack.
Thermodynamically it shouldn’t just reduce AC’s contribution to the heat island effect, it should also make buildings themselves into heat sinks helping to cool the city itself as thermal energy tries to migrate into buildings where the district system soaks them up and pipes it away to the cooling plant.