Green Material for Refrigeration Identified
cam.ac.uk
cam.ac.uk
I'm specifically curious about things that can be done in apartments or condos, where flexibility is low, but I'm also interested tangentially in solutions for (detached) home owners living in sparser settings with more control.
There really aren't good alternatives available for purchase right now. Almost all units sold today will contain gases which have low Ozone Depletion Potential but still have high Global Warming Potential (~2000-9000x as potent as CO2).
There is a heat pump hot water heater available from Sanden using CO2 (ironically) as a refrigerant, which has a GWP of 1. It is pretty darn expensive.
This whole area is really a place we need some startup innovation. Both products that use something other than HFCs for refrigeration and some kind of business model or non-profit which will have the goal of getting old units out of the hands of consumers responsibly.
There aren't really many good alternatives that are cheap, have very low GWP (less than 100), are non-toxic and non-flammable. HFOs are probably the closest to this, but even these are often mildly flammable and typically quite expensive (often > $50/kg).
Considering someone stole the AC unit off the roof of the house next door to me in the middle of the night (it was a rental property and nobody was currently living there).
You know - meth.
Anyhow - something tells me there might be some valuable material inside an AC unit, so why anyone would just take it to the landfill (unless it has an A/C recycling program - some do)...
(Or, you know - meth...)
People are so worried about a little isobutane or propane in their refrigeration devices but we have constant pressure tubes forcing methane into many of our homes at 60psi. HCs would be great refrigerants and I think we can deal with the flammability...
https://inspectapedia.com/plumbing/Gas_Pressures.php#Natural...
Worth noting that coming in at #4 is the one we can all contribute to right away -- https://www.drawdown.org/solutions/food/plant-rich-diet. The amazing thing is your dietary choices impact those around you as well so you end up having a > 1 person impact!
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If you want to make the argument that cows eat plants, while true, often they spend the majority of their lives eating grass. Feed lot stage is generally near slaughter. In addition, many farms use by-products of things such as sugar production to feed animals (molasses, beet pulp pellets, etc...). The only reason corn is used is because it is the single most subsidized crop in America.
This is not a clear cut statistic at all.
Then there’s the opportunity cost for all the land that is used to farm annual crops for animals. That land could be regenerating healthy soil, and capturing carbon.
Bottom line, the official numbers aren’t by far an accurate picture. Animal agriculture, even in America, is a huge piece of the climate puzzle.
R-600a (isobutane) only has 3.3 times the GWP (global warming potential) of CO2 and for a fridge you only need about 80g. For safety reasons, the limit is 150g.
For comparison, the GWP of R-132a is 1,430 and R-12's is 10,900.
R-600a has mostly replaced R-132a in Europe.
Isobutane is of course flammable, but the operational pressure is very low. Aerosol cans also use isobutane. It's comparable to those.
Protons jump across the membrane, creating a small pressure differential that is allegedly big enough to do heat pumping.
Of course, when ammonia leaks, it does some nasty damage.
R134a is still unfortunately widely used in cars. Newer cars are moving to R1234yf, which is expensive, maybe CO2 in the future.
This makes switching to a new gas much harder as the infrastructure for reclaim/recycle does not exist for the new gas, no mater how safe or better it is.
I think the interest for EVs might be due to CO2 systems being capable of working as heat pumps as well, producing hot air. Otherwise you'd waste a lot of electricity in cold climates.
The "problem" with R12 was that it breaks down in the atmosphere in short order (less than 10 years by some calculations). Most of the replacement refrigerants are basically inert. The estimated lifetime of r134a is 50,000 years. So even tiny leaks over a long period are going to do incredible damage to the climate. This was known from the beginning and is by design (the stable molecule bit).
But even now decades later the political ideology that AC units were the "problem" persists, despite the fact that its well documented that CFC's were used for everything from propellants in consumer products like silly string and hairspray, to large scale industrial uses like popcorn production (again recently in china).
Yet in all this time, we haven't really found a better set of refrigerants.
In the end, we would be better off bringing R12/22/etc back with the stringent controls for licensing/recovery/recycling/leak detection/etc that was put in place when they were banned. Combined with proper systems engineering to avoid leaks that are now required due to the refrigerants being extremely flammable or generally dangerous to human life we would both solve the problems of them being in the atmosphere, while avoiding the engineering problems of designing AC units that have to compress azeotropic compounds to extreme pressures, or function close to their critical points in tropical climates or any number of other problems with lubrication/etc.
We already have thermoelectric coolers, which have no working fluid and don't pollute. But they're too inefficient for large scale use. Good for CPU coolers, though.
Actual paper: [1]
if you hang a tensile load of 1000 Newtons from a 1mm x 1mm rod, the rod is under 1 GPa of stress.
This is all I saw to address the pressures required:
> Our higher operating pressures do not represent a barrier for applications because they can be generated by a small load in a large volume of material via a pressure-transmitting medium, e.g., using a vessel with a neck containing a driving piston, whose small area is compensated by its distance of travel.
Gasses can store tons of energy if you get them up to these pressures so it's a hazard to anyone near the thing. If you have gasses in your high pressure system and something fails it can result in shrapnel. Hydraulics can do something similar with spring forces in the casing of the machine, but it isn't nearly as energetic!
There is of course a question about how exactly you build a mechanical device to implement this cycle. In current devices the material which changed temperature physically moves around a circuit and removes and deposits heat energy at different places in the circuit as it moves. They definitely don't talk much about how a practical device could be constructed.
Extract heat to a radiator, turn off the electromagnet, open the coolant circuit valve. It's called Magnetocaloric effect and they were considering it for in-car AC a few years ago, dunno what came of it.
https://en.wikipedia.org/wiki/Magnetic_refrigeration https://www.sciencedirect.com/topics/chemistry/magnetocalori...
The piezo effect is when there's charge separation due to mechanimal stress.
However, ozone depletion isn't the only problem. CFCs/HCFCs/HFCs are also very effective greenhouse gases, often trapping thousands of times more heat than CO2. In an attempt to solve this problem, another class of refrigerants was invented: the hydrofluoroolefins (HFOs). These have low ozone depletion potential, and low global warming potential, but they are somewhat controversial because they compromise the excellent safety of the earlier halogenated refrigerants.
Solid state refrigeration avoids the whole problem, so if it's possible without harming efficiency, as the article suggests, then it's an obviously good idea.
I suspect that modern refrigerators designs/manufacturing can negate a much of that. Higher efficiency better insulation means less refrigerant. Better construction means lower chances of a leak. And flammability of HC refrigerants varies wildly. All you really want to if there is a leak not to create a flammable mixture in a standard sized room.
1. My understanding: this material relies on mechanical work (force x distance = work energy) to add energy to the material by compressing (or tensioning, or "magnetically stressing", which I don't understand) it. Some fraction of this energy is converted phase transitions which absorb heat, and some fraction is retained as spring potential energy. If the material is then heated by ambient air, and then the material is allowed to expand, it will now be at a temperature above the ambient temperature at the start of the cycle. In this way it is similar to a standard refrigeration cycle- just without pipes.
2. The cycle described in point 1 is not particularly unique to this material. You could do a similar process with any mechanical spring (google "rubber band heat engine"), and achieve similar results. This material is likely uniquely well suited to this application because it has usefully large amounts of heat associated with phase transitions at temperatures that correspond well with the temperatures used in a refrigeration cycle.
3. You want the material to dump heat to a hot reservoir while hot and suck heat from a cold reservoir while cold. Standard, fluid based refrigeration cycles do this by pumping the refrigerant to different locations (the condensor and evaporator). (I am assuming) This process would have to open and close dampers to get the hot reservoir air and the cold reservoir air to flow across the material; otherwise you have to move the material between the two locations. Both of these sound expensive/tricky to me.
4. A large challenge here is creating an electrical actuator that can compress the material. It would the following design objectives/constraints:
4a. The material should be shaped into long, narrow rods, or another shape with a large surface area, to be ideal for maximum heat transfer with the air of the hot and cold reservoirs.
4b. The actuator must recover the work energy provided when the material is allowed to expand.
4c. The actuator will have a very short stroke (solids do not compress very far), and large force.
4d. The actuator must last many thousands or millions of cycles without wearing out.
5. This style of refrigeration does not have any higher theoretical or actual efficiency than a fluids-based cycle. However, refrigerants have historically been environmentally damaging when released to the atmosphere. R-12 kills ozone, and is obselete/ outlawed. R-134a is currently in a lot of new systems, there are also newer refrigerants being put into new cars. The only thing particularly bad about R-134a is that 1 kg of R-134a equals several thousand kg's of CO2 in terms of global warming effect.
1. Make the edge of the disc rub against a low friction, spring-loaded compressing element (similar to commutator brushes, but designed to really transfer a large load). This is probably infeasible because friction would eat more energy than your cycle would move.
2. Have electric actuators that are mounted on the disk itself. These would have to be powered by slip rings via the shaft. These would be active for half of the cycle and inactive for the other half. Not sure whether they should be radial, azimuthal, or axial mounted. Seems kludgey.
3. Have the disk pass through a magnetic field, exploiting the magnetic effects the article mentions. I have no idea of any of the implementation details of this, but it sounds like a better idea than 1 or 2...
If you want to cool, you pump heat outside by stopping the water cycle when the material is cold, thus allowing the water to dump it's heat into it.
If you want to heat, you pump heat inside by stopping the water cycle when the material is hot, thus allowing the water to absorb the heat from the material.
You can increase the efficiency of this by having more water touch bot the inside and outside phases (increase material surface area in contact with water and increase surface area of water cycle heatsink).
If you want to allow sub-zero temperatures, add anti-freeze to the water.
1. Mechanical compression using hydraulic fluid and electric pumps? 2. Could the hydraulic fluid be used as the heat transference mechanism? 3. Could this material be used in a liquid Sterling cycle pump?
I'm thinking a combination of these might be the answer; the material at one end of a closed cylinder with a piston compressing hydraulic fluid, and the reciprocating motion through some means (and the hydraulic fluid) moving the heat from the material one end to the other end of the cylinder (where it could be dumped).
For example, in a typical refrigerator loop, there is a restriction to slow liquid flowing from the condenser to the evaporator. A turbine here would collect energy rather than waste it in the joule-thompson effect.
Also, refrigeration typically uses a phase change (liquid to gas usually), but the use of phase changes is incompatible with efficient use of counterflow heat exchangers. Future efficient systems will be entirely gas-phase.
Reciprocatibg cylinder compressors also have large losses to the walls of the cylinder, which for high efficiency need to have no thermal mass, which obviously isn't possible. Turbines are the future for efficiency there.
Don't seem to be an easily automatable work
"HFCs, the primary replacement, spare the ozone layer, but have 1,000 to 9,000 times greater capacity to warm the atmosphere than carbon dioxide."
https://www.drawdown.org/solutions/materials/refrigerant-man...