
Green Material for Refrigeration Identified - vezycash
https://www.cam.ac.uk/research/news/green-material-for-refrigeration-identified
======
makerofspoons
Drawdown.org ranks refrigerant management as the number one way to fight
climate change: [https://www.drawdown.org/solutions-summary-by-
rank](https://www.drawdown.org/solutions-summary-by-rank)

~~~
_verandaguy
Short of digging a pit and lining it with salt, is there anything that a
regular person not actively involved in research about this can do?

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.

~~~
torpfactory
The big issue is what happens to the refrigeration gases at end-of-life
because they have such high global warming potential. The units are nominally
hermetic, so they should last their entire life without leaking much
refrigerant. If you have an old AC unit, try to dispose of it responsibly by
not sending it to a landfill. A responsible recycler/disposal facility will
reclaim the refrigeration gases for recycling or disposal.

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.

~~~
baybal2
CO2 is not an efficient refrigerant, its critical temperature is 31C, but CO2
is darn cheap

~~~
torpfactory
You can also operate the CO2 in a 'trans-critical' mode which gets around some
of the issues of the low critical temp. This is done by using a gas cooler to
cool supercritical fluid in place of the typical condenser.

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).

------
tomatsu
> _The gases currently used in the vast majority of refrigerators and air
> conditioners —hydrofluorocarbons and hydrocarbons (HFCs and HCs) — are toxic
> and flammable. When they leak into the air, they also contribute to global
> warming._

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.

~~~
jabl
I think butane or propane is the standard refrigerant for household
refrigerators all over the world nowadays; the US is the odd man out.

R134a is still unfortunately widely used in cars. Newer cars are moving to
R1234yf, which is expensive, maybe CO2 in the future.

~~~
semi-extrinsic
Mercedes is already doing CO2, and the next-gen EV platforms are going that
route as well, from what I hear. The high pressure of CO2 systems mean that
they're very compact, and thus much easier to integrate with battery pack
temperature regulation, AFAICT.

~~~
jabl
That's good to hear.

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.

~~~
semi-extrinsic
Exactly this, both that they're able to heat the interior of the car, but also
that they can play the role of battery cooling system (just heat a small
radiator instead of inside of car).

------
Animats
Unfortunately this is in _Nature Communications_ , not _Refrigeration and Air
Conditioning_. They have some experimental results on a material. They didn't
even get far enough to build a compressor and heat exchanger using it. No
indication of what the energy efficiency is like.

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]

[1]
[https://www.nature.com/articles/s41467-019-09730-9](https://www.nature.com/articles/s41467-019-09730-9)

------
leguminous
Scanning the original paper linked by _Microft and rmbryan, it looks like the
pressures the researchers used were very high, 0.25-0.5GPa. Maybe someone with
more domain-specific knowledge can answer this: are such high pressures
actually practical? My understanding is that one of the reasons R-744 (CO2) is
not more common is that it requires high pressures, which means specialized
equipment. But the pressures involved here seem to be an order of magnitude
higher even than required with R-744.

~~~
torpfactory
In this case they are compressing a solid, which is much safer than
compressing a gas. There is no explosion risk if the high "pressure" solid is
suddenly released from its container because its volume has not changed by
much. Looks like this solid changed its volume by ~2x (fig 2e). For CO2 the
change is about 28x. If your high pressure CO2 suddenly gets out of its
container, it will immediately expand to 28x its volume.

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.

~~~
camtarn
I'm no refrigeration engineer, but I figure you might need some sort of pulsed
cooling. Compress the solid so it gets hotter, run liquid coolant through it
to extract the heat to a radiator. Then let the solid decompress, and switch
to a coolant circuit that extracts heat from the interior of the fridge and
dumps it in the solid. If you needed continuous operation of both coolant
circuits, you could add a second block of solid material, and switch the
cooling and heat-exhaust circuits between the two.

~~~
gruturo
There is an interesting similar concept using magnetic fields instead of
compression - some materials rise considerably in temperature when immersed in
a strong magnetic field.

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://en.wikipedia.org/wiki/Magnetic_refrigeration)
[https://www.sciencedirect.com/topics/chemistry/magnetocalori...](https://www.sciencedirect.com/topics/chemistry/magnetocaloric-
effect)

------
peteradio
Was going to make some cynical comment about how it's just a new liquid/gas
that we don't know enough about to be scared of yet. Sounds like it's a solid
material that generates cooling from material stresses sounds similar to
piezoelectric.

~~~
_Microft
If you're interested in generation of an electric or thermal current with
heat/electricity, the names to search for are Seebeck-effect and Peltier-
effect.

The piezo effect is when there's charge separation due to mechanimal stress.

~~~
CompelTechnic
Piezo crystals can produce electricity in response to mechanical stress; this
material can produce temperature differentials in response to mechanical
stress. In that regard GP's analogy holds.

------
exabrial
Small point of correction: r-152a is an eco-friendly refrigerant. The article
incorrectly groups all liquid refrigerants together. R12 [and R-134a somewhat]
deserves it's reputation, but that has been out of use in America/Europe for a
long time. It's worth to note in China/India, researchers suspect that R12 is
still in use despite regulations against it.

~~~
HillaryBriss
maybe the fastest way to fight global warming in this instance would be to
commercialize the technology solely in China so that it is adopted widely
there first

~~~
exabrial
I'm not sure why you were downvoted, this is an incredibly important point.
Regulations are so loose in China/India and their population is far more
significant that the USA/Europe.

------
_Microft
Paper (open access):
[https://www.nature.com/articles/s41467-019-09730-9](https://www.nature.com/articles/s41467-019-09730-9)

------
rmbryan
The original article:
[https://www.nature.com/articles/s41467-019-09730-9](https://www.nature.com/articles/s41467-019-09730-9)

------
jtlienwis
I'm surprised no one has mentioned propane as refrigerant. Lots of
environmental benefits. I believe Whole Foods uses it in some of their stores.
Look online for "Propane as a refrigerant. Whats not to love?"

~~~
cvs268
Hi there, Hank Hill.

[https://www.youtube.com/watch?v=9FA__4fLBos](https://www.youtube.com/watch?v=9FA__4fLBos)

------
gnode
This use of a solid for refrigeration reminded me of the elastic band
refrigerator: [https://hackaday.com/2016/08/25/a-refrigerator-cooled-by-
rub...](https://hackaday.com/2016/08/25/a-refrigerator-cooled-by-rubber-
bands/) a not practical but still interesting use of elastic solids for
refrigeration.

------
ulrikrasmussen
Would this be usable for improving heat pumps as well (i.e. for heating the
building instead of cooling it)? It is my understanding that they basically
work as "reverse refrigerators", and that current designs are able to move
about four times as much heat energy as they consume. Would this be able to
improve their efficiency even more, or is there something about the
thermodynamics that I have missed?

~~~
mrob
This doesn't aim to improve efficiency. Most refrigerators use phase change of
volatile liquids to gases and back again. Most suitable liquids were toxic
and/or flammable, so chemists invented the much safer replacement of fully
halogenated hydrocarbons (CFCs). The first to gain widespread use was R-12:
dichlorodifluoromethane (a.k.a. Freon). CFCs turned out to break down in the
upper atmosphere, releasing chlorine that catalyzed destruction of ozone. The
worst ones were banned under the Montreal Protocol treaty, and less damaging
partially halogenated hydrocarbons (HCFCs and HFCs) were developed as a
replacement, e.g. R-22. Modern HFCs like R-134a have even lower ozone
depleting potential.

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.

~~~
Gibbon1
> somewhat controversial because they compromise the excellent safety of the
> earlier halogenated refrigerants.

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.

------
CompelTechnic
A few thoughts after reading this as a mechanical engineer:

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.

~~~
pariahHN
Yeah, I read another article about this material a few days ago and I was
trying to figure out how exactly to handle actually moving the heat. Easy to
do with a liquid, you can pump it fairly easily and piping can be pretty
flexible with routing. Maybe some sort of rotating disk design, with rods
rotating from cold zone to hot zone and static blowers in each zone?

~~~
CompelTechnic
I like that design idea for the rotating disc. It makes me wonder the best way
to stress the material while on the "compressed side."

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...

------
londons_explore
There are already massive efficiency gains to be had in the world of
refrigeration.

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.

~~~
jhloa2
Can you explain to me how an entirely gas-phase refrigeration cycle would
work? The phase change is the whole purpose of the system in a traditional
refrigeration cycle.

------
dm3730
I wish I could understand this article better. I'm wondering how does this
material compare to regular coolants like R22? If I used 1000 watts to
compress this solid versus 1000 watts for a traditional compressor/coolant
scheme, which would generate a lower temperature?

~~~
baybal2
I have no idea how will it gonna work. First you squeeze it, put it into
fridge, unsqueeze it, make it absorb heat, get it out of the fridge, and
repeat.

Don't seem to be an easily automatable work

~~~
code_duck
Pretty sure the mechanisms to do that are built into the fridge - a
compressor, just like current refrigerators but using solids instead of gas.

~~~
baybal2
Hmmm, how do you pump a solid matter?

~~~
Tade0
You don't - you pump coolant around it to exchange heat.

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amitprayal
I hope something comes out of it and does not end up as brief flash in the
pan.

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anfilt
I have read C02 can make a pretty decent refrigerant.

------
hajhatten
Great, but it doesn't solve how most AC units are powered by electricity from
coal.

~~~
giarc
The link provided by another user indicates that the problem with AC units is
improper disposal of HFCs contained within.

"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...](https://www.drawdown.org/solutions/materials/refrigerant-management)

