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https://arstechnica.com/science/2023/11/capacitor-based-heat-pumps-see-big-boost-in-efficiency/
Various forms of heat pumps—refrigerators, air conditioners, heaters—are estimated to consume about 30 percent of the world's electricity. And that number is almost certain to rise, as heat pumps play a very large role in efforts to electrify heating to reduce the use of fossil fuels.
Most existing versions of these systems rely on the compression of a class of chemicals called hydrofluorocarbons, gasses that were chosen because they have a far smaller impact on the ozone layer than earlier refrigerants. Unfortunately, they are also extremely potent greenhouse gasses, with a short-term impact several thousand times that of carbon dioxide.
Alternate technologies have been tested, but all of them have at least one major drawback in comparison to gas compression. In a paper released in today's issue of Science, however, researchers describe progress on a form of heat pump that is built around a capacitor that changes temperature as it's charged and discharged. Because the energy spent while charging it can be used on discharge, the system has the potential to be highly efficient.
[...] For hydrofluorocarbons, the difference in heat content can be controlled by altering the pressure. Compressing a gas will heat it up while lowering the pressure cools it down. However, various other materials undergo similar heating and cooling in response to other external influences, including physical stress, magnetic fields, or electric fields. In many cases, these materials remain solid despite experiencing significant changes in temperature, which could potentially simplify the supporting equipment needed for heating and cooling.
In the new work, done by researchers mostly based in Luxembourg, the researchers focused on materials that change temperature in response to electric fields, generically known as electrocalorics. While a variety of configurations have been tested for these materials, researchers have settled on a layered capacitor structure, with the electric field of the material changing as more charge is stored within it. As charge is stored, an electrocaloric material will heat up. When the charge is drained, they'll draw in heat from the environment.
This has a significant advantage regarding the power needed for the device to operate since the current generated when draining the capacitor can just be used to power something. There's a little energy lost during the round-trip in and out of storage, but that can potentially be limited to less than one percent.
Journal Reference:
Junning Li et al., High cooling performance in a double-loop electrocaloric heat pump, Science, 16 Nov 2023 Vol 382, Issue 6672 pp. 801-805 DOI: 10.1126/science.adi5477
(Score: 2) by YeaWhatevs on Sunday November 19 2023, @02:52PM
To actually "pump heat", it needs to remove heat from the source environment, but all TFA does is describe moving excess heat from a capacitor using a fluid. Is there some effect here where the capacitor does work because some of that heat on the capacitor is from the environment? The TFA fails to mention anything of the sort.
(Score: 1, Insightful) by bzipitidoo on Sunday November 19 2023, @02:57PM (3 children)
Consuming energy to cool has always seemed a bit daft. They all work by moving the heat elsewhere, and therefore there must be some cooler elsewhere to dump the heat. In other situations, this heat difference is tapped for energy.
Even more daft is using up energy for only heating. Why not instead run a small server farm?
(Score: 4, Informative) by maxwell demon on Sunday November 19 2023, @03:04PM (1 child)
The point of heat pumps is that you deposit the heat in a place that's warmer than where you remove it. For example your fridge removes heat from the inside, where it is cooler, to your room, where it is warmer.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 5, Funny) by sjames on Sunday November 19 2023, @11:15PM
User name checks out :-)
(Score: 3, Informative) by gnuman on Sunday November 19 2023, @07:30PM
For that, you don't need a heat pump. You could just open a window.
It's a pump, because it pumps heat in the other direction. Like a water pump, pumps water against gravity.
(Score: 2, Interesting) by Anonymous Coward on Sunday November 19 2023, @03:04PM (16 children)
From the DOI link (I can only see the abstract):
20.9 K (size of the "degree" is same as a span of 20.9 C or 37.6 F) differential isn't enough for a refrigerator or a house heater/cooler, but not bad for early days prototypes.
Here's hoping that some development money is thrown at this tech, because current vapor cycle refrigeration is often (in my personal experience) not very reliable. The AC unit we bought for the house about 10 years ago has leaked about every other year (on average) requiring new parts and expensive re-charging. De-humidifiers needed to keep mold from growing in the basement last a few years before they leak and slowly go bad. Car AC seems to have about a 10 year life before major work is needed. The fridge/freezer in the kitchen is doing OK, still working after 15 years, that's about the only heat pump success story here.
(Score: 4, Interesting) by anotherblackhat on Sunday November 19 2023, @05:15PM (1 child)
20°C might be enough for a home heater/cooler for the economically challenged.
Maybe not ideal, but it would change most environments from too harsh to livable.
If 20°C isn't enough, you could stack them.
It reduces efficiency to stack, but with 64% of Carnot for one, a stack of two would still outperform everything being used today.
I'd accept efficiency slightly worse than modern AC if it didn't break down as often.
(Score: 0) by Anonymous Coward on Sunday November 19 2023, @07:04PM
> 20°C might be enough for a home heater/cooler for the economically challenged.
Climate-ist spotted(grin)! Winter air temps here go down to 0F (-18C) so the first stage 20C would barely bring the house inside temp up to freezing--if outside air is referenced. As AC/cooling single stage it might be OK.
For much more money, ground water sourced temp could be used, I've already looked at that for conventional heat pumps. We're on rock, so either extensive rock drilling to make a long trench 4-5 feet (1.5m) deep to get down to constant temperature. Or, drill a deep well--might be cheaper than all that trenching/rock busting.
(Score: 2) by Unixnut on Sunday November 19 2023, @07:09PM (3 children)
I don't know why they don't use stirling engines [wikipedia.org] more often to pump heat? They are reliable enough to be used out in space where maintenance is impossible, they can cool down to cryogenic temperatures, and they have been in production for decades so it is not exactly new technology needing special manufacturing.
Yet for some reason they are almost completely absent from the market. The only Stirling engined end user good I know of is a fridge made by Samsung. I have had one for years now and it is nice not to have to worry about any vapour leaks. It has worked without a single issue hitch (it is also much quieter than vapor cycle fridge freezers).
I would have expected them to be natural solution for inverters and house heat-pumps, but apparently those are all vapour cycle?
(Score: 0) by Anonymous Coward on Sunday November 19 2023, @07:21PM
> The only Stirling engined end user good I know of is a fridge made by Samsung.
Is this still available? Pointers to the product or brand name to make it easier to search, please?
All I could find (Googling from USA) was Stirling ultra-cold (lab) freezers...at a very high price point.
(Score: 1) by khallow on Sunday November 19 2023, @07:22PM
(Score: 3, Interesting) by PinkyGigglebrain on Monday November 20 2023, @01:17PM
Very true.
But sadly NASA's main project to develop a mission ready Advanced Stirling radioisotope generator [wikipedia.org] was canceled due to high costs so there are currently no missions using the tech. The ASRG is still being developed without being a fully funded project so the soonest NASA hopes to have a flight ready unit is 2028.
"Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."
(Score: 1) by khallow on Sunday November 19 2023, @07:16PM (2 children)
They can stack it with two or more stages. This is sometimes done with thermoelectric/Peltier coolers (for example, here [peltier-thermoelectriccooler.com]) which have a similar maximum temperature variance.
Three stages of the story's coolers would be 60 C differential.
(Score: 0) by Anonymous Coward on Sunday November 19 2023, @07:26PM (1 child)
Yeah, sounds easy, just stack two or three stages, right<sarcasm>. First they have to scale up to something more than 4 watts of cooling, that isn't even enough to cool a hot CPU on a motherboard...much less fit into a reasonable sized package powerful enough to heat/cool a house.
Thus my thread Subject of "In 10 years".
(Score: 1) by khallow on Sunday November 19 2023, @07:38PM
Pretty much that easy.
That's the hard part. Doing it one or two more times is far less hard.
(Score: 2) by gnuman on Sunday November 19 2023, @07:42PM (6 children)
So? You could cascade them... there are many other issues to get this tech into production.
Well, this is really a different problem. The problem you are trying to solve is planned obsolescence. Have you heard about fridges leaking coolant every year? So why is your AC? Is compressor overheating or something? That would be first thing I would ask.
https://en.wikipedia.org/wiki/Planned_obsolescence [wikipedia.org]
(Score: 0) by Anonymous Coward on Sunday November 19 2023, @10:07PM (5 children)
> So why is your AC? [leaking]
Best I can tell we got a lemon, with no obvious way to make lemonade. Other products from the same manufacturer were recalled for early failures, but not our specific model... Compressor is, afaik, still OK, it's the condenser and/or evaporator that keep leaking. One side was replaced early on warranty.
Also: The air circulator (simple squirrel cage fan) has lost all its bearing lube a couple of times and frozen solid, so rusty that bearing replacement isn't possible (fan hub rusted on, removal wrecks the fan). I've worked out how to limp along with the current fan by running it for a few seconds, every week all winter, move the dry bearings so they don't weld in place.
Lost a little condensate pump, I think due to bad luck--had just enough water in the tank and when it froze that raised the level-switch...and the pump tried to turn against ice. Now I know to drain that pump after AC season is over.
(Score: 3, Insightful) by RS3 on Monday November 20 2023, @02:50AM (4 children)
As an engineer, and very hands-on, reading your posts about the lack of product quality frustrates me, even though I know it all too well.
I generally observe, to a great extent, that older things were generally made better and last longer.
Over the years economics have pushed and pushed and squeezed engineers and designers to make things cheaper, cheaper, and cheaper still. The #1 thing I'm supposed to have on my resume is: how I cheapened something.
People love to talk about the energy efficiency of that new whatever thing. But nobody seems to calculate in the costs, including energy use and CO2 production, of making new ones of that thing, or repairing that newer thing, versus keeping that much older thing. It's all about short-term profit and/or energy efficiency.
A friend has a 1950s GE refrigerator in his late mom's basement. Several times he's talked about getting rid of "that old thing". Well, it still runs. As far as I know has never had service. It's dead quiet. It was designed and made when people took great pride in making quality products. Interestingly it has great market value now.
The evaporators and condensers you mentioned are great examples. They used to use much thicker copper tubing and aluminum fins. Way back they may have been copper fins. Now they're so thin they corrode and fail, sometimes within a year.
I have a 30-year old window AC that still works. I don't use it a lot, but one of the things I did to preserve it was to paint some of the internal parts, where they get wet at the bottom, with some anti-rust paint. Also I drilled a hole to allow the water to drain out in off season. I plug the hole for summer because the cold condensate gets sprayed onto the condenser and improves thermal efficiency.
My solution: if govt. wants to force higher efficiency heat-cycle products, I'm okay with that, but also force very long full warranties. Yes, things will cost more initially, but how nice it would be to have a thing last 10, 20, 30, or more years.
(Score: 2) by slap on Tuesday November 21 2023, @04:22AM (3 children)
Our house AC unit is 35 years old, and we live near DC so it gets used a fair bit in the summer. It still works fine, and hasn't been touched for servicing in about 10 years. While a new unit would be alot more efficient it wouldn't last nearly as long.
(Score: 2) by RS3 on Tuesday November 21 2023, @06:00AM (2 children)
That's pretty impressive. What brand unit?
If economics worked the way my Utopian fantasy wishes it would, someone would sell better / ruggedized things for those of us who prefer better quality. I don' t mean Bentley prices, but something reasonable for what it is. What saddens me is that as companies "optimize" (cheapen) products, they don't lower the price, rather raise the price, advertising "NEW!", and people don't have much choice about what they buy. I know someone who has a seashore vacation property and the outdoor heat pump units maybe last 5 years due to corrosion. I haven't researched it but maybe someone makes a unit that's more resistant to the salt air.
(Score: 0) by Anonymous Coward on Tuesday November 21 2023, @03:30PM (1 child)
I'd certainly pay more for a ruggedized house AC, if it was backed up by a long warranty (10 years or more). But it would have to be from a company that seems likely to stick around for the duration of the warranty. Haven't seen anything offered like this, but maybe it's out there?
Possibly related? The newer high efficiency units have much more heat transfer surface than older units. This means thinner fins, more fins, and more tubes to get the working fluid to the fins. These all sound like increasing the "attack area" for leaks and corrosion. Maybe it's the nature of high efficiency to have more leaks?
After several basement dehumidifiers lasting only 2-3 years (they leak and slowly quit working), we bought an extended warranty on the most recent one. Luck of the draw, this one is still doing fine after a few years and maybe we wasted that 10- or 15% extra cost of the warranty?
(Score: 2) by RS3 on Tuesday November 21 2023, @06:51PM
I wish you'd come out of hiding.
Yes, I forgot to mention, but I'm sure I did elsewhere recently, that 10-year warranty should be required by law. Things would have to be made better, and no more "fly-by-night" crap from nobody-knows-where with some old good recognizable but now defunct company's name on it.
Thermal efficiency:
- More surface area- yes, absolutely, pretty much intuitively obvious (to me anyway).
- Thinner fins: no, no, and no. The fins have to conduct the heat away from (or into) the tubes carrying the refrigerant, right? Thinner means LESS heat carrying ability. It's only done because CHEAPER.
- Okay, I'll give you that thinner fins allow more of them per unit area (volume) but as I'll mention further down, they fail sooner and the long-term net result is more waste, which is BAD for environment and overall efficiency.
- Oh, another thing: thinner denser fins = more clogging with dust and debris. So NOT good for efficiency.
- Thinner tubes: I'm not an ME but still very good with thermo. I'll state, unqualified but strong hunch that thinner copper tubes have immeasurable effect on efficiency. They're thinner because it's all about being able to make something that lasts just to the end of the warranty.
A good friend recently did a major research on dehumidifiers. He came up with commercial / industrial ones, some cost more than $1K, but are so efficient they'll pay for themselves, and typically last more than 10 years. I don't know the brand he chose, but he found them at Global Industrial. Some are "Global" branded. It's easy to do a web search and find them (search: "global industrial dehumidifier"). The warranties are not what I want to see, but they're made so well they'll last much longer. One feature many have: "rotary" compressor. Very little vibration, which (should be intuitively obvious) causes metal fatigue and cracks. One thing I notice a lot and hate: newer refrigerant compressors vibrate BADLY, compared to much older stuff. Friend's 1950s GE refrigerator: you can't hear the compressor running. Putting you hand on it, you can barely tell it's running. Designed and made before they figured out how to cheapen things.
Vibration + too-thin tubing = early death.
Finally to mention: the harmful refrigerants are getting into the atmosphere much more than they used to due to high compressor vibration and thinner tubing.