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Nano-engineered thermoelectrics enable scalable, compressor-free cooling

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Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#51

Post by dartharva »

fnordpiglet wrote: post #7

Thermoelectric cooling needs as much research as possible. Mechanical cooling is extraordinarily space consuming. CHESS has the potential over the next 10 years to largely replace vapor compression in most systems other than the most extreme gradients or scales. They are small enough to incorporate into most devices and would allow smaller devices more thermal load. In some ways I think efficient TEC like CHESS could…

Wait, won't thermoelectric cooling need a LOT more surface area to have any comparable cooling performance to compressor-based systems?

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#52

Post by NortySpock »

wrigby wrote: post #49
bigattichouse wrote: post #43

A lot of people throw around 5% efficiency for Peltiers, and it's just not true - it depends heavily on the temperature differential and current vs. IMax. You can (with care) drive them >2.0 COP. This isn't anything like a compressor or heatpump system, but Peltiers get a bad rap... they move heat really well if you're not pushing them to the edge. Here's a nice chart. At 10k difference and 0.1 current max, you're ov…

I didn’t know this, and it jumps out to me because 10k is pretty much the exact difference between room temperature and wine fridge tenperature - I wonder if this is actually not a horrible application for peltiers?

Found a wine fridge at the thrift store last month, pulled the model number, realized it was basically a Peltier cooler and a fan, and thus likely to be still operational. Powered up just fine, so...

$10 and an hour of deep cleaning later, and now we have a wine cooler in our basement. I don't recall the specs or power consumption offhand, but it does keep my beverage-of-choice a few degrees cooler than ambient. :)

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#53

Post by knowitnone »

s_tec wrote: post #21

Thermoelectric cooling is pretty inefficient, because the materials need to balance competing requirements: - Good thermal insulator - Good electrical conductor - Good semiconductor This is because the hot & cold sides are sandwiched closely together as a PN junction, so once you move heat from one side to the other, it just leaks right back. Mechanical cooling doesn't have this problem, because the hot & cold sides…

that's an idea but would you not have to power each one which then destroys efficiency anyway

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#54

Post by johnnyjeans »

petermcneeley wrote: post #3

> the APL team achieved nearly 100% improvement in efficiency over traditional thermoelectric materials at room temperature Peltier effect refrigeration has very low efficiencies (5%) so while this is an amazing accomplishment it will not replace other more mechanical cooling methods.

I'm not sure why we would want to replace mechanical systems. A portable AC unit with 10,000 BTUs uses ~650wh these days, and it'll turn a 50m^2 apartment into an icebox. That's not much more than a flagship GPU pulls. This is also about the least efficient class of aircon you can get.

Sure less energy usage is always better, and if we could get the same out of mere single digit wh power draws that would be cool. But I don't think thermoelectrics are ever going to get us there.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#55

Post by quickthrowman »

bigattichouse wrote: post #43

A lot of people throw around 5% efficiency for Peltiers, and it's just not true - it depends heavily on the temperature differential and current vs. IMax. You can (with care) drive them >2.0 COP. This isn't anything like a compressor or heatpump system, but Peltiers get a bad rap... they move heat really well if you're not pushing them to the edge. Here's a nice chart. At 10k difference and 0.1 current max, you're ov…

You can get 4 COP with a regular air cooled chiller and up to 7 COP if you add an evaporative cooling tower.

Variable frequency drives have made running pumps and fans a lot more efficient, even residential HVAC equipment is starting to get EC motors or VFD driven A/C motors. I can run my 10,000 BTU (1kW) window unit at 68F for an entire month in the summer and it only costs $50 due to the variable speed fans and compressor pump.

What’s the use case for peltier coolers, wearable cooling?

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#56

Post by knowitnone »

NortySpock wrote: post #52
wrigby wrote: post #49

Earlier quoted context omitted.

I didn’t know this, and it jumps out to me because 10k is pretty much the exact difference between room temperature and wine fridge tenperature - I wonder if this is actually not a horrible application for peltiers?

Found a wine fridge at the thrift store last month, pulled the model number, realized it was basically a Peltier cooler and a fan, and thus likely to be still operational. Powered up just fine, so... $10 and an hour of deep cleaning later, and now we have a wine cooler in our basement. I don't recall the specs or power consumption offhand, but it does keep my beverage-of-choice a few degrees cooler than ambient. :)

power consumption is worst than compressor system

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#57

Post by frankus »

wrigby wrote: post #49
bigattichouse wrote: post #43

A lot of people throw around 5% efficiency for Peltiers, and it's just not true - it depends heavily on the temperature differential and current vs. IMax. You can (with care) drive them >2.0 COP. This isn't anything like a compressor or heatpump system, but Peltiers get a bad rap... they move heat really well if you're not pushing them to the edge. Here's a nice chart. At 10k difference and 0.1 current max, you're ov…

I didn’t know this, and it jumps out to me because 10k is pretty much the exact difference between room temperature and wine fridge tenperature - I wonder if this is actually not a horrible application for peltiers?

I think the gotcha is that you need a beefy heatsink and fan (and power for the fan) to keep the hot side anywhere close to room temperature.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#58

Post by frankus »

quickthrowman wrote: post #55
bigattichouse wrote: post #43

A lot of people throw around 5% efficiency for Peltiers, and it's just not true - it depends heavily on the temperature differential and current vs. IMax. You can (with care) drive them >2.0 COP. This isn't anything like a compressor or heatpump system, but Peltiers get a bad rap... they move heat really well if you're not pushing them to the edge. Here's a nice chart. At 10k difference and 0.1 current max, you're ov…

You can get 4 COP with a regular air cooled chiller and up to 7 COP if you add an evaporative cooling tower. Variable frequency drives have made running pumps and fans a lot more efficient, even residential HVAC equipment is starting to get EC motors or VFD driven A/C motors. I can run my 10,000 BTU (1kW) window unit at 68F for an entire month in the summer and it only costs $50 due to the variable speed fans and com…

I'm not sure of the exact reasons but you don't really see vapor-compression heat pumps in the tens- to low-hundreds-of-watts range. So I suspect there are some scaling factors where the reduced size/noise/complexity of a solid-state device starts to be more important than the extra energy that it uses.

I think most of the commercial bed cooling systems are thermoelectric (ChiliPad, Eight Sleep) and they seem to work fine, but by the time you get to the scale of a small fridge or dehumidifiers the products are generally awful.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#59

Post by londons_explore »

dvh wrote: post #37
ajb wrote: post #25

Earlier quoted context omitted.

Twenty years ago there was a company trying to commercialise thermoelectric cooling based on a vacuum gap: https://web.archive.org/web/20031213235132/http://www.coolch... They claimed 55% Carnot efficiency based on a 30-100 angstrom gap maintained by piezoelectric controllers, and a method to construct large electrodes with matched surfaces so that the gap could be maintained over a large area. It all sounded plausib…

But isn't condensation based cooling like 500% efficient?

A Carnot heat pump maintains the temperature in a house at 20C on a day when the temperature outside is 5C. What is the coefficient of performance of the heat pump?

The coefficient of performance (COP) of the Carnot heat pump is 19.5.

The coefficient of performance of a typical heat pump in a british home is around 4.

There is obviously a huge difference between 4 and 19.5 - although a good chunk of this is explained by large temperature differentials in the condenser and evaporator, and a british desire to use a water heating loop.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#60

Post by londons_explore »

frankus wrote: post #58
quickthrowman wrote: post #55

Earlier quoted context omitted.

You can get 4 COP with a regular air cooled chiller and up to 7 COP if you add an evaporative cooling tower. Variable frequency drives have made running pumps and fans a lot more efficient, even residential HVAC equipment is starting to get EC motors or VFD driven A/C motors. I can run my 10,000 BTU (1kW) window unit at 68F for an entire month in the summer and it only costs $50 due to the variable speed fans and com…

I'm not sure of the exact reasons but you don't really see vapor-compression heat pumps in the tens- to low-hundreds-of-watts range. So I suspect there are some scaling factors where the reduced size/noise/complexity of a solid-state device starts to be more important than the extra energy that it uses. I think most of the commercial bed cooling systems are thermoelectric (ChiliPad, Eight Sleep) and they seem to work…

machining metal parts to tight tolerances when they're only a millimeter wide is awfully expensive.

But making tiny things with lithography is really cheap (in volume).

The middle ground is what one needs for a 10 watt vapor compression pump. And to my knowledge nobody has built a 1 watt pump with lithography - although an array of electrostatic scroll compressors does look like it could work.

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