> Researchers use a dimensionless quantity called ZT to describe the strength of the thermoelectric effect in any combination of materials. Two decades ago, combinations such as lead and tellurium yielded ZT values of around 1. After ten years, the search for new, more complex, and more effective materials had yielded ZT values of 2.
These sentences are useless. Going from 1 to 2 probably means doubling the efficiency, if the base value is 0. But even if that's true (which it's not guaranteed to be) is a real-world usable value 3? or 478?
Much later in the article: "Vining predicted in 2009 that a ZT of 4 would be the required threshold for commercialization." There it is. But even with that, the information given tells us very little about the underlying property, or the technology.
As someone who works in this industry - no, thermoelectric heating does not stand at the brink of commercialization. The fundamental issue with thermoelectric heating is that you need a material with high electrical conductivity but very low thermal conductivity. zT is a metric that measures this ratio. Conducting electricity but not heat is a weird property for a material to have and no one even knows if zT can be raised much from where it is today. Even if it could, it would probably be expensive, so you'd probably want to use thermoelectric cooling for things like on-chip computer cooling, not to cool your whole house.
By that standard, a heat pump is something like 400% efficient (it depends on a lot of factors), and replacing an electric heater with a heat pump pays for itself quite quickly if you’re using it to heat an entire house or even a poorly insulated room.
Replacing like for like should be a fairly easy job. But replacing between different systems does seem to be a nightmare.
It's interesting that Americans are retrofitting them into HVAC systems, while in the UK we're trying to retrofit into natgas/water based systems, and seemingly the Scandinavians have gone for .. I'm not sure but it seems cheaper?
I upgraded to a "hybrid" system because it was the least cost / minimal change, so I continue to have natgas hot water which can optionally heat the radiators if the control unit deems it economic (no, it doesn't have dynamic pricing). And that was still £15,000 even though it could reuse all the existing radiators. Apparently having 8mm "microbore" copper plumbing is a problem for "low temperature" heat pump systems, because they rely on higher throughput.
At the end of winter I'll write-up my bills and evaluate the experience.
In Scandinavia we use air to air heat pumps. We generally don't have central heating of any kind so we aren't so tempted to try to shoehorn the heat pump into a system based on hot water.
Air to air is much cheaper and is more efficient because it doesn't need to raise the temperature of the working fluid so much and doesn't require a big fluid to water heat exchanger.
I'm having a Toshiba Polar 35 heat pump installed soon. Nominal output 3.5 kW, maximum output 7 kW. The total cost is 28 kNOK, about 2.6 kUSD, 2 kGBP. Should be enough for the whole ground floor of about 80 square metres.
How do you deal with ventilation? Central unit, or a device per room? Or just opening windows? :-)
> Air to air is much cheaper and is more efficient because it doesn't need to raise the temperature of the working fluid so much and doesn't require a big fluid to water heat exchanger
It might still be worth it to go with water based system if you're going to have underfloor heating. It requires lower water temperatures, so efficiency hit is not that big compared to air-to-air systems (if there is a hit at all).
As a bonus, there are some savings from using the heat pump to heat the hot water for showering and you get the supreme cozyness of warm floors.
On the other hand, now you need some other way of cooling in the summer as underfloor system will not work for that.
Hopefully that lasts! Where I live it didn't use to get hot,
so no one has air conditioning, but for the past three years we've been hit with a week of 32°C/90°f + temperature. Those that can afford it have added air conditioning, but as global climate change kicks in, I'm expecting more extreme weather to become the norm.
I mean, not everyone went out and bought one, a lot of people just put up with it. But a window AC is roughly $200, which fits within the disposable income budget of the middle class.
Do mean air-to-refrigerant-to-air or do you literally mean a big box with ducts coming out? The latter is called a “packaged terminal” heat pump in the US, and they haven’t really caught on except in cheap hotels.
It's two parts, the compressor in a box with a big fan on the outside and a box on the wall indoors containing a refrigerant to air heat exchanger and a fan. The two are connected by pipes, typically three or four metres long, containing the refrigerant.
So yes, air-to-refrigerant-to-air. But your packaged terminal heat pump is also air-to-refrigerant-to-air. Both are just refrigerators turned inside out.
"“Packaged terminal heat pump” means a packaged terminal air conditioner that utilizes reverse cycle refrigeration as its prime heat source, " [1]
Most heat pumps installed in dwellings in Norway are capable of cooling the building as well as heating it. This is the one that will be installed in my house (in Norwegian, Google does a good translation job): https://www.toshibavarmepumper.no/varmepumper-luft-luft/tosh...
Wow, that “packaged terminal” page is terrible. They’re a single object, and the refrigerant doesn’t leave the object. Outdoor air flows through part of it, and indoor air flows through another part of it.
Replacing an AC system with a heat pump might provide you with an avenue to move away from a gas furnace, but I found that avenue to be very expensive. I live in New England and in June 2022 I replaced a broken down AC system with a heat pump. The company installed an electric supplemental heating unit, because the heat pump can work down to only 25F (about -4C) and during Winter it will definitely get colder than that. However, last Winter cost me about $800 more than any previous Winter here (I've lived in the same house in New England for the past 33 years).
After a pipe burst in the baseboard heating system (because it wasn't running, it was only -10F outside, and the pipe passed through a poorly insulated area of the house), I had the HVAC company rewire the system to use the gas-fired, forced hot water baseboard system as the backup. I look forward to much lower heating costs this Winter.
Would a heat pump work? 8 mini-splits sounds like way too. Mini-splits are also the cheaper option, surprised they cost $10k. A heat pump in my area wouldn't be too much more than $10k (excluding duct work).
There are many YouTube videos of people installing heat pumps by themselves in a few hours. Your quotes are likely inflated by permit requirements and price discrimination. Keep in mind that heating with natgas is way cheaper for most Americans so the HVAC guys know that you have money to spare
> Keep in mind that heating with natgas is way cheaper for most Americans so the HVAC guys know that you have money to spare
Where natgas can lose its lustre is on delivery/standing charges. And sometimes transmission and distribution charges (those usually scale with use, but can make cheap gas expensive).
On smaller/well insulated homes, the fixed gas connection cost can really improve heat pumps economics if you're already on electric grid and can cutoff gas entirely. Or have an aux source like oil/propane/wood.
The fun part is that utilities are generally a regulated rate of return business, so as users disconnect, the base costs go up on the remaining subscribers. Pushing more subscribers to disconnect from the gas grid, pushing cost up on the remaining...
I wouldn't invest in natgas distribution companies in mild-moderate climates.
AFAIK the fixed cost of keeping a gas line active is ~$4/mo in most places and many homes still need gas for stoves and dryers so I expect ~0% of Americans to cancel gas in the next decade
Of course the maintenance costs and the amortized cost of infra is a much larger proportion of the gas bill, but the utility can't pass that on to customers as a fixed monthly fee. Gov't tariffs usually make that illegal
CAD$24 or ~US$18 in most of Ontario Canada. But that's every month, so could be 10% or 100% of your bill. But oddly gas stoves and especially gas dryers aren't that common here, despite gas being cheaper than electric (historically, dunno about today).
We got a Mitsubishi Kaiteki[1], which is a mini-split from what I can gather. We just call them "air to air heat pumps" here in Norway.
Anyway, the install itself was about $400, took one guy a few hours like you said. Another $200 for the electrician which had to hook up a dedicated circuit for it as per regulations, though he did it as part of a larger job so would have been $300 as a stand-alone deal.
Total it was $2200. This is considered a premium unit over here, we could have gotten something cheaper but alas looks matter.
Thing is supposedly guaranteed to provide COP of 2 down to -25C. We've had such low temps here a several times (in fact past week has been around -15 to -17C with a harsh 85% humidity, biting!) and we've never had to turn on the backup floor heating so far. Though you can definitely hear it working harder when it's that cold.
Yeah, you can see the two units here[1], also has dimensions for them under specifications.
The plumbing is covered by a plastic cover, both for protection and looks.
We have a small wooden "shed" for the outside unit[2], to protect it from getting clogged up with snow and also to make it less visible. Both the plastic cover and the "shed" is painted in the same color as our home, so blends in nicely.
There are a few zero pipe mini-splits. They hang across the window frame and use 1 inch of height with an inside bidirectional radiator and an external one, SCrewed down to the window jamb and connected to 120/240 volts internally. They resemble a window A/C, but the rads are below the window level and are wider and less deep. I am getting a few next year. This is one of many.
https://www.greenbuildingadvisor.com/article/startup-promise...
If you're system is hooked up to "floor heating", hydraulic stuff that runs under your floor it's still a one man job but can be a little bit harder to do.
(sorry about being a bit off-topic, but I got triggered by standard).
Funny that you mention standards.
It should be possible to swap out the multimedia device in your car with a new one. It should use a standard connector and form factor.
So I guess we should start working on standards that would improve our world and make reuse possible instead of buying even more new shit all the time.
For a mini-split system, or central heat pump? Do you have existing ducts? What's the square footage?
We recently upgraded our central heat pump as the old one died after 15 years or so. IIRC the total was $13k CAD, so around 9-10k USD, which included indoor and outdoor units for a roughly 3000sqft house, with installation. But all the ducting was there already, so it was just a matter of swapping out old unit for new. (Got some nice government grants too, so it was only a few k out of pocket.)
Wow, surprisingly expensive then. It might be worth getting more quotes if you're still interested. I found the ones we got here varied pretty widely, so you may have just gotten a couple of high ones.
>And I don’t get why replacing one is an all day job for three people.
Let's go through the whole process. You need a system changeout for a ducted central HVAC system. Someone comes over and gives a bid. You accept. Your HVAC person needs to go to a supply house and purchase all of the parts and bring them to your residence in a vehicle than can hold everything.
Assuming you have an existing system, the refrigerant has to be recovered with a special recovery pump. You can't just dump refrigerant to the atmosphere. This can take an hour or so.
You've got to find the right breaker(s) and then turn them off. Disconnect the power wiring. Then you've gotta disassemble the old equipment and remove it. Next you move in the new equipment. Rewire the power. Rewire the controls wiring. Assemble the new equipment, assemble plenums, cut holes in plenums, install collars, run duct work from plenums to boxes, attach and seal all ductwork with tape, mastic, etc. You need to strap up the ducts to properly. You still need to solder the line set at this point.
If your new equipment runs on a different type of refrigerant, in all likelihood, you need a new line set (the copper tubes that transport the refrigerant to the evaporator from the condenser and back). Why? Different refrigerants have different working pressures, may require higher flow, etc.
Once you're lineset is soldered back to a condenser AND the evaporator, then you must pull a vacuum on the system to A) remove non condensable gases and B) dehydrate the system so that your refrigerants are clean and the system is efficient. Properly pulling a vacuum is very time consuming. Most guys start by pulling an initial vacuum and then shutting in the system to do a leak test. You may find a leak, this takes more time. You need to repair the leak, then pull another vacuum. Once you past leak test, you pull a final vacuum. You don't want installers skimping on this step as this affects the overall lifespan of the system and system efficiency.
At this point, you can start the system (I've had new units dead from the factory... groan), then you can start charging the system with refrigerant. You need to let the system run for a bit to monitor pressures, monitor return air and supply air temps, etc.
Once the job is done, all of the old equipment and refrigerant has to be taken to specific places for proper disposal.
Everything above is a generally straight forward non-permitted replacement. Other installs may require new circuits run to the equipment, natural gas lines, etc. Some jobs require permits so now the HVAC person has to go to the city, apply for permits, submit plans, have the work inspected, etc.
There's quite a bit of work that has to be done which requires transportation, disposal, specialized knowledge, expensive tools, employees, and most important of all, insurance! Also, keep in mind that a lot of this work is done at temperatures FAR beyond ambient AND in low clearance areas, usually filled with itchy fiberglass. This work is also done with risk of bodily harm (electrocution, poisoning (hello phosgene gas), suffocation (asphyxiation from refrigerants), heat stroke, falls from height, exposure to industrial pollutants like asbestos, burns).
This is a good overview explaining why it's an all-day job, but doesn't explain why it requires 3 people (if that's true). Only moving the equipment in and out is helped by having more than 1 person.
A dishwasher is a single object. A heat pump has an indoor part, and outdoor part, and (at least) two tubes between them. Those tubes can carry one of several refrigerants (with attendant oil contamination), water, or glycol solutions. Or occasionally air. There are quite a few standards for connecting all of these, although the standards for air appear to literally be duct tape [0] or sticky goop called mastic. And refrigerant, which is the most common choice, is under high pressure and needs special handling.
[0] I mean real duct tape: the UL181 stuff. The world is full of kinds of tape, and many of them are excellent. I’ve never seen anything I would call excellent duct tape. It doesn’t conform well to irregularities, and it doesn’t seem to have anywhere near the stretchiness required to actually seal the inherently curved gap between round ducts.
Nope. The really good heatpumps (air conditioners) have a COP of 4 at -7 degrees celcius and a room temperatur of 20 degrees celcius.
In other words, with one part of electrical energy, they manage pull 3 parts of of heat energy from the outside air into the room. Hence, they use just 25% of the electrical energy that a electrical resistance heater would require.
No, because the installer set it up right at 20. We do have a gas furnace that kicks in below that.
It'd be amazing if someone put together some kind of dynamic calculator that could take electricity and natural gas prices and examine inside temperatures based on a smart thermostat system and rejig the cutoff temperature based on all of it.
My Vaillant system claims to do that, but it doesn't have dynamic input of pricing so you have to type it in on the head unit. I'm not sure it's even possible to get an API for dynamic pricing of UK energy prices.
Modern cold-climate heat pumps can definitely handle 20F. Yes they're more efficient at higher ambient temperature, but you can get at least 2.5 COP at 20F. (And good ones can continue to outperform resistive heating at much lower temperatures than that.)
I've been doing a bit of research into air-to-water heat pumps (using a conventional vapor compression cycle) as I'll be installing one soon (Bear with me—I promise I'll get to thermoelectric devices by the end).
They're currently able to replace a boiler for a heating system designed around relatively low-temperature (120°F/50°C) emitters, with lower temperatures leading to better performance (so a large radiant panel in a floor or ceiling is a good choice).
One of the underutilized capabilities they have is to do radiant cooling. The tricky part is that any part of the system that drops below the dewpoint (in whatever space it's located in) will condense moisture out of the air, likely damaging itself or things around it over time. You can address this to some degree by either modulating the heat pump or mixing/recirculating water to keep the emitters a few degrees above the dewpoint, but that limits the amount of sensible heat that you can remove from the space and doesn't do anything for latent heat (i.e. humidity).
One solution is to use an emitter (e.g. fan coil, either central or in a little wall unit like a mini-split) that has a drip tray that drains the condensate away to where it can't do damage, but the pipes leading to the emitters still need to be insulated and vapor-sealed. This isn't terribly expensive to add to a new system but could be quite expensive to retrofit into a system where the pipes are already buried into the walls.
Another approach is to keep the fluid above the dewpoint and use a separate dehumidifier that condenses moisture out of the air and releases the resulting heat into the space. This isn't ideal because you're adding an additional heat source into the space that you're trying to cool.
As I understand it, the strength of thermoelectric devices is that they're silent and relatively small, but their weakness is they're not terribly efficient, especially for cooling, and have a steeper drop-off of efficiency with increasing temperature difference between the cold and hot side.
But for dehumidification, the temperature difference is likely small (from a few degrees above the dewpoint to a few degrees below it), and also the latent cooling load tends to be a fraction of the sensible cooling load.
So the idea would be to build a device that is plumbed inline with the emitter in each room (or possibly just e.g. a bathroom or kitchen) that uses a thermoelectric device to cool a heatsink below the dewpoint (with a fan) and collects the condensate for disposal, but rejects the heat into the return pipe to the heat pump.
The advantage over a conventional fan coil-based system is that the in-wall plumbing (and indeed all of the hydronic plumbing) remains above the dewpoint, so the indoor hydronic piping doesn't need insulating or vapor sealing.
I could see this being especially useful in buildings converting from a condensing boiler to a heat pump and want to add cooling without tearing open all the walls.
Northern Canada we run our wood stoves for ~8 months a year. Temp on the surface of the stove is 200C to 300C. Outside is -20C to -40C.
Let's say an average of 200C temp delta across the TEC.
Throw a radiator on the outside of the cabin, use coolant with a tiny pump to circulate. How much power am I going to generate with a square foot (or two) of TECs strapped to the wood stove, using the coolant loop to cool the other side?
It feels like we have such a huge temperature delta we should be able to do something with.
I disagree with that article for the simple reason that I do not consider burning wood to be sustainable, or healthy for anything with lungs. Wood should be used for long-lasting construction or left alone / carefully nurtured to aid our forests in rebuilding biodiversity.
> I disagree with that article for the simple reason that I do not consider burning wood to be sustainable, or healthy for anything with lungs. Wood should be used for long-lasting construction or left alone / carefully nurtured to aid our forests in rebuilding biodiversity.
In Northern Canada there is almost no other way. Once you are ~10minutes out of town there is no natural gas. Also note wood stoves now are double (or triple) burning with catalytic combustors that extract waaaay more heat from the wood and emit waaaay less particles in the air (because they burn it)
Here in Europe there is so much demand for wood that forests are being grown just to be cut down and turned into pellets - it's not just waste that goes into them.
Maybe it's not as bad as fossil fuels, but it still has the same issues as commercial monoculture farming, which is why there are issues with bark beetles now. And most of these forests start by tearing down old growth forests.
In my vacation house, I’ve got a Hearthstone Heritage wood stove, neither old nor new, and I believe it has been refurbished a bit. When I ran it over Thanksgiving I put an air purifier next to it and ran it on auto. I’d been concerned about air quality with the wood stove. Pleasingly it ran on low and barely blipped when I’d open the door to add logs. Weirdly, it -would- climb up to medium if I opened the door to the garage — I guess it doesn’t like all the varnish and whatnot from there.
So anecdotally, a stove that’s not a rusty old potbelly and has a good draft seems like it could be okay for air quality.
You can sell the trunk of a 200 year oak (though often they’re hollow if they’re that old) but you will have PLENTY of good firewood left behind from harvesting it, with all the branches. The best use of a 200 year old oak is of course to let it be, the backbone of an entire ecosystem. An 80 year old walnut is another story…
Residential pellet stoves sound great but in practice they are not reliable (moving mechanical parts that operate at high temps, electronics poorly shielded from said temps—the manufacturers are pretty shady in my experience), and the cost of fuel varies quite a bit and can be very high. Compare to a wood stove that needs no electricity and can burn just about any combustible solid. Modern wood stoves are pretty efficient, too.
If you run it properly. A good wood stove will run cleanly as well. It’s all about the secondary combustion. An open fireplace will not get hot enough for secondary and be dirty.
you're not wrong per se but no one cuts down a 200 year old oak for construction either. softwood like spruce, fir, and pine is the primary wood for construction (at least in north america).
> I do not consider burning wood to be sustainable
You can't really make such a broad statement. Sure, burning wood isn't a sustainable solution for everyone everywhere, but there's plenty of situations where it's the least-worse option for heating. My parents heat their house with wood they gather from their property which mostly falls naturally. It's impractical to do anything else with it.
Perhaps they could let it decompose - releasing approximately the same amount of carbon it releases in burning - but while that might benefit the local ecosystem marginally, it would also mean they were heating their house with fossil fuels instead.
Doing that pumps energy outside your house without heating your house. A better option is to use the temperature differential between the stove and your house. You get less electrical power, however waste energy from both the stove and the device still heats your house effectively making a system over 100% efficient.
Ie convert 1% of the stoves energy into electricity which you then use to power a fan. The fan‘s waste heat also heats the room thus you get to use both the utility of the fan (1%) + waste heat from stove (99%) + waste heat from fan (1%) = 101%.
You're not going to achieve an over-unity system. Assuming no other losses, you'll be using 100% of heat energy from the stove. The equation is missing a -1% term somewhere.
You’re allowed to make use of the same energy at different points in time. The 1% used by the fan is the same 1% that’s heating your room.
A computer converts 99.9% of the electricity to heat a room just like a space heater. However, you can play video games on the PC while it’s heating your room.
I want a cottage industry of aluminum smelters in cold climates.
Pick up a pile of aluminum oxide from a depot, electrolyze it into aluminum at home, and drop off the finished aluminum at the depot for a cheque that covers your electricity.
"The theoretical minimum energy requirement for this process is 6.23 kWh/(kg of Al), but the process commonly requires 15.37 kWh."
Neat idea. Aluminum smelting isn’t really hands off enough to make this viable at home.
It might make sense at industrial scale while pumping waste heat to nearby office buildings or something. But even slightly higher electricity costs would be a huge issue.
The problem is that heat pumps exist, so resistive heating is never the best option.
An aluminium smelting at home heating solution would have a maximum CoP of 2 (as you're reducing the energy usage of the smelter by the same amount). A heat pump could easily have a CoP of 3 or 4.
You have that math backwards. A smelter turns ~1/2 the energy from electricity into chemical energy and releases the remaining 1/2 as heat thus the COP would be 0.5 not 2. However smelting is profitable because aluminum oxide is less valuable than aluminum which more than compensates for the waste heat having zero value at the smelter.
Thus various schemes for combined heat and power etc which take the valueless waste heat and use it for some other purposes like warming homes or greenhouses etc. So while the COP would be 0.5 the electricity would be subsidized by the smelling process. https://en.wikipedia.org/wiki/Cogeneration
Where such schemes fail is generally economies of scale.
They didn't miss anything. They're just double counting utility. Same thing would happen to get warm next to a computer. You pay for electricity once, and use the computer while getting cozy.
Heating with a wood stove doesn't really have a 'medium' setting. You get 100% while it's roaring away, and that slowly diminishes as the fuel burns down. (Yes you can adjust dampers, and air-flow valves to "slow it down"; but that doesn't really work/happen.)
I've lived in a home heated by a wood stove for 10 years. You would build-up the stove so it blasts away, goto bed, and by morning there would be enough coals left to start it up again but quite chilly in the house.
There is nothing like it. I love it. I don't have the same access my father did to family farms, wood lots, and trees. Today I would look into rocket mass heaters. Spread that heat out and allow it to more slowly heat a house.
You're better off buying a little steam turbine and generating electricity directly off of the stove. On top of the electricity, you get to keep the heat.
Or, better yet, buy a propane tank and a suitably large generac. Then pipe the cooling water into radiators in the house.
What an article of fluff. Doesn’t give any real technical/engineering information. It’s completely useless unless you show us the COP of the system at varying ambient temps. Heat pumps can get to around 4.0 that’s the number to beat.
A whole article for to say that researchers found a ZT of 3.1 for certain temperatures.
This is what since several years ago many researchers are obtaining (those ZT=3.1, that is 20% of efficiency? for eventual temperatures) with a mean of ZT=2 as much. Peltier effect cells remain inefficient, they are electricity guzzlers.
Came for this comment. Why is there no COP/SCOP mentioned at all... If you want to get into the market you should be competitive. And the COP of 4.0 you mention is actually the lower end. I'm heating with an AC as air-to-air heatpump now for the second winter and I chose the most efficient that I could get with a SCOP of over 6. And for the first winter I also could reach these numbers.
Dupont will see that this never sees the light of day. Just like how we don't use butane/propane/CO2 as refrigerants which are just as safe as most of the flourocarbons but have the downside of being too cheap to make any money off of.
Having looked into it more, it appears it is on a country by country basis. And for some uses, flammable refrigerants are not allowed, which further complicates things.
Most of the FC's are highly toxic when exposed to fire.
R-1234yf is not only (slightly) flammable but also releases hydrogen fluoride and carbonyl fluoride when exposed to fire, but this is what is in almost all new cars.
I've run a propane/butane mix in an R12 car before and the fact that it was flammable didn't bother me a bit. The 14 gallons of gas would worry me more than 12oz of propane going up.
> Kinda how we don't use toxic ammonia as a refrigerant.
Ammonia is definitely still used as a refrigerant, just not in consumer equipment. It’s commonly used for ice rink chillers, at least in the US and Canada. Not sure about Europe.
These sentences are useless. Going from 1 to 2 probably means doubling the efficiency, if the base value is 0. But even if that's true (which it's not guaranteed to be) is a real-world usable value 3? or 478?
Much later in the article: "Vining predicted in 2009 that a ZT of 4 would be the required threshold for commercialization." There it is. But even with that, the information given tells us very little about the underlying property, or the technology.