Pretty soon, heat pumps will be able to store and distribute heat as needed
(sintef.no)126 points by PaulHoule a day ago
126 points by PaulHoule a day ago
I was interested to learn about cold district heating recently, which is basically a municipal scale geothermal system.
It uses phase change (solid to liquid) to store heat at about 200 kJ/kg. Compare this to heating water in a boiler from 10c to 60c - stores 209 kJ/kg.
So we already have an effective way to store heat which can work for decades without servicing and is also cheap to produce (in terms of money and energy consumption).
The article omits some critical details:
It says this is both a "heat pump" and also "storage" AND says that it will run when electricity is cheap or plentiful. Thus:
1: Where does it pump the heat from? (Or is this not really a "heat pump" and instead is using resistive heating?)
2: How long does it store heat? Is this something that will store heat on a 24-48 hour basis, or will this store heat during the spring / fall when longer days mean extra power from residential solar, and then use the heat in the winter?
3: Is the unit itself "warm" when storing heat? Or is the heat stored in a purely chemical way and needs to run through a catalyst or similar to get it back?
4: Can this be scaled up for general domestic heating?
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Just an FYI: There are plenty of schemes with resistive electric water tanks to store heat when power is cheap.
I would guess that is intended for a daily cycle, perhaps using air source heat pumps at times of day when the air temperatures are higher and electricity prices are lower, then using it as required.
As it works on phase change (e.g. think of melting ice) heat is added (or removed) without changing the temperature of the store (which, I guess, might be hotter or colder than where the heat is extracted or used).
1. The device is just storage. It would be paired with an air or ground source heat pump.
2. With good insulation you can easily store heat for a day which is all you need. You're never going to get close to storing summer heat for the winter. That's not impossible but not feasible for something this scale (and not cost effective at any scale).
3. You just heat it up and cool it down. There are no fancy chemical processes happening other than the phase change. It's exactly like a phase change hot/cold pack you can buy on Amazon.
4. I'm pretty sure this is designed for domestic heating...
It's kind of an obvious idea tbh. I don't think they've done anything super innovative... They made an aluminium heat sink..
the only new thing- no matter how they do it- is putting it on residential instead of commercial or industrial installs.
my childhood public school took us to some big commercial building- I think it was Sears' HQ- and they proudly showed us the huge blocks of ice providing chill during the day.
In this work the authors use a ceramic-coated extruded aluminum heat spreader to improve thermal conductivity through the bulk PCM, but I wonder if the graphite flake+powder additive demonstrated recently by Tech Ingredients[1] would be a viable alternative? It might need a stabilizer (thickener) to prevent the ingredients from separating.
Perhaps I am missing something; this product already exists as the Sunamp Thermino.
https://sunamp.com/en-gb/hot-water-solutions-thermino-range/
It also exists, as described in the headline, as a tank of heated water.
The phase change stuff has positives like taking up less physical space but it's also a much less mature tech than storing hot water.
It's funny how useful water is for power generation.
There's heat storage as discussed here.
Or you can store cold water in a reservoir as a giant battery, pumping it up high when you've got excess power, and letting it back down to generate hydroelectricity from it later.
Or you can boil water to make steam that spins a turbine and use it to convert anything that can heat water (coal, oil, nuclear...) to electricity.
> It's funny how useful water is for power generation.
It's gravity that does the generation. Water is convenient because it's weight per unit of volume is very high. Higher than most things we can get our hands on and it's also exceptionally safe.
Since water isn't perfectly clean the main problem you face is corrosion. Which can take a great system and turn it into a nightmare of buried leaks and sudden problems.
As far as our options go it _is_ really convenient.
Indeed.
In the UK there was a unfortunate trend of ripping out these energy storage devices and replacing hot water tanks with on demand electric hot water heating ( only heat the water you need ). And new builds often have no tanks ( as it saves space in the new tiny homes ).
Very short sighted in my view - a very simple way to store energy and everyone uses hot water directly.
They don't work well with heat pumps. Heat pumps lose efficiency as the differential increases, so if you try to store heat in a tank, you quickly drop capacity and efficiency.
Versus resistance, which is exactly as efficient at 0°C and 1000°C, and why those storage heaters used to make sense.
(And storage is directly proportional to temperature differential above interior ambient)
My hot water tank once fell off the wall. On Christmas day. Expensive repair.
Hot water tank was in the basement, which was not insulated. So the mass of hot water contributed very little as a heat reserve for the house.
House was in a northern clime.
You are right in your analogy.
Earth's oceans and seas act as giant heat sinks.
And that means more trouble as global climate change impacts..
https://www.earth.com/news/ocean-warming-broke-records-for-4...
I've been keeping an eye on heat pump water heaters for awhile, but right now they mostly make sense in warm climates. The big problem is they're still specialty products and marked up like crazy, but also they tend to use cheap components which makes them loud and prone to failure. If you run A/C for the majority of the year then they pay themselves back reasonably quick, barring early failure, but in colder climates they make your house work that much harder to keep the space warm.
The most optimistic hope is that the government mandate will force enough demand that manufacturers can enjoy some economies of scale and actually try to compete on price. I don't think this will happen anytime soon.
I think a heat pump only for water isn't the right way to go. In the EU, new systems I see use a single heat pump for all heating and cooling in the house including heating water.
I do miss my natural gas on-demand water heater from when I lived in the states though. Unlimited hot water was nice, and it took up almost zero space.
While they are not as efficient or flexible, they are many times more efficient than resistive electric water heaters. I've installed one with in house air intake (due to construction reasons) in my house and it cooled down the basement by a few degrees (and removed air moisture as an added bonus). In summer the thermal capacity of the ground heats up the basement again, in winter it's a bit cooler, but it still works efficiently.
This is promising.
https://www.pv-magazine.com/2026/01/29/samsung-releases-new-...
> The South Korean giant [Samsung] said its new EHS All-in-One provides air heating and cooling, floor heating, and hot water from a single outdoor unit. It can supply hot water up to 65 C in below-zero weather.
> Dubbed EHS All-in-One, the system provides air heating and cooling, floor heating, and hot water from a single outdoor unit. It is initially released for the European market, with a Korean rollout expected within a year. “It delivers stable performance across diverse weather conditions. It can supply hot water up to 65 C even in below-zero weather and is designed to operate heating even in severe cold down to -25 C,” the company said in a statement. “The system also uses the R32 refrigerant, which has a substantially lower impact on global warming compared with the older R410A refrigerant.”
Afaik heat-pumps in the EU can provide unlimited hot water–what am I missing?
Geothermal (and airbased) pumps theoretically do not have unlimited heating capacity. For example my pump (Daikin Altherma Geo 3) has a 180 litre water tank so it can ”only” supply 180 litres hot water at 65 degrees Celsius and takes about a minute to heat two additional lites.
So if I want to quickly scald myself in a 400 litre pool at fifty degrees I can’t. But if I had a gas heater that would be possible!
I don't know what it's like where you're living but here in Switzerland it's completely normal to have one heat pump that does both. Here there's a lot of floor heating, which also uses water, so you usually just run one loop to the "boiler" (a water tank with a copper loop for the water from the heat pump to circulate through) and one through the floor and have a valve to switch which is running through the heat pump.
I have one of these: https://cta.ch/en/private/products/ah-i-eco-innen
I got it in October so most of the time I've had it has been <10C. It's produced 806.3 kWh of heating for hot water and 6587.2 kWh for the floor heating. It consumed 302.7 kWh and 1801.4 kWh respectively, for a COP of 2.66 and 3.66.
There's a lot of different heating systems: If your heating system uses hot water at any point, (baseboards, hydro-air, underfloor, ect,) using a single heat pump makes a LOT of sense.
Personally, I prefer an air-source heat pump hot water tank. It significantly dehumidifies my basement.
Ask This Old House had an episode literally yesterday where they installed a \ solar-assisted split heat pump water heater. There is a component that goes on the outside of the house but not on the roof which simplifies installation.
https://www.youtube.com/watch?v=uqyAWkXXt3A
https://www.neshw.com/residential/solar-heat-pump-water-heat...
I had a heat pump installed in 2010. In a cold climate. Only used for heating. It paid for itself extremely quickly - less than three years. It's still going strong, in 2026. It's important to maintain it regularly, i.e. deep cleaning every two years or so. The first time I got a company to do it for me, and the technician taught me how to do it all by myself, so that's what I do. In any case having a professional doing it wasn't expensive either. And I clean the dust filters (very easy) every second week or so.
Installed mini-splits to replace the propane stove that heated my house, DIY job, so all it cost was the units themselves and some materials.
Propane bill (no natural gas, town of 500) from Oct 24 to Feb 25 (installed the mini splits that month) was $1200, for just heating.
My mini-splits are on a dedicated sub panel with an Emporia Vue 3 energy monitor. $604 in electricity consumption, and that includes air conditioning over the summer months.
For what it’s worth, our winter weather averages 25-35F with the occasional few days dipping to tens, single digits, and the occasional -10 freak; but these units just BARELY have a HSPF4 rating to classify as “cold climate” models. Still going to pay for themselves in 6 years without any tax credits, and 4 or so since I still installed them when they were available.
I'm in the northern US and am very happy with mine. I self-installed with a county rebate, so the total cost was a Saturday and $700. My old electric unit was EPA rated for $450/year, and the new one has averaged $170/year over 4 years, so I've already broken even.
> government mandate will force enough demand that manufacturers can enjoy some economies of scale
So you want the government to pick winners and you want to do business with a monopoly? This is the opposite of what you would want.
If the product saves me money, and it's _actually_ better, I will buy it in a heartbeat. If you're involving the government it's because one of those things isn't true.
Even LFP batteries can work out better.
I live in Switzerland where these are available. A Cowa 58 [0] costs CHF 4692 [1] and stores up to 13.5kWh. If you're heating the water with a heat pump, that's ~6kWh of electricity, so ~CHF 782/kWh.
I'm in the process of installing a 33kWh battery and the battery + inverter cost CHF 13600 in total for just the hardware, so ~CHF 482/kWh.
If you add solar panels, the inverter does double-duty producing AC from both the battery and the panels. The battery does double-duty producing both hot water and allowing you to use solar energy outside the times when the sun is shining.
That said, having ordered a heat pump recently and being in the process of having solar + batteries installed, the amount of electrical work needed for the solar/battery install is substantially higher than was needed for the heat pump and here, the labour costs quite a lot, pushing the upfront cost difference even higher.
I think that's where these heat storage things fit in: they have a much lower upfront cost. No matter how cheap the battery, for it to be useful in a Swiss residence, it needs to output a substantial amount of 3-phase power (3-phase is standard here, even in most apartments), which means you need to spend a couple thousand Francs on an inverter and electrical work. These heat storage devices are quite cheap and don't even need someone qualified to handle refrigerants, I imagine they could be installed by a normal plumber.
That reduced upfront cost makes them far more accessible than electrical batteries, at least for now.
[0]: https://www.cowa-ts.com/uploads/files/Dokumente/Datenblaette...
A heat pump gets more heat from a given amount of electricity than if the electricity is use for resistive heating. So the ideal design is solar cell + sodium battery + heat pump.
There’s also solar thermal panels that heat up a liquid circulating in the system and cut out the need for a battery - and can just store the heated liquid.
Efficiencies and effects are at the point where taking a photon, converting it into an electron, and using that electron to pump heat is more efficient than turning that photon perfectly into kinetic energy.
Similarly, in mild weather, it is more efficient to burn hydrocarbons and turn it into electricity to run a heat pump than use that hydrocarbon for it's heat energy directly.
Pumping heat is more efficient than making it.
Thermal solar panels have the advantage of being very simple and surprisingly effective. But if you're lacking space to put up both solar cells and thermal, you can use combined panels which have a solar cell with a backing thermal system. The interesting thing is that these combined panels outperform solar cells even when it comes to electricity generated because solar panels loose efficiency as they heat up, so cooling them actually improves efficieny. Combined panels are much more expensive, though.
The problem with thermal solar panels is that you can use its heated water only if it gets warmer than the water in your system, which is not always the case, especially in winter.
Compared to nearly 100% usable energy from normal solar panels.
Furthermore if you have a heatpump you can convert this electric energy into heat energy with a factor of >3 (COP).
I wonder if this can store any heat or just heat pump heat. If it can store any heat, it would help a lot to further reduce heating costs in our modern energy efficient house.
Sometimes, in the winter, we get too much solar forcing, so if we don’t heat all, it can be 85F in the day in the house, but 60-65 at night. (We open the windows during the day, and don’t always close them at exactly the right time at night.)
I think this can work and instead of that the heatpump pumps the heat into your house (when "solar is plenty") it would pump it into the storage. (I have a similar setup, but heat the water but of course this is rather limited)
unrelated: a simple technical solution to your window problem would be home assistant and a few sensors to notify you when the windows are open too long or open when too cold inside.
Related, TIL the US is effectively banning residential electric resistance water heaters in 2029, with heat pump water heaters being the only type that can meet the new standards. Users will see a 2-3x in cost difference and a 3 to 8 year payback on savings.
This is exactly the kind of thing government is for, even though it's missing the other half: subsidies. At the very least buying heat pumps for the next 5 years should be tax deductible. Even better: a $2000 or similar rebate.
The problem is, energy use is only one part of the equation. Often times new appliances that are more efficient end up being more prone to breaking due to more complexity and companies trying to cut costs to meet a price point. This leads to people needing to replace there appliances much more often which really makes me question how much energy is actually saved if you include the energy used to produce them...
> even though it's missing the other half: subsidies
It's a double edged sword. In my country everyone bought pellet stoves because of the subsidies, hundreds of companies popped up, now that the subsidies have been phased out, 90% of the companies went down, with their support and warranties of course. The 10% that managed to survive increased their prices, which is easy to do once 90% of your competitors went bust
People who thought they'd save money by having the government (their taxes really) pay the bill are waking up 5 years later with expensive maintenance, the first units are starting to fail and need to be replaced but they can't afford it without the 50%+ subsidies. Not to mention that the prices pellets goes up and down faster than your average shitcoin.
This assumes the consumer doesn't know and can't look up the price of the hardware.
That's probably exactly what will happen.
Energy property - Heat pumps and biomass stoves and boilers
Heat pumps that meet or exceed the CEE highest efficiency tier, not including any advanced tier, in effect at the beginning of the year when the property is installed, and biomass stoves and boilers with a thermal efficiency rating of at least 75% qualify for a credit up to $2,000 per year. Costs may include labor for installation.
Qualified property includes new:
Electric or natural gas heat pumps
Electric or natural gas heat pump water heaters
Biomass stoves and boilers
I don't know about all heat pump systems, but mine at least requires the water tank to have a resistive immersion too. If the tank temperature gets below some threshold the heat pump refuses to work and turns the immersion on instead until it's warmed up enough.
The problem with heat pumps replacing electric heaters (in cold climates) is that the waste cold air gets dumped into the house and needs to be heated again. Generally, electric water heaters are expensive to run compared to gas ones, so people use them in places a gas heater is not possible to install (e.g. no way to vent the exhaust). This also means that the heat pump would have nowhere to vent cold air.
This kind of thing is why I don't like bans like this. The specifics matter a lot.
Is that 2-3x before or after the plumber marks it up?
What an exceptionally moronic thing to ban, the market solves this naturally. Resistance heaters are 100% efficient whatever fraction of the year is heating days. So if that's 1/2 the year and the water heater can't last 16yr because of water quality the heat pump heater will never pay you back.
This reminds me a lot of the time some jerks in west coast desert states convinced the feds to regulate plumbing fixtures so that eastern "we take from the river and put back in the river" municipalities that have more water than they know what to do with have to suffer through low flow everything.
Heat pump water heater (hybrid/HPWH, e.g., 50–65 gallon equivalent): Unit prices range from ~$1,500–$3,000+ (most common models $2,000–$2,500), with total installed costs $2,500–$5,000 (higher if electrical upgrades or space mods needed). Average retrofit/install often lands around $3,000–$4,000.
And for small households they virtually never pay for themselves before they die or need expensive maintenance... It only makes sense if you use a lot of water or if your electricity is very expensive. In my case it's even worse, with solar panels and self sufficiency they literally cannot break even
Is the heat pump heater taking heat from inside or outside the house?
Depends on the model, but a lot use the air from their own room, that's why they can't be installed in small rooms. Models pulling the heat from outside are more expensive and require more labor obviously, and they don't make a lot of sense for places that are bellow 0c multiple month a year as the COP will drop to 1.x and you will most likely need extra electricity for the anti frost cycles
I would love to see a bus-sized version for year-long temperature moderation. Like, drop house heat into it during the summer so it can re-heat the house over the winter, and pull all the heat out of it by Spring so that it can cool the house over the summer.
Bus sized because that amount of thermal mass is bound to take up a lot of space, but capable of being buried so that it doesn’t actually take up property space.
This exists, in german it's called Eisspeicherheizung. You have a few cubic meters of water buried in a concrete bunker and you use a heat pump to pull energy out of the water until it freezes. The system not only uses the thermal mass of the water, but the thawing/freezing energy which is higher than the energy required to heat water by 1degree by a factor of 80 - meaning if you freeze 1kg of water, you need to pull out enough energy to heat one kg of water by 80 degrees.
You can then use a heat pump that's optimized for the expected temperature range and you don't even need to insulate your water storage tank - you actually want the cold in winter to seep out into the surrounding soil, free energy.
In summer you have cold storage for your AC.
I ran the numbers for this a while ago. I live where we have proper winters (currently -22c). I wanted something simple just with solar thermal and water pumps (no heat pump). Sand batteries work at an industrial level, but for domestic use you want something simple so that means just water.
A 100m3 (100,000 litres or 26,500 gallons) cylindrical water tank (approx 5x5m) buried and insulated with 50cm of XPS could provide around 4000kWh of deliverable heat throughout winter. Which would be more than enough for heating and domestic hot water for my house.
In the summer you'd use solar thermal to charge it to 85c. In the winter you'd run water through underfloor heating and discharge it to 35c (so you just need a mixer valve and pump).
The structural engineering part of it isn't actually that complicated (with a garden on top, not a house). You can buy plastic water tanks of that size, it just needs to be buried and have XPS foam placed around it.
Because it's volume, it scales up well. An extra one meter in each direction would increase the volume by around 60%, but you have a lower overall heat loss, so the heat capacity would more than double.
The important part of it is the XPS foam though, without this the loses are too great and you don't retain any heat. This is why insulating your foundation and slab is so effective.
So… store heat in an insulated swimming pool 10ft deep, 30ft wide, and 90ft long, at 185F, above the service temp for XPS foam, got it, ok. At least you could also use it to sous vide an entire cow.
Pedantic Pete here:
• The centigrade is capitalized when used after a number. There is also a singular glyph for the entire degree-centigrade convention: ℃.
• There are also superscript numerical characters to use with volumes, without having to use formatting: m³.
So…geothermal? I wish this was possible too but I don’t see how it will work scientifically. Water is one of the chemicals that have one of the highest thermal mass/specific heat (maybe 1/3 of salt hydrates). Even then, you have to bury a crapton of water underground. This design mentioned in the article is more for short term, like 12 hours storage (since they’re accommodating for solar in nighttime)
To a certain extent, yes. The reason why the water is there is because the thermal flux of the ground is low, so the large mass of water provides a strong buffer. But you can’t cheap physics. You would need a crap ton of salt hydrate to accommodate a whole season of heat needs, even if you don’t factor in thermal loss from the container.
Geothermal needs either a horrifically expensive vertical bore hole going down a few hundred metres, or a good acre of land for laid-down piping. I have neither the money nor the horizontal space. So I am thinking something compact that needs to go only about 6-10m vertically into the ground (so I can hide it fully underground with about a metre of soil on top), and take up the horizontal space of 4 parked cars. I have more than enough room and cash to have that cube of space dug out.
And being on an alluvial plain, if I filter out all the rocks larger than a pea, a good 90+% of what is dug out can immediately be trucked away.
Ground sourced heat pumps need either a horrifically expensive vertical bore hole going down a few hundred metres, or a good acre of land for laid-down piping. I have neither the money nor the horizontal space. So I am thinking something compact that needs to go only about 6-10m vertically into the ground (so I can hide it fully underground with about a metre of soil on top), and take up the horizontal space of 4 parked cars. I have more than enough room and cash to have that cube of space dug out.
And being on an alluvial plain, if I filter out all the rocks larger than a pea, a good 90+% of what is dug out can immediately be trucked away.
Stanford's cogen plant has an underground "ice cube" for campus/municipal chilled water infrastructure. Perhaps scaling something like that makes sense or perhaps to use an absorption heat pump (AHP) that can operate like and the reverse of an Einstein–Szilard refrigerator?
So it's a large version of those rechargeable hand-warmers?
Yes, it's the same tech. There's been products on the market for a while even though this press release tries to spin it like it's new and linked to heat pumps.
Private equity / Wall St. megacorps want to sell you complex systems that are fragile, unaffordable by the 99%, have short warranty periods, wear out quickly, require cloud logins and proprietary maintenance parts, and are mandated by law.
GFL buying a simple resistive-heated clothes dryer, furnace, or tanked/tankless water heater in 2030.
the idea is theoreticaly good, but as it depends on sealing incompatable materials apart, there will be problems, and issues with disposing of failed units.Dry sand works as thermal storage without any issues, and only needs more space, competition will be stiff.Water also works, and ordinary off the floor systems can be used with no modifications. The only advantage the system will have is in places where space constraints combine with the desire for fancy solutions and ecobabble.
Stones has the ability to store heat and keep cool.
What's all this fuzz about ?
It's all about efficiency. You can store heat in anything, but the question is for how long and how much energy can you get back out later. The first part is easy and how we got ovens and stoves, the second part can be pretty tricky depending on your requirements. Large scale energy storage sometimes uses massive amounts of sand for example, but they heat it to hundreds of degrees which is not really feasible in most settings.
They should've used lasagna. You could be in a tundra heating it over a fire and, as long as you get it sufficiently and consistently hot, it'll still burn your mouth 20minutes later.