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.
You seem to be describing ground sourced heat pumps. If you wanted, you could insulate a a chunk of foundation or earth to avoid heat loss. But just the ground under your building seems to work well enough.
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.
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.
I live in a climate where, for most of the year, the daily high-low temperature range includes 20C, so I'd like a whatever sized one is needed to average that out, and run most of the year without any active heating or cooling.
Yeah I always wondered if I ever switched to solar panels, would there be a way to accumulate heat to be used in the Canadian cold months that have little sunlight? The closest I found was electric thermal storage based on heating bricks. They can accumulate more energy than water since they can go to higher temperatures. For example these say they go to 1300°F or 700°C https://steffes.com/ets/roomheater/ . They don't seem to have large models that could heat a house for months however.
This is similar to nighthawkinlight's videos on phase change materials. It was very cool to see how his Ziploc bags of homemade goo helped regulate temperature.
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.
Climates that need a hot tank of water to buffer for heat pumps, will not have meaningful solar panel output during winter. Or do you mean, just load the battery when electricity is cheap? A tank of water is 1k max, probably 10% of a sodium battery.
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.
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.
IIRC BMW used to have a form of this in their cars about 25-30 years back so that the hvac would be able to blow heat before the engine coolant was up to temp after sitting overnight.
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.
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.
That seems like a stupid ban. Heat pump water heaters are impossible to install in many smaller dwellings, even if we're ignoring the need for large storage tanks.
The only problem with resistance heaters is the large current draw to heat water for bathing. Central heating can be done at lower temperatures (as is the case with heat pumps), but bathing cannot.
There are some resistance heaters with built in (electrochemical) batteries aimed at reducing peak current, but I'm assuming the ban would affect those as well...
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.
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.
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.
To whatever degree you are serious, this can be a phase change thing.
Cheese melting takes energy
Cheese freezing, releases energy.
So you do actually get the temperature to remain at the melting point of the cheese for a longer period of time if you have enough % cheese to be significant.
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.
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?
---
Just an FYI: There are plenty of schemes with resistive electric water tanks to store heat when power is cheap.
Not many numbers in there. I would be interested in some measure of energy and effect per volume, e.g how many kWh of heat are we talking about at e.g 1 liter, and how fast (kW) can it produce it?
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).
> But storing the heat they produce has not been possible
Many heat pumps are installed with a large insulated buffer of water (for ex. 300L), which stores heat pretty well?
And homes that use underfloor heating in concrete can store heat pretty well too. Many people use that to heat up the home when energy is cheap and disable the heat pump when it is expensive.
An 85% round-trip efficiency and 4X smaller volume sound great, but how does the installed cost compare to just oversizing a hot water tank or running the heat pump harder during off-peak hours?
41 comments
[ 2.9 ms ] story [ 63.6 ms ] threadBus 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.
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.
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.
[1] https://www.youtube.com/watch?v=s-41UF02vrU
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...
[1]: https://nettoheizungshop.ch/Cowa-COMPACT-Cell-58
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.)
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.
This kind of thing is why I don't like bans like this. The specifics matter a lot.
The only problem with resistance heaters is the large current draw to heat water for bathing. Central heating can be done at lower temperatures (as is the case with heat pumps), but bathing cannot.
There are some resistance heaters with built in (electrochemical) batteries aimed at reducing peak current, but I'm assuming the ban would affect those as well...
https://sunamp.com/en-gb/hot-water-solutions-thermino-range/
https://www.youtube.com/watch?v=7J52mDjZzto
https://www.youtube.com/watch?v=7zrx-b2sLUs
Unless you live in a cold climate, they are worth it for a discounted energy bill =3
GFL buying a simple resistive-heated clothes dryer, furnace, or tanked/tankless water heater in 2030.
Cheese melting takes energy Cheese freezing, releases energy.
So you do actually get the temperature to remain at the melting point of the cheese for a longer period of time if you have enough % cheese to be significant.
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.
What's all this fuzz about ?
https://en.wikipedia.org/wiki/Cold_district_heating
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?
---
Just an FYI: There are plenty of schemes with resistive electric water tanks to store heat when power is cheap.
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).
Storing cold during the night is probably more efficient
I thought about making ice blocks with a freezer on my balcony, probably not a good idea
Many heat pumps are installed with a large insulated buffer of water (for ex. 300L), which stores heat pretty well?
And homes that use underfloor heating in concrete can store heat pretty well too. Many people use that to heat up the home when energy is cheap and disable the heat pump when it is expensive.