3 ms·

The electric version of this is called "electric thermal storage" where the electric heater is used off-peak to heat up ceramic bricks. It seems unlikely to bea

The electric version of this is called "electric thermal storage" where the electric heater is used off-peak to heat up ceramic bricks. It seems unlikely to beat a heat pump, though. Could they be combined?

Gibbon1 4y ago
I'd tried to do back of the the envelope calcs for that sort of thing. Resistive heat has the property that efficiency doesn't change with temperature. So you can heat a small amount of bricks to oven temp with no loss. But heat pump efficiency is very dependent. So yeah in theory you could use a heat pump to heat a heat reservoir. Where I get stuck is detailed calcs are needed to suss out the economics. That people don't tend to do this says the economics aren't strongly in favor.
- thenickdude 4y ago
  Heatpump hot water is an application of this, allowing the tank of water to be heated during off-peak electricity times and act as a thermal battery.
- tgsovlerkhgsel 4y ago
  1 metric ton of water heated by 10 K stores roughly 10000 kcal or around 12 kWh. A rule of thumb from https://www.greenmatch.co.uk/green-energy/central-heating-capacity https://www.greenmatch.co.uk/green-energy/central-heating-ca... suggests 1 kW of heating per 10 square meters (that's likely the output that's required to maintain an adequate temperature during the n-th percentile coldest days). So on a cold day, a 50 square meter apartment would need 24*5 = 120 kWh. I'd say it's pretty impractical unfortunately. Water is already the best (practical) choice in terms of heat stored per weight, and likely also per volume, and cost.
  - Gibbon1 4y ago
    Last time I tried working things out it seems like concrete exterior walls with hydronic heat and external insulation would be a partial solution. But not really a thing you can add to most existing housing stock. And not a thing in the US. Roughing it I think if you used batteries you'd need to supply maybe guessing here 80kwh during the evening and night time. With a heat pump you'd need 20kwh. That's doable. Course likely over all more efficient to let the utility handle the battery end of things. Then again maybe a masonry heater makes sense if you often have excess solar and your utility is screwing you.
    - fy20 4y ago
      I live in Northern Europe where houses are built like this, and a 160m2 (1600sqft) house is typically fitted with a 8kW-12kW heat pump (heat output, so input electricity is 3x less) - which is used for hot water too. That may sound low, but the thing is houses here are very well insulated, so when you heat the masonry walls and floors to 21c it takes a very long time for the temperature to drop - the heat pump is just maintaining the heat We live in a slightly older house (which doesn't meet current insulation standards) and last year the heat consumption was 70kWh per m2. That's for heating and hot water.
abdullahkhalids 4y ago
You could just use a heat pump during off peak hours to heat up ceramic bricks. Then the question is whether the off-peak hours price reduction offsets having to heat the thermal mass of the bricks.
- 10u152 4y ago
  To get good capacity out of that kind of storage you need to heat it HOT - like 400+c and heat pumps can’t really do more than 90c or so.
  - abdullahkhalids 4y ago
    That's not necessary. You can heat a much larger thermal mass to a lower temperature, so that the total heat stored in the mass is the same. This mean that the design of the whole thing will change to modulate the heat flows appropriately.
fy20 4y ago
In the UK these are called "storage heaters". The efficiency is still 1:1 but you can charge them from cheap electricity sources (originally overnight electricity) and have the heat released slowly over time. A unit the size of a typical wall mounted radiator (except thicker) can store over 10kWh of heat. https://www.elnur.co.uk/product/ecombi-hhr-high-heat-retention-storage-heaters/ https://www.elnur.co.uk/product/ecombi-hhr-high-heat-retenti... My parents use these as their main heat source, and once you figure out how they work, the work fine. If I was building new today I'd go with a heat pump, but they have no ducting or central heating, so retrofitting that would not be easy. These could still be useful as a supplementary heat source if you have solar, as they are much cheaper than batteries for storing energy.
tobyhinloopen 4y ago
Heat pumps use hot water tanks to store heat, since you need hot water all year anyway

Gibbon1 4y ago

I'd tried to do back of the the envelope calcs for that sort of thing. Resistive heat has the property that efficiency doesn't change with temperature. So you can heat a small amount of bricks to oven temp with no loss. But heat pump efficiency is very dependent. So yeah in theory you could use a heat pump to heat a heat reservoir. Where I get stuck is detailed calcs are needed to suss out the economics. That people don't tend to do this says the economics aren't strongly in favor.

thenickdude 4y ago
Heatpump hot water is an application of this, allowing the tank of water to be heated during off-peak electricity times and act as a thermal battery.
tgsovlerkhgsel 4y ago
1 metric ton of water heated by 10 K stores roughly 10000 kcal or around 12 kWh. A rule of thumb from https://www.greenmatch.co.uk/green-energy/central-heating-capacity https://www.greenmatch.co.uk/green-energy/central-heating-ca... suggests 1 kW of heating per 10 square meters (that's likely the output that's required to maintain an adequate temperature during the n-th percentile coldest days). So on a cold day, a 50 square meter apartment would need 24*5 = 120 kWh. I'd say it's pretty impractical unfortunately. Water is already the best (practical) choice in terms of heat stored per weight, and likely also per volume, and cost.
- Gibbon1 4y ago
  Last time I tried working things out it seems like concrete exterior walls with hydronic heat and external insulation would be a partial solution. But not really a thing you can add to most existing housing stock. And not a thing in the US. Roughing it I think if you used batteries you'd need to supply maybe guessing here 80kwh during the evening and night time. With a heat pump you'd need 20kwh. That's doable. Course likely over all more efficient to let the utility handle the battery end of things. Then again maybe a masonry heater makes sense if you often have excess solar and your utility is screwing you.
  - fy20 4y ago
    I live in Northern Europe where houses are built like this, and a 160m2 (1600sqft) house is typically fitted with a 8kW-12kW heat pump (heat output, so input electricity is 3x less) - which is used for hot water too. That may sound low, but the thing is houses here are very well insulated, so when you heat the masonry walls and floors to 21c it takes a very long time for the temperature to drop - the heat pump is just maintaining the heat We live in a slightly older house (which doesn't meet current insulation standards) and last year the heat consumption was 70kWh per m2. That's for heating and hot water.

abdullahkhalids 4y ago

You could just use a heat pump during off peak hours to heat up ceramic bricks. Then the question is whether the off-peak hours price reduction offsets having to heat the thermal mass of the bricks.

10u152 4y ago
To get good capacity out of that kind of storage you need to heat it HOT - like 400+c and heat pumps can’t really do more than 90c or so.
- abdullahkhalids 4y ago
  That's not necessary. You can heat a much larger thermal mass to a lower temperature, so that the total heat stored in the mass is the same. This mean that the design of the whole thing will change to modulate the heat flows appropriately.

fy20 4y ago

In the UK these are called "storage heaters". The efficiency is still 1:1 but you can charge them from cheap electricity sources (originally overnight electricity) and have the heat released slowly over time. A unit the size of a typical wall mounted radiator (except thicker) can store over 10kWh of heat. https://www.elnur.co.uk/product/ecombi-hhr-high-heat-retention-storage-heaters/ https://www.elnur.co.uk/product/ecombi-hhr-high-heat-retenti... My parents use these as their main heat source, and once you figure out how they work, the work fine. If I was building new today I'd go with a heat pump, but they have no ducting or central heating, so retrofitting that would not be easy. These could still be useful as a supplementary heat source if you have solar, as they are much cheaper than batteries for storing energy.

tobyhinloopen 4y ago

Heat pumps use hot water tanks to store heat, since you need hot water all year anyway