4 ms·

Water has ~5x the heat capacity of brick. My first thought was a heat-pump water heater combined with radiant flooring. This way the heated water is stored in

Water has ~5x the heat capacity of brick. My first thought was a heat-pump water heater combined with radiant flooring. This way the heated water is stored in an insulated container until it is needed.

jonatron 4y ago
Water can't really go above 100c without being under high pressure though.
walterbell 4y ago
Discussion on practical reasons for using brick vs. water, https://diy.stackexchange.com/questions/133503/installable-storage-heaters-why-manufacturers-bother-putting-the-bricks-in https://diy.stackexchange.com/questions/133503/installable-s... If insulation products can enable safe, economical storage at very high temperatures, sand can be used for energy storage, https://news.ycombinator.com/item?id=33696105 https://news.ycombinator.com/item?id=33696105
mindslight 4y ago
Yes, but the problem is that the hotter the storage water becomes, the lower the COP of the heat pump gets. The problem is one big tradeoff based on how cheap the off peak rates are, how much capital expenditure (oversized heat pump and water storage tanks aren't free), and how variable your day to day heating load is versus peak. Plus most people don't like capital expenditures. I wish the original article touched upon the electricity rates. If you can rely on off peak rates being less than 1/4 of the on peak rates, then I can see this making sense. Otherwise it seems better to use electricity more efficiently, exactly when needed.
Dork1234 4y ago
www.arcticheatpumps.com/ I've been scoping out this company for some time, my boiler is currently in good shape but would love to switch down the road. They heat up water via HeatPumps to required temp during the day when outdoor temps are higher and electric is cheaper. Max water temp can change based off excepted nighttime temp.
- mindslight 4y ago
  The largest tank on their website is 120 gallons, so it seems that the storage isn't actually a significant part of their systems?
- _spduchamp 4y ago
  I recently converted our house from gas to heatpump for HVAC and water. We were considering Artic Heatpumps, but then when it came time to make a final decision, we were talked out of Artic by the contractor. They recommended Mitsubishi for HVAC, and Rheem for water, with the argument that these companies will be around for a long time for parts etc. We have all kinds of problems with the hot water heater, and managing the waste cold air from that unit and not having enough heat to pull in from that utility room. I have to figure out some ductwork to eventually deal with the problem. I really regret the choice, and wish I had gone with Artic with their integrated system for HVAC and water. It just makes so much more sense. There are definitely not enough installers trained on heatpumps, and many just treat them as drop-in replacements for gas fired equipment, because that's what they know. It is rare to find someone who looks at the whole picture and also deals with the heat loss mitigation.
  - bombcar 4y ago
    These considerations are part of the reason I replaced gas with gas - I’ll move to heat pump when I build a house so I can be sure I have it designed for it. As it is a tankless water heater may be the easiest way to “fix” yours - or spend a big amount for a knowledgeable energy contractor.
stcredzero 4y ago
Water has ~5x the heat capacity of brick. I remember the website of one enterprising New Zealander, where he was using an under house water storage tank as a heat sink accessible by his heat pump!
zasdffaa 4y ago
For the storage heaters I had the 'bricks' seemed to be mainly iron oxide IIRC. Also I am struggling to believe water has that multiples of capacity over brick, do you have a ref?
- walterbell 4y ago
  Recent thread on insulating/storage firebricks, https://news.ycombinator.com/item?id=33680429 https://news.ycombinator.com/item?id=33680429
  - zasdffaa 4y ago
    I'm afraid I can't see the relevance of that, can you point to something more specific.
    - walterbell 4y ago
      Previously posted in a sub-thread, https://diy.stackexchange.com/questions/133503/installable-storage-heaters-why-manufacturers-bother-putting-the-bricks-in https://diy.stackexchange.com/questions/133503/installable-s... Feolite specific heat = 920.0 J·kg−1−1·°C−1, density = 3,900 kg·m−3, thermal conductivity = 2.1 W·m−1·°C−1. maximum operating temperature 1000 °C. Water specific heat = 4184 J·kg−1·°C−1 density 1,000 kg·m−3, thermal conductivity = 0.591 W·m−1·°C−1. maximum operating temperature <100 °C unpressurised.
      - zasdffaa 4y ago
        Indeed, thanks. FTR "Feolite is a type of iron oxide sintered into building blocks, which are then used for heat storage" which is exactly the stuff. That's an astonishing difference in capacity.
- at_a_remove 4y ago
  Brick has a heat capacity of 840 J/kg°C. Water has a heat capacity of 4182 J/kg°C. Almost but not quite five times as much heat capacity. Water has a staggering heat capacity.

jonatron 4y ago

Water can't really go above 100c without being under high pressure though.

walterbell 4y ago

Discussion on practical reasons for using brick vs. water, https://diy.stackexchange.com/questions/133503/installable-storage-heaters-why-manufacturers-bother-putting-the-bricks-in https://diy.stackexchange.com/questions/133503/installable-s... If insulation products can enable safe, economical storage at very high temperatures, sand can be used for energy storage, https://news.ycombinator.com/item?id=33696105 https://news.ycombinator.com/item?id=33696105

mindslight 4y ago

Yes, but the problem is that the hotter the storage water becomes, the lower the COP of the heat pump gets. The problem is one big tradeoff based on how cheap the off peak rates are, how much capital expenditure (oversized heat pump and water storage tanks aren't free), and how variable your day to day heating load is versus peak. Plus most people don't like capital expenditures. I wish the original article touched upon the electricity rates. If you can rely on off peak rates being less than 1/4 of the on peak rates, then I can see this making sense. Otherwise it seems better to use electricity more efficiently, exactly when needed.

Dork1234 4y ago

www.arcticheatpumps.com/ I've been scoping out this company for some time, my boiler is currently in good shape but would love to switch down the road. They heat up water via HeatPumps to required temp during the day when outdoor temps are higher and electric is cheaper. Max water temp can change based off excepted nighttime temp.

mindslight 4y ago
The largest tank on their website is 120 gallons, so it seems that the storage isn't actually a significant part of their systems?
_spduchamp 4y ago
I recently converted our house from gas to heatpump for HVAC and water. We were considering Artic Heatpumps, but then when it came time to make a final decision, we were talked out of Artic by the contractor. They recommended Mitsubishi for HVAC, and Rheem for water, with the argument that these companies will be around for a long time for parts etc. We have all kinds of problems with the hot water heater, and managing the waste cold air from that unit and not having enough heat to pull in from that utility room. I have to figure out some ductwork to eventually deal with the problem. I really regret the choice, and wish I had gone with Artic with their integrated system for HVAC and water. It just makes so much more sense. There are definitely not enough installers trained on heatpumps, and many just treat them as drop-in replacements for gas fired equipment, because that's what they know. It is rare to find someone who looks at the whole picture and also deals with the heat loss mitigation.
- bombcar 4y ago
  These considerations are part of the reason I replaced gas with gas - I’ll move to heat pump when I build a house so I can be sure I have it designed for it. As it is a tankless water heater may be the easiest way to “fix” yours - or spend a big amount for a knowledgeable energy contractor.

stcredzero 4y ago

Water has ~5x the heat capacity of brick. I remember the website of one enterprising New Zealander, where he was using an under house water storage tank as a heat sink accessible by his heat pump!

zasdffaa 4y ago

For the storage heaters I had the 'bricks' seemed to be mainly iron oxide IIRC. Also I am struggling to believe water has that multiples of capacity over brick, do you have a ref?

walterbell 4y ago
Recent thread on insulating/storage firebricks, https://news.ycombinator.com/item?id=33680429 https://news.ycombinator.com/item?id=33680429
- zasdffaa 4y ago
  I'm afraid I can't see the relevance of that, can you point to something more specific.
  - walterbell 4y ago
    Previously posted in a sub-thread, https://diy.stackexchange.com/questions/133503/installable-storage-heaters-why-manufacturers-bother-putting-the-bricks-in https://diy.stackexchange.com/questions/133503/installable-s... Feolite specific heat = 920.0 J·kg−1−1·°C−1, density = 3,900 kg·m−3, thermal conductivity = 2.1 W·m−1·°C−1. maximum operating temperature 1000 °C. Water specific heat = 4184 J·kg−1·°C−1 density 1,000 kg·m−3, thermal conductivity = 0.591 W·m−1·°C−1. maximum operating temperature <100 °C unpressurised.
    - zasdffaa 4y ago
      Indeed, thanks. FTR "Feolite is a type of iron oxide sintered into building blocks, which are then used for heat storage" which is exactly the stuff. That's an astonishing difference in capacity.
at_a_remove 4y ago
Brick has a heat capacity of 840 J/kg°C. Water has a heat capacity of 4182 J/kg°C. Almost but not quite five times as much heat capacity. Water has a staggering heat capacity.