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Thanks for your input. So I understand that heating the house requires much more hot water than what my solar heater can probably provide. In that case, connect

Thanks for your input. So I understand that heating the house requires much more hot water than what my solar heater can probably provide. In that case, connecting it to the radiator system is not so beneficial, and probably better to rely on a heat pump for the radiator water (the solar heater will not provide much help to justify connecting to it) Is that correct ?

jonstewart 4y ago
Basically. There are all sorts of neat DIY examples of people using large solarthermal arrays and big storage tanks to provide adequate heat, but they’re major projects and custom. For your system, what I’d potentially recommend is looking at a heat pump that can provide both domestic hot water -and- hot water for your radiators. They exist! Then, explain to your vendor/installer that you want a second heat exchanger in the tank for input from the thermosiphon. Then you would be providing solarthermal to both house heating and DHW— it won’t be enough, but it is theoretically better to apply that input across both loads, in a shared manner. However, the question is cost. You’ve got a DHW system right now that works. To install a new system with a tank that can accommodate the thermosiphon input and provide DHW and radiant heat may be too expensive to be worth it. A second thing for you to consider is the heating area of the radiators. Old radiators are designed for very hot water from boilers, ~180F. Heat pumps for radiant heating operate between about 95F-120F (lower is more efficient, but less responsive). Because of the lower temperature, they need a larger heating surface to deliver the same heat to the house. So, typically there’s a mix of larger European-style radiator panels and in-floor heat. In-floor heat is pretty great! A room at 65F feels like 72F when the floor is warm.
- mderazon 4y ago
  Thanks a lot for the detailed reply. Old radiators operate in high temperature but from what I understand, the fan coil heaters operate in lower temperature more equivalent to radiant floor heating. For cost reasons, installing undefloor heating is not an option, that's why I opted for low temp radiators on top of floor. However, it sounds like the heat pump system will not be cheap either. According to BTU calculator I found online, seems like I need 28K BTUs to heat the home. I thought about pellet burners as well, but here in Europe, the cost of pellets has sky rocketed this year. I don't want to be dependent on gas either, also electricity is not cheap... So I am not sure exactly what i'll go with. I'll do the calculation, but your input on the effectiveness of the theromosiphon system is valuable, thank you.
  - jonstewart 4y ago
    Daikin makes air source heat pumps with water storage, and that can be paired with solarthermal: - https://www.daikin.com/products/ac/lineup/heat_pump https://www.daikin.com/products/ac/lineup/heat_pump - https://airconditionerlab.com/daikin-heat-pump/ https://airconditionerlab.com/daikin-heat-pump/ A "variable speed compressor" is what you want in a heat pump, as these modulate their speed (and electricity usage) to produce a constant amount of heat. You might be okay with a 24K BTU system, especially when coupled with the thermosiphon and then some effort spent on insulation & air-sealing? Here in the US the base system would be about $3K USD, but with installation costs on top of that.

jonstewart 4y ago

Basically. There are all sorts of neat DIY examples of people using large solarthermal arrays and big storage tanks to provide adequate heat, but they’re major projects and custom. For your system, what I’d potentially recommend is looking at a heat pump that can provide both domestic hot water -and- hot water for your radiators. They exist! Then, explain to your vendor/installer that you want a second heat exchanger in the tank for input from the thermosiphon. Then you would be providing solarthermal to both house heating and DHW— it won’t be enough, but it is theoretically better to apply that input across both loads, in a shared manner. However, the question is cost. You’ve got a DHW system right now that works. To install a new system with a tank that can accommodate the thermosiphon input and provide DHW and radiant heat may be too expensive to be worth it. A second thing for you to consider is the heating area of the radiators. Old radiators are designed for very hot water from boilers, ~180F. Heat pumps for radiant heating operate between about 95F-120F (lower is more efficient, but less responsive). Because of the lower temperature, they need a larger heating surface to deliver the same heat to the house. So, typically there’s a mix of larger European-style radiator panels and in-floor heat. In-floor heat is pretty great! A room at 65F feels like 72F when the floor is warm.

mderazon 4y ago
Thanks a lot for the detailed reply. Old radiators operate in high temperature but from what I understand, the fan coil heaters operate in lower temperature more equivalent to radiant floor heating. For cost reasons, installing undefloor heating is not an option, that's why I opted for low temp radiators on top of floor. However, it sounds like the heat pump system will not be cheap either. According to BTU calculator I found online, seems like I need 28K BTUs to heat the home. I thought about pellet burners as well, but here in Europe, the cost of pellets has sky rocketed this year. I don't want to be dependent on gas either, also electricity is not cheap... So I am not sure exactly what i'll go with. I'll do the calculation, but your input on the effectiveness of the theromosiphon system is valuable, thank you.
- jonstewart 4y ago
  Daikin makes air source heat pumps with water storage, and that can be paired with solarthermal: - https://www.daikin.com/products/ac/lineup/heat_pump https://www.daikin.com/products/ac/lineup/heat_pump - https://airconditionerlab.com/daikin-heat-pump/ https://airconditionerlab.com/daikin-heat-pump/ A "variable speed compressor" is what you want in a heat pump, as these modulate their speed (and electricity usage) to produce a constant amount of heat. You might be okay with a 24K BTU system, especially when coupled with the thermosiphon and then some effort spent on insulation & air-sealing? Here in the US the base system would be about $3K USD, but with installation costs on top of that.