ᐅ Heat pump, hot water storage tank, tankless water heater, heat recovery ventilation (HRV), underfloor heating, heating and cooling
Created on: 20 Jun 2023 14:37
H
Havanna86
Hello everyone,
I’m looking for advice on the design of our renovation project.
Key details: built in 1930, ground floor area 90 m² (970 ft²), upper floor area 40 m² (430 ft²), basement used only for storage, semi-detached house, extensive renovation planned (including basement ceiling, facade, windows, roof – all to qualify for BEG EM funding).
We are converting the entire ground floor to underfloor heating. On the upper floor, the plan is to use wall heating installed in the space between the rafters. According to calculations, after renovation the heating demand will be 5.3 kW. A air-to-water heat pump (Vitocal 252 – the 08 model) will be used. This heat pump does not have an integrated water storage tank.
The system will be combined with a hydronic fireplace, which delivers 2 kW of heat directly into the room and 8 kW to the water circuit. Additionally, one or more buffer tanks will be integrated to
a) store the heat from the fireplace,
b) use a heating element to feed in excess solar energy from a photovoltaic system during peak times,
and thus provide hot water for heating and domestic hot water.
Due to limited space in the basement, I will most likely need to place two buffer tanks side by side. I am targeting a volume of 800 to 1000 liters (210 to 265 gallons). To avoid having to constantly store hot domestic water during winter, I will integrate a tankless water heater (solar-compatible). The idea is to use the temperature level in the domestic hot water tank and only raise it by about 15 degrees Celsius (27 degrees Fahrenheit) if needed, preferably less.
This is the basic theory, which I have discussed with the heating engineer. However, I want to fully understand the system and I’m stuck on some points, so I hope for your support.
1.) What is the best way to connect the buffer tanks? From my point of view, a series connection seems suitable, with the domestic hot water tank with the DHW loop as the rear, warmer tank, is that correct?
2.) Where is the best place for the heat pump to feed in? Ideally in the middle, right? But where would the middle be with two tanks?
3.) Where should the hydronic fireplace connect?
4.) Up to what temperature in the buffer tank does it make sense to operate the heat pump?
An additional thought, which is not a priority: There is the possibility of a cooling function in summer. Does it make sense to consider the buffer tanks in this regard or would that only complicate things further? Otherwise, in summer it could be possible to have one cold and one hot buffer tank: one for domestic hot water and one for heating water.
Thank you very much for your interest!
I’m looking for advice on the design of our renovation project.
Key details: built in 1930, ground floor area 90 m² (970 ft²), upper floor area 40 m² (430 ft²), basement used only for storage, semi-detached house, extensive renovation planned (including basement ceiling, facade, windows, roof – all to qualify for BEG EM funding).
We are converting the entire ground floor to underfloor heating. On the upper floor, the plan is to use wall heating installed in the space between the rafters. According to calculations, after renovation the heating demand will be 5.3 kW. A air-to-water heat pump (Vitocal 252 – the 08 model) will be used. This heat pump does not have an integrated water storage tank.
The system will be combined with a hydronic fireplace, which delivers 2 kW of heat directly into the room and 8 kW to the water circuit. Additionally, one or more buffer tanks will be integrated to
a) store the heat from the fireplace,
b) use a heating element to feed in excess solar energy from a photovoltaic system during peak times,
and thus provide hot water for heating and domestic hot water.
Due to limited space in the basement, I will most likely need to place two buffer tanks side by side. I am targeting a volume of 800 to 1000 liters (210 to 265 gallons). To avoid having to constantly store hot domestic water during winter, I will integrate a tankless water heater (solar-compatible). The idea is to use the temperature level in the domestic hot water tank and only raise it by about 15 degrees Celsius (27 degrees Fahrenheit) if needed, preferably less.
This is the basic theory, which I have discussed with the heating engineer. However, I want to fully understand the system and I’m stuck on some points, so I hope for your support.
1.) What is the best way to connect the buffer tanks? From my point of view, a series connection seems suitable, with the domestic hot water tank with the DHW loop as the rear, warmer tank, is that correct?
2.) Where is the best place for the heat pump to feed in? Ideally in the middle, right? But where would the middle be with two tanks?
3.) Where should the hydronic fireplace connect?
4.) Up to what temperature in the buffer tank does it make sense to operate the heat pump?
An additional thought, which is not a priority: There is the possibility of a cooling function in summer. Does it make sense to consider the buffer tanks in this regard or would that only complicate things further? Otherwise, in summer it could be possible to have one cold and one hot buffer tank: one for domestic hot water and one for heating water.
Thank you very much for your interest!
K
KarstenausNRW24 Jun 2023 12:20Havanna86 schrieb:
I think we’re past the point of making changes to the system in general. That’s a shame.
Havanna86 schrieb:
Either invest a lot of money now into the system to reduce running costs in the long term, or install a cheaper system now and accept somewhat higher ongoing expenses over time... This is exactly where your thinking is wrong. You believe you’re reducing costs, but that’s not the case. The house doesn’t care how you generate the required heat energy. Keep it simple and cheap.
That’s why I’m out of this.
R
RotorMotor24 Jun 2023 12:41I have to agree with @KarstenausNRW. The currently planned technology, especially the buffer tanks, reduces efficiency and therefore increases consumption instead of reducing it. Additionally, there is high maintenance effort and cost, as well as problems with system configuration. If you insist on this approach, unfortunately, I won’t be able to help.
W
WilderSueden24 Jun 2023 12:54Havanna86 schrieb:
Certainly, all of this costs money, but the goal is to reduce costs in the long run. The problem is that you are generating significant expenses and need to finance them at around 4%. Let’s say the whole thing costs you an extra 20,000 euros (about 20,000 USD/GBP/AUD/CAD) compared to an option with just a heat pump and no chimney. Then you would need to save 800 euros (about 800 USD/GBP/AUD/CAD) each year just to cover the interest. That’s unrealistic. And we haven’t even mentioned the chimney sweep who expects payment every year. You won’t save money this way; you’re increasing your monthly financial burden.
Havanna86 schrieb:
In the end, this is also a matter of belief.This is not a matter of belief but a technically definable heating system for a single-family home. If you invest the money in a well-designed heat pump and a large photovoltaic system with storage, you will have a net-zero energy cost house, or even one with a positive energy balance.
Havanna86 schrieb:
Certainly, all of this costs money, but the goal is to reduce costs in the long run.Well, what you install today won’t be state of the art in 20 years. We just experienced this with our reverse cycle ducted air conditioning. The new system is much more efficient, cheaper to maintain, and costs less than what we had installed 20 years ago (same company).S
stjoob_at26 Jun 2023 16:30Wow, this system really pains my building services engineer heart.
Inefficient, difficult to control, more expensive to install… that was a salesperson, not a consultant.
Just the idea of heating the domestic hot water with the electric immersion heater (1 part electricity to 1 part heat) when you also have a heat pump (1 part electricity to 4+ parts heat) says it all. Especially in summer when the air-to-water heat pump has its highest efficiency.
A fireplace in a house that, in the worst case, requires 5.3 kW (18,000 BTU) of heating capacity is questionable. Such a fireplace produces several kilowatts of heat. If handled incorrectly, it can easily turn the house into a sauna. The water jacket helps to a certain extent but adds cost and reduces the overall system efficiency (hydraulics, large buffer tank, system temperatures…). Controlling this with a slow-responding underfloor heating system is also not ideal.
Inefficient, difficult to control, more expensive to install… that was a salesperson, not a consultant.
Just the idea of heating the domestic hot water with the electric immersion heater (1 part electricity to 1 part heat) when you also have a heat pump (1 part electricity to 4+ parts heat) says it all. Especially in summer when the air-to-water heat pump has its highest efficiency.
A fireplace in a house that, in the worst case, requires 5.3 kW (18,000 BTU) of heating capacity is questionable. Such a fireplace produces several kilowatts of heat. If handled incorrectly, it can easily turn the house into a sauna. The water jacket helps to a certain extent but adds cost and reduces the overall system efficiency (hydraulics, large buffer tank, system temperatures…). Controlling this with a slow-responding underfloor heating system is also not ideal.
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