Hello everyone,
we are planning a prefabricated house using timber frame construction. It will have 180 sqm (1,937 sq ft) of living space with underfloor heating, and about 230 sqm (2,475 sq ft) of usable area.
So far, the offer included an air-to-water heat pump from Daikin (Altherma 3R, formerly Rotex HPSU compact Ultra).
Now it seems that this unit might not have enough capacity (?) and as an alternative (additional cost around 4,000) we have been offered a "Wolf heat pump CHC Monoblock 10/300-35".
The Daikin is available in the 4-9 kW version—would that really be insufficient for this size? And what do you think about this offer?
I have the energy-saving regulation heat protection certification and a renewable energy heat law document available, if any information from those is needed.
Thank you very much!
Best regards
we are planning a prefabricated house using timber frame construction. It will have 180 sqm (1,937 sq ft) of living space with underfloor heating, and about 230 sqm (2,475 sq ft) of usable area.
So far, the offer included an air-to-water heat pump from Daikin (Altherma 3R, formerly Rotex HPSU compact Ultra).
Now it seems that this unit might not have enough capacity (?) and as an alternative (additional cost around 4,000) we have been offered a "Wolf heat pump CHC Monoblock 10/300-35".
The Daikin is available in the 4-9 kW version—would that really be insufficient for this size? And what do you think about this offer?
I have the energy-saving regulation heat protection certification and a renewable energy heat law document available, if any information from those is needed.
Thank you very much!
Best regards
T
T_im_Norden15 Oct 2020 20:38If your house is insulated, you won’t have large temperature differences.
If a room isn’t heated at all, the warmth will simply move from the other rooms into that space because it escapes less easily to the outside. This means the heated room will get cooler, or the heating system will have to work harder to compensate.
Therefore, I would install underfloor heating in all rooms. You can still control each room with thermostatic radiator valves (TRVs), but you’ll always have the option to use the room normally. For 5.9 kW, a 6 kW system should be sufficient.
If a room isn’t heated at all, the warmth will simply move from the other rooms into that space because it escapes less easily to the outside. This means the heated room will get cooler, or the heating system will have to work harder to compensate.
Therefore, I would install underfloor heating in all rooms. You can still control each room with thermostatic radiator valves (TRVs), but you’ll always have the option to use the room normally. For 5.9 kW, a 6 kW system should be sufficient.
Yes, the 6 kW heating capacity will be sufficient. The building’s heat load of 5.9 kW is only reached at the standard outdoor temperature, which occurs on just a few days per year. Additionally, the building is fully heated through and would need to cool down first.
For comparison: A typical electric space heater usually provides around 2 kW. In theory, that would be enough to keep the place warm for half of the heating season.
Regarding the basement room: My predecessor is correct. The only way to achieve a somewhat meaningful temperature difference would be to insulate the interior walls of the "cold" room against the heated rooms. Whether this makes sense and might potentially cause issues related to moisture damage would need to be examined.
For comparison: A typical electric space heater usually provides around 2 kW. In theory, that would be enough to keep the place warm for half of the heating season.
Regarding the basement room: My predecessor is correct. The only way to achieve a somewhat meaningful temperature difference would be to insulate the interior walls of the "cold" room against the heated rooms. Whether this makes sense and might potentially cause issues related to moisture damage would need to be examined.
D
Daniel-Sp16 Oct 2020 07:56Isn’t it required by energy saving regulations that all rooms within the thermal envelope must be heatable above a certain size?
Regardless of that, I agree with the previous comments. Heat flows from warm rooms to cold rooms, leading to an increased heating load for the warm rooms, which in turn causes a higher supply temperature. The heat pump operates less efficiently, making heating more expensive at the same room temperature.
Regardless of that, I agree with the previous comments. Heat flows from warm rooms to cold rooms, leading to an increased heating load for the warm rooms, which in turn causes a higher supply temperature. The heat pump operates less efficiently, making heating more expensive at the same room temperature.
Thanks for the feedback! How does it actually work with hot water in the NAT system? The heat pump wouldn’t have any buffer then and would have to use the electric heating element to heat, right? The energy consultant calculated a 27°C (81°F) share of hot water.
Regarding the basement: it seems the calculation according to KFW55 worked out. However, the ceiling heights are also below 2.4m (8 feet), so maybe it’s because heating is not required?
Honestly, I’m a bit lacking the energy to have both basement rooms heated afterwards, especially because of the discussion with the general contractor. I would rather focus now on ensuring that the heating engineer really does the 17x2 layout and respects the pipe spacing and heating circuits lengths. He also doesn’t seem enthusiastic about the wall heating system.
The calculation shows that I get more heat in the living-dining area than I need, and the guest toilet still maintains 22°C (72°F) despite the cold basement underneath.
Regarding the basement: it seems the calculation according to KFW55 worked out. However, the ceiling heights are also below 2.4m (8 feet), so maybe it’s because heating is not required?
Honestly, I’m a bit lacking the energy to have both basement rooms heated afterwards, especially because of the discussion with the general contractor. I would rather focus now on ensuring that the heating engineer really does the 17x2 layout and respects the pipe spacing and heating circuits lengths. He also doesn’t seem enthusiastic about the wall heating system.
The calculation shows that I get more heat in the living-dining area than I need, and the guest toilet still maintains 22°C (72°F) despite the cold basement underneath.
T
T_im_Norden16 Oct 2020 09:24You have a significant overlap in all rooms except for the bathrooms and the gallery.
If you plan to install heating under the bathtub in the bathroom and add wall heating, you can either:
- Achieve the desired 24 degrees Celsius (75°F) in the bathroom and reduce the temperature in the other rooms, or even run those at higher temperatures.
or
- Accept lower temperatures in the bathroom and lower the supply temperature accordingly.
You should also remember that the system is designed for the worst-case outdoor temperature scenario, meaning that for most of the time, the heating can operate with a lower supply temperature.
When it comes to the basement, my approach is better to have it and not need it than the other way around.
Have you planned for a mechanical ventilation system with heat recovery?
If the heat pump occasionally activates the electric heater on the few very cold days (NAT days), that can be considered negligible.
If you plan to install heating under the bathtub in the bathroom and add wall heating, you can either:
- Achieve the desired 24 degrees Celsius (75°F) in the bathroom and reduce the temperature in the other rooms, or even run those at higher temperatures.
or
- Accept lower temperatures in the bathroom and lower the supply temperature accordingly.
You should also remember that the system is designed for the worst-case outdoor temperature scenario, meaning that for most of the time, the heating can operate with a lower supply temperature.
When it comes to the basement, my approach is better to have it and not need it than the other way around.
Have you planned for a mechanical ventilation system with heat recovery?
If the heat pump occasionally activates the electric heater on the few very cold days (NAT days), that can be considered negligible.
Hot water plays a rather minor role, unless you constantly use warm water and need continuous reheating. Otherwise, warm water preparation will only take about 2-3 hours per day. Considering the thermal energy stored throughout the entire house, this won’t make a significant difference. The heating element is most likely just there for peace of mind.
Regarding the underfloor heating: You now understand the consequences, which won’t be dramatic. The points you described are much more important. Pay close attention to those, and you’ll be in a better position than many others.
By the way, 22 degrees Celsius (72°F) is not low at all when nearly all surfaces are heated. It will also automatically get warmer once the shower is running. So, you really don’t need to worry about that.
Regarding the underfloor heating: You now understand the consequences, which won’t be dramatic. The points you described are much more important. Pay close attention to those, and you’ll be in a better position than many others.
By the way, 22 degrees Celsius (72°F) is not low at all when nearly all surfaces are heated. It will also automatically get warmer once the shower is running. So, you really don’t need to worry about that.
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