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
That’s why I specified a maximum supply temperature of 30°C (86°F) and a pipe spacing of 10cm (5 inches).
When the concern was raised that 24°C (75°F) might be too low for the bathroom, I pointed out the 20°C (68°F) and the electric heater installed on site.
As I mentioned, most general contractors, developers, and prefabricated house builders have their systems designed free of charge by their suppliers (e.g., underfloor heating manufacturers or heat pump manufacturers), and in those cases it’s usually allowed to go a bit higher as long as the house gets warm.
Higher supply temperatures and wider pipe spacing provide the general contractor with security that the house will be warm, and at the same time reduce costs because less material is needed (heating pipes, actuators, smaller manifolds, less installation effort). However, your electricity bill will go up because the heat pump won’t operate as efficiently as it could. The general contractor doesn’t care about your electricity bill. The main thing is that the house gets warm.
When the concern was raised that 24°C (75°F) might be too low for the bathroom, I pointed out the 20°C (68°F) and the electric heater installed on site.
As I mentioned, most general contractors, developers, and prefabricated house builders have their systems designed free of charge by their suppliers (e.g., underfloor heating manufacturers or heat pump manufacturers), and in those cases it’s usually allowed to go a bit higher as long as the house gets warm.
Higher supply temperatures and wider pipe spacing provide the general contractor with security that the house will be warm, and at the same time reduce costs because less material is needed (heating pipes, actuators, smaller manifolds, less installation effort). However, your electricity bill will go up because the heat pump won’t operate as efficiently as it could. The general contractor doesn’t care about your electricity bill. The main thing is that the house gets warm.
You reduce the required room temperature to lower the heating load? If 20°C (68°F) is not enough, you will have a cold house and a heat pump running at nearly 99% capacity. It is better to set the pipe spacing everywhere to 7 cm (3 inches) or even 5 cm (2 inches), and then throttle the heating circuit.
It can be even simpler. The following should be contractually agreed upon:
- Room-by-room heat load calculation according to DIN
- 30/27/21 (flow temperature/return temperature/room temperature) or 30/27/23 in the bathroom
- Heating circuit length fixed at 80 m (260 feet) per circuit, with a tolerance of ±10%
Then the heating installer is obliged to meet these parameters. By the way, I would follow the same approach even if planning a heating system other than a heat pump. Why? Because this way, I am always on the safe side when it comes to political specifics and changes.
- Room-by-room heat load calculation according to DIN
- 30/27/21 (flow temperature/return temperature/room temperature) or 30/27/23 in the bathroom
- Heating circuit length fixed at 80 m (260 feet) per circuit, with a tolerance of ±10%
Then the heating installer is obliged to meet these parameters. By the way, I would follow the same approach even if planning a heating system other than a heat pump. Why? Because this way, I am always on the safe side when it comes to political specifics and changes.
@tomtom79 For me at least, it’s a strategy to indirectly get the heating engineer to set a lower supply temperature and then plan accordingly. So, if they say we won’t get below 35°C (95°F) supply temperature, I try to manipulate the other parameters I provide so that I can still set the supply temperature to 30°C (86°F) later and achieve my desired temperatures.
For example, 20°C (68°F) would be too cold for me. Maybe it would be better to say, ok, just do 35°C (95°F), but definitely no higher, and I want 23°C (73°F) everywhere?
@Joedreck
I can’t make any direct contractual agreements with the heating engineer. All I can do is communicate my wishes (temperatures) or special requests (upgrades)...
I’m not sure if I can tell him exactly how to plan. Supposedly, he does a room-by-room heat load calculation, although I think he probably has the manufacturer handle that...
For example, 20°C (68°F) would be too cold for me. Maybe it would be better to say, ok, just do 35°C (95°F), but definitely no higher, and I want 23°C (73°F) everywhere?
@Joedreck
I can’t make any direct contractual agreements with the heating engineer. All I can do is communicate my wishes (temperatures) or special requests (upgrades)...
I’m not sure if I can tell him exactly how to plan. Supposedly, he does a room-by-room heat load calculation, although I think he probably has the manufacturer handle that...
The “guideline,” for example max. 10cm (4 inches) pipe insulation and about 8cm (3 inches) in the bathroom, simply comes from not wanting to deal with detailed calculations.
If you have a proper room-by-room heat load calculation, you can size it accordingly. For example, in my "all-purpose room," I definitely didn’t need 10cm (4 inches) insulation at a 30°C (86°F) supply temperature. There, even 15cm (6 inches) was sufficient. Using 10cm (4 inches) insulation over lengths of 70–100m (230–330 feet) would have meant a few extra meters of pipe and probably an additional heating circuit. So I told my installer to keep it tighter in the bathroom.
It partly depends on how and on what terms you can communicate with your installer. I think this varies a lot.
If, of course, you have one who doesn’t want to cooperate at all and you suspect that not much calculation is being done, it’s better to stick with the insulation thickness guidelines.
If you have a proper room-by-room heat load calculation, you can size it accordingly. For example, in my "all-purpose room," I definitely didn’t need 10cm (4 inches) insulation at a 30°C (86°F) supply temperature. There, even 15cm (6 inches) was sufficient. Using 10cm (4 inches) insulation over lengths of 70–100m (230–330 feet) would have meant a few extra meters of pipe and probably an additional heating circuit. So I told my installer to keep it tighter in the bathroom.
It partly depends on how and on what terms you can communicate with your installer. I think this varies a lot.
If, of course, you have one who doesn’t want to cooperate at all and you suspect that not much calculation is being done, it’s better to stick with the insulation thickness guidelines.
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