ᐅ Sizing of Air-to-Water Heat Pumps for New Construction

Created on: 6 Aug 2020 11:45
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Pixelsurium
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
OWLer25 Aug 2021 10:12
Tolentino schrieb:

(50l?)

I received 100 liters (26 gallons). We have quite a large volume of water in the system with our three heated floors.

For now, I’ll let the heating engineer handle it. I’m not doing anything with the heat pump this year and will use the room thermostats. In winter 22/23, I’ll try to better understand the system, perform the hydraulic balancing, and deactivate the thermostats.
D
Deliverer
25 Aug 2021 11:02
Your plumber is legally required to carry out the hydraulic balancing during installation. It probably won't be as precise as if you do it yourself, but it should be fine as a basic setting. Oh, they are supposed to perform the balancing with all room valves fully open, and you want to have the reports!
Tolentino25 Aug 2021 11:07
As my heating technician explained, the purpose of the buffer tank is to ensure that when the room thermostats are closed but there is still a call for heat, the heat pump runs for at least 5 minutes before shutting off again. This is because the refrigerant also lubricates the compressor during operation. This function should actually be independent of the water volume in the heating circuit. But who knows what your technician was thinking when choosing a larger one. It definitely won’t cause much more harm. Maybe he just had it left over....

In any case, I’m glad that my technician’s explanation is correct and I don’t have a huge tank standing somewhere in the utility room, which is already too small and barely usable as such (more like just a utility area).
tomtom7925 Aug 2021 11:39
Your heating technician should have sized the modulating heat pump so that it doesn’t keep turning off. Then, the makeshift buffer tank wouldn’t have been necessary.
Tolentino25 Aug 2021 11:47
Vaillant specifies it that way. And it probably doesn’t work if all ERRs are closed; the heat simply cannot be transferred away. How low should it modulate in that case?
tomtom7925 Aug 2021 11:54
Up to the stop, or do you think that 50 liters of water can absorb that much energy?