Air-to-water heat pump sizing in new construction

In the access to the granny flat, you can either charge a flat rate or allocate it per m2, that's how I do it with our granny flat, but that's my mother-in-law, so it doesn't matter if we lose money.

can someone among the experts here evaluate the Vaillant arotherm 75/6? it’s supposed to easily achieve the annual performance factor, even 4.6. but here in the forum you rarely hear about Vaillant in connection with heat pumps... is there a particular reason for that?

I myself have a Vaillant Arotherm split with Unittower... but it’s only been in the house since April, so I can’t say anything about consumption in winter yet.

I have a calculated heating load of 3.5 kW and the general contractor/house manufacturer wanted to install a 5 kW system. However, I insisted on installing the smallest possible system (I believe 3.5 kW) and got it. All in all, it seems to be a solid product, but we’ll have to wait for winter.

In addition to optimal performance relative to the heating load, there is the modulation range of the system and the design of the underfloor heating.

I also insisted on a max supply temperature of 30°C at NAT and max 10 cm pipe spacing and got that despite pressure and manipulation over the temperatures. Otherwise, I would have gotten a 35°C/28°C standard layout with 15 to 20 cm pipe spacing.

In general, you have to engage intensively with the systems yourself and read up, because the standard builder, house manufacturer and their subcontractors usually no longer explain during commissioning how to set the room temperature and hot water temperature. Let alone how to deactivate the electric heating element, lower the heating curve, or put the system into whisper mode which makes it modulate even a bit more.

Unfortunately, I couldn’t argue away the individual room control and mini return buffer tank. But I disconnect the actuators and luckily the buffer is only 15-20 liters.

My heating technician also thinks nothing of ERR and suggested disconnecting the actuators on his own initiative. However, he also believes we won’t get below 35°C, probably because the 75/6 is oversized and he thinks nothing of laying distances under 10 cm except for the bathroom.

What do you mean by manipulation via temperature? Did you specify a lower desired temperature so that he accepts a lower flow temperature?

and does not approve of installation distances under 10 cm except for the bathroom.

He can disapprove if he wants, there are installation guidelines, for example for edge zones, and it can sometimes make sense to go down to 5 cm, even in other rooms.

Aha! Can you navigate me with appropriate search terms?

Yes, I have, since I already knew in advance that the calculated heating load would be too high anyway.

That’s why I set the requirement to calculate the entire house at 20°C. Otherwise, the 24°C usually assumed for the bathroom would have caused higher flow temperatures for me.

If the bathroom ever does get too cold for me on 1-2 days a year, an electric heater/fan will be installed in the bathroom.

Theoretically and probably practically, the smallest heat pump for the house is still too large... I think the actual heating load will later not exceed 2.5 to 2.8 kW.

However, the best decision so far was the photovoltaic system; I have generated and fed in many times more electricity than I have taken from the supplier. Let’s see how it goes with the photovoltaic system in the autumn and winter months.