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

In the access corridor to the granny flat, you can either charge a flat rate or allocate costs based on square meters, which is how I handle it for our granny flat, but since it’s my mother-in-law, it doesn’t matter if we end up paying extra.

Tolentino schrieb:

Can someone knowledgeable here evaluate the Vaillant arotherm 75/6?
It’s supposed to easily achieve an annual performance factor of 4.6.
But I rarely hear Vaillant mentioned in connection with heat pumps in this forum... is there a particular reason for that?

I have a Vaillant Arotherm split system with a unit tower myself... but we’ve only had it in the house since April, so I can’t say anything about the consumption in winter yet.

I calculated a heating load of 3.5 kW, and the general contractor/home builder wanted to install a 5 kW system. However, I insisted on installing the smallest possible unit (I believe 3.5 kW) and got that. Overall, it seems to be a solid product, but I’ll wait to see how it performs through the winter.

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

I also insisted on a maximum flow temperature of 30°C (86°F) with natural antifreeze and a maximum pipe spacing of 10 cm (4 inches), and I got that after some persuasion and negotiation regarding the temperatures. Otherwise, I would have ended up with a standard 35°C/28°C (95°F/82°F) setup and pipe spacings of 15 to 20 cm (6 to 8 inches).

In general, you need to educate yourself thoroughly about the system because the typical general contractor, home builder, and their subcontractors usually don’t explain during handover how to set room and domestic hot water temperatures. They also don’t show how to disable the electric backup heater, lower the heating curve, or activate whisper mode, which allows the system to modulate a bit more efficiently.

Unfortunately, I couldn’t negotiate away the individual room controls and the small return buffer tank. But I do disconnect the actuators, and luckily the buffer only holds about 15–20 liters (4–5 gallons).

My heating technician also doesn’t believe in ERR and independently suggested disconnecting the actuators. However, he also thinks we won’t get below 35°C (95°F), probably because the 75/6 is oversized, and he doesn’t recommend pipe spacing under 10cm (5 inches), except in the bathroom.

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

Tolentino schrieb:

and doesn’t approve of installation spacing below 10cm except in the bathroom.

He can disapprove all he wants, but there are installation guidelines, for example for edge zones, where it can be reasonable to use 5cm (2 inches) spacing even in other rooms.

Aha! Can you guide me with suitable search terms?

Yes, I did, because I already knew in advance that the calculated heating load would be too high.

That’s why I set the requirement to calculate the whole house at 20°C (68°F). Otherwise, the 24°C (75°F) typically assumed for the bathroom would have resulted in higher supply temperatures.

If I ever find the bathroom too cold for one or two days a year, an electric heater/fan will be installed there.

Theoretically, and probably in practice too, even the smallest heat pump available for the house is still oversized... I expect the actual heating load will not exceed 2.5 to 2.8 kW later on.

The best decision so far, however, was installing the photovoltaic system. I have generated and fed in many times more electricity than I have consumed from the utility. Let’s see how the photovoltaic system performs during the autumn and winter months.