ᐅ Proper Design and Installation of the Heat Pump

Hello forum members,
I have been reading many posts here for some time now, but I would like to post my question again to be absolutely sure.
I want to switch from a gas condensing boiler to a heat pump. I initially considered geothermal energy, but first, it has become very difficult to find a qualified groundworks contractor for this over the past year, and second, my heating installer advised against it because my energy consumption is too low. That certainly makes economic sense, but I was reluctant to have a "noisy" unit on my property. Those concerns have now been resolved, so I have decided on an air source heat pump instead, and I was recommended the smallest model of the Vaillant Arotherm plus 35/6 series. My uncertainty stems from the fact that this is for a single-family home with 180sqm (1940 sqft) of heated living space. A few more details:
Year built 2014, Kfw 55 energy standard, 2sqm (22 sqft) solar thermal system, controlled central residential ventilation (meaning windows generally stay closed), underfloor heating. Current annual gas consumption is about 1,000 cubic meters. Indoor temperature is maintained at 22°C (72°F) during the day and 21°C (70°F) at night. Two adults, two children. It tends to be warmer than 22°C (72°F), so we feel comfortably cozy.
One more upgrade is in the works: A photovoltaic system will be installed on the roof (God willing, and once my battery storage is finally available) with 17kW peak capacity plus a 14kW battery storage. We already have one electric vehicle, and a second one will probably come eventually; we charge both at home using a wallbox.

I hope this is enough information for an evaluation. My main concern is not being sure what would happen if the 35/6 model is undersized. Would it then fail to provide enough heat, or would I just end up consuming more electricity? I understand that oversizing should be avoided because of short cycling, but do I need to worry about the opposite case as well?

Thanks for any help, and if there are any additional details needed for an assessment, please let me know.
Good luck
Philipp

Depending on the calorific value of your gas, that should be around 10 MWh (megawatt-hours).
It’s hard to say if the smaller one is sufficient. It might work.
But why not go one size up? It hardly costs more and, as far as I know, can modulate down just as far.
Where would it be located in terms of noise?

Normally, this air-to-water heat pump is installed with a hydraulic station including a 9 kW (kilowatt) electric heating element.
This can take over if it gets too cold. That does cost quite a bit for electricity, but at least you don’t have to freeze. ;-)

With Vaillant, you always need to pay attention to the pump capacity. I could imagine that the smaller one might be insufficient. I actually had to choose the 75 model instead of the 55 model mainly because of the pump capacity.

RotorMotor schrieb:

Depending on the calorific value of your gas, it should be around 10 MWh.
Whether the smaller unit is sufficient is hard to say. It might work.
But why not go one size up? It costs hardly any more and, as far as I know, can modulate down just as much.
Where will it be installed in terms of noise?

Normally, this air-to-water heat pump is installed with a hydraulic module that includes a 9 kW (30,600 BTU/h) electric heater.
That can take over if it gets too cold. That costs quite a bit in electricity, but at least you won’t freeze. ;-)

Yes, I also thought that the modulating down capability means the 55 model should be just as suitable. With the same dimensions as well. I’ll definitely bring that up, thanks already!
The installation location would be outside, in front of the utility room, with about 20 cm (8 inches) clearance from my building’s wall. From there, the distance to each neighbor is more than 10 meters (33 feet) in a straight line, plus an evergreen hedge. Since we keep the windows closed in winter, I assume there won’t be any noise disturbance. The wall faces north; the children’s bedrooms face south, and ours faces west. Is there anything else I should consider?

Tolentino schrieb:

With Vaillant, you always have to pay attention to the pump performance. I could imagine that the smaller one might be insufficient?
I actually had to choose the 75 size instead of the 55 only because of the pump capacity.

Thanks for the tip, I will ask about that. I will receive the design analysis next week; I assume they also used the Vaillant tool for that.
Here are the parts of the offer—maybe something useful can be found there.

If you originally wanted geothermal energy, try searching for the term ring trench collector. This is a straightforward ground collector installed in trenches following a specific looping pattern. Since the ground is warmer than the air in winter, the annual performance factor is usually better than that of an air source heat pump.