ᐅ Is it possible to install air conditioning as an upgrade if a mechanical ventilation system with heat recovery is already installed?

Hello,
we live in a KfW55 house with a controlled mechanical ventilation system. Since it gets too warm for me in the summer, I would now like to add air conditioning units.
I am planning a total of four units: in the three bedrooms upstairs and in the open living, dining, and kitchen area on the ground floor.
I have looked at units from Gree and would choose 2.7 kW units for the upstairs rooms and a 5.3 kW unit for the ground floor, based on the room sizes.

Now to the main question:
Does it make sense to install air conditioning if we already have a controlled mechanical ventilation system? Do the air conditioning units generally need to be sized larger because the ventilation system removes the cool air too quickly? Or does the controlled mechanical ventilation system prevent the rooms from cooling down effectively in the first place?

If you want air conditioning during this below-average warm summer, there might be an issue with the thermal insulation. Are you consistently shading windows during the day? And ventilating at night?

I live in the Rhine Plain, one of the warmest areas in Germany.
At the moment, it’s manageable, but temperatures of 30 and 40 degrees Celsius (86 and 104 degrees Fahrenheit) will come again.
When it reaches 26-27 degrees Celsius (79-81 degrees Fahrenheit) inside the house, it feels too hot for me. I am more of a winter person.

The mechanical ventilation system generally does not cause any significant issues. It could be automatically adjusted to minimum ventilation when the air conditioning is running.

The air volume of a typical mechanical ventilation system is negligible. Assuming your mechanical ventilation operates at minimum ventilation of 100 m³/h (59 cfm), that is the amount of air a 3.5 kW air conditioner cools down in 10 minutes. So, it’s not really worth mentioning.

How large is the house, meaning how much air needs to be circulated?

So the house has just over 1,100 cubic meters (38,800 cubic feet) of enclosed volume. The ground floor and upper floor together account for about 800 cubic meters (28,250 cubic feet).
On the normal setting (2 out of 3), the mechanical ventilation system for living areas runs at approximately 150 cubic meters per hour (5,300 cubic feet per hour).

McEgg schrieb:

I looked at the units from Gree and would choose 2.7 kW for the upper floor and 5.3 kW units for the ground floor based on the room sizes.

If your rooms aren’t very large, that seems quite a lot to me. What floor areas are we talking about here?

At a total of 13.4 kW, the outdoor unit won’t be cheap, or are you referring to single-split units?