ᐅ Does the ventilation system really pump humid outside air into the house?

What mainly determines the indoor temperature in summer is less the building envelope and more the shading and ventilation. You can have the best building, but if the sun shines directly through the windows or you keep the windows open during the day, heat bypasses the building envelope. Thermal storage inside the house, for example through concrete ceilings, also helps a lot, but this requires that you can ventilate the heat out again at night.

RotorMotor schrieb:

Wrong, modern ventilation systems can recover up to 90% of the heat.
This works at -10°C (14°F) outside and 21°C (70°F) inside.
It also works the same way at 30°C (86°F) outside and 21°C (70°F) inside.
In fact, the temperature difference in summer is often much smaller.

I have already calculated several times here in the forum how low the heat input from operating ventilation in summer actually is.

So keep the ventilation running both in summer and winter to maintain a comfortable indoor climate.
Control based on humidity and CO2 levels can make sense.
Temperature should not be a trigger due to heat recovery.

I can confirm that; the house is always pleasantly tempered despite continuous operation of the mechanical ventilation with heat recovery system. I (unfortunately) do not have an enthalpy exchanger, so currently about 70% relative humidity on the hygrometer. However, it is not uncomfortable, and as far as I understand, it is also not problematic.
Additionally, I often keep the patio door wide open for long periods when I am at home, at least when the temperatures allow it.

Most centralized mechanical ventilation systems with heat recovery have a user interface (web, app) that allows settings to be adjusted by the end user. I have customized the ventilation to my personal needs (when and how much to ventilate, dehumidification, reduced, nominal, and intensive ventilation). Besides the time-controlled operation, sensor-based control would also be possible, but since I only have a humidity sensor installed, it works better for me on a schedule.

Regarding energy savings: it should be noted that this is never the main reason to install such a system. My unit has recovered about 160 kWh of heat energy in approximately 2 years (according to the system).
Assuming a coefficient of performance (COP) of 4, that is roughly 40 kWh of electrical energy multiplied by about $0.40 (USD) per kWh. With system costs exceeding $10,000 and annual filter costs of about €100, anyone can calculate that it is not cost-effective just based on energy savings.