Renovation to KFW85/70: Ventilation including cooling

Hello everyone,

we are planning the renovation of an old building with 3 residential units into a KFW House 85 and possibly even 70.
We would like a solution that brings fresh air into the house and cools it down in the summer.
The idea so far has been to install a heat pump with photovoltaic support and distribute the heat via underfloor heating.

Does anyone have experience and recommendations for such ventilation systems with active cooling function?
An app control would also be great, although I have seen so far that the app from e.g. Nilan is rated rather poorly in the store.

Thank you very much!

Your heat pump may already have a cooling function from the factory or can be upgraded relatively inexpensively to include one. Within certain limits, this works quite well with underfloor heating and brings a noticeable improvement.

If you absolutely want to do the cooling (also) through the ventilation system, you must first install insulated/double-layered ventilation ducts to avoid condensation. They are more expensive than the normal controlled residential ventilation ducts but there are now good solutions (e.g., [Zehnder ComfoTube Therm]). [Zehnder] also has controlled residential ventilation devices with cooling, e.g., [ComfoClime Cool] – however, it must be checked how the sizing fits with your house, and with 3 residential units, it is also about how individually controllable/adjustable the whole system needs to be.

You must consider, however, that the cooling functions, at least when viewed individually, are not comparable to a real air conditioning system – 30 degrees outside and 18 degrees inside is not achievable, especially if you do not also provide proper shading. However, if you use both methods simultaneously (i.e., heat pump with underfloor heating and controlled residential ventilation), you can cool perfectly in summer – provided a smart overarching control system is in place so that both devices work sensibly together.

Controlled residential ventilation units that can also cool (active) exist. The problem is rather: 3 apartments, 3 different requirements. Then the issue of fire protection/sound insulation, those are the very best conditions to really run into trouble with it. Also, these units require a minimum volume flow to deliver at least decent performance.

I don’t know how large the apartments are, but instinctively I would rather think of decentralized ventilation. Well, and if cooling is desired, then small "split" systems (fire and ice for example).