Air conditioning: What is the royal way

We have installed a ground source heat pump with cooling function (additional cost €700) and the controlled residential ventilation has a ground heat exchanger (additional cost €2,000). This is sufficient in our case, together with shading, to maintain room temperatures even during prolonged high outdoor temperatures like recently at a maximum of 24°C

That sounds very interesting. Can you tell us more about your overall solution?

We installed a ground source heat pump with cooling function (additional cost €700) and the controlled residential ventilation has a ground heat exchanger (additional cost €2,000).

Super! After 8 pages of air conditioning yes/no and who has the biggest and the most flashing lights on it, finally an alternative. Thanks! Has anyone also gained experience with green roofing or similar? Green roofing is also supposed to be heat protection (Google).

Addendum, quote from an energy consulting brochure: "Already Kolb & Schwarz (1986) researched at the end of the 1980s that a higher quality extensive green roofing significantly reduces temperature extremes on hot summer days. ... The Berlin Senate Department for Urban Development (2010) builds on these and more recent studies in its brochure [„Konzepte der Regenwasserbewirtschaftung, Gebäudebegrünung, Gebäudekühlung – Leitfaden für Planung, Bau,Betrieb und Wartung“]. It is again clarified here that the evaporation of 1 m³ of water produces an evaporative cooling of 680 kWh, which corresponds to 0.68 kWh per liter..." (Google Energieberatung opti...grün).

Or just try googling the cool greens. Links are unfortunately not allowed here.

That sounds very exciting. Can you tell us a bit more about your overall solution?

What exactly do you want to know?
In our case, it is a new build from 2013, 42.5 cm Poroton masonry with perlite filling, gable roof with 22° pitch, tiles, and normal insulation between rafters.

The heat pump is a Vaillant geotherm VWS 63/3, operated with two deep boreholes of 85 m each. The extra cost for the version with cooling function was about €700 as mentioned. No other measures were taken.

The supply temperature on hot days is 20°C; I think 17-18°C should also be no problem, but 20°C is completely sufficient for us.

On hot days, we keep the shutters upstairs closed two-thirds, and the venetian blinds on the ground floor are tilted open. The indoor temperature reached 24°C only once in the last few weeks; 90% of the time it is below 23°C.

Your constant outbursts and insults do not make your statements true either. You lack basic knowledge of physics.

For the heat transfer between the ceiling and room air, I would have assumed 6 W/(m²*K), but better values can also be found in the literature, so let's assume 10 W/(m²*K). The cooling load in a typical room can be 100 W/m² or more on hot days.

With these conservative values for a hot day, you get a delta between surface and room temperature of 10 Kelvin. If you want 22 degrees in the room, the ceiling must be cooled down to 12 degrees. How cold the coolant is does not matter for this consideration, but due to the much higher heat transfer between the piping and ceiling material, one can assume that a much smaller delta arises here.

Now you can argue that the power peaks are buffered, that you could raise the room temperature, that there are also more effective surfaces for cooling ceilings or whatever else you can think of. All correct; then you arrive at half the delta and 17 degrees ceiling temperature. Never 22.

What you apparently don’t want to understand is the fact that no thermal energy flows between two bodies that are both 22 degrees warm. (Physically not entirely correct, see blackbody radiation etc.)

Now he wants to cool the ceiling down to 12 degrees. OMFG...

I don’t want anything, I just wanted to point out:
-that the surface temperature is far from 22 degrees, and this is physically determined.
-that Recknagel, like many manufacturers, recommends or requires additional moisture regulation for a reason.

Make of it what you will - you cannot be convinced with technical literature and physics, instead you become personal, unobjective, and insulting, so I’m withdrawing from this here.