ᐅ Retrofitting an air conditioning system – will that affect KfW funding?

Deliverer schrieb:

I would like to see a source for that. Until then, I say: "Nonsense!"

The physics behind my claim:
Delta T in winter ~ 35°C (95°F)
Delta T in summer ~ 10°C (18°F)

Why should the latter require three times more energy with the same technology...

Please don’t calculate with the maximum but with the average – for example, the average temperature during the winter half-year 2020/2021 (heating period) in Bavaria was 1.9°C (35°F).

So, roughly 20 Kelvin ΔT (difference). Not 35.

And additionally: solar radiation supports the heating system – up to about 8°C (46°F) with some sunshine, I don’t necessarily need heating. In other words, you have a “tailwind.” In summer, it’s exactly the opposite – now the heating technology has to work against it, so it’s like a “headwind.”

Deliverer schrieb:

I would like to see a source for that. Until then, I say: "Nonsense!"

The physics behind my statement:
Delta T in winter ~ 35°C (63°F)
Delta T in summer ~ 10°C (18°F)

Why the latter should require three times more energy with the same technology...

I’m glad someone with knowledge of physics doubts that!

My source: A phone call with the technician from our house manufacturer. He himself lives in an old prefab house (42 years) and has bought portable air conditioners for it, but unfortunately they rely on expelling the warm air through an open window. Energetically, that makes little difference.

The reason I called was to ask if, in my place, he would actually install the heat pump with cooling function sold by the manufacturer or rather go straight for a proper air conditioning system.

He said he would prepare the building for a proper air conditioning system if he were building new. Reason: Prefab houses don’t have enough thermal mass to buffer temperatures. (Think of a church in a Mediterranean climate!)
If the air doesn’t cool down significantly at night, you simply can’t exchange it effectively.
Unlike a massive church, modern buildings are constructed with large solar gains through huge south-facing windows. Lots of input, little output.

If you tell me where to look, I’d be happy to check my energy report for the house.

I’m having a patient day today. So:

Scout schrieb:

So just under 20 Kelvin ΔT. Not 35.

Still more than my assumed maximum! In summer, right?

Scout schrieb:

And on top of that: solar radiation supports the heating system – up to about 8°C (46°F) and with some sun, I don’t really need heating. In other words, you have a "tailwind."

And in summer, you have cool nights and high sun angles that don’t even shine into the south-facing windows. I’d say that balances out.

Scout schrieb:

But in summer, it’s exactly the opposite – now the heating technology has to work against that, so it’s a "headwind."

Each system always works against the current energy inflows and outflows. At a location with an annual average temperature of 22°C (72°F), you could probably achieve a balance between cooling and heating energy. Unfortunately, Germany has about 10°C (50°F). So most likely, more heating is needed than cooling. From what I see around me, the ratio of heating systems to air conditioners supports my theory. ;-)
And yes, if you manage windows and shading smartly, you can save energy both in summer and winter.

I stand by my statement that I would like to see sources. Until then, my experience with a total of five heat pumps in three households and a bit of logic (see above) must suffice.

Currently, my old building:
Heating: 5000 kWh, Cooling: 1500 kWh

New build (KfW55 standard), occupied by my parents:
Heating: 2300 kWh, Cooling: 300 kWh

Of course, this will vary depending on location and inhabitants’ habits as well as the building itself. However, I don’t see your basic claim that cooling costs three times as much energy as heating confirmed. Rather, the opposite seems more likely.

Reltaw2021 schrieb:

I’m glad someone with knowledge of physics is questioning this!

A thermos flask doesn’t care whether you pour iced tea or coffee into it...

Reltaw2021 schrieb:

He himself lives in an old prefab house (42 years old) and bought portable air conditioners for it, which unfortunately rely on expelling the hot air through an open window.

That disqualifies him from giving advice on cooling. Those things are just energy wasters. Please don’t buy them!
Ah, and please don’t do that nonsense with a wet towel and a fan either. That just makes it even more humid. It helps about as much as scratching when treating bee stings.

Reltaw2021 schrieb:

... who would want to install the heat pump with cooling function sold by the house manufacturer or would rather opt for a proper air conditioning system.

If you build a house with lots of thermal mass, underfloor heating, concrete core activation, etc., it’s always a good idea to take advantage of the heating system’s cooling function. Any manufacturer who charges extra for this should be ruled out immediately. Apart from an additional condensate sensor (which can reasonably cost around 50 €), all that is needed is a software setting in the heat pump. If that’s not available, the heat pump is already obsolete.
BUT: this only works as a supplement to at least one air-to-air heat pump (air conditioning), because the crucial effect—the part that positively influences the indoor climate—is dehumidifying the air. Underfloor heating cannot do this. On the contrary: cooling the indoor air increases the relative humidity, and everything feels sticky.
Together, though, the two systems complement each other very well: the “heavy hitter” (heating) can extract a good 5 kW of heat energy from the house, for example. At the same time, a small, energy-efficient air conditioner can dehumidify the air, which works well even between rooms.
So the answer is yes. Both.

Reltaw2021 schrieb:

He would prepare the building works for a proper air conditioning system if he built new.

I would install it right away. Cheaper, cleaner, and even subsidized at the moment. Two friends just built houses recently, both (against my advice) did not install air conditioning (because the insulation is so good!). One family has been sleeping in the basement for days; the other doesn’t have a basement and is miserable. (Admittedly, nobody has admitted I was right yet ;-)

Reltaw2021 schrieb:

If you tell me where to look, I’d be happy to check my energy report for the house.

Why? In my opinion, every reasonably detached new build should have at least a (small) air conditioning system installed. Just like a controlled mechanical ventilation system and the roof fully covered with photovoltaics. Then it all comes together.

@Scout Sorry, I realized too late that it wasn’t you who claimed the "3 times more energy."

Even at the risk of facing criticism right away.
We recently had our first real test:
Starting point:
36.5 cm (14 inches) aerated concrete, south-facing, very large window areas, external blinds, underfloor heating on the ground and upper floors, attic converted with low-temperature radiators connected to the underfloor heating, brine pump with cooling function, and controlled mechanical ventilation with heat recovery.

Here in the Rhineland, we had many days in a row of 34–36°C (93–97°F).
The heating system switched to cooling mode, the mechanical ventilation ran day and night with the bypass at the lowest level, windows remained closed, including at night. External blinds were lowered during the day, with slats set to 50%.
Result: depending on the time of day, indoor temperatures ranged between 23 and 25°C (73–77°F).
I find this great and very comfortable. The floor is not cold, as you often hear, and the temperature is just right. Personally, I find it quite uncomfortable to come inside from the garden at 35°C (95°F) when the house is only 21 or 22°C (70–72°F). The contrast is too strong for me. Still, 23 to 25°C (73–77°F) feels quite cool. Of course, the humidity at 65% could be better, but maybe it will improve. It is said that in a new building, humidity levels are higher during the first years.
If not, that’s okay too. I found it very pleasant and am very satisfied with our summer thermal protection without air conditioning.

Just wanted to share a different perspective.