ᐅ Assessment of the Heating Concept for a KfW 70 Energy-Efficient House

Hello everyone,

I have already looked closely at the current offer we have for a KfW70 house and am not entirely sure about the air-to-water heat pump being used.
The following is currently included in the offer:

• KfW70 house
• 160 sqm (1,722 sq ft) of living space heated with underfloor heating
• central controlled ventilation system (manufacturer unknown)
• Rotex HPSU 6 compact heating and cooling with 500-liter (132-gallon) stratified storage tank up to 7 kW

I have researched this heat pump online but cannot judge whether these are just some isolated negative experiences and satisfied users don’t speak up, or if the unit is actually that “poor.”
One significant concern for me was that the electric heating element activates already at around 0°C (32°F).
At a house viewing appointment, I was able to experience the heat pump, and despite it not being a very cold day, the outdoor unit seemed quite noisy to me.

What do you think about this combination/heat pump?
Are there alternative units you would recommend?

I am generally comfortable with the idea of an air-to-water heat pump, but those many negative impressions of the above Rotex unit have made me cautious.

Thank you very much for your support!
oerlein

The Rotex HPSU Compact as a split system is the standard chosen by our developer. After much consideration and several discussions, I simply accepted this. In a year or two, I might be able to share some experience.

I can find only a few user reports online, mostly somewhat outdated. There are both critical opinions (usually apparently due to improper settings by insufficiently trained installers, but also concerns about "noise") as well as satisfied users.

Alternatives (such as Vaillant ...) would have been significantly more expensive in our case, and any potential efficiency improvements would hardly pay off.

PS. I dislike that the catalog images are enhanced, but this is probably the case with all manufacturers, so you hardly have a choice.

Heat pumps and buffer tanks are not necessarily the best combination. From personal experience: the house is so slow to respond that you can’t just quickly adjust the temperature—so you can skip the tank. The only situation where it might make sense is during restricted operating hours—do those still exist? Even then, your house won’t cool down significantly.

The brochure for the Rotex is unfortunately very brief, but as far as I can tell, the storage tank is used solely as a hot water tank. Does your criticism include this, BeHaElja? I am not aware of any connection to the (building) heating system. However, I would appreciate a detailed explanation of the function of the Rotex HPSU.

500 l (132 gallons) domestic hot water tank – how many people do you have? I’m starting to get concerned about Legionella.
No, I was only referring to buffer tanks for the heating system.

The tank in question is what is known as a hygiene storage tank, which is highly recommended and poses absolutely no hygienic issues—in fact, quite the opposite. If it is the model I believe it to be, there is a 500-liter (130-gallon) buffer tank that is heated and essentially remains in the system indefinitely without needing to be replaced. This buffer tank transfers heat to the flowing fresh water through a stainless steel heat exchanger, operating on a flow-through principle. In total, there are only about 29 liters (7.7 gallons) of fresh water within the system, meaning the fresh water in storage is replaced very quickly. I hope I have explained it clearly enough. Otherwise, you can search for “hygiene storage tank” or “fresh water station” since the principle is the same here.