ᐅ Experience with KfW 55 house and LWZ 504 unit performance

Hello dear building experts,

we have recently built a new house and moved into our own home in August.
We had the LWZ 504 installed, and since early October the heating operation has also been activated.
Then a series of problems started that the heating system couldn’t solve. After being without heating and hot water in the house for several days, the service from SE came at the beginning of the week – luckily, it is working again now.

I have been looking into our new unit quite thoroughly for a while and can’t shake the feeling that the air source heat pump might be undersized for our house. If I understand correctly, there are two different power versions of this pump, A2 and A7 (is that right?); we have the A2 with 5.16 kW.
However, the user manual says this pump is designed for an output up to 10 kW.

Since we have a relatively high electricity consumption, about 30 kWh daily for the heat pump (3 people), I checked the KfW documents. Here, a heating load of 9 kW including hot water was calculated.
The explanation of the heating system also states that we have a system with 9.3 kW capacity.
Could this be related to the seasonal performance factor or annual performance factor being included in that calculation?

We have a:

KfW 55 house
Building volume: 1309.04 m³ (46236 ft³)
Usable floor area: 419 m² (4511 ft²) (80 m² (861 ft²) of this is a secondary apartment with a separate instantaneous water heater and separate ventilation; this apartment is heated with our heat pump).
We personally occupy and heat 180 m² (1937 ft²) and also have an additional wood stove.
Final energy demand: 23.5 kWh (per m²/year), primary energy demand: 42.3 kWh (per m²/year).

I’m a bit confused – am I misunderstanding something? Does the pump below actually cover the demand? At night it’s always louder than usual, and the electricity meter runs quickly...

Thank you in advance for your help!

So the area that needs to be heated is quite substantial. But the size is sufficient.

Tell me about the settings.
How often is hot water produced and at what temperature?

How are the individual room controls set?

ENGCHRIS schrieb:
A2 and A7 (is that correct?), we have the A2 with 5.16kW

The A stands for the outdoor temperature, the W for the supply temperature, and the sticker shows the power output and demand under these conditions. The capacity will be sufficient. It is important to maintain continuous heating, ideally without thermostats. Search online for thermal/hydraulic balancing and heating curve with low supply temperature. Once you have this set up over the winter, the system will operate significantly more efficiently than if you leave everything as is. You can disregard the Energy Saving Ordinance and KfW specifications when sizing the heating system. For example, the ventilation system is often overlooked there. We had 7kW indicated, calculated 4kW for the heating, and in reality it is less than 3kW.

Thank you very much for your responses; that already puts our minds at ease.
We are currently working on the settings. Here is our current heating curve

Hot water: we have already lowered it as well, during the day to 40.5 degrees Celsius (105°F), in the morning for 3 hours and in the evening for 3 hours to 47.5 degrees Celsius (117.5°F),
because the electric heating element was already activating during the hot water flow. Otherwise, the house temperature is a comfortable 21.5 degrees Celsius (70.7°F),
the bathroom is a bit warmer, and the bedrooms are set to 19 degrees Celsius (66°F). We need to monitor this now; before the service technician came to us, the system had not operated without faults for more than 48 hours. The main cause seemed to be that the flow rate was not correct.

When the system was back in operation Tuesday evening, the house temperature was 17.5 degrees Celsius (63.5°F). During the following 24 hours, it felt like a helicopter had taken off and landed in our basement, obviously because the system had to reheat the entire house. I thought it would soon break down and not manage it. In these 24 hours, it consumed a full 70 kWh, and we supported it with our wood stove.

According to the service technician, all the filters are clogged and need to be replaced. I am still waiting for my order; maybe this will save some kilowatt-hours as well.

Thank you very much for your support!

Hey! Changing filters after three months? Are they really clogged?
We have cone filters in the exhaust vents, and since then, there has been no issue with the system.
What are your heating curve settings? Are the values for HK1 and HK2 the same?

ENGCHRIS schrieb:

Since we have a very high electricity consumption in my opinion, about 30 kW daily for the heat pump (3) people,

You can only find out if your house uses a lot of energy or if the heat pump is running inefficiently by comparing the heat output with the electricity consumed. Ideally, you have an external heat energy meter. However, you can also likely read the relevant values directly from the device.

It is important that the electric backup heater runs as little as possible, that the heat pump operates continuously with minimal cycling, and that the supply temperature is kept as low as possible (deactivate thermostats, lower the heating curve). You will surely find help online specific to your heat pump model.