ᐅ Brötje BWL Neo 8 – Issues with the Settings

Hello everyone,

Since I’m having trouble communicating with my heating installer, I’m asking you all:
What exactly is a “modulating heat pump”?
The Brötje BWL Neo 8 installed in our home is described by the manufacturer as modulating. However, since its commissioning in November 2023, it has been running at full heating capacity: about 7 kW. Although it operates with a good COP (average over the last two months is 4.4), that doesn’t help me much. Currently, it consumes a huge amount of electricity (sometimes well over 30 kWh per day). That doesn’t seem normal for a new build...
The installer says the pump only modulates the flow rates, not the output power. That can’t be right, can it?

I’ve noticed in this forum that @Alessandro has the same pump. However, his posts are somewhat old. Could someone help me out here?

To keep this post concise, I’m leaving out detailed information about the hydraulics and settings for now. These will follow if needed.

Kati2022 schrieb:

What is a "modulating heat pump"?

The heating output adjusts to the demand (by the heat pump). Non-modulating basically means only on/off, where “on” means full power.
You can check the possible power inputs (and heating outputs on page 18 of the user manual).

Kati2022 schrieb:

In our case, it has been running at full heating capacity since the start (commissioned Nov 23): about 7 kW.

Unrenovated old building?

Kati2022 schrieb:

The installer says the pump only modulates the flow rates but not the output. That’s nonsense, right?

Yes, it is fully modulating (the compressor modulates); the pump only ensures the correct flow rate depending on settings or demand.

A question to you: How is your heating system set up? What kind of house? What type of heat distribution (underfloor heating/radiators)? Do you have a heating load calculation? Has hydraulic balancing been done? How is the heat pump configured? My heat pump (different brand) currently runs at about 50–60% capacity at 1–3°C (34–37°F) outdoor temperature. Just for comparison—that’s what modulating means.

Thank you for the explanation.

As mentioned above, it’s impossible to discuss anything with the heating engineer, a complete disaster...

It’s a new building with approximately 180 square meters (1,937 square feet) of heating surface. The final energy demand is 20.9 kWh.

The hydraulics are set up exactly according to Brötje’s specifications. Combination buffer tank with 300 liters (79 gallons) for hot water and 100 liters (26 gallons) buffer tank. The pump is controlled via the return flow. Currently, the mixing curve is set about 4°C (7°F) lower than the heating curve.
I once set the mixing curve equal to the heating curve myself, but the heating engineer said that was wrong and raised the heating curve again.
Currently:
Heating curve (return flow): 27/30/33
Mixing curve (return flow): 23/26/31

At the moment (at 4°C [39°F] outside temperature), the pump is running at 6.5 kW and consuming 1570 W, COP 4.2.

A hydraulic balancing was (supposedly) carried out. Unfortunately, I no longer trust the heating engineer at all.

What other information do you need?

Kati2022 schrieb:

What other information do you need?

At first glance, it looks okay. I’m just wondering where all the heat from the heat pump goes with those curves. It must be producing a massive surplus.

However, I would remove the buffer tank completely. Use only the domestic hot water tank and connect directly from the heat pump to the underfloor heating. You’ve been sold an expensive, unnecessary setup.

Apart from that, the heat pump is oversized for the house.

Sensors malfunctioning? That could be a possibility.

nordanney schrieb:

You were sold an expensive and unnecessary system.

The heating engineer says he has to follow the manufacturer's specifications for the warranty...
The system was also commissioned by a Brötje technician.
At temperatures around 10°C (50°F), the pump cycles on and off rapidly instead of reducing power. The heating engineer says, "That's normal."
To reduce cycling, I have set a 5K (5°C / 9°F) night setback between 9 pm and 6 am. Then the house cools down to 19.5°C (67°F) and takes until the afternoon to reach the desired 21–22°C (70–72°F) again. We would prefer a consistent temperature around 21.5°C (71°F) with longer cycles and lower output.