ᐅ Heat pump combined with Brötje NEO 18 B, 16 kW (hybrid system)
Created on: 1 Jan 2025 20:31
D
DIRAHRAVThe plan was to heat the house—with two granny flats, 450 m² (4,843 sq ft) of living space, and thermal insulation class 75—as flexibly and energy-efficiently as possible. The combination offered by Brötje through the installer seemed suitable. Domestic hot water (DHW) was supposed to be provided by the gas boiler since the 11 kW photovoltaic system would generate enough surplus electricity when there is sufficient sunlight. During cold, dark periods, the heat pump does not deliver much. Also, I did not want to spend 50 minutes producing DHW at an outside temperature of 0°C (32°F) while meeting the demand for three bathtubs. (No electric auxiliary heating and no tankless water heaters were planned.)
Additionally: 55°C (131°F) flow temperature at 16 kW, running at full power and 3°C (37°F) outside, reduces the Coefficient of Performance (COP) to well below 2. In such cases, gas is significantly cheaper and can save CO₂ emissions as well. More on that later. Below 2°C (36°F), the gas boiler should run—possibly even at lower temperatures once the COP is clearly established. In this setup, the electric heating element is not necessary.
Brötje designed the hydraulics and all parameters. However, during installation, it quickly became clear that planning was not done carefully. The hydraulic scheme included unnecessary three-way valves, redundant mixing units, and electrically poorly thought-out specifications, turning the project into a headache.
1. The gas boiler could not produce DHW. When the gas boiler started, the DHW pump for the heat pump also ran. Because it was stronger, it pulled water backward from the gas boiler, which then triggered a fault. The solution was to disconnect the expensive and unnecessary DHW pump of the heat pump electrically.
2. Now: The heat pump ran until it reached the set value. The gas boiler started. Since the outdoor thermostat was missing and the control was primarily for the heat pump, the gas boiler ran with a constant 60°C (140°F) flow temperature. However, it only delivered a maximum of 11 kW. To increase output, the flow temperature had to be manually raised above 70°C (158°F). Reason: The pump does not modulate and stays at around 0.4 m³/h. This is not very efficient. This was then changed. Now the temperature adapts based on conditions. Depending on the outdoor temperature, it modulates between 50 and 55°C (122 and 131°F) with a regulated water flow. However, it frequently cycles on and off. It pumps 15 kW into the storage even though only 9 kW is drawn. With my 300-liter (79-gallon) tank, it stops after just under 15 minutes. Instead of 55°C (131°F), if properly adjusted, it should operate at only 40–45°C (104–113°F), which would increase efficiency to over 4–5 COP.
3. Since the gas boiler at least works for the transition, the heat pump ends up heating the water—a result I did not want.
It has now been discovered that there is a second hydraulic calculation without three-way valves in the DHW circuit. This is supposed to be changed. The Brötje technician then had concerns. He said the DHW pump of the heat pump is needed to supply enough hot water during the defrost phase. So both pumps, the heat pump and the DHW pump, push water into the heat pump for defrosting. This could fill a C-hose. He was apparently unaware that the heat pump has a hot gas defrost cycle with energy supply via the scroll compressor.
4. I noticed that the heat pump did not modulate and always ran at 16 kW. After a call with a colleague, the Brötje technician made an adjustment. And indeed, sometimes the heat pump modulates—but only when it gets really cold. At a temperature of about 8°C (46°F), it still runs at 16 kW and fills the storage tank in 5 minutes, despite a consumption of only 4 to 5 kW. For 400 liters (106 gallons) and a 4 K (7°F) temperature difference, you only need about 1.9 kW. At over 10 kW, that takes roughly 10 minutes. So the heat pump cycles about 60 times a day. Unfortunately, it also modulates only up to about 50%, or 8 kW. (A good scroll compressor ideally operates between 40–60%.)
I did not want to contradict the Brötje technician’s argument that the scroll compressor has to run at full load for some time at the beginning (10 minutes!) to warm up, in order not to completely upset him.
5. I am still hoping for improvements. I tried to calculate the COP stated for the heat pump. I have a heat meter and a second calibrated electricity meter.
The external electricity meter shows 20% higher consumption than the heat pump’s internal meter. The heat pump has a separate fuse. Nothing else is connected to it, not even circulation pumps, because of the heat pump tariff. No electric auxiliary heating.
The heat meter shows 5% less usage.
If I calculate based on the stated COP—I currently run the heat pump only down to 5°C (41°F), with a COP of 3.9—it comes down to about 3.2.
The average COP without condensing boiler with auxiliary heating is thus currently well below 3, closer to about 2.5. Such a value is not eligible for funding under BAFA guidelines.
In conclusion:
It may be that the heat pump runs differently in solo mode. However, it is clear that operating, algorithms, and experience from refrigeration technology are missing. Heating engineers and refrigerant compressors do not seem to get along well.
The hybrid concept is economically the only alternative for buildings built before 2007 when it comes to air-source heat pumps. The heat pump can be designed for up to 2°C (36°F) without an electric heating element. Gas or oil condensing boilers, if available, are efficient. Depending on gas and electricity prices, usage can be adapted. The storage tank does not need to be large for cases where heat pump tariff heating is switched off. Legionella protection in winter is significantly cheaper with fossil fuels than with a heat pump.
Suppliers are relieved from massive electricity peaks because the simultaneous usage factor means the capacity does not need to be tripled.
During high electricity demand in winter, many gas power plants—which are written off rather inefficiently—have to supply additional power. These do not operate in combined heat and power mode and therefore do not achieve 40% efficiency. Adding transmission and transformer losses, the gas boiler in total is significantly more CO₂-saving.
I now also see a change in mindset at Brötje, designing new gas boilers for hybrid solutions.
The problem: The risk that such a system will initially not run properly. See my Brötje NEO 18 B, 16 kW. An upgraded NEO 16 C 16 kW might work better.
Heating technicians, and I see this in comparisons, are inflexible and narrow-minded in their explanations. Practical fundamental refrigeration experience is lacking.
Heat pumps are definitely the right path. If you can drill deep enough, and the effort for trench collectors and other off-grid solutions is possible, it works even for poorly insulated buildings. Collection pipes at 400 m (1,312 ft) depth with 15°C (59°F) into the apartments would also be a solution, achieving efficiency up to 50°C (122°F).
Now I have the Brötje NEO 18 B, 16 kW to deal with. I also have the impression that Brötje tinkers more than professionally plans. The device itself is not bad in principle. Although far too expensive for what’s inside. But that is no better with competitors. The heat pump supplies DHW through insulated pipes into the house but has internal pipes with only 25% insulation. Not all IP56-rated. That’s unfortunate. Extremely complicated installation. The boiler room is almost 120 cm (47 inches) deep. Condensation shaft with gravel, 100 x 100 cm (39 x 39 inches), 100 cm (39 inches) deep.
Everything has to fit perfectly. The fan is very quiet. Great. The flow in the heat exchanger works well. But no effort was made for insulating the scroll compressor. With some professional insulation, I managed to reduce noise by almost 6 dB. Now you can hardly hear anything during normal operation. The scroll compressor itself also seems solid. I wouldn’t bet I know it, probably sourced externally.
In China, the outdoor unit of the same build costs a maximum of 5 to 10% of the retail price. So I expect at least a programming level of standard quality. Even if this sounds unprofessional, I think it can be done much better.
I could list a number of other problems with my project, but Brötje is not solely responsible.
I know a little and see that a layperson quickly becomes overwhelmed. A poorly functioning system will not be corrected without detailed complaint. The heating engineer is almost equally overwhelmed. Manufacturer colleagues are primarily interested in making their machines look good. Many systems that go off track could be realigned with simple adjustments by specialists. In principle, it does not matter which manufacturer’s parts are used—most are essentially the same. Optimal on-site adjustment is just as important as the correct load profile, which the heating engineer must specify. However, he is usually overwhelmed. Low flow temperatures, changed control behavior, and building heat loss assessments are often poorly estimated. You don’t have to calculate everything; sufficient experience is usually enough.
In that sense: Let’s see how it goes.
Additionally: 55°C (131°F) flow temperature at 16 kW, running at full power and 3°C (37°F) outside, reduces the Coefficient of Performance (COP) to well below 2. In such cases, gas is significantly cheaper and can save CO₂ emissions as well. More on that later. Below 2°C (36°F), the gas boiler should run—possibly even at lower temperatures once the COP is clearly established. In this setup, the electric heating element is not necessary.
Brötje designed the hydraulics and all parameters. However, during installation, it quickly became clear that planning was not done carefully. The hydraulic scheme included unnecessary three-way valves, redundant mixing units, and electrically poorly thought-out specifications, turning the project into a headache.
1. The gas boiler could not produce DHW. When the gas boiler started, the DHW pump for the heat pump also ran. Because it was stronger, it pulled water backward from the gas boiler, which then triggered a fault. The solution was to disconnect the expensive and unnecessary DHW pump of the heat pump electrically.
2. Now: The heat pump ran until it reached the set value. The gas boiler started. Since the outdoor thermostat was missing and the control was primarily for the heat pump, the gas boiler ran with a constant 60°C (140°F) flow temperature. However, it only delivered a maximum of 11 kW. To increase output, the flow temperature had to be manually raised above 70°C (158°F). Reason: The pump does not modulate and stays at around 0.4 m³/h. This is not very efficient. This was then changed. Now the temperature adapts based on conditions. Depending on the outdoor temperature, it modulates between 50 and 55°C (122 and 131°F) with a regulated water flow. However, it frequently cycles on and off. It pumps 15 kW into the storage even though only 9 kW is drawn. With my 300-liter (79-gallon) tank, it stops after just under 15 minutes. Instead of 55°C (131°F), if properly adjusted, it should operate at only 40–45°C (104–113°F), which would increase efficiency to over 4–5 COP.
3. Since the gas boiler at least works for the transition, the heat pump ends up heating the water—a result I did not want.
It has now been discovered that there is a second hydraulic calculation without three-way valves in the DHW circuit. This is supposed to be changed. The Brötje technician then had concerns. He said the DHW pump of the heat pump is needed to supply enough hot water during the defrost phase. So both pumps, the heat pump and the DHW pump, push water into the heat pump for defrosting. This could fill a C-hose. He was apparently unaware that the heat pump has a hot gas defrost cycle with energy supply via the scroll compressor.
4. I noticed that the heat pump did not modulate and always ran at 16 kW. After a call with a colleague, the Brötje technician made an adjustment. And indeed, sometimes the heat pump modulates—but only when it gets really cold. At a temperature of about 8°C (46°F), it still runs at 16 kW and fills the storage tank in 5 minutes, despite a consumption of only 4 to 5 kW. For 400 liters (106 gallons) and a 4 K (7°F) temperature difference, you only need about 1.9 kW. At over 10 kW, that takes roughly 10 minutes. So the heat pump cycles about 60 times a day. Unfortunately, it also modulates only up to about 50%, or 8 kW. (A good scroll compressor ideally operates between 40–60%.)
I did not want to contradict the Brötje technician’s argument that the scroll compressor has to run at full load for some time at the beginning (10 minutes!) to warm up, in order not to completely upset him.
5. I am still hoping for improvements. I tried to calculate the COP stated for the heat pump. I have a heat meter and a second calibrated electricity meter.
The external electricity meter shows 20% higher consumption than the heat pump’s internal meter. The heat pump has a separate fuse. Nothing else is connected to it, not even circulation pumps, because of the heat pump tariff. No electric auxiliary heating.
The heat meter shows 5% less usage.
If I calculate based on the stated COP—I currently run the heat pump only down to 5°C (41°F), with a COP of 3.9—it comes down to about 3.2.
The average COP without condensing boiler with auxiliary heating is thus currently well below 3, closer to about 2.5. Such a value is not eligible for funding under BAFA guidelines.
In conclusion:
It may be that the heat pump runs differently in solo mode. However, it is clear that operating, algorithms, and experience from refrigeration technology are missing. Heating engineers and refrigerant compressors do not seem to get along well.
The hybrid concept is economically the only alternative for buildings built before 2007 when it comes to air-source heat pumps. The heat pump can be designed for up to 2°C (36°F) without an electric heating element. Gas or oil condensing boilers, if available, are efficient. Depending on gas and electricity prices, usage can be adapted. The storage tank does not need to be large for cases where heat pump tariff heating is switched off. Legionella protection in winter is significantly cheaper with fossil fuels than with a heat pump.
Suppliers are relieved from massive electricity peaks because the simultaneous usage factor means the capacity does not need to be tripled.
During high electricity demand in winter, many gas power plants—which are written off rather inefficiently—have to supply additional power. These do not operate in combined heat and power mode and therefore do not achieve 40% efficiency. Adding transmission and transformer losses, the gas boiler in total is significantly more CO₂-saving.
I now also see a change in mindset at Brötje, designing new gas boilers for hybrid solutions.
The problem: The risk that such a system will initially not run properly. See my Brötje NEO 18 B, 16 kW. An upgraded NEO 16 C 16 kW might work better.
Heating technicians, and I see this in comparisons, are inflexible and narrow-minded in their explanations. Practical fundamental refrigeration experience is lacking.
Heat pumps are definitely the right path. If you can drill deep enough, and the effort for trench collectors and other off-grid solutions is possible, it works even for poorly insulated buildings. Collection pipes at 400 m (1,312 ft) depth with 15°C (59°F) into the apartments would also be a solution, achieving efficiency up to 50°C (122°F).
Now I have the Brötje NEO 18 B, 16 kW to deal with. I also have the impression that Brötje tinkers more than professionally plans. The device itself is not bad in principle. Although far too expensive for what’s inside. But that is no better with competitors. The heat pump supplies DHW through insulated pipes into the house but has internal pipes with only 25% insulation. Not all IP56-rated. That’s unfortunate. Extremely complicated installation. The boiler room is almost 120 cm (47 inches) deep. Condensation shaft with gravel, 100 x 100 cm (39 x 39 inches), 100 cm (39 inches) deep.
Everything has to fit perfectly. The fan is very quiet. Great. The flow in the heat exchanger works well. But no effort was made for insulating the scroll compressor. With some professional insulation, I managed to reduce noise by almost 6 dB. Now you can hardly hear anything during normal operation. The scroll compressor itself also seems solid. I wouldn’t bet I know it, probably sourced externally.
In China, the outdoor unit of the same build costs a maximum of 5 to 10% of the retail price. So I expect at least a programming level of standard quality. Even if this sounds unprofessional, I think it can be done much better.
I could list a number of other problems with my project, but Brötje is not solely responsible.
I know a little and see that a layperson quickly becomes overwhelmed. A poorly functioning system will not be corrected without detailed complaint. The heating engineer is almost equally overwhelmed. Manufacturer colleagues are primarily interested in making their machines look good. Many systems that go off track could be realigned with simple adjustments by specialists. In principle, it does not matter which manufacturer’s parts are used—most are essentially the same. Optimal on-site adjustment is just as important as the correct load profile, which the heating engineer must specify. However, he is usually overwhelmed. Low flow temperatures, changed control behavior, and building heat loss assessments are often poorly estimated. You don’t have to calculate everything; sufficient experience is usually enough.
In that sense: Let’s see how it goes.
N
nordanney1 Jan 2025 20:53A lot of text. In the end, I couldn’t really follow what you were actually trying to say. Sorry.
Hello,
You may be right.
Statement: Heat pumps are good. Usually, they are set up improperly, often with a hydraulic system that rarely matches the requirements of a heat pump.
If possible, always involve an independent MEP (Mechanical, Electrical, and Plumbing) planner or expert who can provide the installer and designer with a clear set of requirements, and who inspects and approves the installation.
You may be right.
Statement: Heat pumps are good. Usually, they are set up improperly, often with a hydraulic system that rarely matches the requirements of a heat pump.
If possible, always involve an independent MEP (Mechanical, Electrical, and Plumbing) planner or expert who can provide the installer and designer with a clear set of requirements, and who inspects and approves the installation.
N
nordanney1 Jan 2025 22:34DIRAHRAV schrieb:
Statement: Heat pumps are good.Yep DIRAHRAV schrieb:
Usually set up incorrectly.For a typical single-family house, construction is done according to the manufacturers’ specifications, which is proper practice. Not always perfect for that last bit of efficiency, but the house still gets adequately warm. DIRAHRAV schrieb:
If possible, always involve an independent MEP planner or expert who provides a clear set of requirements to the installer and the designer.Not for single-family houses. It’s enough to have the heating load calculation done for only around 250-300€ to size the heat pump and create an underfloor heating installation plan. After that, the heating technician should proceed with the installation. However, they often have to follow the manufacturers’ specifications (such as buffers or similar unnecessary components).
The heating load calculation is one part. The capacity of the radiators and often existing underfloor heating with unknown pipe lengths at now lower supply temperatures. Cost-benefit analysis of enlarging radiators. Heat pumps also require the return temperature to be as low as possible to maintain high efficiency. High pressure negatively affects enthalpy. However, to save on new radiators, high flow rates are often set with high return temperatures. It’s not that simple. As mentioned, I see the implementation in existing buildings with a thermal transmittance (U-value) greater than 80.
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