ᐅ HvH combines an air-source heat pump with panel radiators – what about the temperature settings?
Created on: 17 Nov 2015 22:42 ölschlamm
Hello community,
I just had a conversation with my regional manager from Heinz von Heiden. The houses now typically use an air-source heat pump combined with conventional radiators operating at a flow temperature of 55°C (131°F).
Doesn't this basically mean a seasonal performance factor below 2 is inevitable?
From my intuitive assessment, I would say that a flow temperature of 40°C (104°F) is sufficient for almost all days of the year. But even that is still way too high for a heat pump.
What do you think?
I just had a conversation with my regional manager from Heinz von Heiden. The houses now typically use an air-source heat pump combined with conventional radiators operating at a flow temperature of 55°C (131°F).
Doesn't this basically mean a seasonal performance factor below 2 is inevitable?
From my intuitive assessment, I would say that a flow temperature of 40°C (104°F) is sufficient for almost all days of the year. But even that is still way too high for a heat pump.
What do you think?
A brief online search shows that it is possible—at least up to 45° (with somewhat higher costs, but probably not a total disaster). However, if it’s not necessary, why should you?
There also seem to be special systems designed for even higher supply temperatures—whether that makes sense is another question.
There also seem to be special systems designed for even higher supply temperatures—whether that makes sense is another question.
Hi BH,
Of course, I was already at that point. But just because heat pump companies say a 45°C (113°F) supply temperature is acceptable doesn’t necessarily mean it is. From what you read, the practical experiences of many heat pump users are quite sobering, especially with underfloor heating, mind you.
The pumps designed for higher supply temperatures are also significantly more expensive, and of course, there are special low-temperature radiators as well, but these are even more costly, often include fans, etc. So, they are not a real alternative to gas.
By the way, it would be a Rotex CPU 308 or 508 with a 300-liter (79-gallon) stratified storage tank connected to standard 22mm (7/8 inch) convectors.
Of course, I was already at that point. But just because heat pump companies say a 45°C (113°F) supply temperature is acceptable doesn’t necessarily mean it is. From what you read, the practical experiences of many heat pump users are quite sobering, especially with underfloor heating, mind you.
The pumps designed for higher supply temperatures are also significantly more expensive, and of course, there are special low-temperature radiators as well, but these are even more costly, often include fans, etc. So, they are not a real alternative to gas.
By the way, it would be a Rotex CPU 308 or 508 with a 300-liter (79-gallon) stratified storage tank connected to standard 22mm (7/8 inch) convectors.
If the heating systems are poorly designed and everything is overly optimistic, the 6 kW heater may not deliver the required output at -10°C (14°F), causing the electric heating element to turn on and making it expensive—yes.
If the system is properly calculated and, after the first 1-2 years, the moisture is gone, you should generally avoid an unpleasant surprise.
Simply put: about 2.5% more electricity is needed per degree of flow temperature (that’s what I heard)... so about 25% more -> instead of 80 euros per month, it would be around 100 euros... that’s about 240 euros more per year. If you can get the house 5,000 euros cheaper because of that, it’s worth it—underfloor heating usually isn’t that expensive anyway.
Since your overall tone is quite critical, you probably won’t be happy with this. Choose underfloor heating or gas (or both).
If the system is properly calculated and, after the first 1-2 years, the moisture is gone, you should generally avoid an unpleasant surprise.
Simply put: about 2.5% more electricity is needed per degree of flow temperature (that’s what I heard)... so about 25% more -> instead of 80 euros per month, it would be around 100 euros... that’s about 240 euros more per year. If you can get the house 5,000 euros cheaper because of that, it’s worth it—underfloor heating usually isn’t that expensive anyway.
Since your overall tone is quite critical, you probably won’t be happy with this. Choose underfloor heating or gas (or both).
B
Bieber081518 Nov 2015 20:09ölschlamm schrieb:
Currently, houses typically use an air source heat pump with conventional radiators operating at a supply temperature of 55°C (131°F). Honestly, I wouldn’t want to build a house like that today. (In any case, choose underfloor heating designed for a maximum supply temperature of 35°C (95°F). It doesn’t matter which system generates the heat—whether it’s a heat pump, gas, liquefied petroleum gas, oil, pellets, or something else. This way, you always retain the option to install a heat pump later on.)
We only have standard flat panel radiators. That’s because my wife and I lived with underfloor heating for many years and, for various reasons, we simply don’t like it. With the new house, we were able to change this heating situation to something that suits us better.
Modern flat panel radiators have the advantage over older-style radiators that 70-80% of the heat is emitted through radiation. After more than one heating season, I can say they work very well: they create a comfortable warmth.
Now I make sure to keep the flow temperature as low as possible. The heating technician had originally set it to 75°C (167°F) at -15°C (5°F) outside. That’s obviously excessive. The return temperature becomes too high, which means the benefits of my gas boiler don’t come into full effect, and I lose efficiency in the range of 3-5%, which means more money spent.
In our KfW 70 house (in terms of heating energy demand, the house is actually closer to KfW 55), flow temperatures between 35 and 42°C (95 and 108°F) are sufficient down to outside temperatures of +8°C to around 1-2°C (46°F to 34-36°F). When temperatures drop further (last winter the coldest reached about -12°C (10°F)), I need a flow temperature of 47-53°C (117-127°F) to maintain indoor temperatures of 21.5-22°C (71-72°F).
Underfloor heating typically operates at flow temperatures around 32-35°C (90-95°F), so there is a noticeable difference.
Regarding your question: I personally have serious doubts about whether an air-to-water heat pump combined with flat panel radiators is an optimal solution.
The required domestic hot water production already significantly reduces the annual performance factor of an air-to-water heat pump.
In my opinion, an air-to-water heat pump basically requires underfloor heating to achieve a reasonably useful annual performance factor.
Conclusion: If I were the builder, I would never agree to the described setup.
PS: My supervisor has an air-to-water heat pump in his house. We occasionally compare consumption figures and costs. His system’s energy use per square meter per year is clearly higher. Additionally, the domestic hot water can only reach about 43-45°C (109-113°F) without the backup heater constantly switching on (and the backup heater consumes a lot of electricity). It’s no wonder my supervisor says that from around 0 to -5°C (32 to 23°F) outside he basically has an almost pure electric heating system when the heat pump is running at a ratio of roughly 1:1.4 or so…
Personally, I wouldn’t install an air-to-water heat pump at all, especially not in the cold and windy region where I live. Because it’s difficult to make it cost-effective; it’s often portrayed as efficient, which can work somewhat with decreasing primary energy factors for electricity. At best it achieves around 1.1 and is technically nice, yes.
Hot water heat pumps or ground-source heat pumps are brilliant, but expensive. A ground-source heat pump is unfortunately not possible here where I live.
Modern flat panel radiators have the advantage over older-style radiators that 70-80% of the heat is emitted through radiation. After more than one heating season, I can say they work very well: they create a comfortable warmth.
Now I make sure to keep the flow temperature as low as possible. The heating technician had originally set it to 75°C (167°F) at -15°C (5°F) outside. That’s obviously excessive. The return temperature becomes too high, which means the benefits of my gas boiler don’t come into full effect, and I lose efficiency in the range of 3-5%, which means more money spent.
In our KfW 70 house (in terms of heating energy demand, the house is actually closer to KfW 55), flow temperatures between 35 and 42°C (95 and 108°F) are sufficient down to outside temperatures of +8°C to around 1-2°C (46°F to 34-36°F). When temperatures drop further (last winter the coldest reached about -12°C (10°F)), I need a flow temperature of 47-53°C (117-127°F) to maintain indoor temperatures of 21.5-22°C (71-72°F).
Underfloor heating typically operates at flow temperatures around 32-35°C (90-95°F), so there is a noticeable difference.
Regarding your question: I personally have serious doubts about whether an air-to-water heat pump combined with flat panel radiators is an optimal solution.
The required domestic hot water production already significantly reduces the annual performance factor of an air-to-water heat pump.
In my opinion, an air-to-water heat pump basically requires underfloor heating to achieve a reasonably useful annual performance factor.
Conclusion: If I were the builder, I would never agree to the described setup.
PS: My supervisor has an air-to-water heat pump in his house. We occasionally compare consumption figures and costs. His system’s energy use per square meter per year is clearly higher. Additionally, the domestic hot water can only reach about 43-45°C (109-113°F) without the backup heater constantly switching on (and the backup heater consumes a lot of electricity). It’s no wonder my supervisor says that from around 0 to -5°C (32 to 23°F) outside he basically has an almost pure electric heating system when the heat pump is running at a ratio of roughly 1:1.4 or so…
Personally, I wouldn’t install an air-to-water heat pump at all, especially not in the cold and windy region where I live. Because it’s difficult to make it cost-effective; it’s often portrayed as efficient, which can work somewhat with decreasing primary energy factors for electricity. At best it achieves around 1.1 and is technically nice, yes.
Hot water heat pumps or ground-source heat pumps are brilliant, but expensive. A ground-source heat pump is unfortunately not possible here where I live.
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