ᐅ Interaction between Air-to-Water Heat Pump and Gas Condensing Boiler?
Created on: 19 Dec 2021 09:24
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Forsberg21
Hello,
I recently purchased a newly built condominium (KfW-55 standard) that is equipped with an air-to-water heat pump. During the construction phase, the developer informed me that the HVAC system was supplemented with an additional gas condensing boiler to handle high peak energy demands.
Would it have been possible to heat the domestic hot water for showers, kitchen, and sinks using only the air-to-water heat pump? I understand that a supply temperature of about 35°C (95°F) is sufficient for underfloor heating, but what about the rest? What other alternatives could have been installed alongside the air-to-water heat pump?
I’m asking because air-to-water heat pumps are commonly installed in Germany at the moment, and as far as I know, a separate energy source is needed for hot water; otherwise, the electricity costs for operating the heat pump increase significantly. Gas is becoming more expensive and will probably be increasingly subject to a CO2 tax in the future.
Best regards,
Robert
I recently purchased a newly built condominium (KfW-55 standard) that is equipped with an air-to-water heat pump. During the construction phase, the developer informed me that the HVAC system was supplemented with an additional gas condensing boiler to handle high peak energy demands.
Would it have been possible to heat the domestic hot water for showers, kitchen, and sinks using only the air-to-water heat pump? I understand that a supply temperature of about 35°C (95°F) is sufficient for underfloor heating, but what about the rest? What other alternatives could have been installed alongside the air-to-water heat pump?
I’m asking because air-to-water heat pumps are commonly installed in Germany at the moment, and as far as I know, a separate energy source is needed for hot water; otherwise, the electricity costs for operating the heat pump increase significantly. Gas is becoming more expensive and will probably be increasingly subject to a CO2 tax in the future.
Best regards,
Robert
Hello,
That sounds like a reasonable solution to me, without having done the calculations. Otherwise, the heat pump would probably need to be sized significantly larger.
Quite simply: It doesn’t! That is handled by an electric heating element. According to the relevant standards (DIN), the electric heating element is not included in the efficiency calculation; otherwise, the efficiency would look quite poor... ;-) The same applies to most heat pumps, which basically stop working at outdoor temperatures around -10°C (14°F) and then operate like a direct electric heater with a 1:1 energy ratio. (Yes, there are heat pumps that can reach well above 45°C (113°F) water temperature and still operate at -10°C (14°F), but those are not standard, off-the-shelf models.)
Best regards,
Andreas
Forsberg21 schrieb:
The apartment building has 25 units, and the gas condensing boiler is only intended to be used when outdoor temperatures are really cold and in the morning when perhaps everyone wants a hot shower at the same time.
That sounds like a reasonable solution to me, without having done the calculations. Otherwise, the heat pump would probably need to be sized significantly larger.
Forsberg21 schrieb:
But how does a heat pump manage to keep the water at a constant 60 °C?
Quite simply: It doesn’t! That is handled by an electric heating element. According to the relevant standards (DIN), the electric heating element is not included in the efficiency calculation; otherwise, the efficiency would look quite poor... ;-) The same applies to most heat pumps, which basically stop working at outdoor temperatures around -10°C (14°F) and then operate like a direct electric heater with a 1:1 energy ratio. (Yes, there are heat pumps that can reach well above 45°C (113°F) water temperature and still operate at -10°C (14°F), but those are not standard, off-the-shelf models.)
Best regards,
Andreas
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Deliverer19 Dec 2021 21:48In such cases, fresh water stations are likely a more practical solution. They do not have issues with Legionella bacteria and avoid the need for high water temperatures.
Currently, relatively new monoblock units using propane as a refrigerant are an option. They can heat up to 70°C (158°F) without an electric heating element, support cascade configurations, and are expected to reach outputs of up to 26 kW soon. Since photovoltaic systems are not yet very practical for multi-family buildings, solar thermal energy might actually be a genuinely useful alternative here...
But the topic is interesting – I also own part of a multi-family building, and the heating system is getting old...
Currently, relatively new monoblock units using propane as a refrigerant are an option. They can heat up to 70°C (158°F) without an electric heating element, support cascade configurations, and are expected to reach outputs of up to 26 kW soon. Since photovoltaic systems are not yet very practical for multi-family buildings, solar thermal energy might actually be a genuinely useful alternative here...
But the topic is interesting – I also own part of a multi-family building, and the heating system is getting old...
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Benutzer20020 Dec 2021 10:09andimann schrieb:
Simply put: not at all! This is handled by an electric heating element. According to the applicable standards (DIN), the heating element is not included in the efficiency calculation of heat pumps; otherwise, the efficiency would look quite bad.... ;-) It’s the same with most heat pumps: at -10°C (14°F) outside temperature, they basically stop working efficiently and operate only as direct electric heaters. (Yes, there are heat pumps that can reach water temperatures well above 45°C (113°F) without a heating element and still operate at -10°C (14°F), but these are not typical standard heat pumps.) However, hardly anyone uses 60°C (140°F) in single-family homes. Most heat pumps actually come close to 60°C (140°F) without a heating element.
If a heat pump requires the heating element at -10°C (14°F) outside temperature, there was likely a planning error. Under normal conditions, you can simply turn off the heating element (except in exposed locations such as upland areas) – that’s what I did myself (it only activates for defrosting).
The heat pumps capable of this are just standard, off-the-shelf models. You don’t need high-tech equipment for that. My 3,000€ heat pump handles this without any issues (60°C (140°F) supply temperature + -20°C (-4°F) outside temperature without the heating element).
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Deliverer20 Dec 2021 12:18Benutzer200 schrieb:
(it only turns on for defrosting)Why is that? You should have more than enough energy in the heating water!B
Benutzer20020 Dec 2021 12:34Deliverer schrieb:
Why is that? You should have more than enough energy in the heating water, right?!This is a preset of the heat pump. It cannot be avoided. If I cut off the power to the electric heating element not only through the control system (in terms of heating support) but also physically (by removing the fuse), the system goes into fault mode. So I have to accept that it may activate the heating element for a few minutes.D
Deliverer20 Dec 2021 12:46Hmm. Interesting. I would like to understand the technical background. I personally know five heat pumps from different years of manufacture—three of them do not have any electric heating element and still manage to defrost. May I ask which model it is?
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