ᐅ Heat load calculation is 10.3 kW; is an air-to-water heat pump with 9.5 kW capacity sufficient?
Created on: 5 Mar 2020 22:09
H
hippjoha
Hello everyone,
I just had a brief phone call with our heating engineer. The heating load calculation resulted in a value of 10.3 kW. He would recommend a 9.5 kW air-to-water heat pump (nothing else is possible since drilling, etc., is not allowed), among other reasons because it is eligible for funding through BAFA.
My question now is whether this air-to-water heat pump is adequately sized. In the open-plan living room, we also have a wood stove.
I hope someone here can clarify this for me.
Thank you very much!
Best regards,
Hannes
I just had a brief phone call with our heating engineer. The heating load calculation resulted in a value of 10.3 kW. He would recommend a 9.5 kW air-to-water heat pump (nothing else is possible since drilling, etc., is not allowed), among other reasons because it is eligible for funding through BAFA.
My question now is whether this air-to-water heat pump is adequately sized. In the open-plan living room, we also have a wood stove.
I hope someone here can clarify this for me.
Thank you very much!
Best regards,
Hannes
CrazyChris schrieb:
The heat pump you mentioned will most likely no longer qualify for subsidies in the proposed size! The larger the pump, the worse the seasonal performance factor. Viessmann air-to-water heat pumps, in particular, tend to perform poorly in this regard.
Why do you think it won’t be eligible for subsidies? The seasonal performance factor calculation comes directly from Viessmann. This model has just been newly released, and the value is, as stated, 4.61 (>3.5), so it should qualify, right?
C
CrazyChris26 Mar 2020 12:384.5 is eligible for funding!
The annual performance factor calculation by Viessmann does not indicate the actual annual performance factor. This must be calculated individually.
Please search online for an annual performance factor calculator. Select the appropriate heat pump. After choosing the heat pump, select "new building" one option above. Enter the location for the standard temperature. The supply and return temperatures should be left at the default settings. Calculate.
The annual performance factor calculation by Viessmann does not indicate the actual annual performance factor. This must be calculated individually.
Please search online for an annual performance factor calculator. Select the appropriate heat pump. After choosing the heat pump, select "new building" one option above. Enter the location for the standard temperature. The supply and return temperatures should be left at the default settings. Calculate.
CrazyChris schrieb:
> 4.5 is eligible for funding!
The annual performance factor calculation from Viessmann does not indicate the actual annual performance factor. It needs to be calculated individually.
Please search online for an annual performance factor calculator. Select the appropriate heat pump. After selecting the heat pump, choose the option for new construction. Enter the location for the standard temperature. Leave the supply and return temperatures at standard. Calculate. The above-mentioned annual performance factor calculation was made for my location according to VDI 4650 (standard outdoor temperature -14°C (7°F); supply and return temperatures 35°C / 28°C (95°F / 82°F)).
C
CrazyChris27 Mar 2020 13:11Great, so which heat pump is it exactly? I’m not familiar with a Vito 200 a with 8.1 kW. It should be a model AWO-E-AC 201.AXX.
Hi,
1. The calculated heating load does not account for internal or solar gains. That means it will be lower.
2. Unfortunately, I cannot find any technical data online for this heat pump either. Key information would be the modulation range and performance at low temperatures. Perhaps the heating contractor can provide you with these technical details, and you could share them here. Then it would be easier to assess whether it is suitable or not. Otherwise, it’s just guessing.
3. According to the annual performance factor calculator, the heat pump achieves an annual performance factor (APF) of 4.47 under your conditions (BAFA value 4.5), so it barely qualifies for funding. Even though a value of 4.47 can be surpassed by others, it is still good. You probably won’t notice a 0.1 difference in APF in practice. More important is that the heating contractor and consequently the design of the hydraulic system and heating surfaces are well done to achieve a good annual performance factor. See the following points.
4. Avoid using a heating buffer tank (and bypass valve). These only reduce the annual performance factor and serve no purpose other than increasing your costs and the heating contractor’s profit. To ensure the flow rate, see point 5.
5. No ERR (electronic regulation valve). This restricts the flow rate of a heat pump and forces it to operate at higher supply temperatures than necessary, which lowers the annual performance factor. Temperatures are set through hydraulic/thermal balancing. The idea that you can quickly (<8 hours) adjust room temperature with thermostats in a low-temperature heating system is unrealistic. Thermostats can be installed in individual rooms if needed. Personally, I would still plan the wiring for thermostats in advance. The next points are also important to keep the supply temperature within the heat pump-friendly range.
6. Design heating surfaces for low temperatures and high flow rates. This means the pipe spacing for underfloor heating should be around 10cm (5 inches), and the length of each heating circuit should be approximately the same, around 60–80m (197–262 feet). The bathroom presents a challenge because of its limited underfloor heating area and the need for higher temperatures, which unnecessarily raises the supply temperature. The solution is in the next point.
7. Wall heating in the bathroom! Absolutely! This provides additional surface area, increasing the heating capacity in the bathroom and lowering the supply temperature. Additionally, radiant heat increases comfort, which reduces the actual required air temperature to around 22°C (72°F) because perceived temperature is higher due to radiant warmth.
8. Last but not least, BKA. BKA stands for concrete core activation. This is rarely possible with timber frame construction. In solid construction, it should be incorporated into every concrete ceiling. Cooling with heat pumps and adapting to climate change is becoming more important. Underfloor heating is only partially suitable for cooling. BKA significantly improves cooling capacity, allowing the indoor temperature to be lowered by up to 5°C (9°F). Combined with shading, this makes hot summers much more comfortable. Another benefit is that BKA enables reducing the heat pump supply temperature to below 30°C (86°F) even at a low outside temperature of -16°C (3°F). This increases efficiency and the annual performance factor further. A 1°C (2°F) reduction improves efficiency by about 2.5%. A 5°C (9°F) difference in supply temperature increases efficiency by over 10% and the annual performance factor by 0.2. With a controlled ventilation system and ventilation pipes in the concrete ceiling, BKA has a nice side effect: in winter, the incoming air is pre-warmed, and in summer, pre-cooled. What more could you want?
In my view, the cost of BKA is marginal compared to the efficiency and comfort gains, especially when compared to other investments in the house, such as nicer tiles. Depending on self-installation as well as the flexibility and willingness to innovate by the heating contractor, costs range between 1,000–3,000€.
Best regards,
Nika
1. The calculated heating load does not account for internal or solar gains. That means it will be lower.
hippjoha schrieb:
yes, exactly. It is A09. According to the heating engineer, it was only recently released. There is nothing available online about it...
2. Unfortunately, I cannot find any technical data online for this heat pump either. Key information would be the modulation range and performance at low temperatures. Perhaps the heating contractor can provide you with these technical details, and you could share them here. Then it would be easier to assess whether it is suitable or not. Otherwise, it’s just guessing.
3. According to the annual performance factor calculator, the heat pump achieves an annual performance factor (APF) of 4.47 under your conditions (BAFA value 4.5), so it barely qualifies for funding. Even though a value of 4.47 can be surpassed by others, it is still good. You probably won’t notice a 0.1 difference in APF in practice. More important is that the heating contractor and consequently the design of the hydraulic system and heating surfaces are well done to achieve a good annual performance factor. See the following points.
4. Avoid using a heating buffer tank (and bypass valve). These only reduce the annual performance factor and serve no purpose other than increasing your costs and the heating contractor’s profit. To ensure the flow rate, see point 5.
5. No ERR (electronic regulation valve). This restricts the flow rate of a heat pump and forces it to operate at higher supply temperatures than necessary, which lowers the annual performance factor. Temperatures are set through hydraulic/thermal balancing. The idea that you can quickly (<8 hours) adjust room temperature with thermostats in a low-temperature heating system is unrealistic. Thermostats can be installed in individual rooms if needed. Personally, I would still plan the wiring for thermostats in advance. The next points are also important to keep the supply temperature within the heat pump-friendly range.
6. Design heating surfaces for low temperatures and high flow rates. This means the pipe spacing for underfloor heating should be around 10cm (5 inches), and the length of each heating circuit should be approximately the same, around 60–80m (197–262 feet). The bathroom presents a challenge because of its limited underfloor heating area and the need for higher temperatures, which unnecessarily raises the supply temperature. The solution is in the next point.
7. Wall heating in the bathroom! Absolutely! This provides additional surface area, increasing the heating capacity in the bathroom and lowering the supply temperature. Additionally, radiant heat increases comfort, which reduces the actual required air temperature to around 22°C (72°F) because perceived temperature is higher due to radiant warmth.
8. Last but not least, BKA. BKA stands for concrete core activation. This is rarely possible with timber frame construction. In solid construction, it should be incorporated into every concrete ceiling. Cooling with heat pumps and adapting to climate change is becoming more important. Underfloor heating is only partially suitable for cooling. BKA significantly improves cooling capacity, allowing the indoor temperature to be lowered by up to 5°C (9°F). Combined with shading, this makes hot summers much more comfortable. Another benefit is that BKA enables reducing the heat pump supply temperature to below 30°C (86°F) even at a low outside temperature of -16°C (3°F). This increases efficiency and the annual performance factor further. A 1°C (2°F) reduction improves efficiency by about 2.5%. A 5°C (9°F) difference in supply temperature increases efficiency by over 10% and the annual performance factor by 0.2. With a controlled ventilation system and ventilation pipes in the concrete ceiling, BKA has a nice side effect: in winter, the incoming air is pre-warmed, and in summer, pre-cooled. What more could you want?
In my view, the cost of BKA is marginal compared to the efficiency and comfort gains, especially when compared to other investments in the house, such as nicer tiles. Depending on self-installation as well as the flexibility and willingness to innovate by the heating contractor, costs range between 1,000–3,000€.
Best regards,
Nika
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