Hello everyone,
We have an 8 kW air-to-water heat pump from Kermi and a KfW55 house with about 200m² (2,150 sq ft). Currently, the indoor temperature is quite warm at 24.5°C (76°F). Yes, I know that is quite high. The consumption figures are only for the underfloor heating and are separate from the hot water usage.
I understand that the higher temperature leads to increased consumption, but could it possibly be too high?
We live just north of Hanau and in December maintained around 23°C (73°F) with a daily consumption of 6-8 kWh. When it got colder around Christmas, consumption rose to about 20 kWh. It has gotten even colder recently (-6 to 2°C / 21 to 36°F), and we simultaneously raised the temperature to about 24°C (75°F), resulting in a consumption of 30 kWh now.
I read that average consumption is based on 19°C (66°F), and for every degree above that, you need roughly 10% more energy. That would put us at about 60% higher consumption, but is 30 kWh then reasonable? According to the KfW application, we require around 30 W/m² (3 W/sq ft), which totals about 6 kW. But what exactly does that 6 kW refer to — over 24 hours? At what outside temperature? With an indoor temperature of 19°C (66°F)?
We had days in December with consumption as low as 6 kWh, which I think is quite good. However, with a few degrees colder weather and the heating curve increased by 1°C (2°F), the consumption jumps so much? By the way, we heat only via the heating curve, without any additional controllers.
Thanks in advance 🙂
We have an 8 kW air-to-water heat pump from Kermi and a KfW55 house with about 200m² (2,150 sq ft). Currently, the indoor temperature is quite warm at 24.5°C (76°F). Yes, I know that is quite high. The consumption figures are only for the underfloor heating and are separate from the hot water usage.
I understand that the higher temperature leads to increased consumption, but could it possibly be too high?
We live just north of Hanau and in December maintained around 23°C (73°F) with a daily consumption of 6-8 kWh. When it got colder around Christmas, consumption rose to about 20 kWh. It has gotten even colder recently (-6 to 2°C / 21 to 36°F), and we simultaneously raised the temperature to about 24°C (75°F), resulting in a consumption of 30 kWh now.
I read that average consumption is based on 19°C (66°F), and for every degree above that, you need roughly 10% more energy. That would put us at about 60% higher consumption, but is 30 kWh then reasonable? According to the KfW application, we require around 30 W/m² (3 W/sq ft), which totals about 6 kW. But what exactly does that 6 kW refer to — over 24 hours? At what outside temperature? With an indoor temperature of 19°C (66°F)?
We had days in December with consumption as low as 6 kWh, which I think is quite good. However, with a few degrees colder weather and the heating curve increased by 1°C (2°F), the consumption jumps so much? By the way, we heat only via the heating curve, without any additional controllers.
Thanks in advance 🙂
M. Gerd schrieb:
Where is the overall COP higher than the COP of the heating circuit and domestic hot water? I'm just wondering why there aren't always values available for domestic hot water.
At the moment, I don't use external heat meters. I had considered using external meters, but just connecting calibrated meters to my KNX system would cost me several hundred euros. This way, I could record the consumption of the photovoltaic system, battery, heating, and household myself. I can already do that now, but not with calibrated meters from the manufacturer. However, I don't really see the added value yet. Yes, I would be interested in exact values. Is it worth several hundred euros to me?
What kind of fluctuations can we expect? 1–3%? 3–5%? 5–7%? 7–10%? What COP does the manufacturer specify for the pump? I found something about a maximum COP of 4.3. As always, manufacturers tend to exaggerate. So, calculate with a COP of 4 under ideal conditions. You calculated something around 5? So you "overestimated" by about 25%.
Bookstar schrieb:
What COP value does the manufacturer specify for the pump? I found something about a maximum COP of 4.3. As usual, manufacturers tend to overstate these figures. So, you should calculate with a COP of 4 under ideal conditions. Did you calculate 5? That’s about a 25% overestimation.According to the datasheet, the performance values are as follows: A-7/W35: 3.15
A2/W35: 4.11
A7/W35: 5.04
On Friday, I had a COP of 4.5 and on Saturday 4.62. This is above the manufacturer’s stated value, but that is based on a supply temperature of 35°C (95°F) while we lowered the domestic hot water temperature from 52°C (126°F) to 48°C (118°F). So we are within the expected range.
I wonder if the manufacturer can actually exaggerate the official COP ratings. As far as I know, these values are not determined by the manufacturer.
D
Daniel-Sp17 Jan 2021 13:35M. Gerd schrieb:
is currently at 5.3. Heating alone is 4.9 and domestic hot water 3.6.
Even though it is averaged, it doesn’t seem consistent. Most likely, the heat pump’s value is somewhat optimistic. But even if the average COP were only 4.5, that is still good!M. Gerd schrieb:
According to the datasheet, the performance figures are as follows:
A-7/W35: 3.15
A2/W35: 4.11
A7/W35: 5.04
On Friday, I had a COP of 4.5 and on Saturday 4.62. This is above the manufacturer’s specification, but that is based on a supply temperature of 35°C (95°F), while we lowered the DHW temperature from 52°C (126°F) to 48°C (118°F). So we are within the expected range.
I wonder if the manufacturer can even overstate the official COP values. As far as I know, these figures are not determined by the manufacturer themselves. Well, it’s like with cars, isn’t it? These standardized test cycles from manufacturers never match real-life conditions. So I would always deduct about 20%. This also applies to the consumption of electronic devices, by the way.
bauenmk202017 Jan 2021 13:50Are you a seller of "Kermi" (whatever that is)? Are you trying to "sell me" your heat pump 😎? I have 160m2 (1,722 sq ft) and yesterday I used about 25 kWh just for heating! Temperatures were 20-22°C (68-72°F)...
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