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 🙂
T
T_im_Norden16 Jan 2021 20:09What flow temperature do you run, and what are the operating times of the system?
Bookstar schrieb:
30 kWh per day is absolutely reasonable given the area and temperatures, actually rather good!
Although the question is why you need 24 degrees Celsius (75°F)? In summer, I would turn on the AC and cool down to 21 degrees Celsius (70°F). Crazy! Yes, I also find it a bit warm, but my wife is really sensitive to the cold. We are already trying to lower it without her feeling cold. But if she sits in the evening watching TV with just a sweater and shivers while grabbing a blanket, I’d rather turn up the heating ;-)
hegi___ schrieb:
It would have been cheaper if you had designed the underfloor heating for 24 degrees Celsius (75°F) right from the start. A 1-degree higher flow temperature already costs about 2 percent efficiency, plus the additional consumption.
Still, a hydraulic balancing should be done. What would have been different then? The installer laid it as tight as possible. There should be about 10 cm (4 inches) spacing. If we wanted it tighter, we would have used a “different” underfloor heating system.
I’ll keep the hydraulic balancing in mind for next winter. We have a smart home system and buttons with temperature sensors in every room. These show almost identical temperatures per floor. The ground floor and the first floor differ only slightly. The attic (second floor) is always about 1°C (2°F) colder. The water already arrives about 1°C (2°F) cooler at the manifold there. But that is a different matter.
T_im_Norden schrieb:
What flow temperature do you run, and what are the operating times of the system? At 0°C (32°F) outside temperature, the flow temperature is 30°C (86°F) to maintain 24°C (75°F) indoor temperature. Every 5°C (9°F) change outside affects the flow temperature by 1°C (2°F).
I just checked the logs and currently, it runs almost continuously. On some days it pauses between 2 pm and 6 pm and occasionally runs less during the night. I looked back, and this is already extreme. In late December, it ran significantly less. I can provide the logs if anyone is interested. I have enabled just about everything for logging ;-)
M. Gerd schrieb:
Yes, I also find it a bit warm, but my wife really feels the cold. We are already looking into turning it down without her feeling cold. But if she sits watching TV in the evening with a sweater and comes to get a blanket shivering, I’d rather turn the heating up ;-)
What would have been different then? The installer laid the pipes as tightly as possible. There should be about 10cm (4 inches) spacing. If we had wanted to lay them even closer, we would have chosen a "different" underfloor heating system.
I’ll keep the hydraulic balancing in mind for next winter. We have a smart home system and switches with temperature sensors in every room. These show nearly identical temperatures per floor. The ground floor and first floor differ only slightly. The attic (second floor) is unfortunately about 1°C (1.8°F) colder. The water arrives at the manifold here about 1°C (1.8°F) cooler. But that’s another issue.
At 0°C (32°F) outside temperature, the flow temperature is 30°C (86°F) to maintain 24°C (75°F) room temperature. Every 5°C (9°F) change in outside temperature affects the flow temperature by about 1°C (1.8°F).
We just checked the logs and currently it runs almost continuously. On some days, it pauses between 2 pm and 6 pm, and less often runs less at night. I looked into it and this is already extreme. At the end of December, it ran considerably less. I can share the logs if anyone is interested. I have enabled just about everything to be logged ;-) That all sounds very normal to me. What was the purpose of this thread?
halmi schrieb:
What is your indoor humidity level? It is between 40-50%. Why?
Bookstar schrieb:
That all sounds quite normal to me. What was the purpose of this thread? I wasn’t sure if the values were normal or not. But it seems they are within the expected range. If that wasn’t the case, I wanted to take early action.
T
T_im_Norden16 Jan 2021 23:46Then take a look at how much heat you generated with 30 kW of electricity.