ᐅ Air-to-water heat pump consumption at 30 kWh per day

How do you determine the electricity consumption solely for heating?

Bookstar schrieb:

Well, it’s like with cars, right? Manufacturer test cycles never match real-life conditions. So I would always deduct about 20%. This also applies to power consumption of electronic devices and such.

Hmm, I don’t think that comparison fits. With a car, I can control a lot more factors: how hard I accelerate, how strongly I brake, how fast I drive, when I shift gears, and so on. All of these affect consumption. For an air-to-water heat pump, there are only two factors: outside temperature and water temperature. A flow temperature of 35°C (95°F) is actually on the high side. Only in the case of the TWE might it make sense to set the temperature higher, which would negatively impact the COP. It’s similar with electronic devices like refrigerators: the temperatures they are measured at are realistic, and I don’t see much room for optimizing for the testing method here.

bauenmk2020 schrieb:

Are you a salesman for "Kermi" (whatever that is)? Trying to push your heat pump on me? 😎
I have 160m2 (1722 sq ft) and yesterday my consumption (heating only) was about 25 kWh! Temperatures around 20-22°C (68-72°F)...

No, definitely not, but so far I’m very satisfied. Our architect initially planned for a monoblock system, and we wanted a split system for cost reasons. Our installer usually works with Weishaupt but said he could also offer Kermi. We then looked at Kermi and ultimately decided on the monoblock. I wouldn’t generally recommend one or the other to everyone. If someone focuses solely on cost, a split system can be cheaper. We never did a detailed cost calculation. I informed myself here and on the purple forum, and the feedback pointed to an efficient device.

EdelStoff schrieb:

How do you determine electricity consumption for heating only?

You can do it with a second meter. If you have an air-to-water heat pump, you usually need that meter anyway for the special electricity tariff, or you can install one yourself. I haven’t gone through the effort or expense yet. But since I measure total electricity consumption in the house, I know my base load. So if, for example, we are not at home, any additional power use is from the heating system. This method isn’t exact down to the watt, but it’s quite precise (within about 20-50 watts). The consumption values of the air-to-water heat pump then match my other data.

M. Gerd schrieb:

Hello everyone,

We have an air-to-water heat pump from Kermi with an 8kW capacity and a KfW55-rated house with about 200m² (2,153 sq ft). Currently, the indoor temperature is quite warm at 24.5°C (76°F). Yes, I know that’s quite high. The energy consumption figures are only for the underfloor heating, separate from hot water.

I understand that the higher temperature leads to increased consumption, but could the consumption be too high?

We live a bit north of Hanau and in December, the indoor temperature was around 23°C (73°F) with a daily consumption of about 6–8kWh. When it got colder around Christmas, consumption rose to approximately 20kWh. Recently, it became even colder (between -6°C and 2°C, or 21°F and 36°F), and simultaneously we increased the indoor temperature to about 24°C (75°F), which now results in a consumption of 30kWh.

I read that average consumption rates are based on 19°C (66°F), and for every degree higher, about 10% more energy is needed. So we would expect roughly 60% more energy, but does the 30kWh match that? According to the KfW application, we need about 30W/m² (3 W/sq ft), which totals 6kW – but what exactly is this 6kW referring to? Is it over 24 hours? For which outside temperature? And at 19°C indoor temperature?

In December, we had daily consumption of 6kWh, which I think is quite good, but with a few degrees colder and raising the heating curve by 1°C, such a steep increase? By the way, we only control heating via the heating curve, without any other regulators.

Thanks in advance 🙂

Hi

Funny

There are 2 units totaling 240 m² (2,583 sq ft). For 5 years, I have been tracking consumption and calculating daily averages. Currently, the start of the year is quite tight in terms of consumption, matching your numbers. We are also in Hesse and experience similar subzero temperatures.

I need to correct the consumption shown by the system!

I made a mistake, and since the official consumption values were being questioned here, I checked it again. I don’t want to manipulate any numbers.

Kermi provides the "current compressor input." However, it seems that an additional 200 Wh are consumed during operation. In other words, if the system shows a consumption of 1.9 kWh, I see a consumption of 2.1 kWh in the overall system. I have sent an email to Kermi. I suspect this is correct and that the COP is calculated based only on compressor power. Now I’m curious how other manufacturers handle this.

If I assume a general additional consumption of 10%, the COP drops by about 10%, which brings us closer to the official figures.

HilfeHilfe schrieb:

Hi

funny

There are 2 units with a total of 240 m² (2,583 sq ft). For 5 years I have been recording the consumption and calculating average daily values. The beginning of this year is really tight in terms of consumption, which matches your figures. We are also in Hesse and experiencing similar low temperatures.

What exact data do you record? Where do you read it from?

M. Gerd schrieb:

I need to correct the consumption shown by the system!

I made a mistake, and since the official consumption values were questioned here, I double-checked. I don’t want to manipulate any numbers.

Kermi specifies the "current compressor power input." However, during the system’s operation, apparently an additional 200Wh (0.2kWh) is consumed. In other words, when the system shows a consumption of 1.9kWh, I see 2.1kWh in the monitoring system. I’m sending an email to Kermi. I suspect this is accurate and that the COP is calculated based only on compressor power. Now I’m curious how other manufacturers handle this.

If I assume a flat 10% additional consumption, the COP drops by about 10%, which brings it closer to the official figures.

What data do you exactly record? Where do you read these values from?

I keep an Excel sheet and write down the meter readings, then calculate a daily average per year. This way I can see if something is off.

My brother-in-law had a water damage incident and never noticed it. “Outliers” like that would show up clearly in the consumption data.

How could he not notice a water damage?

We have now lowered the heating curve by 1, and the consumption has dropped from 30 kWh per day to 20 kWh per day. Back then, the consumption rose from 20 kWh to 30 kWh, and I couldn't really believe that it was caused by just one degree, but apparently that is the case.