Experience with KFW55 solid + gas + 5 sqm solar

  • Erstellt am 2017-05-01 20:11:50

Nutshell

2022-05-23 18:09:41
  • #1
Interesting approach with the 2.00kw devices. But according to the datasheet, they are less efficient?
 

Deliverer

2022-05-23 19:14:55
  • #2
I don't know the datasheet and maybe the special case of these models has to be considered. But generally, it's like with heating systems: as big as necessary, as small as possible.
And a 12 sqm room in a KfW house has a heating load of 0.5 kW. The "cooling load" is generally lower because the delta temperature is smaller than when heating.

And the bigger it is, the more it cycles. That is inefficient and causes constantly changing noise levels and fluctuating humidity.

Therefore, in a reasonably well-insulated house, I would always recommend installing a single indoor unit with about 3.5 kW capacity at the highest/central point of the house. It then runs all day (from photovoltaic power) in midsummer 24 hours at low power. All doors open and the house stays comfortable and, above all, dehumidified. Yes, you won't achieve 20°C in the bedroom with that, but maybe that's not even necessary.

PS: Wow, I just saw how old this thread is and what I said back then. :oops: I have since changed my opinion on insulation standards. I would only build passive houses now. Back then, I didn't quite understand the financial advantage of omitting underfloor heating. Small wind power is still cool but probably almost never economical. That’s why I switched to a lot more photovoltaic. Everything under 50 kWp is small. After that, it’s "medium". :cool:
 

Nutshell

2022-05-23 20:58:16
  • #3


Thanks for the idea with the single unit. Yes, the insulation standard is indeed important; at that time KFW55 was already very good and not everywhere to be found :) I had years with a 28€ advance payment for heating, so investing more money in insulation would simply have been nonsense. You couldn't have predicted the war!
 

Deliverer

2022-05-23 22:22:56
  • #4
No. And you still have a decent house. I’m doing it with the one device (3.5 kW for 140 sqm) in the partially renovated old building. That works well and cheaply.
 

Nutshell

2022-05-26 16:42:18
  • #5
I now have an offer.

€11,500 for the split air conditioning system

3 indoor units
Panasonic Etherea Z 2.0kw
1 indoor unit
Panasonic Etherea Z 3.5kw
1 outdoor unit
Panasonic 6.8kw

Thanks to [BEG EG Förderung] -35%,
= €7,475

Application will be submitted on Monday.
 

Nutshell

2023-08-15 21:59:25
  • #6
Update,

the air conditioning has now been in use for 12 months.

The house was handed over turnkey in summer 2014 with 1692 kWh gas consumption due to screed drying.
How have gas prices developed?
2017-2018 4.74 cents / kWh
2022-2023 16.51 cents / kWh
2023-2024 9.7 cents / kWh

How have electricity prices developed?
2017-2018 22.91 cents
2022-2023 29.71 cents
2023-2024 26.60 cents

Installed is a gas heating system, as well as hot water preparation with a solar tank of 300 liters + 2x collectors for hot water without heating support.

Gas meter readings converted in kWh (1 m³ = 11.28 kWh)
Summer 2014 1692 kWh
Summer 2015 11426 kWh = consumption 9734
Summer 2016 19356 kWh = consumption 7930
Summer 2017 27636 kWh = consumption 8280
Summer 2018 34979 kWh = consumption 7343
Summer 2019 41758 kWh = consumption 6779
Summer 2020 48300 kWh = consumption 6542
Summer 2021 56490 kWh = consumption 8190
Summer 2022 63089 kWh = consumption 6599
Summer 2023 65875 kWh = consumption 2786

In summer 2022, the mentioned air/air heat pump was added.

Electricity meter
Summer 2017 7,123 kWh
Summer 2018 9,023 kWh = consumption 1,900
Summer 2019 11,010 kWh = consumption 1,987
Summer 2020 13,266 kWh = consumption 2,256
Summer 2021 15,721 kWh = consumption 2,455
Summer 2022 18,265 kWh = consumption 2,544
Summer 2023 22,512 kWh = consumption 4,247

The control of the Viessmann heating system shows the following regarding solar systems - hot water preparation:
39,247 kWh via solar collectors, period 2014-2023.

The following consumptions I have according to the heat pump app:
Jul 22 consumption 21 kWh
Aug 22 consumption 62 kWh
Sep 22 consumption 33 kWh
Oct 22 consumption 90 kWh
Nov 22 consumption 243 kWh
Dec 22 consumption 385 kWh
Jan 23 consumption 197 kWh
Feb 23 consumption 332 kWh
Mar 23 consumption 87 kWh
Apr 23 consumption 189 kWh
May 23 consumption 45 kWh
Jun 23 consumption 46 kWh
12 months total: 1,730

Heating the last 12 months:
I tried to mainly heat with the heat pump. Only at low temperatures was the heat pump switched off and the gas underfloor heating activated.
There were 1,617 kWh gas consumption for this type of heating support.

Hot water the last 12 months:
In the months of November and April, little was to be gained with the solar system, but the gas heating was off as well.
Here the consumption was 115 kWh and 120 kWh respectively for hot water preparation with gas.
In the months December, January, February, March the gas heating was on, but I tried to estimate the hot water gas consumption.
In May there was more sun, here it was only 70 kWh. In June 18 kWh gas for hot water, meanwhile again completely via collectors.
I estimate that I had a total of 1,170 kWh gas consumption for hot water from summer 2022 to summer 2023.

Normally, we had a total annual gas consumption of around 6,500 - 8,300 kWh.
The winter 2022-2023 was rather cool in comparison, so let's estimate 7,700 kWh.
7,700 - 1,617 = 6,083 kWh that the heat pump had to provide in heating power, estimated.

Consumed for heating, the heat pump used according to the app: 1,556 kWh
The "COP" value based on the assumptions is therefore 6,083 / 1,556 = 3.9

Thoughts on the achieved COP value:
However, the heat pump was activated in a demand-oriented manner per room in comparison to the gas heating.
In the past, we always ran the gas 24/7 with a setpoint temperature of 23°C.
Moreover, when sensible, at least two indoor units were programmed at the same time. I was told that the more load, the higher the efficiency.
What should also clearly positively affect a good COP value is the fact that at low temperatures we switched off the heat pump and switched on the gas heating.

How will it continue?
Gas prices have dropped significantly again: -41.2%
For the next winter, my wife convinced me to set the gas underfloor heating to a base temperature and to use the air conditioning demand-oriented to quickly bring the room to a higher temperature.
I am not quite convinced whether this makes sense. The gas heating will have to cycle more and thus run less efficiently. Whether you really save money that way? We will see.
 

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