ᐅ Ground Source Heat Pump for a 200 m² Single-Family Home with Underfloor Heating, KfW55 Standard – Settings and Optimization

Hello, I’m not sure if this is the right thread for this, but I’ll give it a try anyway.
We are building a single-family house with a ground source heat pump and underfloor heating, and we plan to install a photovoltaic system in the next few years. Now the question arises whether a second electricity meter is necessary. Having a separate meter for the heat pump tariff would make sense. However, our electrician said that if the photovoltaic system is installed, there will only be one electricity meter. We would need to calculate whether a second meter makes sense or not.
I’m totally confused here. How did you handle this? Second electricity meter yes or no, and why? Thanks in advance.

@Pumpernickel1 doesn’t quite fit here. We only have one meter for everything.
Whether a second meter is worthwhile for you depends on your consumption and the rates offered in your area.
Just do the calculations.

Pumpernickel1 schrieb:

We are building a single-family home with a geothermal heat pump and underfloor heating and are planning to install a photovoltaic system in the next few years. Now the question arises whether a second electricity meter is necessary. It would definitely make sense for the heat pump tariff. However, our electrician said that if the photovoltaic system is installed, there will only be one electricity meter. We would need to calculate whether a second electricity meter makes sense or not.
I’m completely lost here. How did you solve it? Second electricity meter yes or no, and why? Thanks in advance.

Please use the search function. There are many threads on this topic.

We have only one electricity meter.
Additionally, we installed a sub-meter to account for self-consumption and to be able to use the photovoltaic system 100%.

Pumpernickel1 schrieb:

Hello, I’m not sure if this is the right thread, but I’ll give it a try anyway.
We are building a single-family house with a ground source heat pump and underfloor heating, and we plan to install a photovoltaic system in the next few years. Now the question is whether a second electricity meter is necessary. It would make sense for the heat pump tariff. However, our electrician said that when the photovoltaic system is installed, there will only be one electricity meter. You would have to calculate whether a second meter makes sense or not.
I’m completely lost here. How have you solved this? Second meter yes or no, and why? Thanks in advance.

So, we have 2 meters and 2 tariffs. We don’t have photovoltaics yet, and I decided to just test it first. I didn’t know beforehand how much heating energy we would use.
As expected, it’s quite close whether it’s worth it—and that’s even without photovoltaics.
With photovoltaics, I would strongly advise against it because that inevitably reduces self-consumption, which is the “most valuable self-generated electricity.” At least, I don’t know of any way to use the same photovoltaic system on two separate electricity circuits for self-consumption. You would have to decide which circuit you want to use the generated electricity for. You can connect it to the heat pump consumption (which doesn’t make much sense because the photovoltaic system generates a lot in summer, but the heat pump needs a lot in winter) or to the household electricity (which means that in summer and possibly even winter, your household electricity would be fully covered by photovoltaics, but the heat pump would run 100% on the heat pump electricity tariff). For me, that risk is too high since you would lose some nice winter sunshine hours that could also support the heat pump’s self-consumption. But that also depends on the type of photovoltaic system you have. If it only generates power from spring to autumn, you could run the heat pump separately. We have a roof angled at 50° facing south, so I expect some output even in winter.
As a last option, you could split your photovoltaic system: use one inverter for the heat pump’s self-consumption part and another for household electricity. I have no idea if there are options to split that more flexibly (for example, almost all photovoltaics go to the heat pump in winter, and in summer about 20% to the heat pump, the rest to household electricity). But the energy supplier must agree to install 2 bidirectional meters. I think they generally reject this (at least for the heat pump electricity tariff, they probably don’t allow it).
And as I said, even for us, the second meter is probably hardly worthwhile (I can say for sure in about 5 months). The (low) basic fees for the second meter almost negate the cheaper kWh rate anyway. But that also depends on how much heating output you generate annually and with what seasonal performance factor. Also consider that the heat pump’s efficiency and comfort decrease because it occasionally hits the utility lockout. So I think from July 1st, we will only have one meter and will calmly approach the photovoltaics topic then.

Here is an update on my heating system:
I have tried different things. I have basically turned off the room thermostats and control valves. I am still working with the thermal balancing method. I called the office that carried out the heating load calculation retroactively for us. So either they did something unusual, or I have often heard it differently before: the heating load of the rooms is the calculation of how much heating energy goes into each room. But when they then calculated the hydraulic balancing, they did not calculate how much heating energy actually comes into the rooms at a certain flow. They only calculated how much flow is needed in each circuit so that a similar heating energy can be supplied to each room at the same time.
Practically:
The heating load in the basement is much lower because only about 15°C (59°F) is required there. But even there, based on pipe spacing and pipe length, they calculated that heating load X can be delivered at time Y, just like in the bathroom and other rooms. This means that hydraulic balancing would only result in the basement being off much more often than the bathroom. But that does me zero good if I don’t have electronic radiator thermostats (ERTs). Therefore, I prefer simpler thermal balancing and am fairly satisfied with it. In the open-plan area, due to the kitchen, many people, and sunlight, there are quite some temperature differences. I am considering activating the ERT there and closing the control valve at a certain temperature.
Question:
Currently, I have control valves that are closed without power (normally closed). That would make no sense here. Do I simply know whether I can replace them with ones that are normally open without power? Are there any recommendations for valves that consume low power? I have 2W devices installed, but I heard there are also ones with 1W? Five circuits/valves are connected to that room.

Regarding consumption: the Coefficient of Performance (COP) has dropped slightly to about 4.75. The annual performance factor has been at 4.35 since May, and I hope to achieve at least 4.4, possibly even 4.5, by the end of the year. The source inlet temperature is now below 5°C (41°F). Let’s see where this goes.

Question:
I only have a temperature difference of about 3°C (5.4°F) from the heat source inlet to outlet. I read that it can actually be 7°C (12.6°F). I have already reduced the pump to level 2 out of 3. That didn’t improve much. At level 1, it seems it no longer has enough power to pump. I then immediately set it back to level 2 because the inlet temperature dropped rapidly and I was afraid it might freeze.
Is this normal?