Experiences with brine heat pump

Heat pump vs. gas is always dependent on how one personally assesses the development of energy prices when it comes to costs.

The costs for the initial installation are now relatively equal due to the extensive subsidies, although it feels like the prices for the heat pump are increasing in the same proportion as the subsidies.

Another aspect is the replacement in case the system should break down; once there are no subsidies, a heat pump becomes really expensive.

How exactly do you "empty" the tank completely?

This is not about emptying the water tank. The drinking water stored in it should be completely replaced once every 2-3 days, i.e. if you have a 300l tank, you should have withdrawn the 300l from the tank after 3 days. This prevents the proliferation of legionella. In a single-family house, legionella hardly ever occur anyway if water is drawn regularly. And as I said, a fresh water station provides a solution if you are still too afraid of it.

And I also see heat pumps increasingly in all new apartments, where to my knowledge the minimum temperature is legally mandated and usually no photovoltaic systems exist. That seems to me to be very disadvantageous for the tenants.

But this is a different issue. We are talking here about a single-family house and not a multi-family house. Therefore, it is not comparable.

I don’t want to badmouth heat pumps either, but I try to evaluate them realistically for myself. Without a sufficiently sized photovoltaic system, they seem rather uneconomical and possibly not really environmentally friendly.

Then you should also want to read up on the subject of ground source heat pumps yourself. That can fill several evenings. Asking that generally in the forum is not very helpful, as every house is different and also brings different prerequisites. In our planned house, a heat pump is extremely economical. We have no gas connection and a tank will not come into my basement. Additionally, I was able to lay the ground collectors myself. Since we are also installing controlled residential ventilation, we now receive 35% funding on the entire system. We are now even below the cost of a gas boiler in terms of price. And electricity you get as 100% green electricity. It may be true that in the end, because of the grid, it is not so, but the energy you draw is definitely fed into the grid by renewable energies. And what is not environmentally friendly about that? You make 5 kWh of heat from 1 kWh of electricity in the best case.

This is not about emptying the water storage tank. The drinking water stored in it should be completely replaced once every 2-3 days, i.e., if you have a 300l tank, after 3 days you should have drawn 300l from the tank. This prevents the proliferation of Legionella. In a single-family house, Legionella hardly ever occur anyway if water is drawn regularly. And as I said, a fresh water station provides a remedy if you are still too worried about it.

Well, as I said: If you don’t stop the inflow of fresh water, you will never actually empty the tank, but only continuously dilute it. This is done anyway in almost every reasonably planned household, but Legionella develop because you simply cannot empty such a tank.
So this approach doesn’t really help. It’s nice for the conscience, but if you ever do have Legionella, you certainly won’t get rid of them this way. And since you are always in the “risky” temperature range, you can never be sure and would actually have to test constantly.

So, as I said, drawing 100 L of hot water per day does not correspond to emptying over 3 days. Especially since probably not 100 L is drawn in one go. One showers in the morning, one in the evening. Always drawing at different times. In reality, you might only draw 50 L and keep 250 L. The fresh 50 L dilute and reduce the Legionella concentration (number per liter), but the proliferation continues. In fact, this approach, if carried out like this, actually brings nothing.

And you also get 100% green electricity. It may be that in the end this is not the case because of the power grid, but the energy you take out is definitely fed into the power grid through renewable energies.

That is not quite correct.
With your surcharge, you promote renewable energies. In other words, you support investments. Nothing more. If suddenly everyone consumed more electricity because everyone heated with electricity, the demand would by far not be covered by production from renewable energies, even if everyone paid for green electricity. Renewable energies in Germany do not cover the market and green electricity is thus in reality not green electricity as you describe it here.
One must also not forget: the best thing for the environment is not to consume more green electricity, but to consume less electricity altogether.

In principle, the calculation with “1 kWh electricity ideally equals 5 kWh heat” is nice and good, but you also have to consider the efficiency in producing electricity. And that is not 100%. So you would have to compare how many kWh heat can be generated from electricity including its production versus gas.
Again, I don’t know the exact numbers, but these “up to” calculations remind me of my landlord and his architect. At the end of the day, it cost a fortune and the consumer was the fool. And whether the enormous electricity consumption was ultimately better for the environment than gas or district heating remains uncertain for now.

Well, as I said: If you don't stop the backflow of fresh water, you will never empty the storage tank, but only constantly dilute it.

Exactly, that's what I meant by "exchange." I never spoke of emptying. This exchange at temperatures between 45-50 °C has now become common with heat pumps and is done this way in countless households. There are certainly different opinions on this and many, many discussions. If this application seems too risky to you, then you should also omit a circulation. Because studies have shown that in single-family houses with circulation, there were significantly more Legionella in the water than in single-family houses without circulation. So you can expand the topic in any direction. Hence my note on the fresh water station, as this is the hygienically best solution at low temperatures (drinking water is then heated when needed).

That is not correct. You promote renewable energies with your surcharge. In other words, you promote investments.

Then take a look at providers like Naturstrom, for example. Not only E.ON and Co. Naturstrom sources 100% of the electricity it offers from wind and hydropower plants in Germany. Of course, support also exists, but this is done anyway through the Renewable Energy Act levy (at least theoretically).

One must not forget: the best thing for the environment is not to consume more green electricity, but less electricity in absolute terms.

I absolutely agree with you there. But I prefer to consume 1 kWh of green electricity (and pay my extra charge for renewable energies) from a renewable energy source than to have to generate the same amount of heat with gas. That also needs to be promoted (fracking says hello).

In principle, the calculation with "1 kWh electricity ideally 5 kWh heat" is nice and good, but one must also consider the efficiency of electricity generation. And that is not 100%. So, you would have to compare how many kWh heat can be generated from electricity including its production compared to gas.

I have already noticed that you like to discuss a lot in the forum (see e.g. the KNX thread). But at some point, one also has to put a stop to the debate between sense and discussing for the sake of discussion. The sun doesn't care whether a photovoltaic panel has an efficiency of 7, 15, or 25% since it taps into an energy source with high finiteness. Okay, photovoltaic panels also cost energy to manufacture, so they're also bad by comparison. You see, the game can be played infinitely here and everything can be scrutinized with a fine-tooth comb.

I am actually not trying to argue for the sake of arguing, but to question everything before betting on a dead horse and then building/buying something you will regret in 10 years. Especially when there are currently high subsidies involved. These often make products now appear cheap and then end up costing you dearly in 10-30 years. That is why it is better to understand now how a KNX system should be structured and which versions exist. And better to understand now where the advantages and risks of a heat pump lie.

I honestly say: in our rental apartment, the hot water preparation is purely electric and although expensive, I find the principle very interesting. Because electricity will be produced more environmentally friendly in the long term and as soon as battery technology becomes more affordable and durable, photovoltaic systems will become increasingly relevant for house construction. That is why I also see it this way: The more I can run on electricity, the better. As long as I have a sufficiently powerful photovoltaic system and preferably a feed-in system with batteries.

But you have to look closely at what is ultimately the most efficient and what you plan when building. If, like back then with geothermal energy, you bet on the pseudo-right horse at the wrong time with the wrong execution, in 15 years you will still be the fool who had high investment plus high operating costs.

That is why I always like to discuss. Especially with people who have more experience or knowledge on a topic. In doing so, you find out exactly what is how good.

They also like to make products appear cheap now and then cost you dearly in 10-30 years.

In this time, you will likely have replaced a heating system once anyway, whether heat pump or gas boiler. As long as you can continue to use the heating pipes (e.g., underfloor heating), switching to another heating medium is even possible. Therefore, I would now rather consider what is also sensible for heating in the future, and for example, I would no longer want to install wall radiators with high flow temperatures today.

To be honest: in our rental apartment, the hot water preparation is purely electric, and although expensive, I find the principle very interesting.

This is not an exclusion criterion with a heat pump either. For example, you can electrically reheate via a heating rod in the heat pump or in the domestic hot water tank. But direct heating at the taps via fully electronic instantaneous water heaters is also an alternative. The drinking water heating does not necessarily have to run via the heat pump or gas boiler. In addition, modern heat pumps also have interfaces for direct photovoltaic integration. In summer, for example, the passive cooling function in the heat pump can be operated this way.

If you, like back then with geothermal energy, bet on the pseudo-right horse at the wrong time with the wrong execution, you are still the fool in 15 years who had high investment plus high operating costs.

Google the "heat pump consumption database" and look for ground source heat pumps in your area. Then you can see roughly what amount of electricity is used annually in these projects and how much heat energy results from it. These are quite good indicators of what the operating costs could be on average.