Experiences with brine heat pump

When referring to the 45 °C water temperature mentioned here, are we talking about warm water for showering etc.? Shouldn't it by now be set to 60 °C due to legionella etc. and calculated accordingly?

I wanted to ask how much cheaper a heat pump really is compared to a gas heating system. In my last rented apartment, a geothermal heating system was installed with the announcement that costs could be reduced by up to 60 %.
The reality was that the costs increased by 100-200 %. When the legionella debate arose and the temperature was raised from 45 °C to 65 °C, the costs increased again.
There was no photovoltaic system. So the electricity came 100 % from the grid.
Are heat pumps equally problematic in this regard? If yes, do you usually really save money when a photovoltaic system is present, or does it just become as expensive as gas?

Yes, 45° C for domestic hot water such as for showering. With a heat pump, it is very inefficient to go up to the 60 °C you mentioned. With sufficient drinking water hygiene and especially a regular complete water change every 2-3 days, there is no problem when using drinking water at 45 °C.

You usually have to heat electrically with the heating rod, which drives the electricity costs up (hence your additional costs based on your previous experience). It is basically a design issue with your heating system. With a heat pump, you have to plan a bit more for the heating surface layout and also for domestic water heating, including pipe spacing, flow temperature, etc.

Does geothermal energy generally pay off compared to a gas boiler? Honestly, I do not know. A gas boiler is at least significantly cheaper to purchase without BAFA funding. Also, whether gas will become much more expensive in the coming decades cannot be said now. It also depends on your personal attitude. For me and my family, I would try to ensure that heating is generated as much as possible without fossil energy.

Yes, 45° C for domestic hot water, such as for showering. With a heat pump, it is very inefficient to go up to the 60 °C you mentioned. With sufficient drinking water hygiene and especially a regular complete water exchange every 2-3 days, it is not a problem to use drinking water at 45 °C.

You usually have to heat electrically with the heating rod, which drives up electricity costs (hence your additional costs in your previous experiences). It is basically a matter of your heating system’s design. With a heat pump, you have to plan a bit more for the heating surface layout and also for the domestic hot water heating, like spacing of the pipes, flow temperature, etc.

Whether geothermal energy is fundamentally worthwhile compared to a gas boiler? Honestly, I don’t know. A gas boiler is at least considerably cheaper to purchase without BAFA funding. Also, whether gas will become much more expensive over the next decades cannot be said now. It is also your personal preference. I would try for myself and my family to ensure heating is produced as much as possible without fossil energy.

Fossil fuels are of course not desirable, but at the same time electric heating from coal-fired power plants is not any better. And if costs double or triple as a result, then the question is whether it might be better to retrofit only 20 years later. That can only be technically advantageous and the money might potentially be saved then.

All of this, of course, only applies if geothermal really is as unprofitable as it was.

Regarding the water temperature, I have to say the statement is confusing. You have no influence on the “water hygiene.” You do not "contaminate" your water. And outside the building, you have just as little influence on the pipes as on the quality of the municipal utilities. I am also not sure how one should completely exchange the water. Apart from possible waste, you cannot empty a hot water tank by showering or similar. Fresh water simply flows in immediately. So you don’t have a complete replacement, only a dilution, which does absolutely nothing against Legionella. You could heat the water tank to 60-80 °C every 1-2 weeks and kill everything, but even then you generate enormous costs.

It all sounds as if the heat pump is a modern but actually still unprofitable and economically rather risky venture (Legionella). It would certainly be worthwhile if you could generate all the electricity for it through photovoltaics combined with batteries. But if I’m not mistaken, such an autonomous system quickly costs 10-30 k€. Plus the cost of battery replacement every x years/decades.

[Fossil fuels are of course not desirable, but at the same time, electric heating using electricity from coal-fired power plants is no better. And if the costs double or triple as a result, then the question is whether it wouldn't be better to convert only 20 years later. That can only be technically advantageous, and the money may potentially be saved.

All of this, of course, only if it really is as unprofitable as geothermal energy was.

Regarding the topic of water temperature, I have to say that the statement is confusing.
You have no influence on the "water hygiene". You are not "polluting" your water. And outside the building, you have just as little influence on the pipes as on the quality of the municipal utilities.
I am also not sure how one is supposed to completely replace the water. Aside from possible waste, you cannot empty a hot water tank by showering or similar. Fresh water flows in immediately. So you do not get a complete change, but only a dilution, which absolutely does nothing against legionella.
You could heat the water tank to 60-80 °C every 1-2 weeks and kill everything, but even then you create enormous costs.

It all sounds like the heat pump is a modern but actually still unprofitable and, in economic operation, rather risky endeavor (legionella). It would certainly pay off if you could generate all the electricity for it through photovoltaics combined with batteries. But if I’m not mistaken, such an autonomous system quickly costs 10-30 k€. In addition, there are the costs for battery replacement every x years/decades.]

No, it can be very economical. True to the motto: it depends. You can save a lot of money by doing the installation yourself. You definitely have to be careful with the design of the underfloor heating. And for those who have a very big fear of legionella, a tank with a fresh water station is installed. However, you cannot argue away the additional costs here.

Fossil fuels are of course not desirable, but at the same time, electric heating using electricity from coal power plants is not any better.

Right, but thanks to the high annual performance factor of a geothermal heat pump, which can be achieved with intelligent design, you then need very little electricity. Additionally, this can be supplied via renewable energy sources, e.g. through your own photovoltaic system or the right electricity provider.

Regarding the topic of water temperature, I have to say that the statement is confusing.
You have no influence on "water hygiene." You don’t "contaminate" your water. And outside the building, you have just as little influence on the pipes as on the quality of the municipal utilities.

Drinking water hygiene does not only refer to dirt in the water. Drinking water hygiene also includes protection against legionella. Legionella are always present in drinking water. But only at certain temperatures is their reproduction promoted. These temperatures lie between 25 - 50 °C. So if you charge your water tank at this temperature, you should regularly completely replace the water. Therefore, the size of the water tank should always be chosen according to the number of people living in the house. Then you basically have no problem with legionella. Otherwise, a fresh water station also helps, but it is easily 1,000 euros more expensive.

You could heat the water tank to 60-80 °C every 1-2 weeks and kill everything, but even then you generate enormous costs.

That is exactly what you should not do, because this short-term increase in temperature (e.g. via legionella control) rather makes legionella resistant to higher temperatures.

It all sounds as if the heat pump is a modern but actually still unprofitable and economically risky venture (legionella).

No, you have just taken out the negative aspects. However, a heat pump that is incorrectly adjusted and designed is indeed less profitable. Legionella are also no problem if designed correctly. With a geothermal heat pump, you can generate 4-5 kWh of heat energy from 1 kWh of electricity with good design. Gas boilers and geothermal heat pumps have similar operating costs. Thanks to BAFA funding, the acquisition costs are now also at a similar level. If you install a controlled residential ventilation system, which nowadays can be co-funded when installing a heat pump (if technically linked together for joint regulation), then you are cheaper with a heat pump.
Additionally, with a geothermal heat pump, you can cool passively and feed your electricity in directly, if you do install a photovoltaic system on the roof.

However, 45 °C has been mentioned several times in this thread, which everyone officially advises against because, as you also said, legionella bacteria multiply ideally at this temperature.
How is a heat storage tank completely emptied? Normally, water always flows in immediately afterward. This could only be prevented if an air intake is opened every few days, thus emptying the tank.
But this would mean that
a) each time you would have to reheat completely from partially just a few degrees in winter
b) you either have to throw warm water directly into the drain or someone will eventually be cold while showering

Personally, that all doesn’t sound really economical or ecological to me.
I understand if the heating doesn’t require temperatures above 55 °C, but what about the hot water? I don’t quite see yet how this could realistically work without the problems mentioned above.

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

How exactly do you “empty” the storage tank completely?

I don’t want to criticize heat pumps, but I’m trying to realistically assess them for myself. Without a sufficiently sized photovoltaic system, they seem rather unprofitable and possibly not really environmentally friendly. Due to the power grid, there is also effectively no green electricity. The lion’s share is still not generated from renewable sources.
If it’s only about the environment, then district heating as naturally occurring waste heat from power plants might actually be interesting. Although I don’t know the key figures there, and it might only be truly environmentally unfriendly with nuclear power plants.