Experiences with brine heat pump

I read through this topic last night in bed (We are about to build a house and so I did get some "doubts about an air-to-water heat pump/brine-to-water heat pump") and also found articles that I consider trustworthy. The Association of Private Builders apparently conducted a study with/at Weberhaus and took samples. Elevated/too high values were reportedly found quite frequently in heat pumps there.

According to the article, heat pumps should generally not be used for hot water preparation or an additional heating element should be used so that the water is regularly heated to 65°C or, even better, a heat pump should be used that can already reach 65°C on its own. Of course, heating elements cause high energy costs – to what extent heat pumps that naturally reach 65°C make sense in a single-family home – no idea.

In general, I am currently also uncertain whether air-to-water heat pumps / brine-to-water heat pumps + subsidies / or rather gas boilers, which easily and efficiently reach 65°C and cost significantly less. (The article states for "general" single-family homes investment/annual costs for air-to-water heat pumps 13,000/1066, brine-to-water heat pumps 23,000/793, gas boilers 5,500/830)

In addition, there are the costs for heating up to 65°C weekly, which are apparently not included.

However, since I only found this article (Association of Private Builders) and am still educating myself – how do you see it? A photovoltaic system could possibly save part of the running costs of a heat pump but also costs money. With the brine-to-water heat pump, you can get 35% from BAFA, thus paying about 15,000 instead of 23,000. The legionella question remains.

What do you actually want with these compulsive 65°C?

Legionella is zero problem in a single-family house, there are also no regulations. One might think about it with a 1000l tank but certainly not with the usual 100-250l in a single-family house.

And of course the heating element should be off. But you don’t need it either, at most in the coldest winter. With a brine-to-water heat pump, not at all, as long as the source wasn’t incorrectly sized.

The legionella issue is not existent at all in a classic single-family house, 3-5 people, and 150-300l storage. Unless you only do laundry on Saturdays.

In addition, there are the costs of having to heat up to 65°C weekly, which are apparently not included.

Exactly this so-called legionella cycle is often discouraged. The short heating of the water is often not sufficient and tends to make legionella temperature-resistant. There are also several articles on this if you Google legionella cycle.

In a single-family house, the water is often exchanged frequently and regularly with a well-sized domestic hot water storage tank, so that normally no critical number of legionella can develop. If there are still concerns, one can also consider the use of a fresh water station. From a hygienic point of view, this is the optimum, as domestic water is only heated immediately before extraction.

Unfortunately, this statement is not found in the article. Very generalized, unfortunately. I have now explicitly searched further all the time and was able to also find the statements with additional search terms that the warning is aimed at apartment buildings with heat pumps and that other precautions are possible there. Other discussions I only found from 2010, in which opinions also vary greatly. In general, there are supposedly fewer problems if you don't have a circulation line in the first place (if you have one, definitely do not turn it off...) and the liter content is less. Since only two people live in our house, the turnover is limited - usually, showers are taken every two days, otherwise just some warm water in the morning/evening for washing the face, etc. Currently planned in construction as standard is "Arotherm Split VWL 75/5" with "uniTOWER VWL 78/5 IS" with 190L. If it really only costs 2000 more due to the BAFA subsidy, which apparently is not available with the air-water heat pump, to a SWWL, it could certainly make sense for me to switch to a SWWL. Is that realistic? How much is the surcharge for the fresh water station - I had read in the 2010 posts that you would only get 40°C with it. That would definitely be too little for me - especially if you want to wash something by hand in the kitchen.

Air-to-water heat pump, just check the list from Bafa and check the annual performance factor on the heat pump calculator.

No idea where this keeps coming from that air-to-water heat pumps should not be funded.

Regarding legionella: try to find a case in recent years that has occurred in a single-family house.