Simple interpretation of heating systems with heat pump

Hello everyone, first of all, thank you very much for your interest!

We are planning to renovate a building from 1936. Ultimately, it will be completely refurbished and well insulated.
Relevant for the question:
It is planned to have underfloor heating in all rooms. At the moment, we are assuming an air heat pump (alternatives are unfortunately too expensive right now). The roof is to be extensively equipped with photovoltaic panels (14 kWp).

At this point, I do not have a U-value calculation available. I am mainly interested in your opinion on whether the heating system I have in mind is also considered sensible by you.

Requirement:
The heat pump is to operate the heating system and also heat the domestic water. Possibly, a fireplace with a water jacket will be integrated in a few years.

My initial consideration is that the heat pump runs more efficiently the less it has to work. This means for me that if the underfloor heating is operated with, e.g., 23 degrees flow temperature, the heat pump should not have to work much more than 25 degrees.
In order to utilize the advantages of the photovoltaic system, a generously sized buffer storage tank will be integrated.
The heat pump would therefore always charge the buffer to 25 degrees, preferably during the day, and depending on solar surpluses, the heat pump could also work hard and supply higher temperatures to the buffer beforehand (e.g., 40 degrees).
That’s the heating system so far.

Now the question always arises how to manage the temperature lift for the domestic water, especially since the legionella issue must be considered.
My idea here would be to tap the buffer just as for the heating system and install two fresh water stations. Two pieces solely for the reason to place the fresh water stations near the points of use (kitchen and bathroom). Now I would each switch in a solar instantaneous water heater so that, depending on the starting temperature in the buffer, it manages the lift from 25 degrees (or possibly more) to 50 to 60 degrees.
In this system, in my opinion, a very simple buffer storage tank can be used, without heat loops.

According to my ideas, this system should involve comparatively low installation costs because it is very simple and contains little control complexity. Thus, it should also be relatively fail-safe. I am aware that the instantaneous water heater causes costs when operating without solar surpluses. However, in my assessment, these should be offset as the heat pump can continuously operate in its efficient "comfort zone."

In the long term, there are also plans to connect a fireplace with a water jacket to the system, which will cause the temperature in the buffer to rise and the instantaneous water heaters to have to work less.

Fire away with criticism and suggestions ;-)

Stefan

I had to smile a bit when I first read your thread title and then the post! :-)

I expected a simple system design and probably found the most complex design ever. My goodness. So:

Water pocket chimney: Absolutely not. That costs an enormous amount of money, requires a huge buffer (we'll get to that later), harms the environment, and can’t even serve as a backup during a power outage.

A heat pump should not work "little," but efficiently. One that works little is oversized. Therefore, renovate first and then have the heating load calculated exactly (room by room). Not by the energy consultant, but by an engineering office. AND ONLY THEN should the underfloor heating be planned and the heat pump selected accordingly. Fitting does not mean bigger than the heating load.

Photovoltaics and heat pumps have nothing to do with each other. Please consider them separately. Photovoltaics should always be as large as possible. An electric car alone can easily use 30 kWp. A heat pump, too. So only be limited by the roof surfaces (including north!).

Buffer: A good heating system does not have the desired huge buffer, but none at all. ZERO. The heat pump goes directly into the heating circuit. EVERYTHING else is an emergency solution that costs money and efficiency.

Legionella problems do not exist in a single-family house if the hot water tank is not oversized. Legionella programs don’t help. Fresh water stations are okay, but separate from the heating system in their own tank. The rest of your ideas were already too complex for me to read.

Simple installation, little control is exactly right. So no individual room controllers, no actuators, no mixing valve, no bypass valve, no buffer, no control of the heat pump via photovoltaics. Make hot water at noon, overheat screed by two degrees during the day. Done.

Sorry for the clear words, but you have really deviated 180° from the planned path.

it is exactly as says.

Apparently you have talked too much with TGA planners who plan 6-12 residential units MFHs? (my brother-in-law is one of them) They install fresh water stations because of the legionella problem, in a single-family house they have no place.

Usually, not even 3 liters of water that stand still and can form legionella fit in the pipes from the producer. If you have a guest WC with a hand basin with 40m piping that is only used 3 times a year, you open the tap occasionally. By the way, circulation belongs just as little in a house as ERR.

Many heat pumps have a combination storage tank. The underfloor heating itself does not require an extra storage tank, the amount of water in the underfloor heating + screed is enough storage.

Alternatively, put 100KWp on the roof, only instantaneous water heaters + infrared heating, that is simple o_O

Regarding the water jacket chimney: You can do it in an old house with "high-temperature technology," i.e., no surface heating and high flow temperature. But it costs relatively much, possibly to do it yourself (a friend of mine did it that way in an old property in combination with an old oil heating system)

Okay... Thanks for the clear words!
Especially critical words help to avoid mistakes!

My approach was:

[*]not to install a combined storage tank or layering tank, as I find it energetically questionable to generate high temperatures with the heat pump here when the electricity is drawn from the grid
[*]Therefore, hot water and heating should be separated

Buffer: A good heating system does not have the desired huge buffer, but none at all. ZERO. The heat pump goes directly into the heating circuit. EVERYTHING else is an emergency solution that costs money and efficiency.

But not even a small storage tank to save solar yields into the evening hours? It should not be charged at all during the day if the photovoltaic yield is too low. In this case, the heat pump could also directly supply the underfloor heating and bypass the buffer?

Apparently you have talked too much with TGA planners who plan 6-12 unit multifamily houses? (my brother-in-law is one)
Because of the legionella issue, a fresh water station is installed

Would a hot water heat pump be the better choice then? (the basement is insulated later on the walls, but since it is not living space, there are no living rooms here)

Make hot water at noon, overheat screed by two degrees during the day. Done.

So with the heat pump then charge a buffer at noon, which is only responsible for the domestic hot water?
But then I would still need the instantaneous water heater or hot water heat pump in case the buffer was not charged with the appropriate temperatures...

Water jacket stove: Absolutely not.

Okay... Good point about the electricity... We will then reconsider an alternative (stove with less storage mass and without water jacket).

Apparently you have talked too much with MEP planners who design 6-12 unit multi-family houses? (my brother-in-law is one of them)
They install fresh water stations because of the legionella problem, in a single-family house they have no place.

Oh right: true
I mostly deal with people who plan schools and functional buildings...

You think very complicated. In the dimensions of a single-family house, all of this is unnecessary and inefficient. As written by : first energetically upgrade. Then have the heating load calculated. Then have the heating and heat pump (usually underfloor heating with an air-water heat pump) designed accordingly and definitely do not oversize. Only design a domestic hot water tank (!= buffer, that is misleading). One heat pump then supplies the domestic hot water tank (for the domestic water) and the heating. Screed and heating together are your thermal buffer, which you can heat a little higher during the day if needed so that you have to heat less at night. All rooms regulated to a maintained average temperature. And then as few gimmicks as possible. That way you save the most and are efficient. Both in terms of purchase and operation.