Diagram of an air-to-water heat pump with 2 storage tanks

Hello, after the decision for an air-to-water heat pump (for now) has been made, I am currently thinking about the (ideal) system. There is a lot of talk and reading about wrong temperatures in the stratified storage tank, 2 separate heat pumps for domestic hot water and heating water, too high flow temperatures, etc. Conditions: 150 sqm living space, 4 people, underfloor heating, renovated old building from 1965. My idea is as follows: One heat pump and 2 storage tanks, one for domestic hot water (200 L) and one for heating water (300-500 L). One heat pump, which alternately fills the tanks "as needed". When heating the heating water tank, it operates in the efficient range (flow temperature approx. 40 degrees), with the domestic hot water tank it is less efficient due to higher flow temperature of about 55 degrees. When supplemented with photovoltaics, "surplus electricity" is first used for heating. If it is not needed there, you can, even if inefficiently if necessary, fully charge the domestic hot water tank, even up to 90 degrees. But then a mixer should be installed at the outlet that mixes it down to 50-55 degrees. Does anyone already have such a system in operation and what are the experiences? Can heat pumps handle this control or do I, as an electronics engineer, have to come up with something myself? I have space for 2 storage tanks and I think the stuff with combined stratified storage tanks and all that mess is neither fish nor fowl. Regards bauibaui

We only get one storage tank, but it comes with a fresh water station, so we can keep the temperature in the tank at 45° and have no problem with Legionella or the like. Surplus from the photovoltaic after the battery storage is then used to increase the boiler temperature; if necessary, the excess is fed into the grid.

We have an integrated storage (230L) for hot water that goes up to 45°. Since last August, it hasn't even reached 350kWh. It takes a while before the costs for the control, storage, etc. are covered. Are you looking for a complicated solution to a simple problem? Do you really have to run the supply line at 40°?

Using photovoltaic electricity to heat water via an electric heating element is extremely uneconomical; it is better to feed this electricity into the grid. If then heating, do it via the heat pump. For control with photovoltaic, corresponding equipment is of course needed. But it is common on the market and nothing special. Lower the temperature for domestic hot water to 45 degrees.

We have an integrated storage tank (230L) for hot water that goes up to 45°. Since last August it hasn’t even used 350kWh. ?

Not even 350kWh over the winter, hard to believe.

Not even 350kwh over the winter is hard to believe.

Only for hot water that would be a realistic value... for 90 to 120 days.