ᐅ What type of storage or domestic hot water heating is suitable with district heating?

Good morning everyone,

I am still busy with my new build. It’s not easy these days with rising interest rates and all the political energy issues. However, it’s getting more concrete now, and I need to plan the utility room. Unfortunately, I have to build without a basement, so space is very limited. The district heating connection is already fixed.

The connected load will be around 8-10 kW. There will be underfloor heating everywhere. A household of 4 people. Only a small photovoltaic system (4.5 kW).

We are building in the town center in a commercial area, so our living, dining, and kitchen area will be on the top floor. There will only be a small kitchen unit there that requires hot water, so I want to avoid running a hot water pipe and instead use an electric tankless water heater under the sink.

I also need to supply two bathrooms. One on the ground floor, diagonally opposite the utility room, and the main bathroom directly above the utility room.

Which hot water system would you recommend that is modern and space-saving?

My options, based on what I have researched so far (I’m no expert):

Option 1: Instantaneous water heater station at the utility connection station:

My preferred option would be a fresh water transfer station with an integrated heating circuit and an integrated instantaneous water heater (tankless). No storage tank. These stations are quite compact (about 120x75x40 cm (47x30x16 inches), wall-mounted).
Unfortunately, this option was discouraged because it is apparently only suitable for larger connected loads. For fresh water, about 30 kW would have to be available briefly, which would result in high demand charges and strain the system (controllers, valves, water hammer, etc.), since the normal operation (without hot water demand) requires much less power, and then suddenly 30 kW for hot water. Unfortunately, I would have found this option hygienic and very space-saving!

Option 2: Hot water storage tank:

The simplest and still quite space-saving option might be to use a floor-standing storage tank (160 liters (42 gallons)) combined with a simple fresh water transfer station with an integrated heating circuit and drinking water heating that heats the boiler. According to my sketch, I could probably fit this in. The question is whether this is still state-of-the-art (hygienically and technically) and if a 160-liter (42-gallon) boiler is sufficient (not much bathing)?

Option 3.1: Buffer tank with instantaneous water heater at the transfer station:

I’m not sure if I have the space for this, but this option would use a 500-liter (132 gallons) buffer tank and a tankless water heater at the transfer station. Since I have limited space and feel this would result in relatively high heat losses, I’m not very convinced by this option.

Option 3.2: Buffer tank with instantaneous water heater at the buffer tank:

To me, this is basically the same as option 3.1.

What do you think? I’m not a professional and don’t know if I’ve understood everything correctly or missed anything, or if I have all relevant options in mind.

Of course, I will hire specialists for all services, but I want to start with a complete concept so I can fit everything in properly in the end.

For option 2, I created the utility room layout in PowerPoint.

Many thanks and best regards

Uh... the tankless water heater is by far the most expensive option for domestic hot water heating.
How much do you actually expect to save? You still have to make openings for the cold water pipe and the drain anyway.
I estimate the plumber won’t give you a discount at all for the hot water line. Maybe 50 EUR for the materials...

Forget about it.

I have also thought in the meantime that no savings are being made there. My idea was whether you could save a circulation pump with the option of having the domestic water station in the utility room, since the pipe runs would be very short if you don’t have to go all the way up.

Which option would you choose?

I would recommend installing a hot water storage tank. However, 160 liters (42 gallons) will be empty after using the bathtub. It would be important to check how long it takes for the water to heat up again.

What is the cost per kWh of heat? What prices can be expected in the future?
Why is the photovoltaic system so small?

A tankless water heater or a small boiler in the kitchen can definitely make sense.
Instant hot water is also a great convenience that otherwise can only be achieved with a circulation system.

So 13 cents/kWh. Predicting the future is of course difficult. However, heat will receive more attention in the future and may soon be regulated. Price increases will probably become more difficult then. However, prices rarely get cheaper when politics get involved.
Photovoltaics are so small because only one side can be used effectively.