ᐅ Fresh water station and buffer tank: a technically better choice?

- A buffer tank (like any other storage tank) experiences heat losses. Better tanks are better insulated, but the water stored in them still loses heat, meaning energy is lost. This also applies to a domestic hot water tank, although here you have 400 liters (105 gallons) compared to 800 liters (211 gallons).

- Heat pumps are more efficient the lower the temperature they need to "produce." With a heating buffer tank, you don’t send water heated to, for example, 35°C (95°F) directly into the underfloor heating system but first into the buffer tank. To ensure that 35°C (95°F) eventually comes out for the underfloor heating, you send water a few degrees warmer into the buffer, then typically draw it from the buffer and lower it to the required supply temperature using a mixer. This is another factor that reduces efficiency.

- The entire hydraulic setup also plays a role, meaning how and where each component is integrated into the circuit.

There is nothing inherently wrong with domestic hot water on demand. This is the more hygienic way to generate hot water but costs more upfront. However, if using a domestic hot water on demand system, it should not be connected to a heating buffer tank but rather to a tank dedicated solely to domestic hot water. Heating water still goes directly to the underfloor heating system. In this case, you don’t need 800 liters (211 gallons). Whether 400 liters (105 gallons) is sufficient for 6–7 people with domestic hot water on demand, I’m not knowledgeable enough to say.

Daniel-Sp schrieb:

An 800L (210 gallons) thermal storage tank with a heat pump is a no-go.

That’s not very well explained in a way I can understand.
You are probably very experienced (judging by your posts), so it would be interesting to know the reasoning behind this.

@face26 thank you for the explanation. According to this, a direct underfloor heating system connected to the heat pump, a smaller or precisely sized buffer tank for the domestic hot water, and a domestic hot water system would be the ideal solution for a new build?

freisinger schrieb:

@face26 thanks for the explanation. So, a direct underfloor heating system connected to the heat pump, a smaller or precisely sized buffer tank for the domestic hot water, and a domestic hot water system would be the ideal solution for a new build?

Whether it is ideal depends on each individual. If a slightly higher initial investment is acceptable and everything is properly sized, it is definitely a very good solution that requires very little ongoing attention.

You should also make sure the domestic hot water system has sufficient flow capacity.

Daniel-Sp schrieb:

An 800l (210 gallons) heating buffer tank with a heat pump is a no-go.

You can’t say that in such a general way. A thermal storage tank is currently the most cost-effective and efficient way to store electricity temporarily. So if you have photovoltaic panels on the roof and your heat pump is connected to the photovoltaic system, a 1000l (260 gallons) buffer tank can also make sense.

Grantlhaua schrieb:

You can't really generalize like that. A thermal storage tank is currently the most affordable and efficient method to store electricity temporarily. So, if you have a photovoltaic system on the roof and your heat pump is connected to it, a 1000-liter (264-gallon) buffer tank can make sense.

How much of the photovoltaic output can the heat pump use? And when is the energy needed again? What about losses until then? And what happens when the sun isn’t shining? Who then heats the buffer tank?
The calculation isn’t quite that simple.