ᐅ Operate fresh water systems with partially very high and low buffer temperatures

Hello.
I have noticed that with really warm weather now, the solar system is delivering good performance to the buffer tank.
The buffer temperature in the afternoon currently rises to about 80°C (176°F) at the top of the tank, where the supply to the domestic hot water is located.
In the evening, however, the buffer temperature at the top drops to about 60°C (140°F).
(The pellet boiler only starts when the sensor reaches 55°C (131°F), so currently it turns on in the mornings).

Question:
The domestic hot water is currently set to a target temperature of 58°C (136°F) for production.
The circulation is set to 53°C (127°F).
The supply line from the buffer to the domestic hot water is limited to 65°C (149°F) using a simple mixing valve.

Does it matter for the domestic hot water if in the evening it is only fed with about 60°C (140°F) from the buffer?

Producing 58°C (136°F) with a 60°C (140°F) supply is actually quite tight. It should really be around 65°C (149°F).

However, I wouldn’t mind if the domestic hot water is produced around 55°C (131°F) instead of 58°C (136°F) during this time.
When the boiler delivers again (with 65°C (149°F) at the top of the buffer), there will be enough supply temperature for the domestic hot water again.

Thank you very much.

Is your water always sufficiently warm? If yes, everything is fine.

Joedreck schrieb:

Is your water always warm enough? If yes, everything is fine.

Yes, the hot water then is not quite 60 degrees Celsius (140°F) anymore, but about 52 degrees Celsius (125°F), still very warm.
Of course, it then needs to be mixed with cold water for showering, etc.
That means, if the fresh water from the buffer tank receives too high supply temperatures, a mixing valve limits it to a set 65 degrees Celsius (149°F).
If the supply temperature is too low (below 65 degrees Celsius (149°F)), the fresh water simply heats the hot water as warm as the supply temperature minus a loss of about 5 degrees Celsius (9°F). So, instead of a 60 degrees Celsius (140°F) supply, the hot water will be around 55 degrees Celsius (131°F).
That is completely sufficient in summer when no heating is needed anyway.
In the morning, the boiler obviously has to reheat a bit, since the buffer cools down overnight.
Thank you

Where exactly is the problem then?

Joedreck schrieb:

Where exactly is the problem then?

I just want to understand how the domestic hot water system handles this when it is set to a target temperature of 58°C (136°F), but the supply temperature is only 58°C (136°F) instead of the usual 65°C (149°F). Does the domestic hot water simply produce about 53°C (127°F) warm water from the 58°C (136°F) supply, or how does it work in the domestic hot water system?

Exactly like that. A domestic hot water system is basically just a heat exchanger. The warm water from the buffer tank heats the cold water from the supply line in a flow-through process.
If the water from the buffer tank is no longer warm enough, the domestic hot water system simply heats the water as much as it can.
This is completely harmless.