ᐅ Solar Thermal Systems: Storage Tank Size / Legionella Prevention

We have planned a 300L (79 gallons) buffer tank for a household of four people. Is a legionella control system recommended here, or will the water volume be replaced quickly enough due to the high flow rate?

Hello
Legionella bacteria are not an issue in the buffer tank since it contains heating water.
You probably mean a domestic hot water storage tank. In a household with three or more people, I don't see any problems. There was also something about a DVGW worksheet concerning 300 liters (79 gallons) of drinking water.

Olli

Exactly, I meant the potable water storage tank. I have also read quite a bit about legionella control systems, and most consider them not 100% reliable. Therefore, it is probably best to properly size the tank so that the contents are renewed multiple times. What happens if the heat cannot be released because no water is being used? Does the fluid in the system then overheat?

Hello
The collector area should be matched to the storage volume.
Approximately five m² (54 ft²) per 300 liters (79 gallons) of domestic hot water is recommended. Stagnation in the solar system is usually not an issue with this ratio.
If no heat is drawn from the storage tank and the system is at a standstill, the temperature of the solar fluid will rise until it evaporates. The additional volume is absorbed by the expansion vessel. When the system cools down, the water vapor condenses again.

Olli