ThermProtect and the heat pipe principle to guard against overheating
Viessmann counters this phenomenon with a special absorber coating – ThermProtect. As part of the process, the absorber radiates more and more heat as it warms up. This increases the heat losses of the collector, while at the same time, the collector temperature rises only slightly and the stagnation temperature remains significantly below the usual values. How does that work exactly?
ThermProtect changes the crystal structure of the flat-plate collectors. The optical properties also change at a temperature of 75 degrees Celsius. This means that the internal temperatures of the collectors cannot rise above 145 degrees Celsius. When temperatures fall again, the crystal structure returns to its original state.
Conversely, with vacuum tube collectors, the heat pipe principle is used to protect the system from overheating. If solar radiation is too high and heat transfer begins to decrease, phased temperature-dependent shutdown kicks in. This blocks condensation at the heat exchanger. The heat transfer medium can no longer liquefy, and heat is no longer transported. Heat transfer only resumes when the temperature inside the solar circuit has fallen.