In our experience brazed plate heat exchangers offer the best heat exchanger value on the market. With solar heating systems we are trying to deliver renewable energy to the customer at the best value proposition. This frequently leads to using brazed plate heat exchangers which we carry and integrate into many of our packaged solar solutions.
One of the problems possible with a brazed plate heat exchanger is it is possible to freeze damage the heat exchanger. While this is a rare occurence, it can be done. In the thousands of heat exchangers we have used and sold we have only seen it one time. See the attached picture. This failure occurred on a glycol system where the heat exchanger was in a heated mechanical room. If the heat exchanger had glycol on one side of the system and was in a heated room how could we have caused the heat exchanger to freeze?
The problem was caused when the system circulated cold glycol fluid on the solar side (at night) while the water side didn’t circulate at all. The system had a faulty check valve on the solar loop. Without the check valve working, the solar side thermo-siphoned at night when the outside temperatures were extremely cold. This super cool fluid moved through the heat exchanger causing the stagnant water on the other side of the heat exchanger to cool and freeze. When the water froze the frozen water expanded and burst the heat exchanger between the plates. The fact that it was freezing water causing the heat exchanger to burst was proven by the distortion in the stainless plates as well as the failure of the pressure relieve valve to release.
So, the moral of the story is…… Be sure that you have a well installed check valve on the solar loop to prevent thermosiphoning and the consequent failure of an external heat exchanger.