Experimental and numerical study on a freeze protection system for flat-plate solar collectors with silicone peroxide tubes

The freeze protection is essential in the majority of solar thermal installations to prevent breakage of solar thermal collectors. Therefore, there are different methods of protection against freezing of flat plate solar thermal collectors, all of them with certain limitations. This paper shows a novel freeze protection mechanism in the solar thermal collector by using flexible silicone peroxide tubes inside the absorber of the solar collector. We demonstrate, in a theoretical and experimental way, that the increase of volume and pressure produced inside a solar collector during freezing process can be absorbed using a flexible silicone peroxide tubes under all exposure conditions. The parameters that optimize the geometric configuration of the solution proposed have been calculated. A collector prototype with silicones peroxide has experimentally complied with the Standard ISO 9806:20 13, including freeze resistance test, without any significantly influence on its efficiency or pressure drop. Therefore, the solution proposed presents an inexpensive, effective, reliable and maintenance-free freeze protection system for flat plate solar collectors.