Experimental characterisation and technical feasibility of a closed two-phase vs a conventional solar water heating thermosyphon

The present paper deals with Domestic Solar Water Heating Systems (DSWHS) for sanitary purposes. A Phase Change System (PCS) was designed and built. The PCS consists of a solar collector – thermo tank set that use a working fluid to indirectly transfer heat to the water. In some regions of Mexico, the high concentrations of minerals in the water accumulate to obstruct the pipes, preventing the solar collector from working. Using a suitable working fluid (different from water) avoids this problem, as well as freezing, corrosion, fouling and scaling, usually presented in conventional DSWHS. A conventional DSWHS with the same dimensions and geometry than the PCS was installed to compare their performance in simultaneous tests. Tests in the PCS were performed using three working fluids: R134a, R410A and acetone, under the actual field conditions of Temixco, Mexico. The technical feasibility of the three working fluids was investigated. Experimental data indicate that the PCS, loaded with either R134a or R410A, has equivalent performance than the DSWHS. However, high pressures and some difficulties to load the working fluid have to be dealt with. Lower performance was shown using acetone, but with the advantages of an easy load and low working pressure.

Research highlights
► A phase change solar system to heat water is compared to a conventional system.
► The stages of operation of the phase change system were recognised and explained.
► A phase change system prevents corrosion, fouling and freezing, increasing lifetime.
► Efficiencies equivalent to the conventional system are reached.