... pressure solar system 1.Certificates: CCC,ISO,CE,KEYMAEK 2.lifetime:15 years , guarantee:5 years compact non pressure solar systemWorking ... principle:The non-pressure thermosiphon systems rely on the nature circulation of the ... . Optional: heat exchanger (red copper), electric heater (1.5kw, 2kw, 2.5kw, 3kw), assistant tank( 5L, 8L, 12L, 15L), ...