... copper and conducted by heat transfer medium liquid. Water can't flow in the vacuum tubes. ... blended with architecture 5)Anti-freeze: No water inside the tubes when it works, it ... capacity: 100L, 200L, 250L, 300L, 400L, 500L Working principle of pressure solar collector: 1) When the temperature ... heating system, when the temperature of the water tank does not reach Tmax, electrical heating system will ...