... solar water heater 150L Solar keymark, CE, ISO Red copper heat pipe, transfer heat quick 58-1800mm tube 1 ... pressure, vacuum tube absorbs solar energy, and conductive copper pipe transfer the heat into the pressurized water tank. ... 6-1700mm; 0.6-1900mm3. Features: 1) There is no water in the vacuum tube, so it can ... tube, the heat transfer more quickly. 3) It is a closed loop, so the heat can be preserved ...