Non-pressure System means that in the system the working pressure is almost 0MPa. It relies on a natural principal - "Thermosiphon". In this system the storage cylinder is always located higher than the collector. As the sun''s rays hit the all-glass evacuated solar collector tubular, the temperature of the water in the collector rises making it less dense or lighter. This hot and lighter water naturally moves to the top of collector and via the evacuated collector tube work to the storage cylinder. This makes the water colder and heavier and moves to the bottom of the collector. This continuous displacement occurs naturally. And it is often referred to "Passive" or "Thermosiphon" System.

It is also called as "Open Circuit" system. An air vent is needed on the top of the storage cylinder, no matter the cold water supply is by a gravity feed tank, a high level storage tank or by the electromagnetic valve of the intelligent controller, to keep the solar system open to the air for safety.

The thickness of the storage cylinder of this system is normally much thinner than that of a pressure system. The testing pressure is 0.05MPa (0.5bar) during the production and the operation pressure should be 0MPa (0bar). The daily efficiency for the whole system is over or equal to 55% normally and in winter it is over or equal to 42%.

To use an AUDSUN Non-pressure System Solar Water Heater you should think about first what kind of cold water supply you have. It is by a high level storage tank on roof or it is from main pipes of the city. Secondly, what kind of backup heating do you want, an Electric heating element, a gas heater or others, since solar water heater works depending on the sunlight.