Evacuated Tube Collector

The Evacuated Tube (EVT) Collector is made up of a number of evacuated glass tubes, which are connected into a manifold through which the water passes; each tube successively heating up the water as it travels through the manifold.

Evactuated Tube Collector

The number of glass tubes used varies depending on the system size. Generally for domestic application in southern Africa, a single tube should heat up approximately 10 litres of water capacity in the tank.

Evacuated Tube 3D Cross Section

The evacuated tube is constructed of two concentric glass tubes, which are fused together at their respective ends. Between the tubes, a vacuum is drawn which insulates the inner tube thereby reducing heat loss. The inner glass tube is coated with industrial absorptive glaze which converts UV radiation into thermal energy and retains the energy by having a very low emittance. This is central to the high efficiency of an EVT collector. The circular cross section of the EVT is also a critical design specification as it means the angle of incidence of the sun rays will always be 90 degrees, even early and late in the day when the sun is low, and consequently improves performance. This ‘automatic’ sun-tracking concept is the single biggest distinguishing feature between Flat Plate and Evacuated Tube Collectors.

For Evacuated Tube Collectors the SABS has stipulated the outer glass tube thickness must be a minimum of 2.0 mm. This specification is to ensure the collector will not be damaged in extreme hail conditions. As the interior (Highveld) of South Africa is subject to some of the most severe hail storms in Southern Africa, this standard is critical for the affected areas. Technically the coastal areas of South Africa which do not experience hail of such sever nature, do not require the thickened glass EVT, however the SABS has made this a nationwide specification to ensure quality and uniform standards.

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