Читать книгу Solar Water Heating--Revised & Expanded Edition - Bob Ramlow - Страница 19

All kinds of plastics have been used as glazing material for collectors, but they have all failed under direct, constant exposure to the sun. Only low iron tempered glass has stood the test of time. Iron in glass causes some of the solar radiation to be absorbed by the glass, diminishing the solar radiation hitting the absorber plate. The glass is usually patterned on one side to reduce glare and reflection. A rubber gasket is fitted to the edges of the glass plate both to protect the edge and to create a good seal where it sits against the collector frame. Some collectors use a silicon caulk to seat the glass against the frame. Though this method does last, it makes it almost impossible to remove the glass when making repairs.

Note that if you ever have to take the glazing off a collector, the edge of the tempered glass is very fragile. If you even tap the edge or side of a tempered-glass pane, it can literally explode, so be very careful and always wear safety glasses and gloves when handling glass.

Some early collector models used either a double pane of glass or a thermopane in an attempt to minimize heat losses from the front of the collector. However, over time we have learned that the second sheet of glazing actually lowered collector efficiency because it reduced the amount of solar radiation that could reach the absorber plate. To our knowledge, no flat plate collectors are made this way any more, but you may still encounter them in service calls.