Читать книгу Solar Water Heating--Revised & Expanded Edition - Bob Ramlow - Страница 17

Flat plate collectors are the most widely used kind of collector in the world for domestic solar water heating and solar space heating applications. These collectors have an operating range from well below 0°F to about 180°F, which is precisely the operating range required for these applications. They are durable and effective. They are the standard to which all other kinds of collectors are compared.

Figure 3.1: Flat plate collector

Flat plate collectors are rectangular shallow boxes that typically are 4 feet wide, 8 or 10 feet long and 4 to 6 inches deep, but they also come in other sizes. A common metric size is 1 meter by 2 meters. These collectors are made with a strong frame, a glazed (glass) front, a solid back and insulation on the sides and back. An absorber plate lies just beneath the glazing. In most cases this absorber plate has manifolds that run across the top and bottom of the collector, just inside the frame. These manifolds are usually ¾-inch or 1-inch-diameter copper pipe and extend out both sides of the collector through large rubber grommets.

These collectors, called internally manifolded collectors, can be easily ganged together to make large arrays. Smaller riser tubes, typically ½-inch copper pipes, run vertically, usually brazed to the manifolds above and below, and are spaced 3 inches to 6 inches apart (the closer the better). Another type of absorber plate has a serpentine tube that meanders back and forth continuously from the bottom of the collector to the top of the collector. A flat copper or aluminum fin is then attached to each riser to complete the absorber plate. The fin must make intimate contact with the riser tube to facilitate effective heat transfer from the fin to the tube. Soldering, welding or roll bonding the fins to the tubes makes the best connection. The plates are also usually dimpled or corrugated to increase absorptivity. The absorber plates are not attached to the frame; they just sit inside it and can expand or contract as they are heated or cooled without being restricted by the frame.