This invention relates in general, to solar heat collectors and, more particularly, relates to solar heat collectors having convection suppressors.
Solar heat collectors or heat panels typically suffer from optical, radiation, conduction, and convection heat losses. A heat panel generally consists of a heat absorbing sheet which is oriented in a direction to receive incident solar radiation and a plurality of conduits which are positioned just below and in contact with the absorbing sheet to conduct a fluid thereby removing heat from the absorbing sheet. Insulation is normally placed around the bottom of the absorbing sheet and conduit to reduce conduction heat losses. A sheet of glass or other transparent glazing is placed above the absorbing sheet and traps a layer of air just above the absorbing sheet and also serves to protect the absorbing sheet from the elements. The glazing causes some losses which are called optical losses. As the trapped air heats up, convection currents are set up which result in heat losses. The convection currents tend to remove heat from the absorbing sheet as the trapped air passes over the sheet and then releases the heat as it passes adjacent to the glazing which is at a lower temperature than the absorbing sheet. These convection currents constitute a major mode of heat transfer away from the absorbing sheet of a high performance flat panel solar collector. If left unchecked, this convection heat loss mechanism severely retards the collection efficiency of such collectors, particularly in the high excess temperature range necessary for driving absorption type air conditioning units. Two general techniques that are used to reduce the convection losses are evacuation and geometrical cellular structures. However, these general techniques suffer from disadvantages which are overcome by the present invention. The evacuation technique involves creating a vacuum between the glass sheet and the absorbing sheet. This requires a sophisticated seal around the edges of the glass to prevent loss of the vacuum which increases the cost of the collector. In addition, the glass must be made stronger to withstand the atmospheric pressure bearing down upon it which also increases the cost of the collector. The cellular structures placed between the glass sheet and the absorbing sheet greatly reduce convection losses, however, the increased heat above a desired excess operating temperature requires the use of more expensive materials to prevent the destruction of the collector at these elevated temperatures. Many techniques for fabricating cellular structures have evolved over the years. These include the intermittent glueing of sheet stock and subsequently forming cells as with many paper goods in the making of honeycombs and the notching and assembling of steps in a regularized manner to achieve a matrix of small rectangular compartments. The use of glue in forming cellular structures is not only messy but is time consuming and costly. Therefore it should be appreciated that it would be desirable to solve the above and other problems.
Accordingly, it is an object of the present invention to provide an improved solar heat collector.
Another object of the present invention is to provide a convection suppressor which allows the use of plastics and other materials previously limited by their maximum operating temperature in solar thermal collectors which exhibit high operating efficiencies.
A further object of the present invention is to provide an improved convection suppressor that minimizes prestresses during manufacture thus preserving both the optical and structural qualities of the suppressor when it is placed within a solar collector and does not require glueing or bonding to assemble yet has a self-locking feature to facilitate handling.
Another object of the present invention is to provide a solar heat collector having reduced convection losses up to a predetermined excess temperature and wherein the convection losses increase rapidly above the predetermined excess temperature.