SOLAR HEATING SYSTEMS

SOLAR HEATING SYSTEMS Solar heating involves more than heat collectors. It also involves distribution of heat to the rooms of a building and the storage of unneeded heat for later use at night or during cloudy periods. Any dark surface that faces the Sun is a solar heat collector; it is dark precisely because it has absorbed some light energy and converted it to heat instead of reflecting the light away. Collector glazings or transparent covers can be made of glass, plastics or fibreglass. Glass is chosen most often because of its long life, high solar transmittance (the fraction of Sunlight it allows to pass through) and low transmittance for Infrared radiation from the collectors. A plane glass is a hard, solid object and yet visible light can pass through it almost as if it were nothing. In addition, glass prevents the transmittance of most radiant heat infrared light. Thus, if we take a dark surface and over it with a sheet of glass, we have a fairly effective solar collector i.e. that really let light in, converts the light to heat and then slows down any radiant heat. One disadvantage of glass cover is that if it is placed within an inch or two on the dark collecting surface, it creates a dead – air space or zone of fairly still air that acts as insulator. The combination of a dark surface with a glass cover results in an “energy trap”. It lets light enter but allows neither light nor heat to escape in large amount. This energy trapping process is known as the green house effect. We have an active solar heating system and passive solar heating system. An active solar heating system actively distributes the heat throughout the building when pumps, fans or other equipment physically move the heat around. A passive system depends on natural forces to distribute heat e.g. natural convection rather than fans move heated air in a passive system. A simple passive Solar Heating System Heat collection is accomplished via the green house effect; the glass admits Sunlight, dark coloured walls and floors absorb the Solar energy transforming it to internal energy which may subsequently be given up as heat. The heat is distributes throughout the room by natural convection; as air near the floor and walls are heated, it rises and is replaced by cool falling air. Heat is stored in the massive concrete walls and floors since heat collected at the surface slowly moves inside. During the night, this absorbed heat energy is slowly released, heating the cool room air. Active Solar Heating System In an active system, solar energy is generally collected by a group of several flat plate solar collector panels, box like devices that are mounted on a south – facing wall or roof. Each solar collector as it is often called has tubes or channels that a heat transfer fluid passes through. The heat transfer fluid is the air, water or other substances that removes the collected heat and carries it to the inside of the building. The basic part of any flat – plate collector are the absorber, the cover, the insulation and the box or frame that holds it. The important part of a typical flat plate solar collector are: ‘black’ solar energy –absorbing surface with means for transferring the absorbed energy to a fluid; the envelop transparent cover which also reduces convection and radiation losses to the atmosphere and back insulation to reduce conduction losses. ENERGY STORAGE IN SOLAR PROCESS SYSTEM Energy storage may be in the form of sensible heat of a solid or liquid medium, as heat of fusion in chemical systems, or as chemical energy of products in a reversible chemical reaction. Products of solar processes other than energy may be stored e.g. distilled water from a solar still may be stored in tanks until needed. The choice of media for energy storage depends on the nature of the process. For water heating, energy storage as sensible heat of stored water is logical. If air heating collectors are used, storage in sensible latent heat effects in particular storage unit are indicated such as sensible heat in pebble heat exchanger. If photochemical processes are used, storage is probably most logically in the form of chemical energy. Thermal energy is the goal of the nuclear industry. To achieve this goal it is necessary to develop a unique family of materials to meet nuclear specifications along with physical and chemical ones.