Semester-VI

Unit 3

(Lecture No. 06)

Solar Space Heating and Cooling

Space Heating
A solar space -heating system can consist of a passive system, an active system, or a combination of both. Passive systems are typically less costly and less complex than active systems. However, when retrofitting a building, active systems might be the only option for obtaining solar energy.
Passive Solar Space Heating
Passive Solar Space Heating takes advantage of warmth from the sun through design features,such as large south-facing windows, and materials in the floors or walls that absorb warmth during the day and release that warmth at night when it is needed most.

Passive solar design systems usually have one of the three designs:

Direct Gain stores and slowly releases heat energy collected from the sun shining directly into the building and warming materials such as tile or concrete.

Indirect Gain uses materials that hold, store, and release heat; the material is located between the sun and living space.

Isolated Gain collects solar energy remote from the location of the primary living area.

Active Solar Space Heating

Active solar space heating systems consist of collectors that collect and absorb solar radiation combined with electric fans or pumps to transfer and distribute that solar heat. Active systems also generally have an energy storage system to provide heat when the sun is not shining.

The two basic types of active solar space-heating systems use either liquid or air as the heat-transfer medium in their solar energy collectors.

Liquid-based systems heat water and air-based systems heat air in the collector.

• Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed.An auxiliary or backup system provides heat when storage is discharged.

• Liquid systems are more often used when storage is included.

Solar Space Cooling

• In the chiller, refrigerant vapor from the evaporator is absorbed by a solution mixture in the absorber.

• This solution is then pumped to the generator.

• There the refrigerant re-vaporizes using a waste steam heat source .The refrigerant - depleted solution then returns to the absorber via a throttling device.

• The two most common refrigerant/absorbent mixture used in absorption chillers are water/ lithium bromide and ammonia / water.

• Systems use a low-temperature liquid refrigerant that absorbs heat from the water to be cooled and converts to a vapor (in the evaporator section).

• This used for space cooling.

• The refrigerant vapor is then compressed to a higher pressure by a compressor or generator and converted back into a liquid by rejecting heat to the external surrounding in the condenser section.

• Next, it is expanded to a low-pressure mixture of liquid and vapor (in the expander valve), which boils in the evaporator section, absorbing heat and producing the cooling effect.

• Then the cycle is repeated.

• Heat provided in the system is by solar collector in the form of hot water.