SOLAR ENERGY IN AIR CONDITIONING

Method of using solar energy in Air conditioning (AC)

Air conditioning could be performed on the basis of power drawn from solar energy

There are various methods developed for application of solar energy or solar power for air conditioning and these are as mentioned below

1. Geothermal cooling
2. Photovoltaic solar cooling
3. Adsorption cooling
4. Air conditioning using desiccants
5. Passive cooling
6. Night free cooling using PCMs (Phase Change Materials)

Geothermal cooling

As we know that outdoor temperature usually varies throughout the year due to variation in seasons. It is concluded that approximate 6 feet below the surface of earth, ground – temperature will remain constant throughout the year because earth absorb approximate 47 % of heat energy reaching over surface of earth from sun.

Geothermal system utilizes this constant temperature by circulating water based solution via geothermal ground loop. 

It is also concluded that a single portion of this system will have ability to heat and cool our house and we may easily save our monthly bill for utilities by 30 to 70 %

Let us discuss how geothermal cooling system works

If we consider the cycle for heating then in that situation, water based solution will extract the heat from ground but in case of cooling cycle, process will be reversed. 

As we know that during summer season, temperature of atmospheric air will be much higher as compared to ground temperature.

Geothermal unit will remove heat from house and will send this heat to ground via circulating water based solution flowing through loop where this solution will be cooled by ground temperature and once this solution will be cooled then this solution will be returned to unit in order to cool the house.

Photovoltaic solar cooling

As we know that during the conversion of sun light in to electricity, there will also be production of heat which is referred as by-product. 

It is observed that approximate 25 % of sun energy will be converted to electricity and around 75 % of sun energy will be loss as heat energy.

Finally this lost heat energy will be utilized to cool the air.

We can easily understand how photovoltaic will be utilized to cool the required area.

Adsorption Cooling

Adsorption Cooling is basically a refrigeration system which is driven by thermal techniques; this system will be driven by waste heat or by solar energy. 

We can also contribute in reduction of emission of CO2 (which is used to produce after combustion of fossil fuels in power sectors) by application of this thermal-driven system.

Adsorption system is very similar to vapor compression system because an adsorption system also consist condenser, compressor, evaporator and expansion valve. 

But there is only one difference as adsorption system utilize thermal compressor which is driven by heat energy instead of mechanical energy. Let us understand two chamber adsorption cooling system with the help of following figure.

Air conditioning using desiccants

Air might be passed over common, liquid (such as lithium chloride/bromide) or solid desiccants (such as zeolite or silica gel) in order to extract the moisture from the air so that efficient mechanical or evaporative cooling cycle could be possible. 

After that this desiccant will be regenerated with the application of solar thermal energy in order to de humidify, low – energy consumption, cost effective, continuously repeating cycle, In order to rotate large disk filled along with desiccant , we can use a photovoltaic system that will drive the motor and also drive the lower energy fan for air circulation .

Passive cooling

Passive cooling is basically design approach for thermal comfort in building that used to focus on dissipation and gain of heat in specified building for improving the indoor- thermal comfort with lower or nil energy consumption.

This technique is based on two basic points

• Avoid the entry of heat inside the building
• Natural cooling for removing heat from building

In simple words we may say that passive cooling techniques involves the natural cooling and heat gain prevention without consuming energy or very-very less energy.

Passive cooling is more suitable for installation thermal comfort system for specified areas as it is less costly, it uses very less energy, and it has no environmental impact.

As we know that heat leaves and enters a house via the walls, roof, windows & floor. These elements are known as the building envelope.

Suitable envelope design will respond to site conditions and climates in order to optimize the thermal performance. It will also reduce the operating costs, improve lifestyle & comfort.

Night free cooling using PCMs

Phase Change Materials or PCMs floats in between liquid & solid phase within a specified temperature range .in case temperature of environment is higher as compared to PCM then heat will be transferred to materials from the environment or surroundings and it will create an effect of cooling and in this way phase of PCMs will be changed from solid to liquid.

When the temperature of environment is lower as compared to the temperature of PCMs then in that case heat will be transferred from the PCMs to the environment and it will create an effect of warming and in this way phase of PCMs will be changed back to its solid state.

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