Early summers usually bring a pleasant relief from the bone chilling winters, but come April & May, the summer heat starts taking its toll, both physically as well as mentally. And when it’s a tropical climate, as in most parts of India, the hot days can be all together stressful. The energy levels of individuals go down and so does their productivity.
This is when the modern day Air conditioning comes as a God Gift. A very large no. of Offices, laboratories, hotels, public buildings are nowadays fitted with air conditioning systems opticlimate. Centralized Air Conditioning Systems ensure cooling in every nook and corner of the working space.
While this all sound hunky dory, its not. Extensive air conditioning is synonymous to heavy power consumption (and wastage) leading to not just heavy electricity bills but also the dreaded frequent power outages. The next step is – of course – DG sets, to bring the desired comfort indoors, while puffing out clouds of black smoke with terribly high levels of sound pollution for the outside world and the environment to endure.
In the midst of saving ourselves from the fury of the nature, we are inadvertently attacking the nature more and more, which keeps returning even more furiously every now and then. One of the biggest points of concern thus is the impending danger due to the rising world temperatures (Global warming!!). So what shall we do to survive and survive with comfort?
Let’s not forget we have an immense source of energy in the very Sun that we’re shielding ourselves from. One answer is Generation of power using sun’s energy. It’s free and for now we can safely assume, unlimited. Yes, solar energy can light up our homes and cook our food. But can it also cool our houses? The answer again is yes. Solar air conditioning, a revolutionary and upcoming technology, provides the answer.
Solar air conditioningrefers to any air conditioning (cooling) system that uses solar power. A liquid or a gaseous substance either accumulates on the surface of a solid, porous substance (adsorption) or is taken up by a liquid or a solid substance (absorption for providing the necessary cooling). In some processes supply air is directly conditioned, i.e. treated in terms of temperature and humidity
This thermally driven cooling and air-conditioning process is at the heart of every solar cooling system. The main principle of Sorption Assisted Air Conditioning is shown in the graphic here. The solar energy is used to dehumidify the sorbent.
This is a 9 stage process. In Stage 1 to 2, Sorptive dehumidification of outside air takes place with simultaneous rise in temperature through the freed adsorption heat. Then the air is cooled in the heat reclamation rotor in the countercurrent to the exhaust air (stage 2 to 3). Air is further cooled (Stage 3 to 4) through evaporation-humidification; Thus the air inflow to the building has a lower temperature and less water vapor than the outside air. In Stage 4 to 5 Heating of the air takes place, and if necessary addition of water vapor. Then during Stage to 6 building’s exhaust air temperature is lowered through evaporative cooling in the humidifier. This exhaust air is heated (Stage 6 to 7) in the countercurrent to the air inflow in the heat reclamation rotor. The exhaust air is further heated (Stage 7 to 8) through external heat sources (i.e. solar thermal system). Finally in Stage 8 to 9 Sorption Rotor is Regenerated through the desorption of the bound water.
Open-cycle systems are more beneficial in buildings with high humidity loads and high air exchange rates. The installation of ducts for the supply air and the return air, as well as a heat recovery unit is required. In this, the outside air is dehumidified through sorption and is then brought to the desired temperature by heat recovery as well as direct and indirect evaporative cooling. Usually dehumidifying is achieved in a rotor containing the desiccant material silica gel or lithium chloride, but increasingly liquid desiccants (desiccant material: lithium chloride) are being tried. In these systems the solar heat is required for the regeneration of the absorption/adsorption unit.
Closed-cycle desiccant evaporative cooling systems are based on the processes of Adsorption (based on solid desiccants like silica gel or Zeolites with water as refrigerant) or Absorption (where desiccants are liquid ex. material pairs of lithium bromide as desiccant and water as refrigerant, or water as desiccant and ammonia as refrigerant, where sub Zero temperatures may be required).
For cooling and acclimatizing of buildings, only solar-thermally driven processes are used.
In actual practice, solar collectors are used to convert solar radiation to heat that is then fed into a thermally driven cooling process or into a direct air-conditioning process. Particularly in special applications, for example for cooling medicines in remote areas that are not connected to the grid, a photovoltaic generator transforms solar radiation to solar power that then drives a refrigeration process – usually in the form of a compression chiller.