The early summers generally provide pleasant relief from chilling winters, but in April and May, the summer heat begins to take its toll, both physically and mentally. And when it’s a tropical climate, as in most of India, hot days can be stressful. People’s energy levels drop and so does their productivity.

This is when modern air conditioning arrives as a gift from God. A not very big. Offices, laboratories, hotels, public buildings today are equipped with air conditioning systems. Centralized air conditioning systems ensure cooling in every corner of the workspace.

While this all sounds good, it is not. Extensive air conditioning is synonymous with high energy consumption (and waste) that leads not only to high electricity bills, but also to the dreaded frequent power outages. The next step is, of course, the DG equipment, to provide the desired comfort indoors, while spewing clouds of black smoke with terribly high levels of noise pollution for the outside world and the environment to bear.

In the midst of saving ourselves from the fury of nature, we are inadvertently attacking nature more and more, which keeps returning even more furiously from time to time. Therefore, one of the biggest points of concern is the imminent danger from rising global temperatures (global warming!). So what will we do to survive and survive in comfort?

Let’s not forget that we have an immense source of energy in the same Sun from which we are protecting ourselves. One answer is power generation using energy from the sun. It’s free and for now we can safely assume, unlimited. Yes, solar energy can light our homes and cook our food. But can it also cool our houses? The answer again is yes. Solar air conditioning, a revolutionary and forthcoming technology, provides the answer.

Solar air conditioning refers to any air conditioning (refrigeration) system that uses solar energy. A liquid or gaseous substance accumulates on the surface of a solid and porous substance (adsorption) or is absorbed by a liquid or solid substance (absorption to provide the necessary cooling). In some processes, the supply air is directly conditioned, that is, it is 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 graph here. Solar energy is used to dehumidify the sorbent.

This is a 9 stage process. In Stage 1 to 2, dehumidification by absorption of the outside air takes place with a simultaneous increase in temperature through the released heat of adsorption. The air is then cooled in the heat recovery rotor countercurrent to the exhaust air (stage 2 to 3). The air is cooled further (Stage 3 to 4) by evaporation-humidification; Therefore, the air inlet to the building has a lower temperature and less water vapor than the outside air. In stages 4 to 5 the air is heated and, if necessary, steam is added. Then, during stage 6, the temperature of the building’s exhaust air is lowered by evaporative cooling in the humidifier. This exhaust air is heated (stages 6 to 7) in countercurrent to the air inlet in the heat recovery rotor. The exhaust air is further heated (Stage 7 to 8) through external heat sources (i.e. solar thermal system). Finally, in stages 8 to 9, the sorption rotor is regenerated by desorbing the bound water.

Open and closed cycle air conditioning systems:

Open loop systems are most beneficial in buildings with high humidity loads and high air exchange rates. Installation of ducts for air supply and return air is required, as well as a heat recovery unit. In this, the outside air is dehumidified by sorption and then brought to the desired temperature by heat recovery, as well as direct and indirect evaporative cooling. Dehumidification is generally achieved in a rotor containing the desiccant material silica gel or lithium chloride, but more and more liquid desiccants (desiccant material: lithium chloride) are being tested. In these systems, solar heat is necessary for the regeneration of the absorption / adsorption unit.

Closed cycle evaporative cooling systems with desiccant are based on the processes of Adsorption (based on solid desiccants such as silica gel or zeolites with water as a refrigerant) or Absorption (where the desiccants are liquids, eg Pairs of materials of lithium bromide as a desiccant and water as a coolant, or water as a desiccant and ammonia as a coolant, where sub-zero temperatures may be required).

For cooling and acclimatization of buildings, onlythermally driven processes are used.

In practice, solar collectors are used to convert solar radiation into heat which is then fed to a thermally driven cooling process or direct air conditioning process. Particularly in special applications, for example to cool medicines in remote areas that are not connected to the grid, a photovoltaic generator transforms solar radiation into solar energy that then drives a refrigeration process, usually in the form of a compression cooler.

There have been considerable advances in the field of solar assisted heating and cooling and this technology is being rapidly tested and adopted around the world.

Recently, Solar Thermal World Magazine reported that India’s latest and probably largest solar thermal based air conditioning system came into operation at Muni Seva Ashram (MSA) in Goraj, located in the Vadodara district of Gujarat state in western India. A total of 100 parabolic dishes (Scheffler type) from the Indian company Gadhia Solar Energy Systems (GSES), each 12.5 m2 in size, now supply the 160-bed hospital’s already existing 100-ton air conditioning system in Muni Seva Ashram. . [i]

Solar air conditioning performance

When designing a SAC system and to judge its performance, the key points to look at are the load profile, outside temperatures, and humidity.

The decision of whether solar cooling is sensitive is highly dependent on the load profile. Solar irradiation and cooling demand must be correlated, as the use of fossil fuels for chiller operation is disadvantageous from a primary energy point of view and should be avoided.

To achieve the highest degree of utilization possible, applications that also require heat to heat water or for the heating system outside of the cooling season should be explored. Therefore, residential buildings and small office buildings are best suited. If year-round cooling is required (process cold, server rooms), the solar cooling system can simply be used as a fuel saver for conventional air conditioning. In such a case, free cooling directly through the heat rejection unit could be an option in colder seasons.

The heat rejection rate greatly affects the performance and efficiency of the cooler. In most systems, waste heat is released into the environment via dry coolers or wet cooling towers. The former are suitable for areas with a moderate climate that only occasionally have high outside temperatures (> 30 ° C). Wet cooling towers have the advantage that cooling water temperatures can be obtained below ambient temperature. However, it only works if the high relative humidity allows evaporative cooling. In regions with water scarcity it is also not suitable. In addition, some countries have imposed strict hygiene regulations on wet cooling towers that make the operation of small systems economically unfeasible.

It is essential to take into account the fact that boundary conditions other than nominal conditions can adversely affect the performance of the cooling machine. If the system is not designed for the rated operating point, the relevant operating data should be obtained from the manufacturer. So, for example, a reverse cycle dry cooler can also be used in hot climates if the solar thermal system adapts accordingly.

Using efficient EC motors in the SAC configuration helps reduce energy consumption. To further reduce electricity consumption, these must be controlled according to operating conditions and cooling demand. Depending on the respective local conditions, the waste heat can also be removed in other ways, for example via wells, pools or groundwater. Ideally, the heat can be used elsewhere.

The advantages of solar air conditioning

Compared to conventional electrically driven compression cooling technology, solar cooling has a no. of advantages. These systems are most useful when the sun shines brightest, in summers. The machines generally use environmentally friendly refrigerants, which reduces greenhouse gas emissions. In most cases, water is used which, compared to refrigerants used in compression cooling machines, has no greenhouse potential. Significant energy savings can result from the fact that these systems simply require auxiliary power for pump operation, heat rejection, etc. if the systems are designed correctly. In addition to cooling, the solar collector system can also provide thermal energy for domestic hot water preparation and heating support, leading to a further reduction in emissions. SACs are also ideal for hotels, supermarkets, schools, factories and large offices, etc. In addition, noise emissions are significantly lower as the machines operate without compressors.

Therefore, solar-based AC systems can offer a reasonable alternative to conventional ACs. In addition to drastically reducing or even eliminating the current air conditioning bill, in many regions, one can receive a large cash back as well as a tax credit for powering their air conditioning with solar air conditioning systems. As of now, capital investments are high, but the system can justify its long-term value. It is only a matter of time before this technology is mass produced, reducing costs to levels affordable for the common man. And then the days that pose the maximum cooling requirements will be the same days that the maximum energy could be extracted from the sun while pocketing all the resulting benefits. The choice would really be ours!