Solar Air Conditioning (SAC) – Guilt-Free Comfort for Summers
The early summers usually bring a welcome relief from the chilling winters, but in April and May, the summer heat begins to take its toll, both physically and mentally. And when it comes to a tropical climate, like 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 like a godsend. A very big no. Offices, laboratories, hotels, public buildings are currently equipped with air conditioning systems. Centralized air conditioning systems ensure cooling in every nook and corner of the work space.
While all of this sounds great, it’s not. The intensive use of air conditioning is synonymous with a great consumption (and waste) of energy, which generates not only high electricity bills, but also the dreaded frequent power outages. The next step is of course DG sets, to provide the desired comfort inside, while expelling clouds of black smoke with terrifyingly high levels of noise pollution to the outside world and environment.
In the midst of saving ourselves from the fury of nature, we are inadvertently attacking nature more and more, which keeps coming back even more furious from time to time. One of the biggest points of concern is therefore the imminent danger due to rising world temperatures (Global Warming!!). So what should we do to survive and survive comfortably?
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 the sun’s energy. 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 upcoming technology, provides the answer.
Solar air conditioning refers to any air conditioning (cooling) system that uses solar energy. A liquid or gaseous substance accumulates on the surface of a solid porous substance (adsorption) or is absorbed by a liquid or solid substance (absorption to provide 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 fundamental principle of sorption-assisted air conditioning is shown in the following graph. Solar energy is used to dehumidify the adsorbent.
This is a 9 stage process. In stages 1 to 2, the sorption dehumidification 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 against the exhaust air (stage 2 to 3). The air is further cooled (Stage 3 to 4) through evaporation-humidification; Therefore, the air entering the building has a lower temperature and less water vapor than the outside air. In Stages 4 to 5 the heating of the air and, if necessary, the addition of steam take place. Then, during stage 6, the building’s exhaust air temperature is reduced through evaporative cooling in the humidifier. This exhaust air is heated (Steps 6 to 7) countercurrent to the intake air flow in the heat recovery rotor. The exhaust air is further heated (Stage 7 to 8) via external heat sources (ie solar thermal system). Finally, in steps 8 to 9, the sorption rotor is regenerated through desorption of bound water.
Open and closed cycle air conditioning systems:
Open loop systems are most beneficial in buildings with high moisture loads and high air exchange rates. Ducting for supply air and return air is required, as well as a heat recovery unit. In it, outdoor air is dehumidified through sorption and then brought to the desired temperature through heat recovery and direct and indirect evaporative cooling. Dehumidification is usually accomplished in a rotor containing the desiccant material silica gel or lithium chloride, but liquid desiccants (desiccant material: lithium chloride) are increasingly being tested. In these systems, solar heat is required for the regeneration of the absorption/adsorption unit.
Closed-loop desiccant evaporative cooling systems are based on the processes of adsorption (based on solid desiccants such as silica gel or zeolites with water as a coolant) or absorption (where the desiccants are liquids, for example, 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 the refrigeration and air conditioning of buildings, only solar-thermally Directed 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 which then drives a refrigeration process, usually in the form of a compression chiller.
There have been considerable advances in the field of solar-assisted heating and cooling, and around the world this technology is being rapidly tested and adopted.
Recently, Solar Thermal World magazine reported that India’s latest and probably largest solar thermal air conditioning system has gone live at Muni Seva Ashram (MSA) in Goraj, situated 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 feed the already existing 100-ton air-conditioning system of the 160-bed hospital in Muni Seva Ashram. . [i]
Solar Air Conditioning Performance
When designing a SAC system and judging its performance, the key points to look at are the load profile, outdoor temperature, and humidity.
The decision whether solar cooling is sensible is strongly influenced by the load profile. Solar irradiation and cooling demand must be correlated, since 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 possible degree of utilization, applications that also require heat for water heating 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 (cold processing, 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 might be an option in cooler seasons.
The heat rejection rate greatly affects the performance and efficiency of the chiller. In most systems, waste heat is released to the environment by dry coolers or wet cooling towers. The former are suitable for areas with a moderate climate that only occasionally have high outdoor temperatures (>30°C). Wet cooling towers have the advantage that cooling water temperatures below ambient can be obtained. However, it only works if the high relative humidity allows evaporative cooling. In regions with water scarcity it is not suitable either. In addition, some countries have imposed strict hygiene regulations on wet cooling towers that make running small systems economically unfeasible.
It is essential to be aware of the fact that boundary conditions other than nominal conditions can negatively affect the performance of the refrigerating machine. If the system is not designed for the nominal operating point, the relevant operating data should be requested from the manufacturer. So, for example, a reverse cycle dry cooler can also be used in hot climates if the solar thermal system is adapted accordingly.
The use of efficient EC motors in the SAC configuration helps to reduce energy consumption. To further reduce electricity consumption, these need to be controlled according to operating conditions and cooling demand. Depending on the respective local conditions, the waste heat can also be rejected 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 refrigeration technology, solar refrigeration has a no. of advantages These systems are more useful when the sun shines more strongly, in the summers. The machines generally use environmentally friendly refrigerants, which reduces greenhouse gas emissions. In most cases, water is used which, compared to the refrigerants used in compression refrigeration machines, has no greenhouse effect potential. Significant energy savings can be achieved due to the fact that these systems only require auxiliary power for the operation of the pumps, 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 further emission reductions. SACs are also ideal for hotels, supermarkets, schools, factories and large offices, etc. Furthermore, noise emissions are significantly lower as the machines run without compressors.
Therefore, solar-based AC systems can offer a reasonable alternative to conventional AC. In addition to drastically reducing or even eliminating your current air conditioning bill, in many regions, one can receive a large cash rebate as well as a tax credit by powering their air conditioning with solar air conditioning systems. As of now, the capital investments are high, but the system can justify its value in the long run. It is only a matter of time before this technology is mass-produced, bringing costs down to levels affordable for the common man. And then the days that present the maximum cooling requirements will be the same days that you could extract the most energy from the sun while pocketing all the resulting benefits. The choice would truly be ours!
