1. Sola r AC
Solar Air Conditioning
Guilt-free Comfort for Summers
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 number of offices, laboratories, hotels, public buildings
are nowadays fitted with air conditioning systems. Centralized Air conditioning
Systems ensure cooling in every nook and corner of the working space. While this
all sound hunky dory, it's not.
- Subhash Chandra Mathur and Sumit Mathur
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2. E
xtensive air conditioning is any air conditioning (cooling) system heated (Stage 6 to 7) in the
Sola r AC
synonymous to heavy power that uses solar power. A liquid or a countercurrent to the air inflow in
consumption (and wastage) gaseous substance either the heat reclamation rotor. The
leading to not just heavy accumulates on the surface of a exhaust air is further heated (Stage
electricity bills but also the dreaded solid, porous substance (adsorption) 7 to 8) through external heat sources
frequent power outages. The next or is taken up by a liquid or a solid (i.e. solar thermal system). Finally in
step is of course DG sets, to bring substance (absorption for providing Stage 8 to 9 Sorption Rotor is
the desired comfort indoors, while the necessary cooling). In some Regenerated through the desorption
puffing out clouds of black smoke processes, supply air is directly of the bound water.
with terribly high levels of sound conditioned i.e. treated in terms of
pollution for the outside world and temperature and humidity. Open and Closed cycle Air
the environment to endure. This thermally driven cooling and Conditioning Systems
In the midst of saving ourselves air-conditioning process is at the Open-cycle systems are more
from the fury of the nature, we are heart of every solar cooling system. beneficial in buildings with high
inadvertently attacking the nature The main principle of Sorption humidity loads and high air exchange
more & more, which keeps returning Assisted Air Conditioning is shown in rates. The installation of ducts for
even more furiously every now and the graphic here. The solar energy is the supply air and the return air, as
then. One of the biggest points of used to dehumidify the sorbent. well as a heat recovery unit is
concern thus is the impending In Stage 1 to 2, Sorptive required. In this, the outside air is
danger due to the rising world dehumidification of outside air takes dehumidified through sorption and is
temperatures (Global warming!!). place with simultaneous rise in then brought to the desired
So, what shall we do to survive and temperature through the freed temperature by heat recovery as
survive with comfort? adsorption heat. Then the air is well as direct and indirect evaporative
Let’s not forget we have an cooled in the heat reclamation rotor cooling. Usually dehumidifying is
immense source of energy in the in the countercurrent to the exhaust achieved in a rotor containing the
very Sun that we’re shielding air (stage 2 to 3). Air is further desiccant material silica gel or
ourselves from. One answer is the cooled (Stage 3 to 4) through lithium chloride, but increasingly
Generation of power using sun’s evaporation-humidification; Thus liquid desiccants (desiccant material:
energy. It’s free and for now we can the air inflow to the building has a lithium chloride) are being tried. In
safely assume, unlimited. Yes, solar lower temperature and less water these systems the solar heat is
energy can light up our homes and vapour than the outside air. In Stage required for the regeneration of the
cook our food. But can it also cool 4 to 5 Heating of the air takes place, absorption/adsorption unit.
our houses? The answer again is and if necessary addition of water Closed-cycle desiccant
yes. Solar air conditioning, a vapour. Then during Stage to 6 evaporative cooling systems are
revolutionary and upcoming building’s exhaust air temperature is based on the processes of Adsorption
technology, provides the answer. lowered through evaporative cooling (based on solid desiccants like silica
Solar air conditioning refers to in the humidifier. This exhaust air is 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 & 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
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3. Sola r AC
fuel-saver for conventional air-
conditioning. In such a case free
cooling directly through the heat
rejection unit might be an option in
the cooler seasons.
Heat rejection rate greatly affects
the performance and efficiency of
the chiller. In most systems the
waste heat is released into the
environment by dry coolers or wet
Graphic: Comparison of open-cycle and closed-cycle cooling systems cooling towers. The former are
suitable for moderate climate zones
then drives a refrigeration process that only occasionally have high
o
usually in the form of a compression outside temperatures (>30 C). Wet
chiller. There have been considerable cooling towers have the advantage
developments in the field of solar- that cooling water temperatures
assisted heating and cooling and below ambient temperature can be
world over this technology is being obtained. However, it only works if
rapidly tried and adopted. the relative high humidity allows for
evaporative cooling. In regions with
a shortage of water it is also
Photo : Solar Powered AC house unsuitable. In addition, some
countries have imposed strict
parabolic dishes (Scheffler type) by hygiene regulations on wet cooling
the Indian company Gadhia Solar towers which make the operation of
Energy Systems (GSES), each small systems economically unviable.
12.5 m2 in size now supply the It is essential to be aware of the
already existing 100-ton air- fact that boundary conditions other
conditioning system of the 160-bed than the nominal conditions, can
Photo: Climatisation of a building hospital at Muni Seva Ashram. negatively affect the performance of
of the University of Sevilla the cooling machine. If the system is
Performance of Solar Air not designed for the nominal
Chiller: Double-stage BROAD Conditioning operation point, the relevant
BZH 15 IX, China. Source of power: While designing a SAC system & operating data must be requested
352 m2 linear-concentrated Fresnel for judging its performance the key from the manufacturer. Then, for
collectors (Mirrox, Germany). Heat points to observe are Load Profile, example, a dry reverse cycle chiller
rejection: Cooling tower. Cooling: Outside temperatures & humidity. can also be used in warm climates if
cold distribution through a central The decision whether solar the solar thermal system is adapted
ventilation system. (Photo source: cooling is sensible at all is influenced accordingly.
Mirrox GmbH). strongly by the load profile. Solar Utilization of efficient EC motors
irradiation and cooling demand must in the SAC set up helps to reduce
be correlated, since the use of fossil the energy consumption. To further
fuels for the operation of the chiller reduce electricity consumption,
is disadvantageous from a primary these should be controlled according
energy point of view and should be to operating conditions and cooling
avoided. demand. Depending on respective
Photo : Solar Powered Air In order to achieve the highest local conditions, waste heat can also
conditioned house possible degree of utilization, be rejected of in other ways e.g.
applications that also require heat through boreholes, swimming pools
Recently, Solar thermal World for heating water or for the heating or ground water. Ideally the heat
Magazine reported that India’s latest system outside the cooling season can be used in other places.
and probably largest solar thermal must be explored. Thus, residential
based air-conditioning system went buildings & small office buildings are Advantages of Solar Air
operational at Muni Seva Ashram most suitable. If cooling is required Conditioning
(MSA) in Goraj, situated in the throughout the year (process cold, In comparison to conventional,
Vadodara district of Gujarat state in server rooms) the solar cooling electrically driven compression
western India. A total of 100 system can be used merely as a cooling technology, solar cooling has
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4. a number of advantages. These offer a reasonable alternative to the the long run. It is just a matter of
Sola r AC
systems are most useful when the conventional ACs. In addition to time when this technology would be
sun shines the strongest in summers. drastically reducing or even mass produced, bringing down
The machines generally utilize eliminating current air conditioning costs to affordable levels for the
environment friendly refrigerants, bill, in many regions, one can common man. And then, the days
leading to lower green house gas receive a huge cash rebate as well that pose the maximum cooling
emissions. In most cases, water is as a tax credit by powering his air requirements shall be the very
utilized which compared to conditioner with solar air same days when maximum energy
refrigerants used in compression conditioning systems. As of now, could be extracted from sun while
cooling machines has no greenhouse the capital investments are high but pocketing all the resulting benefits.
potential. Significant power savings the system can justify its worth in The choice would really be ours!
can result from the fact that these
systems merely require auxiliary ❁
energy for the operation of pumps, Subhash Chandra Mathur, with four decades of experience in thermal
heat rejection etc, if the systems are and renewable power generation and distribution, is an expert in
designed correctly. In addition to Government liaising, Strategic Planning and Project Execution. Under
cooling, the solar collector system the aegis of Bureau of Energy Efficiency and United Nations Industrial
can also provide thermal energy for Development Organization, his organization, Samarpit International
domestic hot water preparation and Group (SIG) works extensively in Energy Conservation, Carbon
heating support which leads to a Management, Climate Change and Sustainable Development. SIG also
further reduction of emissions. SACs helps a wide spectrum of industries in developing cutting edge strategic
are also ideal for hotels, business solutions, to succeed in a highly competitive environment.
supermarkets, schools, factories, ❁
Sumit Mathur is an energy sector enthusiast. He has been actively
and large office premises etc.
involved with both conventional and renewable power systems and is
Furthermore, noise emissions are
a prolific writer.
significantly lower since the machines
work without compressors.
Solar based AC systems thus can
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