CASE STUDY : Solar Powered air conditioning as a solution to reduce environmental pollution in Tunisia

 Aim  Description of the System  Absorption systems  System optimization  Conclusion  Reference

 In Tunisia, during the summer electricity demand over largely because of the large volume use pressure steam air- conditioning systems, This increases the peak electric load, caused major problems in the country's electrical Supply  Use of solar energy to drive cooling cycles for air-conditioning of most buildings is the concept more attractive. Cooling requirements of almost any building in phase with a solar. To cool with solar thermal energy, and one solution is used to absorb the water cooler and use of methyl lithium solution.  Solar cooling systems have the advantage of using absolutely harmless working fluids such as water, or solutions of certain salts. They are energy efficient and environmentally safe.

The system incorporates a number of solar thermal collectors, a thermally vertical storage tank, an absorption chillier, a cooling tower, heat exchangers, a conventional boiler, a building to be conditioned and interconnecting piping.

The solar energy is gained through the collector and is accumulated in the storage tank. Then, the hot water in the storage tank is supplied to the generator to boil off water vapor from a solution of lithium bromide and water. The water vapor is cooled in the condenser and then passed to the evaporator, Cooling water from the cooling tower removes the heat of mixing and condensation. An auxiliary energy source is provided so that hot water is supplied to the generator when solar energy is not sufficient to heat the water to the required temperature level needed by the generator.

Absorption systems are similar to vapor compression air conditioning systems but differ in the pressurization stages. In general an absorbent on the low-pressure side absorbs an evaporating refrigerant. An absorption air conditioning system basically consists of an evaporator, a condenser, a generator, an absorber and an economizer. Of the various continuous absorption solar air conditioning systems, LiBr-H2 O and H2O-NH3 are the major working pairs employed in these systems. It is reported that LiBr-H2O has a higher COP than that of the other working fluids.

A number of simulations were carried out in order to optimize the various factors affecting the performance of the system. The first results of the optimization on the solar component characteristics for a 10 KW cooling capacity machine are the following: Solar collectors area = 30 m2 (15 flat plate collectors in parallels, each of 2 m2 area) Slope = 35 Orientation = due south Coefficient of transmittance-absorbency FR (ta) = 0.79 Coolant: glycolic water þ solution Water flow per unit of area = 54 Kg/ (hr.m2) Storage tank Volume = 1 m3 Total coefficient of loss ULoss = 1.4 KJ/ (hr.m2C) Height/Volume Report/ratio = 1.5 Maximum temperature = 120C

This is a source of major problems in the country’s electricity supply and contributes to an increase of CO2 emissions causing the environmental pollution and global warming. On the other hand, vapor compression air conditioning systems have impacts on stratospheric ozone depletion because of the chlorofluorocarbons (CFC) and the hydrofluorocarbon (HCFC) refrigerants. The use of solar energy to drive cooling cycles is attractive since the cooling load is roughly in phase with solar energy availability.

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