Solar Powered Air Conditioning in Tunisia

The project background

An emerging trend within the field of engineering is the creation and implementation of solar powered air conditioners. At first, such an idea might not seem as a significant trend in the field of engineering. However, the benefits obtained from such an idea would have a positive effect not only in the field of engineering, but also across the world.

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. Cool 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.

Absorption systems are similar to vapour 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.

The wind and solar power, with the aim of generating some 10% of the country's total electricity demand through wind farms by 2015. To the future, the sector looks set to thrive with, for example, BG Tunisia, the largest investor in the country's energy sector, foreseeing the injection of additional investments amounting to 10% in Tunisia between 2010 and 2012.

Sustainable technology objective and issue

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

The issues when solar powered air conditioners our used worldwide the impact will be enormous. Solar powered cooling systems would allow cooling in parts of the globe in which an electric air conditioner could not be used. Growing demand for air conditioning in recent years, particularly in hot and humid regions such as in Mediterranean countries, has imposed a significant increase in demand for primary energy sources. Of course the utilization of solar powered cooling would also reduce the number of resources used by electric air conditioners. These devices would not only help those who could not previously receive cooling, but would also contribute to the improvement of our environment. This is especially critical since global warming poses such a threat to the environment. Solar powered cooling is part of the global movement to help protect the limited number of resources left on our planet and reduce green house gas emissions.

Climate and energy considerations in Tunis: 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 vapour from a solution of lithium bromide and water. The water vapour 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.

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.

How Solar Powered Air Conditioners Work?

Among the various thermal application of solar energy, cooling is one of the more complexes, both in concept and construction. This is why the implementation of solar powered air conditioners has not been as prevalent as it should be. The energy must be converted by means of a suitable device, capable of absorbing heat at a low temperature from the conditioned space, and rejecting it into the higher temperature of the outside air. In thermodynamic terns, a heat pumping operation is required. This poses a problem to environmental engineers, but there have been a number of models created and tested. One of the models developed utilized four main flow circuits, taking into account the collector, generator, chilled water and the cooling water. Solar powered air conditioners have been installed in regions throughout Tunisia and also the University of Hong Kong.

Political effects

Tunisian Energy Minister Afif Chelbi and Italian Economic Development Minister Pierluigi Bersani signed a joint declaration Friday (March 9th) in Rome that envisages setting up a joint working group to finalise the El Haouaria power station and the electric connection between Italy and Tunisia. The project for connecting Italy and Tunisia is an important step towards building the Euro-Mediterranean ring, to create a corridor within which to start the exchange of energy and power, Bersani said. The working group will meet shortly in Tunis to finalise the negotiations.

Italy wills assistant Tunisia to increase use of solar energy in residential buildings under the PROSOL Tunisia programme. A meeting on technical implementation will be held by the Italian Environment Ministry in Tunis on 19 July. The programme aims at the installation of 85,000 square metres of solar panels in the period 2005-2007 and a total of 230,000 square metres by 2011.

Sustainable development from a national perspective

The thermodynamic solar power plant of the National Institute for Scientific Research in Tunisia has been in operation since 1984. The plant served as a pilot unit for exploring the technical reliability and evaluating the economic feasibility of the process of converting solar thermal energy into electricity. This consists of a close evaluation and analysis of the long-term performance of the system and a review of 15 years of successful operation. The aim of this study was to go over the main problems and technical difficulties encountered and pinpoint the major factors affecting the plant operation in order to identify the optimal operating policies toward the enhancement of the plant efficiency. Even though the thermal performance of the plant was relatively low, the impact of such a plant on the energy sector of the country was significant in terms of energy saving and environmental protection. In regions with high solar radiation such as Tunisia with a daily mean in solution of 4.8kWhm-2, the use of solar power plants - similar to this one - essentially for heat production prove to be a good alternative especially for remote and rural areas.

Conclusion

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, vapour compression air conditioning systems have impacts on stratospheric ozone depletion because of the chlorofluorocarbons (CFC) and the hydro fluorocarbon (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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Moncef Balghouthi, Mohamed Hachemi Chahbani and Amenallah Guizani.