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Among various types of clean energies, special attention has given to a solar energy because it is freely available in hot regions where more than half the world's population lives. Use of solar energy in vapor absorption refrigeration systems should be one application which can achieve cooling/heating needs. In general, solar cooling systems can be considered as combination of energy conversion and refrigeration subsystems. The energy conversion subsystem transforms solar energy to power the refrigeration system. In the present work, a solar cooling system for air conditioning applications is simulated and optimized under Egyptian meteorological conditions. According to the required comfort dry bulb air temperature, available cooling water temperature and cooling coil capacity, optimal heat source mass flow rate and temperature to operate a single-stage continuous absorption cycle was obtained. Then, economical optimization of the solar system that can meet the required load was carried out for various types of solar collectors. Results revealed that the flat-plate solar collector is the most efficient collector from the economical point of view. Annual visualization of the system performance was presented to investigate the system behavior under different weather conditions for heating and cooling processes during the year to improve its life-cycle savings. The environmental impact of using such system is considered. It is found that the reduction of CO2 emission is a significant advantage of using solar energy. KEY WORD Solar, Cooling, Absorption, Single Effect, Simulation, Collector, and Environmental Impact. * Professor, Dpt. of Mech. Power Eng., Helwan University, Cairo, Egypt. ** Lecturer, Dpt. of Mech. Power Eng., Helwan University, Cairo, Egypt. *** Associate Professor, Dpt. of Mech. Power Eng., Helwan University, Cairo, Egypt. 350 MP Proceedings of the 13 Int. AMME Conference, 27-29 May, 2008 NOMENCLATURE A total collector array aperture or gross, m Ai surface area of the ith tank segment, m 2 b0 negative of the first-order coefficient of (τα)b/(τα)n vs. (l/cosθ ‐ l) b1 negative of the second-order coefficient of τα)b/(τα)n vs. (l/cosθ ‐ l) cA collector price, US$/m cf fuel price, US$/GJ (12 L.E./GJ is considered) CM price of the storage tank, US$/kg Cpc specific heat of collector fluid, kJ/kg.C Cp specific heat, kJ/kg.C Cpf specific heat of the tank fluid, kJ/kg.C co fixed cost of the system, US$ COP coefficient of performance FR overall collector heat removal efficiency factor FRUL negative of the first-order coefficient of collector efficiency vs (Ti Ta)/IT FR ULcombined first and second-order coefficients of collector efficiency vs (Ti Ta)/IT F' collector fin efficiency factor Fpar fraction of pump/fan power converted to fluid thermal energy h enthalpy, J/kg gi flag for boundary segments Gtest flow rate per unit area at test conditions, kg/m h specific enthalpy, kJ/kg I total horizontal radiation per unit area, W/m IbT incident beam radiation per unit area on tilted surfaces, W/m 2 Id horizontal diffuse radiation per unit area, W/m 2 IT total incident radiation on a tilted flat surface per unit area, W/m 2 L.S. life cycle solar savings, US$ M mass of the storage tank, kg. m mass flow rate, kg/s mc collector mass flow rate, kg/s Mi mass of fluid in the ith section inside the tank, kg N lifetime of the system, yr. (20 years is expected). OM annual charge for operation and maintenance of the system expressed as a fraction of capital cost (2% is assumed). P power consumption of pump, W Q rate of heat transfer, W Q i rate of energy input by the heating element to the tank ith segment, W Qu rate of energy gain of total collector array, W r Real rate of return on alternative investments of comparable risk. rf real fuel escalation rate. r1 factor for correcting FR(τα)n and FRUL’ for operation at flow rates other than that at test conditions T Temperature, ̊C Ta ambient temperature, ̊C Tenv temperature of the environment surrounding the tank, ̊C 351 MP Proceedings of the 13 Int. AMME Conference, 27-29 May, 2008 γ i = m h α j m L Σ j=1 i-1 β j Σ j=i+1 N Ti inlet temperature of fluid or temperature of the ith tank segment, ̊C UL overall loss coefficient of collector per unit aperture area, W/m .C Subscripts 1-10 refer to Fig. (2) i inlet abs absorber L load side con condense n normal e evaporator o outlet h hot or heat-exchanger ref reference g generator s surface or solution j segment number Symbols α absorptance of absorber plate αi a control function defined by αi = 1 if i = Sh; 0 otherwise β collector slope (in degrees) βi a control function defined by βi = 1 if i = SL; 0 otherwise ∆t simulation time step, s η overall collector efficiency ηbackup boiler backup efficiency (75% is normally considered). γi a control function defined by θ solar incidence angle (degree) ρg ground reflectance τ transmittance of collector cover INTRODUCTION There are only two mechanical air-conditioning chillers have been extensively used in various applications. They are vapor compression chillers and vapor absorption chillers. Vapor absorption chiller is principally similar to the well known vapor compression chiller in that it uses a refrigerant which alternatively evaporates at low pressure and condenses at high pressure. The main difference between the two chillers is the driving force that circulates the refrigerant around the system. In the absorption chiller, compressor is replaced with an absorber, circulation pump, expansion device and generator. Another difference is that the energy input to the absorption chiller is mainly of heat supplied to the generator. Hence, low–grade energy such as a solar energy can be used to operate vapor absorption refrigeration systems to achieve cooling needs. In general, solar cooling systems can be viewed as combinations of energy conversion and refrigeration subsystems. The energy conversion subsystem transforms solar energy to power the vapor absorption refrigeration system Therefore, solar absorption 352 MP Proceedings of the 13 Int. AMME Conference, 27-29 May, 2008 cooling can obtain a great potential because it is used during the summer months when they have long day time and higher ambient temperature. Many investigators have developed computer programs or mathematical models to predict performance characteristics of vapor absorption chillers. Investigations on the effect of various operating conditions form a part of such studies with the aim of providing basic information for design of absorption chillers working with different refrigerant-absorbent pairs. In this work, the emphasis is on presentably commercially water lithium bromide based vapor absorption chillers for air-conditioning applications. This is due many advantages of this working fluid such as high heat of vaporization, non-toxic, non-flammable, availability, inexpensive ... etc. Romero et al. (2000) compared the theoretical performance of a solar absorption air conditioning system operating with water/lithium bromide and an aqueous ternary hydroxide mixture consisting of sodium, potassium and cesium hydroxides. The results showed that similar coefficients of performance are obtained for both mixtures. However, it was found that the system operating with the hydroxides may operate with a higher range of condenser and absorber temperatures and the heat delivered by these components can be removed by air. Li and Sumathy (2000) reviewed solar powered air-conditioning systems using water-lithium bromide pair. It is seen that the generator inlet temperature of the chiller is the most important parameter in the design and fabrication of a solar powered air-conditioning system. Performance evaluation of single-glazed and double-glazed collectors for an open-cycle absorption solar cooling system is conducted by YANG and WANG (2001) for airconditioning applications in Kaohsiung, Taiwan via a computer simulation program. It is shown that the double glazed forced convection gives a better system performance. Simulation of an absorption solar cooling system under Cyprus climatic conditions is presented by Florides et al. (2002). Their system operates with maximum performance when the auxiliary boiler thermostat is set at 87°C. The system long-term integrated performance shows that cooling load of 84,240 MJ and heating load of 41,263 MJ are supplied with solar energy. Tsoutsos et al. (2003) developed an economic evaluation of two types of solar absorption and adsorption cooling systems. Their analyses indicated that, because of their high investment cost, these systems would be marginally competitive with compression cooling systems at present energy prices. Assilzadeh et al. (2005) simulated a solar cooling system, which consists of evacuated tube solar collectors and water-lithium bromide absorption refrigeration unit. The optimum solar subsystem for Malaysia’s climate for a cooling capacity of 3.5 kW (1 refrigeration ton) consists of 35 m evacuated tubes solar collector sloped at 20 ̊. Water-lithium bromide absorption refrigeration system is simulated and optimized by Balghouthi et al. (2005) for Tunisian conditions. The simulation results show that absorption solar air conditioning systems are suitable for Tunisian’s conditions. Syed et al. (2005) reported novel experimental results derived through field testing of a part load solar energized cooling system for typical Spanish houses in Madrid during the summer period of 2003. Solar insolation of 969 W m produced 5.13 kW of cooling at a solar to cooling conversion efficiency of 11%. Maximum cooling capacity was 7.5 kW. The absorption refrigeration machine operated within the generation and absorption temperature ranges of 57–67 and 32–36 ̊C, respectively. The results clearly 353 MP Proceedings of the 13 Int. AMME Conference, 27-29 May, 2008 demonstrate that the technology works best in dry and hot climatic conditions where large daily variations in relative humidity an

SIMULATION AND OPTIMIZATION OF H2O-LIBR ABSORPTION REFRIGERATION SYSTEM OPERATED BY SOLAR ENERGY UNDER EGYPTIAN CLIMATIC CONDITIONS