Availability of solar energy at Baghdad, Iraq and its application to absorption refrigeration for cold stores purposes

The purpose of this investigation is to study the availability of solar energy at Baghdad, Iraq for utilisation to produce refrigeration at 10\,1 temperatures where it will be applicable for cold stores and freezer rooms and to prepare design data for such applications. Five years meteorological data are obtained from Baghdad Weather Bureau and the study is based on the averaged data for these five years. The total energy available is collected by a three covers flat plate collector with selective coating applied to the absorber plate surface. The parameters influencing the best year round thermal performance of the solar collector are investigated. These parameters are mainly, the collector tilt and the heat transfer media temperatures. The optimum tilt of the collector for summer operation of an air conditioning system is 200 from the horizontal facing the equator, 300 for year round performance of refrigeration system, the case under consideration, and 500 for winter operation where only heating is needed. The instantaneous efficiency of the collector varies during the day from a minimum of 0.04 during the morning and afternoon to a maximum of 0.55 between 9 a.m. - 4 p.m. Also the efficiency increases with a decrease in the temperature difference between the inlet fluid and the ambient air.The useful energy collected at the optimum tilt of 300 for year round performance and at different collection temperatures are then applied to an aqua ammonia absorption refrigeration system to produce a refrigeration effect. The thermal performance of the refrigeration system is investigated for different evaporator temperatures, condenser temperatures and pressures, solution concentrations and generator temperatures. The solar energy collected in excess of the immediate operating requirement is stored in liquid refrigerant for usage during the night and daytime periods of no or low solar radiation. Storage of liquid refrigerant with its potential for producing a refrigeration effect by evaporation was chosen instead of the alternative of storing energy from the flat plate collector directly. Thermal storage at medium temperatures is only practicable at present using liquid or solid storage media. The promise of using phasechange materials as a means of thermal energy storage has not yet proved practicable due to breakdown during recycling and supercooling problems. Liquid or solid storage give rise to problems because of the size of storage vessel needed and the attendant need to insulate such a vessel efficiently. These last factors have obvious implications in relation to initial capital cost. The results obtained are then analysed to find the best year round performance of the solar refrigeration system per unit area of the solar collector at the most preferable operating conditions of the refrigeration system