| In recent years,the architecture of China has received great development.The area of the buildings in construction is 1600-1900 million square meters per year.By the end of 2001,the total area of the buildings of China has been more than 36000 million square meters.Now,more than a quarter of the total energy consumption of China is on building,and the trend keeps on increasing.As is known,the building energy consumption includes many aspects,such as hot water,heating,air conditioning,lighting,household appliances,etc.As a clean,non-polluting and renewable energy source,solar energy has received considerable attention due to the shortage of the normal fossil energy and the pollution of the environment.In the field of solar thermal utilization,solar cooling has received great development in recent decades since the availability of solar radiation matches very well with the varying cooling load demand and is friendly to environment.Among the solar cooling technologies,the solar LiBr/H2O absorption cooling which has been in the stage of demonstration is ripest.Nevertheless,nearly all the studies on solar absorption cooling system focused on single-effect LiBr/H2O systems.Single-effect LiBr/H2O systems require hot water generator inlet temperatures in a low range of 75-90℃,so collectors of low price such as flat-plate pattern and evacuated tube collectors can be matched with them.Solar single-effect LiBr/H2O systems has the advantage of low cost,but the energy efficiency is low (COP 0.6-0.7).In this study,a solar double-effect LiBr/H2O absorption cooling system is theoretical studied.The system mainly consists of parabolic trough collectors(PTC) and a double-effect LiBr/H2O absorption chiller.PTC has the ability to obtain a high fluid temperature with high energy efficiency.Compared with single-effect chiller, double-effect chiller requires hot water generator inlet temperatures in a high range of 120-160℃.The energy efficiency of double-effect system is higher(COP 1.2-1.5), which means a better energy-efficiency effect.An unsteady,one-dimensional heat transfer model of PTC is presented in this article.The distribution of the concentrated solar radiation along focal axis has been calculated.The thermal performance of the PTC is simulated,and the simulated results are compared with the experimental results.The comparison shows that the simulated and experimental results are in good agreement,and the difference between them is within 4.61%,which means the model set up is reasonable.A steady state concentrated parameter model of hot-water-driven double-effect parallel-flow LiBr/H2O absorption refrigeration system is set up.The effect of the variation of operating conditions such as inlet temperature and mass flow rate of hot water,inlet temperature and mass flow rate of cooling water,outlet temperature and mass flow rate of cold water,solution distribution ratio and mass flow rate of solution on system performance is studied,and the possible faults caused by the variation of operating conditions are analyzed.Results show that the cooling capacity and the COP of the system vary with the variation of the operation conditions;system faults such as solution crystallization,overhigh working pressure, freezing of cooling water or chilled water will be caused if the variation of the operation conditions is out of range.Based on the theoretical study of the PTC and the double-effect parallel-flow LiBr/H2O absorption refrigeration chiller,the system performance of the solar cooling system with PTC and a double-effect LiBr/H2O absorption chiller is studied, and the influence of the operating temperature on the overall efficiency of the system is studied.Results show that the PTC has the ability to work at high temperature with high efficiency;the overall efficiency of the system achieves a maximum value of 0.8250 at operating temperature of 173.5℃;the system with PTC and a double-effect LiBr/H2O absorption chiller has better system performance compared with the solar absorption cooling system with CPC and ETC;when PTC is used,its area is the least under the same design condition,but due to its high price,the cost of the system is still at a high level.A modelling and simulation is carried out for evaluating the system performance of a solar-assisted absorption cooling system under the climatic conditions of Hefei,China.The system consists of 66.125m2 parabolic trough collectors(PTC),a double-effect LiBr/H2O absorption chiller of 16kW cooling capacity and a storage tank.The effects of gas-firing thermostat setting,storage tank size and collector area on the system performance are analyzed.The results show that an optimal performance is attained when the storage tank size is 0.6 m3 and gas-firing thermostat setting is 158.0℃.During the cooling season,the collector energy gain is 113594.52MJ,and the solar fraction reaches 0.5997.Though 4091.11m3 gases are saved per year compared with the gas-fired double-effect absorption cooling system,the system is not cost-effective due to the high initial cost. It is found that the solar-assisted absorption cooling system is marginally competitive with gas-fired absorption system when collector prices reach values less than $350.0/m2.The thermal performance of double-effect parallel-flow LiBr/H2O absorption refrigeration system under dual-heat mode of operation is theoretically studied,and the influence of variation of external heat capacity of low pressure generator and operation parameters on the performance of system is analyzed.Results show that under dual-heat mode of operation,the flux of solution should be adjusted with the variation of the external heat capacity of low pressure generator to ensure the normal operation of the system;an increase in external heat capacity of low pressure generator leads to a better effect of energy-saving and a lower operating cost;the adjustable range of solution distribution ratio changes with the variation of operating conditions.
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