Theoretical Study Of A New Combined Cooling,Heating And Power System Driven By Solar Energy

Developing renewable energy resources is of great significance to decrease environmental pollution and alleviate the energy crisis.The combined cooling,heating and power system(CCHP)is a high efficiency energy conversion system,which would be combined with solar energy technology to reduce the energy consumption.Carrying out related research seems to be an efficient way to increase the energy efficiency,to decrease the carbon and haze weather,to improve the energy consumption structure and to develop the low carbon economy,which shows an important theoretical and academic significance.A CCHP system driven by solar energy is proposed in this paper.The CCHP subsystem combines a Rankine cycle with a diffusion absorption refrigeration cycle to yield electricity and cold capacity to users,and a water-heater is employed to supply heat energy to users.The trough solar collector is adopted to collect the solar radiation and to transform it into thermal energy.The thermal storage unit is installed to storage the thermal energy collected by the collectors to ensure a continuous energy supplement when solar energy is weak or insufficient.The mathematical models of the diffusion absorption refrigeration system are established,and the influence between the solution recirculation ratio and the coefficient of performance(COP)of the refrigeration system under several operating conditions is analyzed.Results show that the COP of the refrigeration system increases firstly and then decreases as the solution recirculation ratio rises under majority of operating conditions.In order to analyze the CCHP system,the mathematical models of the CCHP system driven by solar energy are established,and the performance criteria are provided such as thermal efficiency,exergy efficiency and economic-exergy to evaluate the thermodynamic performance and the thermoeconomic performance of the CCHP system.Based on the mathematical models established,the simulation results of the system in four modes,namely “the cooling and the heating following the electricity loads” mode,“the cooling follows the electricity loads” mode,“the heating follows the electricity loads” mode and “only the electricity loads” mode are obtained.Then the paper examines the effects of several key thermodynamic parameters,namely expander inlet temperature,expander inlet pressure,temperature difference in cooling generator and solution recirculation ratio in diffusion absorption refrigeration,on the thermoeconomic performance of the system.Results indicate that in “the cooling and the heating follow the electricity loads” mode,expander inlet temperature has a negative effect on the thermal efficiency and a positive effect on the exergy efficiency of CCHP system,while expander inlet pressure has a positive effect on the thermal efficiency,and as the pressure increases,the exergy efficiency of CCHP system appears a trend which increases firstly and then decreases.When the CCHP system is in other three modes,expander inlet temperature has a positive effect on both the thermal efficiency and the exergy efficiency,while the thermal efficiency and the exergy efficiency both rise firstly and then decline as expander inlet pressure increases.Considering the thermoeconomic performance,the single-objective has been conducted by the genetic algorithm to find the optimal solution set in the typical “the cooling and the heating follow the electricity loads” mode.The economic-exergy efficiency is defined as the objective function in the single-objective optimization.The results provide the basis for the system optimal design.