| As global energy consumption increases,environmental problems become more and more serious.The dependence on of fossil energy leads to lots of environmental problems.With the goal of carbon neutrality proposed by the Chinese government,the development of renewable energy and energy conservation and emission reduction have become an important development strategy and development goal.Developing renewable energy,reducing the proportion of fossil energy in the total energy consumption,and expanding the application scenarios of new energy in the process of people’s production and life are the themes of the next stage.In the total social energy consumption,the proportion of building energy consumption has increased day by day,and has reached to nearly 40%in recent years,in which refrigeration accounts for a large proportion.As a renewable energy,solar energy is an important alternative to traditional fossil energy.And it has a very close relationship with building refrigeration demand.For the areas where the refrigeration demand is more vigorous,the solar energy is often more abundant.Combining solar energy with buildings,we can make full use of the characteristics of distributed solar energy and use solar energy for air conditioning and refrigeration.It can greatly expand the use of solar energy scenarios,meet the air conditioning load of buildings in summer.And it provides an ideal way of using solar energy for building energy conservation and emission reduction,and what’s more reducing the dependence on fossil energy sources.Solar photovoltaic refrigeration technology is to convert solar irradiation into electric by PV,drive the compressor,then drive the whole refrigeration system.Due to the periodic change of solar energy,the lack of energy storage device can not meet the cooling demand at night.The combination of solar photovoltaic refrigeration and ice storage technology can effectively use solar energy,store cold energy and supply energy for buildings.Therefore,this paper proposes a PDISAC system.The system adopts DC compressor,which is directly powered by photovoltaic array without inverter or batteries.It can receive solar energy in the daytime for ice making and cold storage,and release the cold energy stored by fan coil at night.Compared with the system using commercial power under the same conditions,it can effectively reduce carbon dioxide by about 3.39 tons.The main works are outlined as followed:(1)The experimental platform of PDISAC system is designed and built.The performance of the system in dynamic environment is studied,and the parameters affecting the efficiency of the system are further analyzed.The results show that the system can store 6.38 kg ice and 6.67 MJ cold,and can keep the room temperature below 25℃ for 2 hours at night,while the temperature of the contrast room is more than 32℃.The efficiency of the refrigeration cycle is 1.028,and the coefficient of performance of the ice making and cold storage process is 7.0%.The influence of irradiation on photovoltaic efficiency in this system is also studied.It can be found that the maximum instantaneous photovoltaic efficiency of photovoltaic refrigeration system can reach 13.5%,and the photovoltaic conversion efficiency gradually decreases with the increase of irradiation.In addition,the relationship between ice production and ice diameter,as well as the influence of heat preservation on the process of ice melting are also studied.(2)The theoretical model of ice making and cold storage process in photovoltaic direct-driven ice storage air-conditioning system is established.The model are verified by experimental results.Based on the model,the effects of ambient temperature,initial water temperature and volume of ice storage tank and ice thickness have been studied.The simulation results show that the ambient temperature has a significant impact on the operation of the system.When the ambient temperature increases by 3 K,the cooling efficiency decreases by about 10%.If the ice storage tank is placed in a cool and ventilated place,the system efficiency and cooling capacity can be improved.The initial water temperature and storage capacity of ice storage tank affect the latent heat and sensible heat of the system,and then affect the efficiency and cooling capacity of the system.In addition,the ice thickness also restricts the refrigeration efficiency of the system.And we have proposed a compressor speed control strategy,which can effectively match photovoltaic array with compressor and optimize the number of photovoltaic panels to 3,and the utilization of solar energy increase by nearly 54%. |
