Research On Solar Photovoltaic-ground Source Heat Pump Cold Chain Base Station

This article aims to develop a kind of fresh fruit and vegetable fresh-keeping device based on natural energy—solar photovoltaic-ground source heat pump cold chain base station.It is beneficial to solve the problem of cold storage and freshness of fruits and vegetables at the initial end of the cold chain.The base station uses a distributed photovoltaic power generation system and a ground source heat pump as the energy system,and combines phase change energy storage to provide cooling/heating for the fresh-keeping room.The cold chain base station mainly works in the fresh-keeping room,and the working process is divided into a cold storage period,a pre-cooling period and a fresh-keeping period.This paper first designs the base station energy system based on load calculations,and then determines the layout of the air vents and air supply angles,the arrangement of goods zone,and the atmosphere release rate through the FLUENT simulation.Finally,TRNSYS is used to build a cold chain base station system model,which simulates the operation process of the entire base station and determines the operating parameters of the cold chain base station.The container is the main demand of the base station.According to the requirements,the storage capacity of fruit and vegetables is 5 tons,the cold storage period is 30 days and thepre-cooling period is 24 hours.Based on the results of load calculation,the cooling capacity of the ground source heat pump（GSHP）is 4 k W,and the buried pipes is a double U tube type with a buried depth of 130 m.The flow rate and head of water pump are 23.0L/min and 13.0 m respectively.The air volume of the air outlets is 3645 m³/h.The calculated total power consumption of the electrical equipment is 2.06 k W.Based on the power consumption requirements,the design results of the photovoltaic power generation system are as follows:the inverter power is 5000 W;the battery model is W12-250S,which number is 40,and the connection mode is 4 series-10 parallel;the solar photovoltaic module selects monocrystalline silicon type with the power generation capacity of 290 W,and the connection mode is 2 series-12 parallel.Based on the selection of the energy system and the calculation of the air supply volume,FLUENT software was used to simulate the airflow organization during the cold storage period and the pre-cooling period.During the cold storage period,the number of air vents arrangement,air supply speed,single/double-sided air vents arrangement,and air supply angle were numerically simulated.The results show that the temperature unevenness coefficient decreases with the increase of the number of air vents in single-sided arrangement case.The temperature unevenness coefficient decreases with the increase of the air supply speed,but the excessive air supply speed makes the far-end wall bear more stress;Due to the existence of reflow,heat accumulation is easy to be formed in the double-sided arrangement case,and the phase change layer has poor uniformity.Liquid fraction vs.time of the phase change layer decreases as the air supply angle reduces.Comprehensively considered,the arrangement of the air vents in the fresh-keeping room is a single-sided arrangement with three pair of air vents,the air supply speed of the air outlet is 4 m/s,and the air supply angle during the cold storage period is-20°.During the pre-cooling period,this article numerical simulated the goods zone arrangement and N₂ and CO₂ release rates.The results show that the existence of the phase change layer can effectively increase the cooling effect,and the role of the phase change layer is more obvious when there is no shelf pad.The existence of the shelf pad can play a good role in the uniformity of the temperature of the goods zone.The time required for the concentration of the internal gas components decreases with the increase of the N₂ release rate,and the coefficient of atmospheric unevenness with the CO₂ release rate increases,and the CO₂ release rate is too small will make the atmosphere adjustment time too long.Comprehensive consideration,the final choice of the goods zone arrangement is the inverted U-shaped arrangement with shelf pad,the N₂ application rate is 5.5 m³/h,and the CO₂ application rate is 0.3 m³/h.The TRNSYS software was used to establish a cold chain base station system model,and the two periods with the lowest power generation in summer and winter were selected for simulation.In the case of meeting the power consumption,in order to ensure a high COP of system and a suitable fresh-keeping room temperature,the temperature of the fresh-keeping room selected supply air temperature is 4℃ in summer and in winter.