Research On CA Cold Storage And Its Control Methods

Controlled atmosphere storage (CA for short) is the method to set up a special storage environment with low temperature, proper content of oxygen, carbon dioxide, ethane and relative humidity, through the ways of manual refrigeration and modifying air contents. The CA storage has the advantages of keeping original quality, reducing loss on refrigeration, restraining physiological activities and prolonging storage term and shelf life of fruits and vegetables.The CA storage warehouse mainly consists of building structure, atmosphere control system, refrigerating and humidifying equipment, of which the atmosphere control system plays a key role. As the requirement for freshness is especially high, more attention should be played to the fluctuation of air temperature and loss on refrigeration, apart from air content. This thesis analyses the problems in practice and presents solutions. The results are significant.The change of evaporating temperature and control precision influence the temperature fluctuation of the air, which is relevant to the heat-load matching of warehouse and refrigerating units. Two refrigeration methods are commonly used in cold storage warehouse: direct cooling of one unit to one house with Freon, indirect cooling with glycol.For the first method, each house has a separate refrigerating unit, Freon as the refrigerant evaporates in the cooler to cool the air. The unit is controlled with the set temperature. For the indirect cooling method, glycol liquid as the secondary coolant is cooled in the refrigerating unit, pumped to the cooler in the house to cool the air. The cooling load is regulated by changing the flowrate of the glycol liquid.This thesis compared the advantages and disadvantages of the two methods, concluding that parallel multi-condensing unit is the best cooling system in CA storage.Attentions should be played to the following three systems in parallel multi-condensing unit: lubricant control system, evaporating pressure control system and computer controller.According to the characteristics and technical requirements, the thesis researches and developed the lubricant control system and computer controller for the multi-condensing unit. The equipment cost is reduced and the economic benefit is significant.