串联式二氧化碳双级压缩制冷热泵系统研究

发布时间：2018-03-24 06:14

本文选题：二氧化碳　切入点：双级压缩　出处：《西安建筑科技大学》2013年硕士论文

【摘要】：在民用建筑中实现空调系统同时供冷、制热和供应生活热水是当今社会的普遍需求，热回收式热泵空调的出现不仅满足了这种需求，而且也适应了社会对于节能和环保的要求。但目前热回收系统普遍存在着冷热量互相制约、功能单一、效率较低等问题。本文提出了一种串联式CO_2双级压缩制冷热泵系统，该系统不仅能够回收利用冷凝热，而且可以根据用户的需要同时制冷和生产生活热水，解决了现有热回收式系统所存在的冷热量互相制约问题。本文以系统性能系数为目标分别计算分析了热水换热器出口CO_2温度、蒸发温度、压缩机排气压力，中间压力、过热度、过冷度以及流量系数对串联式二氧化碳双级压缩制冷热泵系统循环性能的影响。研究表明：在全热回收工况下，蒸发温度、热水换热器出口CO_2温度对循环的COP有显著的影响，而蒸发器出口过热度、气液分离器中制冷剂过冷度对COP的影响较小；热水换热器出口CO_2温度决定了随着高压压缩机排气压力的升高，COP是否会出现峰值；也决定了中间排气压力是否存在最优值。当热水换热器出口CO_2温度降到特征温度以下，按用户需要改变系统补气量时，系统循环会出现特征高压排气压力点，当系统高压排气压力低于特征排气压力时，提高补气量，系统的循环性能大于全热回收工况；当高压排气压力大于特征排气压力时，提高补气量，，系统的循环性能将小于全热回收工况。类似地，当热水换热器出口CO_2温度低于特征温度时，同样也存在特征中间压力点。特征中间压力受蒸发温度、热水换热器出口CO_2温度以及高压排气压力的影响。系统循环参数的选择需综合考虑以上因素，才能保证系统高效运行。
[Abstract]:The realization of air conditioning system in civil buildings at the same time to supply cooling, heating and supply of domestic hot water is a common demand in today's society, the emergence of heat recovery heat pump air conditioning not only to meet this demand, It also meets the requirements of the society for energy saving and environmental protection. But at present, the heat recovery system generally has the problems of mutual restriction of cold and heat, single function, low efficiency, etc. In this paper, a series CO_2 two-stage compression refrigeration heat pump system is proposed. The system can not only recover and utilize condensate heat, but also refrigerate and produce domestic hot water simultaneously according to the needs of users, thus solving the problem of mutual restriction of cold and heat in the existing heat recovery system. In this paper, the outlet CO_2 temperature, evaporation temperature, compressor exhaust pressure, intermediate pressure, superheat degree of the hot water heat exchanger are calculated and analyzed respectively with the system performance coefficient as the target. The effects of undercooling degree and flow coefficient on the cycle performance of a series CO2 two-stage compression refrigeration heat pump system are studied. The results show that the evaporation temperature and the CO_2 temperature at the outlet of the hot water exchanger have significant effects on the circulating COP under the condition of total heat recovery. However, the superheat at the outlet of evaporator and the refrigerant undercooling in the gas-liquid separator have little effect on COP, and the CO_2 temperature at the outlet of the hot water exchanger determines whether the cop will peak with the increase of the exhaust pressure of the high pressure compressor. It also determines whether there is an optimum value for the intermediate exhaust pressure. When the CO_2 temperature at the outlet of the hot water exchanger drops below the characteristic temperature and changes the system air supply according to the user's requirement, the system cycle will appear the characteristic high pressure exhaust pressure point, when the system high pressure exhaust pressure is lower than the characteristic exhaust pressure, the supply gas quantity will be increased. The cycle performance of the system is greater than that of total heat recovery. When the high pressure exhaust pressure is greater than the characteristic exhaust pressure, the circulation performance of the system will be smaller than that of the total heat recovery. When the outlet CO_2 temperature of the hot water exchanger is lower than the characteristic temperature, there are also the characteristic intermediate pressure points. The influence of CO_2 temperature and high pressure exhaust pressure on the outlet of hot water heat exchanger. The selection of system cycle parameters needs to consider the above factors comprehensively in order to ensure the efficient operation of the system.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU83

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