Abstract:

Under low-temperature climate conditions,the compressor suction pressure and temperature are reduced owning to the decrease of the temperature of the inlet water and the outlet CO₂of the gas cooler in the trans-critical cycle CO₂ heat pump system.When the compressor suction pressure is less than the lower limit of the suction pressure,it leads to the unstable operation of the system.In order to overcome this drawback,a method of mixing water at the inlet of cold water in the gas cooler is presented.Proper quantities hot water in hot water tank is supplied to the cold water inlet of the gas cooler by a by-pass pipe.Adjusting the three-way valve to change the proportion of mixing water,the inlet temperature of gas cooler is increased to make the system run steadily under low-temperature climate conditions.Test results show that the method of mixing water could not only ensure the system of CO₂ air source heat pump hot water system works steadily under low-temperature conditions,but also increase operation time of the system and reduce the frequency of frosting.However,the heating power and COP(coefficient of performance)of the system declines slightly.Considering the operation stability and thermal performance simultaneously,the suitable temperature of mixing water for this system is 12-18℃ when ambient temperature is -20℃ and heating temperature is 60℃.

Key words: carbon dioxide, compressor, experimental validation, inlet water temperature, mixing water, system performance

摘要：

在低温工况下，因跨临界循环CO₂热泵系统气体冷却器的进水温度和CO₂出口温度降低，压缩机吸气压力和温度随之降低。当系统的吸气压力低于压缩机的吸气压力下限时，将导致系统无法稳定运行。为了改变这种现象，采用在气体冷却器冷水入口处混水的方法，将热水箱的热水旁通至气体冷却器冷水入口。采用三通调节阀调节混水比例，适当提高气体冷却器的进水温度，以期实现系统在低温工况下的稳定运行。实验测试结果表明，采用混水方法不仅可保证低温工况下跨临界循环CO₂空气源热泵热水系统的稳定运行，同时可降低结霜频率，延长系统运行时间，但系统的制热量和COP将小幅下降。兼顾系统的热力性能及运行稳定性，当环境温度为-20℃、制热温度为60℃时，较为适宜的混水温度为12~18℃。

关键词: 二氧化碳, 压缩机, 实验验证, 进水温度, 混水, 系统性能