Abstract:

Air source heat pump units are widely used in HVAC in China, however, when air source heat pumps are operating in winter, frosting of outdoor heat exchangers is an operating problem that cannot be ignored. Under frosting conditions, the heating capacity of air source heat pumps is significant reduced, and must undergo periodic defrost to ensure its normal operation. When the air source heat pump defrosts, the defrost water drops will cause the overall defrost of the heat exchanger to be uneven and affect the defrost performance. In order to study the influence of the defrost on the heat exchanger tube fin surface on the defrost performance of the air source heat pump during the defrost process, a dynamic model of the hot gas defrosting of the outdoor heat exchanger was established, at the same time, the heat and mass transfer analysis of the defrosting process is carried out, and the energy balance equation of the defrosting stage is established. The model is solved by MATLAB to obtain the tube wall temperature, the defrost rate and remaining frost quality and other parameters change with time. The results show that the defrost rate of heat exchanger decreases rapidly under the influence of defrost water, and the remaining frost mass in the upper area becomes 0 at 67 s, while the frost layer in the area affected by falling water does not melt until 78 s. The defrost time in the lower area is obviously affected by the falling water of defrost, and the defrost time is extended by 11 s.

Key words: air-source heat pump, defrost, defrost water, defrost rate, dynamic defrost model

摘要：

空气源热泵除霜时，融霜水下落会造成换热器整体除霜不均匀，影响除霜性能。为研究空气源热泵在除霜过程中换热器管翅表面的融霜下落水对除霜性能的影响，建立了室外换热器的热气除霜动态模型，对模型进行求解得到除霜过程中的管壁温度、除霜速率以及剩余霜质量等参数随时间的变化规律。结果表明，受融霜水影响时，融霜速率迅速降低，在第67秒时上部区域剩余霜质量变为0，而受下落水影响区域直到第78秒时霜层才全部融化。

关键词: 空气源热泵, 除霜, 融霜水, 融霜速率, 动态除霜模型