北美屋顶机设计运行工况下热力膨胀阀选型探讨

Discussion on selection of thermostatic expansion valves working on the North-America rooftop unit design running condition

热力膨胀阀只能在一个较窄的工况和负荷范围下实现调节过热度的功能。现有一批在北美销售的屋顶机,设计运行工况范围较宽,在室外温度为-17.7℃～51.7℃下,机组都要求能运行。仿真结果表明,对这种运行工况的屋顶机组,用传统方法选出的热力膨胀阀未能在较多工况点充分发挥其控制过热度的作用。在考虑热力膨胀阀的振荡现象的基础上,对选型方法进行改进,并通过实验验证,证明在基于最小负荷比大于30%方法选出的热力膨胀阀能够在较多工况点控制空调机组的过热度,且避免了振荡现象的发生。

Thermostatic expansion valve can adjust superheat well only at a narrow working condition. Some rooftop units of North America sales are designed to work at a wide working condition with the ambient temperature - 17.7℃ -51.7℃. The drawback of the conventional method for selecting thermostatic expansion valves with North -America range running condition is indicated by the theoretical analysis. Based on the effect of hunting, an improved method is introduced. Finally an experiment designed to verify this method is demonstrated, the experimental results show that the expansion valve selected by new method can control the superheat of an air -conditioning system at most running points efficiently, and the hunting is also avoided.