What determines the size of the metering device needed for a refrigeration system?

The size of the metering device in a refrigeration system is primarily determined by the capacity of the compressor expressed in Btu at the evaporator operating temperature. The metering device is responsible for controlling the flow of refrigerant into the evaporator, and its size must correspond to the amount of refrigerant that needs to be supplied in order to match the compressor’s capacity efficiently.

When the compressor's capacity is known, the metering device can be selected to ensure that it can accommodate the volume of refrigerant required by the evaporator based on the system’s operating conditions. Proper sizing is crucial because an undersized metering device can restrict refrigerant flow, leading to inadequate cooling, while an oversized device could cause flooding of the evaporator, resulting in inefficiency and potential system damage.

Other factors, such as the size of the evaporator, the ambient temperature of the installation site, and the type of refrigerant, do influence the overall performance of the refrigeration system, but they do not directly determine the metering device's size. The primary function of the metering device is to regulate refrigerant flow based on the system's compressor capacity. Thus, option B is the most relevant criterion for sizing the metering device accurately.