In a heat pump circuit, what is used to bypass refrigerant flow around the metering device?

In a heat pump circuit, an open check valve is used to bypass refrigerant flow around the metering device during certain operational conditions. This is necessary for optimizing system efficiency and ensuring proper refrigerant flow depending on the heat pump's current mode of operation—either heating or cooling. When the heat pump is in heating mode, the refrigerant needs to flow through the reversing valve, and the open check valve allows this bypass to occur, preventing unnecessary flow restrictions that could lead to system inefficiencies.

The inclusion of an open check valve enables the refrigerant to take an alternative path, ensuring adequate pressure and flow throughout the system when circumstances dictate that the metering device should not be part of the refrigerant circuit. This mechanism helps in effectively managing the pressure and temperature differences that occur during heat pump cycles, increasing overall system performance.

In contrast, the other options, such as a closed check valve, would entirely prevent flow, while a receiver drier has a different purpose related to filtering and drying the refrigerant. A thermal expansion valve, on the other hand, is a metering device itself that regulates the flow of refrigerant to the evaporator based on thermal load conditions, rather than bypassing flow.