Heat Pumps: Metering Devices and Internal Components Overview

Metering Devices in Heat Pumps: Thermostatic Expansion Valves (TEVs)

• Comparison to Fixed Bore/Piston Type: Unlike fixed bore or piston devices, the Thermostatic Expansion Valve (TEV or TXV) can modulate refrigerant flow based on the system's load.

• Check Valves Requirement:

  • Traditional TEV installations in heat pumps require check valves. These check valves bypass the refrigerant around the TEV that is not actively metering in a specific mode of operation.

  • Many newer TEVs are manufactured with internal check valves or bypasses, thus eliminating the need for external check valves in many modern heat pumps.

TEV Operation in Cooling Mode

• Function: In cooling mode, the TEV meters refrigerant into the indoor coil according to the heat load.

• Refrigerant Process: The refrigerant boils at a reduced temperature within the indoor coil, absorbs heat, and then vaporizes. The suction line carries this vapor back through the four-way reversing valve and into the compressor's suction.

• Discharge Gas Path: Discharge gas goes to the outdoor coil, where it rejects heat and condenses.

• Liquid Line Flow: The liquid refrigerant leaving the outdoor coil does not flow through the outdoor coil's TEV. Instead, it flows through the path of least resistance, which is typically a check valve. This prevents