CO₂ Heat Pump with Internal Heat Exchanger (IHX)

Heat pumps transfer heat from a low-temperature heat source to a higher-temperature heat sink and are widely used for space and water heating, industrial heat recovery, and simultaneous heating and cooling. CO₂ (R744) is a natural refrigerant with attractive thermodynamic and environmental properties for many heat-pump applications. This example demonstrates a CO₂ vapor-compression heat pump with an internal heat exchanger (IHX). The IHX transfers heat between the high- and low-pressure sides of the refrigerant loop, cooling the high-pressure CO₂ before expansion while heating the low-pressure CO₂ before compression. CO₂ absorbs heat from a water stream in the evaporator, is compressed to a higher pressure and temperature, and then transfers heat to a second water stream. The refrigerant subsequently passes through the IHX and expansion valve before returning to the evaporator, completing the cycle.