Two-Stage Flooded Ammonia Heat Pump

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. Ammonia (R717) is a natural refrigerant with excellent thermodynamic properties and is widely used in large industrial refrigeration and heat-pump systems. This example demonstrates a two-stage ammonia heat pump with a flooded evaporator and intermediate flash separation. In a flooded evaporator, excess liquid refrigerant is circulated through the evaporator so that the heat-transfer surface remains well wetted, while a separator separates the resulting vapor from the remaining liquid. This configuration is widely used in industrial ammonia systems because of its high heat-transfer performance. The refrigerant is compressed in two stages, reducing the pressure ratio across each compressor and enabling operation across a larger overall temperature lift. At high pressure, the ammonia transfers heat to the water to be heated before being expanded and returned through the lower-pressure parts of the cycle.