What happens to the capacity of a reciprocating compressor when the suction pressure is increased?

When the suction pressure of a reciprocating compressor is increased, the capacity of the compressor typically decreases. This occurs due to the relationship between suction pressure and the density of the refrigerant gas entering the compressor.

As the suction pressure rises, the density of the refrigerant gas decreases, which means less mass flow rate through the compressor for a given volumetric displacement. Since the compressor is designed to move a specific volume of refrigerant, a higher suction pressure results in a lower mass of refrigerant being compressed because the gas expands in the intake process. This ultimately reduces the overall capacity of the system to move heat.

Understanding this principle is critical when evaluating the performance of heat pumps and other refrigeration systems. Changes in suction pressure due to various factors, such as system load or ambient conditions, can significantly impact the efficiency and capacity of the equipment.