The use of reciprocating chillers is less common in high-efficiency systems. However, these compressors can still be found in new chillers, primarily designed for low thermal loads.
The operation of a piston compressor chiller is as follows:
- The refrigerant, in its vapor state, is compressed by a piston inside a cylinder.
- A thin layer of oil prevents the refrigerant vapor from escaping the compression chamber and serves to lubricate the system and reduce friction.
- The piston is connected to the crankshaft via the piston rod.
- As the crankshaft rotates, it causes the piston to move back and forth within the cylinder.
- This reciprocating movement draws the refrigerant into the cylinder and compresses it.
- The compressed refrigerant is then discharged to the chiller condenser.
- The piston compressor is equipped with intake and discharge valves, which trap the refrigerant vapor inside the cylinder.
- During the intake stroke, the intake valve is open, while during the compression stroke, both valves are closed.
- As the pressure increases, the exhaust valve opens, allowing the refrigerant to escape.
- For applications requiring less cooling, the chiller with a piston compressor can regulate its capacity.
- This is achieved using a hot gas bypass valve located in the compressor discharge zone.
- The hot gas is directed to the suction or inlet of the evaporator to simulate heat. However, the hot gas method does not offer energy efficiency advantages and can maintain acceptable refrigerant speed for oil return.
- Most reciprocating compressors above 10 tons of refrigeration or 35 kW are equipped with cylinder unloaders to regulate their capacity.
- Unloaders work by deactivating and activating the passage of refrigerant to the piston compressor’s compression chamber.
- A solenoid valve controls the refrigerant flow, directing the pressurized compressor discharge refrigerant to the top to shut off and interrupt the refrigerant vapor flow to the cylinder suction.
- Although the piston continues to move back and forth inside the cylinder, it no longer performs compression as it cannot absorb refrigerant vapor.
For comprehensive learning about chillers, we have prepared a complete training program on chilled water installations with chillers.
