Key Components of Mechanical Compression Chillers

Key Components of Mechanical Compression Chillers



Chillers produce chilled water in the evaporator where cold refrigerant flows over the evaporator tube bundle. The refrigerant evaporates (changes into vapor) as the heat is transferred from the water to the refrigerant. The chilled water is then pumped, via the chilled-water distribution system to the building’s air-handling units.

The chilled water passes through coils in the air-handler to remove heat from the air used to condition spaces throughout the building. The warm water (warmed by the heat transferred from the building ventilation air) returns to the evaporator and the cycle starts over.

Vaporized refrigerant leaves the evaporator and travels to the compressor where it is mechanically compressed, and changed into a high-pressure, high-temperature vapor. Upon leaving the compressor, the refrigerant enters the condenser side of the chiller.

Inside the water-cooled condenser, hot refrigerant flows around the tubes containing the condenser-loop water. The heat transfers to the water, causing the refrigerant to condense into liquid form. The condenser water is pumped from the condenser bundle to the cooling tower where heat is transferred from the water to the atmosphere. The liquid refrigerant then travels to the expansion valve.

The refrigerant flows into the evaporator through the expansion valve or metering device. This valve controls the rate of cooling. Once through the valve, the refrigerant expands to a lower pressure and a much lower temperature. It flows around the evaporator tubes, absorbing the heat of the chilled water that’s been returned from the air handlers, completing the refrigeration cycle.

Newer chillers are controlled by sophisticated, on-board microprocessors. Chiller control systems include safety and operating controls. If the equipment malfunctions, the safety control shuts the chiller down to prevent serious damage to the machine. Operating controls allow adjustments to some chiller operating parameters. To better monitor chiller performance, the chiller control system should communicate with the facility’s direct digital control (DDC).
Safety Issues

Chillers are typically located in a mechanical equipment rooms. Each type of refrigerant used in a chiller compressor has specific safety requirements for leak detection and emergency ventilation. Consult your local mechanical code or the International Mechanical Code for details.

The EPA has enacted regulations regarding the use and handling of refrigerants to comply with the Clean Air Act of 1990. All personnel working with refrigerants covered by this act must be appropriately licensed.