Explain the operational differences between a centrifugal chiller and an absorption chiller.

Centrifugal chillers and absorption chillers are two different types of cooling systems that operate on distinct principles. A centrifugal chiller uses mechanical energy to drive a compressor, which circulates refrigerant through a vapor-compression cycle. The refrigerant absorbs heat from the chilled water in the evaporator, causing it to vaporize. The compressor then increases the pressure and temperature of the refrigerant vapor. The high-pressure, high-temperature refrigerant vapor is then cooled and condensed back into a liquid in the condenser. Finally, the liquid refrigerant is expanded through an expansion device, reducing its pressure and temperature before returning to the evaporator to repeat the cycle. The key component is the centrifugal compressor, which uses rotating impellers to compress the refrigerant. An absorption chiller, on the other hand, uses heat energy as its primary energy source, rather than mechanical energy. It relies on the absorption process, where a refrigerant is absorbed by another substance, called the absorbent. The most common refrigerant-absorbent pair is water (refrigerant) and lithium bromide (absorbent). In an absorption chiller, the refrigerant (water) is evaporated in the evaporator, absorbing heat from the chilled water. The refrigerant vapor is then absorbed by the absorbent (lithium bromide) in the absorber, creating a solution. This solution is then pumped to the generator, where heat is applied to boil off the refrigerant vapor from the solution. The refrigerant vapor is then condensed back into a liquid in the condenser, rejecting heat. Finally, the liquid refrigerant is expanded through an expansion device before returning to the evaporator. The concentrated absorbent is returned to the absorber to repeat the cycle. The primary difference is that centrifugal chillers use mechanical energy to compress the refrigerant, while absorption chillers use heat energy to drive the refrigerant cycle through absorption and desorption processes. Absorption chillers are often used in applications where waste heat is available, as they can utilize this heat source to provide cooling.