Chilled water systems are mainly used in large commercial HVAC air conditioning systems and industrial cooling applications although there are some residential and light commercial HVAC chilled water systems in use. Chilled water systems are popular because they use water as a refrigerant. Water is far less expensive than refrigerant. This makes them cost effective especially in commercial HVAC air conditioning applications. Instead of running refrigerant lines over a large area of the building water pipes are ran throughout the building and to evaporator coils in air handlers for HVAC air conditioning systems. The chilled water is pumped through these pipes from a chiller where the evaporator coil absorbs heat and returns it to the chiller to reject the heat.
Set Points and EvaporatorWhen the water returns to the chiller it is typically 10 degrees Fahrenheit warmer than when it left the chiller. Chiller set points are usually 45 degrees Fahrenheit unless a complex control system and algorithm is used so the return water temperature is typically 55 degrees Fahrenheit unless modern computer controls are used for set point control of the chiller and the chilled water system. Once the 55 degree Fahrenheit water returns to the chiller it enters the evaporator where the heat is absorbed into the refrigerant inside the chiller evaporator barrel. The refrigerant is then pumped into the compressor where it is compressed and sent to the condenser.
CondensersSome HVAC chiller condensers have air cooled condensers while others have water cooled condenser barrels and use a water tower to remove the heat from the water which is ran through the chiller water cooled condenser barrel. Chillers which are water cooled can cost more on initial purchase and installation because a water tower must be installed and piping ran to the water tower to distribute the water which cools the condenser. Air cooled chiller condensers do not need a water tower and generally require less maintenance and upkeep than a water cooled chiller system with a water tower.
Chiller TypesThere are two main types of chillers; the compression chiller and the absorption chiller. These are the most common types of chillers in use today. Compression chillers, depending on the size and load use different types of compressors for the compression process. Semi-hermetic, screw, scroll, and centrifugal compressors are the different types of compressors used in chillers.
- The compression chiller uses a compressor in the refrigeration process and requires all the major components of the refrigeration process.
- Metering Device
- The absorption chiller does not use a compressor for the refrigeration process. These systems use either a chemical process or natural gas to raise the temperature of the refrigerant and then use another chemical process to absorb the heat from the refrigerant.