Large commercial buildings that require a substantial amount of cooling often use water chillers because they are cost effective and there is a reduced hazard by not having refrigerant piped all over the building.
These systems work by pumping cool water throughout the building. Cool air is then transferred to the occupied spaces by terminal devices located within the building or by using coils located in air handling units. Automatic valves at these terminal devices or cooling coils provide the air temperature control. In a large commercial building the heat absorbed by the water may be transferred to the outside air through a cooling tower.
Fundamentally, the function of the chilled water system is to transport the cooling fluid from the chillers, to the load terminals and back to the chillers to maintain space comfort. Because a chilled water system uses water as its secondary refrigerant, a chiller is used to remove heat from the water which is then circulated through other components to absorb the heat from the space.
Chilled water systems include both supply and return piping in a closed circuit, which means they are sealed from the atmosphere and do not need extensive chemical treatment to control contamination and corrosion. The water is cooled by the chiller and supplied to cooling coils or heat exchangers where it cools the air by absorbing energy. Once warmed, the water is returned to the chiller to start the process all over again. As the water cools in the chiller, absorbed energy is transferred through a refrigeration cycle to water circulating in the condenser system and is subsequently transferred to the outside of the building.
A distinct advantage of using water is the fact that it is non-corrosive, has specific heat value, it is non-toxic and inexpensive. This makes it an excellent choice when compared to other secondary refrigerants such as sodium chloride brines, propylene glycols, ethylene, methanol or glycerin. Another advantage to using a chilled water system to provide climate control is that water cooled chillers typically last longer than air cooled chillers. This is due to the fact that the air cooled chiller is installed outdoors, whereas the water cooled chiller
is installed indoors. Additionally, if it is well insulated, there’s no practical distance limitation to the length of a chilled water pipe.
Water chiller types include reciprocating, centrifugal and absorption chillers. Reciprocating water chillers use piston-type, positive displacement compressors which are found in small and medium capacity systems. Centrifugal chillers are the most commonly used in commercial water chillers and are found in a medium and large capacity systems. Absorption chillers, found in large capacity systems, use water as a refrigerant and steam to cause a water and lithium bromide solution to separate. A chilled water system that uses more than one type of fuel is referred to as a hybrid system and absorption chillers are the preferred choice to run on fuels such as natural gas, fuel oil or even waste heat in the form of steam or hot water.