Chillers are machines that utilize a refrigeration cycle to remove heat from various liquids and release it into the atmosphere. The next step in the chilling process involves directing the chilled liquid, or coolant, to a heat exchanger to cool air, process equipment, or another liquid. Chillers come in a wide range of designs and sizes. For smaller applications, chillers may be manufactured as localized, small, or portable units. Alternatively, large chillers can be designed to keep entire facilities cool.
Chillers utilize vapor-compression or absorption processes to carry out their cooling functions. Both of these processes involve a refrigerant that absorbs heat from a particular place. Next, as it condenses, it evaporates and releases the heat in a different place. In the majority of chillers, a four-stage cycle takes place: pressurization, condensation, depressurization, and evaporation.
The first step consists of pressurizing the refrigerant vapor. Second, the refrigerant is transferred into a condenser, which features a set of coiling tubes with air or water circulating around it. Within the condenser, the refrigerant vapor cools and is converted into a liquid. In this process, a significant amount of heat is removed.
The heat is absorbed by the water or air circulating around the tubes. Third, the newly refrigerated liquid moves to an expansion valve, where the liquid is depressurized. Evaporation is now able to occur, causing an extreme decrease in the liquid’s temperature. The final step in the process involves the chilled liquid moving into an evaporator or heat exchanger, which evaporates the liquid and absorbs the heat.
In recirculating chillers, the vaporized refrigerant is forced back into the first stage of the process. Some of the most common types of refrigerants are R410A, R134A and R407C.
There is a wide range of types of chillers. Absorption chillers are a type of chiller that drive the refrigeration cycle using a source of heat. Vapor-compression chillers, on the other hand, drive the cycle using a compressor. One benefit of absorption chillers is that they do not use as much electricity, and can instead be solar powered or generated by heat-producing machinery.
Alternatively, vapor-compression chillers are time-tested, easily accessible, and can be installed more easily than its counterpart. Vapor compression chillers come in different types, and are classified by the type of gas compressor they use. The most common types available are centrifugal compressors, screw compressors, and scroll compressors. Scroll compressors are commonly found in portable chillers, due to their compact and quiet nature.
Chillers can also be distinguished from the type of condenser they use—whether the condensers are air cooled, water-cooled, or evaporation cooled. Air cooled chillers blow ambient air over the condenser and then release the hot air into the atmosphere. Because of the way this compressor releases heat, it can be used to heat a facility in colder weather.
Evaporation cooled chillers operate in a similar fashion, but they evaporate a mist of water that was pre-released into the air. Evaporating the water increases the efficiency of the transfer of heat.
Water cooled chillers utilize flowing water to extract heat from a refrigerant. Although this type of condensing process is the most effective, it needs a consistent water source, and often requires a pump and a cooling tower.
There are quite a few key points to consider in installing a chiller system. First, one needs to consider the machine’s cooling capacity. The cooling capacity of an industrial chiller is measured in tons, or Btu/h. Coolers can be found in a multitude of capacities. For instance, a small portable chiller may have a capacity of a small fraction of a ton.
On the other end, a cooler can consist of multiple units and have thousands of tons’ worth of capacity. The next thing to consider is the type of refrigerant, which will depend on the temperatures that the chiller will be exposed to. Popular refrigerants are methane, brine, alcohol, sulfur dioxide, carbon dioxide, ammonia, and water. Another widely used refrigerant have been fluorocarbons and chlorofluorocarbons, or CFCs. CFCs have decreased in popularity over the years because of its capability to deplete the ozone.
Other important factors include its power source, cooling capacity, evaporator flow rate, and compressor horsepower. Some features that can be found on certain chillers include emergency alarms, pressure indicators, and a remote control panel. Chillers can be effective for a multitude of processes and applications if the appropriate specifications are chosen.