View A Video on Chillers - A Quick Introduction
Chillers
Chillers can be used either for air conditioning or for material and process cooling. Process chillers cool products and machinery in processes such as plastic injection molding, blow molding, metalworking, welding, die casting, chemical and pharmaceutical processing, food and beverage processing, lab equipment, photographic processing, medical imaging machines, gas cooling and lasers. In plastic forming, for example, chillers reduce cycle times in injection molding by quickening the cooling process. Chocolate manufacturers often use chillers to regulate the chocolate's temperature during processing to keep it from burning. Printing presses require chiller systems for rolling and pressing to reduce bleeding and stretching of photographs. Some specific types of industrial chillers and medical chillers include water chillers, recirculating chillers, absorption chillers, air cooled chillers, water cooled chillers, centrifugal chillers and screw chillers.
Chillers use either absorption or vapor-compression refrigeration cycles to produce their cooling effect. Both cycles use a refrigerant that strategically absorbs heat in one place as it evaporates and then releases heat in another place as it condenses. In most chillers this occurs in a four-stage cycle of pressurization, condensation, depressurization, and evaporation. First, the refrigerant vapor is pressurized, either by heating or by means of a compressor. Second, the refrigerant moves into a condenser comprised of a coil or set of tubes with either water or air circulating around it. The refrigerant vapor cools inside the condenser and changes into a liquid, rejecting a large amount of heat in the process. This heat is absorbed and borne away by the water or air flowing around it. Thirdly, the refrigerant liquid proceeds through an expansion valve that decreases the pressure and allows for evaporation to take place. The flash evaporation that occurs at the expansion valve cools the liquid drastically. Lastly, the cold fluid moves into the heat exchanger or evaporator, where the remaining liquid refrigerant evaporates as it absorbs heat from the process (direct cooling) or process coolant (indirect cooling). In recirculating chillers, the refrigerant vapor is then drawn into the first compression stage to start the cycle over again.
Chillers come in a variety of types. Absorption chillers use a heat source to drive the refrigeration cycle, while vapor-compression chillers use a compressor to drive the cycle. The advantage of the absorption model is that it requires much less electricity, and can be powered by heat sources that might otherwise be wasted, such as heat-producing machinery or solar rays. On the other hand, vapor-compression is a readily-accessible and time-tested technology with more versatility and easier installation. There are a number of different types of vapor-compression chillers according to the type of gas compressor they use, the most common being centrifugal compressors, screw compressors and scroll compressors. Portable chillers usually use scroll compressors because they are the most compact and quiet. Another distinction between chillers has to do with the condenser. Condensers can be air cooled, water cooled or evaporation cooled. Air cooled chillers facilitate condensation of the refrigerant by blowing ambient air over the condenser coil or tubes and exhausting the hot air into the atmosphere, or in some cases using it to help heat the facility during the winter. Evaporation cooled chillers operate in the same way as air cooled chillers, except they introduce a mist of water in the air, the evaporation of which makes the heat transfer more efficient. Water cooled chillers employ a flow of water to take heat from the refrigerant in the condenser. This is the most effective condensing method, but also requires a constant source of cool water, and in most cases also necessitates an outdoor cooling tower and a pump to get the heated water there.
When installing a chiller system, there are a number of important considerations. Foremost is cooling capacity. Industrial chillers are measured by their cooling capacity in terms of tons, each ton being roughly equivalent to the heat of fusion of one ton of ice, or 12,000 Btu/h. Capacities range from portable chillers with fractions of a ton to permanent multi-unit "plants" with cooling capacities of thousands of tons. Another significant decision is the sort of refrigerant; this will mostly depend on the range of temperatures the chiller will face. Common refrigerant choices include water, ammonia, carbon dioxide, sulfur dioxide, alcohol, brine and methane. Fluorocarbons, especially chlorofluorocarbons (CFCs) have also been used widely as refrigerants, but they are decreasingly common because of their ozone depletion effects. Other specifications to look at include condenser and evaporator flow rates, power source, cooling capacity, efficiency, location, compressor type and compressor horsepower. Most chillers also come with a local and/or remote control panel with temperature and pressure indicators and emergency alarms. When configured properly, chillers can provide simple and effective solutions for many process cooling and industrial air conditioning applications.
Chiller Types
- Absorption chillers are liquid chillers that use heat to drive the cooling process by means of an absorption refrigeration cycle.
- are chillers that use ambient air to facilitate the condensation of the refrigerant during the condensing phase of the refrigeration cycle. They are the most common chiller type of chiller.
- consist of air handling units fitted with chilled water
coils and are utilized in air condition systems.
- Centrifugal chillers are a type of vapor-compression chiller that uses a centrifugal compressor to drive the refrigeration cycle.
- Chiller systems integrate a number of pieces of equipment in order to provide cooling for industrial processes or facilities.
- are
used to remove heat from an area.
- operate
year-round and are designed to provide specific, capacity-matched cooling
protection and proper temperature/water flow. Dedicated-process chillers
are the best choice for medical applications.
- are uncommon but highly efficient liquid chillers.
Evaporative chillers maintain the lowest condensing temperatures,
which range from 85° F to 105° F.
- provide
process cooling using a secondary fluid.
- are
often installed outside and are available in centralized and modular
designs. HVAC chillers are used in industrial and commercial environments.
- are
refrigeration systems that are used to chill various liquids in industrial
settings.
- are
refrigeration systems that remove heat from various liquids.
- Liquid coolers are typically recirculating chiller systems which recycle the same refrigerant liquid within a closed loop.
- lower
the temperature of coolant that is used in the cutting zone and recirculate
it back to the machine tool in a closed-loop system.
- are
self-contained chillers with higher pressure pumping, temperature stability
and microprocessor controls.
- are
self-contained units and are useful in small and/or dedicated applications.
- Process chillers are chillers specifically designed to cool materials and machines during manufacturing and other industrial and laboratory processes, as opposed to HVAC chillers that are specifically designed for air conditioning.
- constantly
circulate coolant in a closed loop, retaining high efficiency without
wasting water.
- Screw chillers are a type of vapor-compression chiller that uses a rotary screw compressor to drive the refrigeration cycle.
- consist
of a compressor, condenser and chiller with internal piping and controls
all contained within a single unit. The term "water chillers" refers
also to an overall package that includes a refrigeration plant, water
chiller and air or water cooled condenser.
Chiller Terms
- The surrounding environment, including
temperature, pressure and/or humidity, coming into contact with a system
or component.
- Mineralized water consisting of sodium chloride, metallic
and/or organic contaminants.
- A measurement unit reflecting the
amount of heat needed to change the temperature of one pound of water
one degree Fahrenheit.
- Tube located between the condenser and evaporator
that manages the refrigerant flow.
- A chilling system that is self-contained.
A central chilling system has more than one unit and more than one compressor
but no pump tank set.
- A gas consisting of chlorine,
fluorine and carbon that has been used as a refrigerant in such items
as liquid
chillers. CFCs cause ozone depletion, because they do not break down
upon release into the atmosphere, but mix with ultraviolet light to create
carbon dioxide, and eventually ozone-eating chlorine radicals.
- The
measurement of a refrigeration system's efficiency that compares
the system's cooling ability
with the heat input necessary to attain such cooling. COP is calculated
by dividing a system's cooling ability by the system's heat
input and is expressed in BTU/hr.
- A device that
increases pressure on a gas through the act of pumping. Compressors are
responsible for the compaction of
the vaporized refrigerant to a pressure level suitable for liquification,
which occurs in the condenser.
- A device that removes
heat via forced air, water coil, etc., in order to convert a high pressure
gas into a lower pressure liquid.
Condensers remove heat from the compressed vaporized refrigerant, at
which point, the refrigerant returns to a liquid state.
- The
central part of a refrigeration system in which the system is operated
and maintained.
- A liquid used to remove heat.
- Indicates
the efficiency of an air conditioner or cooling system by comparing the
amount of energy needed
to produce cooling with the quality of the system's cooling ability
and is calculated by dividing the system's BTU by its wattage.
For example, if a cooling system maintains 20,000 BTUs and uses 1,500
watts,
the system's energy efficient rating would equal 13.3.
- Consists of a tube inside which the refrigerant soaks
up heat from it surroundings, boils and changes to a vapor.
- Mechanism located between the evaporator and
condenser that controls the refrigerant flow into the evaporator and
controls the temperature of the evaporator.
- Removes moisture and contaminants from vaporized
refrigerants.
- A device that
transfers heat from one fluid to another without mixing the fluids. (Heat Exchangers)
- A substance containing
chlorine, fluorine, carbon and hydrogen that is used as an alternative
to CFCs
as a refrigerant and a propellant. HCFCs produce fewer effects on than
ozone layer than CFCs do.
- A substance containing hydrogen, fluorine
and carbon that is used to replace CFCs and HCFCs because of HFCs lack
of effect on the ozone layer. HFCs produce no ozone depletion because
the substance does not contain chlorine, which breaks down the ozone
layer.
- A process that utilizes light to cool atoms to
a very low temperature.
- A molecule containing three oxygen atoms that absorbs ultraviolet
radiation in the stratosphere. Ozone also remains a harmful component
of smog and can contribute to lung damage and respiratory problems.
- A relative measurement of a substance's
negative effect on the ozone layer as compared to the effects of CFC-11,
which has an ODP of 1, on the ozone. For instance, a substance with an
ODP of 2 can potentially cause approximately twice the ozone depletion
as CFC-11 could.
- Also referred
to as the stratospheric ozone, it is the protective atmospheric layer
in the stratosphere, located 12-30
miles (20-50 kilometers) above sea level, in which ultraviolet radiation
is absorbed.
- The storage area for condensed liquid refrigerants.
- Liquids that produce cooling upon evaporation.
- Unit equal to 12,000 BTUs that refers to the
size of the chiller unit.
- A window in a refrigeration system through which
specialists can view the inner workings of the system.
- Mechanism
in a refrigeration system that controls the flow of refrigerant, especially
into the expansion valve.
- The
total amount of carbon dioxide that a refrigeration system can produce
throughout its lifetime.
