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Different Type Of Chillers &

Their Application
There are basically two types of chillers which may be classified
according on their refrigerent cycles and applications. Examined here
are different types of chillers and their various applications.
A chiller is a heat transfer device that uses refrigeration system to remove
heat from a process load and transfers the heat to the environment. Chillers
may also be seen as cooling machines of choice to condition industrial,
commercial, and institutional facilities.
They are used to lower the temperatures of all kinds of equipment and
processes such as: robotic machinery; semiconductors; injection and blow
molding machines; welding equipment; die-casting and machine tooling;
paper and cement processing; power supplies; power generation stations;
compressed air and gas cooling systems; medical imaging machines;
chemical, drug, food and beverage production; even simply to cool potable
water to desirable levels. Whether for office comfort, keeping data server
centres from overheating, or specialized industrial processes, water
temperature control plays a vital role in many of the behind-the-scenes
activities that affect our everyday lives.
A chiller consists of a reservoir that is filled with a fluid such as water or
ethylene glycol/water mixture which is continually circulated. In a typical
building application, chilled water is circulated to air-handlers or now the
increasingly used chilled beams in order to transfer heat from air to water, or
stated the other way, transfer cooling from the water to the building air. The
schematic diagram of a chiller plant is shown in figure 1.

Figure 1: Schematic diagram of a chiller Plant

Types Of Chillers
Chillers can primarily be classified as absorption chillers and refrigerant
compression chillers, based on the refrigerant cycle on which they work.
Cooling processes are significantly different in the two types of chillers.
Absorption chillers use a heat source such as natural gas or steam to create
refrigeration or cooling effect. Refrigerant chillers use mechanical
compression and are the most common. Refrigerant compression chillers
consist of four main components - a compressor, an evaporator, a condenser
and a valve metering system. Basically, a refrigerant gathers heat, and then
uses an evaporator heat exchanger to remove that heat.
There are two main types of refrigerant compression chillers, air and water. Air
condensers are cooled by utilizing the air, whereas water condensers are
cooled by using water sources. Water cooled chillers are generally located
within the building and use cooling towers, a pond, or river located near the
building to reject water’s heat from the condenser.
Chillers with condensers cooled by air operate essentially the same as those
cooled by water regarding the refrigerant cycle and the steps along the way.
The cooling medium on the condenser is of course air instead of water. Air
cooled chillers are intended for outdoor installation and operation.
These reject heat to the atmosphere by mechanical means such as circulation
of outdoor air by a fan directly through the machine’s condenser. These types
of condenser cooled units do not require a cooling tower as is common with
water cooled chillers since the air rejects heat to the atmosphere. Based on
compression method of the refrigerant in its vapour phase, chillers can also be
classified into four categories. The compressors may be reciprocating,
centrifugal, rotary screw and rotary scroll type.
Reciprocating compressors possess a crankshaft and pistons. The pistons
compress the gas and the gas is heated. The hot gas is discharged to the
condenser. The pistons have intake and exhaust valves that can be opened
on demand to allow the pistons to idle. A few examples of this would be in an
office or school, but not necessarily in a hotel or an apartment building.
Common capacities range from 20 to 125 tons but can even get up to 450
tons. Centrifugal compressors operate much like a centrifugal water pump.
They contain an impeller that compresses the refrigerant. Centrifugal chillers
can provide a very high cooling capacity in a compact design. They have the
ability to vary capacity continuously to match a wide range of load fluctuations
with near proportional changes in power consumption. This provides tight
temperature control and energy conservation.
The capacity can range from 150 tons up to 2400 tons. Rotary screw or helical
DNA type compressors have two mating helically grooved rotors. As the rotors
rotate, the gas is compressed by volume reduction between the two rotors.
These helixes require high tolerances to fit perfectly, thus driving up the initial
cost.
Capacity is controlled by a sliding inlet valve or variable-speed drive (VSD) on
the motor. Capacities range from 25 to 450 tons with the largest capable of
800 tons. Rotary scroll compressors use two spirals to pump and compress
the refrigerant. Commonly, one of the scrolls is fixed while the other orbits
eccentrically without rotating within the other fixed scroll.
This motion traps and compresses pockets of fluid between the scrolls. This
design and operation makes them the most efficient of the four compressor
types. The capacity of single refrigerant loop scroll compressor ranges from 2
to 25 tons. Typical chilled water cooling temperature ranges between 39-45
°F. The classification of chillers from various aspects has been shown in Fig.2.
For proper heat transfer between the circulated water to be cooled and the
refrigerant, it is important to maintain sufficient chiller water flow. The
commonly recommended range of chilled water flow velocity is between 3 and
12 feet per second. Therefore, it is very important for a chiller to maintain this
flow for proper efficiency and corresponding energy usage as well as
maintaining long-term performance.

Absorption Chillers
Absorption chiller is a machine which operates based on vapour absorption
refrigeration cycle. This cycle consists of four major heat exchangers,
(generator, condenser, evaporator and absorber) with two kinds of solution,
(refrigerant and absorbent). During this cycle high pressure will prevail inside
generator and condenser, while inside evaporator and absorber there will be
low pressure. The cycle starts with input waste heat in the generator. As a
result of this heat input, the solution in the generator will be separated into
refrigerant and weak solution. The refrigerant in the vapour form will enter into
condenser and will change into liquid. The solution part will enter absorber,
since there is a pressure difference between condenser and evaporator, the
refrigerant will flow inside evaporator and will absorb heat from cooled water
that is in circulation inside evaporator. Consequently, the temperature of
circulated water decreases and then it is used for air-conditioning purpose.
The evaporated refrigerant will then enter absorber where it will be mixed with
weak solution, the mixture will then get the liquid state and finally it will enter
generator and the cycle is repeated. The schematic diagram of the vapour
absorption refrigeration cycle has been shown in Fig. 3.

Vapour Compression Chillers

The schematic diagram of chiller based on vapour compression refrigeration
cycle has been shown in Fig.4. Refrigerant gets vaporized by taking heat
from chilled water in evaporator thus serving its prime purpose. Refrigerant
comes out of evaporator as vapour but on other side chilled water is
produced. Thus, heat is added to refrigerant at constant pressure but is
extracted from chilled water. Both refrigerant and chilled water don’t get mixed
and are separated by some solid wall in between them in evaporator like shell
and tube design. Refrigerant vapours come out of evaporator and then
compressed by chiller compressor to high pressure and temperature.
Compressor requires energy input for its working and hence electric energy is
supplied to it. Refrigerant vapour rejects heat to outside cooling liquid or air.
Refrigerant in condensed or liquid form coming out of condenser is expanded
in expansion valve and its pressure and temperature are reduced to level of
evaporator so that above cycle is repeated again.
Applications

A chiller can be realized as a refrigeration system that cools water. Air

conditioners and dehumidifiers condition the air while a chiller, using the same
refrigerating operations, cools water, oil, or some other fluid. This chilled
solution can then be used for cooling in a wide range of operations. Some of
the most common applications are as follow:
1. Plastics Industry: Cooling the hot plastic that is injected, blown, extruded or
stamped.
2. Printing Industry-Cooling warm rollers due to friction and ovens curing the
ink, along with ultraviolet lamps also for curing purposes.
3. Medical Industry: MRI Systems-The hospital MRI units need to be cooled to
operate properly.
4. HVAC Industry: Large scale air-conditioning systems pump this chilled
water to coils in specific areas of high rise buildings. The air handling systems
for each area open and close the water flow through specific area keeping the
air of the rooms at a desired temperature.
5. Laser Cutting Industry: Technology has created machines that can cut out
very specific steel products with the precise use of a laser cutting machine.
These lasers run at very high temperatures and must be cooled to run
properly.
6. Brewery Industry- The cooling of the kettles in fermentation has become an
upcoming industry where chiller have been used to keep the kettles and
storage area of beer at cold temperatures.