11-09-2014, 10:17 AM
CHILLER PLANT
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INTRODUCTION:
A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required. As a necessary byproduct, refrigeration creates waste heat that must be exhausted to ambient or, for greater efficiency, recovered for heating purposes. Concerns in design and selection of chillers include performance, efficiency, maintenance, and product life cycle environmental impact
APPLICATIONS
Use in air conditioning
In air conditioning systems, chilled water is typically distributed to heat exchangers, or coils, in air handling units or other types of terminal devices which cool the air in their respective space(s), and then the water is re-circulated back to the chiller to be cooled again. These cooling coils transfer sensible heat and latent heat from the air to the chilled water, thus cooling and usually dehumidifying the air stream can be referred to as a water purifying because it also contained elements such as condenser for cooling. A typical chiller for air conditioning applications is rated between 15 and 1500 tons (180,000 to 18,000,000 BTU/h or 53 to 5,300 kW) in cooling capacity, and at least one manufacturer can produce chillers up to 6,000 tons of cooling. Chilled water temperatures can range from 35 to 45 °F (2 to 7 °C), depending upon application requirements
Use in industry:
In industrial application, chilled water or other liquid from the chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries. They are often used in the plastic industry in injection and blow molding, metal working cutting oils, welding equipment, die-casting and machine tooling, chemical processing, pharmaceutical formulation, food and beverage processing, paper and cement processing, vacuum systems, X-ray diffraction, power supplies and power generation stations, analytical equipment, semiconductors, compressed air and gas cooling. They are also used to cool high-heat specialized items such as MRI machines and lasers, and in hospitals, hotels and campuses.
Chillers for industrial applications can be centralized, where a single chiller serves multiple cooling needs, or decentralized where each application or machine has its own chiller. Each approach has its advantages. It is also possible to have a combination of both centralized and decentralized chillers, especially if the cooling requirements are the same for some applications or points of use, but not all.
Decentralized chillers are usually small in size and cooling capacity, usually from 0.2 tons to 10 tons. Centralized chillers generally have capacities ranging from ten tons to hundreds or thousands of tons
OPERATION:
Vapor-compression chiller technology:
There are four basic types of compressors used in vapor compression chillers: Reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical machines that can be powered by electric motors, steam, or gas turbines. They produce their cooling effect via the "reverse-Rankine" cycle, also known as 'vapor-
CONSTRUCTION AND WORKING:
The chiller can be water-cooled, air-cooled, or evaporative cooled. The compressors
Types typically are reciprocating, scroll, screw or a centrifugal. The evaporator can be
remote from the condensing section on air cooled units. This has the advantage of allowing
the chilled water loop to remain inside the building envelope when using in outdoor chiller.
There can be multiple chillers in chilled water plant. The details of variable multiple chiller
Plants designs will be discussed in future sections. The chilled water flows through the
evaporator ofchiller. The evaporator is a heat exchanger where the chilled gives ups it
Sensible heat and transfer the heat to the refrigerant as latent energy
CONDENSER
In system involving heat transfer, a condenser is a device or unit used to condense a
Substance from its gaseous to its liquid state, typically by cooling it. In so doing, the
Latent heat is given up by the substance, and will transfer to the condenser coolant.
Condensers are typically heat exchangers which have various designs and come in many
Sizes ranging from rather small to very large industrial scale units used in plant process.
For an example, a refrigerator uses a condenser to get rid of heat extracted from the interior
Of the unit to the outside air. Condensers are used in air conditioning, industrial chemical
Processes such as distillation, steam power plant and other heat-exchange systems. Use
of cooling water or surrounding air as the coolant is common in many condensers.
Shell and coil type
These condensers used up to 50TR capacity. The water flows through the multiple
Coils, which may have fins to increase the heat transfer coefficient. The refrigerant flows
Through the shell in smaller capacity condensers, refrigerant flow through the coil while
The coil cleaning is done by circulating suitable chemical through the coils.
Shell-and- tube type
It is the most common type of condenser used from 2TR up to thousands of TR capacity.
In this condenser the refrigerant flowing through the shell and water flowing through the
Tubes in single to four passes. The condensed refrigerant collect at the bottom of the
Shell. The coldest water contacts the liquid refrigerant. So that the sub cooling is obtained.
The liquid refrigerant is drained from the bottom. to the receiver. The shell also as a receiver
The refrigerants reject that to the surrounding from the shell. The most common type is
Horizontal shell type. Vertical shell and tube type condensers usually used with ammonia
In large capacity so that the cleaning of the tube is possible from top. While the plant is
Working.
EVAPORATOR:
The cold refrigerant liquid enters in the chiller, where the flow of refrigerant liquid and
Water is separated; there is a no direct contact between water and cold liquid. Heat
Exchange takes place between cold refrigerant liquid and water. Change of phase
takes place. The cold water in chillers’ is circulated to heat exchanger. Where further cooling
Water present. This cooled water is used to maintain paint temperature. Refrigerant gas
flows through suction line to compression and process continues.
Natural draft cooling towers
The natural draft or hyperbolic cooling tower makes use of the difference in temperature
between the ambient air and the hotter air inside the tower. As hot air moves upwards
through the tower (because hot air rises), fresh cool air is drawn into the tower through
an air inlet at the bottom. Due to the layout of the tower, no fan is required and there is
almost no circulation of hot air that could affect the performance. Concrete is used for the
tower shell with a height of up to 200 m. These cooling towers are mostly only for large
Absorption technology works:
The thermodynamic cycle of an absorption chiller is driven by a heat source; this heat is usually delivered to the chiller via steam, hot water, or combustion. Compared to electrically powered chillers, an absorption chiller has very low electrical power requirements - very rarely above 15 kW combined consumption for both the solution pump and the refrigerant pump. However, its heat input requirements are large, and its COP is often 0.5 (single-effect) to 1.0 (double-effect). For the same tonnage capacity, an absorption chiller requires a much larger cooling tower than a vapor-compression chiller. However, absorption chillers, from an energy-efficiency point-of-view, excel where cheap, high grade heat or waste heat is readily available. In extremely sunny climates, solar energy has been used to operate absorption chillers.
The single effect absorption cycle uses water as the refrigerant and lithium bromide as the absorbent. It is the strong affinity that these two substances have for one another that makes the cycle work. The entire process occurs in almost a complete vacuum.
1. Solution Pump : A dilute lithium bromide solution (63% concentration) is collected in the bottom of the absorber shell. From here, a hermetic solution pump moves the solution through a shell and tube heat exchanger for preheating.
2. Generator : After exiting the heat exchanger, the dilute solution moves into the upper shell. The solution surrounds a bundle of tubes which carries either steam or hot water. The steam or hot water transfers heat into the pool of dilute lithium bromide solution. The solution boils, sending refrigerant vapor upward into the condenser and leaving behind concentrated lithium bromide. The concentrated lithium bromide solution moves down to the heat exchanger, where it is cooled by the weak solution being pumped up to the generator.
3. Condenser : The refrigerant vapor migrates through mist eliminators to the condenser tube bundle. The refrigerant vapor condenses on the tubes. The heat is removed by the cooling water which moves through the inside of the tubes. As the refrigerant condenses, it collects in a trough at the bottom of the condenser.
4. Evaporator : The refrigerant liquid moves from the condenser in the upper shell down to the evaporator in the lower shell and is sprayed over the evaporator tube bundle. Due to the extreme vacuum of the lower shell [6 mm Hg (0.8 kPa) absolute pressure], the refrigerant liquid boils at approximately 39 °F (4 °C), creating the refrigerant effect. (This vacuum is created by hygroscopic action - the strong affinity lithium bromide has for water - in the Absorber directly below.)
5. Absorber : As the refrigerant vapor migrates to the absorber from the evaporator, the strong lithium bromide solution from the generator is sprayed over the top of the absorber tube bundle refrigerant vapor into the lithium bromide solution also generates heat which is removed by the cooling water. Now the dilute lithium bromide solution collects in the bottom of the lower shell, where it flows down to the solution pump. The chilling cycle is now completed. The strong lithium bromide solution actually pulls the refrigerant vapor into solution, creating the extreme vacuum in the evaporator. The absorption of the and the process begins once again.[2]
WATER COOLED CHILLER
A water chiller] is a mechanical device used to facilitate heat exchange from water to a refrigerant in a closed loop system. The refrigerant is then pumped to a location where the waste heat is transferred to the atmosphere.
In hydroponics, pumps, lights and ambient heat can warm the reservoir water temperatures, leading to plant root and health problems. For ideal plant health, a chiller can be used to lower the water temperature below ambient level; 68°F (20°C) is a good temperature for most plants. This results in healthy root production and efficient absorption of nutrients.
In air conditioning, chilled water is often used to cool a building's air and equipment, especially in situations where many individual rooms must be controlled separately, such as a hotel. A chiller lowers water temperature to between 40° and 45°F before the water is pumped to the location to be cooled.
Industrial chiller technology
Industrial chillers typically come as complete, packaged, closed-loop systems, including the chiller unit, condenser, and pump station with recirculating pump, expansion valve, no-flow shutdown, internal cold water control. The internal tank helps maintain cold water temperature and prevents temperature spikes from occurring. Closed-loop industrial chillers recirculate a clean coolant or clean water with condition addititives at a constant temperature and pressure to increase the stability and reproducibility of water-cooled machines and instruments. The water flows from the chiller to the application's point of use and back.
If the water temperature differentials between inlet and outlet are high, then a large external water tank would be used to store the cold water. In this case the chilled water is not going directly from the chiller to the application, but goes to the external water tank which acts as a sort of "temperature buffer." The cold water tank is much larger than the internal water water goes from the external tank to the application and the return hot water from the application goes back to the external tank, not to the chiller.
The less common open loop industrial chillers control the temperature of a liquid in an open tank or sump by constantly recirculatingRDT it. The liquid is drawn from the tank, pumped through the chiller and back to the tank. An adjustable thermostat senses the makeup liquid temperature, cycling the chiller to maintain a constant temperature in the tank.
CONCLUSION
R22 gas can be replaced by R134.because of its environmental friendly in nature. water
cooled units make less noise and give cooling per square foot. While air cooled chillers have
comparatively less cooling per square foot. And are more noisy machines.
From the above study, it is more beneficial to go for water cooled chillers instead of air
cooled chillers.