Chilled water system,Types of Water Chillers, Vapor-Compression Water Chillers
Water chillers are utilized in a spread of air con and process cooling applications. They cool water that's subsequently transported by pumps and pipes. The water passes through the tubes of coils to chill air in an air con system, or it can provide cooling for a producing or process . Systems that employ water chillers are commonly called chilled-water systems.
When designing a chilled-water system, one among the primary issues that has got to be addressed is to work out which sort of water chiller to use.
The refrigeration cycle may be a key differentiating characteristic between chiller types. The vapor-compression and absorption refrigeration cycles are the 2 commonest cycles utilized in commercial air con .
Types of water chillers
Water chillers using the vapor-compression refrigeration cycle vary by the sort of compressor used. Reciprocating, scroll, helical-rotary, and centrifugal compressors are common sorts of compressors utilized in vapor-compression water chillers.
Absorption water chillers make use of the absorption refrigeration cycle.
Vapor-compression water chillers use a compressor to maneuver refrigerant round the system. The most common energy source to drive the compressor is an electrical motor.
Vapor-compression water chillers use a compressor to maneuver refrigerant round the system. The most common energy source to drive the compressor is an electrical motor.
Absorption water chillers use heat to drive the refrigeration cycle. They do not have a mechanical compressor involved within the refrigeration cycle. Steam, hot water, or the burning of oil or gas are the foremost common energy sources for these sorts of chillers.
Vapor-Compression Water Chillers
In the vapor-compression refrigeration cycle, refrigerant enters the evaporator within the sort of a cool, low mixture of liquid and vapor (A). Heat is transferred from the relatively-warm air or water to the refrigerant, causing the liquid refrigerant to boil. The resulting vapor (B) is then drawn from the evaporator by the compressor, which increases the pressure and temperature of the refrigerant vapor.
The hot, high-pressure refrigerant vapor (C) leaving the compressor enters the condenser, where heat is transferred to ambient air or water at a lower temperature. Inside the condenser, the refrigerant vapor condenses into a liquid. This liquid refrigerant (D) then flows to the expansion device, which creates a pressure drop that reduces the pressure of the refrigerant thereto of the evaporator. At this low , alittle portion of the refrigerant boils (or flashes), cooling the remaining liquid refrigerant to the specified evaporator temperature. The cool mixture of liquid and vapor refrigerant (A) travels to the evaporator to repeat the cycle.
The type of compressor used generally has the best impact on the efficiency and reliability of a vapor compression water chiller. The improvement of compressor designs and therefore the development of latest compressor technologies have led to more-efficient and -reliable water chillers.
The reciprocating compressor was the workhorse of the tiny chiller marketplace for a few years . It was typically available in capacities up to 100 tons [350 kW]. Multiple compressors were often installed during a single chiller to supply chiller capacities of up to 200 tons [700 kW].
Scroll compressors have emerged as a well-liked alternative to reciprocating compressors, and are generally available in hermetic configurations in capacities up to fifteen tons [53 kW] to be used in water chillers. As with reciprocating compressors, multiple scroll compressors are often utilized in one chiller to satisfy larger capacities. In general, scroll compressors are 10 to fifteen percent more efficient than reciprocating compressors and have proven to be very reliable, primarily because they need approximately 60 percent fewer moving parts than reciprocating compressors. Reciprocating and scroll compressors are typically used in smaller water chillers, those but 200 tons [700 kW].
Helical-rotary (or screw) compressors are used for several years in air compression and low-temperature refrigeration applications. They are now widely utilized in medium-sized water chillers, 50 to 500 tons [175 to 1,750 kW]. Like the scroll compressor, helical-rotary compressors have a reliability advantage thanks to fewer moving parts, also as better efficiency than reciprocating compressors.
Centrifugal compressors have long been utilized in larger water chillers. High efficiency, superior reliability, reduced sound levels, and comparatively low cost have contributed to the recognition of the centrifugal chiller. Centrifugal compressors are generally available in prefabricated chillers from 100 to three ,000 tons [350 to 10,500 kW], and up to eight ,500 tons [30,000 kW] as built-up machines.
The capacity of a centrifugal chiller are often modulated using inlet guide vanes (IGV) or a mixture of IGV and a variable-speed drive (adjustable-frequency drive, AFD). Variable-speed drives are widely used with fans and pumps, and as a results of the advancement of microprocessor-based controls for chillers, they're now being applied to centrifugal water chillers. Using an AFD with a centrifugal chiller will degrade the chiller’s full-load efficiency. This can cause a rise in electricity demand or real-time pricing charges. At the time of peak cooling, such charges are often ten (or more) times the non-peak charges. Alternatively, an AFD offers energy savings by reducing motor speed at low-load conditions, when cooler condenser water is out there . An AFD also controls the inrush current at start-up. Certain system characteristics favour the application of an adjustable-frequency drive, including:
- A substantial number of part-load operating hours
- The availability of cooler condenser water
- Chilled-water reset control
Chiller savings using condenser- and chilled-water-temperature reset, however, should be balanced against the rise in pumping and cooling-tower energy. Performing a comprehensive energy analysis is that the best method of determining whether an adjustable-frequency drive is desirable. It is important to use actual utility costs, not a “combined” cost, for demand and consumption charges. Depending on the appliance , it's going to add up to use the extra money that might be needed to get an AFD to get a more efficient chiller instead. This is especially true if demand charges are significant.
The capacity of a centrifugal chiller are often modulated using inlet guide vanes (IGV) or a mixture of IGV and a variable-speed drive (adjustable-frequency drive, AFD). Variable-speed drives are widely used with fans and pumps, and as a results of the advancement of microprocessor-based controls for chillers, they're now being applied to centrifugal water chillers. Using an AFD with a centrifugal chiller will degrade the chiller’s full-load efficiency. This can cause a rise in electricity demand or real-time pricing charges. At the time of peak cooling, such charges are often ten (or more) times the non-peak charges. Alternatively, an AFD offers energy savings by reducing motor speed at low-load conditions, when cooler condenser water is out there . An AFD also controls the inrush current at start-up. Certain system characteristics favour the application of an adjustable-frequency drive, including:
- A substantial number of part-load operating hours
- The availability of cooler condenser water
- Chilled-water reset control
Chiller savings using condenser- and chilled-water-temperature reset, however, should be balanced against the rise in pumping and cooling-tower energy. Performing a comprehensive energy analysis is that the best method of determining whether an adjustable-frequency drive is desirable. It is important to use actual utility costs, not a “combined” cost, for demand and consumption charges. Depending on the appliance , it's going to add up to use the extra money that might be needed to get an AFD to get a more efficient chiller instead. This is especially true if demand charges are significant.
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