Vapor compression chiller :
Based upon the condensation process of working fluid, there are two types of chiller:
1. Air cooled Chiller
2. Water cooled Chiller.
Air cooled Chiller & its working principle.
This types of chiller uses the ambient air to cool the refrigerant in the condenser. Fan suck the air through the condenser fins and so exchanging Heat from the refrigerant and into the air.
Advantages
• Simplified installation & higher reliability.
• Better low ambient operation( Below freezing weather conditions)
• Elimination of cooling tower
• Lower maintenance
• Eliminate concerns & Maintenance requirements related to cooling tower
• Reduce operation cost of cooling tower.
Disadvantages
• Higher condensing temperature & therefore condensing pressure means compressor to do work & consume more energy.
• Lifetime is short (approx. 15 to 20 years)
• Efficiency lesser at part load condition
• Higher ambient condition efficiency is less.
Water cooled Chiller & its working principle:
This type of chiller uses a shell and tube condenser to remove heat energy from the refrigerant. The refrigerant condenses from a gas and into a liquid on one side of the tubes. On other side of the tubes, the condenser cooling water is pumped through and so absorbing latent heat from the refrigerant.
The water flows up to a cooling tower where it cascades down through trays and into the sump. In the opposite direction ,air is blown up through the cooling tower and so creating the required heat exchange. The cooled condensed water is then pumped back to the chiller.
Advantages
1) Higher efficiency.
2) Longer lifetime(20 to 30 yrs).
3) Greater Efficiency due to lower condensing Temperature & pressure.
Disadvantages
1) Additional cost of cooling tower & Condenser pump
2) Cooling tower require Special control sequences, basin heaters or oven an indoor sump for safe operation in freezing weather
3) Maintenance requirements associated with water treatment, chiller condenser tube cleaning , tower mechanical maintenance, freeze protection & availability of makeup water with its quality.
Vapor compression Chiller types based on compressor used:
1. Scroll Chiller
2. Reciprocating Chiller
3. Centrifugal Chiller
4. Screw Chiller (or) Helical rotary
Scroll Chiller
1) Capacity of chiller less than 200 tons
2) 10 to 15 % more efficient then reciprocating because of 60% fewer moving parts.
3) Available in hermetic capacity up to 15 tons for use in water chiller
4) Multiple are used in single chiller to meet larger capacities.
Reciprocating Chiller
1) Available in capacity up to 100 tons.
2) Multiple compressor used in a single chiller for capacities up to 200 tons.
Centrifugal Chiller
1) Application : Medium to large cooling load
2) Capacity Range : 150 to 6000 tons.
3) Available in prefabricated chiller from 100 to 3000 tons & up to 8500 tons as built-up machines.
4) High efficiency, superior reliability, reduce sound levels, relatively low cost as compared to others.
Screw Chiller (or) Helical rotary
1) Its is available in both water & air cooled types.
2) Application : Small to medium cooling loads.
3) Capacity Range : 70 - 600 tons.
4) More reliable & better efficiency due to fewer moving parts.
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