Application Considerations
Condenser Water Limitations
Temperature
Trane centrifugal chillers start and operate over a range of load conditions with controlled water temperatures. Reducing the condenser water temperature is an effective method of lowering the chiller power input. However, the effect of lowering the condenser water temperature may cause an increase in system power consumption.
In many applicationsTrane centrifugal chillers can start and operate without control of the condenser water temperature. However, for optimum system power consumption, and for any applications with multiple chillers, control of the condenser water circuit is recommended. Integrated control of the chillers, pumps and towers is easily accomplished withTrane’s CH530 and/ orTracer system.
Chillers are designed to ARI conditions of 29.4°C (85°F), butTrane centrifugal chillers can operate to a five psig pressure differential between the condenser and evaporator at any steady state load without oil loss, oil return, motor cooling, refrigerant hang- up problems. And this differential can equate to safe minimum entering condenser water temperatures at or below 12.8°C (55°F), dependent on a variety of factors such as load, leaving evaporator temperature and component combinations.
Water Pumps
Avoid specifying or using 3600 rpm condenser and chilled water pumps. Such pumps may operate with objectionable noises and vibrations. In addition, a low frequency beat may occur due to the slight difference in operating rpm between water pumps and centrifugal motors. Where noise and
Water Flow
Today’s technology challenges ARI’s traditional design of three gpm per ton through the condenser. Reduced condenser flows are a simple and effective way to reduce both first and operating costs for the entire chiller plant. This design strategy will require more effort from the chiller. But pump and tower savings will typically offset any penalty.This is especially true when the plant is partially loaded or condenser relief is available.
In new systems, the benefits can include dramatic savings with:
•Size and cost for condenser lines and valves
•Size and cost of the cooling tower.
•Size and cost of the water pumps.
•Pump energy (30 to 35% reduction).
•Tower fan energy(30 to 35% reduction).
Replacement chiller plants can reap even greater benefits from low flow condensers. Because the water lines and tower are already in place, reduced flows would offer a tremendous energy advantage.Theoretically, a 2 GPM/ton design applied to a system that originally used 3 GPM/ton would offer a 70% reduction in pump energy. At the same time, the original tower would require a nozzle change but would then be able to produce about two degrees colder condenser water than before. These two benefits would again typically offset any extra effort required by the chiller.
Contact your localTrane Sales Office for information regarding optimum condenser water temperatures and flow rates for a specific application.
Water Treatment
The use of untreated or improperly treated water in a chiller may result in scaling, erosion, corrosion, algae or slime. It is recommended that the services of a qualified water treatment specialist be used to determine what treatment, if any, is advisable.The Trane Company assumes no responsibility for the results of untreated, or improperly treated water.
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