Trane CVGF Application Considerations, Condenser Water Limitations, Temperature, Water Pumps

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 applications Trane 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 with Trane’s AdaptiView and/or Tracer system.

Chillers are designed to ARI conditions of 29.4°C (85°F), but Trane centrifugal chillers can operate to a fi ve psig pressure differential between the condenser and evaporator at any steady state load without oil loss, oil return, motor cooling, or 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. Startup below this differential is possible as well, especially with AdaptiView soft start features

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 vibration- free operation are important, Trane encourages the use of 1750 rpm pumps.

Water Flow

Today’s technology challenges ARI’s traditional design of three gpm per ton through the condenser. Reduced condenser fl ows are a simple and effective way to reduce both fi rst 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 benefi ts 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 benefi ts from low-fl ow condensers. Because the water lines and tower are already in place, reduced fl ows 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 benefi ts would typically offset any extra effort required by the chiller.

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