Trane SYS-APM001-EN manual Condenser-water pumping arrangements, Primary System Components

Primary System Components

Figure 15. Manifolded condenser- water pumps

Cooling

Towers

Manifolded

Pumps

Chillers

water entering and leaving the cooling tower is the range. The temperature difference between the leaving water temperature and the entering wet-bulb temperature is the approach.

Effect of load on cooling tower performance

As the building load—or heat rejection—decreases, range and approach also decrease. This means that when the building is at part load, the cooling tower can provide colder water at the same ambient wet-bulb temperature.

Effect of ambient conditions on cooling tower performance

As ambient wet-bulb temperature drops, the approach—at a constant load— increases. This is counter-intuitive to many, and it must be considered when cooling-tower-control strategies are developed. Detailed descriptions of these conditions appear in “Chiller–tower energy balance” on page 91. For additional information, refer to 2008 ASHRAE HVAC Systems and Equipment Handbook, chapter 39, “Cooling Towers.” 3

Condenser-water pumping arrangements

Water-cooled chillers require condenser-water-system variations to be considered. For a discussion of condenser-water temperatures and flow rates, refer to “System Design Options” on page 27. Since air-cooled-chiller condenser controls are part of the chiller design, they are not discussed in this manual.

Most important, the inlet to the pump must have sufficient net positive head. This often means locating the pump below the cooling-tower sump.

Single tower per chiller

In some applications each chiller has a dedicated cooling tower. This is most likely to occur when chillers, and their accompanying towers, are purchased at different times during the facility’s life—such as when additions are made.

Manifolded pumps

Amuch-used pumping arrangement has a single cooling-tower sump with manifolded pumps, one condenser water line, and separate, smaller, pipes for each chiller as shown in Figure 15. This provides a number of advantages:

•Pumping redundancy

•If cooling towers cells can be isolated, any cooling-tower cell can run with any chiller.

•Hydraulics are generally less problematic than on the chilled-water side.

•Cooling towers can be located remotely from chillers, with only a single supply and return pipe to connect them.

14 Chiller System Design and Control SYS-APM001-EN