Trane SYS-APM001-EN manual Chiller Plant System Performance, Controls, Chiller performance testing

Application Considerations

For more information about chiller plant controls, consult the Trane applications guide, Tracer Summit™ Chiller Plant Control Program (BAS-APG004-EN).

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To minimize power, large systems must be very efficient. The upside of a large system is the amplification of energy savings. A relatively small percentage of energy saved becomes more valuable. For this reason, the highly efficient series-counterflow arrangement is popular for large systems. (See “Series–Counterflow Application” on page 77.)

Controls

The designers of medium and large chilled-water systems are more likely to consider the pros and cons of direct-digital controls (DDC) versus programmable-logic controls (PLC). These platforms deliver similar results, depending on proper design, programming, commissioning, and operation.

One way to think of PLC is “fast, centralized control with redundancy.” PLC has a faster processing speed, with some hot-redundancy features—such as an entirely redundant system processor that is ready to take over if the main system processor fails.

Conversely, DDC can be considered “steady, distributed control with reliability.” DDC controls feature easy programming and user-friendly operation. In the DDC environment, a failure of the system processor results in the lower-level processors defaulting to a pre-determined operating mode.

The speed of the PLC system can be one of its challenges. Controls that are steady and do not overreact to minor changes work very well, even in large chilled-water systems.

Chiller Plant System Performance

Chiller performance testing

All major chiller manufacturers have chiller performance test facilities in the factory, in a laboratory, or both. A chiller performance test in accordance with the test procedures in ARI Standard 550/5905 can be performed at the factory under controlled conditions, with industrial grade instrumentation and computerized data collection devices. This test ensures that the chiller meets its promised performance criteria. If it does not, corrections are made before it leaves the factory.

Limitations of field performance testing

After the chiller is installed at the job site, the system conditions will be less controllable than in a test facility, and therefore unsuitable for chiller acceptance testing. While measuring the performance of the entire chiller plant is more difficult, it can help identify operating problems or evaluate the effectiveness of system control methods and setpoints.

The goal is to operate as efficiently as possible and to sustain a high level of individual equipment and coordinated operation. A proper energy management system can help trend and diagnose problems or changes over time.

Chiller System Design and Control SYS-APM001-EN