A/C Fan Startup Control

Overview

Room temperature can be controlled by using multiple A/C fans. The following is an example of using the UT55A Digital Indicating Controller with its ladder sequence function to control the operation of multiple A/C fans.

Customer Requirements

• Run multiple A/C fans to lower the room temperature in the hot summer months.
• Need to prevent all fans from running at the same time because the inrush current trips the breakers

Yokogawa's proposed solution

Figure 1. A/C fan startup control

With 8 A/C fans

The UT55A can come with up to 8 alarm outputs that can control the fans. Ladder sequencing is build in, allowing you to use a timer or other such function to set up a time delay on each output.

* Ladder programs must be created on the LL50A Parameter Setting Software and loaded onto the UT55A.

Procedure

• Set the setting (SP) value to the temperature at which you wish the fan to turn on (e.g. 23°C).
• Set alarm outputs 1 through 8 so that the 8 fans will turn ON when the room temperature reaches the SP value.
• Set a delay (of 5 seconds, for example) between alarms so that all fans do not turn on at the same time.

User benefits

A single UT55A can automate startup of multiple A/C fans—lowers wiring and components costs and saves space (timers and compact PLC's no longer necessary).