Issue:
Varitrac III CCP Sequence of Operation
Resolution:
Discharge Air temperature control is a PID control function that is time and temperature based. The system has two temperature setpoints. The defaults are 55 degrees for cooling and 110 degrees for heating. There is a default 15 minute minimum mode changeover. Both setpoints use a 7 degree deadband (+/-3.5). During a cool operation stage one comes on at 3.5 degrees above setpoint. The second stage is based on the the occurrence of a strong caller and if the temperature is not dropping with the first stage. Once both stages are running, they both remain on until the temperature drops to 3.5 degrees below setpoint. The heating function follows the same sequence in reverse.
The control algorithm is both deviation- and time-based. During operation, the CCP monitors not only the supply air temperature deviation from setpoint, but also how quickly deviation occurs when a stage is turned off, and how quickly deviation is recovered when a stage is turned on. This allows the CCP to adjust the number of stages required and the stage cycle rate for the most consistent supply air temperature control. The control algorithm always meets the minimum-on and -off time requirements when adjusting stages.
Refer to Chapter 6 in the VariTrac CCP Controller Operator Guide https://tranesupport.zendesk.com/hc/en-us/articles/11744522945677-VariTrac-III-CCP-literature
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Other Question/Problem/Cause Statements:
- Where can I get a copy of the sequence of operation for a VariTrac III CCP system?
- How does a changeover bypass system work?
- How does a VariTrac UCM maintain space temperature control?
- Why is the VariTrac damper 100% open?
- Where can I get a copy of the VariTrac II CCP Controller Operator Guide (VAV-SVU01A-EN)?
Facts:
- VariTrac III Central Control Panel (CCP)
- VAV nonLonTalk
- Voyager/Precedent nonLonTalk
Original wave: wave12517
Document Identifier: DOC-85252
Document Identifier: 85252