Operating Instructions
Table Of Contents
- Table of Contents
- How To Use This Manual
- Chapter 1—Hardware
- Chapter 2—Applications for ATEC— Base VAV
- Chapter 3—Applications for ATEC—VAV with Reheat
- Chapter Overview
- Introduction
- Application 2500: VAV Cooling Only
- Application 2501: VAV Cooling or Heating
- Application 2522: VAV with Electric Reheat or Baseboard Radiation
- Application 2523: VAV with Hot Water Reheat (only one reheat valve)
- Application 2524: VAV Series Fan Powered with One Stage of Electric Reheat
- Application 2526: VAV Parallel Fan Powered with One Stage of Electric Reheat
- Application 2473: Slave Mode
- Chapter 4—Point Database
- Chapter 5—Troubleshooting
- Glossary
- Index
Chapter 2—Applications for ATEC—Base VAV
2-6 Siemens Building Technologies, Inc.
Night Mode Override Switch
If an override switch is present on the room temperature sensor and a value (in hours) other
than zero has been entered into OVRD TIME (Point 20), pressing the override switch resets
the controller to day operational mode for the time period that is set in OVRD TIME. The
status of NGT OVRD (Point 21) changes to DAY. After the override time elapses, the
controller returns to night mode and NGT OVRD changes back to NIGHT.
It is only when the controller is in night mode that the override switch on the room sensor has
any effect on the controller.
Control Loops
The terminal box is controlled by two Proportional, Integral, and Derivative (PID) control
loops: a temperature loop and a flow loop.
Temperature Loop—The temperature loop uses the values of CTL STPT (Point 92) and
CTL TEMP (Point 78) to generate the cooling loopout, which is then used to generate the
value of FLOW STPT (Point 93). See Control Temperature Setpoints (page 2-5). FLOW
STPT is calculated between the values of CLG FLOW MIN (Point 31) and CLG FLOW MAX
(Point 32).
Flow Loop—The flow loop maintains the airflow between the values of CTL FLOW MIN
(Point 76) and CTL FLOW MAX (Point 77) by modulating DMPR COMD (Point 48).
Calibration
Calibration of the controller’s internal air velocity sensor is periodically required to maintain
accurate air velocity readings. CAL SETUP (Point 95) is set with the desired calibration
option during controller startup. Depending on the value of CAL SETUP, calibration may be
set to take place automatically or manually. When CAL AIR (Point 94) has a setting of YES,
calibration is in progress. The damper is commanded closed to get a zero airflow reading
during calibration.
At the end of a calibration sequence, CAL AIR automatically returns to NO. A setting of NO
indicates that the controller is not in a calibration sequence.
Fail-safe Operation
If the air velocity sensor fails, the controller uses pressure-dependent control. The
temperature loop controls the operation of the damper.
If the room temperature sensor fails, the controller operates using the last known temperature
value.