Precedent / Voyager II VAV and MZVAV Morning Warm-Up sequence of operation
Caution: Because MWU (MAX Heat) is a constant volume mode, the system’s VAV boxes must be driven to a maximum position to allow for maximum unit airflow. A six-minute air valve “drive time” is allowed to pass after entering MWU mode before the IGV, VFD or supply fan is driven to full airflow.
Morning Warmup – Stand Alone Application (Variable Air Volume Units Only)
MWU is enabled by default with staged and modulating heating application.
For MWU to be enabled, the unit must have a sensor designated as the MWU Zone Temperature Sensor and the MWU Setpoint must be set on the RTAM using the Morning Warmup Setpoint R31 potentiometer
With MWU enabled, when the RTU transitions from Unoccupied to Occupied mode, the unit compares the MWU zone temperature to the MWU setpoint. If the MWU zone temperature is at least 1.5° F lower than the MWU setpoint, MWU is initiated, and the economizer is held closed. The RTU remains in MWU, until the MWU zone temperature is equal to or greater than the MWU Setpoint. The unit then switches to the VAV cooling mode.
RTAM Module
MWU may be used to support systems with heat sources other than those provided by the rooftop unit (e.g., VAV units with reheat boxes.) Cycling capacity MWU control is used to provide a 60-minute time-out and will transition out of MWU.
VHR Relay
When the unit transitions from occupied mode to morning warm-up, daytime warm-up or unoccupied mode, the VHR relay is energized, as long as the unit has a valid zone temperature input at RTRM J6 1&2, or through a zone sensor.
The VHR relay has a set of contacts on LTB3 for the purpose of commanding the VAV boxes to drive open to maximum airflow position. If the unit has heat, the VAV boxes must be driven open. If the boxes are allowed to stay in control, the boxes may try to close instead of open when the warm air enters the room.
- When RTAM DIP SW1-1 is on, the output voltage range is approximately 0 to 10.5VDC.
- When RTAM DIP SW1-1 is off, the output voltage range is approximately 2.5 to 8.5VDC.
- IGV: When the supply fan is on and the output is 0%, the IGV are closed.
- VFD: When the supply fan is on and the output is 0%, the VFD runs at 35hz.
- If the supply static pressure goes below -0.2" (0.2VDC) the IGV / VFD output will stay at 0% and the diagnostic COOL FAIL + SERVICE FAIL will be present.
- If the static pressure exceeds 3.8" WC the supply fan will stop and the diagnostic HEAT FAIL + COOL FAIL +SERVICE FAIL will be present.
- During the heating modes; Daytime Warm-up, Morning Warm-up, and Unoccupied, the IGV or VFD output is always 100%.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.