Sequence of Operation
54 RTU Open
The system remains in that mode until all zones of that demand are satisfied or until a fixed 30 minute mode
reselect timer causes a forced re-evaluation of the system. If there is no demand for the opposite mode, the
reselect timer starts again and the current mode continues until all zones are satisfied or until the reselect
timer expires, repeating the process. If there is a demand for the opposite mode, the VVT Master sends the
reference zone's space temperature and setpoints to the air source and restarts the reselect timer. The air
source re-evaluates its demand based on the new information and goes to the Vent mode until the new mode
can be verified as described above. The amount of time this takes is determined by the air source’s operating
parameters.
The VVT Master continuously evaluates the system and updates the air source with the most current system
demand. Based on the evaluation, the reference zone can change from one zone to another. The evaluation
process continues until there is no demand from any zone or the 30 minute timer causes a re-evaluation of
the system conditions.
If no heating or cooling is required or the current air source mode is satisfied, the VVT Master calculates the
weighted average of the occupied and unoccupied heating and cooling setpoints. It also calculates a zone
temperature that is midway between the setpoints (occupied or unoccupied based on the system’s current
occupancy status). This information, plus the occupancy status, is sent to the air source so that its current
mode is disabled and the unit ceases heating or cooling operation. If the system is occupied, the air source
fan and OA damper, if applicable, operate to maintain proper ventilation.
Linkage Air Source Modes
In a linked system, the air source determines its operating mode and qualifies that mode based on its own
Supply Air Temperature (SAT). The following modes can be sent by the air source depending on its
configuration:
• Off – Air source fan is off
• Fan Only – Air source fan is on and providing ventilation (neutral SAT) without heating or cooling
• Economizer Cooling – Air source fan is on and providing cooling, using economizer only
• Cooling – Air source fan is on and cooling is provided by economizer and mechanical cooling
• Heating – Air source fan is on and heating is provided (gas or electric)
• Dehumidification – Air source fan is on and Humidi-MiZer™ is active
• Test – The RTU Open Service Test mode is active
• Shutdown – Air source fan is off due to Safety Chain, Fire Shutdown, or invalid SAT sensor
• Unocc Free Cooling – Air source fan is on, with the economizer providing cooling while unoccupied