Sequence of Operation
RTU Open v5
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Integration Guide
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36
The system remains in that mode until all zones of that demand are satisfied or until the system mode reselect
timer (default 30 minutes) 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 system mode reselect 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 also provides a safety and system override function during any RTU heating mode. Whenever the RTU
Open is in a heating mode, the control monitors the supply air temperature (SAT). Normally (and initially) during
heating, the RTU sends the Linkage Heat mode which causes only those zones that require heat to modulate their
dampers to utilize the heated primary air. If during heating the SAT increases and exceeds the Maximum Heating
SAT plus 4 °F, Linkage transmits the Linkage Warm-up mode to all terminals. This allows more zones to utilize
the heated primary air and attempts to prevent any further SAT increase. If this is insufficient, then the rooftop’s
heat stages cycle off and on, subject to the minimum on and off timers specific to the product and the type of heat
provided.
CAUTION
It is important to properly set the value for the
Maximum Heating SAT
to match the value
specified from the equipment product data recommendations. Many rooftops have heat capacity that provide a
higher heat rise, resulting in an SAT in excess of the
Maximum Heating SAT
default value (120°F).
Linkage air source mode determination
Linked air source modes
– In a linked system, the air source determines its operating mode and qualifies that
mode based on its own SAT. The following modes can be sent by the air source depending on its capability and
configuration:
OFF
Air source fan is off. All zone dampers will open to 70% to facilitate the fan
restarting.
WARMUP
Air source fan is on and typically used when providing the first cycle of heat
when changing from unoccupied to occupied operation. It may also be used
as a safety to increase airflow during a heating mode. All zones will
modulate airflow to maintain the zone temperature at the midpoint between
the occupied heat and occupied cool setpoints.
HEAT
Air source fan is on and providing heat. Equipment SAT is above the
reference zone temperature and all zones modulate airflow to maintain the
zone temperature at the appropriate (occ/unocc) heating setpoint.
