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SS-SVX10B-EN
Start-Up
Sequence of Operation
Variable Air Volume Applications (SZVAV)
Supply Fan Mode Operation
Units configured for Single Zone VAV control will utilize Supply Fan Mode selection as is currently
implemented into ReliaTel controls for normal Zone Control and will be selectable between AUTO
and ON via a connected Zone Sensor module or through BAS/Network controllers.
Supply Fan Mode Auto Operation
For active Cooling, and Heating operation the Supply Fan will be commanded ON and will ramp
up to the appropriate minimum speed once the unit determines that there is a request for capacity
control. Once the active request is cleared and all capacity is de-energized normal supply fan off
delays as implemented on constant volume units will be in effect. During the Supply Fan Off-Delay,
the supply fan will remain energized for the predetermined time at the previous unit function's
minimum speed. All other cases which would bring the Supply Fan ON will function as on non-
Single Zone VAV units.
Supply Fan Mode ON Operation
For active unit control with the Supply Fan Mode set to ON, the unit will energize the Supply Fan
and hold the Fan Speed output at minimum speed until there is a request for the fan speed to
increase. This will hold true for all cases except during Unoccupied periods in which the Supply Fan
Mode is forced to AUTO and will operate the Supply Fan as described above for all Cooling, and
Heating requests.
Supply Air Temperature Control - Cooling
For Cooling operation the unit will control the active capacity outputs to meet a varying, calculated
Discharge Air Setpoint that is calculated based on zone conditions in order to maintain the Zone
Temperature to the active Zone Setpoint. Note that this setpoint will be clamped between the user
selected DA Heat and DA Cool setpoints for compressor control. In general, as the zone
temperature rises above the ZCSP, the Active Discharge Air Setpoint will be calculated down. This
calculated setpoint is a direct indication of space demand and is also used to determine the proper
supply fan speed to meet the space requirements. During active capacity control, the unit will utilize
a +/- 3.5°F deadband around the active Discharge Air Setpoint to determine when to request
additional cooling capacity. If the unit is maintaining the discharge air temperature within the +/-
3.5°F deadband around the calculated discharge air setpoint requirements, no additional capacity
will be requested.
Occupied Cooling Operation
For normal Cooling operation, available Cooling capacity will be staged or modulated in order to
meet the calculated discharge air setpoint between the user selected upper and lower limits. If the
current active cooling capacity is controlling the discharge air within the deadband no additional
Cooling capacity change will be requested. As the Discharge Air Temperature rises above the
deadband the control will request additional capacity as required (additional compressor
operation). As the Discharge Air Temperature falls below the deadband the algorithm will request
a reduction in active capacity.
NOTICE:
Equipment Damage!
Ensure the disconnect for the indoor air handler is closed before operating the system.
Operating the outdoor unit without the indoor fan energized can cause unit trip-out on high
pressure control and/or liquid flood back to the compressor.
