Single Zone Variable Air Volume (Single Zone Vav) Control - Trane Voyager TS 150-300 Series Installation, Operation And Maintenance Manual

Low Ambient Operation on Units with 2-
Speed Indoor Fan
The indoor fan motor (IDM) will continue to operate at
100% fan speed during this evaporator defrost cycle (EDC)
and the compressor and outdoor fan will return to normal
operation once the defrost cycle has terminated and the
compressor "Off" time delay has been satisfied.
Heating Operation
Standard unit operation for heating will continue on units
equipped with a two-speed indoor fan. During heat mode,
all units configured with staged electric, or reheat/
dehumidification will heat and reheat/dehumidify the
supply air and space as normal utilizing full speed indoor
fan by energizing the RTRM supply fan output.
Failure and Override Modes
• Supply Fan Proving - If there is a supply fan failure
condition all outputs associated with the supply fan
output control will be de-energized.
• Ventilation Override Mode - For all VOM modes that
require supply fan operation (Purge and Pressurize),
the supply fan will operate at high speed.
• All failure modes that require the Supply Fan to
operate, the Supply Fan will energize at high speed. For
instance if the Frostat switch closes, the Supply Fan will
operate at high speed.
Single Zone Variable Air Volume
(Single Zone VAV) Control
Note: Single Zone VAV is designed to be used with a zone
sensor. If a unit is configured for single zone VAV
operation but is connected to a thermostat, the
control will revert to multi-speed (2-speed) indoor
fan control.
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 or economizer). As the
Discharge Air Temperature falls below the deadband the
algorithm will request a reduction in active capacity.
Cooling Operation
If the control determines that there is a need for
compressor stages in order to meet the discharge air
requirements, once supply fan proving has been made,
the unit will begin to stage compressors. As the zone
cooling demand continues to increase, if additional
capacity is required, the supply fan output will be
modulated above minimum speed in order to meet the
RT-SVX25Q-EN
zone requirements. Note that the supply fan speed will
remain at the compressor stage's associated minimum
value until the control requires additional capacity to meet
the zone demand. As the cooling load in the zone
decreases the control will reduce the speed of the fan
down to minimum per compressor stage and control the
compressor outputs accordingly. As the compressors
begin to de-energize, the Supply Fan speed will fall back to
the Cooling Stage's associated minimum fan speed but
not below. As the load in the zone continues to drop,
cooling capacity will be reduced in order to maintain the
calculated discharge air setpoint.
Minimum Fan Speeds for Cooling Stages
As the unit begins to stage compressors to meet the
cooling demand, the following minimum Supply Fan
Speeds will be utilized for each corresponding Cooling
Stage. Note that the Supply Fan Speed will be allowed to
ramp up beyond the minimum speed in order to meet the
zone cooling demand.
2-Stage Cooling Units
The minimum fan speed for units with 2 stages of DX
Cooling will be 63% of the unit's full airflow capacity. At
Stage 1 of DX Cooling the Fan Speed will be at a minimum
of 63% and at Stage 2 of DX Cooling the Fan Speed will be
at a minimum of 83%.
3-Stage Cooling Units (High Efficiency Units with
Short Orifice)
The minimum fan speed for units with 3 stages of DX
Cooling will be 63% of the unit's full airflow capacity. At
Stages 1 and 2 of DX Cooling the Fan Speed will be at a
minimum of 63% and at Stage 3 of DX Cooling the Fan
Speed will be at a minimum of 83%.
Economizer Cooling
During normal Economizer Cooling, the fan speed will
operate at its minimum. However, if the economizer is able
to meet the demand alone, due to desirable ambient
conditions, the supply fan speed will be allowed to
increase above the minimum prior to utilizing mechanical
cooling.
Note: Economizer Enable/Disable decisions will be made
based on the previous sections; however, the
economizer control point will now be variable
based on the zone cooling demand.
Demand Controlled Ventilation
Units configured for SZVAV and Demand Controlled
Ventilation (CO sensor value available) require a new
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control scheme comprised of 2 existing schemes that have
been traditionally mutually exclusive; DCV and OA CFM
Compensation. Units configured with DCV will invoke the
new Demand Controlled Ventilation scheme which allows
variable Bldg. Design and DCV Minimum Positions and OA
Damper Position Target setpoints based on the supply fan
speed and space CO requirements.
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Sequence of Operation
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