Trane IntelliPak 2 Series, Installation, Operation And Maintenance Manual

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92 RT-SVX24Q-EN
Unit Startup
Sequence of Operation
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Cooling Sequence of Operation
Time delays are built into the controls to increase
reliability and performance by protecting the
compressors and maximizing unit efficiency.
SZVAV Cooling Sequence of Operation
Single Zone VAV units will be equipped with a VFD
controlled supply fan which will be controlled by the 0-
10VDC RTM VFD output and the RTM Supply Fan
output. With the RTM Supply Fan output energized and
the RTM VFD output at 0VDC the fan speed output is
37% (22Hz) from the VFD motor, by default, and at
10VDC the Fan Speed output is 100% (60Hz). The
control scales the 0-10VDC VFD output from the RTM
linearly to control between the 37%-100% controllable
range.
If the RTM determines that there is a need for active
cooling capacity in order to meet the calculated
Temperature Setpoint (Tset), the unit will begin to
stage compressors accordingly once supply fan
proving has been made. Note that the compressor
staging order will be based on unit configuration and
compressor lead/lag status.
Once the Tset calculation has reached its bottom limit
(Tset Lower Limit Setpoint) and compressors are being
utilized to meet the demand, the Tset value continues
to calculate below the Tset Lower Limit Setpoint and
the algorithm will begin to ramp the Supply Fan Speed
up toward 100%. Note that the supply fan speed will
remain at the compressor stage’s associated minimum
value (as described below) until the Tset value is
calculated below the Tset Lower Limit Setpoint.
As the cooling load in the zone decreases the zone
cooling algorithm 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 discharge air within
the ± ½ Tset deadband.
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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 37% as determined by the active
Tset calculation; the speeds below are only the
minimum speeds per cooling stage. Note that when
transitioning between active cooling stages,
compressors may energize prior to the supply fan
reaching the minimum speed for the associated step.
1. 2-Stage DX Cooling - The minimum fan speed for
units with 2 stages of DX Cooling will be 37% of the
unit’s full airflow capacity. At Stage 1 of DX Cooling
the minimum Fan Speed will be 37% and at Stage 2
of DX Cooling the Fan Speed will be at a minimum
of 67%.
2. 3-Stage DX Cooling - There are no IntelliPak
applications with 3 stages of DX Cooling.
3. 4-Stage DX Cooling - The minimum fan speed for
units with 4 stages of DX Cooling will be 37% of the
unit’s total airflow. At Stage 1 the minimum Supply
Fan Speed will be 37%, at Stage 2 the minimum
Supply Fan Speed will be 58%, and at Stages 3 & 4
the minimum Supply Fan Speed will be 67%.
Rapid Restart
This feature will occur after every power cycle. Once
power is restored (e.g., via a backup generator), the
RTM will maximize cooling capacity within 3-5 minutes.
Once the space has returned to its Zone Temperature
Setpoint, the RTM controls the load using normal
capacity control algorithms. The supply fan will be
turned on immediately after a power cycle, module
initialization, or after the Unit Start Delay has timed out.
The supply fan proving switch input must be closed
prior to continuing with Rapid Restart.
Once the supply fan proving switch input has closed,
the unit will consider the outside air temperature to
determine whether economizing or DX mechanical
cooling will be utilized to provide the necessary
cooling. If the outside air temperature is less than 50°F
and economizing is enabled, the outside air damper
will be utilized. If the outside air temperature is above
50°F, the outside air damper will remain closed and DX
mechanical cooling will occur for the duration of Rapid
Restart.
Compressor Sequence of Operation
Each compressor is equipped with a crankcase heater
and is controlled by a 600 volt auxiliary switch on the
compressor contactor. The proper operation of the
crankcase heater is important to maintain an elevated
compressor oil temperature during the “Off” cycle to
reduce oil foaming during compressor starts.