System Start-Up; Cooling Sequence Of Operation (Intellipak Controls Only) - Trane IntelliPak WEHE Series Installation, Operation And Maintenance Manual

System Start-up

Cooling Sequence of Operation (IntelliPak
Controls Only)
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 via 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.
Cooling Stages Minimum Fan Speed
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
64
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%.
Units without an Economizer
Upon entering an "occupied" mode of operation, the RTM
receives input from the remote panel to start the supply
fan. For constant volume applications, the RTM supply fan
contacts K2 close which energizes the supply fan contactor
1K16. When the supply fan starts, the fan proving switch
(3S68) closes, signaling the RTM that airflow has been
established. The VFD will begin to ramp the fan, (if
equipped).
When a cooling request is sent to the RTM from a zone
temperature sensor, the RTM evaluates the operating
condition of the system using the supply air temperature
input and the outdoor temperature input before sending
the request to the SCM/MCM. Once the request is sent to
the SCM/MCM, the compressor module checks the
compressor protection circuit before closing "Stage 1"
(K10 on SCM or K11 on MCM). After the first functional
stage has started, the compressor module monitors the
saturated refrigerant temperature and closes the
condenser fan output contact "1A", when the saturated
refrigerant temperature rises above the "lower limit"
setpoint.
Units with an Economizer
Upon entering an "occupied" mode of operation, the RTM
receives input from the remote panel to start the supply
fan. For constant volume applications, the RTM supply fan
contacts K2 close which energizes the supply fan contactor
1K16. When the supply fan starts, the fan proving switch
(3S68) closes, signaling the RTM that airflow has been
established. The RTM opens the economizer dampers to
the specified "minimum position".
When a cooling request is sent to the RTM from the zone
temperature sensor, the RTM evaluates the operating
condition of the system using the supply air temperature
input and the outdoor temperature input before sending
the request to the SCM/MCM for mechanical cooling. If the
outdoor conditions are suitable for cooling (temperature
and humidity are within specified setpoints), the RTM will
attempt to maintain the zone temperature without using
any compressors. If the zone temperature can not be
maintained within the setpoint deadband, the RTM sends
a cooling request to the SCM/MCM. The compressor
module checks the compressor protection circuit before
RT-SVX35H-EN