Trane LPC, Install And Operation Instructions

Page: 84 / 110

84 LPC-SVX01C-EN
Operation
sequence of
operation
Dehumidification
This sequence applies only to space
temperature control.
The Tracer AH540/541 controller provides
both occupied and unoccupied dehumidifi-
cation control when cooling and reheat
capacity is available. The dehumidification
control sequence is allowed on unit
configurations with hydronic or DX
cooling and hydronic or electric reheat.
Both occupied and unoccupied space
humidity setpoints are provided as well as
setpoint offset values (10% default) to
terminate dehumidification mode. To
disable occupied space dehumidification,
set the Occupied Space RH setpoint to
0%. Likewise, to disable unoccupied space
dehumidification, set the Unoccupied
Space RH setpoint to 0%. Use the Rover
service tool to edit these setpoints.
Space dehumidification requires a space
relative humidity sensor input hard-wired
to the universal analog input IN13 or a
communicated RH value. If both a hard-
wired relative humidity sensor and a
communicated RH value is present, the
communicated value will be used for
dehumidification control.
Occupied and unoccupied mode dehu-
midification
When the space relative humidity is
greater than the Occupied Space RH
Setpoint, dehumidification control is
initiated. The dehumidification control
mode will remain active until space
relative humidity is less than the Occupied
Space RH Setpoint minus Occupied Space
RH Offset value. The controller will
automatically revert back to occupied or
occupied standby space temperature
control.
When in unoccupied mode and the space
relative humidity is greater than the
Unoccupied Space RH Setpoint, dehu-
midification is initiated until space relative
humidity is less then the Unoccupied
Space RH Setpoint minus Unoccupied
Space RH Offset value. The controller will
automatically revert back to unoccupied
space temperature control.
Space temperature and relative humidity
are both controlled when dehumidification
is active. Cooling capacity is modulated or
staged to reduce space humidity, while
heating capacity is modulated or staged to
control space temperature. Hydronic
cooling capacity is modulated (increased
and decreased) to offset the relative
humidity load in the space. DX cooling
capacity operates as a limit control and is
only allowed to stage up (increase) to
maintain or decrease the relative
humidity in the space.
Occupied and unoccupied mode
dehumidificiation: Cooling only
In occupied or unoccupied mode, when
dehumidification mode is active and
space temperature is greater than the
space occupied cooling setpoint
minus 1.5°F (0.83ºC), dehumidification is
controlled with only cooling capacity.
Cooling capacity is increased to further
dry the supply air to the space (see A in
Figure O-SO-4).
Occupied and unoccupied mode
dehumidificiation: Cooling and reheat
If the space temperature drops 1.5°F
(0.83ºC) below the occupied cooling
setpoint, reheat capacity is invoked and
modulated to maintain space
temperature control. Cooling capacity
continues to modulate or stage to reduce
space humidity (see B in Figure O-SO-4).
Occupied and unoccupied mode
dehumidificiation: Reheat only
Anytime the space temperature drops
below the occupied heating setpoint
(occupied, occupied standby, or
unoccupied), cooling capacity is disabled
and reheat only is provided until the
space temperature raises to 3°F (1.67ºC)
below the occupied cooling setpoint.
At the time dehumidification is initiated, if
space temperature is greater than 3ºF
(1.67ºC) below the occupied cooling
setpoint, reheat only is provided until
space temperature rises to within 3ºF
(1.67ºC) of the occupied cooling setpoint
(see C in Figure O-SO-4.)
Unit protection strategies
The following strategies are initiated, for
both space temperature control and
discharge air temperature control, when
specific conditions exists to protect the
unit or building from damage:
• Run/stop binary input (see “IN8: Run/
stop” on page 25)
• Supply fan status (“IN10: Supply fan
status”)
• Condensing unit protection
1. Coil defrost (see “Defrost operation”)
2. Compressor minimum On/Off timers
(see “DX cooling operation”)
Figure O-SO-4. Space dehumidification heating & cooling control