Unit Protection Strategies - Trane LPC Install And Operation Instructions

Packaged climate changer air handler

Table of Contents

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

Operation

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).

Figure O-SO-4. Space dehumidification heating & cooling control

sequence of

operation

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.)