Trane FADA, Installation & Operation Manual, Page: 66 / 84

66 FAXA-SVX01B-EN
Operation
sequence of
operation
Zone Dehumidification Unit
Sequence of Operation
1
Occupied Sequence
During occupied mode, the primary
function of the unit is to provide
ventilation air to the space. Upon entering
the occupied mode, the outside air
damper is opened and the supply air fan
will start.
Drying Mode
The unit enters the drying mode when
the zone relative humidity exceeds the
zone relative humidity setpoint (%RH). In
the drying mode, the capacity is
controlled to meet the default supply air
drying setpoint (dewpoint). The SA drying
setpoint can be reset down based on
zone relative humidity conditions. Drying
functions have priority over cooling
mode. Upon entering drying mode, the
first compressor stages up. While in
drying mode, the first compressor stage
always remains active. This allows
condenser reheat option (if ordered) to be
available as required during the drying
operation. Additional compressors will
sequence to match unit capacity to the
latent load.
Reheat is controlled to meet a supply air
reheat setpoint that is a minimum of 3°F
greater than the supply air drying
setpoint. The supply air reheat setpoint
can be reset up based on OA or zone
temperature conditions. When available,
condenser reheat will cycle to achieve a
time-weighted average of the reheat
setpoint. If primary heat reheat is user-
enabled, additional reheat capacity is
made available to match the sensible
load.
Drying mode stops when the zone
relative humidity falls below the operator
adjustable setpoint for leaving drying
mode.
Cooling Sequence
When not in drying mode, the unit stages
cooling capacity to maintain the supply
air cooling setpoint. The supply air cooling
setpoint can be reset down based on HI
selectable parameters (OA sensor, zone
sensor if installed).
Heating Sequence
When not in drying mode, the unit will
stage heating capacity to maintain the
supply air heating setpoint. The supply air
heating setpoint can be reset up based on
HI selectable parameters (OA sensor,
zone sensor if installed). The supply air
heating setpoint must be lower than the
supply air cooling setpoint.
2
Unoccupied Sequence
In unoccupied mode, the fan is stopped
and the OA damper is closed.
Drying Mode
During unoccupied mode (with return air
damper option installed), the unit enters
the drying mode when the zone RH
exceeds the unoccupied zone RH
setpoint. In the drying mode, capacity
cycles to maintain the supply air drying
(dew point) setpoint. The SA drying
setpoint can be reset down based on
zone relative humidity conditions and will
be based on the unoccupied zone RH
setpoint.
Supply air reheat functions are active to
maintain the supply air reheat setpoint.
Supply air reheat reset functions are
active and reset based on unoccupied
zone setpoints. Exhaust fan operation
control cycles off during unoccupied
modes unless unoccupied economizer
operations are active.
Cooling Mode
During unoccupied cooling mode, the fan,
economizer, and mechanical cooling cycle
to control zone temperature. Economizer
functions enable when the difference in
the enthalpy of the OA and zone is
adequate. Mechanical cooling
supplements economizer capacity as
required.
Heating Mode
During unoccupied heating mode, fan
and heating capacity cycle to maintain
the unoccupied zone heating setpoint.
Zone Dehumidification with
Outside Air RH Reference Unit
1
Occupied Sequence
During occupied mode, the primary
function of the unit is to provide
ventilation air to the space. Upon entering
the occupied mode, the outside air
damper opens and the supply air fan
starts.
Drying Mode
The unit enters the drying mode when
the zone relatiave humidity exceeds the
zone relative humidity setpoint (%RH). In
the drying mode, capacity is controlled to
meet the default supply air drying
setpoint (dew point). The SA drying
setpoint can be reset down based on
zone relative humidity conditions or OA
dew point conditions. Drying functions
will have priority over cooling mode.
Upon entering drying mode, the first
compressor stages up. While in drying
mode, the first compressor stage always
remains active. This allows condenser
reheat (when ordered) to be available as
required during drying operation.
Additional compressors will sequence to
match unit capacity to the latent load.
Reheat is controlled to meet a supply air
reheat setpoint that is a minimum of 3°F
greater than the supply air drying
setpoint. The supply air reheat setpoint
can be reset up based on OA or zone
temperature conditions. When available,
condenser reheat will cycle to achieve a
time-weighted average of the reheat
setpoint. If primary heat reheat is user-
enabled, additional reheat capacity is
made available to match sensible load.
Drying mode stops when the zone
relative humidity falls below the opera-
tor-adjustable setpoint for leaving drying
mode.
Cooling Sequence
When not in drying mode, the unit stages
cooling capacity to maintain the supply
air cooling setpoint. The supply air cooling
setpoint can be reset down based on HI
selectable parameters (OA sensor, zone
sensor if installed).
Heating Sequence
When not in drying mode, the unit stages
heating capacity to maintain the supply
air heating setpoint. The supply air
heating setpoint can be reset up based on
HI selectable parameters (OA sensor,
zone sensor if installed). The supply air
heating setpoint must be lower than the
supply air cooling setpoint.