FAXA-SVX01B-EN
65
Operation
sequence of
operation
Supply Air Dehumidification
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 is opened and the supply air fan
will start.
Drying Mode
The unit will enter the drying mode when
the OA dew point exceeds the SA drying
setpoint (dew point). The SA drying
setpoint can be reset down based on OA
dew point conditions. Drying functions
will have priority over cooling mode.
Upon entering drying mode, the first
compressor will stage up. While in drying
mode, the first compressor stage will
always remain active. This allows
condenser reheat (when ordered) to be
available as required during drying
operation. Additional compressors will be
sequenced to match unit capacity to the
latent load.
Reheat will be 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 be cycled to
achieve a time-weighted average of the
reheat setpoint. If primary heat reheat is
user-enabled, additional reheat capacity
will be made available to match sensible
load.
Cooling Sequence
When not in drying mode, the unit will
stage 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.
Supply Air Dehumidification
with Zone 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 is opened and the supply air fan
will start.
Drying Mode
The unit will enter the drying mode when
the OA dew point exceeds the SA 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 will stage up. While in drying
mode, the first compressor stage will
always remain active. This allows
condenser reheat (when ordered) to be
available as required during drying
operation. Additional compressors will be
sequenced to match unit capacity to the
latent load.
Reheat will be 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 be cycled to
achieve a time-weighted average of the
reheat setpoint. If primary heat reheat is
user-enabled, additional reheat capacity
will be made available to match sensible
load.
Cooling Sequence
When not in drying mode, the unit will
stage 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
When the return air damper option is
installed and a request for unoccupied
operation is received, the fan, cooling,
and heating capacity will be cycled in a
recirculating mode to maintain zone
requirements. See below for a detailed
description of the operating modes.
If no return air damper is installed, the fan
is stopped and the OA damper is closed
in unoccupied mode.
Drying Mode
During unoccupied mode (with return air
damper option installed), the unit will
enter the drying mode when the zone RH
exceeds the unoccupied zone RH
setpoint. In the drying mode, capacity will
be cycled 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 will be active
to maintain the supply air reheat setpoint.
Supply air reheat reset functions will be
active and reset based on unoccupied
zone setpoints. Exhaust fan operation
control will be cycled off during unoccu-
pied modes unless unoccupied econo-
mizer operations are active.
Cooling Mode
During unoccupied cooling mode, the fan,
economizer and mechanical cooling cycle
to control zone temperature. Economizer
functions will be enabled when the
difference in the enthalpy of the OA and
zone is adequate. Mechanical cooling will
supplement economizer capacity as
required.
Heating Mode
During unoccupied heating mode, fan
and heating capacity are cycled to
maintain the unoccupied zone heating
setpoint.