Economizer Control - KMC Controls FlexStat Application Manual

Economizer Control

If the economizer option is enabled, the economizer mode is determined
by comparing outside air temperature (OAT) to the economizer enable
temperature. The economizer mode is enabled if the OAT is 1.0° F (0.56°
C) below the economizer enable temperature and disabled if the OAT is
1.0° F (0.56° C) above the econ enable temp.
If the application is configured for econ enable/disable, the economizer
mode is determined as above. Any time the econ mode is enabled, the
econ output is energized at 100% (12vdc). If the econ mode is disabled,
the econ output is deenergized.
If the application is configured for modulating operation, the following
sequence is used:
During occupied mode, if the economizer mode is enabled, the OA
damper will open to the greater of the minimum damper position set-
ting (adjustable, for ventilation) or the mixed air temperature PI loop.
The mixed air temp loop will modulate from 0% to 100% as the mixed
air temp rises above the mixed air temp setpoint.
During occupied mode, the mixed air temp setpoint is determined based
on a reset schedule. If the space temperature is at or below the active
cooling setpoint, the mixed air temp setpoint is 68.0° F (20.0° C). If the
space temperature is 2.0° F (1.1° C) above the active cooling setpoint, the
mixed air temp setpoint will be 53.0° F (11.7° C). The mixed air setpoint
will vary linearly in between.
During unoccupied mode, if the space temp exceeds the cooling setback
setpoint by deadband and the econ mode is enabled, the OA damper
shall open as called for by the mixed air temp loop. The OA damper
BAC-1xx36/1xxx36 Series (3 Relays and 6 Analog Outputs) Section
shall modulate to maintain 53.0° F (11.7° C) until the space temp reaches
the cooling setback setpoint at which point it shall close. If at any time
during unoccupied mode the economizer mode is disabled based on
OAT, the outside air damper will close.
If the system mode is set to "heating" during occupied mode, the
damper will open to minimum position when the fan is on. If the system
mode is set to "heating" during unoccupied mode or is set to "off" in
any occupancy mode, the outside damper will close. If at any time there
is a fan alarm, the OA damper shall shut.
If the mixed air temp drops below the low limit alarm temp, a low limit
alarm is generated and the outside air damper will close. Other safety
actions are taken and described in their respective sections of the se-
quence.
Dehumidification
If the dehumidification sequence is enabled on models BAC-
10136C/11136C, the dehumidification mode is started and stopped as
described in the Common Features section. Upon activation of the dehu-
midification mode, the cooling valve is opened 100%. The heating valve
then reheats the space as called for in a modified heating sequence to
maintain the active cooling setpoint. Upon termination of the dehumidi-
fication mode, the valves return to their normal sequence.
52 Application Guide L