A
base
IOM67
10
February 2021 R0
high fire to low fire at a 20:1 turndown ratio to
maintain the requested discharge air temperature
by modulating the gas and air actuators. If heating
is not required the burner will be disabled and the
combustion blower will enter a post purge time,
and then shut down.
HE DIRECT FIRED
For direct fired HE style direct fired heaters.
On a call for heating, and with the supply blower
enabled, the ignition control will be enabled to
start and prove pilot flame, then open the main
safety valve (SSOV). Once the pilot flame has
proven and the main flame is established, the M-XM
will then disable the pilot valve. The burner is
allowed to operate from low fire to high fire to
maintain the requested discharge air temperature
by modulating the fuel control valve. The heating
will remain on as long as the heating enable circuit
is energized.
The
base
can control either a Maxitrol magnetic
style modulating valve or an actuator and ball valve
combination.
Variable air volume systems include a burner
bypass damper which modulates to maintain the
correct burner profile pressure drop.
STAGED COOLING
For staged compressor operation the
base
will
sequence on and off up to 5 compressor stages to
attempt to maintain the discharge temperature
setpoint. As with all staged systems, expect the
discharge temperature to fluctuate from setpoint
as compressors are turned on and off.
SH(X) HUMIDIFIER
SH and SHX series gas fired humidifiers are
controllable using the humidifier version of the
base
controller.
SHX models use a second fill valve for the side
tank.
On a call for humidification the tank first fills with
water, then the burner gas-fired heat is enabled to
produce steam. Water level is controlled by the
water level probes. Water quality dictates the
minimum tank drain cycle times. Drain
temperature is monitored and cooled with the
supply water if required.
Drain cycle times are preprogrammed based on
water quality, or may be initiated by a time clock
contact.
