Weather-Rite XT112 Installation, Operation & Service Manual - page 51
SECTION 16: E
LECTRICAL
45
16.7 Interlocks
16.7.1 Carbon Dioxide Interlocks
All air handlers that recirculate air from the heated
space require either a control to limit the temperature
rise in proportion to the amount of outdoor air or the
use of a room carbon dioxide sensor. The carbon
dioxide sensor is field provided and set to maintain a
CO2 concentration below 5,000 ppm.
16.7.2 Carbon Monoxide Interlocks
Carbon Monoxide Detector is a ship loose sensor
that monitors the CO levels in the space. It can either
sound an alarm and/ or force the air handler into
100% outside air if its threshold set point is
exceeded.
16.8 Control Options
16.8.1 Mild Weather Outside Air Stat
This option is designed to turn the burner off when
the incoming outside air is at or above the
temperature setpoint. The blower is allowed to run for
continued ventilation. The mild weather outside air
stat is located in the control enclosure. It has an
adjustable setting between -20° F (-29° C) and
100° F (38° C).
16.8.2 Low Temperature Limit with Override Timer
This option is designed to turn the unit off when air is
discharged below the temperature setpoint for a
period in excess of timer setpoint. The low
temperature limit switch is located in the air handler’s
control enclosure. The low temperature limit switch
has an adjustable setting between -20° F (-29° C)
and 100° F (38° C). The timer by-passes the low
temperature limit switch for the first 5 minutes to allow
the burner to establish a flame when the air handler
is turned on. If the air handler’s discharge
temperature falls to the predetermined low
temperature limit setpoint, after the 5 minute
establishing period, the air handler’s blower will be
turned off. To reset the low temperature limit switch,
set the fan switch to off and then on again. The air
handler will return to the normal sequence of
operations.
16.8.3 MUA / Exhaust Failsafe Interlock
This option incorporates the low temperature limit
with override timer and an exhaust fan airflow switch
monitor. The exhaust fan airflow switch is field
provided and field wired as per the option sheet
supplied with the unit. When the air handler is turned
on there is a 5 minute establishing period for the low
temperature limit switch and the exhaust fan
interlock. If the air handler’s discharge temperature
falls to the predetermined low temperature limit
setpoint, after the 5 minute establishing period, the
air handler fan will be turned off. If there is a failure of
the exhaust fan to activate the field supplied airflow
switch, after the 5 minute establishing period, the air
handler fan will be turned off. To reset the
MUA/exhaust failsafe interlock, set the fan switch to
off and then on again. The air handler will return to
the normal sequence of operations.
16.8.4 Motorized Inlet Damper
The motorized inlet damper covers the outside air
inlet of the air handler. When the air handler blower is
turned on, the damper motor is energized and opens
the damper. The damper motor has an auxiliary
switch that prevents the blower from starting until that
damper has opened sufficiently to allow the required
air volume to pass through the air handler.
16.8.5 Motorized Discharge Damper
The motorized discharge damper is mounted in the
duct downstream from the discharge opening of the
air handler. When the air handler fan is turned on the
damper motor is energized and opens the damper.
The damper motor has an auxiliary switch that
prevents the blower from starting until that damper
has opened sufficiently to allow the required air
volume to pass through the air handler.
16.8.6 Control Enclosure Heater
The control enclosure heater is an electric heater that
keeps the temperature in the control enclosure within
the range for the control components. This option is
intended for extremely cold climates, but
recommended for installations below 15° F (-9° C).
The air handler controls are rated to perform at
temperatures as low as -30° F (-34° C). In
environments where the air handler may be exposed
to lower temperatures, a control enclosure heater
may be required.
16.8.7 Auxiliary Relay
An auxiliary relay may be added to an air handler for
either an interlock or a customer defined purpose.
Refer to the option sheet supplied with the air handler
to indicate whether the relay is wired for an intended
purpose or left unwired for a future interface. Each
relay will be double pole double throw (DPDT) type.
Maximum switching capacity on the normally open
contact is 8A, and for the booth light relay, 15A.
16.8.8 Smoke Detector
A smoke detector interlock allows for the air handler
to operate (either off or on) based on signal input
from the fire alarm.