Sterling RT - Manual (Page 16)

– 16 –
AIR DISTRIBUTION
Two basic air control systems are used to deliver
conditioned air to the occupied space: “constant” fan
operation and “intermittent” fan operation.
INTERMITTENT FAN OPERATION
This air control system is available on duct furnaces
when the fan time delay relay is ordered (optional). The
thermostat turns the gas on whenever the temperature
drops below the thermostat setting. The fan time delay
relay allows the unit to fi re for a period of 60 seconds
before fan operation. It also allows the fan to operate for
120 seconds after burner shutdown.
AIR THROUGHPUT
Static Pressure through the duct furnace should not
exceed 2.0 inches (0.50 kPa) water column. The
standard outdoor duct furnaces are operated at a
temperature rise range of 20° to 60°F (17° to 50°C)
rise. The fur naces are also available at a higher
temperature rise range of 30° - 90°F (17° - 50°C).
NOTICE: It is important that the final temperature
leaving the furnace does not exceed 150°F (66°C).
When final air throughput adjustments are being
made, a quick check of the final temperature can
be made by locating a thermometer approximately
6 to 12 inches (152 to 305 mm) downstream from
the air discharge and approximately 3 to 4 inches
(76 to 102 mm) from the bottom of the duct. The
unit should be operated at least 15 to 20 minutes
before temperature readings are made.
A unit should never be allowed to
cycle over a prolonged period on the high limit.
The high limit is not an operating control. It is a
safety control to prevent a fire. If cycling on the
high limit is noted, corrective measures should be
taken immediately. Failure to do so could cause unit
damage and possible fi re.
AIR FILTERS (ON MATED AIR MOVING DEVICE)
It is recommended that air filters be changed or
cleaned at least twice a year. More frequent attention
will be required if the air being handled is unusually
dirty. Air fl ow reduction, caused by clogging air fi lters,
will increase the discharge air temperature and may
cause nuisance tripouts.
Filters (by others) should be serviced regularly and
changed or washed when necessary to maintain the
required throughput. In a dusty environment, fi lters may
clog up in less than one month. A clogged fi lter switch
is recommended to assist with fi lter maintenance.
CONSTANT FAN OPERATION
Duct Furnaces: This air control system is standard
on duct furnaces without a fan time delay relay. The
blower operates constantly, circulating air through
the unit, through the discharge, continuously into the
occupied zone, and back to the return. The thermostat
turns the gas valve on or off, raising the temperature of
the air to maintain comfort conditions in the occupied
area.