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To change the desired minimum supply or discharge air temperature scroll through the
SETPOINTS menu tree, locate the HTG MIN DA Setpoint, and enter a new temperature.
This temperature must not be greater than the HTG MAX DA Setpoint. The allowable
temperature range is 40°F - 130°F. This sets the lowest discharge air temperature that will
leave the unit.
To change the desired maximum supply or discharge air temperature scroll through the
SETPOINTS menu tree, locate the HTG MAX DA Setpoint, and enter a new
temperature. This temperature must not be less than the HTG MIN DA Setpoint. The
allowable temperature range is 40°F - 130°F. This sets the highest discharge air
temperature that will leave the unit.
If the maximum and minimum discharge temperature setpoints are set for the same
temperature, the supply air temperature will be the same as the setpoint regardless of the
room temperature setpoint or actual room temperature.
Recirculating Direct-Fired Heaters
Using different controller software, the AireLogic DDC system can accommodate three
distinct types of recirculating direct-fired units: those that return air before the burner and
employ a special airflow station, those that return air before the burner and do not employ
a special airflow station, and those that recirculate air after the burner. Recirculating
direct-fired units, like all direct-fired units, deliver all of their products of combustion
directly to the heated air space. For this reason it is extremely important that the proper
ventilation rate be maintained to dilute these emissions.
AireLogic units, that recirculate air before the burner and employ an airflow measuring
station, utilize a control scheme that measures air pressure to determine the ratio of
outside air and return air. These units
are listed
by an independent third party testing
agency and use the
equivalent temperature rise
control scheme to limit burner
modulation. The AireLogic system accurately measures the ratio of outside and return air,
calculates the allowable
equivalent temperature rise
and automatically limits the burners
firing rate. This insures the products of combustion, delivered to the space by the unit, are
held at or below allowable OSHA thresholds. The outside air percentage is the driving
parameter for this function. A greater percentage of outside air or dilution air enables the
unit to generate a higher allowable equivalent temperature rise. The maximum allowable
equivalent temperature rise
for 20% outside air is 48.9°F. The maximum allowable
equivalent temperature rise
increases 1.22°F for each 1% increase in outside air.
AireLogic units, that recirculate air before the burner and do not employ an airflow
measuring station, utilize a control scheme that measures damper position to determine
the percentage of return air. These units
are not listed
by an independent third party
testing agency but do use the
equivalent temperature rise
control scheme to limit burner
modulation. The maximum allowable
equivalent temperature rise
for 20% outside air is
48.9°F. The maximum allowable
equivalent temperature rise
increases 1.22°F for each
1% increase in outside air.
For AireLogic units that recirculate air before the burner and use the MDT or
MDT-Expert control, the maximum burner firing rate is limited by the discharge
setpoint or the maximum allowable
equivalent temperature rise
whichever is less.
