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MUA-SVP01A-EN • Direct-Fired Indoor and Outdoor Units 13
Unit Operating Modes
Setpoint. The allowable temperature range is 55°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
AdaptAire 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.
AdaptAire 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 AdaptAire 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.
AdaptAire 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.
AdaptAire units that recirculate air after the burner are physically constrained to
limit the percentage of return air. These constraints are meant to provide the
proper dilution air. An independent third party testing agency and do not use the
equivalent temperature rise control scheme to limit burner modulation does not
list these units.
In order of lowest to greatest priority the burner modulation parameters are:
room temperature, discharge or supply air temperature, and equivalent
temperature rise.
There are three Energy Savings modes that could disable the burner.
Energy Savings Mode 1—Mixing Box Recirculating Units. Energy Savings Mode
1 will automatically disable the burner if the mixed air temperature is equal to or
greater than the minimum discharge air temperature setpoint, and the room air
temperature is 5°F above the room air temperature setpoint. This function is
intended to restrain the room temperature from rising uncontrollably in buildings