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14 Direct-Fired Indoor and Outdoor Units • MUA-SVP01A-EN
Unit Operating Modes
with internal heat gain. In certain conditions it may be necessary to readjust the
minimum discharge air or room temperature setpoint upward or adjust the
outside/return air ratio to provide a warmer supply air temperature.
Energy Savings Mode 1—Non-Recirculating Units. Energy Savings Mode 1 will
automatically disable the burner if the outside 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
with internal heat gain. In certain conditions it may be necessary to readjust the
minimum discharge air or room temperature setpoint upward or adjust the
outside/return air ratio to provide a warmer supply air temperature.
Energy Savings Mode 2—Mixing Box Recirculating Direct-Fired Units. Energy
Savings Mode 2 will automatically disable the burner if the burner's minimum
firing rate exceeds the allowable equivalent temperature rise. This condition is
unlikely to occur unless the burner's minimum firing rate is misadjusted and set
too high, or the inlet air opening is restricted.
Energy Savings Mode 3. Energy Savings Mode 3 will automatically disable the
burner if the outside air temperature is above the Outside Air Economizer
setpoint. This function is similar to an inlet duct thermostat. The burner will cycle
back on if the supply air temperature drops 3°F below the Outside Air Economizer
setpoint.
To change the desired outside air economizer temperature scroll through the
SETPOINTS menu tree, locate the ECONOMIZER Setpoint, and enter a new
temperature. The default for this setpoint is 65°F. The allowable temperature
range is 40°F - 80°F.
Ventilation Mode
Ventilation Mode occurs when the fan is running but the unit is not providing
heating or cooling.
On an MDT control system the heating mode is activated when the remote
temperature setpoint knob is turned to start the unit. See Energy Savings Modes
for more information.
On all other systems the ventilation mode is dependant on the room
temperature. The heating/ventilation/cooling operation is demonstrated below.
The dotted line in the middle of the diagram represents the change between
room temperature rise and room temperature fall. Select a point on the heavy
line in the diagram to determine the mode of operation.
EXAMPLE: Start at point "A". The unit is in the ventilation mode and the room
temperature is rising. Follow the dashed line upward. If the room temperature
rises to a temperature that is 2°F over the cooling setpoint, the cooling will be
enabled, and the unit will be in the cooling mode. Follow the solid line clockwise.
Once the room temperature has fallen to the cooling setpoint, the cooling mode
will be disabled, and the room will be in the ventilation mode. Follow the dashed