Daikin MicroTech III Operation Manuals page 135

Sequence of Operation (Modulating Burner)
5–1 Gas Burner
The following details the sequence of operation for the low
heat option .
• Unit DDC controller calls for heat
• Furnace DDC control module receives a call for heat
• Furnace safety switches and DDC control are checked for
safe conditions
• 45 second prepurge cycle starts. Proof of airflow switch is
checked for combustion airflow
• Spark ignitor is activated
• Gas valve receives a signal to open fully
• Burner is ignited and runs for 20 seconds in high fire
NOTE: If call for heat is interrupted during this timing, the
furnace will be locked in for the 20 seconds cycle .
• Gas valve and induction blower motor receives a signal
to modulate burner output to match the unit discharge air
temperature setting
10-1 gas burner
• Unit controller calls for heat .
• Top furnace DDC receives call for heat .
• Steps 3-9 from Low Heat Option are followed .
• If top furnace is unable to meet the unit controllers DAT
heating setpoint then the furnace DDC calls for 3rd stage
of heating
• Top furnace is reduced to low fire
• Bottom furnace receives a call for heat and sequences
similar to steps 3-9 from Low Heat Option .
• Staged burner gas valve receives a signal to open 50% .
• Top furnace receives a signal to modulate the gas valve
to meet the unit controllers DAT heating setpoint .
• If stage 3 and modulating furnace are unable to meet
DAT heating setpoint then stage 4 heat initiates
• The bottom furnace stages up to high fire and the top
furnace reduces to low fire
• Mod gas valve and inducer blower motor receive a
signal to modulate to match the unit controllers DAT
heating setpoint
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Discharge Air Temperature Setpoint Reset - Heating
The Heating DAT Setpoint may be reset for units with DAT
Heating Control . The Discharge Air Temperature Setpoint
will never be set below the Minimum DAT Heating Setpoint
or above the Maximum DAT heating Setpoint on the Heating
Reset menu . The reset type may be set to one of the following:
• None: Discharge Heating Spt is user adjustable
• Network: Discharge Heating Spt is equal to the Network
DAT Htg Setpoint when it is valid
• Space: Discharge Heating Spt is based on the Space
Sensor
• Return: Discharge Heating Spt is based on the Return
Air Sensor
• OAT: Discharge Heating Spt is based on the Outdoor Air
Temperature
• Ext mA: Discharge Heating Spt is determined by a 0-20
or 4-20 mA signal
• Ext V: Discharge Heating Spt is determined by a 0-10 or
2 - 10 VDC signal
Reset reverts from Return to None when the return air sensor
opens or shorts . Reset reverts from Space to None when the
space sensor opens or shorts . Reset reverts from OAT to None
when the outdoor air sensor opens or shorts .
When Space, Return, OAT, Ext mA, or Ext V is selected, the
Discharge Heating Spt equals the Max Htg Spt when the
selected value equals the Max Htg Spt @ value . Similarly,
the Discharge Heating Spt equals the Min Htg Spt when the
selected value equals the Min Htg Spt @ value .
When Space, Return, or OAT is selected, the reset schedule
should be set so that the DAT Heating setpoint decreases as
the selected temperature increases as shown in the graph .
When Ext mA is selected, the values "Min Htg Spt @" and
"Max Htg Spt @" are entered as mA values . When Ext VDC is
selected, the values "Min Htg Spt @" and "Max Htg Spt @" are
entered as VDC values .
If Ext mA or Ext V is selected as the type of reset, the Min Htg
Spt @ value may be set above the Max Htg Spt @ value to
cause a decrease in the DAT setpoint as the external signal or
the Min Htg Spt @ value may be set below the Max Htg Spt @
value to cause an increase in the DAT setpoint as the external
signal increase .
When ever the Clg Reset Type or Engineering Units is
changed, the Min Clg Spt @ and Max Clg Spt @ values revert
to default values as follows:
• None: Min Clg Spt @=0NA, Max Clg Spt @=100NA
• Network: Min Clg Spt @=0NA, Max Clg Spt @=100NA
• Space, Return: Min Clg Spt @=73 .0F, Max Clg Spt
@=71 .0F
• OAT: Min Clg Spt @=90 .0F, Max Clg Spt @=70 .0F
• ExtmA: Min Clg Spt @=4 .0mA, Max Clg Spt @=20 .0mA
• ExtVDC: Min Clg Spt @=0 .0V, Max Clg Spt @=10 .0V
135 OM 920-6 • MICROTECH UNIT CONTROLLER
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