Daikin MicroTech I User Manual

OM 920-6 • MICROTECH UNIT CONTROLLER 134 www.DaikinApplied.com
operaTor’s guIde
Special Start Sequence for 100% Outdoor Air Units
with Gas Heat
A special start sequence is used for units 100% outdoor air
units with gas heat. The special start sequence applies to both
Zone Control and DAT Control units. If heat is required at unit
startup, the furnace enters a special burner startup sequence
as the unit enters its Startup operating state. Pre-ring the
burner allows the gas heat pre-purge sequence to occur and
the burner to re and warm up so that tempered air is available
immediately when the fans start.
Once a 100% Outdoor Air unit equipped with gas heat
completes one of the start up sequences described below the
gas heat operates the same for both return air units and 100%
outdoor air units.
The sequence described in the following paragraphs is initiated
for a 100% OA Zone Control unit any time during the Startup
operating state when the Control Temperature is less than
the Effective Occupied or Unoccupied Heating Setpoint† by
½ the Occupied or Unoccupied Heating Deadband or the
OAT is less than the Min DAT Limit by the amount of the DAT
Htg Deadband. The sequence described in the following
paragraphs is initiated for 100% OA DAT Control units during
the startup operating state when the Min DAT Ctrl parameter is
set via the keypad and the OAT is less than the DATClgSpt by
the amount of the DAT Htg Deadband.
The Effective Occupied or Unoccupied Heating Setpoint
equals the Occupied or Unoccupied Heating Setpoint for
Zone Control units. Otherwise it equals the Morning Warmup
Heating Setpoint (DAT Control units). The special start up
sequence is initiated during the Startup operating state.
The fans will remain off. The main gas valve is energized
so the burner starts during the Warmup Time (default = 240
seconds) and operates at low re.
At the end of the Warmup Time, the modulating gas heating
valve is set to a calculated position. This calculated position is
based on the “Application Discharge Air Temperature Setpoint”,
the outdoor air temperature, and the Maximum Temperature
Rise of the gas heat exchanger using the following formula:
Gas Heat Actuator Position = 100% x (Setpoint - Outdoor Air
Temp) / Temp Rise
The Application Discharge Air Temperature Setpoint is the
Occupied or Unoccupied Heating Setpoint if the control
temperature initiated the special start sequence. If the OAT
initiated the special start sequence, the setpoint is the Min DAT
Limit for Zone Control units and the Eff DAT Clg Spt for DAT
Control units. The Temp Rise is the Maximum Temperature
Rise of the gas heat exchanger that is entered at the factory
for the specic unit. After the modulating gas heating valve is
set to the calculated position, there is a HeatUpDelay (default
= 60 second) to allow the heat exchanger to heat up. After this
delay, since the unit is 100% Outside Air, the unit immediately
transitions from Startup to the Fan Only state. As soon as
the unit enters the Fan Only state, the unit will immediately
transition to either the Heating state or the MinDAT state.
The unit remains in either the Heating or Minimum DAT
operating state for the duration of the Hold Period (Default
= 240 seconds). The gas heating valve does not modulate
from its calculated value to allow the temperature to approach
equilibrium with modulating gas heating valve at a xed
position.
The unit reverts to normal modulation of the gas heating valve
when the Hold Period has elapsed since the unit entered
Heating or MinDAT.
Return Air Units
When the unit enters the Heating operating state, the controller
rst holds the gas valve at the minimum re position (5%
or 33% depending on the burner model) until the Heating
Interstage Timer expires. Then, the controller modulates the
gas valve to maintain the discharge air temperature at the
Discharge Heating Set Point.
MPS Gas Heating
Sequence of Operation (Staged Control)
2-Stage Control
The following details the sequence of operation for the low
heat option.
• Unit controller calls for heat
• Furnace DDC control module receives a call for heat
• High limit switch is checked for safe condition
• Proof of airow switch is checked for combustion airow
• 60 second prepurge cycle starts
• Spark ignitor is activated for 3 seconds
• Gas valve receives a command for stage 1 of heat
• Burner is ignited
• Unit controller calls for stage 2 of heat
• Furnace DDC controller receives a stage 2 heat
command
• Gas valve receives a command for stage 2 of heat
4-Stage Control
For a unit with the optional high heat the above sequence is
followed for the rst two stages. For the remaining 2 stages the
above procedure is repeated on the second furnace module.

Daikin MicroTech I Specifications

General

Brand	Daikin
Model	MicroTech I
Category	Controller
Language	English