Daikin MicroTech I User Manual

Dehumidication Reheat Control
During dehumidication control either an analog or digital
Hot Gas Reheat (HGRH) output or the standard modulating
heating output is controlled to maintain the current Reheat
Setpoint. If Reheat Type software conguration parameter is
set to Staged Hot Gas, then a digital HGRH output is controlled
to maintain the Reheat Setpoint. If the Reheat Type software
conguration parameter is set to Modulating Hot Gas, then
an analog HGRH output is controlled to maintain the Reheat
Setpoint. If the Reheat Type software conguration parameter
is set to Standard Heat, then the normal heating analog output
is controlled to maintain the Reheat Setpoint.
• Cooling/Fan Only: In the Cooling and Fan Only states,
a PI Loop is used to control the HGRH valve to maintain
the Discharge Air Temperature at the Dehumidication
Reheat Setpoint. The deadband for this loop is the same
one used for other control of heating to maintain the DAT
Heating setpoint.
• Cooling: In the Cooling state, the Dehumidication
Reheat Setpoint equals the DAT Cooling Setpoint. For
DAT units, this is the normal DAT setpoint resulting from
any reset. For Zone Control units, this setpoint is the
result of a PI Loop based on the control temperature as is
done in the Economizer state or with modulated cooling
in the Cooling state.
• Fan Only: In the Fan Only state, the Dehumidication
Reheat Setpoint equals an editable MaxReheatSpt
(Default = 65°F) when the control temperature drops to
the Occupied or Unoccupied Heating Setpoint and equals
an editable MinReheatSpt (Default = 55°F) when the
control temperature rises to the Occupied or Unoccupied
Cooling setpoint. The Dehumidication Reheat Setpoint
varies linearly between these two points.
This means that no matter what the Control Temperature
is, including OAT, the temperature leaving the unit is at a
maximum just before the unit needs to go into heating and at
a minimum just before the unit needs to go into cooling. This
reduces opportunity for unit to go into heating or cooling during
dehumidication.
Staged HGRH Control
In the Cooling and Fan Only states, a staged output is turned
ON and OFF to control the HGRH valve to maintain the
discharge air temperature at the Dehumidication Reheat
Setpoint. The deadband for this setpoint is an adjustable.
When the DAT is above the Dehumidication Reheat Setpoint
by more than half the deadband, cooling capacity is greater
than 0% and the Dehumidication Reheat Timer has expired,
the reheat output is turned on. When the DAT is below
the Dehumidication Reheat Setpoint by more than half
the deadband and the Dehumidication Reheat Timer has
expired, or if the cooling capacity is 0%, the reheat output is
turned OFF.
Modulating HGRH Control
In the Cooling and Fan Only states, a PI Loop is used
to control the HGRH valve to maintain the discharge air
temperature at the Dehumidication Reheat Setpoint. The PI
Loop is enabled when the unit is in the Cooling or Fan Only
operating state and dehumidication becomes active.
NOTE: When congured for modulating hot gas reheat the
reheat valve is stroked open and then closed every
day at 2:00 AM as long as dehumidication is inactive
and the unit is not in the Cooling operating state at
the time.
Reheat Compressor Limiting Control
A special cooling capacity limiting function is used when a
unit is congured for Hot Gas and/or Liquid subcooling control
types of reheat. During dehumidication, if the unit cannot
provide enough reheat to meet the discharge temperature
setpoint this limiting function will act to reduce the cooling
capacity of the circuit opposite the reheat circuit in an attempt
to increase the leaving coil temperature and therefore the
reheat temperature. An Event will also be logged.
Reheat compressor limiting is allowed during dehumidication
operation if the following are true for longer than the cooling
stage time:
• Reheat compressor limiting is set to Yes
• Reheat type equals ModHGRH, ModLSC or ModHG &
LSC
• A xed compressor in the circuit opposite the reheat
circuit in ON
• The Reheat capacity equals 100%
• The DAT is less than the Reheat set point-1/2 DB
If all of the above items are true for longer than the cooling
stage timer setting, the limiting function would reduce the
cooling capacity of the circuit opposite the reheat circuit by one
stage. This reduction in cooling capacity would continue until
all compressors opposite the reheat circuit have been staged
off as long as all of the above remained true.
The limiting function will remain active until the following are
true for longer than the cooling stage time:
• Reheat capacity is less than or equal to the minimum
reheat capacity
• The DAT is greater than the Reheat set point-1/2 DB
• All of the xed stages have been staged back ON.
OM 920-6 • MICROTECH UNIT CONTROLLER 98 www.DaikinApplied.com
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Daikin MicroTech I Specifications

General

Brand	Daikin
Model	MicroTech I
Category	Controller
Language	English