Water Pump Control; Cooling: Multistage - Daikin MicroTech III Operation Manuals

In the Economizer state, the Water Regulating Valve is
normally closed . The WRV Start Sequence described below
is initiated in the Economizer state whenever either of the
following is true:
All of the following are true:
• All of the following are true:
– Cooling Status=Enabled or Off Ambient
– Economizer Position is greater than 95 .0% for more
than the Cooling Stage Time AND
– Discharge Air Temperature > DAT Cooling Setpoint +
½ the cooling dead band for more than the Cooling
Stage Time
• Both of the following are true:
– Cooling enabled AND
– Economizer Disabled
WRV Start Sequence
The following Startup Sequence is followed when a stage up
from stage zero is required and the Water Regulating Valve is
closed .
The Water Regulating Valve is set to an minimum
(Default = 10%)
The Entering Water Temperature (EWT) is measured after
the WRV has been at its minimum position for a default of 60
seconds . An Initial WRV Position is then calculated based on
the measured EWT . The Unit transitions to Cooling and the
first compressor is started when the time to initial position
has passed. The first compressor runs for an editable Initial
Operation Time with the WRV at the calculated initial position .
Control then reverts to normal PI control .
Special Procedures for Units with WRV and More
• When the unit enters Cooling, a compressor on either
circuit # 1 or # 2 must start first if one is enabled because
the pressure sensors are on circuits # 1 and # 2 .
• If both circuits # 1 and #2 are disabled due to High
Pressure or Low Pressure alarms, the lead compressor
is determined by the compressor circuit that contains the
compressor with the fewest run hours .
• If both circuit # 1 and circuit # 2 are disabled, The WRV
will be controlled based on the EWT and the calculated
initial position .
• Control of the WRV reverts to normal PI control if either
circuit # 1 or circuit # 2 is enabled and its compressor is
turned ON .
• All compressors are disabled if EWT drops below the
minimum WRV temperature value by more than the
Outside air cooling lockout differential .
• Compressors are re-enabled if EWT rises above the
minimum WRV temperature value .
OM 920-6 • MICROTECH UNIT CONTROLLER

Water Pump Control

The Pump output is in the on position if any of the following
are true:
• The Bypass Valve output is being driven above 0%
• The Water Regulating Valve output is being driven
above 0%
• A waterside economizer is installed and the unit is in the
Economizer state
• The unit is the Cooling state
• The Unit is in the Start Initial state and Flush Mode is set
to Yes
• The unit has a waterside economizer and a Freeze Fault
or Freeze Problem is active
• The unit has a waterside economizer and 10 minutes
have not yet passed after a Freeze Fault or Freeze
Problem has disappeared

Cooling: Multistage

Entering the Cooling Operating State
The unit enters the Cooling operating state from the Fan Only
operating state when the control temperature rises above the
Occupied or Unoccupied Cooling Set Point by more than half
the Cooling Dead Band and the discharge air temperature is
above the discharge cooling setpoint by more than half the
cooling Dead Band . The unit transitions from Cooling to Fan
only when the control temperature falls below the Occupied or
Unoccupied Cooling Set Point by more than half the Occupied
or Unoccupied Cooling Dead Band . The unit will also transition
from the Cooling to Fan only operating state if Cooling
operation is disabled due to OA ambient lockout .
Staging -DAT Control
In the Cooling state, compressor stages are turned on
and off to maintain an average Discharge Air Temperature
near the Discharge Cooling Setpoint . When the load is
such that cooling capacity is being staged up and down
between two stages, this control sequence causes the unit
to operate longer at the stage that produces the discharge
air temperature that is closer to the setpoint over time which
results in an average discharge air temperature that is very
close to the Discharge Cooling Setpoint .
This setpoint may be fixed or reset as described in the
Cooling DAT Reset section . External devices such as VAV
boxes maintain the desired space conditions . The unit may
be a Constant Volume unit, but it is normally a Variable Air
Volume unit . If the Discharge Air Temperature is approaching
the setpoint, the number of stages continues to increase or
decrease until the actual temperature gets within half the
deadband . Control of cooling stages is based on two values,
the Degree Time Above and the Degree Time Below the
Discharge Cooling Setpoint . The difference between the actual
discharge air temperature and the Discharge Cooling Setpoint
is added to one of the Degree Time values every ten seconds .
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