Daikin PreciseLine Series Installation And Maintenance Manual page 52

Minimum Compressor On/Off Time
When a compressor is turned off, it must remain off for the
duration of the Compressor Minimum Off Time. When a
compressor is turned on, it must remain on for the duration
of the Compressor Minimum On Time. After initial power
up of the controller, clearing of a fault, or transition from
unoccupied, all compressors must remain off for the duration
of the Compressor Minimum Off Time plus a randomly (at each
power up) generated value of up to 60 additional seconds. This
prevents multiple units from turning on their compressors at
the same time when power is applied. If Compressor Minimum
On Time or Compressor Minimum Off Time is '0' then that
functionality is disabled.
Lead Compressor Selection
If Lead Compressor Configuration is Run Hours, when a
compressor is needed to satisfy the cooling requirement, the
controller will turn on the compressor with the lowest total
runtime. If Lead Compressor Configuration is Compressor
1, when a compressor is needed to satisfy the cooling
requirement, the controller will turn on the compressors in
numerical order. Compressors will be turned off in the reverse
order that they were turned on.
VAV Box Signal/Fan Operation Signal
Digital Output #6 (MCB-T4-DO6) will be energized any time the
fan is running.
Dehumidification Operation
In dehumidification mode, mechanical cooling is used to
cool air low enough to lower the moisture content of the air
and then reheat it to comfort conditions. Dehumidification is
only available on units with a reheat coil that are equipped
with space humidity, discharge air temperature, and (when
necessary) leaving coil temperature sensors.
Passive Dehumidification
Passive dehumidification can be field-enabled on constant
air volume units with space humidity sensors, but without
reheat coils. Passive dehumidification can be used to reduce
the supply fan speed when the unit is cooling and the space
humidity is above the dehumidification setpoint.
Dehumidification Initiation
An analog sensor is mounted in the space to sense Relative
Humidity. Active dehumidification is disabled when the unit
is in the cooling or heating state. Passive dehumidification
is only available when the unit is in the cooling state. When
dehumidification is enabled, operation is initiated when
Humidity Control is set to either Relative Humidity or Dew Point
and that value rises above the appropriate setpoint by more
than half its deadband.
IM 1267-7 • PRECISELINE AIR HANDLER
MicroTech 4 Lite Unit Operation
Dehumidification Termination
Dehumidification is terminated if the selected variable, Relative
Humidity or Dew Point, drops below the appropriate humidity
setpoint by more than half its dead band plus the appropriate
differential. Dehumidification is also terminated if cooling is
disabled for any reason or the unit enters either the Heating or
Cooling state.
Chilled/Hot/Changeover Water Valve
Operation
Two-Position On/Off Valves
Appropriate valve will be open when cooling or heating is
required and closed when it is not.
Modulating Valves
When cooling or heating is required, valves will modulate open
or closed to meet demand. For Single Zone VAV and DSP
fan control, the valve will modulate to maintain a discharge
air temperature. For constant speed fan control, the valve will
modulate to maintain a control temperature (space, return, or
an average of the two).
Valve Action
Valve control is factory configured to be direct or reverse acting
based on how they were ordered. If necessary, this can be
configured in the field using the controller's operation manual.
Entering Water Temperature Sampling
Units with a changeover chilled/hot water valve come with an
entering water temperature sensor (field installed for certain
applications) required to ensure that the water temperature
is adequate for the appropriate mode of operation. On a
call for heating or cooling, the valve will be opened to a
minimum position and the water temperature monitored. If
the temperature is deemed to be adequate within 2 minutes,
normal operation will occur. If the temperature is deemed to
be inadequate, the mode of operation (heating/cooling) will be
locked out for 2 hours.
Electric Heat Operation
Single Stage Electric Heat
Electric heat will be enabled when heating is required and off
when it is not.
4 Stage/SCR Electric Heat
When heating is required, the heating output will stage/
modulate on/off to meet demand. For Single Zone VAV and
DSP fan control, the electric heat output will modulate to
maintain a discharge air temperature. For Constant Speed
fan control, the electric heat output will modulate to maintain a
control temperature (space, return, or an average of the two).
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