Compressor Operation; Compressor Cooling Lockout; Compressor Heating Lockout; Compressor Minimum On And Off Timers - Daikin MicroTech Operation And Maintenance

Compressor Operation

The UVC is configured to operate the compressor as secondary
(mechanical) cooling when the economizer is available. When
the economizer is not available and the compressor is available,
the UVC uses the compressor when cooling is required.
Compressor operation is interlocked with the F&BP damper
position such that the compressor cannot be energized unless
the F&BP damper is 100% open to face position.

Compressor Cooling Lockout

The UVC is configured to lockout compressor cooling when the
OA temperature falls below the Compressor Cooling Lockout
setpoint (63.5°F/17.5°C). Below this point, only economizer
cooling is available.

Compressor Heating Lockout

The UVC is configured to lock out compressor heating when
the OA temperature falls below the Compressor Heating
Lockout setpoint (30.0°F/1.11°C). Below this point, only
secondary heating (electric heat) is available.
Compressor Minimum ON and OFF
Timers
The UVC is provided with minimum on (3-minute default)
and minimum off (6-minute default) timers to prevent adverse
compressor cycling.

Compressor Start Delay

The UVC is provided with a Compressor Start Delay
configuration variable, which is intended to be adjusted as part
of the start-up procedure for each unit. This variable is used
to delay compressor operation each time the compressor is
required.
NOTE: To prevent strain on a building's electrical supply
system from multiple unit compressors all starting
at the same time after a power failure or after an
unoccupied-to-occupied changeover, Daikin strongly
recommends configuring each unit or groups of units
at start-up with different start delays.
OM 1280-2 • MICROTECH UNIT CONTROLLER

Reversing Valve Operation

The UVC is configured to minimize reversing valve operations.
The reversing valve switches to Heat mode (energized) 5
seconds after the compressor comes on in Heat mode. The
reversing valve remains energized until the UVC enters Cool
mode and the compressor has been running for 5 seconds
(reversing valve de-energized). If the UVC modes are changed
manually (via the keypad/display or network connection) from
Heat-to-Cool or Cool-to-Heat during compressor operation, the
compressor de-energizes immediately.

Motorized Water Valve Delay

For WSHP units (AR or GR), the UVC is provided with a
Motorized Water Valve Delay configuration variable (30
seconds, default). This variable can be used, if necessary
to provide a delay in compressor operation when using a
motorized water valve, allowing time for the valve to open. This
delay, if used, is added to the compressor start delay.

Outdoor Air Fan Operation

For self contained units with a condenser section (AE and
AZ) the UVC is configured with a fan on delay that delays OA
fan operation for a time period (10 seconds, default) after the
compressor starts. The OA fan stops with the compressor.
Water Coil Leaving Air Thermostat
(Freeze-stat)
Unit ventilators ship with a normally-closed low temperature
thermostat to detect low leaving air temperature conditions on
the indoor air coil. This thermostat is mounted on the discharge
air side of the unit's water coil. The low temperature thermostat
cut-out is 38°F +/–2°F (3°C +/– 1°C) and the cut-in is 45°F
+/–2°F (7°C +/–1°C). When the low temperature thermostat
detects low leaving air temperatures (contacts open), the
following occurs.

Valve Control

When the freeze-stat cuts-out:
1. The OA damper closes immediately.
2. The space fan stops.
3. The wet heat and chilled water valve minimums are set
to 50%.
4. If heating is required, the wet heat valve modulates
above 50%, as needed. Auxiliary heat may be used as
needed.
When the freeze-stat cuts-in, the UVC returns to normal
operation.
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Description of Operation
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