Daikin WGZ200DW - Page 45

OMM 1130-2 45
Stage Down Now
The Stage Down Now flag is set based on the following tests:
If U
nit Mode = Cool AND
LWT error < -0.5 * Control band AND
More than one compressor running AND
Stage down timer expired THEN
Stage Down Now = True
If U
nit Mode = Cool AND
LWT error < (-0.5 * Control band - stop delta) AND
One compressor running AND
Stage down timer expired THEN
Stage Down Now = True
If U
nit Mode = Cool AND
Number of compressors running > Demand limit AND
Stage down timer expired THEN
Stage Down Now = True
If Un
it Mode = Heat AND
LWT error < -0.5 * Control band AND
More than one compressor running AND
Stage down timer expired THEN
Stage Down Now = True
If Un
it Mode = Heat AND
LWT error < (-0.5 * Control band - stop delta) AND
One compressor running AND
Stage down timer expired THEN
Stage Down Now = True
Compressor Sequencing
Compressor staging is based primarily on compressor run hours and starts. Compressors that have less
starts will normally start before those with more starts. Compressors that have more run hours will
normally shut off before those with less run hours. In the event of a tie on number of starts, the lower
numbered compressor starts first. In the event of a tie on run hours, the lower numbered compressor shuts
off first. Run hours are compared in terms of tens of hours.
If possible, only one compressor per circuit will start before starting the second compressor on any circuit.
If a circuit is unavailable for any reason, the other circuit shall be allowed to stage the second compressor
on. When staging down, one compressor on each circuit shall be left on until each circuit has only one
compressor running.
Low Ambient Start (WaterCooled = NO)
In order to avoid low evaporator pressure alarms at startup, low OAT start logic allows for running at low
evaporator pressures for a longer time than normal as well allowing multiple compressor restart attempts
before locking out the circuit.
Low Ambient Start Procedure
A low OAT start is initiated if the condenser refrigerant saturated temperature is less than 85.0°F when the
first compressor starts. Once the compressor starts the circuit is in a low OAT start state for a time equal
to the Low OAT Start Time set point. During Low OAT Starts, the freezestat logic and low evaporator
pressure events are disabled. The absolute limit for low evaporator pressure is enforced and the