Daikin Maverick II MPS062E Installation And Maintenance Manual page 37

Stage Up After Stage Up:
If the time since the last stage change exceeds the cooling
stage timer, the discharge air temperature is greater than the
Discharge Cooling Setpoint by more than half the deadband,
the last stage change was a stage up, and dehumidification is
not active; cooling capacity is increased by one stage
Stage Up After Stage Down:
If the time since the last stage change exceeds the cooling
stage timer, the discharge air temperature is greater than the
Discharge Cooling Setpoint by more than half the deadband,
the last stage change was a stage down, the Degree Time
Above value is greater than or equal to the Degree Time Below
value, and the dehumidification is not active; cooling capacity
is increased one stage.
Stage Down After Stage Down:
If the time since the last stage change exceeds the cooling
stage timer, the discharge air temperature is less than the
Discharge Cooling Setpoint by more than half the deadband,
the last stage change was a stage down, and dehumidification
is not active; cooling capacity is decreased one stage.
Stage Down After Stage Up:
If the time since the last stage change exceeds the cooling
stage timer, discharge air temperature is less than the
Discharge Cooling Setpoint by more than half the deadband,
the last stage change was a stage up, the Degree Time Below
value is greater than or equal to the Degree Time Above
value, and dehumidification is not active; cooling capacity is
decreased one stage.
The Degree Time Below and Degree Time Above values
change whenever a stage change occurs. If the previous stage
change was a stage up and the number of stages increases
again, both Degree Time Above and Degree Time Below are
set to zero.
If the last stage change was a stage up and the stage
decreases due to the Degree Time Below exceeding the
Degree Time Above, the Degree Time Below is reduced by
an amount equal to Degree Time Above and then the Degree
Time Above is set to zero.
If the last stage change was a stage down and the stage
increases due to the Degree Time Above exceeding the
Degree Time Below, the Degree Time Above is reduced by an
amount equal to Degree Time Below and then the Degree Time
Below is set to zero.
Degree Time logic is not used when dehumidification is
active. When dehumidification is active, cooling capacity is
increased if the time since the last stage change exceeds the
cooling stage timer and the Leaving Coil Temperature (LCT)
is greater than the Maximum Leaving Coil Setpoint. When
dehumidification is active, cooling capacity is decreased if
the time since the last stage change exceeds the cooling
stage timer amd the leaving coil temperature is less than the
minimum leaving coil setpoint.
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Average Discharge Control Method Illustration
Figure 42 on page 38
compressor staging control method and is meant to show
a variety of staging possibilities not normal unit operation.
Figure 42 shows nine points on a graph of the discharge air
temperature changing with time. The Cooling Interstage Timer
setting is 5 minutes.
Point 1 Assume that the controller has just staged up and
that DTA and DTB are zero. As a result, the discharge air
temperature drops and the Cooling Interstage Timer is reset.
Point 2 DTA (Area A) equals DTB (Area B). The discharge air
temperature is below the Effective Discharge Cooling Set Point
by more than half the Discharge Cooling Dead Band. However,
since the Cooling Interstage Timer has not yet expired, no
staging action occurs.
Point 3 The Cooling Interstage Timer has expired. DTB (Area
B + Area C) is greater than DTA (Area A) and the discharge
air temperature is below the Effective Discharge Cooling Set
Point by more than half the Discharge Cooling Dead Band.
Therefore, cooling is staged down. As a result, the discharge
air temperature rises, the Cooling Interstage Timer is reset, and
DTA is subtracted from both DTA and DTB. This zeros DTA and
leaves DTB equal to Area C.
Point 4 The Cooling Interstage Timer has expired. The
discharge air temperature is above the Effective Discharge
Cooling Set Point by more than half the Discharge Cooling
Dead Band. However, since DTA (Area E) is not yet equal
to DTB (Area C + Area D), no staging action occurs and the
discharge air temperature continues to rise.
Point 5 The Cooling Interstage Timer has expired. The
discharge air temperature is above the Effective Discharge
Cooling Set Point by more than half the Discharge Cooling Dead
Band and DTA (Area E + Area F) is equal to DTB (Area C + Area
D). Therefore, cooling is staged up. As a result, the discharge
air temperature drops, the Cooling Interstage Timer is reset, and
DTB is subtracted from both DTB and DTA. This zeros both DTA
and DTB since they are equal. Note that the elapsed time since
the last stage change in
Point 6 The Cooling Interstage Timer has expired. Because the
cooling load is now increasing, the discharge air temperature
does not fall below the Effective Discharge
Cooling Set Point by more than half the Discharge Cooling
Dead Band. No staging action occurs for two reasons: (1) the
discharge air temperature is within the Discharge Cooling
Dead Band and (2) DTB (Area H) is not yet equal to DTA
(Area G). Even if the discharge air temperature falls below
the Effective Discharge Cooling Set Point by more than half
the Discharge Cooling Dead Band (as shown just after Point
6), a stage down does not occur because DTB remains less
than DTA. The discharge air temperature starts rising again
because the load is increasing.
37
Sequences of Operation
is an illustration of the "Degree Time"
Figure 42 is 6.3 minutes.
IM 991-2 • MAVERICK II ROOFTOP