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Ramp Loading
— Ramp loading (Configura-
tion
SLCT
CRMP) limits the rate of change of leaving
fluid temperature. If the unit is in a Cooling mode and config-
ured for Ramp Loading, the control makes 2 comparisons be-
fore deciding to change stages of capacity. The control calcu-
lates a temperature difference between the control point and
leaving fluid temperature. If the difference is greater than 4° F
(2.2° C) and the rate of change (°F or °C per minute) is more
than the configured Cooling Ramp Loading value (CRMP),
the control does not allow any changes to the current stage of
capacity.
Low Entering Fluid Temperature Unloading
— When the
entering fluid temperature is below the control point, the
control will attempt to remove 25% of the current stages being
used. If exactly 25% cannot be removed, the control removes
an amount greater than 25% but no more than necessary. The
lowest stage will not be removed.
Hot Gas Bypass
— If equipped, the hot gas bypass valve is
energized only when one compressor is running on circuit A. If
the close control feature is enabled the hot gas bypass valve
may be used as needed to obtain leaving fluid temperature
close to set point.
Cooler Freeze Protection
— The control will try to prevent
shutting the chiller down on a Cooler Freeze Protection alarm
by removing stages of capacity. If the cooler fluid selected
is Water, the freeze point is 34 F (1.1 C). If the cooler fluid
selected is Brine, the freeze point is the Brine Freeze Point (Set
Points
FRZ
BR.FZ). This alarm condition (A207) only
references leaving fluid temperature and NOT Brine Freeze
point. If the cooler leaving fluid temperature is less than the
freeze point plus 2.0° F (1.1° C), the control will immediately
remove one stage of capacity. This can be repeated once every
30 seconds.
Low Saturated Suction Protection
— The control will try to
prevent shutting a circuit down due to low saturated suction
conditions by removing stages of capacity. The circuit alert
condition (T116) compares saturated suction temperature to the
configured Brine Freeze Point (Set Points
FRZ
BR.FZ).
The Brine Freeze point is a user-configurable value that must
be left at 34 F (1.1 C) for 100% water systems. A lower value
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0 200 400 600 800 1000
TIME (SECONDS)
2 STARTS
3 STARTS
DEADBAND EXAMPLE
LWT (F)
MODIFIED
DEADBAND
STANDARD
DEADBAND
8
7
6
5
LWT (C)
LEGEND
LWT — Leaving Water Temperature
Fig. 11 — Deadband Multiplier
1
60
170
130
140
150
160
110
120
130
80
90
100
50
60
70
30
40
-30 -20 -10 0 10 20 304050607080
SCT (F)
SST (F)
LEGEND
Fig. 12 — Operating Envelope for R-410A Compressor
SCT —
Saturated Condensing Temperature
SST —
Saturated Suction Temperature
a30-4969