71
(13) Crystallization Sensing
Detection and Recovery (SDR)
SDR is a control system strategy that through continuous
sensing will detect unusual solution flow patterns, and
upon detection, a recovery cycle is executed and operating
adjustments are made to correct the condition. The system
protects the generator solution cycle from solution
crystallization and in worst case shuts the machine down
safely when it cannot produce the required chilled water
temperature. See Figure 22.
*SDR becomes functional when the solution temperature
difference between the strong leaving High Temperature
Heat Exchanger (HTHX) and the solution leaving the Low
Temperature Generator (LTG) becomes greater than 10°F;
at other times, SDR temperature will be displayed as
“invalid”.
The SDR system feature provides a secondary line of
defense against crystallization over and above the routine
Low Temperature Heat Exchanger (LTHX) concentration
control system. The SDR feature protects the machine from
transient conditions that the machine does not control. This
system replaces the PCL float and logic of prior designs.
Some transient operating conditions may cause salt
crystals to precipitate out of the solution. Continued
operation with this condition can restrict solution flow
through the heat exchanger, resulting in a chiller failure that
may be difficult to correct. The SDR control system detects
this condition and takes corrective control action first, to
correct the condition, and second, to maintain limited
machine operation. The SDR will cycle twice before the
machine is actually shut down upon the third occurrence.
Figure 22. Solution flows
Input sensor (A)
Strong solution
from level
control-float or
HTHX.
Input sensor SDR (C)
Solution from Low
Temperature Generator
(LTG)
SENSING
Normal flow indicated by solid arrows.
DETECTION
-Abnormal (reverse ) flow is shown by dashed arrow. If restriction
to solution (B) occurs in Low Temperature Heat Exchanger (LTHX)
the flow pattern reverses and follows the dotted line.
Low Temperature
Heat Exchanger
(LTHX)
Input (B) Mix solution
sensor-entering
absorber
RDV1 valve remains closed until reverse flow
is detected.
Electrical Block Diagram
Circuit Module
Detection Logic
Software
Controlled
De-Energized = Normally Open
Energized = Closed
Unit Power OFF = Normally Open (Dump)
115 Vac
RDV1 Valve
(A) Solution Entering Level
Control Sensor
(C) Crystallization Sensing
Detecting Sensor
(B) Solution Leaving
LTG Sensor