87
(20) Generator Entering
Hot Water Limit Control
(Hot Water Only)
Generator Entering Hot Water Temperature Limits apply to
both single and two stage absorption units. The purpose is
to limit the heat energy to the generator to prevent tube
expansion damage within the generator. See Figure 36.
This is a proportional limit control that will limit loading as
the hot water temperature approaches the temperature
limit value. There is a one-degree dead band above and
below the limit value where no loading is allowed. If the
limit value is reached and exceeded beyond the dead band,
the limit algorithm will cause the unit to unload at a rate
that is proportional to the amount of error that is sensed.
The loading and unloading proportional rate is 3%/°F. The
limit value for a single stage unit is fixed at 270°F and the
limit value for a two-stage absorber is fixed at 370°F.
Figure 36. Loading region and temperature limits
Allowed %
Loading
SIngle Stage 269 Degree F
Two Stage 369 Degree F
Single Stage 271 Degree F
Two Stage 371 Degree F
Hot Water
Temperature Entering
HTG
Hold Region
UnLoad Region
Load Region
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