Carrier 16DF013-050 - Manual (Page 11)

PLOTTING THE HEATING SOLUTION CYCLE — A heat-
ing solution cycle at typical full load conditions is plotted in
Fig. 8 from Points 1 through 11. The corresponding values
for these typical points are listed in Table 3. The heating cycle
operates with lower (more dilute) solution concentrations than
used with the cooling cycle because most of the refrigerant
water is drained from the evaporator into the solution. Note
that these values will vary with different loads and operating
conditions.
Point 1 represents the strong solution in the absorber after
being sprayed from the absorber nozzles, before it begins to
mix with condensed water vapor draining from the evapo-
rator. The temperature of the solution to the spray nozzles
can be measured, but the concentration cannot be sampled.
Point 2 represents the diluted (weak) solution, with the con-
densed water, leaving the absorber and entering the low-
temperature heat exchanger. This point can be measured with
a solution sample from the pump discharge.
Point 3 represents the weak solution as it leaves the low-
temperature heat exchanger. It is at the same concentration
as Point 2 but at a slightly warmer temperature after gaining
some heat from the strong solution. This temperature can be
measured. At this point, the weak solution is split, with ap-
proximately half of it going to the low-stage generator, and
the rest of it going to the high-temperature heat exchanger.
Although the solution sent to the low-stage generator is not
used in the heating function, the solution distribution and
flow rates are maintained approximately the same as in the
cooling cycle to minimize piping and control differences.
Point 4 represents the weak solution as it leaves the high-
temperature heat exchanger and enters the high-stage gen-
erator. It is at the same concentration as Points 2 and 3, but
at a higher temperature after gaining heat from the strong
solution. This temperature can be measured.
Point 5 represents the weak solution in the high-stage gen-
erator after being preheated to the boiling temperature. The
solution will boil at temperatures and concentrations corre-
sponding to a saturated temperature established by the vapor
condensing temperature in the evaporator. This condition is
internal and cannot be measured.
Point 6 represents the strong solution leaving the high-stage
generator and entering the high-temperature heat exchanger
after being reconcentrated by boiling out refrigerant water.
The heat energy in the vapor produced in this process is used
directly for heating the circulating hot water in the evapo-
rator. The leaving strong solution temperature can be mea-
sured but the saturation temperature cannot be measured ac-
curately to plot the point.
Point 7 represents the strong solution from the high-temperature
heat exchanger as it flows between the two heat exchangers.
It is the same concentration as Point 6, but at a cooler tem-
perature after giving up heat to the weak solution. It is an
internal condition and cannot be measured.
Point 8 represents the weak solution leaving the low-stage
generator and entering the low-temperature heat exchanger.
It is at a slightly higher concentration than the entering so-
lution because it has picked up some heat from the hot vapor
in the generator tubes, as an incidental occurrence in the flow
process.
Point 9 represents the mixture of strong solution from the
high-temperature heat exchanger and the weak solution from
the low-stage generator after they both enter the low-
temperature heat exchanger. It is an internal condition and
cannot be measured.
Point 10 represents the combined strong solution before it
leaves the low-temperature heat exchanger, after giving up
heat to the weak solution. This is an internal condition and
cannot be measured.
Point 11 represents the strong solution leaving the low-
temperature heat exchanger and entering the absorber spray
nozzles, after being mixed with some weak solution in the
heat exchanger. The temperature can be measured, but the
concentration cannot be sampled. After leaving the spray
nozzles, the solution is somewhat cooled and concentrated
as it flashes to the lower pressure of the absorber.
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