Solution Decrystallization; Condensing Water Tube Scale; Water Treatment - Carrier 16JT Series Start Up & Operation Manual

Solution Decrystallization —
when strong solution concentration and temperature cross
over to the right of the crystallation line on the equilibrium
diagram (Fig. 22A and 22B). It should not occur if
machine controls are correctly adjusted and machine is
properly operated. Refer to the Troubleshooting Guide,
pages 41 and 42, for probable causes and remedies.
If crystallization occurs, it generally takes place in the shell
side of the low-temperature heat exchanger and blocks the
flow of strong solution from the low-stage generator. The
strong solution then overflows into a pipe that returns it di-
rectly to the absorber sump. The solution pump(s) then re-
turns the hot solution through the heat exchanger tubes, au-
tomatically heating and decrystallizing the shell side.
If crystallization results from a long, unscheduled shut-
down (such as from a power failure) without proper dilu-
tion, the solution pump(s) may become bound and fail to
rotate. This will cause the overloads to trip out. In such a
case, decrystallize as follows:
1. Heat the solution pump casing and adjacent lines with
steam.
Under no circumstances apply heat directly to pump
motor or controls when warming the casing. Do not
apply direct heat to any flange connections; high tem-
perature can deteriorate the gasket material.
2. Rotation of a hermetic pump cannot be viewed directly.
Check the solution pump rotation by installing a com-
pound gage on the pump service valve and reading dis-
charge pressure. Reset the pump overloads in the control
panel if they are tripped.
If the pump is rotating normally, the gage will show a
reading above atmospheric pressure. If the pump casing
and discharge line are completely blocked, the gage will
show zero atmospheric pressure. If the pump interior is
only partially blocked, a deep vacuum will indicate that
the pump is not rotating.
3. Continue heating the casing until gage pressure shows above
atmospheric pressure with pump overloads reset. Do not
reset pump overloads more than once in any 7-minute
period.
If the heat exchanger is also blocked, the decrystalliza-
tion process will begin as soon as the solution pump starts
rotating and the adjacent weak solution lines have de-
crystallized. If the heat exchanger or adjacent piping does
not decrystallize automatically, heat the blocked area ex-
ternally with steam or a soft torch flame. Crystallization
in purge piping can be broken up by applying heat in the
same manner.
Crystallization occurs
40
4. If the strong solution line from heat exchanger to ab-
sorber spray nozzles is blocked, turn off the condensing
water pump and operate the machine with capacity con-
trol valve open. Turn the Cycle-Guard™ switch to
MANUAL to dilute the solution. The entire unit will pick
up heat and the crystallization will dissolve. Do not heat
solution leaving absorber above 140 F (60 C) to avoid
overheating the solution pump motor. If severe crystalli-
zation is present, it may take 4 to 6 hours to fully
decrystallize.
When heating the machine in this manner, remove the
low-temperature cutout (LTCO) and thermoswitch sens-
ing bulbs from their wells and insulate them to prevent
overheating. When machine temperatures return to nor-
mal, recalibrate the LTCO and thermoswitches (see Low-
Temperature Cutout Adjustment and Thermoswitch Ad-
justment section, pages 35 and 36).

Condensing Water Tube Scale

perature difference between condensing water leaving the con-
denser and refrigerant condensate from the condenser is greater
than the normal 4 to 7° F (2 to 4° C) difference at full load
(capacity control valve fully open). Scale reduces heat trans-
fer, increases steam consumption, and limits machine capac-
ity. Scale can also cause serious corrosion damage to the tubes.
Soft scale can be removed from tubes with cleaning brushes,
specially designed to avoid scraping or scratching the tube
walls. The brushes are available through your Carrier rep-
resentative. Do not use wire brushes.
Hard scale may require chemical treatment for its pre-
vention or removal. Consult a water treatment specialist
for proper treatment.
Water Treatment —
Untreated or improperly treated wa-
ter may result in corrosion, scaling, erosion, or algae. The
services of a qualified water treatment specialist should be
obtained to develop and monitor a treatment program.
Water must be within design flow limits, clean, and treated
to ensure proper machine performance and reduce the
potential of tubing damage due to corrosion, scaling, or
erosion. Carrier assumes no responsibility for chiller dam-
age resulting from untreated or improperly treated
water.
is indicated if the tem-