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Chief Procurement Officer Email List
Depending on whether heating is required in the perimeter zone, the operating modes of a centrifu-
gal chiller that is incorporated with a heat recovery system in a building with perimeter and interior buy CPO database online
zones can be divided into cooling mode and heating mode operation. Both the cooling and heating
mode operations can be further divided into occupied and unoccupied periods, based on whether
the conditioned space is occupied. The typical operation of a centrifugal chiller that is incorporated
with a heat recovery system is described below. CPO email database
_CPO email database (1)[/caption]
A special four-way valve is mounted at the condenser water entrance, as shown in Fig. 13.8a.
When the four-way valve is in normal operation, the upper half of the brushes are caught by the
baskets at the right-hand end of the condenser tube, and the lower half by the left-hand end baskets.
During normal operation, the condenser water enters the condenser through the lower entrance so
as to provide better subcooling for the liquid refrigerant accumulated at the bottom of the con-
After a predetermined time, a signal is given to the control system to unload the compressor by
closing the inlet guide vanes or reducing the speed of the compressor. The four-way valve reverses
the water direction, which causes the brushes to move in the opposite direction, from right to left
for the upper half brushes and from left to right for the bottom half, until they are caught by the bas-
kets at the ends. As soon as the brushes are caught, a signal is given to the control system to reverse
the water flow again, so that the four-way valve is in normal operation. The brushes stay in the end
baskets during normal operation for about 1 to 4 h until a signal reverses the water flow to repeat
the process. The frequency of the cleaning cycle depends on the contaminants contained in the con-
denser water. The nylon brushes usually have a service life of 4 to 5 years
The maintenance cost can be reduced because the interval for cleaning the condenser tubes is
extended from 6 to 12 months or even longer.
Chemicals for water treatment are still required, but the quantity can be reduced appropriately
according to the actual operating conditions.
The performance of a centrifugal compressor can be illustrated by a compressor performance map
or, simply, a compressor map.
Like a centrifugal fan, a compressor map includes the volume flow,
specific work or power input, efficiency, surge region, and opening of the inlet vanes. Volume flow
and system head are expressed by the compressor performance curve or, simply, compressor curve.
The centrifugal compressor can be operated either at constant speed or at variable speed.
A compressor map of a single-stage centrifugal compressor operating at variable speed is illustrated
in Fig. 13.10b. The abscissa, ordinate, and required system head curves are the same as those in the
compressor map at constant speed (see Fig. 13.10a). The inlet vanes are fully open at both design
load and part-load operations. Their main differences are these:
Compressor curves are curves at various rotating speeds, such as 105 percent, 100 percent, . . .,
80 percent of speed at design condition, instead of curves at various inlet vane openings on a con-
At lower heads, the surge region is enlarged.
Difference between Centrifugal Compressors and Centrifugal Fans CPO email database
During part-load operation, the following means are used to modulate the capacity of a centrifugal
Open the inlet vanes.
Use an adjustable-frequency ac inverter to vary the compressor rotating speed. Adjustable-
frequency variable-speed drive is discussed in Sec. 15.4.
Combine the opening of inlet vanes and variable-speed control by means of an inverter.
Vary the speed of the steam- or gas-turbine-driven large centrifugal chillers.
A hot-gas bypass provides no energy saving at reduced system loads as specified in Sec. 11.5.
Although centrifugal compressors and centrifugal fans are both centrifugal turbomachinery, and
both centrifugal chillers and centrifugal fan duct systems use inlet vanes and variable-speed drives
to provide capacity control during part-load operation, there is an important difference between the
centrifugal chiller and centrifugal fan duct system. In a fan duct system, the total pressure of the
centrifugal fan is used mainly to overcome the friction and dynamic losses in airflow. This required
fan total pressure drops considerably when the air volume flow is reduced. In the centrifugal chiller,
on the other hand, the system head is used mainly to lift the evaporating pressure to condensing
pressure to produce the refrigerant effect. The pressure drop due to friction and dynamic losses of
refrigerant flow is only a small part of the required head. Reduced volume flow of refrigerant at
part-load operation has a minor influence on the required system head.
The primary factor that affects the system head at part-load operation is the difference between
condensing and evaporating pressures or temperatures, pcon pev or Tcon Tev . For a water-cooled
condenser using condenser water cooled from a cooling tower, the outdoor wet-bulb temperature buy CPO database online
directly influences the entering temperature of condenser water and, therefore, the condensing
temperature and pressure.
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During part-load operation, because the condensing and evaporating surface areas at reduced
volume flow of refrigerant are greater than the required area, there is a drop in condensing tempera-
ture Tcon and an increase in evaporating temperature Tev . Most probably, the outdoor wet-bulb
temperature also drops at reduced load. Therefore, the profiles for required system head at part-load
operation for a water-cooled centrifugal chiller usually fall into the following three schemes:
Inlet vanes are pivoted movable vanes installed at the inlet of the impeller, as shown in Fig. 13.1. In
Fig. 13.1 only one set of inlet vanes is shown. For a three-stage centrigugal chiller with three im-
pellers, actually there are three sets of inlet vanes, one for each impeller, to improve the chiller’s
performance. These vanes are linked mechanically so that they can turn simultaneously around the
axis. When the opening of the inlet vanes at the inlet of the centrifugal compressor is reduced, it
throttles the volume flow of vapor refrigerant and imparts a spin or prerotation on the refrigerant
flow before it enters the impeller. If the direction of the spin is the same as the direction of rotation
of the impeller, the tangential component of the absolute velocity of the fluid elements has a posi-
tive value. The head lift thus developed is smaller than if vapor refrigerant enters the impeller with
a radial entry. This effect produces a new performance curve at a lower head and volume flow at
each position of reduced vane opening.
The compression efficiency
com decreases as the inlet vane opening angle decreases, as the va-
por refrigerant at inlet is further deviated from the radial entry and the inlet area is reduced. At high
load ratios with larger openings, compression efficiency is only slightly affected. At low load ratios,
throttling at the inlet vanes causes considerable reduction of compression efficiency. However, the
reduction of shaft power from the decreases in head lift p and volume flow of vapor refrigerant
compensates for the effect of the drop in CPO Email
com and shows energy saving from inlet vane capacity
A large modern centrifugal chiller plant usually includes multiple chillers to prevent the entire shut-
down of the refrigeration system when one chiller fails to operate. Control of a centrifugal chiller
plant, therefore, includes the functional controls and optimizing controls, as well as the unit control
of a single chiller and the system control of a multiple-chiller plant. Unit control consists of spe-
cific, safety, diagnostic, and optimizing controls. Only a microprocessor-based DDC system can
possibly perform all these duties. For functional controls, a DDC unit controller monitors and
controls the following:
Chilled water leaving temperature control
Safety features, including oil pressure, low-temperature freezing protection at the evaporator, high
condensing temperature control, motor overheating, and time delaying
Status features, including condenser water flow, chilled water flow, electric current, and refriger-
ant and chilled water temperatures and pressures at key points
Chiller plant optimizing control with multiple centrifugal chillers includes the following:
Optimize the on /off staging of the multiple chillers.
Optimize start and stop.
Control condenser water entering temperature.
Continuous modulation control is extensively used for chilled water leaving temperature Tel control
in centrifugal chillers. A temperature sensor located in the chilled water pipes at the exit of the
evaporator is used to sense Tel. The DDC unit controller either varies the position of the opening of
the inlet vanes or varies the speed of the compressor motor through an adjustable-frequency ac in-
vertor. The volumetric flow of refrigerant then decreases or increases, as does the capacity of the
centrifugal chiller. Chilled water leaving temperature control is actually the capacity control of a
centrifugal chiller. CPO Email
Interaction of the centrifugal chiller and the cooling tower must be considered when one
optimizes the condenser water temperature entering the condenser T ce so as to minimize power
consumption. The control strategy is to minimize the total power consumption of the chiller and
According to Cascia (1988), the condenser water temperature should be floated; i.e., it should
rise and fall with the outdoor wet-bulb temperature in agreement with the following requirements:
Temperature Tce must be maintained above the lower limit specified by the centrifugal chiller
manufacturer, such as 60°F (15.6°C), in order to maintain a necessary head pressure for proper
operation. If the lower limit is reached, the tower fan must be turned off first; then the tower by-
pass valve should be modulated to maintain Tce equal to or above the specified limit.
If Tce reaches the high limit, possibly more tower fans should be added so that Tce does not exceed
the high limit.
Electric Demand Limit Control. Electric demand or electric current limit control is used to pre-
vent the electric current from exceeding a predetermined value. A motor current is measured at the
current, transformers, and a proportional signal is sent to the DDC unit controller. If the current
exceeds a predetermined limit, the controller directs the inlet vanes to close or reduces the rotating
speed of the compressor through the adjustable-frequency ac inverter. The limit could be from 40 to
100 percent of the electric demand.
Motor Protection. The compressor motor assembly is the most expensive part of the centrifugal
chiller. For a typical control that protects a motor against high temperatures, if the resistance tem-
perature detector in the motor stator winding senses a temperature under 165°F (73.9°C), the DDC
unit controller introduces a time delay, normally of 4 min, after the chiller switch is turned on. If CPO email database providers
the sensed temperature exceeds 165°F (73.9°C), a start delay of 15 min is required. If the stator
winding temperature exceeds a dangerous upper limit, such as 265°F (129.4°C), the DDC unit con-
troller then prohibits the operation of the motor because of its high temperature.
There are also protection controls against current overload, temporary power loss, low voltage,
and phase unbalance.
Low-Temperature and High-Pressure Cutouts. Refrigerant temperature at the evaporator is de-
tected by a sensor. This information is sent to the DDC unit controller so that if the predetermined
low-temperature cutout is approached, inlet vanes hold or close to provide freeze protection for the
A pressure sensor detects the condensing pressure of the refrigerant. The DDC unit controller
outputs override the inlet vane position instruction to close the inlet vanes if the condensing pres-
sure reaches the predetermined limit.
High Bearing Temperature. If the bearing temperature detected by a temperature sensor exceeds
a preset value, the chiller is stopped immediately.
Short-Cycling Protection. Usually a time delay, typically of 30 min, is needed to restart a cen-
trifugal chiller after it has been turned off to prevent short cycling.
Surge Protection. A surge detection device is used to send a signal to the DDC unit controller. A
head relief scheme is implemented by lowering the condenser water temperature. If the surge con-
tinues beyond a predetermined time period, the compressor is shut down.
Loss of Flow. If a loss of flow in evaporator or condenser is detected by the flow switch, the
chiller will be shut down accordingly.
Air Purge. An automatic purge operation includes the operation of an air purge unit within a spe-
cific time interval, for instance, 5 min of air purge every 2 h. Both condensable gas and condensable
vapor, mainly water vapor, leaking into the centrifugal chiller raises the purge drum pressure. If an
increase in drum pressure is detected by a pressure sensor, the period of operation of the air purge
unit is lenthened.
Fault Detection and Diagnostics
As discussed in Sec. 5.15, fault detection and diagnostics aid in detecting a problem, solving a CPO Email
problem, and getting the chiller on-line quickly in case there is a problem. For a typical diagnostic
display module, more than 100 diagnostic checks and displays are available. Diagnostic modules
are also able to display the run test to verify the thermistor, potentiometer, oil pump, air purge unit,
and compressor before the chiller is started.
All the inputs (such as switches and set points), output displays (such as operating mode indicators,
key parameter monitors, and status lights), and diagnostic displays should be visible at a glance on
the control display panel. They should be easy to understand and to use.
The sensed chilled water leaving temperature Tel is higher than the set point, indicating a de-
mand for refrigeration.
2. The interlocked chilled water pump switch starts the chilled water pump, and the chilled water
flow is sensed by the chilled water flow sensor.
3. A signal is issued to start the condenser water pump and the tower fans; the condenser water
flow is sensed by the flow switch.
4. A signal is sent to start the oil pump, and the oil pressure is sensed by the pressure sensor.
5. The short-cycling protection timer is checked to see whether the time period after the previous CPO email id list
shutdown is greater than the predetermined limit.
6. A command is sent to close the inlet vanes and is confirmed.
After the oil pressure has been established for 10 to 20 s, a start command is sent to the com-
pressor motor starter.
8. A successful start is followed by a display of “run normal.” Failure to perform a successful start
shuts down the compressor, and the diagnostic code is displayed for correcting the fault. After
correction and reset, the start sequence may be repeated to attempt a successful start again.
9. During “run normal” operation, the current limit, the condenser high-pressure limit, and the CPO email database providers
evaporator low-temperature cutout are monitored to see whether these limits have been
approached. If so, the relevant controls hold or close the inlet vanes so that these limits are not
exceeded. When a surge is detected, the head relief relay is energized. If surge continues for
15 min, the compressor will shut down.
10. When the DDC unit controller originates a stop signal based on the timer’s schedule, a “prepar-
ing to shut down” message appears as the inlet guide vanes close or the variable-speed com-
pressor unloads. The compressor and condenser pump motor starter are deenergized. The oil
pump will continue to run for about 10 min. Finally, the chilled water pump for this chiller is
deenergized. The chiller can be manually stopped at any time by pushing the Stop key.
On the other hand, if the capacity of the selected compressor is greater than the evaporator, more
evaporized refrigerant is extracted than the liquid refrigerant vaporized in the evaporator. The evapo-
rating pressure and temperature gradually drop until the mass flow rate of suction vapor of the cen-
trifugal compressor is just equal to the mass flow rate of the vaporized refrigerant in the evaporator.
If the capacity of the selected condenser is greater than the compressor at design conditions, more
hot gas can be condensed to liquid form in the condenser than the compressor can supply. The result is
a drop in condensing pressure pcon and temperature Tcon. Because the condenser water entering tem-
perature remains unchanged, a drop in Tcon results in a lower log-mean temperature and a reduction in
the condensing capacity. A new system balance is then formed between the mass flow rate of hot gas
condensed in the condenser and that discharged from the centrifugal compressor at a lower Tcon.
On the other hand, if the capacity of the selected centrifugal compressor is greater than the con-
denser, more hot gas is discharged to the condenser by the compressor than can be condensed in the
condenser. The result is a rise in condensing pressure pcon and temperature Tcon . A rise in Tcon means
a higher log-mean temperature and a greater condenser capacity, as well as a greater head lift,
which reduces the discharged volume flow rate of the hot gas from the centrifugal compressor. Both
effects are helpful to make a new system balance between the compressor and the condenser.
If there is a reduction of coil load in the AHUs or in the terminals, the chilled water temperature
entering the evaporator Tee falls. Because the rate of heat transfer and the amount of refrigerant
evaporated are only slightly affected, Tel is lower than 44°F (6.7°C), the set point. CPO lists
When the temperature sensor at the exit of the evaporator senses a drop in Tel and signals the
DDC unit controller, the positioner of the inlet vanes is actuated to close the opening.
compressor is now operating at less than the design head, and the mass flow rate of the refrigerant
extracted by the compressor is reduced from to . At part load, both the evaporating pressure pev
and temperature Tev tend to increase. Such an effect further reduces Tm, the boiling heat-transfer co-
efficient hb, and the overall heat-transfer coefficient Uo. The increase in mass flow rate due to a smaller
head lift at part-load operation is offset by the closing of the inlet vanes of the compressor. The rate of
heat transfer and the rate of evaporation are, therefore, decreased until the mass flow rate of evaporated
refrigerant is equal to the mass flow rate of the refrigerant extracted by the centrifugal compressor.
Because the rate of condensation of refrigerant in the condenser is greater than the reduced mass
flow rate of hot gas discharged from the compressor , the condensing pressure pcon and tempera-
ture Tcon tend to drop until the rate of condensation is equal to . Consequently, there is a reduc-
tion of total heat rejection in the condenser.
CPO email database
A higher evaporating pressure and a lower condensing pressure result in a small pressure differ-
ence pcon -pev , head lift, as well as a lower hydrostatic liquid column in the condenser. As a result,
the liquid refrigerant flow through the float valve or orifice plates is reduced.
When the compressor operates with the inlet vanes closed at a small angle, i.e., at a load ratio
between 0.8 and 1, the compression efficiency decreases only slightly. However, because a lower CPO email database providers
head and a lower volume flow have a great effect on the work input and power consumption of the
compressor, the result is a reduction in the power input. The energy performance index, in kW/ton,
of the compressor is reduced less than power input because of the reduction of Qref.
The reduction in the mass flow rate of the refrigerant that flows through the centrifugal compres-
sor and the orifice plates and the reduction of the rates of evaporation and condensation create a
new system balance during part-load operation.
For a constant-speed centrifugal chiller, power consumption, in kW/ton, rises when the load
ratio drops below 0.55 (see Fig. 13.11). This increase occurs because the fall in compression
efficiency exceeds the savings in power consumption at a lower head and flow during low load
ratios when inlet vanes are closed to a smaller opening. CPO lists
Free refrigeration means the production of a refrigeration effect without the operation of a compres-
sor. This effect can be achieved because refrigerant tends to migrate to the area of lowest tempera-
ture in the system when the compressor ceases to operate.
Air-free refrigeration operation for a single-stage, water-cooled centrifugal chiller is illustrated
in Fig. 13.14. When the free refrigeration is turned on, the compressor ceases to operate, the inlet
vanes are fully opened, and the valve in the passage that connects the condenser and evaporator is
When the temperature of condenser water from the cooling tower is lower than the temperature
of the chilled water leaving the evaporator, the higher saturated pressure of the refrigerant in the
evaporator forces the vaporized refrigerant to migrate to the condenser, where the saturated pressure
of the refrigerant is lower. The absorption of latent heat of vaporization from the chilled water in
the evaporator’s tube bundle causes the temperature of chilled water to drop. The condensation of
vaporized refrigerant into liquid results in the rejection of the latent heat of condensation to the con-
denser water through the tube bundle in the condenser, raising the temperature of condenser water a
few degrees. Liquid refrigerant drains to the evaporator as a result of gravity. Free refrigeration is
Automatic free refrigeration control can be provided by the DDC system. When the condenser
water temperature is a specified number of degrees lower than the required chilled water tempera-
ture, the DDC unit controller starts the free refrigeration cycle. The shutoff valve is opened, and an
interlocked circuit shuts the compressor off. The free refrigeration cycle lasts as long as the
condenser water from the cooling tower is a few degrees higher than the temperature of the chilled
water leaving the evaporator, and as long as the free refrigeration capacity meets the refrigeration
load required. CPO lists For a two-stage centrifugal chiller with a flash cooler, or a three-stage chiller with a two-stage
flash cooler, there are more connecting passages and shutoff valves. The principle of operation
of free refrigeration is still the same. Once the refrigeration required is greater than the free
refrigeration capacity, as determined from the temperature of the chilled water returned to the evap-
orator, the DDC unit controller closes the vapor and liquid shutoff valves and starts the compressor.
The vaporized refrigerant from the evaporator is extracted by the compressor, discharged to the
condenser, and condensed to liquid refrigerant as in normal operation
Multiple chillers can be piped in parallel, as shown in Fig. 13.15a. Each chiller usually has its own
chilled water pump. If a butterfly valve is installed for each chiller-pump combination, both the
cooling capacity and the chilled water flow are turned on and off in sequence and are controlled by
the DDC system controller. The flexibility and reliability of operation of parallel chillers are excel-
lent. Chillers can be withdrawn from operation for maintenance without affecting the others.
In a multiple-chiller plant using a plant-building loop combination, the principle of staging the
chillers, on or off, is based on these considerations: (1) The chilled water flow rate in the plant loop buy email database
is always slightly higher than the building loop; (2) staging on the chiller(s) must meet the require-
ments of the increased system load; (3) power input to the chillers and chilled water pumps should
Cascia (1988) recommended the following for staging the chillers on or off:
Calculate the required refrigeration load.
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Determine the load ratio of each chiller and the chiller plant.
Calculate the part-load power consumption for each chiller, and the combination of the chiller and
water pumps including chilled water and condenser water pumps. Select the combination with the
minimum power consumption.
Austin (1991) recommended in a multiple-chiller plant to start a lag chiller when the leading chiller CPO address lists
exceeds its optimum load point. The leading chiller is always the most energy-efficient chiller and
the last one to turn off. The last chiller to be turned on is the least energy-efficient one and the first
chiller to turn off.
For a multiple-chiller plant:
A higher compressor efficiency always means a lower kW / ton energy use.
It is always energy-efficient to operate a single chiller with its chiller pump, instead of two
chillers of the same size and their chiller pumps, if a single chiller can meet the required refriger-
ation load. The saving of the power input to the chilled water pump lowers the energy use.
If all the multiple chillers are equal in size, have the same chilled water flow rate, and have the
same full-load cooling capacity, then when two or more chillers are turned on, each must be
loaded approximately equally. This is because the chilled water entering and leaving temperature
differential Tee Tel is the same, and each turned-on chiller must have the same refrigeration load
ratio Rload, which can be calculated CPO lists
Many manufacturers of centrifugal chillers now offer different sizes of evaporators and condensers
to match a specific size of compressor. The designer can thus select the centrifugal chiller that
meets the designated minimum performance.
Equipment Sizing. Although a single chiller is less costly than multiple chillers, there is a danger
of total loss of service when the chiller fails to operate or needs maintenance. Multiple chillers are
usually the best choice for a large chiller plant. A plant installed with three chillers ensures a 66
percent of capacity even if one of the chillers fails.
If continuity of service is critical, a standby chiller that has a capacity equal to the largest chiller
in the refrigeration plant should be provided. A smaller chiller used during light-load conditions, es-
pecially in after-hours operation, in addition to several equally large chillers is often beneficial. The
refrigeration load always increases as building usage grows. The possibility of future growth should
be considered. CPO mailing lists
Plant Location and Layout. Generally, the central plant should be located near the system load as
well as near to the sources of utilities. For a high-rise building, the ideal location is often the hub of
the building, near shopping and public areas. If space at the hub is not available, the chiller plant
may be located in the basement, on an intermediate floor, or on the top floor, depending on the type
of building and the architectural design.
Equipment should be laid out in an orderly arrangement for efficient piping. Vertical and lateral
clearances must be maintained. Equipment may be 10 to 12 ft (3 to 3.6 m) in height. Provision of
access platforms and ladders to valves and piping should be considered in the design stage. A code-
specified clearance of 3 to 5 ft (0.9 to 1.5 m) from electrical panels and devices must be maintained.
Size Minimum efficiency Efficiency as of 10/29/2001
In the 1950s and 1960s, both centrifugal chillers driven by electric motors and absorption chillers
using steam as heat input to provide summer cooling were widely used in central refrigeration
plants. Steam was widely used because excess steam was available in summer in many central
plants that used steam to provide winter heating, and because energy costs were of little concern.
After the energy crisis in 1973, the price of natural gas and oil used to fuel steam boilers drasti-
cally increased. The earliest single-stage, indirect-fired steam absorption chillers had a coefficient
of performance (COP) of only 0.6 to 0.7. They required more energy and could not compete with
electric centrifugal chillers. Many absorption chillers were replaced by centrifugal chillers in the
late 1970s and 1980s.
Because of the high investment required to build new power plants, electric utility companies
added high-demand charges and raised cost-per-unit charges during peak usage periods. In recent
years, double-effect, direct-fired absorption chillers have been developed in both Japan and the
United States with a COP approximately equal to 1.
According to the Air Conditioning, Heating and Refrigeration News, April 14, 1997, the shipments
of new absorption chillers from the manufacturers in the United States in 1996 numbered 579,
whereas the shipments of centrifugal and screw chillers in 1996 numbered about 9200. Absorption
chillers had a share of about 5 percent of the new large chiller market in the United States in the
Absorption chillers have the advantage of using gas and are therefore not affected by the high
electric demand charge and high unit rate at on-peak hours. Most absorption chillers use water as
refrigerant, and its ozone depletion potential is zero. Absorption chillers are advantageous to com-
bine with electric chillers so that electric chillers will undertake the base load and the absorption
chillers handle the load at on-peak hours. Although absorption chillers have a higher initial cost
than centrifugal compressors, in many locations in the United States where the cost ratio of electric-
ity to natural gas is favorable, installation of absorption chiller for use during on-peak hours or even CPO email database
normal operating hours is sometimes economically beneficial. Absorption chillers may have a sim-
ple payback of several years.
CPO email leads
When LiBr is dissolved in water, the boiling point of the solution at a given pressure is raised.
However, if the temperature of the solution remains constant, the dissolved LiBr reduces the vapor
pressure of the solution.
When a solution is saturated, equilibrium is established. The number of molecules across the CPO address lists
interface from liquid to vapor per unit time is equal to the number of molecules from vapor into
liquid. If the number of liquid molecules per unit volume is reduced due to the presence of a solute
then the number of vapor molecules per unit volume is also reduced. Consequently, the vapor pres-
sure of the solution is decreased.
At the bottom of the concentration lines, there is a crystallization line or saturation line. If the
temperature of a solution of constant mass fraction of LiBr drops below this line — or if the mass
fraction of LiBr of a solution of constant temperature is higher than the saturated condition — the
part of LiBr salt exceeding the saturated condition tends to form solid crystals