Carrier 16JB User Manual
Carrier
Application Data
Application Detail
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Hermetic Absorption Liquid Chillers
16JB
GENERAL
Application details in this publication cover
various methods of applying the 16JB absorption
machine to meet liquid chilling needs. Throughout
this publication, the chilled liquid will be water.
Subjects covered are chilled water temperature
control, condenser water temperature control,
system design for steam and hot water machines,
and general information.
CHILLED WATER TEMPERATURE CONTROL
The absorption machine is basically a water
chiller that can be connected to any conventional
open or closed system. However, circulation of
chilled water must be continuous during operation
of the machine and during the shutdown dilution
cycle. Chilled water flow may be restricted at
partial load.
For fine chilled water temperature control
within narrow limits, such as required in precision
control of industrial processes or maintenance of
laboratory conditions, the chilled water system
may require additional storage volume to allow the
machine to adjust slowly to changes in load.
Normal air-conditioning applications are not
subject to such requirements.
Systems having large storage volumes of chilled
water transmit load changes to the machine slowly,
allowing accurate chilled water temperature con
trol. Small storage systems transmit load changes
rapidly, making temperature control more diffi
cult. For fine temperature control, the chilled
water system volume should be at least ten times
the gpm flow through the cooler. If a tank is added
to the system for extra storage volume, it should
be located in the line from the load to the cooler.»
Two-Pipe Cooling-Heating Systems — When
machines are used in conjunction with a two-pipe
cooling-heating system, certain precautionary steps
should be taken during changeover from heating to
cooling.
Maximum water temperature permitted thru
the evaporator is 130 F because of the possibility
of tube stress. If system water temperature is above
80 F but less than 130F at changeover time,
evaporator flow should be throttled to prevent
machine overload.
It is recommended that hot water temperatures
be reset, based on outside air temperature. If a
reset-type control is used, the entering hot water
temperature at changeover will normally be lower
than 130 F.
STEAM MACHINES
Boilers — Generally, any boiler capable of modu
lating its input to maintain design operating steam
pressure within 1 psi under varying loads, is suit
able for application with the absorption machine.
This generally includes all gas- and oil-fired boilers.
Some oil-fired boilers are conversions from
coal-fired to oil-fired and may have control systems
which are too sluggish to give proper response to
machine load changes. Direct control of oil feed
rate normally ensures proper response.
Coal-fired boilers, due to slow buildup and
shutdown characteristics, should be used only
when the absorption machine represents less than
15% of boiler operating load. This generally limits
coal-fired boiler applications to large industrial jobs
where process steam is generated in large quantities
year-round.
BOILER CAPACITY — Minimum boiler capacity
for use with the absorption machine is equal to full
load steam consumption, plus sufficient capacity
to offset piping radiation losses. In the absence of a
detailed study of radiation and vent losses, a
minimum 10% safety factor should be used.
Pressure Reducing Valves — Maximum unit ratings
are based on 14 psig steam pressure at the
generator inlet. Operation at higher inlet pressures
or with more than 100 F superheat is not per
missible. Higher inlet pressures may lead to over
concentration.
Where steam supply pressures are above 15 psig
(14 psig + 1 psig for control) and below 20 psig,
the steam control valve can be used to reduce the
pressure. If steam supply is above 20 psig, a
pressure reducing valve must be provided between
the steam supply and the control valve inlet. A
safety relief valve should be provided between the
steam control valve and the generator inlet. This
valve must be set in accordance with paragraph
UG-133 (f) of the ASME code to relieve at a
pressure not exceeding 17 to 18 psig or the setting
determined by apphcable local codes.
Further specific details relative to pressure
reducing stations should follow accepted standards,
such as the ASHRAE Guide and manufacturer’s
recommendation. For applications on high-pressure
district heating, the steam utility should be con
sulted for local codes or standards.
Steam Piping should be sized to avoid excessive
pressure drop or excessive velocities. Recommenda
tions and pipe sizing tables are given in the Carrier
System Design Manual. It is recommended that
lines be sized on the basis of design system flow for
the machine plus a 10 to 20% safety factor to
allow for normal radiation losses.
© Carrier Corporation 1971
Form 16JB-2XA
Start-Up Demand — Steam demand by the absorp
tion machine is greatest at start-up (see Table 1 for
values).
Table 1 — Maximum Condensate Flow (Ib/hr)
VALVE VALVE INLET STEAM PRESSURE
SIZE (in.)
2
2Y2
3
4
5
20 psig
2450 2025
4825 4000
8175 6760
14540 12025
21650
14 psig
17900
12 psig 10 psig
1880 1750
3710 3430
6285 5810
11190 10350
16655 15400
When boiler capacity is unable to keep up with
start-up demand, the steam pressure will fall off.
On boilers serving only the absorption machine,
this reduction in steam pressure will have no
adverse effect on the absorption machine other
than to lengthen start-up time. However, the
increased steam demand may have an adverse
effect on the boiler, causing it to run dry and fail.
As steam pressure is reduced, the steam control
valve pressure drop will eventually limit the de
mand on the boiler provided the steam control
valve is properly sized.
On boilers serving other loads simultaneously,
the start-up demand can reduce boiler pressure
sufficiently to cause adverse effects on other
steam-driven equipment. When a reduction in
boiler pressure cannot be tolerated without up
setting other equipment, the boiler capacity avail
able for absorption machine operation (with other
loads deducted) must equal or exceed the start-up
demands. If it does not, the start-up demand can
be reduced by using demand Hmit controls, or
installing a back-pressure regulator in the steam
line(s) between the boiler and the control valve(s).
VALVE LOCATION AND PIPING - The steam
control valve should be located a minimum of 3 ft
away from the generator inlet. This is dictated by
good piping practice, to allow equal distribution of
steam in the generator tube bundle. Unequal
distribution of steam in the tube bundle may cause
a loss of capacity. Recommended steam supply
piping for low-pressure steam applications is
illustrated in Fig. 1.
STEAM CONTROt
NOTE; Separate supoiy piping "for each end of machine sizes
16JB077 thro '24,
Fig. 1 — Low-Pressure Steam (2 to 15 psig)
Supply Piping
Machine sizes 16JB077 thru 16JB124 have
steam supply inlets on each end. These are to be
considered as two generators and should be piped
from a common steam header as in multiple
machine installations (see Fig. 2). Each inlet should
then be piped in accordance with Fig. 1.
HEADER FOR N0.2 END
NOTES:
1. Piping appiies to moitipie macbiries connected in paraiief
(3 shown).
2. Each end most be consdered as a separate generator.
3. The feed to each end of each generator should be piped as
shown in rig. 1.
Fig. 2 — Steam Piping For 16JB077 thru 124
Steam piping to the absorption machine should
be designed and supported to allow for thermal
expansion without imposing undue stresses on the
generator inlet. The machine is not designed for,
nor expected to act as, a piping support or anchor
for withstanding thermal stresses.
Condensate Systems — Satisfactory operation of
the absorption machine requires a condensate
handling system designed with the specific characteristics of the absorption machine in mind. The
following is intended to supplement available
reference data on condensate systems such as
Carrier System Design Manual, ASHRAE Guide
and individual manufacturer’s recommendations.
ATMOSPHERIC CONDENSATE RETURN
SYSTEMS (VENTED) - These systems usually
consist of steam traps, vented receiver, condensate
pump, and condensate cooler. Fig. 3 illustrates
typical atmospheric condensate return systems. On
larger machines, with dual steam generators, the
condensate outlet from each generator must be
piped thru separate steam traps.
Trap Selection — Steam traps should be located as
far below the generator outlet as possible. Actual
pressure drop available for trap selection will
depend on exact trap location below the generator
FROM SEMERATOR
(LEFT END)
MACHINE Sizes 16J8077 THRU IZA
Fig. 3 — Typical Atmospheric (Vented) Condensate Return System
outlet, and trap outlet pressure. A vacuum breaker
is factory installed to ensure that operating steam
pressure in the generator does not fall below
atmospheric pressure. Use the following formulas
to determine available trap pressure drop:
Trap pressure drop = trap inlet ~ trap outlet
psig.
Trap inlet pressure = 0 psig + hydrostatic
head to trap inlet -- condensate leg pressure
drop.
Trap design outlet pressure receiver pres
sure + line pressure drop from trap outlet to
receiver.
In determining trap outlet pressure, discount
any liquid head drop to the receiver. This line may
not run full. If there is liquid lift from trap outlet
to the receiver, it must be added to trap outlet
pressure.
Either float-and-thermostat or inverted-bucket
traps may be used, provided the trap is recom
mended by the manufacturer for rapid handhng of
noncondensables. For fast start-up with invertedbucket traps, install an external thermostatic air
vent around the trap.
Traps should be sized for capacity to handle
more condensate than twice the design full-load
steam rate. See steam trap manufacturer’s recom
mendations. Maximum load on the trap will occur
during start-up when generator pressure falls to
atmospheric (0 psig) and steam condenses rapidly.
At this time, pressure drop across the steam
control valve is maximum. If boiler capacity is
large enough, the control valve inlet pressure will
stay at design, then flow rate will be limited by
control valve capacity.
Table 1 gives maximum condensate flow for
different inlet steam pressures. Interpolate for
intermediate pressures.
If steam demand on start-up can be held within
a controlled limit, the trap(s) may be sized
accordingly.
When traps are undersized, condensate wiU
back up in the generator with loss in machine
capacity and may cause dangerous water hammer.
Depending on boiler size, the boiler water makeup
system could operate and add water to the boiler.
Sooner or later, excess water would return to the
boiler room and either overflow the hot well to
drain, or if it flows directly into the boiler, it may
shut the boiler down on high boiler water level
control.
Condensate Cooler is used on some atmospheric
condensate systems to reduce or eliminate loss of
flash steam from the open receiver vent. The
condensate cooler must be sized for handling and
condensing flash steam as well as cooHng the
condensate. Condensate is normally cooled to
about 180 F. Pressure drop thru the condensate
cooler should be very low, as it must be added to
trap outlet pressure. If there is a liquid leg down to
the condensate receiver, the condensate cooler and
trap should be located at the bottom of this leg.
When a condensate cooler is used, it is desirable
to use either cold boiler feed water or other cold
water source which can benefit by heat rejected
from hot condensate. Cooling tower bleed water
can be used, but it may be heavy with dissolved
solids and may rapidly foul the cooler. Tower
makeup water can be used when large cooling
towers are part of the system. Extra load to the
tower would be insignificant.
Receiver and Condensate Pumps — When open
receivers are used, the vent should be directed
outside the equipment space to eliminate fogging.
Be careful in using small receivers and closeconnected condensate pumps. Some commercially
available systems may work well on standard
heating systems but can present problems in
handling condensate from absorption machines.
The basic difference in absorption machine oper
ation lies in higher condensate temperatures and
greater amounts of flash vapor. Commercial
heating systems normally deliver condensate to the
receiver thru long return runs. This lowers con
densate temperature to 200 F or lower with
relatively little flash steam.
Absorption machines commonly located close
to the condensate receiver have little or no
condensate cooling. During full load, condensate
may be delivered to the trap at close to 12 psig and
240 F. This creates large amounts of flash steam at
the trap outlet and in the condensate receiver.
Very hot condensate drawn into the condensate
pump may cause cavitation.
To minimize these effects, the following guides
are offered:
1. If equipped with a vented receiver, the inlet line
to the receiver should enter above the receiver
water level. Flash steam can go directly out the
vent without creating turbulence or frothing.
2. Locate the condensate pump as far below
receiver water level as possible to give maxi
mum Net Positive Suction Head (NPSH) to the
pump.
3. If pump suction pipe is located at bottom of
the receiver, use a vortex breaker at the receiver
outlet.
4. Locate pump suction at opposite end of re
ceiver from the condensate inlet. This will
minimize agitation and frothing at pump inlet.
5. A properly selected condensate cooler, as
previously described, will eliminate problems
with flashing.
VACUUM PUMP CONDENSATE RETURN
SYSTEMS are sometimes used to return con
densate from space heating installations. The
vacuum pump maintains the condensate return
system at a subatmospheric pressure and permits
the heating system to operate with subatmospheric
pressure when the heating load is small.
It is generally impractical to use an existing
vacuum pump condensate return system. Con
densate from the absorption machine is far higher
in temperature than condensate from the original
heating system for which the vacuum return pump
■; was selected. Hot condensate forms excessive
quantities of flash vapor when released into the
vacuum return system and will usually cause vapor
lock in either the return piping or the vacuum
return pump, or both. When the existing
condensate return system is a vacuum pump type,
the recommended method of returning condensate
from the machine is a separate wet-return system,
if possible.
As an alternate choice, condensate can be
discharged thru a steam trap to an atmospheric
vent receiver. The receiver discharges flash-cooled
condensate thru a second trap into the vacuum-
return system.
If a condensate cooler is used, condensate may
be cooled to an acceptable level and discharged
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