A three ton lithium bromide absorption water chiller was tested for a number of conditions involving hot water input, chilled water, and the cooling water. The primary influences on chiller capacity were the hot water inlet temperature and the cooling water inlet temperature. One combination of these two parameters extended the output to as much as 125% of design capacity, but no combination could lower the capacity to below 60% of design. A cooling system was conceptually designed so that it could provide several modes of operation. Such flexibility is needed for any solar cooling system to be able to accommodate the varying solar energy collection and the varying building demand. It was concluded that a three-ton absorption water chiller with the kind of performance that was measured can be incorporated into a cooling system such as that proposed, to provide efficient cooling over the specified ranges of operating conditions

Namkoong, D.

English

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NASA TECHNICAL	 NASA TM X-73496
MEMORANDUM
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MEASURED PERFORMANCE OF A 3-TON LiBr ABSORPTION WATER CHILLER
AND ITS EFFECT ON COOLING SYSTEM OPERATION
by David Namkoong
Lewis Research Center
Cleveland, Ohio 44135
TECHNICAL PAPER presented at the
International Solar Energy Society Meeting
Winnipeg, Canada, August 15-20, 1976
(NASA-TM-X-73496) MEASURED PERFORMANCE OF A
	 N77-12518
3 TON Li Br ABSORPTION WATER :HII.Li;R AND ITS
EFFECT ON COOLING SYSTEM OPERATION (NASA)
10 p HC A02/MF A01
	 CSCL 10A
	 Unclas
G3/44 56894
MEASURED PERFORMANCE OF A 3-TON LiBr ABSORPTION WATER CHILLER
AND ITS EFFECT ON COOLING SYSTEM OPERATION
by David Namkoong
Lewis Research Center
ABSTRACT
A 3-ton lithium bromide absorption water chiller was tested for a
number of conditions involving hot-water input, chilled water, and the
cooling water. The primary influences on chiller capacity were the hot
water inlet temperature and the cooling water i-alet temperature. One
combination of these two parameters extended the output to as much as
125% of design capacity, but no combination could lower the capacity to
below 60% of design.
A cooling system was conceptually designed so that it could provide
several modes of operation. Such flexibility is needed for any solar
cooling system to be able to accommodate the varying solar energy collec-
t
ON	 tion and the varying building demand.
00
w
	
	 It is concluded that a 3-ton absorption water chiller with the kind
of performance that was measured can be incorporated into a cooling system
such as that proposed, to provide efficient cooling over the specified
ranges of operating conditions.
INTRODUCTION
NASA. Lewis has been conducting research on solar heating and cooling
systems and components. In addition to performance tests of components.•
such ad on flat-plate collectors (refs. 1 to 4), the testing of complete
systems incorporating such components is essential for an overall solar
heating and cooling system evaluation. A laboratory-scale solar heating
and cooling system has been built and operated to provide an experimental
means for such an overall evaluation (ref. 5). At the present stage of
the experimental system design, no differentiation has been made aL; to
whether the building demand is a heating load or a cooling load. In
either case, the demand results in a transfer of heat energy out of the
system.
Solar cooling has been receiving increased attention over the past
year. A recent study (ref. 6) indicates that combined solar heating and
cooling systems have greater economic attractiveness than heating only
systems (ref. 7). Also, greater attention has been directed to solar
1L*,.icat'ons in commercial buildings, where cooling is normally the pre-
r
2dominant building energy demand.
Solar cooling can be complex and requires study and tests prior to
integration into actual systems. Currently the only type of solar cool-
ing machine commercially available is a lithium bromide water absorption
type modified to operate at flat-plate solar collector temperatures. The
particular unit under discussion in this paper is a 3-ton cooling capacity
water chiller. The unit was operated in a test loop under the following
parameters and values to determine performance:
Hot water source flow rate, gpm . . . . . . . 8, 9.5, 11
Hot water source inlet- temperature, OF. . . . . 216, 2201, 224
Cooling water inlet temperature, of . . . . . . . 75, 80, 85
Chilled water inlet temperature, of . . . . . . . 50, 54, 58
DESCRIPTION OF CHILLER TEST SYSTEM
A system was designed to perform a component test on the LiBr ab-
sorption water chiller.
Overall Test System
Testing the performance of the chiller involved controlling the flow
rate and inlet temperature of the hot water heat source, cooling water,
and the chilled water. The flow schematic is shown in figure 1; the com-
ponents and apparatus in figure 2. Steam provided the heat source for
the hot water supply of the chiller. A controller automatically adjusted
the steam flow rate so that the hot water could be maintained at the man-
ually set temperature. The cooling water temperature was controlled by
recirculating some of the heated water back to the inlet. The chilled
water inlet temperature was controlled by a combination chilled water
storage tank and a heater. The tank served to store the cold water dis-
charge while the upper (and warmer) region of the tank was heated as nec-
essary to control the water temperature entering the chiller.
Absorption Water Chiller
The solar absorption water chiller operates very much like the con-
ventional gas air conditioner (fig. 3) except that the gas heat is re-
placed by water that is heated by -olar energy, and where the output is
chilled water instead of cooled air. The operation is sufficiently sim-
ilar so that an existing gad air conditioner could be modified for our use.
Besides the modification involved in the heat input and the water output,
modifidations were also made to the strength of the LiBr-water solution,
This was required to compensate for the additional thermal barrier - the
chilled water loop - between the cooling coil and the building heat ex-
changer.
3Briefly, the absorption cycle (fig. 3) involves a heat source that
serves (1) to separate the water vapor (the refrigerant fluid) from the
LiBr-water solution and (2) to promote slug flow in the vertical tube and
thereby "pump" the liquid. The water vapor is liquefied in the condenser
and vaporized in the cooling coil. It is the heat exchange during vapor-
ization that the "air conditioning" or the water chilling takes place.
The vaporized water is recombined with the LiBr solution in the absorber
and the original solution returns to the generator to be cycled again.
The external cooling water functions in both the absorber and the con-
denser parts of the cycle.
A more detailed description of the absorption cooling operation can
be found in reference 8.
TEST PROCEDURE
Each of the four parameters (inlet temperature to the chiller of the
hot water, cooling water, and chilled water, and the hot water flow rate)
were varied. Using three operating points for each parameter, data were
obtained at 81 operating points. It was recognized that at some condi-
tions there would be a danger of simmering and thereby cryst?-1.1 2.ing the
lithium bromide. Such conditions were approached cautiously, and indeed
there were 9 conditions that could not be stabilized. 7%ese points oc-
curred for the three flow rates and three chilled water temperatures at
the low hot water temperature 216 0 F and at the highest cooling water
temperature 85 0 F. All remaining 72 points were obtained with no diffi-
culty.
At the beginning of each day's test, a data point was taken at one
set of conditions:
Hot water flow rate, gpm .
	 . . . . . . 11
Hot water inlet temperature, °F. 	 224
Cooling water inlet temperature, °F.
	
85
Chilled water inlet temperature,°F .	 58
This test point served as the reference chiller output for the data taken
that day.
TEST RESULTS
The results of the test are shown as performance curves in figure 4.
The curves are presented on coordinates of hot water temperature flowing
to the water chiller and of the percentage output of the design capacity.
The design capacity is the cooling accomplished on the chilled water and
is referenced to the test point obtained by operating at design condi-
tions.
i
1
y. A
4The primary influences on the output capacity of the chiller were
the hot water inlet temperature and the cooling water temperature. The
hot water flow rate and the chilled water inlet temperature to the
chiller had secondary effects. For a given cooling water inlet tempera-
ture, the chiller varied approximately 25 percentage points for an 80
change of the hot water inlet temperature. For a unit designed for
36 000 Btu/hr, an 80 drop means a decrease in cooling capacity down to
27 000 Btu/hr. The cooling water temperature was quite significant in-
affecting the chiller capacity. A change of 5 0 resulted in a 15-
percentage point change in the chiller output.
The hot water inlet temperature ranged from the design point of
2240 to 2160 F. This minimum temperature was that recommended by the
manufacturer to prevent the LiBr solidification by simmering. Simmering
is that condition in which the water vapor separates from the LiBr solu-
tion but where the vigorous boiling required for liquid lift operation is
absent. With continuous vaporization without "pumping," the solution would
eventually crystallize. However, the hot water temperature was carefully
controlled below 2160 F to obtain the actual minimum temperatures. This
was found to be a function of cooling water temperature - that the colder
temperatures enabled lower hot water temperatures. At 85 0 F cooling
water inlet temperature, the hot water was lowered to 210 0 F and still
was operating stably. At 800 F cooling water temperature, the hot water
was lowered to 206 0 F, and at 75 0 F cooling water temperature, the hot
water was lowered to 202 0 F. The minimum AT between the hot water and
the cooling water averaged 126 0 . In each of these cases, the output
associated with the minimum temperatures was approximately constant at
63% of design.
The coefficient of performance (COP), which remained approximately
constant at 0.65 while operating within the prescribed conditions, in-
creased to approximately 0.73 at the minimum hot water temperature points.
The COP values obtainec verify other findings that this type of
3-ton machine operates at lower COP's than do larger industrial chillers.
The main --ason is the use of the hot water energy for the liquid lift
"pumping" in the small unit. The large industrial units utilize pumps
to drive the liquid; the heat energy utilized solely for the separation
of the water vapor from the solution. Secondary effects of using a pump
is the higher liquid solution pressures that permit a more effective
spray operation in the absorber. Incorporation of a pump for the 3-ton
unit, which is being developed, should help in increasing the efficiency -
the COP - of the small unit.
DISCUSSION OF RESULTS
The performance curves indicate that the range of hot water tempera-
ture over which the chiller can operate depends upon the cooling water
inlet temperature. In no case, however, does the minimum output drop be-
5low 63% of design. The lower cooling water temperatures extend output
above the design point to as much as 125% of design, but extend to the
same minimum 63% as the higher cooling water temperatures.
Where the building load requires cooling below the chiller minimum
output_ point, two alternatives are possible. One mode of operation is
that of directly coupling the chiller to the building load and operating
full-on or full-off. The cyclic operation is inefficient, however, be-
cause of the thermal inertia of the system.
A more desirable mode of operation is that of continuous running.
To match the chilled water output with building load, one can incorporate
a chilled water storage tank. Whenever the chiller output exceeds the
building load, the chilled water output can be divided between the load
and the tank. This mode is shown in figure 5. The flow circuit also
accommodates other modes of operation. When the tank water is chilled,
flow can be circulated between the tank and the load (fig. 6). If hot
water to the chiller (from the collectors and/or heat storage tank) is
available and there is no building load demand, the chiller output can
be stored in the tank (fig. 7). On those occasions, expected to be rare,
when the chiller output can be matched with the load demand, there can be
a direct exchange between the chiller and the load (fig. 8).
The cooling subsystem described integrates the particular character-
istics of the chiller into a flexible mode of operation required of a
solar heating and cooling system.
CONCLUDING REMARKS
A 3-ton lithium bromide absorption water chiller was tested over a
range of conditions of hot water input, chilled water output, and the
cooling water. The primary influences on chiller capacity were the hot
water inlet temperature and the cooling water inlet temperature. No com-
bination of parameters, however, permitted operation of the chiller below
60% of design capacity. This limitation is in contrast to larger absorp-
tion units which can operate below this point.
This chiller is but one component, albeit a very important one, of
a solar cooling system. A cooling system was conceptually designed so
that it could provide several modes of operation. Such flexibility is
needed for any solar cooling system to be able to accommodate the vary-
ing solar energy collection and the varying building demand.
It appears that a 3-ton absorption water chiller with the kind of
performance measured can be incorporated into a cooling system such as
that proposed to provide efficient cooling over the specified ranges of
operating conditions.
i
i
i
l^
6
REFERENCES
1. R. W. Vernon and F. F. Simon, Flat-Plate Collector Performance Determined
Experimentally with a Solar Simulator. NASA TM X-71602, (1974).
2. F. F. Simon and P. Harlamert, Flat-Plate Collector Performance Evaluation.
The Case for a Solar Simulator Approach. NASA TM X-71427 (1973).
3. P. W. Vernon, Solar Collector Performance Evaluated Outdoors at NASA
Lewis Research Center. NASA TM X-71689 (1974).
4. G. E. McDonald, Spectral Reflectance Properties of Black Chrome for Use
as a Solar Selective Coating. NASA TM X-73596 (1974).
5. Namkoong, David, Tests of a Reduced -Scale Experimental 16de1 of a Build-
ing Heating and Cooling System. NASA TM X- 	 (1976),
6. G.O.G. Lof and R. A. Tybout, The Design and Cost of Optimized Systems
for Cooling Dwellings by Solar Energy. Solar Energy 16 9(1974).
7. R. A. Tybout and G.O.G. Lof, Solar House Heating. Natural Resource
Journal 10( 2), 268 (1970).
8. Cycle of Operations. Arkla Air Conditioning Co. Bull. No. SV57T-4.
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COOLING WATER IN
STEAM
IN	 j
P	 HEATER
	
HOT	 — —
---^ ' WATER IN	 P	 CHILLED
	
I CHILLED WATER	 WATER TANK
IN
^	 I	 P
L -- HOT WATER	 — J CHILLED WATER OUTT
OUT
	CONDENSATE	 CHILLER-j
OUT	 COOLING WATER OUT
Figure 1. - Flow schematic of chiller performance test.
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Figure 2. - System for testing tiBr ahsorption water chiller.
PRECDING PAGE BLANK NOT FILMED
Ar I O" `RA , ABSORBER
ONTROL
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1 6
5_._^. Ip rCONDENSING
I lQUID WATER INLET
7 TRAP
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17 t + n STRONG SOLUTION
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WEAK SOLUTION
REFRIGERANT VAPOR
GENERATOR I
HEAT
REiRIGERANTIIOUID
EXCHANGER
GAS BURNER CONDENSING WATER
Figure 3.	 - Diagram of an Arkla lithium bromide -water absor p tion cooler.
COOL. WATER
INLET TEMP.
130 01
HOT WATER FLOW	 0 CHILLED WATER
8 GPM ss	 75 INLET TEMP,
R
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100
85 —
58
— — —	 54
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COOLING LOAD
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Figure 5. - Cooling subsystem - chiller to tank and load.
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HOT WATER
INLET	 P1 11M,_
HILLER	 CHILLED
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Figure b. - Cooling sub-system - tank to load.
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COOLING LOAD
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Figure 7. - Cooling subsystem - chiller to tank.
	
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COOLING LOAD
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HOT WATER
INLET	 PUMP
CHILLER	 CHILLEDWATER
STORAGE
---^v ---	 TANK
3-WAY VALVE-- 	 LJ
Figure 8. - Cooling subsystem - chiller to load.
NASA-Lewis
A


Measured performance of a 3 ton LiBr absorption water chiller and its effect on cooling system operation

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