This document discusses solar powered absorption refrigeration systems. It provides details on: 1) LiBr-H2O is considered the best working pair for solar absorption air conditioning systems due to its higher COP compared to other pairs like H2O-NH3. 2) A single effect system with refrigerant storage can accumulate refrigerant during high sunlight but has a lower COP, while a double effect convertible system has a higher COP. 3) A two-stage system lowers the generator temperature allowing use of conventional flat plate collectors, reducing system costs.

1. http://www.appropedia.org/The_Design_and_Development_of_
a_Solar_Powered_Refrigerator
The study of solar absorption air-conditioning systems
V Mittal
AssistantProfessor,Mechanical Engineering,BRCM College ofEngineering & Technology,
Bahal (HR) and Research Scholar,NIT, Kurukshetra (HR)
KS Kasana
Professor,Mechanical Engineering,NIT, Kurukshetra (HR)
NS Thakur
AssistantProfessor,Mechanical Engineering,NIT, Hamirpur (HP)
The solar thermal technologies are:
• Flat plate collectors
• Evacuated tube collectors
• Stationary, non imaging concentrating collectors
• Dish type concentrating collectors
• Linear focusing concentrators
• Solar pond
• Photovoltaic
Performance and selection of working
pairs for a solar absorption cooling
system and comparison of libr vs nh3
Performance of the refrigeration system is represented
as a ‘coefficient of performance (COP)’. It
shows how much heat can be removed from a cold
region (Qe) for each unit of energy used (Qg).
(1)
For the solar-driven systems, the performance can
be written as the product of the COP and the solar
collector efficiency (c). Besides, it can be defined
as a ratio of the refrigeration effect and the solar
energy input (I) for the thermal-driven systems,
which is called ‘system thermal ratio (STR)’.
(2)
(3)
Wilbur and Mitchell (1975) compared the
Coefficient of Performance (COP) of the absorption
system with the different working fluids. Of the various
solar absorption air conditioning systems, LiBr-
H2O and H2O-NH3 are the major working pairs
available in these systems. It is reported that the
LiBr – H2O pair has higher COP than any other pair
of the working fluids.
Though it has a limited range of the operations,
due to the onset of the crystallization occurring at
the point of the recouperator discharges into the
absorber and stopping solution flows through the
device, the low cost and the excellent performance
of this system make it a favourable candidate for the
solar absorption cycle systems. Also by the comparison
(Ward 1979; Ward et al 1979), the ammonia
water pair has the following disadvantages:
• The coefficient of the performance for the H2ONH3
systems is lower than for the LiBr-H2O system.

2. Generally, the H2O-NH3 system operates at
10-15% lower solar fraction than the LiBr-H2O
systems.
• It requires a higher generator inlet temperature.
Generally, the LiBr-H2O system requires the
generator inlet temperature of the 70-88ºC,
while the H2O-NH3 system requires 90-180ºC;
which results in the H2O-NH3 system achieving
a lower COP when using a flat plate collector.
• It requires higher pressures and hence higher
pumping power.
• A more complex system requiring a rectifier to
separate ammonia and water vapour at the generator
outlet is required.
• There are restrictions on the in-building applications
of the ammonia –water-cooling units
because of the hazards associated with the use
of ammonia.
For these reasons, the LiBr-H2O system is considered
to be the better suited for the solar absorption
air conditioning applications.
Why absorption is suitable for solar refrigeration?
One of the improvements that would make the
absorption machine more suitable for solar operation
is refrigerant storage. Basically, the idea is to
provide, in association with the condenser, a storage
volume where the refrigerant can be accumulated
during the hours of high solar insolation.
Then, this stored liquid refrigerant can be expanded
at other times to meet the required loads. Storage is
also needed in the absorber to accommodate, not
only the refrigerant, but also sufficient absorbent to
keep the concentration within allowable limits.
The advantages of the refrigerant storage over
other methods include:
• The energy storage per unit volume is high as
the latent heat of evaporation, which is larger,
compared to available sensible heat changes, is
involved;
• Losses are low as the storage occurs at or near
room temperature;
• Further advantages arise when the storage is
applied to the lithium bromide-water cycle;
• Water has one of the highest enthalpies of evaporation
among known liquids;
The disadvantages of this system may be that:
• Generation of refrigerant ceases several hours
before sunset and, although a significant
amount of energy is still being collected, a lot of
useful solar energy is wasted;
• The system may be very complicated. The generation
power is not easily matched with the
absorption and refrigeration power; besides, the
control of valves 1 and 2 is difficult;
• Although the machine could store sufficient
refrigerant during a typical day to allow overnight

3. operation, the performance of the chiller is
very low because of the decrease in concentration
of the solution and the increase of the temperature
and pressure in the system.
Conclusion
Among the major working pairs available, LiBr-
H2O is considered to be better suited for solar
absorption air-conditioning applications.
• Generator inlet temperature of the chiller is the
most important parameter in the design and fabrication
of a solar powered air-conditioning system.
• A Single effect system with refrigerant storage
has the advantage of accumulating refrigerant
during the hours of high solar insolation but the
double effect convertible system has a higher
overall COP.
• A Two-stage system has the advantage of lowering
the generator temperature, which provides
the use of conventional flat plate collectors,
thereby bringing down the cost of the system.
Investigation of a Novel Solar Powered Absorption
Refrigeration
System with Solar Point Collector
At present there are no thermally driven absorption cooling
machines available on the market which could provide smallcapacity
cooling for domestic housing applications as well as
offices and hotel rooms of less than 10 kW. This paper
investigates the development and testing of single-stage solar
or waste energy heated ammonia/water (NH3-H2/H2O)
absorption cooling machines (ACM). The designed cooling
capacity of the cooling machine is 2.5 kW at evaporator
temperatures between -10°C and +15°C with indirect heating
through novel solar collectors. Here are two main types of
refrigeration system: Mechanical vapour compression and
absorption refrigeration system. The mechanical vapour
compression system is outstanding due to its higher
coefficient of performance, flexibility and compactness in
manufacturing and operation. However, the fact that it is
generally powered by electricity results in the emission of a
large amount of CO2, which, in turn, causes the greenhouse
effect. In addition, CFCs used as the working medium
seriously affect the ozone layer around the globe.
The absorption system, powered by either electric or wasted heat,
is mainly used in large air conditioning and refrigeration

4. systems. Owing to the environmental problem caused by
CFCs and the huge energy consumption of conventional
cooling system, this novel solar powered absorption
refrigeration system has been developed3-5.
Novel solar powered absorption refrigeration system has
many advantages in refrigeration or heat pumping
application such as: Materials are environmentally friendly,
chemically stable and the system can be powered by either
solar energy or wasted heat.
Solar refrigeration vs normal ref
Air-conditioning is one of the major consumers of electrical
energy in many parts of the world today and already today
air-conditioning causes energy shortage. The demand can be
expected to increase because of changing working times,
increased comfortexpectations and global warming. Airconditioning
systems in use are most oftenbuilt around a
vapor compression system driven by grid-electricity
However, most ways of generating the electricity today, as
well as the refrigerants being used in traditional vapour
compressionsystems,have negative impact on the
environment.
Solar air-conditioning might be a way to reduce the demand
for electricity. In addition many solar air-conditioning
systems are constructed in ways that eliminate the need for
CFC, HCFC or HFC refrigerants6.
Alternatives to using solar energy are to use waste heat from
differentindustrial processes such as refineries, garbage
treatment facilities etc. Even driving the air-conditioning
systems directly with fossilfuels might in some cases is a
more environmental friendly alternative than using
electricity6
.
Environmental benefits of solar cooling
Energy consumption and carbon emissions decreased
Including ancillary components, a solar assisted cooling system can reduce electricity
demand for room cooling by 60% compared with conventional cooling systems. As CO2
emissions go down accordingly, this make an important contribution to reducing our carbon
footprint. Cooling, traditionally an energy-consuming process, becomes resource-saving.

5. Absence of harmful substances
To be faithful to the concept of sustainable solutions, we are aware that the materials and
fluids used should be ecologically benign. The minerals used as adsorbate, silica gel or
zeolite, are chemically inert. The refrigerant used in most cases is quite simply water. The
materials used for the assembly are fully recyclable metallic alloys. Environmental
responsibility goes beyond the useful life of an installation.
Noiseless systems
The lack of reciprocating and rotating parts results in a vibration-free and noiseless operation
that can be important in specific applications.
Main advantages of solar air conditioning technologies:
 reduction of summer peak loads in electricity demand
 close seasonal and hourly coincidence of solar radiation and a building's cooling
demand profile
 absence of any ozone-depleting refrigerants
 decreased primary energy consumption
 decreased global warming impact
 maximization of the exploitation of solar energy for heating, hot-water production and
cooling by the same solar system
Libr valsad gives nice explaination for libr abs