VAR System .... Air Conditioning using Waste HEAT Solar HEAT etc

Literature Review

Absorption refrigeration was discovered by Nairn in 1777, though the first commercial refrigerator was only built and patented in 1823 by Ferdinand Carré, who also got several patents between 1859 and 1862 from introduction of a machine operating on ammonia–water. The absorption refrigeration system went through ups and downs, being the antecessor of the vapor compression

refrigeration system in the 19th century.

By that time systems operating on ammonia–water found wide application in residential and industrial refrigerators. Systems operating on lithium bromide–water were commercialized in the 1940’s and 1950’s as water chillers for large buildings air conditioning. Substitution of petroleum-based combustion fuels in the 1970’saffected the application of absorption refrigeration, but, at the same time, new opportunities arose, such as usage of solar energy to operate this system. 

Increasing energy costs and other factors has contributed to frequent use of low temperature energy waste from chemical and commercial (supermarket) industries to operate absorption refrigeration systems. Absorption refrigeration system differs from vapor compression refrigeration system due to utilization of thermal energy source instead of electric energy. In the absorption refrigeration system two working fluids are used: a refrigerant and an absorbent. Among themost applied working fluids are the pair ammonia refrigerant–water absorbent (NH3–H2O) and water refrigerant–lithium bromide absorbent (H2O–LiBr). A limitation of the pair water–lithium bromide is the difficulty to operate at temperatures lower than 0deg.C.

Besides, lithium bromide crystallizes at moderate concentration, and, at high concentration, the solution is corrosive to some metals and is of high cost. The system water–lithium bromide operates below atmospheric pressure, resulting in system air infiltration, which requires periodical purge. Moreover, special inhibitors needed to be incorporated to retard system corrosion

[1] Diesel Engine energy source for absorption refrigeration system

Manzela Alexio Andre, Sergio Morais Hanriot, Luben Gomez presented an experimental study of an ammonia–water absorption refrigeration system using the exhaust of an internal combustion engine as energy source. The exhaust gas energy availability and the impact of the absorption refrigeration system on engine performance, exhaust emission, and power economy are evaluated. A Production automotive engine was tested in bench test dynamometer with absorption refrigeration system adapted to its exhaust pipe.The calculated exhaust gas energy availability suggests the cooling capacity can be highly improved for a dedicated system Exhaust hydrocarbon emissions were higher when this system was installed but CO emissions were reduced.

[2] Experimental analysis of an automotive a/c system with two phase     flow measurements

Shujun WANG and Junjie GU  presented an experimental study of automotive a/c test system consisting of a compressor, condenser, evaporator and accumulator. R-134a refrigerant. The COP, evaporator cooling capacity, compressor power consumption, and mass flow rate, oil in circulation, p and T were measured. The experiments were conducted with real time thermocouples, sensors, transducers, and other signal conditioning instrumentation devices clubbed with computer with a s/w LAB view. The systematic experimental results obtained from this real sized test system depict the relations of all above mentioned parameters in the automobile a/c system. Which was a later a useful tool in designing the automobile a/c systems. The two phase flow measurements realized in the work gives an extremely important tool to diagnose system performance

[3] Simulation of Absorption refrigeration system for Automobile application

Anand Ramanathan and P. Gunashekaran simulated an automotive air-conditioning system based on absorption refrigeration cycle. By developing a steady-state simulation model performance analysis of vapor absorption refrigeration system is done. The water lithium bromide pair is used as a working mixture for its favourable thermodynamic and transport properties compared to the conventional refrigerants utilized in vapor compression refrigeration applications. The pump power required for the proposed vapor absorption refrigeration system is found lesser than the power required to operate the compressor used in the conventional vapor compression refrigeration system. A possible arrangement of the absorption system for automobile application is proposed.

[4] Absorption refrigeration system for mobile applications utilizing exhaust gases

J. Koehler, W. J. Tegethoff, D. Westphalen, M. Sonnekalb made breadboard prototype of an absorption system for truck refrigeration using heat from the exhaust-gases was designed, built and tested. Measured COP values of the unoptimized single-stage ammonia-water absorption cycle varied between 23 and 30%, but system modelling shows that this can be improved to values considerably over 30%. Computer simulation for the system included cycle analysis as well as component modelling, using a detailed two-fluid model for flow of the ammonia-water mixture in the condenser and absorber.  This detailed model was also validated using test data. In addition, there coverable energy of the exhaust gases was analyzed for representative truck-driving conditions for city traffic, mountain roads and flat roads.  The results show that the system is promising for long distance driving on flat roads.

[5] Theoretical performance of combined turbo charged diesel engine and absorption A/C system

In this paper Agnew et al. explored the theoretical performance of four different configurations of a turbocharged Diesel engine and absorption refrigeration unit combination when operating in a high ambient day temperature of 35deg.C. The simulation is performed using SPICE, a well known Diesel engine simulation program. The air consumption of the engine increases with charge air cooling as does the power and efficiency. The exhaust gas temperature and engine BSFC both decrease with increased charge air cooling. The high exhaust temperatures resulting from the high charge inlet temperatures of the cycles with no or a small amount of CO.

[6] Modeling and experimental evaluation of an automotive air conditioning system with a variable capacity compressor

J.M. Saiz and Jabardo made steady state computer simulation model has been developed for refrigeration circuits of automobile air conditioning systems. The simulation model includes a variable capacity compressor and a thermostatic expansion valve in addition to the evaporator and micro channel parallel flow condenser. An experimental bench made up of original components from the air conditioning system of a compact passenger vehicle has been developed in order to check results from the model. The refrigeration circuit was equipped with a variable capacity compressor run by an electric motor controlled by a frequency converter.

Effects on system performance of such operational parameters as compressor speed, return air in the evaporator and condensing air temperatures have been experimentally evaluated and simulated by means of developed model. Model results deviate from the experimentally obtained within a 20% range though most of them are within a 10% range.

Effects of the refrigerant inventory have also been experimentally evaluated with results showing no effects on system performance over a wide range of refrigerant charges

In a study Mostafavi et al. [7]  investigated the influence of ambient temperature on the generator temperature, concentration of strong solution, flow ratio of the solution and on the evaporator temperature attainable for air-conditioning purposes of a lithium bromide/water absorption unit. It has been shown that an increase in the ambient temperature causes an increase in the generator temperature. Pise et al. [8] carried out extensive investigation on the enhancement of heat and mass transfer in absorbers of LiBr-H2O refrigerating system. It is showed that the heat and mass transfer in the absorber can be improved by creating wavy and turbulent flows by means of introducing extended surfaces, splashing using additives or simply by increasing the solution flow Reynolds Number