Absorption chillers
of absorption chillers with more compact, lightweight and efficient design are desired by the market,” says Dr Vilas G Gaikar, Bharat Petroleum Professor of Chemical Engineering, and Head, Department of Chemical Engineering, Institute of Chemical Technology (ICT), Mumbai. Besides, government initiatives are steadily encouraging the use of chillers; rising consumer awareness and gradual phasing out of traditional refrigerants are also pushing the adoption of absorption chillers.
Novel developments The conventional form of compressor air-conditioning chillers is powered by electricity. Absorption chillers, on the other hand, use high-temperature heat as the chief energy source. “When it comes to energy consumption, a small amount of electricity is needed in absorption systems when compared to compression cycle systems. This is because only the pumps in the system are operated by means of electricity,” says a spokesperson from Carrier Transicold India. However, the investment cost of the absorption chiller system is considerably higher than that of a compressor system. “Depending on the unit size, the capital cost of single-effect absorption chillers is roughly 20-50 per cent higher compared to an equivalent electric or engine-driven chiller,” adds Carrier Transicold India’s spokesperson. As a result, keeping cost efficiency in mind, absorption chillers are used mainly for large installations where electricity is limited or heat is plentiful. The most efficient model of modern absorption cycle chillers uses water as the refrigerant and a solution of lithium bromide (LiBr) as the absorbent. “The concentration of LiBr is characteristically around 64 per cent after the generator and approximately 60 per cent after the absorber,” notes the spokesperson from Carrier Transicold India. In conclusion, the simplest absorption system is a onestage system, which is equipped with a single absorber and generator. According to Carrier Transicold India’s spokesperson “One is benefitted by lower investment costs; however, the trade-off is the lower efficiency. The use of multistage absorbers or generators not only increases the system performance, but also the investment cost.” However, absorption chillers come with inherent challenges for which solutions need to be designed, so that a larger market accepts this equipment. “Absorption chillers have a high rate of heat rejection limited unit selection and support, large physical size and weight, and toxic ammonia, which is used as the absorbent,” states Dr Collins. Machines that are capable of simultaneous cooling and heating are also available in the market. Absorption chillers-heaters possess the capability to eliminate the need for separate boilers, thereby reducing the cost and space requirements. Email: mahua.roy@network18publishing.com
November 2012 | Chemical World
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