The impact of work input to sorption cycles

In recent years the interest in cooling machines or heat pumps combining th e principles of compression and sorption technology is increasing. The reas on is that both technologies have specific drawbacks which can be overcome by the combination. Our discussion is centred around absorption cycles whic h use a compressor, and, consequently, an input of a significant amount of mechanical work in addition to heat. In most publications cycles of this ki nd are discussed in terms of one single COP as usual in the refrigeration i ndustry. This, however, is wrong from a thermodynamic, and misleading from a technical and economical point of view. In order to highlight the need fo r a strict thermodynamic approach, a fundamental difference between distinc t kinds of work input, namely "recoverable work", "dissipative work" and "h eat transformation work" is discussed in the first part of the paper. In th e second part it is shown how the input of both work and heat into a energy conversion system has to be handled with both mechanical and thermal COP. The method is thermodynamically sound and straightforward, technically feas ible and easy to apply, and most quickly transferred into economical terms. In the third part, a practical example of a compression-absorption hybrid is investigated. (C) 2000 Elsevier Science Ltd and IIR. All rights reserved .