Carbon dioxide as a working fluid in drying heat pumps

Carbon dioxide as a working fluid in refrigeration and heat pump systems is increasingly important in view of the CFC substitution problem. It is both under ecological and economical aspects an attractive alternative to the H FC working fluids at present in practical use, The thermophysical propertie s and characteristics of carbon dioxide are quite different from those of r efrigerants used in conventional vapour compression cycles, Its application in conventional vapour compression refrigerating systems is limited by its critical parameters (t(c) = 31.1 degreesC and p(c) = 73.8 bar), The possib ility to use carbon dioxide also beyond these limits in high temperature pr ocesses, e.g. heat pumps, is given by the application of a trans-critical p rocess. The design and construction of a commercial drying heat pump system (batch type cabinet dryer with 12 kW heating capacity and closed air circu it! using the natural working fluid carbon dioxide is shown and experimenta l results of investigations carried out are presented. Energy savings are g iven compared to manufacturer's data of energy consumption, (C) 2000 Publis hed by Elsevier Science Ltd and IIR, All rights reserved.