EXPERIENCES OF A NONAZEOTROPIC MIXTURE AS REPLACEMENT FOR CFC12

In the paper theoretical and experimental comparison between the perfo rmance of a two-stage heat pump working with the nonazeotropic mixture HCFC22-HCFC142b and that of one working with CFC12 is presented. An e xperimental full-scale plant consisting of two heat pumps of 1 MW each , one working with the mixture HCFC22-HCFC142b and the other pure CFC1 2, has been in operation, since May 1991, in a small district heating system. The main aims of the project are: to verify theoretical calcul ations; to get practical experience of the handling of nonazeotropic m ixtures; to experimentally study the influence of different parameters . The HCFC22-HCFC142b mixture was chosen since it is one of the few no n-flammable mixtures, suitable for CFC12 replacements, that was availa ble at the beginning of the project. Three problems have occurred: dar kening of the oil; instability of the suction gas superheat; and probl ems with the initial sealing material. These problems are now solved. A rigorous computer program has been developed and used to calculate t he COP and capacity for mixtures and pure fluids for the same heat out put, under the same operating conditions and assuming equal heat trans fer areas for pure and mixed fluids. The measurements of the COP have in principle confirmed the results from the theoretical calculations.