Optimal distribution of condenser area for retrofits

摘要

Test results from field retrofit situations, where R22 has been changed to Isceon 59 and R407C in two identical chillers, shows that both substitutes require more subcooling than R22 to give the system a satisfying performance. It was also notedthat to achieve the same subcooling, one had to charge the system with a larger amount of refrigerant. To achieve the same efficiency, COP{sub}2, with Isceon 59 as with R22, one had to add approximately 25% more refrigerant, than the system had with R22.A computer model of a system consisting of coaxial heat exchangers, with refrigerant in the inner tubes, has been made. In the model five R22 substitutes (R134a, Propane, R404A, R407C and Isceon 59) and R22 were compared. The simulations showed a similarbehaviour as was experienced in the field tests: To make the system perform its best with Isceon 59 the area used for subcooling had to be larger than when R22 were used. With other substitutes, like Rl34a, a smaller subcooling area gave the maximumperformance of the system. R134a can be a very interesting R22 alternative if it is energy efficiency that is important, and not primarily capacity.To find the correct amount of refrigerant charge for a specific system, it is necessary to look at the shape of the wet region when plotted in a property plot, but it is also important to look at the relative size of the heat exchanger area in bothcondenser and evaporator, for the specific refrigerant used.