We show in this article that the common method of specifying Delta T-min for individual heat exchangers may lead to wrong decisions and should be used with care when designing heat exchanger systems. In particular, design with constraints on AT in may result in operation conditions that are not optimal when the resulting areas are installed. In addition, different U values for the heat exchangers are not easily handled. We propose an alternative method (simplified TAC) to avoid these problems and compare it with the Delta T-min method on three vapor compression (refrigeration) cycle case studies.