This paper reports the thermodynamic optimization of air conditioning systems with one or more evaporators, for one or more rooms. First, the paper shows that the minimization of the total power requirement leads to the same results as the minimization of entropy generation in the whole system, which includes the insulation between the cold space and the ambient. The results also show that there is a trade-off between the power lost by fluid friction in the distribution network and the power required by the refrigerant. This trade-off determines the optimal allocation of hardware in the installation. The optimum diameters of the refrigerant pipelines are independent of their lengths. © 2013 John Wiley & Sons, Ltd.