with S ˙ ˙ i the sum of the rate of entropy production by all processes inside the system. The advantage of this formulation is that it shows the effect of the entropy production. The rate of entropy production is a very important concept since it determines (limits) the efficiency of thermal machines. Multiplied with ambient temperature T a it gives the so-called dissipated energy P d i s s = T a S ˙ ˙ i .