1. Introduction

Hierarchical systems (Figs. 2.​3, 2.​4, 3.​1, 3.​2 and 3.​3) are multi-level, clockwise or anticlockwise systems. The clockwise systems include heat engines, while the anticlockwise—heat and power machines. The basic property of hierarchical systems is the fact that heat from an external heat source is input only for one cycle. For an engine it is the cycle superior in hierarchy, i.e. the cycle operating at the highest temperature range, while for a heat and power machine, chiller or heat exchanger it is the lowest cycle in the hierarchy, i.e. the cycle operating at the lowest temperature range. For each remaining cycles the input heat is the heat exported from cycles, in the case of engine, in the hierarchy directly above them, while for a heat and power machine, from cycles located directly below them (Figs. 2.​3, 2.​4).