Energy rationalisation, the elimination of unnecessary energy consumption, is becoming increasingly important in a resource constrained world. The use of energy is a significant contributor to greenhouse gas emissions and much research has been done to reduce energy use in manufacturing. So as to enable the rationalisation of energy consumption, it is essential that it is understood where energy is being used. This paper describes the design and implementation of a simulation model that has been generated to support the modelling of energy consumption within manufacturing systems. The simulation model allows various ‘what-if’ scenarios to be investigated thereby enabling engineers to understand the impact of various manufacturing parameters on energy consumption and thus reduce reliance on energy and the production of greenhouse gas emissions.