In a larger research program on ‘cost versus value evaluations in the early design stages of technical buildings’, a study and software implementation has been made to simulate HVAC expertise using an Integrated Early Design Environment. Basically the idea is to create a virtual early design software environment where the development of the requirements, concept designs and evaluations on costs and values is supported. A prototype implementation has been made that uses Product Data Technology (PDT) in combination with Knowledge Technology (KT) and which is able to calculate certain HVAC aspects. This paper describes how an existing HVAC simulation program has been used to support the design process in the inception and early design phases.