This paper deals with the development and validation of a simulation algorithm for the temperature behaviour and the flow characteristics of double facades. It has been developed in order to obtain a tool which enables the energy consultant to make quick design decisions without being required to use fairly complicated CFD tools. In order to determine the degree of accuracy of the algorithm, a double facade has been monitored under controlled conditions and the results have been compared against the predicted values for several design situations. The resulting inaccuracy in some cases can be traced back to how the flow resistance of various geometries are modelled.