In the near future a large number of dwellings in Switzerland dating from the 50s to the 70s will need to be retrofitted in order to upgrade the comfort levels to today's standards and to reduce the energy consumption. By carrying out an overall retrofit of both the envelope of the building and the building services this can be successfully accomplished. Two retrofit projects of apartment blocks, one in Meilen and one in Cossau, demonstrate how a well-balanced strategy can achieve a comprehensive and economical retrofit.

This paper reports the results of a study to test two novel procedures to model dynamic thermal conditions of an enclosure within Computational Fluid Dynamics (CFD). The main area of investigation is the performance of the procedures in simulating the varying thermal response of the building fabric, the effects of external thermal load changes and the consequential effect on the air inside the enclosure. The dynamic thermal modelling procedures proposed utilise a transient time-varying grid schedule and Freeze-Flow techniques.