Is the transfer function method reliable in a European building context? A theoretical analysis and a case study in the South of Italy

The available tools for dynamic simulation of the buildings thermal behaviour are manifold, and the most modern ones, known as TRNSYS, are founded upon the use of the Z-transform (ZT) set also called transfer function method (TFM). The transfer function method (TFM), recommended by American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), is one of the most modern tools available to solve heat transfer problems in building envelopes and environments. TFM utilises Z-transforms to solve the equation system that describes the heat transfer in a multi-layered wall. Due to an analogy with an electric circuit, it is possible to write the equation system in a matrix suitable to be solved by computer. The authors have investigated TFM mathematical features, especially concerning the reliability and the quality of the thermal dynamic simulations. Using some basilar control systems tools such as plots, step response and model validation, results show clearly that, for a massive building, a simple application of TFM very often fails. The target of the work was to identify an automatic procedure able to optimise the reliability of the simulation by selecting and using in a more correct way poles and the residuals of the transfer functions.