Improvement to EN ISO 52016-1:2017 hourly heat transfer through a wall assessment: the Italian National Annex

Energy efficiency in buildings is a crucial topic to reduce worldwide energy consumption and fight climate changes. A key aspect is the assessment of the heat transfer through the opaque elements of the building envelope. One way to do it is modeling the element as a resistors and capacitors network (RC), using the thermal-electrical analogy. In the hourly dynamic method introduced by the recently published standard EN ISO 52016-1:2017, each opaque element is modelled with an RC-network. Italy has implemented in the National Annex A of the Standard an alternative methodology for the definition of the number of nodes and position, based on the detailed layers’ characteristics. In this work, the two methods are described and compared with the exact analytical solution for three cases under sinusoidal boundary conditions. In all the test cases, the results obtained applying the Italian Annex provide better results, with a reduction of the error on the internal flux amplitude between 14% and 67%. In addition, it has been verified that the Italian model is actually well-tuned. Indeed, the amplitude of the external flux is overestimated on average of only 3%, and the phase differences are limited (maximum ±1 h). Lastly, also the effect of the change of the number of nodes, and to move the nodes from the layers’ mid-point to the interface, have been analysed, but none of these strategies were demonstrated able to increase significantly the model accuracy, which can be obtained only reducing the calculation timestep.