Transient thermal response of opaque building envelope elements: EPFL campus case study

The building envelope acts as a shield against varying weather conditions and modulates thermal energy flow between outdoors and indoors. The choice of layers used in the assembly impacts the heat loss and gain through the wall structure and potentially can affect the comfort indoors. Thus, the building envelope plays an essential role in the thermal performance of the building. Optimizing the cladding design in the envelope has recently become increasingly important to reach sustainable development strategies for reducing greenhouse gas emissions by 2050. This paper aims to analyze several cladding types used on the EPFL campus in Lausanne and compare their impact on the energy performance of the building envelopes. The building assemblies constructed on the EPFL campus in different years vary in composition and thermo-physical properties of the layers used. The impact of these parameters on the thermal performance of the wall assembly is evaluated by comparing the variation of heat flux and temperature fluctuations within the wall structure. The results obtained highlight the importance of the building envelope layers and materials used in the wall structure. Due to the variations in the thermal inertia of different wall assemblies, a time shift of more than 3 hours in the transient response of the building envelope to the fluctuation of the outdoor weather conditions is observed.