Integration of moisture transfer through walls into an urban climate model and application to the medieval city centre of Cahors (France)

Abstract

Moisture transfer is a key phenomenon for simulating the energy balance of the walls of historical buildings as it has an impact on indoor and outdoor comfort, energy consumption and the durability of the walls. It is therefore essential to consider moisture transfer through walls when simulating old city centres, in order to properly assess the impact of different retrofit solutions on building and city energy balances. However, urban climate models neglect this phenomenon. The objective of this paper is to integrate the coupled mass and heat transfers into the urban climate model Town Energy Balance (TEB). A specially designed numerical method for solving hygrothermal transfers at the urban scale is updated and the hygrothermal transfer through walls is integrated using an IMplicit/EXplicit (IMEX) discretization scheme with large spatiotemporal scales. The reliability of this modified version of TEB for representing a historical district is verified by comparing the simulated results with in-situ measurements in a building of the medieval city centre of Cahors (France). The comparison is carried out for several points in the wall and for indoor conditions, running from June to December 2021. The integration of the moisture transfers through the walls greatly improves the moisture estimation inside the building. This new version of the model gives a good representation of the hygrothermal behaviour of a historical building and could therefore be used to compare several renovation scenarios for the medieval centre of Cahors, with regard to durability, energy and microclimatic issues.