Energy and financial considerations related to wall design for a conditioned cell in Tunisian conditions

A previous study has shown that most wall designs will necessitate in a Tunisian climate some means of heating and cooling to reach comfort levels. In the present work, we want to investigate the behaviour of different wall layer arrangements in the case of conditioning. In order to compare the thermal performance of these wall designs we have defined a new thermal performance indicator: the dynamic heat transfer coefficient gives the heat flow across the wall taking into account the thermal capacity of the wall and solar gains. Twenty-three different wall arrangements are studied by computer simulation of a dwelling test cell and are compared according to the dynamic heat transfer coefficient to the total energy expenses for production of the wall, and conditioning of the cell, and also according to the total cost associated with the wall arrangement, including investment cost and expenses of energy for conditioning during the whole lifetime of the dwelling. This study shows that thermal insulation plays a more important role in the case of conditioning especially for heating conditions. For summer conditions, thermal capacity is more decisive. Charts of global energy costs and global financial costs are given and can be used as design aid tools for the choice of wall composition.