ON-SITE EXPERIMENTAL ESTIMATION OF THERMAL CONDUCTIVITIES AND HEAT CAPACITIES IN MULTILAYER WALLS UNDER ARBITRARY TRANSIENT CONDITIONS USING EXPLICIT AND IMPLICIT FINITE DIFFERENCE SCHEMES

摘要

It is often required to estimate the thermal properties of the layers of a multilayer wall, which is already part of an existing building. Such cases are encountered when an ex post check is required in order to find out if the design specifications have been followed, or if air conditioning loads have to be calculated in old buildings, the walls of which are composed of layers of unknown materials and thermal properties. In the present study, a method is proposed for estimating the thermal conductivities and heat capacities of the layers a multilayer wall is composed of. The method is based on explicit and implicit finite difference schemes and uses on-site temperature measurements at various locations within the wall. It is applicable to multilayer walls which are already parts of buildings. The outdoor and indoor conditions may be arbitrary, i.e. transient, nonperiodic, with solar radiation. The accuracy of the method, which has been verified by numerical and experimental applications, depends on the available number of temperature values in space. For example, in a 10-cm thick wall layer, measurement at five locations gives satisfactory accuracy, which is considerably improved by increasing the number of values in space using fourth-order polynomial interpolation.