Retrofitting of old Exterior Wall with Vacuum Insulation Panels: Measurements of Thermal Properties, Moisture Performance and Practical Considerations
Abstract: The building industry is facing one of its most challenging tasks ever. Until 2050 the energy use for heating of buildings should be decreased by 50% which means a large part of the building stock have to be retrofitted to become more energy efficient. One of the possible solutions is to add thermal insulation to the exterior wall of the buildings. The insulation can be placed on the interior or exterior of the existing structure. Adding insulation on the exterior of the façade means that the architectural, historical, environmental and artistic features of the building may be lost. Vacuum insulation panels (VIP) is a novel thermal insulation component used in refrigerators and cold shipping containers which, during the last decade, also have been introduced in the building industry. The VIP is a composite which has a thin metalized multi-layered polymer film wrapped around a porous core material from which the air has been removed. A problem associated with the use of VIP is the fragility of the product. A punctured VIP has a loose film which is easily detectable by visual inspection. However, a VIP can be damaged without having a loose film. This requires a measurement procedure that can determine the thermal conductivity of a VIP in situ, before integrated in the construction. Such a method is lacking today but in the scope of this project the transient plane source (TPS) method has been evaluated. Initial investigations show that the TPS method possibly can be used, with some modifications, to determine the thermal properties of VIP. The main purpose of this study is to investigate the applicability of VIP when retrofitting the exterior wall of old listed buildings. The applicability has been evaluated in a field study and by theoretical assessments. The VIP cannot be cut on site which requires design with high precision. In places where VIP could not be used due to lack of space, glass wool was used instead. Hygrothermal sensors were installed in the field study building which monitors the temperature and relative humidity at various locations in the façade and in a neighboring reference façade. Initial results from the hygrothermal sensors showed that the relative humidity in the retrofitted wall was lower than the reference wall. The lowest and highest relative humidity was found behind the center of a VIP and at the window frame respectively. The hygrothermal monitoring of the wall will continue in the next phase of this project. A theoretical assessment of the moisture performance of the wall before and after retrofitting was carried out using hygrothermal simulation software. The hygrothermal simulations showed that the relative humidity in the wall decreases with time after the retrofitting. The results of the simulations showed that the indoor climate was an important parameter for the moisture performance of the wall. Therefore a stochastic simulation model was developed of the indoor moisture supply which could be used in future hygrothermal simulations.
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