Kjartan Gudmundsson

Simulations of Heat and Moisture Conditions in a Retrofit Wall Construction with Vacuum Insulation Panels

Vacuum insulation panels provide unprecedented possibilities for renovating the existing building stock in a manner that reduces the thermal losses through the building envelope. This study is focused on the implementation of VIPs (vacuum insulation panels) in energy retrofit projects with rendered outer walls. Particular emphasis is put on reducing the thermal bridges due to mechanical fasteners and at the joints of the panels. These are evaluated through a parametric study of the impact of the thermal conductivity of the joints of the panels and the adjacent insulation layer as well as the material of the fasteners. The study is carried out with 3D FEM (finite element method) simulations software. Furthermore, the moisture conditions in the construction are studied. The dynamic moisture behavior of a wall construction is modeled with a two dimensional FEM model. The long term effects of vapor diffusion are investigated in terms of accumulated moisture and the risk of condensation. The results illustrate that vacuum insulation on the outside of the wall construction does not pose a moisture problem to the construction. The simulations are based on a draft of a new technical solution for the refurbishment of a building that is typical for the great Swedish building program of the 1970s.

Sampling and Analysis of Natural Isotopes in Moisture Transport from Porous Materials: Applications to Capillary Suction:

Apart from the most common 1H and 16O we have the sister isotopes: deuterium D and 18O in water. Isotope fractionation (the change in its concentration) occurs in any thermodynamic reaction. The isotopic composition serves as a distinct mark for each water sample. To carry out the isotope analysis of pore water, which may be used to reveal the source of excessive water in building elements, firstly one has to extrude water from voids. For this we tested three different methods of retrieving water from the porous material: squeezing and evaporation - the direct methods, dilution - the indirect method. The influence of capillary suction on the hydrogen and oxygen isotopes abundance ratio was also analysed. Materials whose substantial part of voids are gel pores (cementitious materials) act as a membrane during isotope transport separating lighter from heavier isotopes and therefore cause the fractionation of isotopes. The results of performed experiments indicate that moisture transport (capillary suction) has an influence on the isotopic composition of water. Therefore the isotope analysis can be useful in the investigation of moisture behaviour of porous building materials.