academic work UCL 2013 Hygrothermal behaviour of internally insulated brick walls under UK climate conditions Introduction A quarter of UK’s greenhouse gas emissions are the result of high energy consumption, primarily due to space heating. To achieve the 80% reduction by 2050 target a series of energy efficiency strategies –i.e. ECO and the Green Deal– have been introduced to improve the building fabric of the housing stock. 8 of the 27 million UK housing stock is comprised of solid brick wall buildings. Some of them are listed buildings that can only be insulated internally. In the case of moisture permeable solid-wall buildings, contemporary sources indicate that careful attention must be paid to the hygrothermal behaviour of the insulated wall, to limit the risk of interstitial and surface condensation. This dissertation presents an initial investigation of the impact of different climate parameters on the hygrothermal performance of four types of internal insulation systems, breathable and nonbreathable. Effects of internal conditions - high moisture load and low airtightness of the building envelope - have also been investigated. Software: WUFI, Meteonorm, Microsoft Excel & Word, Adobe Illustrator & InDesign.
Methodology and UK climate analysis The study utilized WUFI, a software package that calculates transient heat and moisture transport in multi-layer building components exposed to the weather. Using the guidelines of the BS EN 15026, the study tested the effect of temperature, relative Humidity (RH), solar radiation, rainfall and wind speed on the hygrothermal behaviour of the insulated wall. The maximum, minimum and average values used for modelling iterations were the ones resulted from analysing the climate of 11 locations across the UK. The interstitial RH profile of the internally insulated wall was simulated for a duration of 20 years, with a detailed analysis focusing on the hygrothermal behaviour during a typical year.
Results Simulation results indicated that rainfall and solar radiation have a major impact on the insulated wall’s ability to dry over the year, while the other parameters produced minor changes compared to the “UK average” climate conditions. Similarly, combined high rainfall and high solar radiation produced the strongest overall effect, since water can transfer both as liquid and vapour. The high interior moisture load produced a significant effect, while the airtightness of the insulation system was found to have minor effects, possibly due to a fault in the simulation software. The hygrothermal behaviour of internally insulated brick walls is the result of water being transported both in liquid and gaseous form. Simulations have shown moisture transfer depends on both location and orientation. Conclusion Moisture transfer within an insulated wall depends on the amount of water brought on the façade by rain, the wind pressure that drives it inside (wind speed and direction) and the amount of solar radiation transforming the water into vapour. Hygrothermal behaviour of the internally insulated wall therefore depends on both location and orientation.