Transient simulation of the influence of wind conditions on the airtightness of windows. A case study for a tertiary building

Abstract

Achieving a reasonable level of airtightness is important for the energy efficiency of living spaces and the comfort of occupants. The benefits of improved insulation levels and more energy efficient heating systems are lost if warm air can leak out of a building and cold air can leak in. Poor airtightness can be responsible for up to 40% of heat loss from buildings. Airtight buildings require airtight windows. Airtightness of windows is often evaluated in lab conditions in the context of initial type testing. Testing methods can be found in several international standards, leading to airtightness classifications of windows for building codes. The level of airtightness achieved is measured as air permeability, as the quantity of air that leaks into or out of the window per hour. Airtightness of windows is typically expressed per meter opening joint or per square meter. Nevertheless, airtightness of window is highly sensitive with respect to wind conditions, mostly speed and direction. Increased attention to energy efficiency and airtightness of buildings has led to more research on the performance of windows, and can be estimated by appropriate simulation. This work presents a case study of the influence of wind speed and direction on the thermal load of a tertiary building due to leakage through windows. Transient simulation by means of Transient System Simulation (TRNSYS) package is presented. Results are analyzed as a function of standardized window type. Besides, relative influence of the internal layers of the façade on the thermal load of the building is studied. Three alternative cases of high thermal inertia are compared with the existing one with low thermal inertia.