Contribution of windows to the overall building environmental performances

Between the building components windows are of high interest within the European policy activity as directives and regulations set out roles to manage, more or less directly, their environmental performance. The product group “Windows” is subjected to the Construction Products Regulation and it is indirectly addressed by the Energy Performance of Buildings Directive. The Working Plan for energyrelated
products (2012-2014) in the context of the Ecodesign Directive, includes windows in the lists of Energy Related Products (ErPs) that have to be considered in priority for the adoption of implementing measures on Ecodesign and Ecolabelling and
estimates the energy savings potential in 785 PJ/year as of 2030.
Moreover there have been EU founded calls within the FP7 Programme specifically addressed for the development of “Smart Windows”. In particular the EU FP7 HarWin Project (Harvesting solar energy with multifunctional glasspolymer
windows) which in part holistically evaluates through the Life Cycle Assessment Methodology, the impacts related to the different phases of the window life
from construction, through the operating phase and to the end of life.
Some authors state that up to 60% of the total energy loss of a building can be related to its windows, it is therefore clear that efforts have to be made to optimize the window performance during the operating phase. As a matter of fact that windows serve multiple purposes from thermal insulation to light transmission, ventilation, noise reduction, pressure, fire protection among many functions. For this reason, within the HarWin Project, dynamic building level simulations were undertaken varying the following window thermophysical and optical properties, visible light transmittance, GValue and UValue.
This paper discusses how these variations affect the whole performance of buildings from a life cycle perspective. The environmental analysis of the different scenarios have
been evaluated according to different building types and age, climate location, internal gains, heating, ventilation and air condition (HVAC) systems. Among the results on the environmental analysis run for the different scenarios, it emerged that the impact is deeply affected by the National Energy Mix, which brings out the importance of the multi criteria approach since the set of relevant impacts categories changes with the Country. Lessons learnt from the EU FP7 HarWin Project are described and recommendations are
formulated.