One of the basic principles of the sustainable development is minimization of energy needs. European Union 2010/20/UE Directive clearly shows the direction of contemporary construction – after 2020 almost zero-energy buildings will be constructed. What prepares us to the changing reality of the market and the Construction Law is the Regulation of the Minister of Transport, Building and Water Management, which 1 January 2014, introduced a number of changes to the subject of technical conditions to be met by buildings and their location.
In many European countries, including Poland, there are certain actions taken, aimed at rationalization of energy use and implementation of new, high-efficiency window, door and facade systems - says PhD. Andrew Polijaniuk, director of marketing and product Schüco International Poland. The new regulation doesn’t leave out window joinery industry either. The required energy performance ratings for windows were changed.
What about this „g”?
One of them is called Solar Factor, or G-value, which tells us how much sunlight will pass through the transparent partition into the room. Previously, experts in the field of energy auditing and glazing manufacturers tried to convince us that the higher g, the better, and a greater amount of light directly translates into profits from solar energy (e.g. when the heat collected during the heating season by the glass is used to heat the object by mechanical ventilation with heat recovery). Currently, the trend is reversed - the analysis of the advantages and disadvantages of sustainable and passive building and a revision of our knowledge of these fields has allowed us to reflect. It turns out that the cooling process is much more energy-intensive than the process of heating. Glazing which obtains a large amount of energy in the winter, in the summer causes overheating of the room . Accordingly, G-value in the new regulation has been reduced from 0.5 to 0.35.
There has been changes in case of the heat transfer coefficient. For a long time, the windows with the parameters equal Uw ≤1,7-1.8 W/m2K were considered energy efficient, due to the existing legislation - explains Andrew Polijaniuk. Although there was no definition of such a window, year after year the minimal requirements were further away from the reality. When on the first of January, 2014 a new regulation on technical conditions to be met by buildings and their location came into effect, the minimal heat transfer coefficient was reduced to Uw = 1.3 W/m2K. Thus, the windows with such parameter became standard. Although an analogous requirement has been mandatory in Germany for five years (EnEV 2009), in reality an average heat transfer coefficient of the windows produced is lower than the minimal value by 37%. This tendency is favored by to increasingly stringent requirements on the demand of buildings for non-renewable primary energy (EP) – he continues.
Energy efficiency and the windows
How to choose the type of glazing for a given investment then? Apart from the recent regulations, a number of different factors should be considered. The choice of windows with the right parameters, such as heat transfer coefficient heat transfer coefficient (Uw), solar energy transmittance (g), light transmission (LT), weighted sound reduction index (Rw), the size of the glazing and its impact on the energy performance of the building depend on many factors. Above all, the factors are the way the building is used, the location of individual elevations and the sunscreen solutions used – explains PhD Konrad Witczak, main consultant for energy efficiency ofr the BuildDesk Polska company. On the one hand, windows contribute to heat loss (their Uw is mostly much higher than for the walls and roof), on the other – they make it possible to obtain heat from the sun. A large glazing surface considerably increases the demand for the heating energy and for the cooling energy, in case of air conditioned buildings. However, the comfort of the rooms increases due to greater access to daylight - the expert emphasizes.
It is worth noting that the content of the new regulation convinces us that an equally important role of the window is to protect against excessive heat loss and to protect against excessive profits from solar radiation. Many investors do not realize that the selection of the appropriate window frames will influence not only the aesthetics of the object but above all, it will influence its energy efficiency. An analysis of the solution from the point of view of cost-effectiveness of energy is the more advisable especially because the windows are bought with a view of long-term operation.
Energy efficient windows in an office building
The issue of energy efficiency of the transparent partitions is even more complicated in case of the objects such as office buildings and hotels, in which the proportion of glazing in the facades is constantly rising. Some of the modern buildings are constructed with the use of large glass coatings, i.e. structural-glazing facades. Fortunately, solutions which were impossible ten years ago now are increasingly often used by the glazing manufacturers. The whole thing is interesting from the point of view of aesthetics - as structural profiles are visible only from the side of the premises, while outside the facade looks like a constructed entirely of glass panes separated by fine lines. Aesthetics doesn’t mean that the parameters of thermal insulation are worse, and installation of large glazing doesn’t cause overcooling of the rooms in winter and overheating in the summer. The technology of producing aluminum facades is so advanced right now, that it is possible to design class coatings of the buildings in the passive standard – explains Andrzej Polijaniuk. Last year we introduced mullion/transom FW 50+.SI Green facades, which meet the strict criteria of the Passive House Institute in Darmstadt and which are additionally produced with the use of renewable raw materials. This series is dedicated in particular to objects applying for LEED and BREEAM. The directions of development of construction clearly show that reaching for better technology now is worthwhile so that the investment may be still attractive in the future.