The selection of the correct window in a passive house plays a prominent role in the ultimate efficiency of the building in two ways. Firstly the heat loss, despite large glass surfaces, can be reduced and secondly the correct choice of windows can increase the possibilities for heat gain through solar irradiation.
Windows which perform both these tasks are often referred to as highly thermally insulating energy saving windows. It is a bit of a mouthful but the technology within these windows, which are typically triple glazed, achieves U values of up to 0.5 W/m2K and g values (overall energy transmission factors) of up to 62% depending on coating and gas fillings.
Besides the actual glazing however you also need to consider the insulation of the window frame as well, including the thermal bridges at the glass edge and in the connecting area between the window and the wall.
Spacers are usually used to form thermal bridges and are usually made of aluminium. Passive House standard windows also have specially designed thermally insulating window frames which also reduce thermal losses at the glass edge. Additional stainless steel spacers can also further reduce losses at the glass edge.
For passive house certified components completely thermally optimized systems like ISO spacers are used. Following earlier developments in the automobile industry all glass panes are glued to improve structural stability.
Essential Principles for Construction of Passive House Windows
Passive House - A Sustainable Investment
A passive house provides consistent, comfortable temperatures in winter, as well as in summer without using conventional heating or air conditioning systems. Using the existing temperature provided through solar irradiation through the windows as well as the heat from appliances and inhabitants is sufficient and as a result the necessary heating energy for a passive house is only 10 % of that needed for a conventional house.
Optimised Energy Demand
Careful optimisation of the energy demands in a Passiv Haus building can result in an annual heating demand of not more than 15 kWh/m2a. The overall energy demand including warm water and household electricity for a passive house is less than 120 kWh/m2a. The heating load of a passive house is not more than 10 W/m2, for a room of 30 m2, this results in a heating load of approximately 300 Watts.
To illustrate all these figures: the heating power of a tea candle is 30watts.
Adherence to Passive House standards means that 10 tea candles are enough to heat 30m2 in a passive house!
This incredible efficiency in generating and using energy means that extraordinary savings can be achieved along with a huge reduction in the carbon footprint of the building and the family or business within.
All of these efficiencies discussed above are rooted in the two basic principles of minimising thermal loss and optimising thermal gain a principal which is worth investigating even if you are not aspiring to achieve full passive house status.