Passive House - 6 reasons why you still need opening windows
...do I need to keep the windows closed at all times?
Wrong – Absolutely not! There are multiple reasons why there needs to be at least one opening window in each room typically used for living (bedrooms, living room, kitchen). The best option is a turn and tilt fitting. At least this is true for all places on the planet, there external conditions are at least sometimes near to a comfortable range (well, and as long as you are not building on Mars, there are only a few exceptions). Saving costs on windows is a bad idea and might cause several problems later on:
1. During warm periods, opening your windows is the easiest, cheapest, most effective and environmentally friendly way of cooling your building, with cross ventilation offering the most effective solution; at least in climates, in which the external temperatures cool down during the night. The standard air exchange provided by Passive House ventilation systems generally is far lower, and with the fan giving off additional heat, the cooling effect is reduced even more. The air change rates of ventilation systems are typically laid out for really cold (or hot) periods and may not be too high to keep the air from getting too dry (or too humid). A completely different type of ventilation system would be needed to allow for significantly higher air change rates. Such systems would be more expensive and less efficient; of course, in some circumstances such systems can provide another solution. Providing large volumes of air by opening your windows, on the other hand, is fairly inexpensive.
2. Users typically expect to have openable windows anyway as they offer maximum flexibility. Most users would not want to miss windows as a “connection to the outside world”, and want to be able to choose whether to keep the windows open or closed. Eliminating this option might cause discontent amongst users whose wishes should be respected – unless it would be unreasonable to do so (for example in a submarine or a spaceship).
3. Cleaning fixed glazing is usually much more difficult than cleaning windows that can be opened and cleaned from the inside. Openable windows thus make a building much easier to maintain and can help reduce running costs.
4. Monitoring results suggest that there is little risk of Passive Houses not getting warm or requiring significantly more energy for heating due to users keeping the windows open. There is no need to fear that « human errors » might cause problems, even when bedroom windows are tilted all night long during winter. In this case, the only negative effect is a slight increase in heating energy (see article on user behaviour).
5. Even during cold periods, sometimes it may be nice to be able to open the windows to let in some fresh air, for example during a party or an assembly.
6. Last but not least, an openable window could save one's life as it offers an easy way out in the unfortunate event of an emergency.
There are few Passive House buildings partially or entirely fitted with fixed glazing. Most reports or enquiries regarding these building concern complaints about excessive temperatures in summer or users feeling closed in – something that can be prevented with a turn and tilt fitting.
Based on these reasons and experiences, providing at least one openable window per room used for living is a prerequisite for Passive House buildings to be eligible for certification; there might be well justified exceptions (if the building is in the direct vicinity of an airport e.g.).