Natural ventilation in Israel
Vernacular architecture employs methods that utilize natural ventilation for cooling purposes during the hot season.
Green architecture adopted some of these ideas to improve comfort and to save energy.
Natural ventilation can be used for multiple purposes:
To cool the body: when we are hot inside a room, air flow makes us feel as if the temperature in the room is significantly lower than it is.
To cool the house itself
For night cooling: night cooling uses the lower external temperatures at night to reduce the temperature of the building fabric (which absorbed heat during the day), using automatic ventilation devices. The cooled thermal mass of the building is used the next day to reduce internal temperatures. As a result, in the morning the house is cooler, and if we close windows early in the morning, we can maintain these good conditions for some hours, subsequently delaying the use of energy-consuming cooling equipment.
In Israel, the leading wind is the Mediterranean breeze (sea breeze and land breeze). On the coast the main wind direction is western, and as we move inwards, away from the coast, the wind direction shifts northward. We can find more precise data on the winds intensity and directions on the wind roses of each region. It is also recommended to take into consideration other buildings or trees in the vicinity that may obstruct or influence wind flow. To achieve the most satisfactory results, we have to consider all these elements from the beginning of the design process.
Two main natural ventilation strategies are:
1. Thermal stratification (hot air is lighter than cold air. Therefore it rises). We can enjoy this principle positioning a window in the upper part of the wall. This way, we allow hot air to exit. As a result, we create natural air movement in the room together with a significant reduction of inside temperature. This window should stay open all the time from Pesach until Succot.
Another interesting solution suitable for villas is roof bellows (מפוח) which pump hot air outside from the roof area. When hot air rises, fresh air takes its place. This solution is crucial because otherwise, the roof radiates the heat inside the house which makes cooling the house more and more expensive.
The bellows operate on a thermostat, so it works when it is necessary which further saves energy and money.
2. Air flow as a consequence of winds.
To plan air flow in the house, we have to allow winds to enter and to let them go out. The best way is to install windows both on the side that the wind is blowing in and on the opposite side (i.e. on the north/west facade and in the south/east one).
The “entrance air” window should be smaller than the exit one. The recommended ratio is 1:2
and they should not be positioned one in front of the other but offset. This way we can cool a larger area of the house.
Considerable importance also has internal walls and openings position.
An attractive solution to improve ventilation inside the house is to construct interior doors integrated with an upper ventilation opening that reaches the ceiling.
Some mechanical ventilation strategies can be combined with the natural ones.
One of them is installing a ceiling fan. Modern fans have two operating options: summer and winter. The summer one is ideal when the outside air is still hot, keeping the windows shut. In the winter mode, the fan turns in the opposite direction and sends the air downwards. As we know, hot air rises so with the fan we can we move it down where it's needed, keeping people warmer.
In conclusion, natural ventilation won't replace air conditioning systems, but it can significantly reduce the need to use them.
All the above design strategies don't require any extra investments and can have considerable economic and healthy consequences.
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