Ventilation is the movement of air within a building and between the building and the outdoors. The control of ventilation is one of the most subtle and yet the most important concerns of the building designer. How to make air move about the building in a way that satisfies, and even delights, the occupant.
There is, of course, a simple solution - to use a fan - but this can be a noisy and expensive business and is not the preferred first option for an ecohouse in which mechanical systems should only be used as a last resort.
So how does air move without a fan? Actually, air moves very easily and always down a pressure gradient. Positive pressure exists on the windward side of a building where the air is pushed with some force against the building. Negative pressure occurs on the leeward side of a building, in the wind shadow, and sucks air from the structure.
The trick is to create that pressure gradient. This can be done in two ways:
1 using pressure differences around the outside of the building caused by wind;
2 using pressure differences caused by the pressure variations within the house. Warm air is less dense than cold air, therefore pressure variations that cause warm bodies of air to rise also cause cold bodies of air to fall. This is called the 'stack' effect and can be used to ventilate a space. It can also be in conflict with wind-driven cross-ventilation.
Using wind pressure to ventilate is common, particularly if the house is in a windy part of the world. There are many challenges in designing properly for ventilation including the variability of the wind, its speed and direction, but if carefully handled and understood it can be of real benefit to the indoor climate of a house, for most of the time.
Wind and ventilation are not the same thing. Wind is very variable and can present itself in many different guises.
A wailing rushing sound, which shook the walls as though a giant's hand were on them; then a hoarse roar, as if the sea had risen; then such a whirl and tumult that the air seemed mad; and then with a lengthened howl, the waves of wind wept on. Dickens.
How different was Dickens' description of the wind from that of Longfellow:
The gentle wind, a sweet and passionate wooer, kisses the blushing leaf.
The wind can be an agent of terror or delight, it can soothe or destroy and it is one of the most important of the invisible building blocks of architecture. This chapter begins by considering the wind, and its usability for a building for a particular site and form. The reasons why and how to use air in buildings for maximum effect are then outlined. Finally, a section is included on how to protect a house from strong winds, such as result from hurricanes and cyclones. A major impact of global warming over the last decade of the twentieth century has been the increase in wind speeds and damage experienced in many countries of the world (Headley, 2000). We cannot predict how badly climate change will affect any of us, but we have taken this opportunity to include design for extreme wind environments, just in case. This section is complemented by two case study buildings, one on a strong
Positive (+) and negative (-) wind pressures around different building configurations.
wind site in Findhorn, Scotland and the second in cyclone-prone St Maarten in the Caribbean.
To ventilate a house well you first have to develop a relationship with wind. To do this you need to understand the regional and local climate of the site, the form and surroundings of the site and building. Key, also, are the building's occupants and their comfort requirements.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.