One of the most important factors leading to energy loss from buildings is the wind. There are two reasons for this:
- When the wind blows on a building, it creates different areas of higher and lower air pressure around the building. These pressure differences force cold air in, and draw warm air out through all the cracks and gaps in the doors, windows, roof and walls.
- If you want to cool down a hot potato chip, you blow on it. Well, when the wind blows on a building, it will cool it down in exactly the same way (assuming the outside air temperature is lower than the temperature of the building). This cooling effect will still happen even if all the cracks and gaps have been filled.
Trees as a windbreak
So, if a building is exposed to the wind, a very effective way of reducing heating costs is to shelter the building from the wind by planting trees. Research in the USA has found that a well-positioned row of trees can reduce the heating costs of a building by between 10% and 25%. The size of the energy saving depends on how windy the location is, and how cold the winter air temperature is.
To be effective, the trees must be planted in the correct place. There are several points to consider:
- Decide which direction strong winds blow from most frequently, and plant trees accordingly. In much of Europe, this would be on the west side of a building. Although northerly wind is less common, you might want to plant trees on the north side as well, because the northerly wind is usually the coldest.
- Don’t plant the trees on the south side of the building, because they will block the sunlight and prevent natural solar heating.
- Don’t plant trees too close to buildings, or the roots might damage the foundations. There is no need to plant trees close to a building in any case, because the sheltering effect of trees occurs for up to five times their height. In other words, a row of trees 10m high will provide some shelter for up to 50m.
Clearly this is a long-term solution to save energy, and it might need the involvement of the whole neighbourhood, but it has many additional advantages beyond energy saving. Trees make hot summers more comfortable by providing shade and increasing evaporative cooling. They can also improve air quality by absorbing pollutants including particulate matter. Trees will also help to reduce noise levels in cities, and they can reduce flooding by slowing down the surface run-off of rain water. Finally, there are also psychological benefits to living in a greener environment.
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