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==Summary==
Many ways to keep cool have been invented, including many techniques that are cheap and effective. For instance, simply planting trees or shrubs around a house could substantially cool a home. Air blown on water was known to cool places probably already by the Bronze Age in the 3rd millennium BC, but the Romans could have been the first to capitalize on this to create something akin to a central cooling system. Electric fans in the late 19th century and air conditioning in the early 20th century have now transformed homes. However, this has meant many homes today depend more on these modern conveniences and use materials, such as concrete, that have made cooling impossible without the use of modern appliances.
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