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Hanging your laundry out to dry

Graeme Brittain, Wednesday April 25, 2018 - 09:55 EST

There are several things to consider when deciding whether to hang your clothes outside to dry.

First and foremost, what are the chances it will rain rain today? Clearly it is not a good idea to hang clothes outside if frequent heavy showers are likely — the moisture you are trying to get rid of will simply be replenished when it rains.

Following from this, taking into account the relative humidity can give an idea of how fast wet clothes will dry. High relative humidity (usually higher than 80%) means that the air cannot hold much more water vapour, therefore it takes more time for the excess moisture in the wet clothes to escape into the air.

On a still day, when winds are light, the air surrounding a sodden pair of shorts can become 'full' of water vapour (in other words, the relative humidity of the air is high). For the shorts to dry faster, the saturated air around the shorts essentially needs to be pushed away and replaced by drier air, which can be achieved when it is windy outside.

The temperature also affects how quickly clothes dry. A higher air temperature means that there is more heat energy in the air that can be used to evaporate the water from the damp clothes.

Last but not least, sunlight. Wet clothes left in direct sunlight will dry much more quickly than if left in the shade. This is because direct sunlight provides some extra energy in the drying process, in the form of radiation.

There are some savings to be had by taking advantage of natures free 'dryer'. A back-of-the-envelope calculation (based on 1kWh costing $0.25) indicates that some households could be saving over $200 each year on their energy bills.

Although winter is approaching, temperatures are generally dropping and days are getting shorter, there is still plenty of opportunity to hang your washing outside to dry.

It is worth taking a few seconds to consider the forecast relative humidity and wind speed next time you have a wet load of laundry.

All of this information is available, with an hourly breakdown, on the Weatherzone App.

- Weatherzone

© Weatherzone 2018

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