Should you leave window OPEN with fan on hot day? Science of cooling revealed

THE WAY you’ve been using your fan to stay cool this summer could be completely wrong.

According to air quality experts, there are a number of rules you should follow in order to prevent overheating and sleep better during the hotter months, including where you should place your fan and whether you should keep your window open.

A fan can definitely cool you down – but are you using it correctly?[/caption]

The July heatwave that is currently in full swing across the UK has caused a host of problems for Brits, especially when it comes to sleep. And the worst of the extreme heat is not over yet. Next week, temperatures are expected to soar even higher, hitting 35C.

Ensuring bedroom temperatures are kept to a minimum with the use of a fan or cooling purifier can help keep your body temperature down and thus mitigate sleeping problems.

But what’s the right bedroom set-up for a fan or purifier?

According to Andrew Persily, an indoor-air quality engineer at the National Institutes of Standards and Technology in Maryland, USA, this can be achieved by simply ensuring you have air in the room blowing on your skin.

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‘The sensation of [air speed] improves thermal comfort in a cooling situation,’ Persily tells Quartz, adding that this is because when sweat evaporates into the air, it takes heat with it and makes us feel cooler.

This works because, even if we’re not noticeably sweating, our bodies are constantly generating small amounts of moisture to cool down, Persily says. Therefore, air moving over our bodies, be it from a fan or wind from a window, speeds up that evaporation process, making us feel cooler.

Should I leave my window open?

One sure-fire easy way of cooling down a room and increasing ventilation is by opening a window.

This can be helpful if there’s a breeze outside that’s blowing in. However, since during hotter months the air is actually warmer outside, it may be that opening a window is only letting out the cooler air in your room and allowing warmer air to come inside.

In this instance, it’s better to position your fan so it’s blowing on you, but with the window shut.

Opening windows can mean poor air quality from the outdoors comes inside, especially if you live near a high-traffic area.

So when it comes to cooling purifiers, use the device in a sealed environment as they will work more efficiently there.

Where to place your fan in a room

Fans and purifiers tend to be engineered to work in single rooms, so when placing the machine, make sure there are at least a few feet of clearance on all sides so that the air can circulate effectively.

If the air outside is cooler than the inside, Persily says you should place your fan by your window with it facing the interior. This way, the cooler air from outside will be blown towards your body, helping the sweat to evaporate even faster.

During the current heatwave, however, it’s probably best to keep your windows closed and direct the fan towards your body while you sleep so the movement of air over your skin can more effectively speed up the sweat evaporation process.

Close your curtains and blinds during the day

There are many other hacks you can take advantage of to stay cool this summer, one is especially useful for preventing your room from getting warm in the first place.

Dyson’s head of environmental Care, Evan Stevens, recommends closing your curtains and shutters during the day to ensure sunlight doesn’t cause a greenhouse effect

‘Up to 30% of unwanted heat gain comes from windows,’ he said. ‘So keep the windows, curtains or shutters closed during the day to minimise the amount of sunlight entering the home.’

Night-time is when summer temperatures tend to dip, so make a habit of opening windows at night to allow cooler air to enter, he adds.

‘Then be sure to close them in the morning before temperatures rise and open them again in the evening as the temperatures gradually drop.’

Reduce heat sources at home

Electronic devices can also generate excess heat, contributing to the ambient temperature of the room.

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‘Traditional lightbulbs for example use up to 90% of their energy generating heat, with only 10% being converted to visible light,’ says Stevens.

Therefore, he says it’s best to opt for energy-efficient lights and get into the habit of turning off and unplugging all electronic devices that are not being used.