Should you leave a window OPEN with the fan on hot days? Experts reveal the science of cooling
THERE'S no doubt you've been using the fan and keeping windows open the past week as Brits feel the heat.
Ensuring your bedroom temperature is kept down using a fan or cooling purifier can help you feel more comfortable at night.
But air quality experts have warned your set-up could be making things worse.
According to Andrew Persily, an indoor-air quality engineer at the in Maryland, USA, this can be achieved by simply ensuring you have air in the room blowing on your skin.
‘The sensation of [air speed] improves thermal comfort in a cooling situation,’ Persily explained to .
This is because when sweat evaporates into the air, it takes heat with it and makes us feel cooler.
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So even if you're not noticeably sweating, your body is constantly generating small amounts of moisture to cool down, Persily says.
Therefore, air moving over our bodies, whether it's coming from a fan or wind from a window, speeds up that evaporation process, making us feel cooler.
Should I leave my window open?
Your first thought to cool a room down is probably to open a window.
This is usually helpful if there’s a breeze outside that’s blowing in.
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But the problem during hotter months is that the air is warmer outside.
So, opening a window is only letting out the cooler air in your room and allowing warmer air to come inside.
Therefore it’s better to position your fan so it’s blowing on you, but keep the window shut.
On top of this, if you live somewhere near lots of traffic opening windows can mean poor air quality from the outdoors comes inside too.
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.
When choosing where to place your 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.
However, during a heatwave 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 loads of other hacks you can do to keep your home cool too.
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 per cent 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," he added.
Reduce heat sources at home
Electronic devices can also generate excess heat, contributing to the ambient temperature of the room.
"Traditional lightbulbs for example use up to 90 per cent of their energy generating heat, with only 10 per cent being converted to visible light," Stevens continued.
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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.
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