Snoozing in the heat

This morning Janet Barlow was the Mystery Guest on Radio 2’s Chris Evans Breakfast Show. Listen to Janet from 2:10:00 (if available in your country). The show had previously asked the question of its listeners “how do you get to sleep in this heat?”. Today’s show was dedicated to everyone that has been using the show’s sleep tips to snooze in the heat. Chris wanted to hear a bit more about the physics behind the many ways for us to keep ourselves, our buildings and cities cool in a heat wave. We provide three ‘physics tips’ to help you create a comfortable indoor environment during the summer heat.

Physics tip number one is to block out the sun! Heat energy from the sun streams in through the windows of buildings (known as ‘solar gain’), so shading the windows, or simply closing blinds and curtains during the day will help a lot. Incoming heat through walls and roofs is more difficult to eliminate. In warmer climates, buildings are usually painted light colours to help reflect away the incoming solar energy. One of the ways we can cool down our cities in the UK is to adopt this principle for our rooftops. Another strategy is to rely on vegetation; putting green roofs and walls on buildings is more complicated to do, but uses up the sun’s heat through evaporation of the moisture in the plants.

Physics tip number two
is ventilate, ventilate, ventilate! We all know that installing an air conditioning unit is an easy way to exchange hot, humid air inside the building for cool, dry air – but it takes a lot of electricity, and dumps the heat outside the building, making the neighbourhood just that bit hotter. Natural ventilation is a way of harnessing physical processes to get a cooling flow of air through a building without using electricity. Hot air rises and cool air sinks: so create a pathway across the house that allows air to move. Opening the windows at the front of the house AND those at the back (and any doors in the way!) allows “cross-ventilation”. Opening windows or loft hatches at the top of the house, and windows on the lower floor, lets warm air escape out the top and “suck” cooler air in the bottom: and at night-time cool air can “sink” down through the house, purging out the warm air. This is called the “stack effect”.

Natural ventilation Image
Image credit: Wikolia Maile at

Physics tip number three is sleep downstairs! Hot air rises, so if you can, decamp to the living room during a heatwave – keeping the windows open upstairs and downstairs if you can to let a ventilating flow of cooler air in to replace escaping hot air.

A new research project called Refresh is looking into how to design buildings that we work in so that we can keep our cool and think straight through future heatwaves. Sometimes we need to adapt the buildings, and sometimes it’s how we use them that counts. We will be researching the physics of ventilating flows, the engineering of sustainable buildings, and how we can use smart phones and computers to feedback our own physical performance to the building control systems – putting humans back at the centre of building design.

More advice can be found on the Met Office website.

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