Monday, 6 July 2015

Keeping cool

It has been a hot week in the UK (at least by our standards) and for most of Europe it seems. I have been out doing energy surveys every day, and despite sweltering and having aching feet from all the walking, I love to see how buildings perform under peak conditions.

The UK has a relatively mild climate. Being surrounded by sea and benefiting from the warm Gulf Stream, means that our winters and summers are not as extreme as for mainland Europe. This is reflected in the design of our buildings. For instance French buildings traditionally have shutters. These aren't purely decorative, but have a functional purpose, to prevent solar gain. When the sun shines in through the window, it heats the building up like a greenhouse. The shutters on the outside of the house are more effective than blinds, because they stop the sun's rays before they get inside.

Typical French shuttered windows
Closing the shutters at night and then waking up to throw them open to the daylight is one of the delicious moments of staying in a French house. If you have tried this you will notice that just opening the shutters a slit will still bathe the room in daylight, and often keep most of the hot sun out. The strategy is to use the shutters in the daytime to prevent the suns ray from heating up the house. In addition the shutters can often be closed at night, but with the glass windows inside left open, so that the cooler night air can cool the building down and help to slow down the process of warming during the day.

Traditionally English townhouses were close together, providing a shady walkway
British buildings don't have shutters as a feature, because we don't get a lot of hot days and love it when we do. But it is not pleasant to work or live in a hot building, so here are some strategies that may help to keep buildings cooler and more comfortable.
Aptly named 'Thrift House' with the curtains drawn
1. Shut your blinds and curtains during the day to keep out the suns rays. This is especially important for South and West facing windows. If you are worried what your neighbours may think of your curtains being closed all day, then try using net curtains, as they are effective at blocking the sun too. By standing in front of a sunny window with the sun's rays on you, you can feel the difference when the curtains are shut. It won't stop the house warming up, but at least it will be less of a greenhouse. Canopies, overhanging roofs or trees can all be used externally to shade the building in summer too.

Glass greenhouses in central London ;-)
2. Keep windows closed if the air inside your home feels cooler than the air outside. It is an automatic reflex when you feel hot to open the windows, but if it is the hottest part of the day you could just be bringing in hot air from outside and making things more uncomfortable. Stand in the doorway and check first, because then you can feel whether the air outside is actually cooler or not.

3. Open your windows at night (if you can without inviting burglars) or early in the morning for an hour or two, to help flush out the warm air and allow the building fabric to cool down again. The bricks, concrete, tiles, fixtures and fittings all retain heat. so often you will find that when the air outside has cooled, the building still feels warm on the inside. You can use the cooler morning air to purge the heat, so that you start the day with a cool building. I throw open the windows at 6:30am, before everyone else is up, and once the stone tiles on my kitchen floor feel cold again, I shut my windows against the rising temperature outside. This helps the house to stay cooler for longer.

The majority of dwellings in the UK are constructed with brick, stone or concrete and these materials are all good for holding heat or coolth. Lightweight timber constructions tend to heat up a lot quicker and cool down faster too, so you may find that point 3 doesn't help much. You can try incorporating some more heavyweight materials in a lightweight house, by adding stone tiles to floors.

4. Every appliance that is switched on, from a light to a mobile phone charger, will be kicking out waste heat, into your lovely cool building, so make sure that everything possible is switched off. Fridges and freezers may be keeping the food cool, but in doing so they kick out a lot of heat from the coils at the back, which is adding to the heat in your house. The higher the air temperature the harder they have to work and the more heat is emitted, so try not to open them unnecessarily. You could also try using timers to run dishwashers or breadmakers in the early hours of the morning when it is cooler (unless you have PV panels and want to make use of the solar energy).

Landline phone that only works when it is plugged in
Incidentally, you are also kicking out waste heat energy that is created when you breath or move. Only an average 100W if you are resting but that increases to 250W if you are dancing around. Save the workout or physical housework for the mornings or late evening, when the temperature has dropped, to avoid overheating yourself and your house.

5. If you get to the point where it is too hot inside and you need to get a breeze going to help cool you down, then remember to get a crossflow of air. This means trying to open windows or rooflights on at least 2 faces of the building, with an open flow between them. Heat tends to rise, so it will gather at high points. Opening a rooflight or upstairs window will allow the hottest air to escape, whilst opening a window on a lower level will draw in cooler air to replace it. I have seen lots of hot offices this week where the office windows are open, but the office door is kept shut for privacy. This means that the air cannot flow across the building, so the occupants don't benefit from getting a breeze from their windows.

6. Putting a fan near your window can help to draw in fresh air from outside, but if the air outside is hot already then it makes more sense to aim the fan at you. A fan blows air across your body, encouraging the heat to transfer from your hot skin to the marginally cooler air. Hence it makes you feel cooler.

Trees for company
7. Have you ever noticed that the air around trees feels cooler? This is because they act like an evaporative cooler. Their roots suck moisture from the soil and when the sun shines on the leaves the water evaporates. This process uses heat energy from the surrounding air and works faster on a hotter day, leaving cooler air around the trees. Planting trees and shrubs near windows and in courtyards can help to keep the air around the building cooler (as well as providing some shading). A fountain works in a similar manner and was why they were popular in Roman courtyards.

Stone house surrounded by trees for shade and cooling
8. Insulation in lofts and walls helps to protect buildings from the heat, as they are another layer that the heat needs to pass through. Insulation helps to make the building feel more comfortable in the summer and winter, with the added benefit of leading to reduced energy bills.

9. Hot air rises, so if you are having trouble sleeping in your bedroom upstairs, then camp out on the ground floor or even in the basement if you have one. This will help you stay cool and get a good nights rest.

10. I heard on the radio today (for the first time) an advertisement for air-conditioning for homes and it made me groan. Air-conditioning is expensive and uses a lot of electricity to provide you with artificial cooling, so please try some of the cheap and easy methods to stay cool first. If you are a 'battery-farmed' office worker, in a large open plan office with only a couple of square metres of space, then the chances are that you will have cooling provided, and on a hot day it will be working flat out. If you can, take this opportunity to request to work from home. The less bodies in the office and computers in use, the less heat is being produced. This will save energy, reduce the load on the air-conditioning and help everyone to stay cooler.

Remember to always switch air-conditioning off in an empty room and to keep windows shut whilst it is in use, otherwise your expensive chilled air will be escaping. How many of you have walked past an open shop door and felt the rush of cooled air coming from within?

You may already do all of these things, but hopefully someone may find the odd tip helpful. Hope you have a lovely sunny summer where you are, with a nice cool house to retreat into when it gets too hot :-)


  1. Such practical advice- thanks for all these tips!!

    1. We probably won't need it now - looks like I have scared the sunshine away ;-)

  2. I love that you are doing a post on how to keep cool, while mine is all about how to stay warm. Hope your garden is happy in the heat:)

    1. Well just know that it is short-lived and summer will soon come. Summer is such a busy time, watering, harvesting and cooking, I am thinking that being wrapped in a blanket on the sofa seems like a pretty good option right now.

  3. Hi Judy, just wanted to check that everything is ok with you as you haven't written your blog in a while?..

    1. Thanks and sorry for the long silence. Just had a rather large project which has kept me working late nights trying to complete it. Things are back to normal now, but I am busy catching up with everyone else's blogs to see what I missed :-)

    2. Lol, as long as you are well then that's ok. Life comes before writing blogs, so take care and take time to catch up with yourself