When summer temperatures overshoot the 30-degree mark, we'd prefer to keep it cool within our own four walls. But especially in big cities – thanks to the dense built environment – many buildings retain heat even during the night. While air conditioning systems or compact air conditioners provide a short-term solution, their high energy consumption sends electricity costs rocketing. Christian Stolte, expert on energy-efficient buildings at the Deutsche Energie-Agentur (dena) – the German Energy Agency –, has some tips for tenants and home owners on how to keep a cool head, even without an air conditioning system . His basic recommendation is: 'The most important thing is not to let the heat enter in the first place.'
Roller blinds, awnings or Venetian blinds keep heat out
Once a ray of sunlight has penetrated a pane of glass, heat gets in along with it. Drawing the curtains therefore offers only minimum protection. 'Shade-providing devices fitted on the outside are considerably more effective. Roller blinds, awnings or Venetian blinds can reduce solar radiation through windows, balcony doors and terrace doors by up to 90 per cent,' explains Stolte.
Good insulation also protects against heat
Whatever keeps interiors comfortably warm in winter conversely protects against too much heat in summer. 'The indoor ambience in a house with good heat insulation is more pleasant than in buildings with poor insulation, or none at all,' says Stolte. External layers of insulation prevent external walls from absorbing too much heat. So the building's insulation also ensures better protection of the building against heat in summer.
Keep doors and windows closed during the day
For this reason, doors and windows should be kept closed as far as possible on hot days. Once the heat has entered the interior of a building, the room temperature can only be lowered again with difficulty. 'Instead, you should let in plenty of air during the cold morning hours or at night,' says Stolte.
Turn off electrical appliances and other sources of heat
Many electrical devices produce heat when they're in operation. Lights, plasma screens or computers should only be switched on when they're actually needed. The less excess heat is produced inside a house, the better it stays cool.
Additional protection against the sun indoors
If it's not possible to install external protection against the sun – for example, in rented apartments – glare protection on the inner side of the window can provide an alternative. In this case, sun-protective roller blinds that admit little light, or curtains with good blackout properties, are the best solution. Even bright, reflective roller blinds reduce sun irradiation by up to one-third.
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