With a special temperature-sensitive camera mounted under COWI’s Cessna plane, pilots flew over a sample area of Århus in Jutland and took 1,800 photos in order to map the municipality’s energy emissions.
Known as thermography, this technique shows the heat loss from buildings into the environment, providing information which makes it possible to determine whether the greatest heat loss into the surroundings is from the windows, walls or roof.
Heat loss from facadesThe Århus project shows that the greatest heat loss is from facades, particularly through windows and doors.
"Aerial surveys offer an excellent means of identifying major heat loss in the building stock as a whole. In this instance, for example, the survey showed significant heat loss from the city centre and that the roofs in Gellerup Parken housing development are well insulated," says COWI project manager Rasmus Lindeneg Johansen.
Thermography Thermography can be described as aerial infrared photography. An image of the temperature of the external surfaces of a house is shown on a screen. Where the surface is coldest the image is blue or green, while the hottest spots are shown on red or yellow. A hot surface indicates that there is a leak, a thermal bridge, where the cold penetrates the structure of the house or a spot which is poorly insulated.
"This is not new technology, but the idea of using it in a plane is new. This allows us to cover a whole city such as Århus in the space of three to four hours. The municipalities can use this snapshot of energy emissions in their climate strategy," elaborates Lindeneg Johansen.
Winter flights Aerial thermography must be conducted when there is a difference of at least 20 degrees between the indoor and outdoor temperature, because any heat loss from buildings then shows up more clearly. It is therefore best to make these flights from late autumn to early spring. The sky must also be cloudless, otherwise the camera cannot pick up the buildings.
Aerial thermography can also be used to identify discharges of wastewater into waterways, leaks in district heating pipelines on the basis of temperature differences, and points of poor insulation in overhead railway cables.
Christina Tækker, cht@cowi.com Published: 02.06.2009