Refurbishing old buildings to make them energy efficient often leaves them so tightly sealed that indoor air quality suffers, with possible damaging consequences for human health and productivity.
The European Union (EU)-funded CETIEB research project is working to solve this problem by devising innovative ways of both monitoring and controlling the indoor environment in the most cost-effective ways possible, so that Europe can achieve the ‘best of both worlds’ – highly energy efficient buildings together with optimal indoor air quality and climate.
It is estimated that, in Europe, people spend more than 90% of their time indoors, and that in more than 40% of these enclosed spaces people suffer from health - or comfort-related complaints. As far back as 1984, the World Health Organisation (WHO) reported an ‘increased frequency in buildings with indoor climate problems’. This phenomenon later became sufficiently widespread to be given its own name: ‘sick building syndrome’. So the problem is not new. But it is being given new impetus by the increased focus on energy efficiency.
One solution being developed by the CETIEB team is a plant-based ‘biofilter’ to clean indoor air. This consists of a ‘living wall’ of plants, with an air fan and a water-pump being used to draw air from the room and pump it up through the roots of the plant. While the wall of plants acts at one level as a simple decorative feature, the roots cleanse the air of volatile organic compounds (VOCs), a class of chemicals which can be damaging to human health, especially in enclosed environments. The clean air is then passed back into the room.
The research team is also pioneering the use of special purifying molecules built directly into walls or other surfaces. This technique involves mixing titanium dioxide (TiO2), or titania, into a thin surface layer of plaster. Titania is a photocatalyst which, when activated by light, automatically oxidises and removes pollutants and pathogenic micro-organisms from the air.
A further novel technique being developed by the CETIEB team uses what are known as ‘phase-change’ materials (PCMs). These materials give out heat when they freeze or solidify, and absorb heat when they melt. Built into walls, they can act as a super-efficient form of insulation or heat storage. “By using a phase-change material which freezes at 18°C and melts at 25°C,” says CETIEB’s Project Coordinator, Dr Jürgen Frick of the University of Stuttgart, Germany, “we can regulate the temperature fluctuations of a room. If the temperature falls to 18°C, the PCM freezes and heats the room. When it rises to 25°, the PCM melts, energy is absorbed, and the room is cooled.”
Just as important as these indoor environment control techniques, are accurate monitoring mechanisms to detect patterns and changes in the environment. This information can be fed into ‘intelligent architecture’ systems which automatically trigger adjustments in the room’s heating, ventilation and air-conditioning. Here too the CETIEB team has been making important advances. It has developed a method of detecting VOCs using infrared light, which can identify VOCs at the level of parts per million. Even lower concentrations can be detected using metal oxides, although these are unable to specify exactly which VOC is present. The research team has also set up a ‘thermal comfort system’ which uses infrared light focused on walls and floors to monitor heat patterns and even assess how these patterns are affected by the number of people in a room at any given time.
The techniques being developed by the CETIEB team are being extensively tested at a number of demonstration sites around Europe and in Taiwan, and a patent has already been applied for in relation to the thermal comfort monitoring system. As a result of the ground-breaking work of CETIEB, Europe is taking a major step towards a new generation of highly innovative ‘intelligent’ buildings, able to regulate their own indoor environment in a cost-effective way and helping the world move closer to its energy efficiency targets.