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Indoor air pollution: the invisible enemy

Researchers are developing low-cost technologies to tackle indoor air pollution that is a growing menace. A new generation of electrostatic filters can capture even the smallest particles of household pollutants, using a little amount of energy

Indoor exposure to air pollutants has become a major problem in general, but especially in new low energy consumption houses that are very well insulated. This is because they trap contaminants that are released, for example, when you burn fuel to cook your food or heat your home.

Contrary to popular belief, indoor air maybe more polluted than outdoor air. Furniture and construction materials can also emit toxic substances, as the traditional building industry has increasingly used synthetic and chemical products that can be hazardous to human health.

Dampness and lack of ventilation may further increase indoor air pollution, which can cause noncommunicable diseases including stroke, ischaemic heart disease, chronic obstructive pulmonary disease and lung cancer, according to the World Health Organisation. Researchers are therefore testing new technologies and in particular new generation ventilation units to address the problem and achieve better energy efficiency in air renewal.

Mario Smaniotto is a systems engineer at Clivet, a company that is collaborating with the EU project BuildHeat, aimed at developing innovative solutions for energy efficient retrofit of residential buildings. They are testing a heat pump and ventilation device called "ELFOPack".

It contains, among other technologies, an electrostatic filter which is active both in the indoor and in the inlet air, and it is able to capture most of the common pollutants. What is new is that this technology, generally limited to industrial applications due to its high cost, has been adapted to the residential sector.

How does this filter work? Can you describe this new technology?

The filtration with the active electrostatic system allows us to locate, separate and eliminate solid or liquid particles of pollutants contained in the air flow, through the action of an electric field. The electrostatic air purifier charges or ionises air particles. In this case it generates positive ions. The machine then draws those charged particles into the collection plates that are negatively charged. Because of the opposite polarity, the ionized particles can easily stick to the collection plates of this electrostatic air cleaner. Therefore the pollutants are captured.

What is new and what are the advantages compared to traditional filters?

There are essentially two major advantages of the electrostatic filter: the first is the small size of the particles it can capture, even less than one micron in size. One micron corresponds to one millionth of a metre, or one thousandth of a millimetre. Typical pollutants smaller than one micron are: cigarette smoke, oil vapours, pollen, bacteria and germs, viruses and nanoparticles, etc. The electrostatic filter efficiency is measured and tested against particles measuring around 0.4 microns in diameter.

The second advantage is that in traditional filters air must physically pass through the filter, requiring a great amount of energy. And the filter itself is an obstacle to the flow. The electrostatic filtering, on the other hand, does not obstruct it, enabling very low pressure, and therefore less energy consumption.

What about your contribution to the BuildHeat project?

This air filtering technique will be tested in some apartments in a demonstration building in Zaragoza, Spain. In particular we will install 53 ELFOPack units able to meet the energy and comfort needs of the new low energy consumption houses (heating, cooling, domestic hot water, dehumidification, air renewal and filtering). Besides the advantage of the electrostatic filtering, the technology can reach the highest efficiency standards, thanks to the heat pump permitting thermal recovery and air recirculation.

Furthermore, the units integrate a solar inverter, which converts the variable direct current output of a photovoltaic solar panel into alternating current, which is good for domestic use. The device is designed to optimise the exploitation of the available solar energy. When too much solar energy is produced, compared to unit consumption, it will be automatically redirected towards domestic hot water production. This will mean increased comfort for end users, more rational use of renewable energy and low CO2 emissions.

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