According to the French National Agency for Food Safety, Environment and Labour (ANSES), indoor air is five to ten times more polluted than outdoor air. This is due to the presence of CO2 (an adult emits approximately 18 g of CO2 per hour while breathing) and volatile organic compounds (VOCs), such as benzene or formaldehyde, resulting mainly from materials inside the premises or cleaning products. Poor air quality thus contributes to the appearance of various pathologies or the aggravation of certain respiratory diseases. In offices, poor air quality also contributes to lower employee productivity. Increasinly regular outdoor pollution alerts, coupled with the obligation to strengthen the airtightness of buildings, means that indoor air quality is now a public health issue. Air filtration is therefore essential in this environment.
Ventilation systems make it possible to continuously provide satisfactory fresh air flows for each occupant and to extracting stale air. Air handling units combined with diffusion vents, for example, perform the following functions: air circulation, filtration, heating, cooling, heat recovery, humidification, dehumidification and air mixing (Eurovent certification programmes "Air handling units" and "Hygienic air handling units"). The dual flow ACTUs allow all possible combinations of air intake, fresh air, rejected air and treated air.
The filtration is carried out by prefilters, flat filters or bag filters. The efficiency of the filters depends on the speed with which the contaminated air is filtered. Under ideal conditions, a filter can remove 99% of the contaminants that pass through it. The blowing terminals can also be provided with filters.
Prefilters are mainly used in the first stage of air treatment. They remove larger particles such as pollen from the air. Often placed in the first stage of filtration, they also protect the more sensitive filters of the following stages. Fine filters can also be used in the first filtration stage for a thorough treatment of air in tertiary buildings. They can also be used to effectively protect the end filters. The latter provide filtration up to 0.001 μm, effective for fumes and soot, for example. As for activated carbon filters, they can stop contaminants at the molecular level and can eliminate odours and protect industrial process type facilities.
But the quality of the air has a price. Air filtration accounts for an estimated 15% of building energy costs (or 30% of the energy consumption of ventilation systems*). Effective filters generate additional energy expenditure which is proportional to the flow rate, the average pressure drop of the filter, its resistance to air flow and the operating time. Loaded with dust, a filter sees its pressure drop increase and the air handling unit will use more energy to circulate air through the filter. Increased energy consumption can be traced directly to the pressure drop.
The paradox between efficiency of filters and energy savings can be solved by adopting suitable filters. The Eurovent "Air Filters class M5-F9" programme certifies the following performances: filtration class: M5, M6, F7 - F9; initial pressure drop Δp0 in Pa; initial efficiency (only for filters F7 to F9); minimum efficiency (only for filters F7 to F9); Eurovent energy class (only for filters rated at 0.944 m3 / s); annual energy consumption (only for filters rated at 0.944 m3 / s). The Eurovent energy efficiency classification makes it easier to compare filters. It applies to all high efficiency filters that have been classified in terms of their energy efficiency (A + to E, A +) after testing according to EN 779-2012. Their classification also depends on their annual energy consumption, initial efficiency and minimum efficiency.
In addition, in application of the Eco-design Directive, three regulations concerning, in particular, air handling units entered into force on January 1, 2016. They reinforce the requirements for the eco-design of electric motors, cooling fans an electrical power between 125 W and 500 kW and ventilation units whose function is to replace the stale air of a building with fresh air. As of 1 January 2018, the last stage of this European regulation will be implemented. Among the new obligations, the equipment will need to display a signal when the filter is dirty.
*Source : Camfil.