Controlled mechanical ventilation… what air do you suck in?

By now it should be a fairly known system that of Controlled Mechanical Ventilation. In an era in which new houses are being built with the "coat", windows with triple glazing, super insulated roof and increasingly sophisticated and increasingly performing heating and cooling systems ... it is no longer convenient to open the windows to ensure sufficient air exchange in inhabited rooms (see previous article).

This task is entrusted to the VMC system, which 24 hours a day extracts the stale and polluted air from inside our home and replaces it with fresh and clean air taken from outside.

The companies that market this type of system leverage on some topics that are easily understood by everyone. The air inside our homes can be very stale and can contain many pollutants! In fact it is exactly like this: the air we breathe during the day is always richer in carbon dioxide (deriving from our own breath), formaldehyde (furniture and parquet), radon (possible rising from the ground under the foundations), of harmful chemical compounds (think of all the products we use for cleaning the house). Not to mention the pollutants released in the office by laser printers: we worry about wearing gloves to replace the toner cartridge, but we don't think about how much of that highly carcinogenic dust we breathe in the air!

The Controlled Mechanical Ventilation system seems to be the solution to all our problems! It continuously extracts bad air from our home and replaces it with new and clean air, without having to resort to prolonged opening of the windows that would put our air conditioning system in crisis.

But is it really so? Are we sure that the air taken from outside the house is less polluted than the inside?

Well ... in most cases it should be. However, if you decide to build a VMC system in your home, know that in addition to the various types of filters for outdoor air (the absolute best is the electrostatic filter, which retains the finest dust and particles of any type), above all there are some precautions to be taken for the correct positioning of the nozzle from which to take outside air. It would seem obvious but ... many designers and installers very often forget these precautions!

Not only that ... even the manufacturers of these systems use advertising images where often the clean air intake is incredibly placed in at least questionable positions!

Dispassionate advices!

What then are these precautions? They are very simple, although I assure you that they are systematically ignored:

1. The suction and extraction vents must be positioned at least 1 meter apart, to avoid interference between the two air flows.
2. The suction vent must not be positioned too close to the ground, preferably at a height of at least 2.5 meters, to prevent the entry of dust, odors and radon.
3. It must be positioned away from other outlets belonging to other systems (cooking fumes intake, boiler or water heater exhaust, etc ...).
4. Away from particularly polluted areas, such as the street front (especially if it is a busy road!), a parking lot or a parking or maneuvering area for vehicles, to avoid the entry of fine dust and combustion gases from the engines.
5. If positioned above the pitch of the roof, it is preferable to use the pitch opposite to that intended for extraction, to prevent the wind from creating easy short circuits.

The best solution ever?

The best solution is to place the suction vent on the facade of our house facing the garden (not towards the street!), at a height of at least 2,5 meters from the ground.

And in this case my advice is to use the garden as a real "filter" for the air that must be treated by our VMC system. What does it mean? It means using the so-called anti-pollution garden plants, capable of purifying the air, retaining dust and eliminating chemical compounds.

Here is a list of garden plants useful for this purpose:

• Bagolaro (Celtis australis): wins the general classification, because it is able to retain the greatest amount of fine dust with its hairy leaves.
• Wild lime (Tilia cordata), Hawthorn (Crataegus monogyna), Curly maple (Acer platanoides), Warty birch (Betula pendula) and Ash (Fraxinus ornus): essences capable of assimilating the greatest amount of carbon dioxide.
• Holly (Ilex aquifolium), Viburnum (Viburnum L.), Strawberry tree (Arbutus unedo), Fotinia (Photinia serrulata), Laurel (Laurus nobilis), Eleagno (Elaeagnus), Privet (Ligustrum lucidum): essences suitable for the construction of hedges and antismog barriers.
• Gerbera (Gerbera jamesonii): excellent flowering plant against benzene, trichlorethylene and formaldehyde.
• Ivy (Hedera Helix): has the primacy in the absorption of formaldehyde

In short ... transform your garden into an oasis of clean air, an excellent quality air reserve for your controlled mechanical ventilation system!

Images source: web