- Master the drafts
- Choosing the right ventilation
- Use a powerful VMC
- Exploit the thermal inertia of the soil
- A Canadian well = five degrees less
To feel the coolness in a house, a difference of 5° C is enough. Natural or mechanical, good ventilation succeeds.
To isolate too much, a home is not ideal. The replacement of old joinery by watertight models eliminates the natural (and involuntary) ventilation of old buildings. If the energy savings are indisputable, the drawbacks are not lacking. The non-renewed air leads to more or less serious housing problems: residents' discomfort, carbon dioxide emissions, persistent humidity, mold, condensation...
To remedy, there are several solutions such as natural ventilation or the establishment of mechanical ventilation.
Master the drafts
Natural ventilation is based on a simple physical phenomenon: thermal draft. Hot air being lighter than cold air, it rises and in doing so "sucks" the cold air that replaces it and warms up in turn. By bringing in a cooler air than that of the dwelling (in this case in the evening), walls, ceilings and floors are cooled: they store a coolness that will be restored during the day. The house is obviously better ventilated if it opens on two facades of opposite orientations. And if the house has several levels, it creates a "chimney effect" by circulating the air between the floor and the ground floor. This is an effective way to ventilate the attic.
Choosing the right ventilation
To compensate in the winter for the loss of calories due to this aeration, these processes were improved in the years 50-60 by ventilating only the service rooms (kitchen, bathroom, toilets). Or on the same front wall (so-called horizontal ventilation). Or by organizing a permanent ventilation by vertical draft which implements ducts located in the service rooms (ground floor) and opening on the roof. Refreshed, these systems work if they are well designed.
Use a powerful VMC
An increasingly used solution is the cooling through a VMC (Controlled Mechanical Ventilation). In the simplest case, that of the "single flow VMC", the fresh air intake is directly on the outside. The process is improved by the "VMC double flow" which solves the inconvenience of the loss of calories in winter.
Compared to a standard installation, the recovery reaches about 80%. More sophisticated, the "thermodynamic VMC" combines a dual flow VMC with a thermodynamic power plant, a mini heat pump (PAC).
Depending on the season, air taken outside is preheated or cooled by PAC before being blown into the house. Hence significant heating savings and appreciable summer comfort. The investment can go from 4 000 to 10 000 € (VMC Reversible Tempering, Aldès.)
Exploit the thermal inertia of the soil
Remain a last solution more and more adopted in individual house: the Canadian well (or Provençal). This very old process involves pretreating the air used to ventilate the house by exploiting the thermal inertia of the basement: at two meters depth, the temperature is around 15° C in summer and 5° C in winter.
In the garden, a mouth of entry takes the air that leads to the interior of the house. Between the two, the air circulates in a network of pipes buried between 1.50 and 2 m (the geothermal heat exchanger). These ducts are connected to an independent fan or to that of the VMC (in this case, the air inlets above the windows are locked).
A Canadian well = five degrees less
This fresh air reduces the ambient temperature by 3 to 5° C. In winter, the system reverses and we can expect an energy saving estimated at 12%. This idyllic picture must be nuanced. The relative complexity of the installation implies an implementation compatible with a comfort requirement that excludes odors or sizing errors. Better to go through a specialized company (Aldès, Canada Clim, Helios, Rehau...) or by a thermal studies office. Outside VMC and earthworks, a Canadian well to heat / cool a house of 150 m2, then costs from 3,000 to 5,000 €.
The Provençal (or Canadian) Well These two diagrams summarize the principle of operation.
In summer, the outside air (30° C) is cooled in the underground pipe network. It reaches 24° C inside the house (minus 6° C).
In winter, outside air -10° C is warmed up and blows inside an extra 2° C.
"Awadukt Thermo" by Rehau
The air inlet of the Provençal well must be at a sufficient height (1.20 m) to avoid sucking dust and far from sources of pollution (road, compost...). The orifice must be equipped with a filtration system regularly maintained and protected with a fine grid of animals (rodents, mosquitoes...) and dead leaves.
The tubes of the geothermal heat exchanger are buried at an average depth of between 1.70 and 2 m. It depends on the "calorific value"
field, diameter (15 to 20 cm) and length (25 to 50 m) of the tubes. The calculation involves the soil temperature, the exchange surface, the air flow...