Renovation projects should involve the implementation of effective ventilation or optimization of the existing system.
Overview of constraints and systems.
The absence of ventilation in an existing habitat can have adverse effects on occupants’ health, leading to the development of allergies and respiratory problems. It can also have an impact on the building, with increased condensation and proliferation of mould. Energy overconsumption is also linked to humidity and the renewal of air by opening the windows.
Renovation projects often reduce energy losses by reinforcing thermal insulation. This generally improves air tightness. Frequently, replacement of old glazing by insulating double glazing with thermal and acoustic performance is undertaken. In the case of dwellings equipped with a regulated ventilation system, the replacement of the windows must ensure that the air intakes conforming to the ventilation system are respected (self-adjusting or hygro-adjustable, sections, etc.). This point is often ignored by carpenters who may not understand the principles of ventilation. In older building without existing mechanical ventilation, the reinforcement of the airtightness diminishes the renewal of air which had hitherto been effected by opening windows or by unseen infiltrations and by all the small sealing defects of the house frame. Indoor air quality may be affected.
Renovation projects are an opportunity to implement a ventilation system in accordance with regulations, ensuring continuous ventilation in all rooms. If this is neglected, further deteriorated indoor air quality will ensue, even if there is already a ventilation system.
For example, if the renovation involves the replacement of the flooring, the height of the flooring may be altered, thereby altering the height of the gap in the lower part of doors and adjusting air flows. Other defects can result in significant pressure drops, such as existing air ducts that are drilled, disconnected or not sufficiently tightened. This results in extraction flows that may be insufficient and ineffective ventilation. The audit of the existing ventilation system is therefore the first step.
If the house already has mechanical ventilation, optimization can be achieved by replacing the old system with a hygrometric system for better energy efficiency. This system modulares air flow according to outdoor and indoor humidity rates. If the house is not already ventilated, it is possible to opt for a controlled mechanical ventilation system, either single or double flow. In the case of single flow systems, fresh air enters by openings in the main rooms (living room, bedrooms). Mechanical extraction of the stale air takes place in the service rooms (kitchen, WC, bathroom) where air exits by an extraction vent.
Double-flow systems extract stale air in the same way as a single-flow system but control air intake and often incorporate a heat exchanger that recovers heat from stale air to warm incoming air. This energy-efficient solution modulates the flows according to real needs, with an energy gain of up to 35% compared to the single flow. ADEME (*) estimates that a double-flow CMV system can recover about 3,500 kWh per year in a well-insulated house requiring only 8,000 to 10,000 kWh per year in heating *.
However any renovation projects are not suitable for CMV systems. In an existing single-family house, it may be difficult to install an extraction box with its network of ducts. The alternative solution is to turn to a decentralised distributed ventilation (DDV) system which will provide "general and permanent" ventilation. Each service room is equipped with an extractor called a ventilator and each main room has new air inlets. The ventilator incorporates a fan that depressurises the room to be treated. It releases exhaust air to the outside, via a duct leading to the front or to the roof, or even directly through a cross wall. The flow of air from the main parts towards the service parts is achieved by the space created under the doors or by means of transfer grates. In order ensure general ventilation of the dwelling, the DDV requires at least two aerators, one in the kitchen and the other in the bath-room. There are many models of low consumption and quiet ventilators, with discrete finishes. In addition, since the mouths are removable and cleanable, the DDV is hygienic.
« Individual Housing – Attaining perfoming renovation », collection Agir !, Ademe, 2012.