Ventilation and air quality: also being renovated!

The challenge of ventilation is to reconcile indoor air quality with penalising energy perfor-mance. Yet, it is often the great forgotten work in renovation! A restoration project should ide-ally 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 the occupants’ health, with the development of allergies and respiratory problems. It can also have an impact on the building, with increased condensation and prolifer-ation of mould. Energy overconsumption is also linked to humidity and the renewal of air by opening the windows.

Renovation works often aim to limit losses with a reinforced thermal insulation. In doing so, the air tightness is generally improved. Frequently, replacement of old glazing by insulating double glazing with thermal and acoustic performance is carried out. 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 not always taken into account by carpenters who do not necessarily know the principles of ventilation. In the oldest dwellings, 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, uncontrolled infiltrations and by all the small sealing defects of the house frame. Indoor air quality may be affected.

The importance of diagnosis

Renovation works are an opportunity to implement a ventilation system in accordance with the regulations, ensuring contin-uous ventilation in all rooms. If this aspect is neglected, further constraints can be added and 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 the doors which ensured the circulation of the living space where the new air enters the technical rooms where the exhaust air is extracted. Other defects can result in significant pressure drops, such as existing air ducts that are drilled, disconnected, not sufficiently tightened ... Consequences: the extraction flows may be insufficient. Ventilation will not be effective enough. The diagnosis of the existing ventilation system is there-fore the first step.

Single and double-flow CMV (Controlled Mechanical Ventilation)

If the house already has mechanical ventilation, its optimization can be achieved by replacing it, preferably by a hygromet-ric system, for better energy efficiency: the air flow is thus modulated according to the outdoor and indoor humidity rate. If the house is not equipped, it is possible to opt for a controlled mechanical ventilation system, single or double flow. In the case of single flow, the supply of fresh air is effected by openings in the main rooms (living room, bedrooms). The air passes through the corridors, the mechanical extraction of the stale air being done in the service rooms (kitchen, WC, bathroom). The air extraction to the outside is ensured by an extraction vent.

Dual-flow systems extract stale air in the same way as a single-flow system but also control incoming air through a network of ducts and insufflations in the rooms which are lived in from taking controlled fresh air, generally located on the roof. Most often, they incorporate a heat exchanger that allows the energy of the exhaust air to be recovered and transferred to the incoming air, thus limiting the energy consumption of heating or even cooling. They allow to modulate the flows according to the real needs, with an energy gain of up to 35% compared to the single flow. ADEME (*) estimates that a dual-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 *.

DDV for continuous ventilation

However, a large number of units to be renovated are not readily amenable to the development of a CMV system. In an existing single-family house, it is indeed difficult to install an extraction box with its network of ducts connecting it to the exhaust ducts of the humid rooms and a fortiori to living rooms (in the case of double flow). 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 incor-porates a fan that depresses 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 (relief) or by means of transfer grates. In order to be considered as ensuring the 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.