Single ventilation Flow for habitat

Single flow ventilation

The principle of single-flow ventilation is to ventilate the home by sweeping with:

• Fresh outside air inlets in the living rooms (living room, bedrooms, office, games room, etc.). These air inlets are generally installed on exterior joinery, but they can also be located at the level of the roller shutter boxes or in the wall facing the outside.
• Air extraction vents in service rooms or shower rooms (kitchen, bathroom, WC, laundry room, etc.).
  These extraction vents are connected to the ventilation box equipped with a fan which must be able to operate continuously. The extraction vents are usually self-adjusting to extract a fixed air flow depending on the room. or hygro-adjustable with operating conditions defined by a technical notice published by the CSTB.

Single-flow ventilation has a major advantage over double-flow ventilation: its investment cost.

There is less technology in a single-flow box: a fan that consumes more or less electricity and a plastic shell. The ducts are traditionally in flexible network because the ventilation is placed in lost attics. This is only the discharge of outside air without danger of deterioration of the fresh incoming air.

However, single-flow ventilation which ensures the protection of the building and the renewal of air in the home brings cold air into the living rooms and rejects hot air outside. To mitigate energy loss, air renewal rates are reduced. For homes that are increasingly airtight and where window opening habits are lost, indoor air quality can very quickly deteriorate.

In general, whatever the choice of means of ventilation for the building, the user must be made aware of this means of ventilation in order to adapt and maintain acceptable indoor air quality.

Self-adjusting or hygro-adjustable single-flow ventilation?

Self-adjusting single-flow ventilation allows rooms to be ventilated with a fixed flow rate both at the extraction vents and at the air inlets. The only flow variation is in the kitchen with the possibility of having a boost mode. Energy losses are relatively high, but indoor air renewal is theoretically correct.

Hygro-adjustable single-flow ventilation is gradually replacing the self-adjusting model. The extraction and insufflation vents open or close depending on the humidity in the room. This system makes it possible to significantly reduce the air renewal rate when the humidity level is low and therefore saves energy. The humidity of the home is supposed to represent the occupancy rate, the more people and human activity there are, the more humidity there is. In addition, it is the excessively high humidity level which is most quickly visible in terms of deterioration of the building. However, in reality, there are other pollutants (volatile organic compounds - VOCs) which are present even if there is little humidity and the operation of the humidity-controlled vents is not necessarily reactive. The air renewal rate of the ventilation system is then not always sufficient in a house made very airtight. There are 2 types of humidity-controlled ventilation:

• Hygro A single-flow ventilation: the air inlets are fixed and self-adjusting, the vents are hygro-adjustable.
• Hygro B single-flow ventilation: the air inlets and extraction vents are hygro-adjustable.

In new buildings, single-flow hygro B ventilation will most often be prescribed to meet the level of RT2012. In this case, you will have to open the windows a lot more, especially if your indoor activities and equipment turn out to be polluting. Find out!

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Single flow hygro A or hygro B ventilation?

The hygro A or hygro B single-flow ventilation systems are both humidity-controlled single-flow ventilation systems.

Hygro A single-flow ventilation is made up of self-adjusting air inlets with a fixed flow rate in the living rooms (living room, bedroom, office, etc.) and this system is to be preferred in both new builds and renovations. Indeed, with this system you ensure a sufficient supply of fresh air in all circumstances, which is not necessarily the case for hygro B ventilation.

Hygro B single-flow ventilation is the ventilation system that most limits the entry of fresh air into the house and promotes energy savings. It is often prescribed in the RT2012 thermal study because it gives the best results and favors less insulation.

This advantage has a downside in terms of indoor air quality. Indeed, if humidity is the most visible indoor “pollutant” (condensation, mold stains, etc.), it is not the only one. It is undoubtedly better for a living room such as the bedroom or living room to be sufficiently open to the entry of fresh air.

What precautions should be taken when installing a single-flow VMC?

The installation of a single-flow VMC must meet certain rules to ensure normal long-term operation:

• Respect the positioning of vents and air inlets set by regulations,
• Use insulated ducts in cold spaces to avoid condensation,
• Use rigid or semi-rigid ducts (flexible network prohibited) in technical spaces (false ceiling, partitions, technical ducts),
• Pay attention to very good sealing of the networks,
• Finally, the most important thing, carry out a commissioning to check the proper functioning of the installation (operation of the kitchen boost, extraction and non-inflation on all vents, respect of the air flow in each room via a pressure gauge).