How to compose an efficient dual-flow ventilation network?
A dual-flow CMV installation is composed of:
- A ventilation box generally including, the heat exchanger, the exhaust and insufflation fans, the VMC regulation
- A ventilation network broken down into 2 parts: the primary network and the secondary network.
1) The primary network
The primary network connects the dual flow ventilation box
- to distribution boxes as part of a secondary octopus distribution network.
In individual housing, there are 3 main primary network section sizes:
- DN125 recommended for a maximum flow rate of 170 m3/h/h
- DN160 recommended for a maximum flow rate of 280 m3/h
- DN180 recommended for a maximum flow rate of 360 m3/h
The larger the duct has a large cross-section, the better the acoustic performance and the less electricity the machine will consume.
Our advice: choose first the machine adapted to the air renewal rate necessary for the house.
Depending on its power, the VMC will have air outlets in DN125, DN160 or DN180, it is then enough to carry out the installation with the same network diameter as the machine without reducing or increasing the network diameter.
Primary networks are preferably rigid and calorifuge.
A rigid network is more efficient at the aeraulic level and more durable than a flexible network, it increases the performance and durability of the installation.
The calorifuge avoids internal condensation or outside the network and the resulting inconveniences.
The primary network can be:
- En Insulated Galva. This is the most economical solution. But the insulation is tedious to set up. Care should be taken to use gasket connection accessories for network sealing.
- En eMP or expanded EPE. This is the most common solution on high-performance dual-stream CMV installations. These ducts are quick and easy to install. They are sold as a bar 1 to 2m long, with 45 or 90° elbows, sleeves and fixing collars.
On the exterior side, the primary ventilation network is connected to either a terminal façade. It is ideally equipped with a rain visor and an anti-harmful grid for air intake and rejection.
External air rejection can also be done on the roof using a roof terminal.
For the primary ventilation network connecting the VMC to the distribution boxes, it is advisable to install a silencieux on insufflation and extraction.
The silencer will attenuate the vibrations emitted by the fan blades. It is installed as straight as possible for better efficiency, vertically or horizontally.
2) The secondary network
- An octopus distribution:
Hy suction or insufflation mouth is connected by a duct (simple, double or triple depending on the desired flow rate) to a distribution box itself connected to the machine.
The octopus distribution network is more advantageous of the linear distribution network because it does not transmit noise by telephone and makes it easier to balance the flow on each mouth.
The octopus distribution network connecting the box to the insufflation vents
- Distribution boxes are the starting point for a secondary octopus network. Each installation has a box dedicated to insufflation and a box dedicated to extraction.
These boxes can be either galvanized or powder coated steel, or increasingly now in HDPE.
The inner shape of the box, its size is important to have the least pressure drop and the best possible acoustic comfort.
The caissons HDPE more easily incorporate highly aerodynamic interior shapes while it is better to choose metal boxes with a foam coating. The new generations of HDPE distribution boxes allow multi-configuration installations for which it is possible to mix round and/or flat network and/or diameter 75 mm and/or 90 mm.
This type of box adapts more easily to the constraints of passage of the networks of its housing.
In gray the insufflation and extraction boxes
- Rigid semi-rigid HDPE sheaths.
The semi-rigid HDPE sheath is food grade (PVC sheaths that can release chemical compounds should be avoided) with an optional anti-static antibacterial treatment to reduce cleaning operations.
Semiline sheaths are both strong (they do not crash) and easy to install (usually a continuous length is enough to connect the distribution box to the mouth). Depending on the installation constraints, it is possible to use flat or round semi-rigid ducts. Most manufacturers offer 2 duct diameters (75 mm or 90 mm outer).
The 90 mm diameter network is more efficient since at the same desired flow rate, the air speed will be lower. This will result in less pressure drop and aeraulic noise.
- Connection tee or mouth tee
A HDPE dual-flow ventilation system is connected to the blower or extraction vents by a connecting tee or round mouth tee of diameter DN125 or rectangular of equivalent size.
It is preferable to use vents of this size rather than smaller vents (usually DN80) for acoustic comfort. The connection of the muzzle tee to the HDPE sheath can be done at 90° or from the back.
- Seals and fixing clips:
The seals ensure sealing and the clips allow a solid fastening that is easy to install and undo if necessary.
The attachment by clips and seals of the accessories of the HDPE ventilation network is faster, more efficient (better sealing of the network) and more durable than the usual use of aluminum tape and serflex collar on flexible networks.
- Dual flow vents:
They can be auto adjustable, hygroadjustable, adjustable or fixed.
Given the performance of new generation dual-flow CMVs and the hygro-variable mouth renewal rate based solely on humidity and not on other typical pollutants VOC or CO2, we do not offer hygro-variable vents. Self-adjusting vents make it possible to strictly comply with the regulations on air flows extracted in toilets, bathrooms or kitchens.
These vents are unsightly and can be noisy, which is why they are often replaced by adjustable mouths, which are prettier and which make it possible to adjust the flow rates room by room more finely during commissioning.
Toils or grids with flow fixed are not adjustable and are more easily used with boxes on which it is possible to install flow reducing rings.