7 tips for choosing your double flow VMC for your home
Want quality indoor air? Installing controlled mechanical ventilation is an effective solution for your home. It plays an essential role in properly ventilating and preventing mold and pollutants that can accumulate in your children's rooms.
Good VMC means more comfort for occupants, healthy air while benefiting from optimal thermal comfort. Positioning, exchanger, consumption, operating silence: the choice of a double flow VMC for your home will no longer hold any secrets for you.
1. Choose the air flow suitable for your home
What do the regulations say for double flow ventilation?
The decree of March 24, 1982 and October 28, 1983 is the most important concerning the calculation of the flow rate of your ventilation.
Here are the main elements:
- Ventilation is general and permanent at least during the heating period (windows generally closed)
- Air circulation from main rooms to service rooms
- Install air inlets in each main room
- Positioning of air inlets to avoid any discomfort
- Non-obstructable air inlet
- Possible maintenance of air inlets and outlets
- Case of combustion appliances in the home: sufficient ventilation to ensure operating flow rates
- Air discharge from the roof preventing any backflow towards the accommodation.
- It is prohibited to connect a kitchen hood to the VMC
- The ventilation system must extract the flow rates in accordance with the following table:
|
Number of main rooms in the dwelling |
EXTRACTED FLOWS Expressed IN M 3 /H |
||||
|
Kitchen |
Bathroom or shower shared or not with a toilet |
Other bathroom |
Laundry room |
||
|
Unique |
Multiple |
||||
|
1 2 3 4 5 and above |
75 90 105 120 135 |
15 15 30 30 30
|
15 15 15 15 15 |
15 15 15 30 30 |
15 15 15 15 15 |
| Number of main parts |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
| Minimum total flow in m 3 /h |
35 |
60 |
75 |
90 |
105 |
120 |
135 |
| Minimum flow rate in the kitchen in m 3 /h |
20 |
30 |
45 |
45 |
45 |
45 |
45 |
The decree of 10/28/83 modifying the decree of 03/24/82 authorizes a reduction in the minimum overall flow rate extracted for controlled systems (see humidity-controlled systems).
| Number of main parts | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Minimum total flow in m³/h | 10 | 10 | 15 | 20 | 25 | 30 | 35 |
Lacentrale-eco advice for air renewal volume
We advise taking into account the actual volume of the accommodation, aiming for a renewal of the air in the entire accommodation every 3 hours (0.3 volume of air per hour).
Once the basic flow rate is determined, that is to say the one which operates in normal mode, choose a machine so that this basic flow rate is less than 50% of the maximum power of the VMC.
For example, if you have calculated a basic flow rate of 200 m²/hour, let's select a VMC whose maximum flow rate is at least 400 m²/hour.
2. Noise from the VMC
To avoid discomfort, pay attention to the noise generated by the dual-flow box and that caused by too high air speed in the networks. This information, expressed in decibels, is visible on the energy sheet of all VMCs.
Find our article on a silent VMC
Everything you need to know about Silent VMC
To reduce the air speed in the networks, have sufficiently large pipe diameters and respect the following recommendations :
| Diameter (mm) | Max flow in m3/h |
| 80 | 40 |
| 100 | 70 |
| 125 | 130 |
| 160 | 250 |
You must then choose:
- a silent double flow box
- and/or use silencers
- and/or use silent boxes
- and/or use sound attenuating vents.
The machine is preferably placed in a room with reinforced acoustic insulation, far from the rooms and fixed using anti-vibration studs or fixings.
3. Exchanger with good performance and certification
What is a VMC exchanger?
The exchanger is a key element of your double flow VMC. It allows the calories to be transferred from an incoming air flow to the outgoing air flow, without ever mixing them. Stale air is evacuated, without bringing in cold air.
For example, in winter, instead of bringing in cold outside air, the exchanger will recover calories from the hot air in your home. Thus, you have quality air, but which is already "warmed" by the calories in the air in your home.
Remember that only calories are transferred, never airflow.
Performance of a double flow VMC
It is expressed in %, with the following calculation: Efficiency (in %) = (Insufflation temperature - Exterior temperature) / (Exhaust air extraction temperature - Exterior temperature) x 100.
Please note, this efficiency calculation is theoretical. For the proper functioning and optimal performance of a dual-flow installation, the airtightness of the building must be as efficient as possible.
The airtightness of the building must, at least, be at the level of a new house subject to RT2012 (i.e. Q4pasurf < 0.6 m3/(m².h)).
If you buy the best VMC on the market, but it is installed in a thermal strainer, the end result will not perform well.
Standards for the performance of a VMC
To ensure an installation of excellent quality, you should choose an exchanger whose efficiency is greater than 85%.
It is necessary to rely on the yield values from certifications and to compare the yields ( NF certification in France). This French standard has merged with Eurovent Certita.
You can find all the products that have this approval on their site.
In the context of a building aiming for the Passiv Haus label, the PHI certificate of the machine is used. It has existed since 2001.
Not all machines have a PHI certificate and/or NF certificate. It is therefore very important to check that the certification of the selected product corresponds to the objectives and its building.
To do this, we invite you to go directly to the dedicated site: it is in English, but it is very simple to find if a vmc has PHI certification
Please note that to benefit from MyPrimeRenov assistance, it is the NF yield which is taken into account.
The different types of double flow VMC exchangers
- With cross-current plates: yields are relatively low (50-60%).
- With countercurrent plates: yields are significantly higher (70-90%).
- With enthalpy countercurrent plates: the composition allows the humidity to be recovered from the extracted air to be blown into the incoming air. It presents the other advantagege to operate without a pre-heating battery at temperatures below -15°C.
- Rotary: the operating principle helps to have the same advantages as the enthalpy exchanger.
Find our article on the subject.
4. Consumption of double flow ventilation
A double flow VMC is equipped with two fans which operate constantly . You must therefore be careful with their consumption.
As for the efficiency of the exchanger, it is necessary to rely on certified consumption values:
- NF certificate gives W-Th-C consumption which represents an average consumption.
- PHI certificate of the machine, consumption is given in Wh/m3 , the value is independent of the operating flow.
5. Choose a VMC that can be positioned in an isolated space (pay attention to the dimensions)
To guarantee the best possible overall performance of the dual-flow VMC installation, the ventilation networks connecting the dual-flow box to the interior vents must be placed within the insulated and airtight envelope.
When the dual flow box is positioned in the house, but the ducts pass into uninsulated attics, consider installing lengths of conduit as short as possible and isolated.
Then, to limit the length of the networks and have a more easily balanced installation, the dual flow ventilation box must be positioned in the most central location possible .
Finally, remember to position your ventilation box to facilitate its maintenance ( changing filters for example).
VMC manufacturers have created more compact VMC models, both for VMC for false ceilings and for small spaces. The Flair 225 from BRINK measures 11 cm less than its large one on the 325.
This difference will help you resolve space constraints.
Possible positions and installation advice
Double flow box installed in the insulated cellar near the kitchen.
The box should be positioned so that the exterior air intake duct is as short as possible, against the exterior wall for example. Exterior air is generally discharged from the roof.
It can also be carried out on a facade other than the outside air intake. The length of conduit should be as short as possible. Also check that the ducts are insulated to prevent the cold air passing through from cooling the house. Usually, they are made of polyethylene foam, the insulation of which is sufficient in most cases.
In the case of passive house design, if the ducts are too long, it may be necessary to addr an additional layer of insulation. The distribution boxes (also called plenums or collectors) can be positioned near or above the double-flow box.
The semi-rigid or rigid networks which connect to the vents generally pass in a false ceiling provided for this purpose, in the partitions or in technical ducts and are positioned on the interior side of the insulation and the sealing limit to the air.
Synthesis
air intake duct as short as possible
insulated conduits, add a layer of insulation if necessary
Double-flow box installed in the laundry room, not insulated and positioned against the house.
In this scenario, the double-flow box is positioned against the insulated wall of the house to limit the lengths of conduit connecting the double-flow box to the distribution boxes.
These ducts are made of insulating polyethylene foam and over-insulated when they are too long to prevent the hot air passing inside from cooling.
The distribution boxes are installed on the interior side in the insulated and waterproof volume. They can be installed in a false ceiling, a cupboard or a technical box.
The rigid or semi-rigid networks then connect the vents to these boxes by passing through the technical spaces also located on the interior side of the insulated and airtight volume.
Synthesis
insulating polyethylene foam conduit
interior side distribution box
6. VMC duct: Choose a rigid or semi-rigid airtight network
To preserve indoor air quality, durability and optimal operation of the installation, it is important to choose a rigid or semi-rigid network , food grade and with antistatic and antibacterial properties.
These networks limit pressure losses, do not collapse in technical spaces, are hygienic and cleanable, are in fact much more durable and allow optimal air quality to be maintained.
Discover our article dedicated to the design of a VMC network
7. Check these various precautions
- For summer comfort, the machine must be equipped with a by-pass , preferably automatic.
- An anti-freeze device using an electric battery or reduction in the inflation rate is mandatory in areas where the outside temperature drops below 0°C.
- In very cold areas or in perfectly airtight houses, an anti-freeze electric battery is mandatory.
- Condensate drainage is to be expected. In very cold areas and when the air renewal rate is too high, double-flow ventilation dries the air in the house and can create discomfort.
To remedy this, it is necessary to ensure that the air renewal is not oversized and/or install an enthalpy or rotary exchanger which recovers the humidity from the extracted air to reinfuse it into the fresh air.
- There is not yet a standard regulating the start-up of dual-flow VMC. In addition to the generalities stated above, it is therefore advisable to refer to the recommendations given by the manufacturers.
Air renewal flow rates are regulated in France by the decree of March 24, 1982 amended by the decree of October 28, 1983. The passive design of dual-flow installations concerning ventilation flow rates does not strictly comply with the regulations. French. It is based on another approach to combine comfort and performance of the installation.
- Commissioning must allow the machine to be adjusted, to ensure its proper functioning and to check the flow rate of the outlets which can be of the adjustable or self-adjusting type.
- Ensure regular maintenance of your ventilation system
To complete the list of precautions and implementation advice, the installer can refer to the Sustainable Development Practical Guide - Double flow ventilation in residential areas, Design, implementation and maintenance
Conclusion
Essential equipment for the comfort of your home, but also an ally for energy savings, your dual-flow ventilation system must be chosen carefully. The different certifications are there to help you.
However, first make a fairly precise diagram of your installation to help you then determine the right model. This will also help you better manage your work, whether you are tackling a renovation or a new project.
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