How to choose between a single-flow MCV, a dual-flow MCV or other types of ventilation system?

What is MCV (Mechanical controlled ventilation), and why is it essential?

MCV is a ventilation system that provides constant air renewal inside a building. It is used to combat moisture, eliminate indoor pollutants and improve the thermal comfort of the occupants. Ventilation is a particularly crucial issue in well-insulated buildings, where the air tends to stagnate, causing condensation problems and health risks. To ensure optimal air circulation, it is essential to make the right choice of MCV air grilles, to ensure that the main rooms get a sufficient and suitable air supply.

The main types of MCV

There are two main types of MCV systems: single-flow MCV and dual-flow MCV. Each has specific characteristics, and meets different needs depending on the type of building. There are also decentralised MCV systems, which provide autonomous room ventilation, without the need for a centralised duct network. This is an advantageous solution for renovations, or in spaces where installing a centralised MCV would be complex.

Single-flow MCV: efficiency and simplicity

Single-flow MCV is the most common home ventilation system. It works by extracting the foul air from wet rooms (bathrooms, kitchens, etc.) via extraction vents, while fresh air enters naturally via MCV air vents situated in dry rooms (bedrooms, living rooms).

MCV flow rate: How to size your installation correctly?

For an MCV to operate properly, the flow rate must be calculated to suit the surface area and volume of the rooms to be ventilated. This calculation must factor in the number of wet rooms to be treated and the regulatory flow rates (e.g. 75 to 135 m³/h for a kitchen). An incorrect choice of sizing, with too low or high a flow rate, may cause thermal or acoustic discomfort, or excessive energy consumption.

The various types of single-flow MCV

• Self-regulating single-flow MCV: Maintains a constant flow thanks to self-regulating vents, regardless of the humidity level. It is a simple solution, but may lead to high energy consumption.
• Type A humidity-sensitive single-flow MCV: This system adapts the extraction to the humidity level in wet rooms, thanks to humidity-sensitive vents. The air inlets are self-regulating. This model is more energy-efficient than the self-regulating system.
• Type B humidity-sensitive single-flow MCV: Unlike the type A, this system regulates both air inflow and outflow based on the humidity, providing finer control and better energy performance.

Advantages of single-flow MCV

• Ease of installation: A single-flow MCV system is relatively simple and cheap to install. Particularly in renovations, it can easily replace natural ventilation.
• Easy servicing: Little servicing required, besides regularly cleaning the extraction vents.
• Low energy consumption: Especially for humidity-sensitive systems, which reduce heat loss.

Limitations

• Heat loss: Because of the absence of a heat recovery system, the extracted air is discharged outside without heat reclamation, which affects heating costs.
• Thermal comfort: Inferior performance in terms of comfort, especially in the winter, when the cold outdoor air enters the home directly.

The various types of extraction vent:

• Self-regulating vents: Maintain a constant flow rate, and are adjusted during installation.
• Humidity-sensitive vents: Adapt to the ambient humidity, for optimal ventilation.
• Presence detection vents: Increase the extraction flow rate when people are detected, ideal for bathrooms or toilets.

Dual-flow MCV: For better energy efficiency

The principle of a dual-flow MCV is based on a heat exchanger used to recover heat from the foul air extracted from wet rooms (kitchen, bathroom) and transfer it to fresh air entering the main rooms (living room, bedrooms). Hence the extracted and supply air flow through separate ducts, but the heat is retained, thereby limiting energy loss and improving thermal comfort. This system ensures continuous ventilation while optimising heating savings and indoor air quality.

Dual-flow MCV is a more efficient system, since it not only provides foul air extraction, but also the fresh air supply. The great advantage of this system is that it is equipped with a heat exchanger which recovers the heat from the foul air before discharging it outside, thereby heating the incoming air. The choice of MCV grilles also contributes to the system’s performance, ensuring smooth air diffusion in every room.

Advantages of dual-flow MCV

• Heat recovery: Up to 90% of the heat contained in the extracted air can be recovered, enabling significant heating savings.
• Air quality: The supply air is filtered, thereby eliminating outdoor pollutants (dust, pollen, etc.) before they enter the living spaces.
• Thermal comfort: Thanks to heat recovery, the dual-flow MCV ensures optimal comfort, even in winter.

Limitations

• More complex installation: The installation cost and complexity of a dual-flow MCV are higher, because of the presence of two duct networks (one for the extracted air, and one for the supply air) and the heat exchanger.
• Servicing: The filters need regular replacement to ensure the supply air quality, and prevent clogging of the system.

How to install a single-flow MCV system correctly?

A single-flow MCV system must be installed as per these steps to ensure optimal operation:

• Choose the location: Place the ventilation casing fan in a ventilated area such as an attic or suspended ceiling.
• Install the extraction vents: The vents must be placed in wet rooms (kitchen, bathroom, WC).
• Fit the air inlets: Install the air inlets in the main rooms (bedrooms, living room).
• Connect the ducts: Link the extraction vents to the casing fan via ducts, and connect the extraction to the roof outlet.
• System check: Make sure that everything is correctly connected, and that the casing fan is working correctly.

Correct installation will ensure efficient air renewal, and prevent excessive heat loss.

How to service a dual-flow MCV?

Servicing is essential for a dual-flow MCV system, to ensure its efficiency and the indoor air quality. Here are the key steps for good servicing:

• Cleaning the filters: The filters must be cleaned or replaced every 3 to 6 months, since they retain dust and pollutants.
• Checking the air vents: The supply and extraction vents must be cleaned regularly to prevent dirt build-up.
• Checking the duct network: Make sure that the ducts are properly insulated and free from obstructions.
• Annual inspection: Have the heat exchanger and the whole system professionally checked every year.

These actions will help ensure good energy performance and decent ventilation.

Current European standards on MCV

The European standards on MCV (Mechanical Controlled Ventilation) are mainly governed by European Directive 2010/31/EU on the energy performance of buildings, and the ErP regulations (Energy-related Products). These standards stipulate strict requirements relating to the energy efficiency, indoor air quality and noise levels of ventilation systems. They also promote the use of ventilation systems with heat recovery, such as dual-flow MCV, to reduce energy losses and optimise building performance. A correctly sized MCV flow rate is essential in order to comply with these standards, while ensuring suitable ventilation and energy savings.

European Directive 2010/31/EU on the energy performance of buildings

This directive is aimed at improving building energy performance in the European Union. Member States are bound to:

• Set minimum energy performance standards for new and existing buildings.
• Encourage renovations to improve energy efficiency.
• Require that all new buildings are “Net Zero-Energy Buildings” (NZEB) by 2021.

The Ecodesign Directive (Energy-related Products)

The Ecodesign Directive  (2009/125/EC) stipulates eco-design requirements for energy-related products, including ventilation systems (MCV). It is aimed at reducing the environmental impact of products throughout their life cycle, by increasing their energy efficiency, and thereby reducing their energy consumption and CO2 emissions.

Key points :

• Introducing minimum energy efficiency thresholds for products.
• Encouraging technological innovations to improve energy performance.
• Gradual application, with the requirements reinforced over time.

These two directives play an essential role in the transition to more sustainable and energy-efficient buildings within the EU.

Why choose a CAIROX MCV?

At CAIROX, we offer single-flow MCV systems suited to the needs of all types of buildings. Our solutions provide reliable performance, especially with humidity-sensitive models which combine thermal comfort and energy savings. We support the installers and engineering departments with sizing software and technical expertise tailored to every project.