All you need to know about demand controlled ventilation

All you need to know about demand controlled ventilation

The most efficient way to balance indoor air quality and energy savings

It is commonly accepted that most water distribution facilities work on demand, and not permanently. Thus why should it be different for ventilation, with each cubic meter of fresh air to warm during all the heating season having a significant economic and environmental cost?

The concept of demand controlled ventilation rests on the principle of providing occupants with the right amount of fresh air, when they need it, where this is useful. With intelligent airflow management (included demand controlled ventilation), energy savings are made on every occasion that the need for ventilation is low or null, which can represent more than half the time. Conversely, an activity which emits indoor air pollution such as preparation in a kitchen, a shower, or even the release of odorous metabolic compounds, generates a need for a greater ventilation to remove the pollution quickly.

At every moment, demand controlled ventilation offers an optimization of heating consumption and indoor air quality, on a fully automated basis. Every Aereco ventilation system is design on this concept of demand controlled ventilation, which beyond being particularly effective for the comfort of the occupant, has many other benefits on the working of the demand controlled ventilation system.


Better air renewal for greater comfort

By providing the most ventilation for the places that need it most, Aereco’s demand controlled ventilation systems largely contribute to improving air quality in dwellings. When a main room is occupied, its relative humidity increases; the air inlets then open more to increase airflow and better evacuate stale air. Activity in wet rooms (kitchen, bathroom, toilets, etc.) is accompanied by water vapour emissions; the opening of the exhaust units increases with the relative humidity, increasing the airflow and so evacuating polluted air more rapidly.


Protection against moisture

The higher relative humidity generated by breathing and human activity in the kitchen or shower, for example, can lead to destructive condensation, in which moulds can grow. When the relative humidity increases dangerously, humidity sensitive exhaust units open quickly to evacuate excess moisture and eliminate the risk of condensation.


Reduced and controlled heating consumption

Ventilation is often held responsible for a large share of the thermal losses in a dwelling, sometimes as much as 50 %. While this is true of the majority of traditional ventilation processes, Aereco systems preserve heat in less occupied rooms and dwellings by automatically reducing the airflow.


Numerous additional benefits

In addition to combining indoor air quality and energy savings optimisation, demand controlled ventilation demonstrates many indirect benefits resulting from the reduction of average airflow:


v4a-whole-house-exhaust-fan-ventilation Reduced average power consumption of the demand controlled exhaust fan

By reducing the average airflow rate, demand controlled ventilation systems allow the exhaust fan to work well below the maximum airflow, thus at a very low power. This aspect clearly promotes unbalanced demand controlled ventilation systems such as those from Aereco, when compared with the standard heat recovery ventilation systems that typically have two motors operating at a higher speed (with higher average airflow), and are then particularly penalized in terms of environmental impact and consumption of electrical energy (primary notably).


Demand controlled ventilation: less clogging of filters, air ducts and terminals Less clogging of filters, air ducts and terminals

The inherently reduced airflow of demand controlled ventilation leads to the reduction of the total amount of particles that can clog the components that make up the demand controlled ventilation system, which is directly proportional to the total volume of air introduced by the ventilation system in any given period. Thus, maintenance of air ductwork and filters (where these have been used), can be reduced with the power consumption of the demand controlled exhaust fan (when presence of filters).


Demand controlled ventilation: increased life of demand controlled exhaust fans Increased life of demand controlled exhaust fans

By reducing average airflow over the year, demand controlled ventilation permits a reduction of the demands placed on the exhaust fan, and thereby increases its longevity. This is because the longevity of the exhaust fan depends in particular upon the power at which it works, and that power is directly related to the request of average airflow through the ventilation system.


Demand controlled ventilation: greater availability of pressure and airflow for terminals Greater availability of pressure and airflow for terminals

In a collective air ductwork system, serving either an individual home or collective dwellings, the airflow modulation at the various vents permits the avoidance of overloading the air ducts with unnecessary airflow rates, as would be the case with a constant airflow ventilation system. Thus, the rooms or dwellings with a low airflow requirement release the air duct space for the rooms or dwellings with a higher need for ventilation. These can then benefit from the demand controlled ventilation, from all the pressure and flow potential of the air ductwork, with losses in the air ducts being optimized and reduced.


Demand controlled ventilation: reduced size of air ductwork to gain on valuable floor space Reduced size of air ductwork to gain on valuable floor space

In demand controlled ventilation, airflow modulation permits a reduction in the size of the ventilation ductwork, exploiting the advantage presented by the fact that in a collective system, not all of the exhaust vents are working at the maximum level simultaneously. This phenomenon, called airflow time-dispatching, has been verified during numerous in-situ experiments carried out by Aereco. The air ductwork can therefore be sized for a total airflow lower than the sum of the maximum airflows, unlike that of a constant airflow ventilation system where the size of ducting corresponds to the strict sum of airflow. This use of smaller air ducts, can thereby allow a reduction in the total floor space required for ducting.



By offering airflow adapted moment-by-moment to occupants’ needs, Aereco demand controlled ventilation systems reduce thermal losses due to ventilation, improve indoor air quality and limit moisture problems.

Invented by Aereco in 1984, humidity sensitive ventilation  is still regarded as a major technological breakthrough in demand controlled ventilation today.

An activation mode for each pollutant

Ventilate Right: This is the concept that underlies the design of all Aereco ventilation products. The ventilation system terminals are controlled and activated in various ways according to pollution and the needs of each room. The activation modes most often used in Aereco products are:


Humidity sensitive airflow

Principle: the airflow is controlled by the local relative humidity.

This is the first activation mode of Aereco systems. The detector and actuator of the humidity sensitive products, the sensor, makes use of a well-known physical phenomenon: the tendency of some fabrics to become longer when the relative humidity of the air increases and shorter when it decreases. The 8 or 16 polyamide strips of the sensor use this principle to activate one or more shutters, thereby adjusting the passage of the air according to the ambient relative humidity.


The higher the humidity in the room, the wider the shutters open. The sensor is isolated from the incoming airflow; it measures only the interior moisture content. Moreover, thanks to a thermal correction, the opening of the shutters is unaffected by the external climatic conditions.

Aereco’s humidity sensitive technology is applied to air inlets, grilles, and exhaust units located in the rooms where the humidity reflects the level of indoor pollution (lounge, bedrooms, bathrooms).


Manually activated airflowManually activated airflow

Principle: let the occupant increase the exhaust airflow at times of intensive pollution.

Where the relative humidity cannot be used as an indicator of high pollution (kitchen, toilets, etc. in use) the occupant can manually activate the maximum airflow at the exhaust unit to quickly evacuate stale air, unpleasant odours, and excess moisture. This boost can be activated by a pushbutton (‘on-off switch’), by pulling a cord, or through a remote control. This function can also supplement a humidity sensitive function on an exhaust unit.



Airflow activated by a presence detectorAirflow activated by a presence detector

Principle: automatically increase the airflow when a presence is detected in the room.

The presence of somebody in the room automatically activates the presence detector, which then opens the shutters of the exhaust unit for maximum airflow. This process is used when moisture is not sufficient to reveal of a high pollution level (use of the toilets, random occupation in offices, etc.). This technology makes it possible to save heating energy during the period of non-detection.

The presence detection module comprises a pyroelectric sensor that detects infrared radiation focused by a Fresnel lens. With a 4-meter range and a 100° angle of detection, this is very effective. The infrared radiation focused on the sensor is continually analysed; when a variation is perceived, a signal is sent to the electronic board, which analyses it and then activates the motor controlling the opening of the exhaust unit shutters.

The presence detection technology is used on exhaust units and mechanical ventilation terminals in rooms where the relative humidity cannot be used as an indicator of the pollution level (toilets, offices, etc.).


CO2-COV sensorAirflow activated by a CO2 or VOC sensor

Principle: control the airflow automatically according to the level of CO2 or VOC.

Both sensors operate the same way: the opening threshold is selected at the time of installation. When the level of CO2 (or of VOC, depending on the version of the product) is below the opening threshold, the airflow is at the baseline rate (minimum). When the level of the pollutant rises above this threshold, the exhaust grille opens to the maximum airflow for as long as the level of pollution exceeds the preset threshold.



Airflow demand controlled ventilation parameters

Modulation parameters should allow adjustment of the air change rate based on actual needs and for this reason, the choice of a parameter depends on the application (local type), its tenure and activity (type and level of pollutant emitted). The table below gives the different parameters of ventilation modulation depending on applications as a guide:


Humidity Presence Humidity + switch Humidity + presence Presence with timer Humidity + presence with timer
Kitchen ++ ++++
Bathroom ++++ +++ +++ +++
WC ++++ ++ +++ ++++ +++
Bathroom with WC + + ++ +++ ++++
Laundry ++++ +++ +
Classrooms +++ + + +
Lavatories ++++ ++ +++ ++++ +++
Companies Administrations
Offices +++ + + +
Meeting rooms +++ + + +
Fitness center
Locker rooms +++ ++ ++ +++ +++
Shower rooms ++++ +++ +++ +++
Cabins (bathroom – WC) ++ ++ +++ +++ ++
Mobile Homes
Kitchen ++ ++++ +++
Bathroom and WC + + ++ +++ +


Carbon Dioxyde (CO2) Volatile organic compounds (VOC) Remote control Fixed rate, settable at installation
Kitchen ++ +++ +
Bathroom +
WC ++ +++ +
Bathroom with WC ++
Laundry ++
Classrooms ++++ ++++ +
Lavatories ++ +++ +
Companies Administrations
Offices ++++ ++++ +
Meeting rooms ++++ ++++ +
Fitness center
Locker rooms ++++ ++++ +
Shower rooms + ++
Cabins (bathroom – WC) ++++ +++ ++
Mobile Homes
Kitchen +++ +++ +++
Bathroom and WC +++ ++++ ++



Humidity sensitive ventilation

Invented in 1984 by Aereco, the humidity sensitive ventilation systems automatically adjust the airflow depending on the room humidity, without electricity.

Comparison between demand controlled ventilation and heat recovery ventilation

Aereco Demand Controlled Mechanical Exhaust Ventilation: a relevant, low cost alternative to constant Heat-Recovery Ventilation

A study was conducted in 2008 by the Fraunhofer Institut Bauphysik to evaluate the performance of the Aereco humidity controlled mechanical ventilation system and compare it with several other heat recovery systems.

The simulation was carried out in a 75 m² apartment occupied by 3 persons. The indoor temperature was a constant 21°C. The U-factor assumed was 0.25  W/m².K. Three representative types of weather were used (data supplied by the German Meteorological Institute):

  • Hof (cold)
  • Würzburg (temperate)
  • Freiburg (warm)

The results presented here are based on the Hof weather data (with which heat recovery yields the largest energy savings).

Document : Calculation of the primary energy needs of a supply and extractor fan with heat recovery compared with demand controlled mechanical ventilation (humidity controlled). Detailled study here.


Energy savings

The study showed that the Aereco demand controlled MEV system consumes only slightly more energy – 1 070 kWh – per heating period than an 80 % heat recovery system, under the conditions of the study. The corresponding extra cost – €47 – is much smaller than the cost of the annual filter change necessary to maintain the level of performance of HR units (see graph 1 below).

The long-term projection of the graph 2 below shows that the initial extra cost of the heat recovery system (supply and installation), compared with the Aereco demand controlled MEV, is never paid back (even without counting the required annual filter change).

Total energy consumption of various ventilation systems

Graph 1

Operating costs and R.O.I. of various ventilation systems

Graph 2

Environmental benefits

The energy performance of Aereco’s demand controlled MEV system is reinforced by the fact that its single fan consumes less electricity than the two fans and preheating of the heat recovery system. With a PE-factor (primary energy factor for electricity, value for Germany) of 2.7, the impact on primary energy consumption – and so on COemissions – favours humidity controlled ventilation for the share of energy necessary to run the system.

Indoor air quality

This study also showed that, under real occupancy conditions, Aereco demand controlled MEV keeps CO2 levels below 1  200 ppm, guaranteeing optimal indoor air quality (IAQ) in the dwelling (see graph below).

Daily variation of CO2 inside the dwelling equipped with Aereco demand controlled MEV



Thermal behaviour of the humidity sensitive air inlet

Thermal behaviour of the humidity sensitive air inlet


Manage the temperature at the humidity sensitive sensor level of the air inlet, for an optimal working in all seasons

The position of the shutter of the humidity sensitive air inlet is directly determined by the relative humidity read at the level of the sensor. However the relative humidity at the sensor can be different from that found in the centre of the room in which the humidity sensitive air inlet is installed. This is because for the same absolute humidity, the relative humidity varies according to temperature. From this, one can deduce that the temperature at the level of the sensor can have a major impact on the relative humidity reading. It is therefore fundamental to manage this temperature difference in order to control the position of the shutter whatever the climatic conditions (indoor and outdoor temperature, indoor and outdoor relative humidity) and to closely follow the emission of indoor humidity.


The importance of a “good” thermal coefficient

The thermal coefficient CT is determined by the formula: Tsensor = Tindoor – CT x (Tindoor – Toutdoor)

Where T = temperature in oC

Several years of researches has made it possible to determine and to manage an ideal value of CT thermal coefficient. With a CT between 0.25 and 0.32, the Aereco humidity sensitive air inlets offer the perfect amplitude of ventilation modulation for every season, and are ready to react to the lowest emission of interior moisture. In winter, in an unoccupied room where the relative humidity is low, the shutter is in closed position, but is ready to react and to open for any emission of humidity, even low. More than 25 years of experiment has enabled Aereco to obtain a perfect control of the industrial reliability and durability of this thermal coefficient.


Consequences of a too high thermal coefficient

With a higher thermal coefficient (TC > 0.32) due to poor sensor insulation against the outdoor air, the sensor temperature would be too low in winter. So the sensor would read a too high humidity rate which would generate an excess of humidity sensitive air inlet opening, even when the relative humidity is low in the room. Its modulation capacity would then be greatly reduced, even null. A poorly managed thermal coefficient would increase the thermal losses, particularly through cross flow, and would decrease the air quality in the occupied rooms (as airflow would not be well distributed according to the needs). In addition, a too low sensor temperature would cause a big increase of hysteresis (difference between both ends of the opening-closing/humidity curve), which would then be unable to determine the correct shutter position for a known relative humidity rate.


Comparison of various products according to the EN 13141-9 standard

Offset curve of an Aereco humidity sensitive air inlet depending on the temperature

EN 13141-9 standard, which defines the humidity sensitive air inlets test method, requires measurements known as isothermal (indoor and outdoor air with the same temperature) and non isothermal (colder outdoor air) in order to evaluate the thermal coefficient impact on the operation of the humidity sensitive air inlets. As shown on this graph, the Aereco humidity sensitive air inlets characteristic (model presented: EHA2 5-35) is shifted towards the left (lower relative humidity needed for the opening) when the outdoor air temperature is lower (10°C, blue curve). This way, a great modulation amplitude and a similar operation to isothermal operation (grey curve) is kept even with the low average indoor relative humidity in winter.


Offset curve of a Brand X humidity sensitive air inlet depending on the temperature

When the air inlet thermal coefficient is too high (badly isolated sensor) as it is the case in the test of the humidity sensitive air inlet show here (other brand), the non isothermal operation at an outdoor temperature of 10oC (blue curve) does not allow anymore real airflow modulation according to the indoor relative humidity. The sensor temperature is too low and this increases the relative humidity it reads in comparison with the actual one at the centre of the room. The humidity sensitive air inlet is therefore almost permanently open, and does not control the airflow anymore. This phenomenon is accentuated as the outdoor temperature decreases.


Air inlet installation

The slot realisation is very important as only a conform hole will ensure the right airflow of the air inlet. This section gathers the major points relative to the slot drilling process.

EHA2 on window - Slots drilling for window air inlets

Example of a humidity controlled air inlet on a PVC window with its slot in the fix part.


Slot dimensions

Most of Aereco air inlets for windows require the following slot, which guarantees the indicated airflow under the pressure reference (no air section reduction with this slot). Made of two parts, this slot is recommended to keep the rigidity of the window. Some other slots can also be realised; dimensions are precised in the technical data sheets.

Slot dimensions

General recommendations

  • Be sure that the slot is continuous between the canopy and the air inlet, without size reduction, so that the air section is kept along the hole (no airflow reduction)
  • Some windows may require additional sleeve to ensure the continuity of the slot between the canopy and the air inlet. Aereco offers a specific accessory (E-TFR)
  • Respect the slot dimensions indicated in the installation instruction of the air inlet to guarantee the airflow
  • It is recommended to inform the occupants that the air inlets should never be obstructed, even in cold period, to ensure sufficient ventilation

 Type of windows

Aereco air inlets can be installed on PVC, wooden or aluminium window profiles. Most of profiles are compatible with Aereco air inlets.


Position of the air inlet

Slots positions must be chosen in order to prevent the window structure from weakness. Unless not possible, air inlet must always be placed on the top of the window, this for several reasons:

  • The outdoor air, cold in winter, can be progressively introduced and heated on the ceiling as the flow is introduced in the upper part of the window, thus preventing occupants from discomfort.
  • The sensitivity for humidity controlled air inlet to humidity is optimum at this place.
  • The air renewal will be better ensured in the room, as the air is often exhausted from the main room through the bottom of the door.
  • The top position prevent from water introduction, even in case of strong rain.

Slot drilling process

The slots drilling process for window air inlet depends on the type of work.

During the manufacturing process of the window:

If the window is prepared in factory the slot can easier be realised at this step, before the installation on site, through a professional drilling machine such as the one presented below:

Example of a drilling machine for PVC and aluminium profiles

Example of a drilling machine for PVC and aluminium profiles


On existing windows:

If the window where the air inlet must be placed already exists in the building, the slot cannot always be realised through a drilling machine. When possible, it is recommended to use a machine similar to the one used in factory (see previous paragraph). When not possible nor available, then several tools can be used to realise the slots. Below are presented some of possible tools.


Portable-drilling-machine2-300x270Portable drilling machine






Cutting-disc1-300x270Cutting disc


Process for slot drilling and inlet + canopy installation on existing window:

Installation on existing window - Slots drilling for window air inlets

  1. Drill a slot in the highest part of the window to the dimensions specified in the installation instruction delivered with the product. According to the type of window the slot can be realised on the mobile or on the fix part of the window.
  2. Fix the back-plate using screws (some air inlets are directly fixed, without any backplate).
  3. Clip the air inlet on its back-plate. Make sure that the air inlet is well stuck to the window, without space to avoid noise and airflow leakage.
  4. Fix the canopy on the window (outdoor side) using screws. According to the type of window it can be on the mobile or on the fix part of the window.

See video examples on:


Standard slot on a PVC window

Views of a standard slot realised on the mobile part (air inlet) and on the fix part (canopy) on a PVC window


 Examples of slots on various profiles

Examples of slots on various profiles - wood

Wooden profile

Air inlet (left) and canopy (right)
installed on the mobile part.

Examples of slots on various profiles - PVC

PVC profile

Air inlet (left) installed on the mobile part.
Canopy (right) installed on the fix part.