Multi-sensor probes for Indoor Air Quality on Construction 21

NanoSense is an SME based in the Ile-de-France region and has been involved in indoor air quality (IAQ in the following text) since 2002. The company designs and produces various multi-sensor (CO2, VOC, T°, RH, Radon, PM) IAQ probes with control (ventilation) algorithms and are compatible with the main interfaces of the major intelligent building standards. The purpose of this article is to share its expertise in Indoor Air Quality and to study different ways to improve it.

His expertise also extends to autonomous systems known as "Energy Harvesting" as well as the representation of IAQ in the form of human impacts and like all knowledge, it is meant to be shared.

Knowing that the buildings are the largest energy consumers in the country, the legislator has put in place different instruments: tax incentives for renovations for old buildings (the most fuel-consuming), thermal regulations for New buildings (the last in force being the RT2012) and for the first time a regulation for the larger existing tertiary buildings thus obliging them to renovate them.

The various successive thermal regulations have firstly favoured the insulation of the envelope, then its airtightness, through heating with improved efficiency (condensation and heat pumps). Since the 2012 RT, new buildings are therefore "airtight", which requires controlled mechanical or natural ventilation.

Indeed, a well insulated building mainly loses calories through the release of warm air in winter or fresh air in summer due to ventilation. Heating and air conditioning consumption then becomes mainly related to the flow of renewed air.

It is therefore necessary to properly control air renewal in order to minimise energy consumption, but first of all we must ask the main question: Why do we need to renew the air in buildings?

Our brain functions distinguish us from other mammals, the brain is our most precious heritage. This, even if it only represents 2% of the weight of our body consumes alone 20% of the oxygen of the air breathed through the blood flow. And the blood also provides other foods to the brain which it nourishes with frugality.

Respiration is similar to a combustion: we inhale oxygen that our lungs assimilate and that is transported through hemoglobin but they also reject the one that was consumed (oxidation) in the form of CO2 and water vapour (H2O). The volume breathed in one day represents a volume of air 15m3. The developed surface of our lungs is about that of a tennis court. This gigantic surface is very porous and absorbs off the oxygen of volatile organic compounds (VOCs) and fine particles contained in the air. If these elements were not absorbed, the bottom of our lungs would be as dirty in a day as the underside of our bed after a month. This is how, by inhaling alcohol vapours (one VOC among others) you can quickly get drunk, not to mention inhalation drugs.

All these elements absorbed by respiration are conveyed by the blood to feed mainly our brain.

For this reason, poor indoor air quality impairs cognitive function and productivity.

For example, a concentration of CO2 1000ppm (the air we exhale), i.e. the regulatory threshold for a classroom, corresponds to a reduction in cognitive functions of more than 23%. When you know that in a classroom you are fluent in more than 3000ppm after an hour of class, you should not be surprised at the poor results of the students. High levels of CO2 are also achieved in a bedroom with a closed door which alters the quality of sleep.

While CO2 has no health impact (except at extremely high levels) VOCs and fine particles affect health. Fine particles alone are responsible for more than 48,000 deaths a year in France. VOCs are harmful overall but some are now subject to specific regulations for establishments receiving the public (ERP) because they are recognized as proven carcinogens: Formaldehyde and benzene. Formaldehyde is found in wood (natural) but mainly in glues (chipboard). Benzene is found in some plastics and in gasoline fumes (replacing lead). The cases where benzene is the most important concern parking lots connected to the dwelling.

For these different reasons it is therefore essential to ventilate the buildings, but the dilution with the outside air is not always the optimum solution both in terms of energy and quality as will be seen below.

NanoSense Solution: Multi-pollutant driven IAQ

As mentioned above, a sufficiently low level of CO2 must be guaranteed so that cognitive functions are not affected. But we must not neglect olfactory comfort and productivity. In spite of a CO2 probe in a meeting room, how many of us felt an olfactory discomfort after a coffee break when we returned to the room! The human body regulates its temperature by sweating. It's the evaporation of sweat that creates refreshment. It is this sweating that exhales valeric acid and that we perceive. But valeric acid, like most other VOCs, is absorbed into the bloodstream during respiration and, like CO2, affects cognitive functions. This is a recent discovery but one with far-reaching consequences.

NanoSense was the first IAQ sensor manufacturer to integrate VOC sensors. This allows ventilation that ensures olfactory comfort, better productivity (cognitive functions) and better long-term health.

But good ventilation control must also take into account the humidity inside. Air that is too humid causes damage to the building (stained or peeling paint, mould, warping parquet floors). Air that is too dry causes cracks in furniture, joinery and parquet floors, but it can also affect the occupants: producing static electricity, drying out the skin and lips and irritating the mucous membranes and respiratory tract.

Ideally, an IAQ probe should be able to take into account the humidity of the outside air. If the absolute humidity of the outside air is higher than that of the inside air to be reduced, it is not advisable to use dilution. Drying must then be achieved by other means such as air conditioning.

The NanoSense IAQ sensors can be connected to an external temperature and humidity sensor for this purpose. In addition, the outside temperature is used for "free cooling" control (cooling in summer when the outside air is cooler, typically at night).

Naturally, the NanoSense IAQ probes integrate ventilation controls on exceeding multi-pollutant thresholds CO2, VOC, Humidity, PM1, PM2.5 and PM10, Radon. Temperature control is performed with an auto-adaptive algorithm (using a very accurate Integral Proportional Derivative PID whose parameters are filled by learning).

EnOcean and/or KNX Ecosystem

But optimising ventilation also means integrating into the building's ecosystem. Presence sensors typically used to automatically turn lights on or off can be used to adjust IAQ requirements to occupancy. Window opening sensors can also be used to switch off the heating and ventilation when windows are opened.

These elements make IAQ management even more involved in the energy efficiency of the building.

Ecosystems generally use a standardized means of communication that allows interoperability between equipment from different manufacturers. The same presence sensor can thus be used for heating, air conditioning, ventilation, lighting and even roller shutters.

The most common standards are KNX (wired digital bus) and EnOcean (radio for batteryless and wireless sensors).

The KNX protocol is the most sophisticated and allows very fine tuning. It is mainly used in the tertiary and hotel sectors. The equivalent of KNX on the North American market is the LON standard sometimes used in High-rise buildings (HGI) in Europe.

The EnOcean radio protocol is simple to deploy, but with a limited number of parameters. It is the radio reference standard for batteryless and wireless sensors and actuators because it is an international ISO standard. It uses a frequency of 868 Mhz which gives it a large range inside buildings. The radio energy used is particularly low (100 times less than that generated by the spark inside a traditional switch) making this technology the ideal solution for nurseries and schools where electromagnetic radiation is not welcome.

There is also a standard inherited from industrial installations called Modbus. It is a very inexpensive wired digital bus that can reach large distances (1.2Km) but does not have a standardized language and requires a centralized PLC making the architecture more vulnerable compared to previous standards with distributed "intelligence" and therefore, by nature, more resilient in case of failure.

There is no ideal standard, which is why NanoSense offers IAQ probes that meet all these different standards. As it sometimes makes sense to mix several standards, there is even a gateway function integrated in the IAQ probes. Typically a KNX IAQ probe with EnOcean wireless battery-free window handles.

Optimal Solution: Taking into account Cocktail effects

A multi-pollutant measurement and control system is, as we have just seen, much more relevant than "blind" or ventilation systems on CO2 and/or Humidity.

However, if you want to be really relevant you have to look at the picture as a whole! Aren't there many harmful indoor air pollutants? Although there is a threshold for each one that it is not advisable to exceed, if all of these thresholds reach or exceed their limit at the same time, wouldn't it be more dangerous to breathe this air rather than one air or one of the pollutants being at the limit concentration?

In non-prescription drugs for example, it says "do not exceed X tablets per day" but if you take 10 boxes of different drugs and you ingest the recommended limit dose each time... The impact on your body will be tenfold and the same goes for the impact on your brain which is the most irrigated part of the body.

With this in mind, NanoSense quantifies and integrates into its physiological impact calculations the cocktail effects of different indoor air pollutants.

Indeed, with the Smart IAQ algorithm, ventilation can be triggered without any of the pollutant thresholds being exceeded if the overall impact is greater than the desired set point.

Democratization and popularization of Air Quality

Current and future thermal regulations affect the entire population, and it is not possible to democratize remediation systems based on IAQ measurement without providing the visibility that is provided by a thermostat that displays setpoint and room temperature.

It would be unreasonable to think that it would be possible to educate an entire population in IAQ to the point where they could understand and interpret ppm, ppb, and µg/m3. It is therefore essential to find a simple and intuitive way to represent IAQ.

The use of current IAQ probes to control ventilation systems also faces the difficulty of parameterization by integrators. Moreover, regulatory thresholds, where they exist, are guided more by health aspects than by their immediate physiological effects.

A new way to express IAQ is by its induced physiological effects rather than by measurement.

The table below summarizes the various physiological effects and the elements of IAQ that contribute to them.


The problem of productivity mainly concerns the tertiary level but also concerns schools where cognitive functions are central to the mission of national education.

Current market probes control remediation based on individual thresholds (CO2 mainly, see humidity and VOCs at best) without concern for physiological effects or the combination of different constituents.

The above table shows that productivity is related to CO2, VOC, Fine Particles and Temperature concentrations (see noise).

Thanks to the power of the microprocessors embedded in the IAQ probes, it is now possible to implement algorithms that automatically determine ventilation control thresholds based on ambient temperature and productivity objectives. If a threshold is exceeded by one of the elements, the thresholds of the other contributors can be automatically adjusted to meet the productivity target defined on the average of the contributing pollutants.

The impact of CO2 on cognitive functions has been known for a long time. It has recently been quantified by the NIH (National Institute of Environmental Health Science) in the USA for different activities which corresponds to the following graphs:

These curves can be averaged as follows

More surprisingly, in the same study, this institute demonstrated the impact of total VOCs.

In another study of pear packers paid by the job, it was possible to demonstrate and quantify the impact of PM2.5 on productivity.

The impact of temperature was also modelled based on an average of more than 20 studies and synthesised as follows:

Indeed, it seems obvious that if it is too hot or too cold, it is difficult to concentrate on a task, but this impact had to be modelled mathematically.

The impact of ambient noise on concentration can also be modelled.

Olfactory comfort can also affect productivity, but the phenomenon is more complex than it may seem at first glance. Indeed, the notion of good or bad smell is very subjective and very much linked to culinary culture (e.g. a hundred-year-old egg) and to the olfactory memory of early childhood, which associates certain smells with feelings of well-being and others with past suffering. In addition, the brain adapts the olfactory threshold for each smell (a system related to the acceptance of personal body odours).

The consideration of olfactory comfort will therefore be based on rapid variations in VOC levels.

There are therefore, for cognitive functions, simple mathematical models for each contributor (see previous graphs) from different academic research.

However, in real life, all these effects studied and quantified individually in the laboratory combine (cocktail effect) and it should be possible to establish an overall impact.

There are no studies yet on the cocktail effect of contributors to cognitive impairment, but NanoSense has developed a mathematical model that is currently being tested.

When a building is equipped with remedial measures such as recirculation through a PM filter it is possible to reduce PM without air renewal, which is more efficient and economical than dilution. The dilution may or may not be equipped with a filtering system for the incoming air. The control of the various remediation methods therefore requires taking into account their characteristics and optimizing their commitment according to their effectiveness and economic impact.

Consideration of Outdoor Air Quality (IAQ: Atmospheric Air Quality)

An optimal remediation policy is the compromise between indoor pollution, outdoor air pollution, energy consumption (different according to the means of remediation) and user instructions. The most common case is a high exposure to CO2 which mainly affects cognitive functions with outdoor air loaded with fine particles (PM2.5) and an unfiltered CMV. Particles also affect cognitive functions, but they mainly affect long-term health. The compromise therefore concerns consequences of a completely different nature for very different exposure times.

 NanoSense QAA Probe

The energy cost of dilution and other remediation contributes to the remediation policy.

The purpose of this solution is to determine the remediation instructions to be applied whether they are manual and/or automatic.

At the beginning of 2018, the City of Paris and the Urban Lab of Paris&Co decided to make the major issue of air quality the theme of their new experimental programme, with the support of Airparif's technical expertise.

The SmartQAI solution from NanoSense is one of the 5 Indoor Air Quality projects to have been selected, along with "Air4kids", a solution proposed by VentilairSec which implements NanoSense IAQ probes to control an innovative VentilairSec VMI system.

Emergence of Autonomous Products in the Building Industry

In these energy efficiency policies for buildings, the installations (the envelope, heating...) must not be the only contributors, building automation can contribute to 30% energy savings. It must therefore be possible to multiply the number of sensors for automated systems (presence sensors, window opening sensors, IAQ sensors, T° sensors, etc.) at low cost.

The installation of a wired probe costs almost as much as the probe itself. The use of autonomous energy sensors is therefore a cost-effective way of deploying automation in the building. Moreover, this deployment is rapid and non-invasive (business continuity in the tertiary sector).

This is why NanoSense has been investing for several years to create autonomous products for buildings and their users!

NanoSense has developed an IAQ probe (CO2, VOC, T°, RH) entirely powered by ambient light. It communicates by radio according to various low consumption standards including EnOcean.

To complete the ecosystem, a controller display also self-powered by ambient light was also created.

These products are designed to last more than 10 years, but theoretically infinite! In addition, they continue to function, even during a prolonged absence, for 60 days in the dark.


We have seen here the need to control the different means of ventilation mainly due to the increased airtightness of buildings with a view to energy efficiency. However, energy efficiency should not be achieved at the expense of good air quality. It would be wise, in this respect, not to over-ventilate permanently for fear of intoxicating the occupants. We have seen that the existing system, in terms of ventilation control, was at best content to control in Humidity or CO2.

This control is far from being optimal, which is why it is preferable to use ventilation control solutions using multi-pollutant detection (CO2 + VOC + PM) and control intelligence integrated into the sensors.

For these solutions to be democratized, it is important to take several factors into account, the sensors and their deployment must be cost effective, access to IAQ data in intelligible terms must be democratized through simple and direct access. In order for the occupants to be enlightened actors of their IAQ, it seems necessary to use a visualization of Air Quality data in physiological impacts on smartphones or tablets.

The integration of Outdoor Air Quality, cocktail effects and energy consideration seems to us to be the future in terms of representation and management of Indoor Air Quality.

Find here the article on the Construction 21 website!

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Our press release 2020.

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Article written by Alliance HQE

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