Introduction
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 IAQ sensors (CO2, VOC, T°, RH, Radon, PM) with control algorithms (ventilation and heating/climate) 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.
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. The latter, even if it represents only 2% of our body weight, consumes 20% of the oxygen in the air we breathe via the bloodstream. The blood also provides other food for the brain, which it feeds frugally.
The volume breathed in a single day represents a volume of 15m3 of air. The developed surface area of our lungs is about the size of a tennis court. This gigantic surface is very porous and absorbs, in addition to Oxygen, 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 bottom of our bed in a month. For example, by breathing in alcohol vapours (one VOC among others) you can quickly become drunk, not to mention the drugs you inhale.
All these elements absorbed by respiration are carried by the blood to feed mainly our brain.
For this reason, poor indoor air quality impairs cognitive function and productivity, in addition to its more well-known impact on health.
For example, a concentration of 1000ppm of CO2 (the air we breathe out), which is the regulatory threshold for a classroom, corresponds to a reduction in cognitive functions of more than 23%. When you consider that in a classroom it is common to reach more than 3000ppm after one hour of class, 3x more than the regulatory threshold, it is not surprising that students perform poorly. Very high CO2 levels are also reached in a bedroom with a closed door, which affects the quality of sleep, even for infants who ventilate as much as we do.
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 62,000 deaths per year in France (i.e. 20x more deaths than on the roads!). 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).
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.
State of the art ventilation control
Until now, air leakage from buildings has been sufficient to ensure uncontrolled but sufficient ventilation at the cost of significant energy expenditure. Efforts to reduce energy consumption have begun to create awareness of the importance of indoor air quality.
Due to their cost and maintenance constraints, double flow CMVs (Mechanically Controlled Ventilation) (controlled incoming and outgoing air, often accompanied by a heat exchanger) may never become established in the residential sector, which is why CMVs and MVVs (Mechanically Insufflated Ventilation - blowing rather than extracting) with no heat recovery must be controlled more than any other with IAQ (Indoor Air Quality) probes according to needs.
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 health and olfactory comfort. 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! Valeric acid (VOCs contained in perspiration), 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 a good ventilation regulation must also take into account the indoor humidity that can affect the building (mould, ...) and the occupants: dry skin, lips and irritate mucous membranes and respiratory tracts.
Naturally, the NanoSense IAQ probes integrate ventilation controls on exceeding multi-pollutant thresholds CO2, VOC, Humidity, PM1, PM2.5 and PM10...
To go further: 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, ventilation can be triggered without any of the pollutant thresholds being exceeded if the overall impact is greater than the desired setpoint.
Focus on the impacts of Air Quality
We have seen that an optimal representation of Air Quality takes into account several pollutants, but how can we compare different pollutants and "different cocktails"?
It is therefore essential to find a simple and intuitive way to represent IAQ that takes into account several pollutants and a "cocktail" effect of these pollutants.
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.
A representation in the form of physiological impacts can then emerge thanks to the various quantified interactions of pollutants in one or other of the impacts presented here:
It would thus be possible to continuously monitor the evolution of health and productivity in a building or an entire building stock!
Consideration of Outdoor Air Quality (IAQ: Atmospheric Air Quality)
With frequent pollution peaks in urban areas and wood fires and pesticides in rural areas, is it still relevant to open the window (or switch to "fresh air") to improve Indoor Air Quality? Instinctively, you'd say no, and you'd be right! But it depends on the times, the geographical location and even the direction of the wind!
It is therefore necessary to compare the Indoor Air Quality and the Outdoor Air Quality before making the choice to open the window (or to ventilate)! But knowing that the pollutants are not the same, how can we compare "cabbages" and "potatoes"?
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 unfiltered ventilation. Particles affect not only cognitive functions but also long-term health. The compromise therefore concerns consequences of a completely different nature for very different exposure times.
We come back to our global indicators capable of taking into account different pollutants and quantifying their impacts and the use of outdoor air quality probes.
Synthesis
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 therefore be wise 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 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 January 2020 edition of the magazine in its entirety.
