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The 7 Essentials of Healthy Indoor Air

Basic requirements for HVAC systems for healthy indoor air quality.

On average, we spend around 90% of our lives indoors and breathe in around 12000 litres of air every day. We also assume that air in buildings is clean and that it does not have a negative effect on our health. It is therefore very surprising how little users and operators actually know about indoor air quality at their premises. Essential variables such as air humidity, CO2 content or VOC concentration are hardly ever measured and even less often displayed.

Belimo interviewed consulting engineers and experts in the ventilation sector around the world to find out what the priorities are when aspiring to create a healthy indoor air environment in a building. In the process, 7 essential factors for ensuring healthy indoor air in non-residential buildings have emerged.

1. Indoor Air Quality (IAQ) and comfort measurement, visibility and monitoring. 
2. Precise amount of air flow to the zone and controlled removal of contaminated air.
3. Good air dilution and air-flow pattern.
4. Consistent pressurization of envelope and spaces.
5. Correct temperature and humidity conditioning.
6. Effective filtration.
7. Proper amount of outside air.

1. Indoor Air Quality (IAQ) measurement, visibility and monitoring

Ideally, air humidity, CO2 content or VOC concentration are measured by sensors for the monitoring of air quality. This is because only measured variables can be regulated. From today's point of view, both the measurement and the display of these values should represent the minimum standard for indoor air quality measurement.

Air humidity
It is important that relative humidity indoors be between 40-60%. It is important that relative humidity indoors is held between 40-60%. In too dry air droplets from an infected person speaking or sneezing easily evaporate and the contained virus travels further in the room as a light aerosol. If the humidity is higher droplets do not evaporate as quickly and fall to the ground before the person. In addition, many bacteria and viruses are considerably more contagious in dry air, as the drying-out of mucous membranes caused by excessively dry air weakens the immune system.

CO2 concentrations of more than 1000 ppm (parts per million) decreases the brain's ability to concentrate; starting at 2000 ppm and higher, it can lead to further concentration difficulties, fatigue or even headaches. In addition, CO2 concentration in indoor air is an excellent indicator of potential bio-contamination, for example from COVID-19 viruses. A high potential risk from infectious aerosols is to be assumed if the CO2 value is high due to the presence of large numbers of people and little air exchange.

Volatile Organic Compounds (VOCs) are organic compounds that originate from many different sources, including perfume, paint, printers, carpeting, building materials and smoke.
Even low concentrations of VOCs can cause irritation to mucous membranes (eyes, nose and respiratory tract) as well as headache, fatigue and nausea.

It is essential to measure these variables using suitable sensors so that appropriate measures can be implemented, for example, ventilation, air purification or humidification.

2. Supplying and discharging the exact amount of air in a zone

Central ventilation units usually supply air to several zones in the building. It is important that each room receives exactly the amount of fresh air it needs. If the number of people in a room increases, e.g., in a larger meeting room, we expect the air supply will be increased accordingly. Similarly, the polluted air must also be removed from the room. To ensure this, zones and rooms must be supplied individually with variable air volume (VAV). If, for example, a room sensor detects excessively high CO2 content, the VAV units are opened and the room is flooded with additional fresh air.

3. Optimal air distribution in the room

When it comes to air hygiene, the decisive factor is the way in which the air introduced into a room flows through that room and then exits it again. Ideally, fresh air flows from the bottom up past a person and is then extracted directly from the room. It must be ensured that indoor air does not "swirl" around the room several times or become trapped in certain zones of the room. Modern air flow simulations enable typical flow patterns in a room to be studied in detail. The correct design, placement and orientation of air outlets can help prevent major air hygiene errors.

4. Correct overpressure and negative pressure

Air hygiene in a room is also negatively affected by unwanted air currents entering a zone from outside (e.g., from a busy road) or from other rooms (e.g., from a canteen). This typically occurs when air-pressure ratios are not properly balanced. Especially in connection with the spread of COVID aerosols in buildings, much discussion has taken place regarding «cross-contamination» between different rooms. The use of VAV controllers in the supply air and extract air of rooms and the use of differential pressure sensors and controllers between zones can prevent such unwanted air currents.

5. Correct conditioning of temperature and humidity

In a central ventilation system, the supply air can be conditioned relatively precisely to the desired temperature in the Air Handling Unit by the heating or cooling coils. High-quality control components at the coils such as the Belimo Energy Valve™ ensure that this is not only done with high precision but also in an energy-efficient manner.

In addition to temperature, humidity is also crucial for healthy indoor air quality. If aerosols or viruses present in a room encounter dried-out mucous membranes, the risk of infection increases considerably. It has also been scientifically proven that viruses on dry surfaces survive considerably longer than under more humid conditions. Proper humidification of the supply air (40-60% relative humidity) is therefore an essential factor for safe indoor air.

6. Proper air filtration

To prevent dust from entering indoor spaces through supply air ducts, proper filtration must be implemented at the air handling unit. In systems where a part of the extract air is mixed back into the supply air, suitable filters must be used to prevent contamination from infectious microbes (HEPA filter H13 pursuant to EN1822:2009). To ensure that the filtration remains effective and clogged filters do not decrease the energy-efficiency of the ventilation plant, monitoring of these filters is a must. It is highly recommended to use pressure sensors and dynamic air flow measurement in parallel. If the filter gets clogged and the risk of contamination at the filter increases, the pressure drop across the filter also increases. By simultaneously measuring the volumetric flow through the filter, a relatively precise statement can be made as to whether and when the filter needs to be replaced. This allows for a more efficient, demand-based filter maintenance strategy; filters are replaced timely and when really needed rather than on a fixed time scheme.

7. Correct amount of outdoor air for the building

A large proportion of smaller and medium-sized non-residential buildings today do not have an automated, mechanical fresh air supply. It is too often assumed that users ventilate with a window from time to time. If this does not occur, then the concentration of infectious aerosols can greatly increase. A ventilation system with central air conditioning should therefore be considered part of minimum standard equipment when planning a new building or renovation. Many countries have therefore issued recommended or even mandated standards on mechanical ventilation in commercial buildings and required minimum air-change rates per, depending on the type of building and its occupation.

Learn more about indoor air quality and its impact on health from Eddy

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Influence of indoor air quality on our health

People spend approximately 90 percent of their time indoors, and breathe 12000 litres of air per day. It is therefore important to understand the powerful influence that indoor air quality has on our well-being. Belimo shares its deep insights into the effects of indoor humidity, VOC and central air treatment systems and offers valuable suggestions for your health.

A study on the influence of air quality in schools

The platform joined forces with the Zurich Teachers' Association (Züricher Lehrerverband) and the Zurich Lung Organization (Organisation Lunge Zürich) to discover how air quality affects schoolchildren and teachers. In November 2016, installed measuring devices in over 250 classrooms.

Read the study to see how the mere installation of these measuring devices affected the ventilation habits of teachers and pupils.

Our products in use for healthier indoor air

Belimo Sensors – The Foundation of Comfort

Belimo HVAC sensors offer the highest level of reliability, easy installation and seamless integration into common building automation systems. The innovative housing design allows for quick and tool-free installation, easy commissioning and provides IP65 / NEMA 4X protection. The product range includes precise sensors for measuring temperature, humidity, pressure, CO2 and volatile compounds (VOCs) as well as the flow in pipe and duct applications.

Refer to the regional websites for more information: