Basic Requirements for HVAC Systems for Healthy Indoor Air Quality
On average, we spend about 90 % of our lives indoors and breathe in around 12,000 liters of air every day. We assume that the air in buildings is "clean" and will not harm our health, but this is not always the case. Astonishingly few users and operators of buildings actually know the quality of the indoor air at their premises, or how this may be impacting their productivity or wellbeing. Essential variables such as humidity, CO2 content, or VOC concentration are hardly ever measured, and even less often displayed.
Belimo consulted leading engineers and experts in the ventilation sector around the world to identify the priorities for creating a healthy indoor air environment in a building. Through this process, the seven essential factors for ensuring healthy indoor air in non-residential buildings have emerged.
- Continuous and reliable measurement, display and monitoring of indoor air quality
- Accurate amount of air to the zone and controlled removal of contaminated air
- Well designed air dilution and airflow pattern
- Active pressurization of envelope and spaces
- Correct temperature and humidity conditioning
- Effective filtration
- Proper amount of outside air
1. Continuous and reliable measurement, display and monitoring of indoor air quality
Ideally, air humidity, CO2 content or VOC concentrations are measured by sensors, to monitor safe levels and ensure healthy indoor air. This is because only measured variables can be controlled. 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.
It is important that relative humidity indoors is held between 40-60 %. In 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 at a shorter distance. In addition, many bacteria and viruses are considerably more contagious in dry air, as mucous membranes dry out when there is a lack of moisture, weakening the immune system.
A CO2 concentration of more than 1,000 ppm (parts per million) decreases the brain's ability to concentrate and, at 2,000 ppm and higher, it can lead to fatigue or even headaches. The CO2 level in indoor air is also an excellent indicator of potential biocontamination by infectious agents, such as COVID-19. If the CO2 value is high due to increased occupancy and limited air exchange, there is a greater potential risk of infectious aerosols.
Volatile organic compounds (VOCs) originate from many different sources, including perfumes, paints, printers, carpeting and building materials. Even low concentrations of VOCs can irritate the eyes, nose or throat, and indicate insufficient fresh air intake.
It is essential to measure these variables using suitable sensors so that appropriate measures can be implemented – such as ventilation, purification or humidification.
2. Accurate amount of air to the zone and controlled removal of contaminated air
Central ventilation units usually supply air to several zones in a building. It is important that each room receives the exact amount of fresh air it needs to maintain healthy indoor air quality. If the number of people in a room increases, e.g. in a large meeting room, one would expect the air supply to increase accordingly. Similarly, the polluted air must be removed from the room. To ensure this, zones and rooms must be individually supplied with variable air volume (VAV) control. For example, if a room sensor detects excessively high CO2 content, the VAV units are opened, and the room is flooded with additional fresh air.
3. Well designed air dilution and airflow patterns
The way the air flows into, through and out of a room is an important factor. Ideally, fresh air flows undiluted from the bottom up, past a person, then is extracted directly from the room above. It must be ensured that air does not "swirl" around the room several times, or become trapped in certain zones of the room. Modern airflow simulations enable typical flow patterns in a room to be studied in detail. The correct design, placement and orientation of air outlets can help to maintain healthy indoor air quality.
4. Active pressurization of envelope and spaces
Air hygiene in a room is negatively affected by unwanted air currents entering a zone from outside (e.g. a busy road) or from other rooms (e.g. a cafeteria). This typically occurs when air pressure ratios are not properly balanced. There has been much discussion about "cross-contamination" between different rooms in connection with the spread of COVID-19 aerosols inside buildings. The use of VAV controllers in the supply air and extraction of air from a room, as well as the use of differential pressure sensors and controllers between zones, can prevent such undesired airflow.
5. Correct temperature and humidity conditioning
In a central ventilation system, the supply air can be conditioned to the desired temperature in the air handling unit (AHU) relatively precisely, by 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. If aerosols or viruses present in a room encounter dried-out mucous membranes, the risk of infection increases considerably. It has also been shown that viruses on dry surfaces survive longer than under more humid conditions. Proper humidification of the room air (40-60 % relative humidity) is therefore essential for safe indoor air.
6. Effective filtration
To prevent contaminants from entering indoor spaces through supply air ducts, filters must be integrated into the air handling unit. In systems where part of the extract air is mixed back into the supply air, suitable filters must be used to prevent contamination from infectious microbes (for example, HEPA filter H13 pursuant to EN1822:2009). To ensure that monitoring of these filters is effective, pressure sensors and dynamic airflow measurement can be used. If the contamination of the filter increases, the pressure drop across the filter also increases. By simultaneously measuring the volumetric flow through the filter, a relatively accurate statement can be made as to whether and when the filter needs to be replaced.
7. Proper amount of outside air
Today, a large proportion of small and medium-sized non-residential buildings do not have an automated, mechanical fresh air supply. It is often assumed that, from time to time, users ventilate by opening a window. If this does not occur, the concentration of infectious aerosols can greatly increase. A ventilation system with central air conditioning is therefore part of the minimum standard equipment to supply healthy indoor air when planning a new building or renovation. Many countries have issued recommended or mandated standards on mechanical ventilation in commercial buildings, as well as required minimum air exchange rates depending on the type of building and number of occupants (for example ASHRAE 62.1 Ventilation requirements). Other considerations focus on poor inner-city air quality in many countries. Ideally, outside air variables are measured before the air is mechanically introduced into a building. An automated system can supply more outside air when pollution levels from traffic and industry are low, and return to the minimum required ventilation rates when pollution levels increase.
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Our products in use for healthier indoor air quality
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 NEMA 4X / IP65 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.
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