The role of air-conditioning systems in the regulation of indoor air quality in typical commercial office space
By Edward Hector
As vaccinations roll out and we return to life in the “new normal”, indoor air quality and ventilation will be a key determining factor in convincing people to return to public spaces.
Indoor air quality and air-conditioning systems are much more complex than one would think. The purpose of this article is for you to take a more holistic approach to indoor air quality.
Green building ratings have primarily been focused on water, waste, and energy, with a certain amount of recognition of Indoor Environmental Quality (IEQ). However, Indoor Air Quality (IAQ) is one aspect of IEQ that is receiving considerable attention as a result of the Covid-19 pandemic.
What to do when the threat is airborne
The concern is that a virus that is airborne can be spread via air-conditioning systems. Many property owners and tenants are turning to consultants and service providers to determine how to mitigate this risk.
Some suggestions on risk mitigating strategies include:
- increasing ventilation rates
- upgrading filtration to a High Efficiency Particulate Air (HEPA) filter
- creating a purge cycle to introduce fresh air
- redesigning a chilled water air handling unit system to avoid the return of air that is in the current system – effectively create a full fresh air system
What is needed is a rational approach that minimises the need for a major design change, bearing in mind that most current systems are compliant designs in terms of National Building Regulations.
First, what is indoor air quality
It is important to unpack what indoor air quality is and how air conditioning systems operate.
The World Health Organisation focuses on the particle size you breathe in and measures the amount of particles in the air which is called Particulate Matter (PM). The larger the PM, the less risk is present as your body protects itself through mechanisms such as coughing and sneezing.
We refer to particle size of 10 microns (PM10) as being a standard filter for a building, while the WHO is concerned about the level of concentration of PM2, and smaller, that we are breathing in.
The smaller the size of the PM, the greater the risk. This is because the body is unable to prevent the particle from entering, and a pathogen ends up in your bloodstream.
The current landscape in South Africa
South Africa has high levels of air pollution and fresh air is often not as fresh as we assume. Before you can mitigate the danger of small airborne pathogens, you need to know which PMs are present.
We currently have a range of sensors that can measure IAQ:
- CO2 levels
- PM levels
- Volatile Organic Compounds (VOC)
Only once you know the prevalence levels can you start to address this.
For example, CO2 is caused by people exhaling and you may have to review your design based on occupancy levels while the source of VOC’s may be internal.
Other external factors contributing to poor IAQ may be Carbon Monoxide produced by vehicles or Sulphur Dioxide produced by factories. This is why there is a large focus on reducing vehicle emissions and discontinuing the use of coal fired power stations.
We are starting to have a better understanding of air quality, for example the table below shows an American index used to measure AQI and indicated the 5 key metrics.
There are other indices around the world that can give an indication of various locations such as the one below.
Once we understand the quality of our air, we can improve it with minimum design changes as we now have the technology available to do it.
Ventilation rates are important and we need to consider that the National Building Regulation refers to minimum standards and that research has shown that improved ventilation rates can improve the cognitive ability of occupants. It is necessary to start managing ventilation more dynamically in order to have optimum results under varying ambient conditions and occupancy levels.
This is important because, in terms of Green Buildings, we try to minimize fresh air intake since bringing hot air into a building requires additional cooling, and vice versa, adding to energy consumption.
The balance between a healthy and an energy efficient building is evidently more complex than initially envisaged.
When we speak of indoor air quality, we should not forget outdoor air pollution, as it is intrinsically linked to healthy indoor spaces. A recent study showed that pollution from power plants and vehicles caused close to 9 million deaths globally in 2018 while the total number of Covid deaths is approximately 4,5 million.
The impact on our respiratory systems from particulate matter is a part of the impact of pollution, and a global issue we need to pay attention to.
This is particularly relevant in South Africa, where we continue to see the development of coal fired power stations and the failure to install scrubbing technology on the cooling towers to reduce pollution. In a country with high levels of poverty and rising energy costs, cooking with open fires is also another major contributor to air pollution.
Industry cannot wait on government guidance and will have to take the lead towards healthier Indoor Air Quality (IAQ) and one major criterion to look at is to immediately increase ventilation rates to that of double the minimum standards.
In places like the UAE for example, there has also been talks of setting up certifications and standards for indoor air quality for its towers and skyscrapers. At the core of creating and maintaining proper indoor air quality is a building’s ventilation system.
Ventilation systems function much like the human body – they bring in air and remove air from spaces at specific speeds, volumes, and rates of exchange through mechanical or natural systems. Ventilation systems bring outdoor air indoors, and without proper treatment, pollutants can enter the space.
According to a research institute, approximately 65% of exposure to outdoor air pollution occurs indoors, a staggering statistic. It is clearly important to consider both indoor and outdoor air quality when managing the facilities.
The impact of poor indoor air quality
Poor indoor air quality can be caused by several factors, one of the most dangerous being particulate matter: a complex mixture of small, solid particles and liquid droplets.
Inhaling elevated levels of particulate matter can lead to a multitude of health problems that range from respiratory illnesses to reduced immunity. Exposure to high levels of particulate matter is the leading source of mortality among all outdoor air pollutants.
Aside from the loss of productivity, the potential impact of poor indoor air quality on the immune system is particularly concerning given the pandemic. People need to feel safe in their offices and public spaces in order to return to meaningful economic activity.
How to improve indoor air quality
We need to pay attention to indoor air quality at various stages of the air-conditioning systems’ design and operation.
Poor system design can accumulate mould that can lead to high levels of particulate matter filtering through indoor air over the years. We can also ensure that the design eliminates condensation issues that lead to the formation of mould.
It is also important to ensure that we have the correct quantity of air arriving at the designated destination, by minimising leakages, drops in pressure and ensuring optimal distribution routes.
Ducting systems designed with these principles in mind are able to filter out particulate matter and keep air ducts clean over a long period of time which contributes to improved indoor air quality.
Buildings need to regularly check the levels of indoor air quality through sensors. Monitoring indoor air quality is gaining momentum with the ability to measure temperature, humidity, CO2, Particulate Matter (PM) and Volatile Organic Compounds (VOC’s) at relatively low cost.
Technologies such as air purifiers, bipolar ionisation and UVC Germicidal Irradiation lamps are also gaining traction with clients looking to improve indoor air quality without major system design changes.
The way forward
A conscious effort is needed by the property management industry, combined with possible increased government regulation on particulate matter concentrations in indoor air. This will firmly place HVAC systems and indoor air quality top of mind for building operators, ultimately achieving better indoor air quality than outdoor air quality.
The result? A healthier working environment, improved cognitive ability and productivity, with less time lost due to absenteeism due to the reduction in the spread of pathogens within the workplace.