Journey into the interior

Journey into the interior

As we learn to live with COVID-19, improving indoor air quality (IAQ) has been touted as a potential solution in our return to the workplace. Sean McGowan explores the issues with VA Sciences national division director Simon Witts, M.AIRAH; Mechanical project engineer, principal and Australian discipline leader at Stantec Patrick Chambers, Affil.AIRAH; Litmas technical and managing director Claire Bird, Affil.AIRAH; and Probuild technical director Sean Treweek, F.AIRAH.

By Sean McGowan

Simon Witts, M.AIRAH

Simon Witts, M.AIRAH

Patrick Chambers, Affil.AIRAH

Patrick Chambers, Affil.AIRAH

Claire Bird, M.AIRAH

Claire Bird, M.AIRAH

Sean Treweek, F.AIRAH

Sean Treweek, F.AIRAH


What are the links between IAQ and COVID-19? Does improvement of the former lead to better management of the latter, or is this too simplistic?

Witts: Far too simplistic. Linking indoor air quality and COVID-19 transmission is like monitoring how much petrol someone buys and using that as an indicator of whether they are likely to regularly break the speed limit.

You can be in a space with good air movement, good IAQ and still have a good chance of COVID-19 transmission. The factor that IAQ does not account for is time. If you are in a room with an infectious person for a few hours, it doesn’t matter how good the air quality is. I accept that poor IAQ can indicate poor outside air ventilation and in a poorly ventilated space the chances of transmission are way higher than in a well ventilated one. But saying IAQ is an indicator of likely disease transmission is an oversimplification.  

Treweek: Although a simplistic view, studies suggest solid links between IAQ and COVID-19, and that improving IAQ can significantly reduce aerosol COVID-19 transmission.  

Bird: Indoor air quality is determined by gases and particles that only become hazardous when they exceed a certain concentration. COVID-19 is released on very small particles of mucous when we vocalise, cough or sneeze, so the only physical measurement we can make that is linked directly to COVID-19 transmission risk is the number of airborne particles small enough to be inhaled or reach our lungs.

Transmission reduction from viral-laden so-called aerosol particles can be achieved by particle filtration, or by introducing virus-free or particle-free air at a suitable rate to remove the virus before it is inhaled. At present we do not have a safe level of airborne virus, nor any way of reliably measuring active airborne virus, even indirectly. Therefore, we have no deployable virus warning systems to alert us to unsafe conditions.

Groups such as OzSage and other scientists suggest monitoring exhaled carbon dioxide levels in a room on the basis that exhalation is the source of the virus.

Carbon dioxide build-up from building occupants is a long-recognised cause of poor indoor air quality, and underpins the ventilation industry. If we keep carbon dioxide levels low, we are assuming that we will also be diluting airborne infectious agents; however, we have yet to demonstrate a direct link between viral and carbon dioxide levels. However, by ventilating we will also be diluting other indoor contaminants from furnishings or chemicals used in the building. Ventilation, however, does not always reduce risks of mould growth. Special consideration should be given to moisture control when deciding if HVAC control for COVID-19 will improve overall air quality.

Chambers: The real risk of COVID-19 transmission via airborne means is fundamentally dependent on the quantity and concentrations of suspended respiratory aerosols in air over time. This is one facet of indoor air quality, but far from the entire picture.

Traditional mechanisms for maintaining IAQ such as increasing outside air dilution rates and filtration efficiency in air handling equipment is helpful for reducing the quantity of suspended respiratory aerosols, but potentially not the most effective solution for this problem specifically.


Given commercial HVAC systems are designed for thermal comfort and energy efficiency rather than infection control, are we expecting too much of existing systems to manage COVID-19 without radical changes being made?

Treweek: Fundamentally, commercial HVAC systems are not close-controlled systems to maintain infection control. Although we may be able to tweak or improve the systems to increase outdoor air rates or filtration efficiencies, without major changes to pressure regimes, air distribution paths to avoid mixing, etc., the ability to manage COVID-19 through existing systems is limited.

Chambers: There are always limitations in what can be achieved within the constraints of existing infrastructure, and it is naïve not to consider the importance of this. Solutions therefore need to be grounded in practicality and context, or they simply won’t get applied. This is why industry and academic partnerships are so important in driving solutions.

However, it should not be considered as “expecting too much” that we strive for workable solutions. One of the fundamental tenets of a professional institution is public service – to put the public good before financial reward and professional convenience. I therefore do not think it is too much to expect that the HVAC industry adapts as necessary to address the problem of airborne disease transmission in buildings. It is our obligation inherent in adopting the ‘V’ within our headline acronym.

Witts: We don’t design commercial buildings to accommodate sick people, and we shouldn’t. The ventilation rates in AS1668.2 reflect that.

Designers could do a lot more to prevent infection spread in a building within the constraints of AS1669 for outside air. If you asked most commercial building HVAC designers when they last considered the direction of air movement within a design, you’d get some blank looks. Just simple changes could make a difference. For example, in buildings where there is a staff-to-public interface, make sure the airflow is from the staff spaces toward the public spaces.

This obviously only works where sick people don’t come to work, or with diseases that show symptoms before they are infectious (this is one of the reasons the Omicron variant has spread so efficiently, because you are already spreading the virus before you feel unwell). This also doesn’t have to be about COVID-19, making these changes will reduce sick days in the winter from coughs/colds and influenza. If it makes money, why not do it?

“If you asked most commercial building HVAC designers when they last considered the direction of air movement within a design, you’d get some blank looks. Just simple changes could make a difference.”


What would be the cost to thermal comfort and energy?

Witts: If we were to just bump up outside air rates – significant. Per square metre, hospitals consume far more energy than a commercial office, and a good proportion of that is due to the higher ventilation requirements. 

Chambers: Thermal comfort and air quality have traditionally been addressed with similar solutions; however, they are different problems.

A key constraint associated with increasing outside air dilution rates is that the energy penalty is somewhat linear, whereas the benefit in reducing relative risk follows the Wells-Riley asymptotic relationship. Un-checked increases to outside air dilution rates becomes cost-prohibitive quite quickly. Hence, the industry should be considering a myriad of solutions applied on an application-specific basis.

Treweek: Designing/modifying commercial buildings to operate in a similar fashion to close-controlled laboratories and thereby improving infection control, will have a significant impost to thermal comfort and/or energy efficiency. Systems become more complex, larger and more costly, with far greater spatial impact.

In a competitive leasing market, this throws a whole new set of market dynamics into the mix, and potentially disrupts the viability of a particular office building or development in the market.

Bird: To increase ventilation in naturally ventilated spaces with split systems, we face the challenge that if windows are open and cooling or heating demand increased, the cost of energy and the greenhouse gas footprint of a building may raise significantly. As climate change poses an even greater challenge than COVID-19, we need to focus on technologies that improve air quality without compromising our energy requirements. Filtration plays a role in naturally ventilated environments where thermal discomfort can create its own health risks from hypothermia and heat stress.


With the emergence of technologies such as Needlepoint Bipolar Ionization (NPBI), UVC disinfection and others, will they become part of the future mix of strategies as we learn to live with COVID-19? Stantec’s Patrick Chambers, Affil.AIRAH, Litmas’s Claire Bird, Affil.AIRAH; Probuild’s Sean Treweek, F.AIRAH; and VA Sciences’ Simon Witts, M.AIRAH, discuss.

Chambers: It is hard to imagine a future where sterilisation and disinfection technologies don’t play a role. These types of technologies are commonplace in the water quality industry, so why not air quality? I think the question is to what extent and in what applications.

As we come to get a better handle on the performance and shortfalls of these types of systems, their application will become more commonplace. What is missing currently is an independent certification framework and recognition within legislative frameworks such as Australian Standards that will enable designers to specify these products with confidence of their performance.

Witts: Upper volume UVC is appropriate in spaces that are designed to accommodate it. It has been using effectively to mitigate tuberculosis (TB) transmission in emergency departments for years.

In duct systems such as NPBI and UV are ok if the source of contamination is in the duct. But if you are dealing with a contaminant that is in the building that is aerosol based (i.e. people), a decent filter in the AHU sorts that out without all the maintenance.

Bird: We need to ensure that any technologies we recommend have demonstrated and measured effectiveness against any claims they are making. Demonstrating that a technology removes particulate matter from air is different to demonstrating that it has reduced an active virus to a safe level. We do not currently have acceptable methods to measure active virus from an air sample, so any technology that claims to reduce transmission risks to a safe level is likely making claims based on other factors which may or may not be proven to be linked to infection risk. 

Pathogens include bacteria and fungi too. The benefit of reducing overall microbial load in our HVAC systems extends beyond this current pandemic.

Some technologies also change the chemical make-up of the air, especially where we introduce gases from products such as adhesives and cleaning products. Establishing that a given technology does not worsen air quality under common scenarios such as when using air freshener, should be part of any tests or claims made by a technology provider. This applies to current and future HVAC innovations.

Treweek: It could be argued that air cleaning/disinfection technologies may have a role to play in commercial HVAC, however may be more relevant in a retrofit situation where filtration or air change rates are not able to be easily improved.

Office workers during COVID-19


Has there been too much focus on thermal comfort in the past and not enough on health? Where does the right balance exist?

Witts: Having been a healthcare facility designer for 35 years, my immediate instinct is to say yes. However, hospitals are a very small part of the building portfolio.

Commercial buildings must look after more than just the people in them, and in a climate like Australia’s that takes energy, and the environmental impact of that energy use is potentially way more deadly than COVID-19 has been. There must be a balance – loosening of fan energy targets in the NCC or Green Star to allow oversizing of fans so that when more outside air is needed the systems can provide it, might be an answer. But that energy must be offset somewhere else in the design. 

Another alternative would be widening the thermal comfort criteria to relax energy use. Why do we need rooms to be at 24˚C when it’s 34˚C outside? The answer is in most buildings we don’t, it’s just we have got used to the convenience and comfort of it.  

Chambers: Thermal comfort is a key part of occupant health and well-being, and has traditionally attracted more focus than indoor air quality in the industry because it is more easily recognised by our bodies. The pandemic has brought renewed focus on the importance of IAQ and health. Our understanding of this relationship will continue to expand in the coming decades, as advancements in technology and digital data interrogation techniques drive more rigorous population-level epidemiology than has ever been possible before.

I suspect the secrets of air quality and health are yet to be fully realised, and when they are it will drive significant fiscal investment from the public and private sector.

Treweek:In years gone by, thermal comfort has taken the front seat. However, over the past decade elevated focus around wellness has come to the fore. This wellness focus does bring with it design around health aspects in a balanced manner. Overt design for infection control in a commercial HVAC environment could be seen as far too stringent; however, design for occupant wellness does provide a good balance, and one in which the market already understands and can factor into new developments.

Bird: The Omicron wave is thankfully passing; however, CSIRO is predicting a likely new variant, or variants, in the winter months. While we are all hopeful that new variants may be less harmful, we have no guarantee of this from scientific evidence to date.

HVAC systems are designed for thermal comfort and ventilation. Thermal comfort in turn reduces physical and psychological stress and so has a positive impact in health extending beyond air quality.

We have a wonderful opportunity in the HVAC space to reduce disease transmission by introducing appropriate technology to allow us to manage energy efficiency, climate change and health. The real balance is one between risk and opportunity.


Has COVID-19 made activity-based working (ABW) less or more palatable?

Treweek: From a purely reactive perspective, activity-based working has been hampered by COVID-19 over the past couple of years. However, with a major uptick in flexible working arrangements, when staff come into the office it is often for a specific reason, activity or experience. It could be argued that this will drive more offices to cater for ABW in response to these flexible working arrangements.

The value of being in an office for interactions is becoming much more prevalent, and office design will need to cater for the aspects of community, problem-solving and innovation, rather than just providing a desk for everyone with some ancillary spaces. As we learn to live alongside COVID-19 and maintain strong hygiene practices, negative perceptions around shared spaces are reducing.

Witts: Before COVID-19 a lot of companies – aka managers – said working from home and activity-based working would harm productivity and would take years to implement. Along comes the pandemic and it happens overnight, and in my experience productivity increased. It will be hard for companies to insist on everyone being back in the office, and employers who offer the flexibility will end up being the employers of choice. And it is hard to get people at the moment.

Bird: Activity-based working allows us to devise local air quality control and resource allocation strategies that protect multiple workers. Activity-based air monitoring can also be employed to reduce overall daily exposure risks across a range of planned activities.

Chambers: Activity-based learning is about empowering employees to vary their work setting to suit the work they are doing. Pandemic-led lockdowns haven’t specifically helped people do this, but it has helped change the mindset of workforce efficiency being dependent on high-density office occupancy. Provided lockdowns don’t continue, I think the awareness that people can be productive with workplace flexibility will in the long run support more activity-based working.

The four Ds

Dr Claire Bird, M.AIRAH, is a member of AIRAH’s IAQ STG.

Here she talks about the four Ds of indoor ventilation.

To prevent airborne spread of infections, of which COVID-19 is only one, we need to do an assessment based on density (of people), distance (from each other), duration (of time spent with an infected person) and dilution (ambient and respiratory air filtration and ventilation) – the four Ds of reducing airborne transmission.

It is vital to work out which of these may work for you. A mechanically ventilated space is different to one with a split system and openable windows.

“AIRAH is teaming up with the global Integrated Biosciences and Indoor Environment Consortium (IBEC). IBEC and the AIHA recently produced a CDC-funded series of free simple online exercises based on the four Ds through which you or your organisation can find the best risk-management strategy for you particular setting. While the assessment looks at filtration and ventilation, it also considers the other control measures you can put in place and helps you prioritise. This Commit-2-Care program is easily accessible and provides a certificate upon completion.


Is there a role for task air conditioning here – we don’t hear much about it anymore?

Witts: There’s a blast from the past! It brings to mind incredible moustaches and Merv Hughes.

Task air conditioning provides local comfort air conditioning, not local ventilation suitable for prolonged infection control. The move to activity-based working may lend itself to this – i.e., if only half the team are in the office, air condition the spaces being used, not the whole floorplate, and there’s your energy saving, allowing the system to have bigger fans with redundant capacity in case you need to accommodate increased outside air or upgraded filters in flu or COVID season.

Chambers: The concept of task air did re-appear in literature recently under the guise of ‘personalised ventilation’ at the workstation (A paradigm shift to combat indoor respiratory infection – Morawska et al., 2021).

While I feel there is some merit in this, a far more effective solution would be to flip this on its head and consider workstation exhaust/filtration to remove the aerosols from as close to the source as possible. Our initial internal research and modelling suggests this approach yields significantly lower total suspended aerosols in the room than other more mainstream strategies such as increasing outside air ventilation.

Treweek: Traditionally, task air conditioning has been designed around thermal comfort so provides little benefit in terms of infection control.



Have any real lessons yet to be learned about COVID-19 and commercial HVAC? Do we need more studies/investigation into COVID-19, IAQ and workplace culture?

Bird: Politicians globally have focused on human diagnostics and vaccination. They have chosen to underplay airborne transmission and the ability of our built structures to reduce the impact of the pandemic on our critical workers and supply chains.  We need to better understand the interplay between the three future HVAC pillars – achieving reduced emissions, providing thermal comfort and keeping us healthy. To achieve an overall picture of this interplay may require a coordinated and substantial research program.

Witts: It would be good to spend some time exploring the COVID-19- considered office of the future. What does it look like, how do we match the needs of energy, activity-based working and infection control?

It needs to be a multi-disciplinary study and one we’d love to be part of. 

Treweek: We now understand enough about the transmission and control of COVID-19 in indoor environments and the impact it has on commercial HVAC. The industry will optimise its response as we move forward and new developments commence their design processes. It’s an evolution rather than a revolution.

Chambers: There have certainly been lessons learned, but there is still a long way to go. More investigation is needed to expand the knowledge basis of virus-laden aerosols released from human expiration including their size distribution, viral content and infectivity as a function of temperature and humidity. From a better understanding of this, we can then apply more rigorous quantitative assessment of engineering controls – such as ventilation system configurations and disinfection technologies – and undertake application-specific risk assessments for different building types and uses

I do not think we will arrive at a “one solution fits all” conclusion. With an appropriate knowledge base, solutions will be bespoke and application-specific.

“Possibly the one good thing out of all this could be the death of the “office warrior” mentality. It’s not OK to go to work and soldier on dosed up with Panadol and get through the day.”


After last year’s aborted return to the office – at least in Victoria, and to some extent NSW – what now?

Witts: I wish I knew. COVID-19 is probably here forever in some form or another, as it continues to mutate, and the variants roll around the globe as endemic diseases do. Vaccine inequity means there will always be places in the world where populations are vulnerable, and that will almost inevitably lead to new variants. Get used to having a COVID-19 shot as we do with influenza.

Possibly the one good thing out of all this could be the death of the “office warrior” mentality. It’s not OK to go to work and soldier on dosed up with Panadol and get through the day. It used to be seen as a mark of dedication to the company. If it’s now viewed as an act of pure selfishness. I’m all for it.

Treweek: The workplace as we know it will evolve. Office workers will expect a more flexible way of working and commercial offices will be fitted out accordingly. Will this change the fundamental drivers of commercial HVAC? I don’t think so.

We’ve already seen a push towards wellness as a key design driver for commercial HVAC and that will continue, albeit potentially with a more rapid uptake.

Chambers: We should not get complacent. It is obligatory of the HVAC industry to work to address the issues of infectious disease transmission in buildings. Not only because of the COVID-19 pandemic, but also to mitigate other more endemic issues such as sick building syndrome.

Bird: When we decommission buildings for indefinite time periods, we need clear procedures to prevent indoor air quality risks upon return, such as risk of catching Legionnaire’s disease or of mould build-up. We need to keep up with scientific information and advice on what may lay ahead, as the information is out there to help us prepare for the next variant should it arise.


What are the best ways that workplaces might manage COVID-19? Could changes to filtration, increased ventilation rates, occupancy densities and the like be the best approach?

Sometimes the simplest method can prove to be the most effective solution.

For Simon Witts, M.AIRAH, the best way of dealing with COVID19 in the workplace does not involve sophisticated technology nor elaborate techniques.

First of all, if you feel unwell don’t come to work – get tested,” Witts says. “What you can achieve with your systems is dependent on multiple factors – when it was designed, the type of system, and the spare capacity in AHU motors and coils.

“If it’s a system designed to the limit to minimise energy use, it will not have the flexibility to increase outside air to the amounts needed to make a difference to infection spread. Before 2020, how often do you remember someone saying, “There is a cough going round the office? More than once I’d wager.”

Stantec’s Patrick Chambers, M.AIRAH, says when it comes to traditional offices, there is a bias towards thermal comfort.

“The problem of suspended respiratory aerosols in air starts with the source – us,” Chambers says. “The impractical but best outcome would be to stop aerosols being emitted into the room air entirely. The next best thing would be to stop them spreading throughout the entire volume of the room/building. Unfortunately, traditional HVAC design philosophy is to dilute, mix and ubiquitously spread room air around. This is a thermal-comfort-bias solution.

“Not enough focus has been given to more local solutions such as desktop extraction/filtration systems to remove as many respiratory aerosols as possible from as close to the source as possible. While the industry catches up with how best to achieve this, perhaps the simplest way that workplaces can better manage COVID-19 is via simple off-the-shelf portable air purifiers to be mounted on workstations.”

Probuild’s Sean Treweek, F.AIRAH, says start with the basics.

“Reinforcing public health measures such as social distancing, contact tracing, mask wearing, isolating if feeling unwell and the like is perhaps the strongest way workplaces can manage COVID-19; in conjunction with flexible working arrangements such as staggered work hours and locations,” Treweek says.

“Where staff are attending workplaces, then improvements to IAQ through filtration rates, outdoor air rates, humidity control etc., do have a positive impact.”

Would you like to know more?

To read Propagation of droplets in an HVAC system by Simon Witts, M.AIRAH, and Sam Coleman, click here.

Ecolibrium has explored COVID across several editions now, including in the cover stories from August-September 2020 and May 2021. AIRAH members can visit to read them.

Ecolibrium cover – April 2022

This article appears in ecolibrium’s April 2022 issue

Want to read more?


Click here to view our archive of issues and features.


Become an AIRAH member or subscribe to Ecolibrium.

What lies beneath

What lies beneath

Geothermal cooling is relatively underdeveloped in Australia, but as Ecolibrium staff writer Nick Johns-Wickberg discovers, its potential is huge.

Esteemed air

Esteemed air

AIRAH’s APER has been approved to register engineers in the ACT.

An eye for innovation

An eye for innovation

As CEO and co-founder of Conry Tech, Sam Ringwaldt, M.AIRAH, is rethinking our approach to HVAC&R.

Meet the experts

Meet the experts

Mitsubishi Heavy Industries Air-Conditioners Australia, (MHIAA), is celebrating its 25th anniversary in 2024, with some special celebrations planned for ARBS.

The fans of Sydney

The fans of Sydney

Ecolibrium staff writer Nick Johns-Wickberg explores how a mobile cooling hub in the Harbour City prevented three medical emergencies this summer past.

Cool comfort

Cool comfort

Federico Tartarini is Senior Research Associate at the Heat & Health Research Incubator, Faculty of Medicine and Health, at the University of Sydney. And soon he’ll be starting a new position as a Sydney Horizon Fellow, Senior Lecturer at the School of Architecture, Design, and Planning, also at Unisyd.