22nd May 2020
As governments around the world begin to ease lockdown restrictions and consider the roadmap back to “normal” life, it becomes increasingly clear that this will be no mean feat. There are undoubtedly a multitude of factors to consider when ensuring a safe transition back to building occupancy in a post-lockdown world, while preventing the risk of further infection spikes remains the top priority.
As the global economy continues to plummet, a key focus over the coming weeks and months will be on how countries can allow their citizens to return to places of work in a safe and responsible manner. Although many are keen to return to work as soon as possible, it is vital that businesses consider the transition carefully, following the advice of governments and other specialist industry bodies such as CIBSE and ASHRAE.
CIBSE, for example, have published their guidance on re-occupying workplaces from a building services perspective, while the International WELL Building Institute have also issued advice on how strategies from the WELL Building Standard can support in the fight against COVID-19. It is important to bear in mind that the advice may differ across building types, with sectors such as healthcare required to follow their own unique guidance and regulations. Regional variations, such as climate, will also impact on which measures need to be considered.
As IES Consulting are recognised experts in analysing buildings, many clients have already approached us on this issue and are keen to understand how they can best adapt their buildings to adjust to a post-lockdown world. With social distancing measures likely to remain in place until a vaccine for COVID-19 is found, suggestions of more flexible working hours and staggered shift patterns, and heightened concerns around indoor air quality and the risk of cross-contamination between workspaces, we can expect changes in the way we operate and use our buildings. This will have wide-ranging implications, not only for the health and comfort of staff, but also on resultant energy consumption, running costs and carbon emissions.
The scale of potential change may seem overwhelming, and many businesses may be struggling to determine the likely impacts of changes they might make as we navigate through this period. However, modelling can help to remove some of the guesswork from this process and increase confidence in decision making.
We already use building modelling and simulation techniques, such as DSM (dynamic simulation) and CFD (computational fluid dynamics), to perform studies for our buildings on ventilation, occupant comfort, energy, carbon and cost predictions. So, there is no reason why responsible employers cannot run those same simulations to predict the implications of post-lockdown measures prior to implementation, to help plan more effectively for the challenges ahead.
This approach would involve a redefinition of the input characteristics you want to test within a DSM or CFD model. Below we have collated some key thoughts to consider on existing and new designs.
Air Conditioning (AC)/Mechanical Ventilation (MV)
To minimise the risks of airborne transmission of SARS-CoV2, the general advice is to increase the air supply and exhaust ventilation - the aim being to supply as much outside air as is reasonably possible to dilute the pathogens that might be present. Spaces without an obvious ventilation strategy are likely to be discouraged from use unless they are transient spaces.
This means running an AC/MV ventilation system at a higher volume flow rate, which may require changes to control strategies based on temperature or CO2 set points.
Extended operation times are likely through either a longer daily operation, or moving to a 24/7 operation with lower rates when occupancy is not present Both the higher flowrate and extended operation times where AC/MV systems are present will lead to increased fan energy use.
There will still be a need to keep relative humidity (RH) within a controlled range wherever possible, so the impact to humidification/dehumidification loads is an aspect that needs balanced in light of the points above.
If we consider the recirculation/transfer of air from one room to another, this would increase the likelihood of spreading potential pathogens, unless this is the only way of providing adequately high ventilation to all occupied rooms. Recirculation of air within a single room where this is complemented by an outdoor air supply would be acceptable. However, if those spaces are not to be used, the impact from reduced internal loads becomes part of the equation.
Considerations are being put in place to stagger occupancy, which matches up to extended operation times, but the reduced heat gain that would typically be present will impact the operation of heating and cooling capacity needs and will need to be addressed.
Heat recovery methods are potential routes for cross contamination so building owners will need to look at changing mixing boxes to run in full outdoor air mode and bypass rotor wheels if possible. Consideration to alter the damper control would be needed to keep the pressure higher on the extract side. Meanwhile, if recirculation dampers are to be closed, it should be noted that this can impact the building heating and cooling capacity.
Expired filters can reduce the supply airflow and have a negative effect on dilution of contaminants. While the supply airflow can be increased to compensate for this, it will lead to increased fan energy and impact upon whether heating and cooling coils can manage temperature set-points.
Fan Coil Units (FCUs) could increase air movement that spreads contaminants if the zone has little to no outside air ventilation, in which case running these with the fan off would reduce their effectiveness to impact space temperature. However, where good outside air ventilation is present the FCU could help de-stratify and reduce stagnant air pockets, to improve mixing in the space. Passive chilled beams would follow the same principle as FCUs.
Overall, with the priority shifting to focus on air quality, there will be significant impacts in terms of thermal comfort control. Thermal comfort assessments will need to take this new refactoring into account, which may require education for building occupants and a relaxing of dress codes due to the wider comfort band that is the end result of what the HVAC system produces.
Natural Ventilation lacks the certainty of airflow management, due to its reliance on external wind speed and direction, and may not be suitable in some instances, due to the seasonal impacts from outdoor temperatures.
In this case thermal comfort becomes a much bigger driver to maintain effectiveness of the space, especially if the occupant is near to a window or supply diffuser that would present a draughty feel.
Earlier opening of windows will be required to maintain the need for air mixing, even when it is cooler outside. Although the external conditions can make opening windows impractical, it would be required where reasonably possible without causing discomfort, for example opening upper windows.
From a thermal comfort perspective, while leaving openings overnight to purge air on warm/hot days is effective, this could lead to discomfort on a cold day.
To counter this, heating may need to be turned on more than normal during cooler periods to overcome the higher ventilation heat loss. At times, heating in the morning may exacerbate overheating later in the day, so it will be a delicate balance into the transition and summer seasons.
Single sided ventilation with lower flowrate will mix less effectively so utilising if available both lower and upper openings to generate a flow path that enhances mixing potential is advantageous. Local recirculation, such as stand-alone fans, may be needed to boost this.
Cross-ventilation is a more effective strategy to draw in fresh air but potential for contamination could exist in cases where the cross-ventilation pathway uses another space.
The removal of window restrictors can also boost airflow, and offer potential for use pre- and post-occupancy flushing when the space is not in use, but this needs to be matched up to present safety and security issues.
To boost airflow it may be necessary to set wind-catchers and other automated systems to be fully open with the controls disabled or set to manual override, such as the CO2 set-point set to match atmospheric air at ~400ppm.
Additionally, if we consider external door openings, the additional infiltration could lead to significant additional heat loss and the need for over door heaters to be active at a higher capacity for longer.
Our Team Can Help
Ultimately, making significant changes to your building’s operation and airflow regime without proper consideration could run the risk of a number of unintended consequences. However, our team is positioned to help clients assess the impact of potential retrofit strategies and operational adjustments to their workplaces post-lockdown. If you would like to find out more about how our team can support you through this time, please contact firstname.lastname@example.org.