COVID-19 | ENGINEERS RESPONSE Richard Walder, science + tech UK sector lead, Buro Happold I t is inevitable that there will be nervousness about being inside public buildings for some time at least until a vaccine is found, assuming that proves possible. The guidance issued by industry bodies to date is comprehensive for existing buildings, but in the short term I expect new designs to consider different approaches. Longer term, its too early to say whether there will be any fundamental design changes. Lower occupancy densities as people consider more home working may mean reduced cooling density and resulting increased fresh air rates per person, which will help. I suspect well see more consideration of natural ventilation in many buildings, and the enhanced fresh air rates this can bring, although its important that it is designed thoroughly, with properly considered controls. There may even be interest in creating more semi-outdoor work areas, although the UK climate poses challenges for this. There is likely to be increased interest in displacement ventilation, potentially in conjunction with passive chilled beams. The fact that it can be full fresh air and gives unidirectional flow will be a significant attraction and, of course, the supply temperatures are typically less demanding on energy than other systems. With higher primary air supply flowrates, however, consideration needs to be given to ensuring that plantrooms and ductwork distribution routes are sized sufficiently to keep pressure drops low. Appropriate design of ventilation systems will avoid the need for significant additional filtration and the energy penalty this can bring; incoming viral load is generally minimal, so adding Hepa filters onto fresh-air systems will have negligible effect, and a move away from recirculating systems will mean that internal Hepa filtration is unnecessary. As well as continuing to maintain low specific fan power, scrutiny of heat exchanger efficiency and avoiding leakage paths will become even more critical with higher fresh-air rates and increased operating hours. Quadram Institute, Norwich, showing natural ventilation and no fan coils Credit: Luke Hayes and NBBJ (architects) Andrew Jackson, partner, Foster + Partners I t remains to be seen whether Covid-19 will have a fundamental impact on the design of buildings. When people return to their places of work, however, we can be certain they will be much more aware of how the buildings they occupy affect their health. The existence of the airborne transmission mechanism is still being debated, so its prudent to assume that it is possible, even if it is unlikely. Other coronaviruses, such as common cold and flu, have very well-documented airborne transmission mechanisms, so we may miss a trick if we base a design response specifically on the contagion characteristics of SARS-CoV-2, as the next viral outbreak may have different characteristics. This may precipitate a move away from traditional recirculation and mixing HVAC systems, such as VAV and FCUs, towards ones incorporating radiant cooling and displacement ventilation, in which fresh air passes through a space once and contaminants are displaced upwards, away from occupants. Natural ventilation and mixed-mode will again come to the fore. Research indicates that increased fresh-air rates and improved indoor air quality are associated with improved cognitive performance and reduced absenteeism. This can come at a cost, however, and there is often a tension between improving environmental quality and reducing energy consumption. Humidification in colder climates consumes water and energy, and enhanced filtration increases fan power. To counter this, we may need much smarter HVAC control systems and increased use of innovative filtration systems, such as UVGI, ionisation or electrostatic. Increased fresh-air rates may be manageable in temperate climates, but the energy penalty is significant in more humid climates. Demand-controlled ventilation will become ubiquitous, which coupled with a reduced occupant density will help to mitigate the impact of this. However, there is a clear need for innovative energy recovery systems, which prevent the transfer of contaminants between incoming and outgoing air streams, and novel dehumidification technologies such as liquid desiccant to reach maturity quickly. The challenge for built environment engineers and designers is about to get tougher. Its an exciting time to be in the industry. Apple Store, Regent Street: displacement ventilation integrated into the joinery for improved indoor air quality and energy efficiency, and radiant floor heating and cooling Credit: Nigel Young/Foster+Partners 22 July 2020 www.cibsejournal.com CIBSE July 2020 p20-22 Covid design.indd 22 19/06/2020 15:51