In the final part of our series looking at the impact of a pandemic on building services design, and the reoccupation of buildings, we take a look at the measures to be considered in the design, operation and maintenance of existing and new buildings.
A good building is one where the engineering services systems can react quickly to changing circumstances and provide flexibility to the Building Managers and Occupiers to adopt published guidance during times of a pandemic, whilst not sacrificing the drive towards reduced (or zero) energy consumption and the long term benefits of adopting the ethos of a circular economy.
INTERIM MEASURES FOR EXISTING BUILDINGS:
- Run ventilation systems 24/7, but at a lower rate outside normal hours, to maintain dilution of contaminants and to purge the building when not in occupation. Alternatively, extended hours of operation (2 hours before and after occupation hours) at normal ventilation rates should be applied.
- Run toilet ventilation plant 24/7, ensuring that a negative pressure is maintained in toilet cubicles to minimise any risk of faecal–oral transmission.
- Disable any demand-controlled ventilation during outbreaks.
- Some heat exchangers may allow cross-contamination from exhaust to fresh air. Rotary heat exchangers (thermal wheels) are more susceptible than cross flow heat exchangers, but are more thermally efficient, so have grown in use in recent years. It may be necessary to consider temporarily suspending their use during virus outbreaks.
- Where a central ventilation plant includes F7 Grade filters, these should be upgraded to F9 Grade during outbreaks and then returned to Grade F7 once the outbreak is over.
- Where an existing centralised ventilation system employs recirculation of air, either disable the recirculation during a pandemic, or consider HEPA filters.
- Fan coils, fan-assisted VAV terminals, active and passive chilled beams all recirculate air locally in the occupied space and should be frequently and thoroughly cleaned. Frequently maintain areas where condensation occurs such as fan coils, drain pans and traps, to prevent growth of bacteria and mould.
- Actively use operable windows and openings to provide natural ventilation to occupied spaces, even at the expense of thermal comfort.
- Introduce portable room air purifiers. Incorporating HEPA filters can also be considered for smaller areas.
- Review the occupation density within meeting rooms and the maximum number of occupants clearly displayed. Enforce a period of time between meetings to allow the ventilation to ‘purge’ the room and for the room to be cleaned before the next users.
- Faecal oral transmission is water droplet to human contamination. This will mainly take place in WC’s and changing facilities. Changing facilities are classified as risk areas because of the risk of infected persons using the facility resulting in shower water carrying faecal viral particles in the wastewater. Effective mitigation such as conscious actions of closing of toilet lids before flushing will contain the plume of water droplets that enter the air stream.
- Temporarily disable hand dryers and introduce paper towels, only during the pandemic, however, the value of this is still unclear at the current time.
- It is not generally considered necessary to clean existing duct systems under REHVA guidance. Those systems that continued to run 24/7 will not require any cleaning of the ducts. The likelihood of any trapped nuclei being present is low considering the life span in internal conditions is 3 days. System maintenance and cleaning regimes should be regular and scrupulous and particularly focus on ‘high touch’ areas, such as door handles/push plates, photocopier touch screens etc.
CONSIDERATIONS FOR NEW BUILDINGS:
- Fan coils and other types of terminal units should be designed to avoid condensation wherever possible.
- Up-flow and displacement air systems will minimise local air recirculation and may aid the removal of contaminants from the occupied space. They may gain popularity over traditional overhead systems, which rely on mixing and diluting the pollutants in the room air.
- Decentralised ventilation offers greater segregation and can also offer lower energy solutions, so are likely to become more popular.
- Natural ventilation (or mixed mode) should be promoted wherever possible
- Ventilation systems relying on recirculation of air should not generally be used in new buildings. Where they are used, they shall include (or have the facility to easily add) HEPA filters.
- Heat recovery measures on ventilation systems should still be promoted for long term energy savings, but should be designed so they can be disabled during times of pandemics
- Humidity control should be considered, but where it is not part of the base building provision, space and utilities should be provided for later installation of humidification in air-handling units. The base build building management system (BMS) should include the measurement of relative humidity at each demise.
- Centralised ventilation plant should incorporate features to allow the future introduction of humidification or higher grades of air filtration without modification.
- Mechanical ventilation plant shall be variable volume to allow 24/7 operation during times of pandemics, with reduced volumes outside of occupied hours.
- Toilet ventilation should have its own dedicated supply ventilation plant, rather than drawing make-up air from adjacent spaces.
- Demand controlled ventilation shall be capable of being disabled during times of pandemics.