Paul Parfitt - Associate Director (Technical)
Heating, ventilation and air-conditioning (HVAC) systems are used to maintain indoor air temperature, humidity and, most importantly now, air quality at healthy and comfortable levels. Employers are required by law to ensure an adequate supply of fresh air and a minimum working temperature in order to provide a healthy working environment. This has not changed.
A well maintained and operated system providing good ventilation can help reduce the spread of coronavirus. The Health and Safety Executive (HSE) advises focusing on improving general ventilation, preferably through fresh air or mechanical systems.
The risk of air conditioning spreading coronavirus (COVID-19) in the workplace is extremely low as long as there is an adequate supply of fresh air and ventilation. Many air conditioning systems not only provide heating and cooling but also distribute fresh air to the occupied areas. HSE suggests distributing outside air using fans or similar to prevent pockets of stagnant air. Air conditioning units by design provide this air distribution.
In short, you can continue using most types of air conditioning system as normal. Some may require adjustments to controls and air distribution. If you use a centralised air conditioning / ventilation system which introduce a percentage of fresh air whilst recirculating air between different rooms, it is recommended that recirculation mode is isolated and the system is switched to full fresh air.
The spread of COVID-19 has been linked to many factors in indoor environments. Research is ongoing to determine the exact mechanisms, this includes the impact of airflows within a space. Terminal units, such as fan coils and DX units, usually provide both local cooling/heating and fresh air and so are often integral to the distribution of fresh air in a building.
During the summer the guidance was to increase outside air by adding mechanical ventilation and/or opening windows. Now the lower outside temperatures have created issues where the indoor temperature has become too cold, frequently dropping below the minimum statutory temperature. This is also creating a heating load that is often unattainable with existing plant or is imposing an energy demand that is unaffordable and wasteful.
The following guidance is provided to:
Whether to switch the unit off depends on the location, use and occupation density of the area it serves.
Unit serves an area occupied by just 1 person and the air recirculation is all local to that zone:
The fan coil can operate as normal. Any contaminated droplets of moisture in exhaled air will only be recirculating to the person who exhaled it in the first place. The fan coil should be switched off when that person leaves the zone in case others enter in their absence. If the area is to be subsequently used by another person, the surfaces should be cleaned down before it is switched back on again.
Unit serves a multiple occupied area with limited fresh air being supplied into the zone:
Switch the fan coil off as the potential for air flow distributing a contaminated air droplet towards other people is higher. If it cannot be switched off, follow the guidance below.
Unit serves a multiple occupied area and it cannot be switched off or there is a good supply of fresh air to the zone:
Care should be taken as to where people are positioned in the area in relation to the air flow emanating from the unit. The fan speed should be turned down to a low
speed setting to minimise air throw. Modifications to grille locations or air deflections could be considered. Fans should be continuously operated to avoid resuspension of virus sediment in filters when the fan is turned on. Continuous operation and exhaust ventilation will remove virus particles. Timer setting can be changed to fan only or lower temperature operation during time of non-occupancy to reduce energy usage.
Extra duct cleaning, over and above the normal procedures, is not deemed necessary as ventilation systems are not a contamination source and viruses attached to small particles will not deposit easily in ducts.
Increasing ventilation is more efficient but if this is not possible, room air cleaners with HEPA filter efficiency, can effectively remove particles from the air in a comparable way to ventilation. Electrostatic filtration (not the same as room ionizers!) can be considered. Studies have shown electrically charged hydroxyl radicals to be effective in combatting viruses and contamination in air.
This guidance has been put together using information from Health and Safety Executive (HSE); Building Engineering Services Association (BESA); Chartered Institute of Building Services (CIBSE); Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA).
The information is current at the time of publication. Research is ongoing and may supersede this information at any time.
HSE Air Conditioning and ventilation during the coronavirus pandemic
BESA Summary of Practical Measures For Building Services Operation
REHVA COVID 19 Guidance - How to operate and use building services / Coronavirus outbreak
CIBSE COVID 19 Guidance - Guidance for staff, members and visitors
Workplace Health, Safety and Welfare Regulations 1992 - Approved Code of Practice and Guidance
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