Humidification
www.heatingandventilating.net
Dave Marshall-George, UK sales manager at Condair plc, examines the potential for improving public health through humidification and other HVAC strategies
E
very winter we suffer a rise in colds, flu and respiratory illnesses. It seems as inevitable as an increase in pollen allergies in the spring or sunburn in the summer.
The main reasons put forward for this seasonality of illness are that people spend more time together indoors, cold dry air weakens our immune system and it offers a more hospitable environment for viruses to thrive in. These factors combine to create a situation where respiratory viruses spread more easily from person to person, resulting in increased infection. But, does it need to be this way? Could we better
manage our indoor environments to counter these factors, curb the rise of seasonal illness and provide a return on the investment through increased productivity and reduced healthcare costs? I think the answer is yes, yes and yes! The SARS-CoV-2 pandemic has focused public
attention on how viruses are transmitted. Public awareness has already come a long way from washing hands whilst singing happy birthday, to understanding more about how a room’s CO2 concentrations provide an indication of adequate ventilation in a building. This awareness is here to stay, even beyond
a vaccination programme that will hopefully wipe COVID-19 off the face of the earth. And this awareness will grow. Informed building occupants are going to be demanding much more from a building operator or employer than the correct temperature, adequate lighting and a comfy chair. The need for improved ventilation has taken centre stage recently in media coverage, but awareness of other factors, such as the impact of indoor humidity on our health, is also increasing. In their recommendations on how to operate
buildings safely, CIBSE and ASHRAE have prominently endorsed 40-60%RH as the ideal humidity level to mitigate viral transmission. The European Centre for Disease Prevention and Control also recently recommended this level in its HVAC guidance, as have authoritative international bodies, such as Germany’s FGK and Australia’s AIRAH. In the recent online BESA Conference, Dr Taylor, of ASHRAE’s Epidemic Task Force, gave a thorough presentation on the science behind why 40-60%RH is the optimum indoor humidity for respiratory infection control. The ASHRAE Distinguished Lecturer said numerous studies had identified an RH “sweet spot” of between 40% and 60%, because “there are fewer virus particles in the air, they are less infectious and our health and immunity is much better, when we have our humidity in this zone.” Dr Taylor also presented a study she recently
undertook in association with the MIT research university in the US. COVID-19 infection and death rates were examined in 125 different countries alongside a huge variety of other variables and examined for correlations. The study found that when the indoor relative humidity was low, the COVID-19 infection rates were higher. Conversely, when the indoor humidity was midrange, death rates were at their lowest. In the UK, we can expect to experience an indoor
Indoor dry season London 2019 calculated from outdoor weather data January 2021
humidity below this “sweet spot” of 40-60%, when the outside temperature is around 8°C and the indoor environment is heated to 20°C or more. This will typically happen from around November through
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