As the fight against COVID-19 continues, creating a healthy built environment is now more important than ever. Where optimising buildings for occupant comfort was a priority before, now optimising buildings for occupant health is at the forefront. Research has shown that humidity has a particularly important role to play in both the transmission and contraction of COVID-19 and with restrictions easing, understanding how the virus is spread will play a huge role in determining mitigation strategies.
What is humidity?
Relative humidity (RH) is a measure of the amount of moisture in the air, compared to the maximum amount that the air can hold at that temperature. Typically, when the temperature increases, humidity decreases as the air becomes less saturated with water vapour. This behaviour is the same for humidity both outside and inside, but the relationship between the two is not proportional. A study states that outdoor RH is a poor indicator of the level of indoor RH, due to the fact that the temperature inside and outside can differ greatly.
How does the built environment affect humidity?
Over the years, there have been considerable changes in both the style and construction of buildings. Humidity has been affected by the increase in the number of airtight building envelopes and by the rise of built in HVAC systems. Airtight buildings and poor ventilation systems can cause an accumulation of warm, humid air and lead to decreased air movement, thereby increasing humidity levels. By cooling the temperature indoors compared to outdoors, air conditioning systems raise RH as the air becomes more saturated with water vapour. Conversely, heating tends to dramatically decrease indoor humidity levels as the air temperature is raised and can therefore withhold more water vapour.
Maintaining the level of indoor humidity between 30-70% is deemed essential in the built environment. Levels of relative humidity that fall outside of the optimum range of 40-60% can begin to have a negative effect on the wellbeing of occupiers and on the health of the building itself.
Ways to control your humidity
How does humidity affect COVID-19 and our health?
Humidity has a notable influence on the survival rate and transmission of biological pollutants, including pathogens. Like COVID-19, most infectious diseases are spread from human to human by droplet nuclei which are expelled into the air by coughing, sneezing and talking. A decrease in indoor relative humidity of about 20% makes it easier for airborne viral particles to travel. Studies have shown that at a relative humidity above 80% or lower than 20%, most coronaviruses are still active after two days at a constant temperature of 20°C. However, at a constant temperature and relative humidity of 50%, less than 1% of the viruses survived after 2 days.
Not only can humidity influence the survival of COVID-19, research has demonstrated that humidity can also impact our body’s defence mechanisms against such diseases. For example, outside the cells lining our body’s airways, there are hair-like organelles known as cilia. These organelles have decreased functionality in dry conditions, diminishing their ability to remove viral particles. Another example of a natural defence mechanism compromised is nasal mucus. The viscidity of nasal mucus reduces by 50% when relative humidity drops from 100% to 60%. In addition, low humidity levels can also lead to respiratory ailments, skin and eye irritation and a range of symptoms that are associated with Sick Building Syndrome. Health issues such as these can put us in a more vulnerable position to fight off COVID-19.
Ways to control your humidity
Nonetheless, humidity can be easily controlled and monitored and there are different ways to do so for both offices and homes. To quickly gain insight into the relative humidity of any room you can use hygrometers or indoor air quality sensors. These allow you to see and monitor the level of humidity in your space. From this, alerts can be set for when levels fall outside of the optimum range and thus necessary actions can be taken to alleviate impacts.
Opening windows is a simple and very effective way to swiftly change the relative humidity indoors by allowing optimal air ventilation. In offices or homes where this is not possible, turning on dehumidifiers is equally effective.
For offices, the recent government guidelines for getting back to work state that all HVAC systems must be reviewed in order to ascertain whether they need to be replaced. As mentioned previously, HVAC systems can greatly determine humidity levels. It is paramount that they are set to appropriate levels to maintain a steady environment and are checked regularly.
For homes, it is just as important to use exhaust and ventilation systems where applicable. Cooking and showering can significantly increase levels of humidity and turning on ventilation fans ensures this is controlled efficiently.
Is the end of COVID-19 in sight?
As the UK finishes its second month in lockdown, restrictions are starting to ease but the battle to curtail COVID-19 is not over. Buildings can act as barriers to the virus, but it is also important to maintain a balanced indoor environment. Having a healthy built environment with adequate engineering controls to eliminate environmental variables such as high and low humidity levels is an effective mitigation strategy.
A humidity limit should be specified by the appropriate building code for the acceptable air temperature range, to allow the necessary control of the indoor environment. Many studies have shown that humidity has a direct impact on the built environment and those that occupy it, so it essential for it to be controlled appropriately.