HVAC
WHAt iS FreSH Air And iS it reAlly FreSH? C
OVid-19 is a highly contagious disease and to mitigate the spread of the virus especially indoors, the common refrain is
to make sure the space is well ventilated with fresh air. But what exactly is fresh air? Fresh air is typically defined as cool, unpolluted air in natural surroundings. But as there is no agreed parametric definition of what fresh air is, how can you determine if the air indoors is really fresh? Although the World Health Organisation (WHO) has not formally confirmed that COVid-19 is spread by airborne transmission, it is probably only a matter of time as other similar viruses such as norovirus and the flu are acknowledged to be spread in this way. in the case of COVid-19, it is believed that ventilation plays an important part in reducing transmission by dilution and removal of infected particles and droplets. Ventilation is the intentional introduction of fresh air
into a space while the stale air is removed. it is done to maintain the quality of air in that space. According to the American Society of Heating, refrigerating and Air-Conditioning engineers (ASGrAe), acceptable interior air quality is where there are no known harmful contaminants in harmful concentrations. But what constitutes harmful contaminants in harmful concentrations is left to individual States to define, such as the title 14 California code of regulations, which stipulates for example maximum permissible
levels of CO2 in a building. in the UK, there are guidelines such as the Building regulations 2010 for manufacturers, architects and engineers involved with building design and services to assist in the process of reducing poor air quality and ensuring there is enough fresh air ventilation. the Health and Safety at Work etc Act 1974 is the primary piece of legislation covering occupational health and safety. it states that employers have a duty of care to ensure there is a safe and healthy work environment. new and revised workplace exposure limits (Wels) came into force from January 2020 under the auspices of the Health and Safety executive eH40/2005 containing a updated list of maximum exposure limits and occupational exposure standards for specific gases as required
Wireless CO2Sensor
by the Control of Substances Hazardous to Health (COSHH) regulations. However, there are currently no regulations on
what constitutes ‘good quality’ indoor air. Although there have been calls on the Government to make measuring and monitoring of indoor air quality a legal requirement in commercial buildings and schools especially in urban locations, legislation has not yet been forthcoming. the established benchmark test for indoor air
quality is to assess CO2 levels. ignoring particulate matter, VOCs and other contaminants, it is generally
understood that indoor CO2 levels are a good proxy for the amount of pollutant dilution in densely occupied spaces and can therefore be used as a good indicator for fresh air.
So how do CO2 levels equate to fresh air? the amount of carbon dioxide in a building is usually related to how much fresh air is being brought into the building. in general, the higher the concentration of carbon dioxide in the building in comparison to outdoors, the lower the amount of
fresh air exchange. the background level of CO2 outdoors is generally considered to be in the range
of 350-450 parts per million (ppm). CO2 is a by- product of normal human activity and is removed from the body via the lungs in the exhaled air. Unless an indoor space is adequately ventilated,
CO2 will naturally build up over time. CO2 levels in a well manged indoor space are generally 350- 1,000ppm. Above 1,000ppm and most people will begin to complain about the stuffy atmosphere or
poor air quality. High levels of CO2 indoors are also associated with headaches, sleepiness, poor concentration, and loss of attention and in
extremely high concentrations, CO2 is harmful to life due to oxygen deprivation.
CO2 sensors along with temperature and humidity sensing are often used as part of automatic ventilation control systems. But what if the building or school does not have such a sophisticated environmental control setup? Ample natural ventilation is considered to be the
best method to prevent the Sars-CoV-2 virus from spreading indoors. the amount of fresh air that needs to be supplied is a matter of conjecture, but good
38 MAy 2021 | FACtOry&HAndlinGSOlUtiOnS
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