Indoor sourced air pollution is also present and needs to be considered. The most encountered indoor air pollutants are gaseous Volatile Organic Compounds (VOCs) and Aldehydes such as Formaldehyde (CH2O). Organic gases and odours may also be a problem and, in certain areas of the UK Radon, a radioactive gas can find its way into basement areas from bedrock below.
Indoor sourced particles tend to be larger sized and of a biological nature such as mould spores, skin flakes and expelled aerosols. They can harbour bacteria and be infective which is of greatest concern in hospitals and healthcare facilities or schools.
The health issues relating to airborne combustion particles largely stem from their small size and therefore their capability to penetrate the human body. If these particles are also toxic or of chemically damaging nature they have a double jeopardy.
The new air filter standards BS EN ISO 16890:2016 and BS EN ISO 10121-2:2013 have easy to understand filter performance classification; simply the particle size or pollutant gas range, followed by the removal efficiency.
For example, in the performance classification ePM1 85%, 'e' denotes filtration efficiency, 'PM1 is the particle size range and 85% is the tested removal efficiency for PM1. Because this performance is easy to understand HVAC air filter performance is now transparent and understandable to the end user.
As a guideline ePM1 rated air filters should be used as a minimum for all city located buildings occupied by people.
If low energy air filters are used (Eurovent A or A+ rated) not only pollution but also costs can be minimized. It is however worth noticing, that both can only be achieved at the continuous, desired level if regular maintenance of the filters is ensured.
The same type of analysis applies to molecular gas filter efficiency to reduce nitrogen dioxide levels (NO2).
Using the latest technical standards mentioned above, it is possible to calculate the required air filter efficiency, with accuracy, by knowing the inside and outside levels of air pollution for the building under consideration. For example, local air monitoring data for levels of air pollutant of concern can be measured directly or even found by looking at local authority air monitoring stations. In London for example, King’s College have a historic database and map presenting annual mean levels for several air pollutants of concern.
The table below, extracted from Eurovent document 4/23 provides information about categories performance for each of the standards (use colour coding for guidance)