Feature
Air treatment has become essential in building spaces for many reasons – including the management of airborne pathogens which potential tenants prioritise amid growing concern around steadily worsening pollution . Many existing buildings have little option but to retrofit by having specialist services performed on their HVAC equipment . For new builds , technology can be included from the design stage .
There are many risks attached to air and air treatment of buildings , but technology exists for the HVAC engineer and contractors to include . These range from physical treatment such as ozone , nano silver , UV , as well as products available for sterilisation where required .
At its basic level , airborne contaminants can be split into natural and man-made . Pathogens like viruses ( of which Covid-19 is today the most infamous , but there are many ) and bacteria fall into the first category , as well as pollen and mold . Man-made contaminants come in the form of gases , chemical vapours and pollution particles .
The differing techniques of air purification enjoy varying degrees of effectiveness . For instance , filters with a minimum efficiency reporting value ( MERV ) of eight can capture pollen . MERV 11 filters capture mold spores and pollution particles , while MERV 13 filters can capture viruses , as well as bacteria and indoor tobacco smoke .
Ventilation systems have a range of techniques able to help reduce air pollutants and microorganisms . These include :
• Filtration
• Ventilation
• Humidity control
• UV lighting
• Ionisation
Let ’ s take a look at each of these : Filtration : Air filters are rated for efficiency at removing particles of different sizes , and MERV ratings of 13 or 14 are recommended by ASHRAE for HVAC systems in buildings . The most penetrating particle size is 0.3 microns – in comparison a virus such as SARS-CoV-2 particles have diameters between 0.06 and 0.14 microns . MERV 13 filters are more than 75 % effective at trapping coronaviruses and similar-sized viruses . HEPA filters can trap over 99 % of 0.3-micron particles , but put strain on an HVAC system creating other problems like stagnant air or differences in room pressures . Consequently , they are usually only used in hospital environments and other healthcare settings . Airflow and ventilation : Good airflow does much to reduce contaminants . The CDC ( Centre for Disease Control and Prevention , the US national public health agency ) recommends buildings open outdoor dampers as high as 100 % to allow the maximum amount of fresh air , though this
Benjamin Brits can be hard to achieve if it ’ s extremely hot or cold outside . Maximising ventilation is important , but there ’ s a balance between that goal and energy efficiency . Taking in 100 % fresh air without recirculation requires more energy from the HVAC system since it needs to condition all of it . A solution is to use an energy recovery ventilator ( ERV ) which rotates between intake and exhaust air streams . A wheel transfers the temperature and relative humidity of the conditioned exhaust air stream to the intake air , and vice versa . Humidity : Lower humidity allows viruses to survive longer and reduces some of the body ’ s natural respiratory defences . A typical example is climate control during long range flights , where air is cooled down to extreme levels without being humidified , hence quite a few people present with some kind of respiratory or breathing problems . Post-Covid , ASHRAE recommends building environments be kept between 40 % and 60 % humidity . Above that range , other issues like bacteria , fungi , and mites can develop . UV-C lights : These can be used in ductwork to neutralise pathogens in moving air and wet surfaces like evaporator coils . There are different applications :
• In-duct UV to disinfect air
• In-duct UV to disinfect surfaces
• Upper room UV
www . refrigerationandaircon . co . za RACA Journal I February 2023 29