News analysis with BESA
We must tackle Net Zero and air quality together
More eff ective mechanical ventilation solutions demanded by building users should not lead to poor energy performance or add to the country’s carbon burden, according to BESA.
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wareness of the role of better ventilation in protecting people from the worst eff ects of airborne pollutants and viruses has never
been higher. As a result, more building managers are looking at how they can increase ventilation rates and target airfl ows to ensure they reduce the risk of indoor infection transmission. Employers are legally obliged to provide
conditions that make their staff feel safe and protected in their workplace, but many assume this means they will have to increase energy consumption and take a hit on their running costs. However, this is not an either/or situation and, in fact, joining the two targets together is the best way to deliver all-round building performance improvements.
The fact that the government addressed Parts F and L of the Building Regulations in tandem during the recently completed revision period shows that it recognised improving ventilation should not come at the expense of energy effi ciency – and vice versa. It also took the opportunity to produce new standards for reducing overheating in buildings which will also have important consequences for engineers responsible for improving indoor air quality (IAQ) alongside comfort.
Techniques
Speaking at a BESA webinar last month, AECOM’s Ella Clark said there were several proven techniques that could deliver the required air change rates for comfort and health while still maintaining the push to reduce energy consumption. “We can make our HVAC systems pandemic
resilient and design buildings with excellent IAQ that are also low carbon,” said Clark, who is a mechanical engineer and committee member of the British Council for Offi ces (BCO).
She said the use of technologies like radiant heating and cooling panels, mechanical ventilation with heat recovery (MVHR), and direct evaporative cooling can all improve the indoor conditions without undermining energy effi ciency. “Displacement ventilation is a good option
showed the average relative humidity (RH) in offi ces was 38% whereas for good health it should be between 40 and 60%. At 35% people will experience eye irritation, nasal dryness, and sore throats. This also has important implications for future health emergencies.
Infectious
because it is more eff ective at drawing away pathogens compared to top-down air mixing,” she explained. “It can reduce energy costs by 20% because it allows air to be introduced into the occupied space at higher temperatures so reducing the need for cooling power. However, it does require larger volumes of air so needs bigger air handling units etc.” Natural ventilation is the most energy effi cient option with energy savings as high as 79% depending on what it is replacing – equivalent to as much as £30,000 per annum in running costs for a commercial building. However, it increases the risk of introducing polluted air into occupied spaces. “Many studies show that the IAQ can be
considerably worse than the outdoor air in these circumstances…and 75% of urban areas in the UK are above the World Health Organisation’s recommendations for air quality,” said Clark. Health experts have been quick to highlight the crucial role played by ventilation in maintaining health and comfort through temperature and humidity control and by reducing moisture, odours, and gases. A NASA study also showed that human productivity fell by 3.6% for every 1˚C the indoor temperature rose above 22˚C. The BCO recommends temperature in offi ces should be maintained at between 20 and 24degC and there should be 12 litres per second per person (l/s pp) of clean air introduced with an additional 10% in high density occupied spaces. It also says that controlling humidity is crucial. Clark told the BESA webinar that BCO studies
“At 23% RH more than 70% of fl u particles remain infectious after an hour in the air, but at 43% that falls to just 14% according to a range of studies,” she explained “However, providing those conditions can lead to an energy penalty if you use humidifi ers. Adding an extra 0.28 l/s pp can increase energy demand by 0.6kWh/m2 per annum which is 5,000 kw annually for a large offi ce.” Mechanical ventilation off ers a more controllable
approach that can also make use of fi ltration to reduce the ingress of pollutants into occupied spaces. “We want to ensure that we are fi ltering down to PM2.5. There are HEPA fi lters and ULPA fi lters which are typically used in clean rooms in hospitals,” said Clark. “You will get a higher pressure drop across these
fi lters and they do also have to be maintained, but we can still fi nd the balance between healthy indoor conditions and sustainability if we use the right design approach.” The right approach will be increasingly important as medical studies have also shown that doubling the rate of ventilation reduces the spread of Covid- 19 by around half and that the WHO recommends ventilation as a fi rst-line strategy for getting people back to the offi ce. BESA also believes the UK government should be more ambitious with its proposed changes to national air quality standards to help reduce wider exposure to airborne health threats. The Environment Act 2021 requires the
government to set at least one long-term target for air quality; water; biodiversity; and resource effi ciency and waste reduction – and one specifi cally for fi ne particulate matter (PM2.5). DEFRA’s public consultation, which closes on
10 May 2022
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