Online presentation has heard from an engineering expert about how better design can ensure lower carbon approaches to improve indoor air quality and ventilation in buildings

A recent BESA webinar has argued that it is possible to improve IAQ and ventilation rates in buildings in line with national decarbonisation ambitions.

Ella Clark, a mechanical engineer with AECOM and a committee member with the British Council for Offices, said it was important to build understanding that lower carbon approaches to improving air quality were possible with sufficient design.

She said during the webinar, “We now know that doubling the rate of ventilation reduces the spread of Covid-19 by around half and that the World Health Organisation (WHO) recommends ventilation as a first-line strategy for getting people back to the office.”

“We can make our HVAC systems pandemic resilient and design buildings with excellent indoor air quality (IAQ) that are also low carbon.”

Ms Clark argued that effective natural ventilation was the most energy efficient approach to ensure air flow into buildings. This approach could also save money in terms of operational costs of running a building.

However, there were some setbacks due to the risk of polluted external air and contaminants entering a building without additional treatment, Ms Clark added.

She said, “Many studies show that the IAQ can be considerably worse than the outdoor air in these circumstances…and 75 per cent of urban areas in the UK are above the WHO recommendations for air quality.”

Technologies such as radiant heating and cooling panels, ventilation with heat recovery (MVHR), and direct evaporative cooling systems were all highlighted by Ms Clark as technologies that can efficiently ensure better IAQ rates.

The webinar was told that displacement ventilation could also play a part in addressing occupant demand for lower carbon solutions by affectively removing pathogens in an air supply.

Ms Clark said, “Displacement ventilation is a good option because it is more effective at drawing away pathogens compared with top-down air mixing,” she explained. “It can reduce energy cost by 20 per cent 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.”

The BCO’s own recommendations suggest that a good standard for ensuring occupant comfort and wellbeing was to ensure that a temperature that is maintained between 20 deg C to 24 deg C, while also ensuring 12 litres per second per person of clean air into a building. This figure should be increased by 10 per cent in cases of higher density occupancy, according to the research.

Humidity challenge

The relative humidity of an indoor space was another vital factor for consideration by engineers and building managers.

Ms Clark noted during the BESA webinar that studies performed by the BCO found the average relative humidity of surveyed buildings to be at 38 per cent.  Current recommendations for acceptable humidity levels to ensure a healthy and productive environment to work in are set at between 40 and 60 per cent.

Ms Clark argued that a relative humidity of 35 per cent in an environment had been linked to sore throats and eye irritation. Lower levels of humidity were then linked to even more serious conditions.

She said, “At 23 per cent relative humidity, more than 70 per cent of flu particles remain infectious after an hour in the air, but at 43 per cent [humidity] that falls to just 14 per cent according to a range of studies.”

“However, providing those conditions can lead to an energy penalty if you use humidifiers. 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 office.”

The webinar also heard how mechanical ventilation should be seen of providing a more controllable approach to meet the specific air quality needs of a building, such as by using filtration solutions to limit the ingress of pollutants into occupied spaces.

Ms Clark said, “We want to ensure that we are filtering down to PM2.5. There are HEPA filters and ULPA filters which are typically used in clean rooms in hospitals.”

“You will get a higher pressure drop across these filters and they do also have to be maintained, but we can still find the balance between healthy indoor conditions and sustainability if we use the right design approach.”

The webinar followed the recent publication of a free IAQ guidance from BESA. The ‘Buildings as Safe Havens – a practical guide’ document, which has been produced with support from Mitsubishi Electric, provides practical guidance around assessing and implementing ventilation, filtration and air cleaning solutions.

BESA said the document was the third free IAQ guide it has published over the last year with the aim of addressing the “significant number” of under-ventilated buildings across the UK.


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