Fan coil units do contain filters to catch dust and particles, but these must be maintained. “Over time, the filters get clogged and they need to be cleaned or replaced, and quite often this isn’t done properly,” says Justin Turnpenny, who leads WSP’s fit-out team in London. “Good maintenance is a key thing we need to manage going forwards.” (The role that smart technologies can play in remote monitoring of building health will be covered in a forthcoming article.)
Improving filtration can improve the general quality of the air, but higher grades of filtration add resistance to the system: the finer the mesh, the more energy it takes to push the air through – which increases the energy consumption of the building. “All of the guidance and regulations are pushing us into a low-energy office, so improving air quality in this way would run contrary to that” says Turnpenny. “It would definitely go against where we currently are in Building Regulations, so it requires a balanced approach.”
Gary Pomerantz, a building systems specialist and executive vice president at WSP in New York, has also been exploring options for cleaning air within air-handling units. One way to do this would be to install larger air-handling units with better filters and UV light. “HEPA filters are probably the only ones that are proven to remove viruses – they’ll get things down to 0.3µm.” High MERV rated filters, which are typically specified in central air-handling units, can remove 90-95% of bacteria and small particulates, but not particles the small size of most viruses. A UV light could kill the rest – “but it would have to be really bright because there’s very little contact time.” Pomerantz’s rough calculations found that on a project in New York, equipping a 25,000 CFM (cubic feet per minute, equivalent to 11,000 litres per second) air handler with HEPA filters would add US$5,000 to the annual operation cost. Adding UV lights would add half as much again. “So it’s not small numbers and that’s just for one air handler. On a large project, there might be 75 of them.” That additional cost could be reduced by increasing the size of the air-handling units, reducing the impact of the added resistance, though that would increase the space required for each.
But a lot of particles never make it to the air-handling units. How to address those? One proposed solution is ultraviolet germicidal irradiation (UVGI), which uses short-wavelength UVC light to kill or deactivate microorganisms. However, this comes with its own risks – “humans are lifeforms too,” Pomerantz points out. Strong UVC light can damage our skin and corneas, as well as degrading plastics. It could perhaps be installed at high levels only, away from people – but that would not clean the air in the breathing zone.
Pomerantz has been exploring an alternative solution for capturing the droplets as close to the source as possible, talking to furniture manufacturers about integrating a clear screen and an exhaust slot into desks. “So when we talk, anything coming out hits the screen and gets drawn into the desk, and into a small unit with a HEPA filter and a light source.” The desks could be arranged in a line, all exhausting into the same unit.