In Light of Covid-19
In light of COVID-19 we are seeing increased rates of Ventilation across all building environments. Co2 setpoints, being lowered to around 400ppm, and plant operating time being increased. Modern AHUs supplied with packaged controls, pressure sensors and EC fans allow fast and accurate changes to be made to existing plant.
Under Eco-design requirements, providing high efficiency heat recovery fresh air plant to commercial buildings is a must, but considering the current pandemic what changes will we see in the future? A move to plate heat exchangers in favour of thermal wheels? Increased levels of filtration?
UV light boxes?
Both thermal wheels and plate heat exchangers provide high levels of sensible heat transfer, but in commercial applications only thermal wheels offer latent heat transfer. This additional efficiency means a transfer of moisture must take place between the room air and fresh air. This transfer of moisture and ultimately air leakage, may raise concerns by some.
So, what will be the driving factors moving forward. Will energy efficiency win over ultimate air quality? The benefits in efficiency and plant space offered by thermal wheels cannot be easily over looked.
Modern Thermal wheels that are correctly set up and maintained only have a leakage rate of 2~3% The correct set up of fans is vital to avoid high pressure on the exhaust side. The leakage rate is not linked to the wheels speed, in fact, higher air flow rates can reduce leakage. The key element in the ventilation system is to not recirculate room air and moisture back into the supply duct. The issue posed by thermal wheels is the latent recovery and the transfer of moisture from the extract air from a building.
There is little reason to move away from all types of thermal wheels completely in the future, and the benefits they can offer. Producing a safe air supply to the occupied space is key, and other simple solutions should not be over looked in the future design and maintenance of AHU plant.
Increasing filtration grades will not ultimately stop Covid-19, unless we move to HEPA filtration. The associated pressure drops with this long-term, will have an adverse effect on energy consumption by the fans.
UVC lights can deliver a 24/7 non-invasive disinfection level cleaning regime, eradicating the biofilm build up within AHU components. Most viruses on surfaces can be eradicated in a matter of minutes under UVC light. Reflective surfaces used within the AHU can improve system performance by reflecting UVC energy back in the AHU.
Improved maintenance regimes will be vital, ensuring heat exchange surfaces and drain pans are kept clean, and condensate drain traps are not allowed to run dry.
As we can see, there are many factors effecting ventilation plant, but by engaging with designers, building owners and maintenance teams, the challenges posed by Covid-19 can be reduced.