The CHEPA model : assessing the impact of HEPA filter units in classrooms using a fast-running coupled indoor air quality and dynamic thermal model

The quality of the classroom environment, including ventilation, air quality and thermal conditions, has an important impact on children's health and academic achievements. The use of portable HEPA filter air cleaners is widely suggested as a strategy to mitigate exposure to particulate matter and airborne viruses. However, there is a need to quantify the relative benefits of such devices including the impacts on energy use. We present a simple coupled dynamic thermal and air quality model and apply it to naturally ventilated classrooms, representative of modern and Victorian era construction. We consider the addition of HEPA filters with, and without, reduced opening of windows, and explore concentrations of carbon dioxide (\co), \PM, airborne viral RNA, classroom temperature and energy use. Results indicate the addition of HEPA filters was predicted to reduce \PM~ by 40--60\% and viral RNA by 30--50\% depending on the classroom design and window opening behaviour. The energy cost of running HEPA filters is likely to be only 1\%--2\% of the classroom heating costs. In scenarios when HEPA filters were on and window opening was reduced (to account for the additional clean air delivery rate of the filters), the heating cost was predicted to be reduced by as much as -13\%, and these maximum reductions grew to -46\% in wintertime simulations. In these scenarios the HEPA filters result in a notable reduction in \PM~and viral RNA, but the \co\ concentration is significantly higher. The model provides a mechanism for exploring the relative impact of ventilation and air cleaning strategies on both exposures and energy costs, enabling an understanding of where trade-offs lie

What is the microbiome of the human home?

There is currently little known about the range and diversity of microorganisms in the indoor home, particularly in the context of modern airtight homes. People spend a great deal of time in their homes, especially those at the extremes of age, and it is possible that the indoor microbiome could impact upon human health in ways not yet understood. This project aimed to systematically screen sites in 100 houses in the Lanarkshire community in order to determine the amount and type of cultivable aerobic bacteria and fungi in the home. It was hoped to be able to characterise the microbiome of the ‘normal’ home. Chosen sites were: indoor bathroom handle; telephone; kettle handle; bedside table; top of bedroom door; TV remote; toilet handle; and bedroom window sill (Table 1). These sites were screened using double-sided dipslides coated with nutrient and staphylococcal selective agars (Figure 1). Bacteria and fungi were quantified for each site and staphylococci and Gram- negative bacilli identified if possible. Each of the eight sampled sites revealed its own distinct microbiological character, both in the type and amount of cultivable microbes. Human pathogens, particularly S.aureus, were more likely to be associated with commonly touched sites such as TV remote, kettle handle and telephone. Whole houses also demonstrated unique microbiological characteristics, with morphologically similar and identifiable microbes observed at multiple sites within the same home. Each home thus displayed it own unique microbiome but with identifiable similarities between other homes according to site