Well remembered LL. Done a fair bit of heating and ventilation design and installation over the years. It wouldn’t be a cheap or easy job to retro fit kit successfully to serve an unventilated space such as a classroom.
We have installed reasonably cheap CO2 monitors in any offices where people may have to congregate for any length of time. These give immediate indication of the freshness / staleness of the air. Above 1000ppm = not good, you are breathing someone else’s exhaled air. People are reassured to see the generally low readings proving that the ventilation system is working.
We have also installed humidifiers (Dyson) with inbuilt high efficiency filters as stand alone units. Not a scientists view, just from reading and researching it appears logical that the very low humidity typically seen in UK indoor spaces in winter promotes an environment for a virus, or anything else small enough, to circulate freely in the air as they will be buoyant. Fill that air with water vapour and hopefully anything in the air adheres to the water and tends to settle out.
The high efficiency filters will certainly help clean up the air.
The dryness caused by the low humidity also removes the moisture from your nasal membranes making you more susceptible to any infection.
Touch wood, very successful so far in highly populated and unavoidable indoor areas.
