During our first conversations things seemed pretty straightforward. However, it is easy to be deceived and fall in the rabbit hole almost without noticing. So the premise was pretty simple: 

How can a simple, old fan be enhanced and useful for the current times?

Because of COVID, many people are more conscious of the need for ventilation in closed spaces. keeping windows closed is great for energy conservation, but it does not good to the need for constant air circulation. Spaces such as offices and workshops get a lot of airborne contaminants from places that I never imagined before I read ASHRAE's papers...  rugs, clothes, shoes, equipment, faucets, sinks, and of course, exhalation. The easiest answer to this challenge is: getting a brand new HVAC system, ducts and HEPA H14 air filtration systems!  This is not always possible, and sometimes not even desirable. We could open windows whenever the weather allows it. So, how can we know if the air is starting to get saturated with VOC's and CO2?

There are several papers that study the correlation between CO2 saturation and higher risk of catching COVID. I used Zhe Peng and Jose L. Jimenez's work as a reference. 

All this made it evident that we would not be able to rely solely on a simple VOC sensor with estimated CO2 readings. An closed office space may not be exposed to a lot of contaminants, but it could be filled with CO2 due to breathing

We went for the Sensirion sensor. 

References:

1. Exhaled CO2 as a COVID-19 Infection Risk Proxy for Different Indoor Environments and Activities

Zhe Peng and Jose L. Jimenez

Environmental Science & Technology Letters 2021 8 (5), 392-397

DOI: 10.1021/acs.estlett.1c00183