2022 HDP 3 - Hack it Back

Repurposing of an old fan to promote a healthier life and work environment

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We are connecting an old standing fan to a series of sensors across a room. When CO2, other pollutants or temperature levels are higher than normal in the surrounding environment, the fan will automatically turn on to promote air circulation.

*This project involves AC current. Work on it only if you or someone in your team knows how to work with it safely! *

The concept

While the COVID-19 pandemic is starting to recede, a few things stay true:

  • People are increasingly aware of the benefits for health of an environment with clean air  
  • Open windows remain recommended by several Health Administrations around the world 
  • Air purifying systems and A/C systems are expensive both in installation and in energy consumption

Under the hood

The project consists of two separate components: 

  • A main hub or receiver,
  • Sensors (up to 4)

The standing fan is plugged directly onto the Main hub, which is in turn is plugged to the power outlet. It includes Bluetooth connectivity to the sensors, and a relay to control current flow. Current can be modulated automatically, based on the readings of the sensors. 

Each sensor will be packed with:

  • CO2 sensor (not digital),
  • VOC sensor
  • Thermometer
  • Bluetooth transmitter

The data

This is an enthusiast project and as such, no part of it should be construed as professional advice or instruction of any kind, be it (but not limited to) on the areas of health policy, COVID-19, electronic and electrical wiring, or anything else found in it.

In order to determine what is a good indoor environment in terms of air quality, we will use two widely recognized standards:

  • ANSI/ASHRAE Standard 62.1-2019 Ventilation for Acceptable Indoor Air Quality
  • ANSI/ASHRAE Standard 55-2020 Thermal Environmental Conditions for Human Occupancy

We checked the specs on each sensor to make sure they would provide useful, real-life data.

stp - 407.30 kB - 06/17/2022 at 20:29


stp - 255.74 kB - 06/17/2022 at 20:29



AC Receptacle

step - 2.74 MB - 06/17/2022 at 20:24


stp - 605.21 kB - 06/14/2022 at 20:57


stp - 588.39 kB - 06/14/2022 at 20:57


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  • Communication

    Giovanni06/17/2022 at 18:13 0 comments

    This was a very important milestone in the project.

    Having just one sensor connected to the hub would not provide accurate readings. By the time the CO2 reaches that sensor, the concentration would be too high. 

    The concept revolves around having anything from two to six small, wireless sensors scattered around an area, that send signals to the main hub every few minutes (5-10). When the CO2 averages are too high, the Hub detects that and starts the fan. Bluetooth does the trick as the distances are of a few meters only. 

    Wero had some problems with the Bluetooth communication but he worked his magic. To the right we see the data that is being sent from the node, and to the left, the hub is receiving it. Great success! 

  • Working fast

    Giovanni05/04/2022 at 00:43 0 comments

    From the very beginning, the concept revolved around having as much air available for the CO2 sensor to do its job. The first iterations for the node had a towered design with a steel mesh covering almost 360 degrees. I liked this design, but it proved to be a bit difficult for construction. The meshes were either too rigid to bend to a cylindrical shape, or too flimsy to keep that shape.

    Additionally, these units would be too fragile, and even a slight bump may damage, dent or even break them. So it was time to move to a single body shape.

    PCB design was already underway so we had three main components for the nodes: 

    - the main board,

    - an independent pcb for the CO2 sensor, 

    - a second independent PCB for the air quality sensor.

  • First steps

    Giovanni05/04/2022 at 00:33 0 comments

    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. 



    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

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