Fresh Air for a building due to Covid-19.


I would like to add fresh air to the furnace air return to improve the air quality within a building.  I would like to design the system to control CO2 using an incremental approach. Using a Raspberry PI (or similar controller board) to monitor CO2, inside temperature, outside temperature, day of week, time of day, and damper position, a program would determine every 10 minutes it it is necessary to adjustment a fresh air damper. When CO2 levels rise above 600 ppm, the program will increase the damper position by 5 percent. This will occur every 10 minutes, until CO2 levels are no longer above 600 ppm.


The damper will continue to open until the CO2 levels are decreased or the damper position is fully open. The damper will remain at its current position until the CO2 level drop below 600 ppm. If the levels is below 600 ppm, the program will begin to decrease the damper position every 10 minutes. This incremental approach should keep the CO2 levels between 500 and 700 ppm, preventing unnecessary flooding of outside air into the building.


Utilizing a schedule based on day of week, start and end times, the system will ignore the CO2 levels and close the damper to improve heating and cooling effectiveness.


What are safe levels of CO and CO2 in rooms?


250-400 ppmNormal background concentration in outdoor ambient air
400-1,000 ppmConcentrations typical of occupied indoor spaces with good air exchange
1,000-2,000 ppmComplaints of drowsiness and poor air.
2,000-5,000 ppmHeadaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.
5,000Workplace exposure limit (as 8-hour TWA) in most jurisdictions.
>40,000 ppmExposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma, even death.

The vast majority of COVID-19 transmission occurs indoors, most of it from the inhalation of airborne particles that contain the virus.


Researchers have determined buildings with a CO2 levels below 600 ppm, stops the outbreak completely. An increase in fresh air ventilation can decrease the transmission by 97%. Since the COVID-19 is spread through the air, a higher CO2 levels in a room likely means there is a higher chance of transmission if an infected person is present. Based on the study above, It is recommend that buildings should try to keep the CO2 levels below 600 ppm.


Consideration for development:


  • Controller board - Arduino or Raspberry PI
  • CO2 Sensor - Adafruit SGP30 Air Quality Sensor Breakout - VOC and eCO2
  • Temperature sensor -
  • 8" Duct Damper, Normally Closed
  • Interface to furnace/thermostat to determine blower motor off/on
  • User interface to allow remote administration and monitoring
  • logging of data for evaluation of performance