Main Content

How do people know there is enough air exchange in their rooms? There is a simple way to make that determined by Seeeduino XIAO.

Project Background
Most transmissions of coronavirus occur indoors, the majority of those cases are caused by the inhalation of particles containing the virus. The best way to prevent the spread of the virus into the home or workplace is to keep infected people out. However, about 40% of cases are asymptomatic, and these asymptomatic infected people can still spread the virus to others, which is difficult to avoid.

Shelly L. Miller, a professor of mechanical engineering at the University of Colorado Boulder, recently published an article on the Popular Science website, which is about the best way to reduce the risk of indoor infections;

Getting fresh air

Monitoring carbon dioxide concentrations, and using air purifiers. Fresh air The safest indoor space, according to Miller, is one in which there is a constant supply of outdoor air replenished to replace the dirty air inside.

In commercial buildings, outside air is usually imported through heating, ventilation, and air conditioning systems. In homes, outside air can enter through open doors, windows, and various gaps.

In short, the fresher the outside air into the room, the better. The introduction of such air can dilute all indoor pollutants, such as viruses, and reduce human contact with viruses. Environmental engineers use the air replacement rate to quantify how much outside air enters the room.

Although the specific replacement rate depends on the number of people and the room size, most experts believe the ideal condition is about six air exchanges per hour for a 100 square foot room with three or four people present (about 9 square meters).

During the global pandemic of infectious diseases, the replacement frequency should be higher. A 2016 study showed that nine air exchanges per hour reduced the spread of severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and H1N1 influenza in hospitals.

However, many buildings in the US, especially in school, do not reach the recommended air exchange rate. Fortunately, it is not difficult to import more outside air into the building. To begin with, keep doors and windows open is a good way. Furthermore, placing an electric fan at the top of a window can increase air exchange a lot. And in buildings without operable windows, one can modify the mechanical ventilation system to bring more outdoor air indoors. But in any room, the more people in the room, the faster the air should change.

Monitoring air circulation using CO2 concentration

How do people know there is enough air exchange in their rooms? There is a simple way to make that determination. Every time we exhale, we release carbon dioxide into the air. Since coronaviruses are most often spread by breathing, coughing, or talking, carbon dioxide concentration can be used to see if a room is filled with the potentially infectious exhaled breath. The carbon dioxide concentration allows us to estimate if enough fresh air is coming into the room.

The outdoor CO2 concentration is only slightly above 400 ppm, and the CO2 concentration in a well-ventilated room is about 800 ppm. If the ppm of a room is higher than that, then the room may need more ventilation. A researcher reported last year that ventilation problems impacted an outbreak of tuberculosis transmission within Taipei University. Many rooms on campus were inadequately ventilated, with carbon dioxide levels exceeding 3, 000 ppm, and the outbreak was subsequently brought under control when engineers improved air circulation and reduced carbon dioxide levels to less than 600 ppm.

Since coronaviruses are airborne, a higher concentration of carbon dioxide in the room may mean a greater chance of spreading the virus if an infected person is indoors. Based on the above research, Miller recommends keeping the carbon dioxide concentration below 600 ppm so that we can effectively control the large spread of the outbreak. We will use the existing electronic module to make an instrument that assists us to monitor the indoor CO2 concentration, you can customize the alarm message, and even determine whether to open the windows and doors for ventilation automatically based on the current CO2 concentration. Of course, you can also buy CO2 detectors, just make sure they are accurate within 50 ppm.

Step 1: Preparation
Before we start, we have to prepare some electronic modules and devices we needed:

Grove - Carbon dioxide and temperature and humidity sensors
Seeeduino XIAO Expansion board
Seeeduino XIAO
3.7V Lithium Battery
300mm300mm3mm basswood board (quantity: 1)
M360 double-end stud (quantity: 4)_
20 double-end stud (quantity: 6)

fM2*60 double-end stud(quantity: 5)
M3 screws (5mm≤length≤10mm) (quantity: 20)
M2 screws (5mm≤length≤10mm) (quantity: 10)
double-sided glue”

Link to article