Data Insights #I: The colder it's outside, the worse the air gets inside

That too much carbon dioxide in the inhaled air can make you tired or cause headaches is mostly known. Even so, air ventilation is not a matter of course in all offices and households, especially when it's cold. Conrad Connect has identified a correlation between indoor CO2 and outdoor temperature, which proves exactly this fact.

Opening a window
Windows must be opened regularly - it's getting forgotten
often during Winter. Image by Ruslan Solntsev –

But not only high CO2 values can become a problem in winter, but also the humidity is often higher inside when it’s cold outside - water drops on the windows, up to even mould can be the result. But why is it a challenge for many, to do ventilation right in winter times? Whether the reason is that the one who opens the windows every two hours and lets the cuddly heating air escape, gets attacked, or the reason is, that it simply gets forgotten to let fresh air in regularly, we can not say.

But here are a few projects that can solve the problem very easily and we also share our full study on the subject. After logging in, anyone can access or adopt a variety of smart projects for free, solving the problem of too much carbon dioxide in the inhaled air:


Ventilate properly during the cold season

1. Ventilation system CO2 control

As soon as the CO2 content measured in one or more rooms exceeds 800 ppm, the ventilation system, which is plugged in via a smart socket, is activated. If the CO2 content in each room falls below 500 ppm, the ventilation system is switched off again.


2. CO2 control over color lamp

Konzentation im Berü bei schlechetr Luft
Stay focused in the office when the air is bad isn't easy.
Image by fizkes –


From green to red: A smart lamp uses the traffic light colors to show the CO2 status in the room and reminds you to let some fresh air in.


3. SMS, warning lamp and automatic ventilation

If the CO2 content is excessive, an SMS will be sent with the reminder to open a window. At the same time a red light comes on and an intelligent socket is activated. Connected to it can be an air filter, a humidifier or fan connected. Once the air quality is better, the outlet is switched off again to save energy.

Auch Nässe kann zum Problem werden
Wet air in rooms can be a problem. Image by andrei310 –

Complete research results: Correlation between indoor CO2 and outdoor temperature

The aim was to investigate the correlation between indoor CO2 and the outside temperature in Berlin. The hypothesis behind this goal is that the indoor CO2 level is affected by the colder outdoor temperature, which is influenced by the use of heaters or the closing of doors or windows. The following analysis was performed in R. The outdoor temperature was downloaded from the Deutscher Wetterdienst (copyrights info here). The CO2 data were from Netatmo and Foobot indoor CO2 sensors. The data collection period ranges from 2018-01-01 until 2018-10-31. 

Observed a significant high negative correlation (R = -0.9, p-value < 2.2e-16) between outdoor temperature (y-axis) and indoor CO2 (x-axis). Meaning that lower the outside temperature, the higher the indoor CO2.


We observed a consistent significant negative correlation between indoor CO2 and outdoor temperature (when measured for the complete raw data or separately for different clusters of sensors). In other words, the indoor CO2 is higher when the outdoor temperature was lower.