’Tis the Season: How Ventilation, Indoor Temperature, and Carbon Dioxide are Linked

3 min read
December 22 2016

With the holidays upon us, many companies and organizations are bringing together employees and colleagues to celebrate accomplishments from the year and look forward to the next. Whether it’s a large company holiday party, or a small gathering by a fireplace, many of us don’t stop to think about how we influence our indoor spaces and are, in turn, affected by them. The interaction between the number of people in a room and the ventilation rate of that room dramatically affects how each of us experiences a space.

Earlier this month, Aclima’s platform team participated in the San Francisco Python holiday party. Many of Aclima’s software engineers are long-time members of this dynamic community, and enthusiastically recommend it to any local “Pythonistas”. As part of the event, we ran a live demo of one of Aclima’s sensor “nodes” to demonstrate its ability to measure factors determining indoor health and comfort during a big event. The node measured carbon dioxide (CO2), temperature, humidity, and noise over four hours. Looking at the data, we can see how the event space responded as guests arrived and the program began.


“CO2 levels rose steadily throughout the night,” observed Nicole Goebel, Aclima’s data scientist. “It was around 500 ppm when I walked in and kept increasing from there.”

People exhale CO2, and one of the primary purposes for building ventilation is to remove this from indoor spaces. The figure above shows how the concentration of CO2 in the event space changed throughout the evening. As people arrived, the concentration of CO2 began to increase from 595 parts per million (ppm). The concentration leveled off at around 1730 ppm where it remained until the end of the night. This value of 1730 ppm indicates the balance reached between the ventilation rate of the room and the CO2 exhaled by the guests. Some of the large spikes in CO2 seen earlier in the night occurred when event attendees decided to breathe directly on the device to test its effectiveness (not recommended if you want to get a feel for ambient air quality). Temperature, which is shown in blue, started at 17°C (62°F) and steadily rose to 24°C (75°F), marking a 7°C (13°F) increase in temperature over four hours.

Finally, we can see a pattern in noise in the event space by looking at the green line. The lower sound readings from 7:00 pm to 7:50 pm and 8:20 pm to 9:30 pm correspond to the times when event speakers were giving a presentation. This meant that chatter around the nodes practically ceased, producing an average sound reading of approximately 60 decibels, which is consistent with the decibel level associated with normal conversation.


Studies have shown that CO2 impairs our brain’s ability to make decisions at levels as low as 1000 ppm. Higher levels can cause drowsiness or headaches. When we feel foggy-headed, we may be suffering from CO2 build-up in our space. Looking at the shaded region in the CO2 figure, about 60% of the event — from 7:00 pm to 10:00 pm — took place above the 1000 ppm threshold.

But why did the event space respond poorly to the increase in occupancy, with respect to temperature and CO2? Aclima learned that the venue’s ventilation system was turned off during the event. While buildings have some degree of natural ventilation, mechanical ventilation systems are necessary to keep spaces healthy for occupants. Without systems to move and condition the air, the event warmed up quickly and CO2 concentrations rose as partiers gathered and conversed, adding CO2 with each breath.

The tools to decipher these environmental signals allow us to see the vital signs of our indoor spaces. Aclima’s environmental intelligence platform allows building portfolio owners and facilities managers to understand how their spaces work and to make informed decisions to promote health, comfort, and productivity. We’re excited to bring you more insights in 2017.