Background: In the context of the fight against the COVID-19 pandemic, exhaustive ventilation strategies have been implemented in classrooms that have resulted mainly in the permanent opening of doors and windows.

Objective: to analyse whether permanent and direct ventilation to exterior spaces compromises thermal comfort.

The place: a classroom at the Barri Besòs Institute in Barcelona during a workshop on the healthy and socially responsible use of mobile phones within the Impulsem Program of the Barcelona City Council.

Starting situation:

a) Classroom with constant ventilation to exterior spaces (windows open) but keeping interior doors closed.

b) Absence of air conditioning system.

c) Number of students: 15-18.


a) A sensor has been placed in a busy classroom to monitor the CO2 concentration and the indoor temperature. CO2 has been used as an indicator of the level of air renewal.*

b) Values ​​have been taken on 3 different days: March 3, 19 and 24, 2021.

c) When the CO2 concentration approaches that which is considered indicative of not being in a safe environment to prevent the spread of COVID-19, the classroom renovation rate is increased by generating cross ventilation (opening the door interior) between the exterior and interior corridors of the building.

* When we breathe we emit CO2, if we manage to maintain a low CO2 concentration, it means that the CO2 that we have emitted has been eliminated thanks to the renewal of air. Guide for classroom ventilation, Institute for Environmental Diagnosis and Water Studies, IDAEA-CSIC-Mesura. November 2020. Based upon 5 Step Guide to Checking Ventilation Rates in Classrooms (Harvard).

Results: the internal temperature of the classroom has always remained below 21ºC (winter), which is the temperature required by the applicable Spanish regulations (RITE-Regulation of Thermal Installations in Buildings) for winter. Therefore, it is considered that a comfort temperature has not been achieved.The students coped with the temperature by keeping warm clothes on inside the classroom.