Indoor environment in Danish apartments during the Covid-19 lockdowns

During 2020 and 2021 a large part of the population was forced to work from home due to the COVID19 pandemic. Many homes were used as offices during the lockdowns, potentially altering their indoor environment. To investigate the effects of the lockdowns, on the indoor environment, data from 1068 apartments in Denmark was analysed using linear mixed-effects models. The measurements included indoor temperature, relative humidity and CO₂ concentration measured in 5-minute intervals during the period from January 2019 to September 2021. Hourly outdoor temperature and wind speed was acquired based on the closest weather stations. The “COVID-19: government Stringency Index” was used to define the severity of the lockdown. The indoor environmental parameters were modelled based on both indoor and outdoor conditions. Models of indoor temperature, relative humidity and CO₂ concentration were developed separately. The indoor temperature increased with increasing stringency. The correlations between stringency and CO2 concentrations were highly significant, but the effects were small. The indoor relative humidity was lower in periods with high stringency than in periods with low stringency. Since the weather was only represented by outdoor temperature and windspeed, the variable “stringency index” could have acted as a proxy for other seasonal effects.