Temperature, Relative humidity and Indoor Air Quality in office buildings and their subjective evaluation

Long-term continuous measurements of temperature, humidity and CO₂ concentrations were conducted in offices in three buildings of over 3,000 m² and three non-specified buildings of less than 3,000 m². These measurements were carried out to investigate the effect of the hygrothermal environment in winter and summer, with a particular focus on the impact of humidity in winter and the hot and humid environment when air conditioning is turned off in summer, on microbial contamination. The impact of temperature and humidity conditions in winter and summer, particularly winter humidity and the high temperature and humidity environment in summer, on microbial contamination was examined. 
Regarding relative humidity, the specified buildings A, B and C, which are humidified, are humidified to a sufficient degree to create an average absolute humidity difference of 2.75-6.10 g/kgDA with respect to the outdoor air. However, the percentage of time meeting the standard is not necessarily high: A: 58.9%, B: 9.3% and C: 3.9%. In contrast, non-specified building D exhibits a relative humidity below 40% (with an average of 15.7 ± 6.2%), while non-specified buildings E and F also meet the standard at a rate of 7.8% and 3.4%, respectively. In the subjective evaluation of the office workers, there was no statistically significant difference in the perceived relative humidity between those who reported feeling dry and those who did not. Conversely, the perception of dryness was found to be less pronounced in areas with higher absolute outdoor humidity. 
Regarding microbiological contamination when air conditioning is turned off in the summer, in the specified building C, which has a high proportion of I/O ratios exceeding 1, there was no odour when arriving at work. In other buildings, 10-15% of office workers perceived some kind of odour. Buildings A, B and D also reported a mouldy odour. Furthermore, during normal office hours, 10-15% of employees reported an olfactory sensation, except for building B, which exhibited a mouldy odour. There were notable discrepancies between the specified buildings subject to the law and the non-specified buildings that were not obliged to comply, particularly regarding the humidification control. Additionally, significant differences were observed in the indoor relative humidity. Furthermore, differences were identified due to differences in building size, particularly regarding HVAC controls and the stability of non-steady-state temperature and humidity.