Maintaining a satisfactory indoor environmental quality (IEQ) is an integral element of improving occupant health and well-being. In particular, IEQ is an essential factor in some facilities, such as school buildings, to improve student academic performance. This study employed an objective and subjective measurement approach to assess IEQ in a government high school (GHS) and a private high school (PHS) located in Oman, which is characterized by its extreme hot climate. A total of 212 high school students were surveyed during the summer season across 10 different classrooms to ascertain their perception of IEQ situations. The results suggested that most of the observed IEQ factors, including air temperature, relative humidity, and lighting levels across the classrooms in GHS and PHS, satisfied the ASHRAE standard, except the indoor air temperature, which was slightly above the maximum threshold of the European Standard (EN). The average indoor sound levels (>60 dB) exceeded critical limits of 35 dB for school buildings, which may pose the risk of high annoyance (HA) to 30% of students. Satisfactory predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) scores were obtained from both schools when they were evaluated against the ASHRAE standard compared with the EN standard. The maximum proportion of the students reported their classroom's air temperature (33%), relative humidity (25%), and air movement (47%) levels as not acceptable, and thermal comfort (33%), visual comfort (22%), and air quality (41%) as bad (P < 0.001). Multiple regression analysis revealed a strong linear relationship between indoor air temperature (R2 = 0.89) and other IEQ parameters, while PPD (R2 = 0.45) and PMV (R2 = 0.17) showed a weak relationship with outdoor environmental factors. Outdoor air temperature and humidity levels accounted for greater changes in indoor air temperature levels in the PHS than in the GHS. Providing increased urban vegetation, green façade, and retrofitting and the utilization of passive cooling could help improve IEQ in Oman schools.
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