Assessment of indoor air quality and thermal comfort in Portuguese secondary classrooms: Methodology and results

doi:10.1016/j.buildenv.2014.06.008

Building and Environment

Volume 81, November 2014, Pages 69-80

https://doi.org/10.1016/j.buildenv.2014.06.008 Get rights and content

Highlights

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We conducted a field study on TC and IAQ in Portuguese secondary classrooms.
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The investigation was carried out during the mid season in free running conditions.
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The study compares TC indices and subjective votes from questionnaires.
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Students in Mediterranean climate accepted indoor T_a up to 25.2 °C.
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Higher temperature ranges are accepted than those presented in the norms.

Abstract

This work shows the results of a field study about indoor thermal comfort, based on investigations in Portuguese secondary schools' classrooms. The surveys herein presented were carried out in a school in Beja, in the South-East of Portugal.

The field study was conducted by physical parameters monitoring and survey questionnaires. Both field monitoring and subjective surveys were performed at the same time during the regular class period (either at the end or at the beginning of the class). The measurement campaign consisted in measuring the environmental parameters – air temperature (T_a), air relative humidity (RH), CO₂ concentrations. Outdoor air temperature values were registered hourly at the nearest climatological station. Through these data, along with the actual people clothing and metabolic rate being know, both Fanger's comfort indices were calculated (predicted mean vote and predicted percentage of dissatisfied people).

The subjective survey investigated the thermal acceptability, the thermal sensation and the thermal preference.

The judgments about the thermal environment were compared with the results of the field measurements. Draught preference votes, air stiffness and global air quality votes were also collected.

The results show that the students found temperature range beyond the comfort zone acceptable, and revealed the occupants' accommodation to CO₂ exposure, confirming the results obtained in other studies. Moreover, it was verified that running on naturally ventilation mode, CO₂ concentration limits were highly exceeded.

Introduction

Indoor Environment Comfort results on the combination of four major environmental factors, such as Thermal Comfort (TC), Indoor Air Quality (IAQ), Acoustic Comfort (AC) and Visual Comfort (VC) [1]. Thermal comfort in schools (classrooms) has lately been receiving more research attention [2], [3], [4], [5]. Either because indoor environmental quality (IEQ) has a repercussion on buildings' energy use [3] but also because this might condition students and teachers performance [6], [7], [8], [9], [10], [11], [12]. On the latest case some research has been developed but most studies are not very conclusive or show limited evidence, recalling further investigation [6], [8], [13].

Assessing occupants' satisfaction about the indoor environment has been common practice for evaluating thermal comfort (TC) and indoor air quality (IAQ) perception [14], [15], [16]. In this context, an empirical study has been driven in a Portuguese school focusing on these two factors: TC and IAQ. Monitoring parameters were faced up with perceived TC and IAQ responses.

Field research, or «the analysis of “real-world”» [3] is important to test the validity of the PMV (Predicted Mean Vote), that provides the basis of the main thermal comfort standards [17], [18].

Several field studies have been investigating the thermal sensation votes (TSV) regarding the indoor thermal environment (ITE). In various cases it has been found that people in naturally ventilated indoor environments are comfortable within a larger range of values than in fully conditioned environments. In warm climate it has even been shown that people can achieve comfort at higher temperatures, compared to the recommendations based on PMV calculation [19].

The work herein presented aims at evaluating TC and IAQ in a recently refurbished school running in free running conditions/natural ventilation mode during the mid-season. In this study, the comparison between the subjective votes (TSV) and predicted votes, deriving from the objective monitoring of some environmental parameters (T_a, RH and CO₂ concentrations), allows the test in field both in the “traditional” approach and in the adaptive one. Although adaptive opportunities in classrooms are relatively strait, in the Portuguese public schools, there is no obligatory uniform, for which students may add or remove layers of clothing. Adaptive actions to control microclimate conditions also include windows opening or closure, shading device manipulation, etc. In many situations these depend on teacher's actions, more than students' [20]. Lesson breaks are good opportunity moments for air renewal.

The field campaign was performed during spring time, for two weeks during lesson periods and weekends. Although provided of HVAC systems, namely air handling units (AHU), during the monitoring period classrooms were in “free running” conditions.

Section snippets

Object of the study

The study was conducted in the continental Portuguese territory, in a secondary school in the southern part of the country. This study is part of a wider research project [21], covering a total of eight-school selection distributed over the Portuguese mainland territory.

The school currently under study is located 85 km from the oceanic line coast, 255 m above the sea level, in the climatic zone W1S3 (Winter 1, Summer 3) – the number of heating degree days (HHD) are 1290 (according to the

PPD & PMV indices. Simulation results: estimation on comfort indices

The recorded data were elaborated in order to evaluate Fanger's thermal comfort indices, PMV and PPD, according to ISO 7730 [18]. The procedure has been previously exposed [4]. Based on a simulation tool developed by Gameiro da Silva [36], [37], TC indices were calculated. In the presented case-study, data input relating to environmental conditions were: air temperature (monitored value), mean radiant temperature (estimated: based on T_a ± 1 °C), air velocity (estimated in accordance to Ref. [18]

Conclusions

In this work, the results of a field study investigations on TC and IAQ in Portuguese secondary classrooms located in Beja (south-east of Portugal) are shown. The investigation was carried out during the mid season in free running conditions (no HVAC systems were active during the study).

The environmental parameters influencing TC and IAQ were measured, while parallel subjective assessments of the occupants were collected.

The study allowed a comparison between TC indices predictions (calculated

Acknowledgments

The presented work is part of a wider research project, called Energy Efficient Schools (Escolas Energeticamente Eficientes, 3Es), granted by Teixeira Duarte on the framework of the Portuguese Program of R&D Projects associated to Large Public Tenders. The authors are thankful to Parque Escolar E.P.E. for the provision of the database on the Portuguese secondary schools. The presented work is framed under the Energy for Sustainability Initiative of the University of Coimbra and was supported by

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