indoor comfort in school buildings: a case study, palermo ...2 indoor environmental quality in...

Indoor comfort in school buildings: a case study, Palermo, Italy

S. Pennisi1, G. Scaccianoce2 & V. Vaccaro2 1Department of Architecture, DARCH, Palermo University, Italy 2Department of Energy, Information Engineering and Mathematical Models, DEIM, Palermo University, Italy

Abstract

The primary energy consumption in buildings in developed countries accounts for about 40% of whole uses. Therefore, a large number of regulations have been promulgated by the European Union concerning energy saving issues; in particular, Directive 2002/91/EC has been issued regarding the energy performance of buildings and its Recast Directive 2010/31/EU, promoting the Nearly Zero Energy Building targets, introducing stricter parameters with regards to this specific aim. Furthermore, the latter Directive asks Member States to include, within their national plans, measures aimed at supporting public authorities becoming early adopters of building energy efficiency improvements. At the same time, public authorities should implement effective examples of use of energy efficiency criteria in public buildings. Furthermore, the energy consumption of buildings depends significantly on the criteria used for the indoor environment, as well as, the building’s design and use, as clearly indicated in the EN 15251 standard. Recent studies have shown that the costs of a poor indoor environment on the employer, building owners and society, on the whole, are often considerably higher than the cost of the energy used within the same building. In this context, school buildings play a key role. They should have high levels of indoor environmental performance. In the present paper, the authors analyse the comfort conditions in a school in Palermo (Italy) in order to draw attention to the building’s design weaknesses. The analyses have highlighted that the requirements for indoor environmental quality and for energy efficiency may be controversial at times. It finally emerges that energy refurbishment actions will have to start from the requirements of indoor environmental quality. Keywords: indoor environmental quality, thermal comfort, indoor air quality, visual comfort, acoustics comfort, school buildings.

WIT Transactions on Ecology and The Environment, Vol 191, www.witpress.com, ISSN 1743-3541 (on-line)

© 2014 WIT Press

doi:10.2495/SC141432

The Sustainable City IX, Vol. 2 1685

1 Introduction

The aim of this paper is to contribute to the knowledge and methodology used to address the problem of indoor comfort in schools. There are different elements which influence indoor comfort: air quality, acoustic and thermal conditions. These elements have an impact on human comfort [1], satisfaction, as well as, on health. Indoor environmental quality has a significant influence on productivity [2] and learning [3] too. Italian pupils spend around 30% of their lives at school [4] which were for the most part built fifty years ago. Consequently, both the lay-out and construction materials used in these building are often inadequate in ensuring acceptable levels of comfort. Moreover, building standards in many schools of recent construction are not optimal [5] either, probably due to the lack of attention paid to the issues of environmental comfort during the project phase. The complexity of the topic lies not only in the individual perception of comfort indoors, but also in the planner’s sectorial approach. Indoor air pollution – partly depending on the outdoor quality of air [6] and the location of the building [7] – is one of the analysing elements [8]. The indoor air quality is the main cause of the increase in cases of respiratory [9] and allergy related diseases [10] in pupils. There have been various efforts made to raise the public and local government’s awareness, yet it is often limited to a single area. In recent years the European Commission has promoted significant programs and projects on IAQ in schools, with the aim of increasing the knowledge of this topic and find ways to impact positively on the number of cases of respiratory diseases and childhood asthma in Europe. The Italian Acoustics Association has recently brought the profound lack of acoustic quality in schools to the attention of the Government, as it has a negative impact on pupils listening and learning [11]. The classrooms are not acoustically insulated, sound-absorbing materials have not been used and schools are often located in places where there is a lot of traffic and, therefore, outside noise. Finally, the warm and sunny climate of Sicily influences thermal comfort in classrooms [12] which are often exposed to the sun with unprotected windows. This research has taken into consideration the indoor environment, as a whole, and has assessed its characteristics thanks to individual opinions and instrumental methods. The pupils’ and teachers’ personal level of satisfaction have been evaluated using a questionnaire. In addition, instrumental tests have given us a fundamental base on which to plan improvements in environmental comfort in the school that has been analysed. Only by having a deep knowledge of the contextual and constructive characteristics can there be conscious building rehabilitation.


© 2014 WIT Press

1686 The Sustainable City IX, Vol. 2

2 Indoor environmental quality in school buildings

People’s indoor comfort mainly depends on four factors: thermohygrometrics, acoustics, lighting and indoor air quality. Poor control of these factors in enclosed spaces can cause discomfort to the people who live inside them e.g. thermo hygrometric discomfort can cause shivering or perspiration, visual discomfort can inhibit reading, acoustic discomfort can cause misunderstanding in speech, while lower levels of indoor air quality can trigger the onset of allergies and/or the transmission of bacterial or viral diseases. As far as indoor air quality is concerned, the health effects of exposure to pollutants are only known for high concentrations found in industrial buildings; whereas, for residential environments the cause-effect relationship is often only alleged. In relation to this, only in a limited number of cases (such as, acute allergic reactions or poisoning by carbon monoxide), a direct relationship between exposure to a given pollutant and the consequent occurrence of a particular adverse health effect exists; whereas, cases of respiratory diseases or cancer are very often not directly associated with a specific substance or with a single factor. Only then, when there is a reasonable certainty of the link to cause-effect, can we talk about Building Related Illness (BRI), whereas, when effects are known, but it is not easy to determine the causes that produce them, we are dealing with Sick Building Syndrome (SBS). Building Related Illness (BRI) includes allergic diseases (allergic alveolitis, asthma, legionella) and infectious diseases (due to bacteria, fungi and viruses) caused by the combined effect of long-term toxic substances. Sick Building Syndrome (SBS) is detected via statistics on groups of workers employed mainly in buildings where air conditioning systems, as well as, unpleasant smells provoke respiratory, eye, skin and neuropsychological manifestations. These disturbances disappear during weekends and holidays, and are present again on coming back to work. The symptoms are more marked in women, in air conditioned buildings, in warm buildings and among workers who are less satisfied with their jobs. It follows that it is important to make enclosed spaces more comfortable to improve people’s productivity. The indication of possible actions for improving the environmental comfort of enclosed spaces should be preceded by the audit of enclosed spaces in relation to their use, in order to point out possible critical points in environmental conditions. The following reports on a case study audit of indoor conditions in a school in Palermo (Italy). The surveys and analysis of the recorded data were carried out in compliance with standards and rules in force in Italy and/or Europe. In particular, the evaluation of the visual comfort conditions was based on Italian and European standards, such as, UNI 10840, UNI 11165:2005 and UNI EN 12464 [13–15], the latter also suggests a level of illuminance equal to 300 lux and a max value of UGR equal to 19 for schools; whereas, the estimation of acoustic comfort was based on ISO 140-5, ISO 3382-2 and DIN 18041 [16–18] standards. The thermo hygrometric comfort was evaluated as suggested by ISO 7730, ISO 7726 and ISO 9920 [19–21] standards, while the limit values of the PMV indicator are set to +/-0.5 corresponding to Category B in compliance with UNI EN 15251 [22]. Finally,


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the indoor air quality was evaluated with reference to the CO2 concentration (maximum limit value set to 1000 ppm [23]) and NO2 concentration (maximum limit value set to 0.03 mg/m3 [24]).

3 The case study: “Mendelsshon” school in Palermo (Italy)

The analysed school building is a mixed primary/ middle school in Palermo (Italy), in which there are about 300 pupils in 15 classrooms, three in primary school and twelve in middle school. Only six classrooms – representative of all the classrooms – were investigated with reference to environmental indoor comfort (see fig. 1). The information gathered has then been analysed in order to assess whether or not pupils’ conditions of comfort and safety are up to acceptable limits. The present work was developed on the basis of the study contained in [25].

Figure 1: Plan of the ground floor of school building. Identification of the six investigated classrooms.

3.1 Description of the school building and the surrounding area

The school area is 12900 m2, but the building in itself is 4400 m2 and it develops on one floor only in a circular way. Its height ranges from a minimum of 3.20 m to a maximum of 9.70 m. The building is divided into four main blocks, including, classrooms and toilet facilities, a gymnasium, the caretaker’s house and a technical room. Furthermore, in the center of the circular plan there is a large outdoor atrium. The supporting structure is made of framed reinforced concrete, its flat roofs are only accessible for the maintenance of HVAC equipment. The outer walls are made of hollow brick (thickness = 25–30 cm, and U = 0.95–0.76 W/m2K transmittance), while the partition walls are made of lightweight concrete in expanded clay or pumice with a thickness equal to 12 cm. The interior walls are finished with light coloured gypsum, while the floors are made of reinforced concrete bricks and rafters, as well as, having porcelain tiled flooring. The door and window frames are made of thermal-break aluminium (2.8 W/m2K ≤ U ≤ 3.5 W/m2K).


© 2014 WIT Press


In order to compare the data recorded during the survey to outdoor data for the same period of the survey, climatic data has been obtained by the “Osservatorio Astronomico” in Palermo.

3.2 Visual comfort analysis

The survey, relating to lighting parameters, was carried out on 29th January, 2014 from 10:30 to 14:00, following these steps. The first step consists in the measurement of outdoor illuminance. For this purpose, a portable lux meter was placed on the roof of the school on a horizontal plane, in such a way that the probe of the lux meter was facing skywards and registered the degree of outdoor illuminance every 3 minutes. At the same time, measurements of indoor illuminance were taken in the six selected classrooms – with pupils inside – by means of a lux metering probe (the second step). The recorded data were stored in a “Babuc/A” data logger connected to the lux metering probe. In each classroom, the measurements were taken in six points (see fig. 2) every 3 minutes and with a sample rate equal to 10 s, as well as, being in the condition of use that usually occurs during the winter season. Furthermore, the authors recorded the positions of the lighting devices for each of the selected classrooms as well as the their technical characteristics, such as type of lighting, power (W), luminous flux ( lm), colour rendering index (CRI), colour temperature (K), luminous efficiency (l m/W), lifetime (h). After completing the analysis of illuminance, the authors performed the measurements of surface luminance in five positions within the visual cone for each selected classroom (the third step). The measurements were taken using a luminance meter (at a height of 1.25 m above floor level). The surfaces included within the visual cone are those of the school desks, the window facing wall, the blackboard, the windows, the floor, the ceiling and the lighting device closest to blackboard. In fig. 2 the position of the lighting devices, points of measurement, illuminance and points of measurement of luminance for classroom number 1 are shown.

Figure 2: Positions of lighting devices for points of measurements of illuminance (filled circle) and luminance (x symbol) – classroom 1.


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The collected data were processed by means of a spreadsheet and visualization software. The latter enabled the displaying of a rough distribution of illuminance for all of the analysed classrooms (e.g. see fig. 3 for classroom 1). Fig. 3 highlights an irregular distribution of illuminance with a peak value of about 820 a lux near the farthest window from the blackboard and a minimum value of 380 lux in a position diagonally opposite to the one of peak value. An analogous distribution was noticed inside classroom 2, whereas, a more uniform distribution was noticed inside classroom 3.

Figure 3: Illuminance distribution, classroom 1, survey January 29th, 2014 from 10:30 to 14:00.

With reference to another corridor with classrooms overlooking the central outside space (see fig. 1), a more uniform distribution was noted inside classroom 4, whereas, an un-uniform distribution of illuminance was noticed in classroom 5 and 6 with very low values of illuminance (i.e. in areas farthest from windows) that could drop below the recommended value. Finally, the recorded data of luminance were processed in order to compute a Unified Glare Rating in order to evaluate the incidental discomfort glare caused by lighting devices. In table 1 the results were reported.

Table 1: Results of UGR analysis.

UGR values

Position A Position B Position C Position D Position E

Classroom 1 16.85 9.92 -1.89 1.83 6.59 Classroom 2 16.73 4.73 -0.26 16.32 9.15 Classroom 3 14.46 2.99 -6.22 15.67 11.08 Classroom 4 22.35 9.38 1.80 18.57 7.60 Classroom 5 -12.68 0.56 -3.51 16.41 -5.86 Classroom 6 16.47 7.52 -0.67 18.97 14.48


© 2014 WIT Press


The grey cells of the table contain values of UGR that are too low, probably due to values of luminance of lighting devices lower than the average of the luminance values of the other surfaces within the visual cone. Whereas, the value in bold format, that refers to a position near the wall opposite the windows in classroom 4, is higher than the limit value (UGRmax = 19), therefore this position is probably characterized by a condition of glare discomfort due to artificial lighting. Anyway, the values, reported in table 1, point out that the glare discomfort, due to artificial lighting, is usually almost non-existent or not annoying.

3.3 Acoustic comfort analysis

The only parameter considered for the evaluation of acoustic comfort is reverberation time [17]. The survey was carried out inside the six selected classrooms without the presence of pupils or a teacher. In order to proceed with measurements, the bursting of balloons was used as an acoustic source and a sound level meter. The bursting of balloons was performed near the blackboard, while the sound level meter was placed in two representative positions amongst the desks. The measurement of the reverberation time was taken by placing the sound level meter at a height of 1.5 m above floor level and checking that the distance between the sound level meter and acoustic source was greater than 2 m. Furthermore, the distance between the sound level meter and all reflective surfaces, as well as, between the two positions of the sound level meter were greater than 1 m. The collected data were then processed with suitable software in order to calculate the reverberation times at different frequencies. Reverberation time calculated values were averaged over time and space (two measurements were made for each of the two positions of the sound level meter) with the aim of obtaining a single value. The optimal reverberation time value, Topt, was estimated for a space used as a classroom with pupils by means of eqn (3) at a frequency of 500 Hz. The value was calculated considering a mean volume of the analysed classrooms, expressed in cubic meters.

Topt = 0.32 * log (V) – 0.17 (1)

According to [18], without pupils, the optimal reverberation time cannot be greater than 0.2 s the optimal reverberation time computed with pupils. In table 2 the results concerning the frequency of 500 Hz are reported.

Table 2: Comparison among the optimal value and the measured values of reverberation time at a frequency of 500 Hz for each of the analyzed classrooms.

Topt Room 1

Room 2

Room 3

Room 4

Room 5

Room 6

Reverberation time (s)

0.73 [0.93] 2.41 2.42 2.19 2.17 2.18 2.27


© 2014 WIT Press


The reported values point out that the reverberation time for each classroom is greater than the optimal value, thus revealing a poor condition of acoustic comfort.

3.4 Thermo-hygrometric comfort analysis

The quality of thermo hygrometric comfort was evaluated by means of a PMV (Predicted Mean Vote) indicator [19]. In order to evaluate the PMV indicator, some parameters were measured by means of a psychrometer probe and a globe thermometer probe, both of them connected to a “Babuc/A” on 29th January, 2014. The instruments were placed in the same six positions as shown in fig. 2. The sample rate and the measurement period for each position were set equal to 10 s and 3 minutes respectively. The mean radiant temperature (in °C) was computed by means of the following formula, applicable in a condition of natural ventilation [20]:

tr̅= tg+273 4 + 0.4*108|tg-ta|1 4* tg-ta1

4 – 273 (2) where tg is the globe thermometer temperature (°C) and ta is the air temperature (°C). The analysis of the recorded data shows an irregular distribution of air temperature, a good condition of relative humidity and low values of the mean radiant temperature in the analyzed classrooms. The air velocity was not measured and was set equal to 0.2 m/s. Furthermore, the metabolic rate was assumed to be equal to 90 W/m2, corresponding to a seated person, and the thermal insulation of clothing was assumed to be equal to 0.16 m2°C/W, corresponding to clothing including undergarments, a shirt or blouse with long sleeves, trousers, sweater, thick socks and thick soled shoes [21].

Figure 4: Distribution of PMV values, classroom 1.


© 2014 WIT Press


The analysis of collected PMV values (see an example in fig. 4) show negative values of PMV corresponding to a cool condition due to the non-working of the HVAC equipment due to vandalism. However the values of the PMV indicator often fall within an optimal range of Category B (+/- 0.5), with the exception of classroom 3, in which slightly lower than -0.5 PMV values are noticed, therefore outside of the recommended range of comfort conditions.

3.5 IAQ analysis

The CO2 and NO2 concentrations were measured in order to assess the quality of indoor air. Carbon dioxide, CO2, is not a dangerous pollutant in a normal concentration e.g. 3% or 4% of 30,000–40,000 ppm, but it is used as an indicator of the air exchange rate or gas driving. Nitrogen dioxide, NO2, on the contrary is a strong irritant to the lungs: in a moderate concentration it causes acute coughing and chest pain. It could lead to irreversible damage to the lungs that could occur even later on. The purpose of this analysis is to identify the main risk factors for the pupils’ respiratory health. As a matter of fact, asthma in children and adolescents is often linked to several factors existing in the school environment, such as humidity, mold, volatile organic compounds, formaldehyde, allergens and bacteria. Several studies state that poor air quality and bad microclimatic conditions affect students’ school work performance [1]. In order to measure the concentration of CO2 and NO2, an indoor air monitor was placed inside a classroom representative of all of the classrooms. Classroom 6 was chosen and the results are reported in fig. 1. The instrument also recorded the air temperature and relative humidity. The measurement period was from 27/01/2014 to 3/02/2014. The sample rate was set equal to 30 s.

Figure 5: Trends of NO2 and CO2 concentration from 27/01/2014 to 3/02/2014, classroom 6.


© 2014 WIT Press


The analysis of recorded data points out that the CO2 concentrations are greater than the considered limit value (1000 ppm), whereas, the NO2 concentrations are almost always equal to 0.03 mg/m3, a lower value than the legal limit for outdoor air (see fig. 5). The measured data of air temperature and relative humidity were compared with outdoor data, provided by “Osservatorio Astronomico” of Palermo. It has been noted that the difference between inside and outside air temperatures is about 7°C. This information provides an indication of the school building’s door and window frame tightness as being good, while, at the same time, confirming that the air exchange rate is very low, as already deduced by the high recorded values of CO2 concentrations.

4 Conclusions

The analysis has shown different conclusions concerning to the four analysed ambits (visual, acoustic and thermo hygrometric comfort, as well as, indoor air quality). With regards to visual comfort, it is possible to give a good evaluation to the use of daylight in the classrooms, with the exception of classrooms 3 and 5, in which values are very close to the limit value and, therefore, a discomfort condition is likely to arise. The values of illuminance are suitable for performing tasks in any position within all of the classrooms, although the distribution of illuminance is very irregular; as a matter of fact, the illuminance has high values close to windows and low values close to the walls facing the windows. The UGR results are excessively low in zones farthest from windows, revealing an inadequate luminous flux of lights. With regards to acoustic comfort, it can be asserted that a problem of acoustic comfort undoubtedly exists in all classrooms. With regards to thermo hygrometric comfort, the PMV values obtained show a slightly cool condition, due to the non-functioning HVAC systems. Finally, inside the classroom, there is a low level of indoor air quality, due to the high holding of the window and door frames; this is good for energy efficiency but, when the air exchange system does not work or when the windows are not equipped with a smart system for controlling their opening and closing, this is unsuitable.

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[11] Associazione Italiana Acustica, lettera aperta al Governo Renzi “La fatica di imparare e insegnare nelle scuole italiane”, 2014.

[12] Wong, N.H. & Khoo, S.S., Thermal comfort in classrooms in the tropics. Energy and Buildings, 35(4), pp. 337-351, 2003.

[13] UNI 10840, Luce e illuminazione – Locali scolastici – Criteri generali per l’illuminazione artificiale e naturale, Italy, 2007.

[14] UNI EN 12464-1, Luce e illuminazione – Illuminazione dei posti di lavoro – Parte 1: Posti di lavoro in interni, Italy, 2004.

[15] UNI 11165, Luce e illuminazione – Illuminazione di interni – Valutazione dell’abbagliamento molesto con il metodo UGR, Italy, 2005.

[16] ISO 140-5, Acoustics – Measurement of sound insulation in buildings and of building elements – Part 5: Field measurements of airborne sound insulation of façade elements and façades, Geneva, Switzerland, 1998.

[17] ISO 3382-2, Acoustics – Measurement of room acoustic parameters – Part 2: Reverberation time in ordinary rooms, Geneva, Switzerland, 2008.

[18] DIN 18041, Acoustical quality in small to medium-sized rooms, Germany, 2004.

[19] ISO 7730, Ergonomics of the thermal environment – Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria, Geneva, Switzerland, 2005.


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[20] ISO 7726, Ergonomics of the thermal environment – Instruments for measuring physical quantities, Geneva, Switzerland, 1998.

[21] ISO 9920:1995, Ergonomics of the thermal environment-Estimation of the thermal insulation and evaporative resistance of a clothing ensemble, Geneva, Switzerland, 1995.

[22] UNI EN 15251, Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics, Italy, 2008.

[23] RSECE Decree-Law n. 79/2006. Regulation for the energy and HVAC systems in buildings (in Portuguese: Regulamento dos Sistemas Energéticos de Climatização em Edifícios-RSECE), Official Gazette of the Portuguese Republic, Series A, n. 67, 2006.

[24] DIRECTIVE 2008/50/EC of the European Parliament and of the Council, Ambient air quality and cleaner air for Europe, 2008.

[25] Wargocki, P. & Wyon, D.P., Providing better thermal and air quality conditions in school classrooms would be cost-effective. Building and Environment, 59, pp. 581-589, 2013.

[26] Agusta, F.M, Studio delle prestazioni indoor del plesso Mendelsshon dell’istituto comprensivo statale cruillas di Palermo, thesis University of Palermo, 2014.


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