Indoor environmental quality of classrooms in Southern European climate

Highlights

• Indoor environmental quality of 24 classrooms of 9 school buildings were studied.

• Both non-retrofitted and recently retrofitted buildings were used as case studies.

• A long term monitoring was defined with three measurement campaigns.

• Non-retrofitted schools do not have suitable conditions of comfort and IAQ.

• The use of demand controlled ventilation might be an interesting solution.

Abstract

The indoor environmental quality within a classroom is linked to the health, comfort and performance of students. It is well established that there are classroom environments where indoor environmental quality is poor. Therefore, the rehabilitation of school buildings is assumed as an appropriate strategy. Consequently, some countries have sponsored nationwide programs for the rehabilitation of school buildings, whose result has been, in some cases, other than the expected. Classrooms performance in service conditions must be evaluated and, from the results, optimized solutions should be established and carefully designed and executed to have the desired effect. Thus, a research project was defined, aiming to assess the impact of retrofit on the indoor environmental quality of school buildings. The methodology used included the in situ measurement of temperature, relative humidity, carbon dioxide concentration and ventilation rates. A total of 24 classrooms of 9 school buildings (2 non-retrofitted and 7 recently retrofitted) were studied. A long term monitoring was defined with three measurement campaigns: winter, mid-season and summer conditions, each with three weeks length. The results confirmed that non-retrofitted schools need to improve their indoor environmental conditions and in retrofitted buildings mechanical ventilation systems are not being used, with important consequences on the indoor air quality.

Introduction

Excellence in education is a clear aim of any modern society. Several international studies have been conducted to evaluate student performance and the factors that most influence it, namely the indoor environmental quality (IEQ) of the classrooms [1], [2].

In recent decades the occupancy levels of the buildings, the construction practices (lower air permeability of the envelope and the generalized use of heating, ventilation and air conditioning (HVAC) systems) and the users’ expectations have dramatically changed, leading to a growing interest in the theme of the IEQ. In fact, nowadays the IEQ is an important factor for the health, comfort and performance of populations, since in developed areas of the planet people spend most of their time inside buildings [3]. In addition, indoor environmental factors significantly affect the energy consumption of a building and, therefore, their evaluation and quantification during the design process has been widely debated [4], [5].

The concept of IEQ is very broad and depends on many variables such as temperature, relative humidity, air velocity, air flow, occupancy, concentration of pollutants, noise, lighting, etc. These can be grouped into four major areas that define the quality of the environment inside a space, namely: thermal comfort, indoor air quality (IAQ), visual comfort and acoustic comfort [6], [7].

Environmental conditions inside classrooms, including the effect of temperature and IAQ, influence students’ health, attitude and performance. It is well established that there are classroom environments where IEQ is poor [1], [8], [9], [10], [11], [12], [13], [14]. Knowing that children spend a large amount of their time inside school buildings and that they are more susceptible than adults to the adverse effects of indoor pollutants, since their ratio of air breathed volume versus weight is greater and their tissues and organs are still growing, the rehabilitation of school buildings is assumed as an appropriate strategy, and that will have repercussions throughout the school environment, ensuring that users have the adequate conditions for carrying out their work. This issue has gained particular importance in recent years and has been studied by several researchers [2], [15], [16], [17], [18], [19], [20], [21].

Furthermore, the rehabilitation of school buildings is also an exceptional opportunity to guarantee a significant improvement in their energy efficiency, which is essential, since these buildings are responsible for a large percentage of the energy consumption in the public sector. In 2002, the Directive 2002/91/EC [22] (EPBD) of the European Parliament and Council was published, recently recast by Directive 2010/31/EU [23], with the main objective of “to promote an improvement in the energy performance of buildings”, establishing very tough targets for the reduction of energy consumption. It sets the year 2020 as the date on which all new buildings must be “Nearly Zero Energy Buildings”, and in public buildings the date is anticipated to 2018 [23]. In relation to school buildings, in Europe there is a growing concern and awareness of the need for the use of sustainable strategies, measures and constructive solutions, both in new and renovated buildings. In a study sponsored by the International Energy Agency (IEA) in order to assess the impact of different strategies for the rehabilitation of school buildings concerning their energy consumption, it was found, by analyzing actual cases, that the heating load can be reduced by up to 75% and the electricity consumption can be reduced by 40% [24]. Yet it must be referred that this study was developed in northern European countries.

Consequently, some countries have sponsored nationwide programs for the rehabilitation of school buildings, whose result has been, in some cases, other than the expected. Several studies have shown that the performance of buildings after rehabilitation is substantially different from that assumed in the design stage [25], [26], [27], [28]. Typically, the indoor temperature is higher than the one predicted. In fact, the models used in codes of practice have proved inadequate in some situations, since the users’ behavior is impossible to predict with accuracy. Sociological and cultural aspects are sometimes crucial for the understanding of their behavior [29]. Table 1 presents the hygrothermal requirements in several international standards.

Classrooms performance in service conditions must be evaluated and, from the results, optimized solutions should be established and carefully designed and executed to have the desired effect. This is particularly important in a time of severe economic crisis, with few available financial resources and, as such, their management and the investment decisions require great prudence from the decision maker. In southern European countries, with mild climate, these problems are under discussion and some studies are being published [21], [26], [30], [31], [32], [33], [34].

Recently was performed a study in France that included 489 classrooms of 108 school buildings [13]. The most representative ventilation system was mechanical ventilation, installed in 20% of schools, 60% of which had mechanical extraction. Three air pollutants were measured, including CO₂, for 2 weeks and throughout a total period of one year. In the occupation period, 33% of the schools revealed CO₂ concentration above 1700 ppm in more than 66% of the records. Conceição and Lúcio [21] monitored 2 unoccupied classrooms of 1 school in the south of Portugal, ventilated in accordance with the philosophy of cross ventilation, using the bottom-hung windows opening, located above the main doors and windows (sliding windows). Santamouris et al. [33] monitored the IAQ in 62 classrooms of 27 naturally ventilated schools of Athens. The measurements were taken in the spring and fall seasons when window opening is the main ventilation procedure. Three situations were assessed: (a) empty rooms and windows closed, (b) during classes, with some windows opened; (c) between classes, with most of the windows opened. The average flow rates obtained were 1.5 l/s/person, 4.5 l/s/person and 7 l/s/person, respectively. During the three measurement periods, 52% of the classrooms presented a CO₂ concentration greater than 1000 ppm with a median of 1070 ppm. At the end of the class period, there was a maximum concentration of 3000 ppm with a median of 1650 ppm. A statistically significant relationship between the window opening and difference in indoor–outdoor temperature was confirmed. Katafygiotou and Serghides [35] conducted a field study in a secondary school building in Cyprus, to assess the indoor thermal conditions during the students’ lesson hours. Air temperature and relative humidity were monitored throughout the four seasons of the year. During winter temperature ranged between 19 °C and 26 °C and relative humidity between 50% and 60%, during summer temperatures varied from 27 °C to 35 °C and relative humidity from 40% to 46%. Giuli et al. [36] evaluated the indoor environmental comfort, from March to June, in four Italian classrooms by means of spot-measuring campaigns, long-term monitoring, and surveys. The school building were not equipped with a mechanical ventilation system, therefore CO₂ concentrations were extremely high in all the classrooms, and they decreased as hot season approached since the windows were opened more frequently. Operative temperatures varied from 20 °C to 30 °C during the spot-monitoring campaigns and, considering the whole monitoring period, it came to light that from May indoor temperatures were unacceptable most of the time, since they often exceeded 30 °C. This paper describes the results obtained on the evaluation of the IEQ of 24 classrooms, of 9 schools, by in situ measurement of temperature, relative humidity, carbon dioxide (CO₂) concentration and ventilation rates in school buildings located in Portugal. A long term monitoring was defined with three measurement campaigns: winter, mid-season and summer conditions, each with three weeks length. Results enhanced the discussion about the “in-use” performance of schools, which is decisive to understand how designed performance is actually experienced, including the impact of refurbishment efforts.