THERMAL COMFORT IN A UNIVERSITY CLASSROOMS IN RIETI, CENTRAL ITALY

Abstract


The study investigated the indoor climatic issues in a university classroom. Data were collected in 2 days, at the peak of sunlight exposure, with each sampling lasting 2 hours. To measure microclimatic indexes HD32.3 instrument (Delta OHM) was placed in the barycenter of the enclosed space; the average values of the indoor parameters were monitored every 15 seconds. The maximum values of temperature and humidity were detected using a multi-meter; a tridimensional volume was built and the surface temperature variation analyzed. During the first sampling campaign (empty classroom) high thermal discomfort was estimated. PMV resulted >1.3 and PPD showed values >40%. During the second investigation (classroom full) physical variables kept growing despite ventilation/air circulation/air movement. The results show high thermal stress, consequence of a bad built envelope. It is necessary to modify it, considering its key role in reducing the indoor thermal stress and its energy requirements.

Relevance. Italian legislation on school architecture is obsolete, and must be updated, considering also the importance of thermal comfort on wellbeing and performances of users. This type of investigations can contribute to guarantee a safe environment through the definition of precise and targeted legislative prescriptions. Introduction. Indoor environment is one of the major health determinants in both developing and developed countries [1,2]. In particular in developed countries people nowadays spend over 90% of their lifetime indoor [3,4]. Among the different working and life spaces schools and universities play a key role in indoor health determination for both students and teaching staff. In general, high levels of indoor environmental quality can lead to positive effects in terms of satisfaction and productivity [5]. Several studies show the association between indoor parameters, health and academic performance of students [6,7] and thermal comfort, in both naturally and mechanically ventilated classrooms, is than a basic requirement [8]. Thermal environment includes a number of parameters such as air temperature, mean radiant temperature, relative humidity, thermal radiation, air speed, as well as human activity, gender, and clothing insulation [9,10]. Recently studies showed that schoolwork performance was increased at temperature levels around 21±1°C in regions with moderate climate. It was calculated the percentage of performance change, per degree increase in temperature [11] and the results show an increase in performance with up to 21.5±0.5 °C temperature, with the highest productivity being at 22 °C. On the contrary, the performance tends to decrease with an increasing of the temperature (above 23.5±0.5°C). As reported in the Italian registry of schools of the MIUR - Ministry of Education, University and Research [12], the majority of Italian schools are housed in old buildings and they have structural and functional problems (e.g. insufficient space and safety, poor indoor air quality, low thermal and acoustic comfort). They are mostly energy-inefficient due to obsolete systems, the facades are poorly or not at all insulated, and often windows are single-glazed. Similar data are reported in the literature [13] Several investigations performed in Italian schools showed a widespread indoor thermal discomfort [14-17]. Students are one of the most reactive categories to indoor air quality, because they spend most of their daily time within the classrooms. Unhealthy microclimatic values influence mental and physical development of the students, as well as their attention and concentration levels, hindering in turn both the achievement and maintenance of healthy conditions. The aim of this study is to investigate on the thermal comfort of the classrooms of a university building located in Rieti (Part of Sapienza University of Rome), a small Italian town situated in the Latium region (Central Italy), in order to promote a balanced integration between architectural features, indoor thermal requirements, human health safeguard and energy consumption saving. Methods. This investigation, based on Fanger’s indexes [18], reports the evaluation of the thermal comfort of a classroom of Rieti’s university. Rieti is situated in the North-East of Latium, central Italy, and it’s characterized by an inland transition climate with dry hot summers and humid winters. The university itself is in a development area nearby the city center (Fig.1 (a)). The three floors building, object of the study, houses one of the Engineering schools of Rome’s Sapienza University on its top floor. The four facades of the building are respectively oriented on the East-West axis the long ones, and North-South the short ones. The analyzed classroom is located on the South-South-Est facade of the building, and it is almost always sunny during the day (Fig.1 (b)). a) b) c) Fig. 1. a) Building location, b) Classroom individuation, Building characteristics, Sun trend, c) Classroom detail The classroom has an octagonal shape and its facade is single-glazed, shaded with internal blinds (black). The surface of the classroom was schematized by a regular grid, a barycenter and 14 points were pinpointed respectively for automatic and manual measuring. Three heights were considered in each of the 14 points of the grid (0.95 m - 1.60 m - 2.15 m). Data was collected in 2 separate days, at the peak of sunlight exposure (Fig.1 (b)), that’s considered the worst case, with each sampling lasting 2 hours (12:00 pm to 02:00 pm, summertime). The first sampling (May 6th, 2015) was performed in an empty classroom and monitored under “controlled” conditions, keeping windows, blinds and doors closed. The measure was performed in an attempt to minimize window and door influences. Heating, ventilation, air conditioning systems were operated with fans in the “off” position during the monitoring period. The second sampling (May 12th, 2015) was performed in a crowded classroom (20±2 occupants). Data loggers recorded under “normal use” conditions, keeping windows, doors and blinds opened. Lighting was switched on only during the second monitoring; the air conditioning was kept off, as chosen by the students, because it was considered both noisy and ineffective. The primary aim of this study was to assess thermal comfort based on the predicted mean vote (PMV) and predicted percent dissatisfied (PPD) indices using subjective (clo and met) and experimental measurements (UNI EN ISO 7730, 2006) in the most critical classrooms (object of the study) at a university in the summer time. To measure microclimatic parameters and indexes a HD32.3 instrument (Delta OHM) was used. It was placed in the room’s barycenter (Fig.1 (c)); the instrument monitored automatically the average values of the indoor parameters every 15 seconds. The environmental parameters measured have been: wet bulb temperature, dry bulb temperature, medium radiant temperature, relative humidity and air velocity. PMV and PPD indexes were laid out from the experimental measurements made with HD32.3 instrument and imposing values set a priori, which aim to represent a person at rest with light clothing (with thermal resistance of clothing = 0.45 clo and metabolic expenditure =1.59 met). At the same time, without interfering with the analysis, the maximum values of temperature, humidity were detected by means of a multi-meter. Through manual measuring of data, it was possible to build a tridimensional volume (14 points x 3 heights) and analyze the surface temperature variations. Results and discussion. Table 1 shows the average values of indoor and outdoor parameters and comfort indices detected during the investigations, and Table 2 shows their Δvalues. During the first sampling (classroom empty), the outdoor parameters values are proportional to those indoor. Indoor relative humidity decreases slightly complying with outdoors; this phenomenon is due to high indoor temperature and to lack of ventilation. Table 1. Average values and standard deviations of indoor and outdoor parameters and indices during the experiments Outdoor Indoor Date T (°) RH (%) Va (m/s) T (°) RH (%) Va (m/s) PMV PPD (%) May/06/2015 29.3±0.1 36.3±0.1 5.1±0.4 27.9±0.2 41.0±0.4 0.00±0.00 1.3±0.1 40.4±2.6 May/12/2015 26.0±0.1 28.5±0.1 2.9±0.4 29.0±0.1 26.9±0.1 0.02±0.01 1.5±0.1 51.5±0.9 Table 2. Δ values of indoor and outdoor parameters and indices during the experiments Outdoor Indoor Date ΔT(°) ΔRH (%) ΔVa (m/s) ΔT(°) ΔRH (%) ΔVa (m/s) ΔPMV ΔPPD (%) May/06/2015 28-31 29-45 2.1-16.7 27.4-28.3 40.1-42.1 0.00 1.2-1.4 34.0-45.3 May/12/2015 25-27 28-29 1.0-5.6 28.5-29.2 24.3-29.2 0.01-0.17 1.4-1.5 47.6-53.7 It’s interesting to analyze the relationship between indoor and outdoor temperature during the second sampling, where a low temperature outdoor meets a higher temperature indoor. In the sampling, under “closed” conditions, the variations of air temperature and relative humidity have raised PMV (from 1.2 to 1.4) and PPD parameters (from 34.0 to 45.3). During the second analysis (classroom full) physical variables kept growing despite ventilation that, however, within the classroom is very low (0.02 m/s (±0.01). In fact, although outdoor ventilation is 2.9 m/s (±0.4), it did not interest the indoor environment due to unfavorable wind direction (mainly from West-North-West; variable azimuth direction from 270±15° to 315±12°). In both sampling campaigns the average values of the indices PMV (Table 1) are respectively 1.3 (empty classroom) and 1.5 (full classroom), showing a high level of discomfort, which means that about one out of two persons is dissatisfied; PPD value ranges from 34-45.3% in the classroom empty, to 47.6-53.7% in full classroom (Table 2). The 3d graphs reported in Fig. 2 and Fig. 3 represent surface variation of temperature at levels 1.60 m and 2.15 m in the enclosed space. Manually collected data were used to build these tridimensional diagrams. In the “empty classroom” condition (Fig. 2) it can be noticed that temperatures are higher at level 1.6 m than 2.15 m. This is due to direct solar radiation at 1.6 m. A convective scheme is set with one current going upwards, over heated surfaces, and one going down where heat is dissipated through walls. The temperature near the partitions results higher, if compared with other points of the surface. This is explained with the fact that heat is re-radiated, and by convection transferred in great quantities within the building itself. In the “full classroom” condition (Fig. 3), height 2.15 m shows the maximum surface temperature, given that at this altitude air is heated by convection from the roof, hit by direct solar radiation. Fig. 2. Overlay of superficial temperature variation graphs and classroom map (classroom empty) Fig. 3 Overlay of superficial temperature variation graphs and classroom map (classroom full) Conclusions. As observed in similar investigations performed in other Italian education facilities [14-17] our study shows high thermal discomfort in the examined classroom. This is a consequence of several factors, that include poor building envelope characteristics, but also a badly arranged air-conditioning system. The inadequate indoor temperature is mainly related to the solar radiation transfer at mid-day (summer-time case), that alters the microclimatic environment parameters. Air conditioning systems (two devices) inside the classroom were not used, mainly because they are noisy, but also because they have not enough power to maintain optimal indoor climate. First of all, it should be useful to modify built envelope, which plays a key role in reducing directly the indoor thermal stress and its energy requirements. In our opinion it is necessary to reduce the thermal exchanges between indoor and outdoor environment using insulation on cladding and better fixtures. Currently the structure presents many thermal bridges due to the obsolete building techniques. In the warm season the need to adopt solutions to control solar radiation during critical hours of the day is clear. The installation of a new air conditioning system would not solve the upstream problems, with an expenditure of energy probably ineffective. Many systems were taken in consideration, ranging from the cheapest to the most expensive. In general, external solar filters (brise-soleil, venetian blinds) are more efficient than internal ones, like indoor venetian blinds or curtains that gather heat indoors. These solutions, combined with a more efficient air conditioning system can contribute to improve indoor thermal comfort. Finally, accurate studies need to be conducted on thermal comfort in the classrooms located on the North side of the building, especially during cold season, considering that Rieti has long winters and temperatures often drop below 0°. These rooms in fact communicate with the masonry, which by convection will cool adjacent spaces, leading to an increase in energetic expenditure. More attention ought to be paid by both university and lawmakers in order to protect students’ health, improving hygienic conditions of classrooms, as expressed also by recent legislative interventions and scientific statements on the matter. (19, 20)

Valeri Diego

Rieti Unit c/o “Sabina Universitas”; Department of Civil; Building and Environment of Sapienza University of Rome

Capasso Lorenzo

Experimental and Forensic Medicine

D’Alessandro Daniela

Rieti Unit c/o “Sabina Universitas”; Department of Civil; Building and Environment of Sapienza University of Rome

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