Analysis of energy consumption in the high schools of a province in central Italy

Energy and Buildings 34 (2002) 1003±1016

Analysis of energy consumption in the high schools of a province in central Italy Umberto Desideri*, Stefania Proietti Dipartimento di Ingegneria Industriale, UniversitaÁ di Perugia, Via G. Duranti 93, 06125 Perugia, Italy Received 15 October 2001; accepted 1 February 2002

Abstract This paper presents an energy analysis of the school buildings of a province in central Italy. The analysis is aimed at calculating the main thermal and electric energy consumption indexes to determine the status of energy consumption and the possible intervention to save energy in the school sector. Two applications of energy auditing to school buildings are also presented. It is also shown that if the optimal energy consumption indexes could be valid for all the school buildings, thermal energy savings could reach 38% and electric energy consumptions could be reduced by over 46%. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Energy consumption; Schools; Energy saving in buildings

1. Introduction The electric and thermal energy consumption of the 8000 Italian school buildings can be estimated in about 500,000 PET per year corresponding to 60 kg of oil per student per year [1]. Such a considerable amount of oil consumption can be signi®cantly reduced if appropriate energy saving techniques and renewable sources are used. Moreover, through a careful control of the energy consumption, all the internal environment factors can be ef®ciently managed. At the same time, a correct energy management may also improve the environmental comfort in the school buildings. In the ®eld of energy saving in buildings, the interest towards the school sector is deeply motivated: schools have standard energy requests, and high levels of environmental comforts have to be guaranteed. The typology of Italian school buildings is quite varied. The age and insulation of walls, roofs and windows can be signi®cantly different, and therefore, energy consumption can differ considerably. In many cases, energy management is not available and obsolete technologies for lighting and climatization are often used. The total number of school buildings makes it a priority issue for an intervention of energetic upgrade and improvement. With reference to the province of Perugia, which is located in central Italy, only *

Corresponding author. Tel. ‡39-075-585-3743; fax: ‡39-075-585-3736. E-mail address: [email protected] (U. Desideri).

few school buildings have been monitored or studied to determine energy consumption. In most cases, the technical interventions have only considered a technology and safety upgrade of thermal and electric plants to comply with new safety regulations. In order to make a complete proposal in the ®eld of energy saving, qualitative and quantitative information on the energy consumptions and on the up-to-date conditions are necessary. The study described in this paper was carried out in collaboration with the Energy and Environment Agency (AEA) of the province of Perugia within the framework of the training pupils for energy analysis in school buildings (TEACH) European union project [2]. The main purpose of the project is to promote a methodology of energy analysis for energy saving and rational use of energy in schools buildings. The methodology of study can be applied to all the European school buildings, can be shared by the students and it involves the data collection about the structural characteristics and the energy consumptions of the schools, the energy diagnosis and the de®nition of possible interventions. The results of this action can be addressed to schools, students and private and public administrations that manage schools at local level and that will be provided with a concrete instrument to decide energy saving initiatives. The energy auditing of the schools has an additional aim: to build a report on the energy use in the school ®eld. It represents a way to experience, in the case of a joint analysis, the self-diagnosis of a system and to identify needs and

0378-7788/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 7 7 8 8 ( 0 2 ) 0 0 0 2 5 - 7

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U. Desideri, S. Proietti / Energy and Buildings 34 (2002) 1003±1016

priority interventions. The costs-bene®ts analysis of the project is connected to the diffusion of the joint analysis methodology and to the number of energy improvements that will be applied. Further bene®ts, that cannot economically be quanti®ed, come from the growing awareness of the students about energy savings problems and the use of renewable sources, themes that ®nd little space in the didactic ®eld. During the auditing phase in the schools, it was experienced that problems connected to energy saving are hardly ever discussed in classes. 2. Energy consumption and rational use of energy in schools The diffusion of school buildings overall the Italian territory is quite uniform in relation to the population. In the last years, the Italian government has signi®cantly reduced the number of schools increasing the number of students per school and concentrating the number of schools in major towns and cities. 2.1. Energy audit of school buildings electric and thermal plants The method of analysis of the energy consumption in school building is based on the following points:  identification of thermal and electric consumption parameters which could be used for an energy re-qualification without any kind of alteration on the internal environment comfort;  establishment of the steps for a correct energy diagnosis;  definition of the energy saving and rationalization interventions which are economically feasible. A school building is characterized by a peculiar use: the daily and weekly hours of occupation, different uses during the day, and different uses of the volumes: classrooms, toilets, of®ces, laboratories, exercise rooms. The problem of a rational use of energy in school buildings is strictly connected to a correct plants management and to a quali®ed maintenance. These two points are important in order to ensure an environmental comfort with the highest level of energy ef®ciency and economic convenience. The rational use of the energy in the school ®eld is related to many factors, such as the building structure, lighting, technological uses, heating systems, occupation density of the school structures. School buildings of the province of Perugia differ signi®cantly for the age and location of the building, but are representative of the situation in Italy. The old-structured school buildings, generally located in the historical centres, are in most cases one bloc structures, built with bearing walls with high thermal inertia, but having low insulation single-glass window frames. The most recent school buildings, generally located in the outskirts of towns,

are often modular prefabricated buildings and they are divided in blocks, often on a single ¯oor and have high energy consumption. Rooms' lighting plays an important role in energy consumption of school buildings, and it is the only energy consumption in schools without laboratories. In nearly all the school buildings, the presence of high quality ef®cient lighting systems is important. Ef®cient natural lighting is only applied in new buildings, equipped with wide windows both in classrooms and in workshops and laboratories. More recently, the introduction of classes of computer science has increased the number of laboratories equipped with personal computers. In the laboratories of the technical high schools, there are often machine-tools and electronic instruments. For the classrooms and laboratories with signi®cant energy consumption, it is very important to determine the free heating supplied by machines, scienti®c instruments and personal computers. Thermal energy is the main consumption in all kinds of schools, representing about 80% of the total energy consumption. The heating system in most schools is traditional, without a control systems for the ¯ow rates and without thermal control of the classes. The heating elements are radiators, except in big spaces such as gyms and laboratories where forced convection heat exchangers are generally used. The most common fuels are natural gas and oil. The particular use of school building volumes causes situations where spaces may be crowded in certain times and completely empty in others. It is clear that the internal climatic conditions affects the free heating supply due to human presence, the needs of lighting, and obviously the essential air changes. The main factors that determine a healthy environment and that weigh on the energy consumption are the air changes, the temperature and the humidity, the average temperature of the walls and the level of lighting. The ®rst and necessary stage of a diagnostic procedure for the energy audit of school buildings is the analysis of the building and the analysis of the thermal and electric plants. To analyze a building means to examine carefully its structural typology, in order to identify possible defects in thermal insulation and the thermal±hygrometric characteristics of the outer surfaces. Moreover, net heated volumes are to be determined, in order to estimate thermal needs. To analyze the electric consumption, a preliminary veri®cation on the electricity bills was performed. To reduce costs, it is sometimes suf®cient to modify the contract with the electric company, but further interventions are necessary to reduce consumption. One of the ®rst interventions consists in correcting the power factor of the installation which is particularly important where machine-tools are present. A second step is the evaluation of the lighted surfaces to verify the possibility to install high ef®ciency lamps. The analysis of the heating system should focus on the control system of the thermal power plant and the building and should evaluate if the combustion ef®ciency is high. It is now common to sign contracts for a ``heating service'',

U. Desideri, S. Proietti / Energy and Buildings 34 (2002) 1003±1016

where a full service including maintenance is provided by external suppliers and the bill is based on the calculation of the heat supplied instead of the fuel consumption. 2.2. Interventions for a rational use of energy It is possible to decide interventions to reduce energy consumption after an energy diagnosis of the structure, the plants and their utilization, starting from the electric and thermal consumptions history. The interventions for a rational use of energy in school buildings can be summarized as follows:  interventions on the electric plant;  power factor correction,  replacement of low-efficiency with high efficiency lighting,  interventions on the heating system;  evaluation of the heat generator,  thermal insulation of piping,  installation of thermostatic values,  control of internal thermoregulation efficiency,  different thermal regulation for different space utilization,  evaluation of the fuel,  interventions on the building;  insulation of the external walls,  external window frames thermal upgrade,  management interventions;  optimization of the contracts with suppliers. Energy savings interventions have to be determined with a cost-bene®t analysis. One parameter used to evaluate the quality of an investment is the net present value (NPV). For every energy re-quali®cation the following parameters have to be ®xed: the life of the investment as the number of years during which the intervention preserves its ef®ciency, the interest rate, the initial investment at the starting date, the cash ¯ow as the reduction of costs during the life. Summing up the discounted cash ¯ows for the total duration of the investment and subtracting the initial investment, we obtain the NPV of the intervention. An intervention can be considered economically convenient if the NPV is positive: the higher is the value of the NPV, the more economically pro®table will be the intervention. In the case of schools, where the comfort of the students is a major priority, the NPV can also be slightly positive. Further economic evaluation parameters of the energy requali®cation interventions are the back discounted time of amortization, that indicates how long we need to recuperate the investment costs; the internal ®nancial gain rate, that indicates the percentage value of the interest of calculation so that the NPV is of no value at the end of the investment's length; the limit investment, i.e. the investment's cost for whom the NPV becomes of no value, that represents the economic limit of the investment's cost so that we retain the economic earning power of the intervention.

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3. Energy consumptions in the high schools in the province of Perugia 3.1. High schools in the province of Perugia During the school year 1999/2000, 7,590,892 students were enrolled at public schools in Italy of every level and typology. There was a decrease of 10.4% in comparison with the school year 1989/1990. The employees in the school sector are more than 961,000, 83% of which is teaching staff, and the rest is administrative and management personnel [3]. In Italy, there are 7952 high schools and they represent 12% of the total amount of schools. The students enrolled in high schools in the year 1999/2000 were 2,419,409, i.e. 31.87% of the total school population. The average number of students in high schools is 304 with an average classes of 22.2. Italian high school population in 1999/2000 has signi®cantly increased compared with the school year 1998/1999. The new law about the raising of the compulsory school age has allowed to recuperate 30,000 students, compensating for the population decrease that continues both in high and junior high schools [3]. The province of Perugia is located in Umbria, which is a region in central Italy divided into two provinces. Umbria has 977 schools, 745 of which are located in the province of Perugia. A total of 85 of them are classical and technicalprofessional high schools and represent 75% of the Umbrian high schools, and 1.07% of Italian high schools. In the school year 1999/2000, 27,396 students were enrolled in the high schools of the province of Perugia [4], divided into 1308 classes. 10,794 students were enrolled in classical and scienti®c high schools, teachers' training and arts schools, 11,040 were enrolled in technical high schools and 5562 in professional training schools. High schools students in the province of Perugia represent 74.8% of the total regional number of students enrolled in high schools and 1.12% of the total national high school population [3]. The statistics of the number of the enrolled students is important not only to validate the meaning of the examined sample, but also to calculate energy indexes. The energy auditing of school buildings in the province of Perugia was restricted to high schools for the following reasons: 1. The maintenance of the buildings and the plants are directly managed by the Perugia Local Administration. 2. The province of Perugia holds the budget for the overall heating costs and contributes with a 35% of the amount (the remaining 65% has to be paid by the single school) for the electric energy. 3. The province is also in charge to do energy savings interventions and for the optimization of the energy sources and of the energy consumption. 4. In high schools it is easier, than in the other schools of different level and typology, to test a ``shared'' energy

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U. Desideri, S. Proietti / Energy and Buildings 34 (2002) 1003±1016

analysis, i.e. an energy analysis of the building-plant system made in cooperation with the students, who are more aware of such problems. 5. High schools generally present a higher school population density. The enrolled students in the examined high schools of the province of Perugia represent 34.14% of the whole school population that attends schools of every level and typology [3]. 3.2. The analyzed sample The ®rst part of this study allowed to know, from a qualitative and a quantitative point of view, the energy consumption in the high schools of the province of Perugia in order to get indications that might de®ne strategies for energy saving. Data on energy consumptions in the high schools were gathered and analyzed. Data was provided by the technical of®ce of the province of Perugia and was correlated to information about the building volumes, school typology and school population [4]. Some schools were visited for a more detailed energy survey. For each school a short report was written, where the causes of particular high or low energy consumptions were described, together with the possible interventions in terms of saving opportunities. For some schools with heating records, data on thermal consumptions for the school years 1995/1996, 1996/1997 and 1997/1998 where collected, for other schools, which have been managed by the province only in the last 3 years, data on thermal consumption was not available. Therefore, the effective consumption was available for only 29 high schools out of 85 schools managed by the province. The electric energy consumptions was available for 13 schools. The analyzed sample corresponds to the 35% of the high schools in the province of Perugia for heating consumptions, and to the 15% for the electricity consumption. This sample was suf®ciently diversi®ed and representative of the whole province, as the buildings that have been analyzed are both classical and technical-professional schools. They all have a number of enrolled students that goes from 100 to 1100 [4] and they are uniformly located on the entire territory of the province. The choice of the most restricted sample of high schools to visit and survey has been made on the consumption data. School buildings were also chosen for each typology (structure of the building, school typology, number of students) in order to respect the proportions of the data population. The schools, where energy survey was performed, were 10, i.e. 35% of the sample. Thermal energy data contained information about room heating load (MWh), installed thermal power (kW) and the type of fuel used. Electric energy data was the active energy (kWh), the reactive energy (kVAh) and, in a few cases, the absorbed power (kW). Structural characteristics of the buildings such as the volume (m3), the orientation and a general indication about the engineering typology and the period of construction were also known.

3.3. Thermal and electric energy consumptions The analysis of collected data allowed to identify situations of high and low energy consumptions and to correlate them to building-plant solutions and engineering techniques. For each school the speci®c consumption's indexes were calculated, that made possible to compare energy consumption of very different building schools in terms of size, typology and number of students enrolled [5]. The indexes used in the analysis are the following:  IV: Thermal energy specific consumption per unit volume (kWh/m3 per year) calculated as the ratio between the annual thermal energy consumption provided by the heating plant and the total heated volume of the building [6].  IS: Thermal energy specific consumption per student (kWh per student per year) calculated as the ratio between the annual thermal energy consumption provided by the heating plant and the number of enrolled students [6].  IC: Thermal energy specific consumption per class (kWh per class per year) calculated as the ratio between the annual thermal energy consumption provided by the heating plant and the number of classes [6].  EV: Electric energy specific consumption per unit volume (kWh/m3 per year) calculated as the ratio between the total annual active electric energy consumption and the volume of the building [6].  ES: Electric energy specific consumption per student (kWh per student per year) calculated as the ratio between the total annual active electric energy consumption and the number of enrolled students [6].  EC: Electric energy specific consumption's index per class (kWh per class per year) calculated as the ratio between the total annual active electric energy consumption and the number of the classes. It was chosen to calculate the energy indexes per unit volume instead of unit surface because the structure of the schools is so different that the surface could not be considered a reference unit. Energy consumption is mainly linked to the height of the rooms and rooms with the same surface and comfort but different heights have different energy consumptions. The elaboration of the indexes has outlined a ®rst general description of energy consumptions related to the different characteristics of the schools. We have compared the energy data, expressed with the speci®c consumption's indexes and the parameters that characterize the different schools: building typology and construction period, school typology (industrial and professional technical schools, and scienti®c and humane science schools), characteristics of the technological systems. 3.3.1. Thermal energy consumptions The total consumption of thermal energy for the 29 school buildings located in the different climatic zones of the province territory is 811 PET per year. For the analyzed

U. Desideri, S. Proietti / Energy and Buildings 34 (2002) 1003±1016

schools, thermal consumption is about 80% of the total yearly energy consumption, and it is within the average reported in the literature [6,7]. On the basis of the consumption reported for the selected school buildings, the `thermal energy speci®c consumption index per volume unit (IV), per student (IS), and per class (IC)' were calculated for each school and were reported in Table 1. Calculated values considered the 3-year consumption mean [6]. The necessity to calculate the `speci®c consumption indexes' has been determined by the fact that the school buildings are not similar. It includes schools with very different characteristics, in terms of number of enrolled students, disposition of volumes and destination of use. The values of the consumptions indexes are consequently different on the basis of the building typology, school typology, kind of fuel of the thermal system, as shown in Table 2. The values of the thermal energy speci®c consumption index per volume unit (IV) are shown in Fig. 1, the values of the thermal energy speci®c consumption index per student (IS) are shown in Fig. 2. From the analysis of the data, it derives the structure of thermal consumptions in examined school buildings. A reinforced concrete structure and an external plugging of various materials, dated 1970±1980s, are the building typology with the highest consumptions. The old and historicmonumental buildings with a masonry structure, often located in the historic centers, have average IV values and the lowest IS values. This demonstrates that these structures preserve their own energy value, in spite of the age of technological plants. The lowest speci®c consumption values characterize the reinforced concrete structured buildings with plugged-in prefabricated panels, built in the 1990s. It is more dif®cult to interpret the data of the consumption indexes reported for the didactic typology: we have

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Table 1 Values of thermal energy specific consumption indexes Schoola

IV (kWh/m3 per year)

IS (kWh per student per year)

IC (kWh per class per year)

C1 A1 A2 B1 B2 A3 C2 A4 C3 B3 B4 B5 A5 B6 B7 B8 B9 A6 B10 A7 C4 C5 B11 A8 C6 C7 B12 B13 B14

23.1 18.5 17.8 20.9 17.7 18.6 15.4 84 13.7 40.6 19.3 18.4 19.5 25.1 20.7 18.5 15.4 25.9 22.9 23.0 16.1 17.8 15.3 15.0 11.3 12.7 14.4 96 n.a.

510 392 354 342 931 452 534 427 911 1368 974 467 498 1375 1061 1254 652 458 1721 703 421 898 815 320 308 1349 323 585 2012

11142 8127 7568 7060 21420 10329 11283 9565 18213 25377 21531 10181 11336 32254 21854 27598 13684 9695 32698 15204 8552 17971 18442 7831 6873 27649 6062 12237 42387

a

A: scientific and humane science high schools; B: technical commercial schools and technical schools for geometers; C: technical and industrial schools with technical laboratories.

Table 2 Mean values of the thermal energy specific consumption indexes Distribution Building typology Old buildings Reinforced concrete and plugging Reinforced concrete and prefabricated construction Didactic Typology A Scientific and humanistic high schools Technical schools for geometers B Technical commercial schools Commercial schools C Industrial and technical schools Fuel Natural gas Gas oil 5/7 oil

IV (kWh/m3 per year)

IS (kWh per student per year)

IC (kWh per class year)

17.5 21.7 15.8

493 1003 744

10812 21283 15352

18.3 20.3

451 1326

9957 27059

21.2 17.4

989 569

21135 12022

15.7

704

18009

18.5 17.9 19.1

699 680 986

14496 13963 21781

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Fig. 1. Thermal energy specific consumption's indexes per unit volume: (A) scientific and humane science high schools; (B) technical commercial schools and technical schools for geometers; (C) technical and industrial schools with technical laboratories.

considered classic and scienti®c schools (Liceo) and Technical schools (industrial, commercial, experimental and those for geometers). The IV is lower in industrial technical schools, as they are equipped with irregularly heated laboratories. The lowest IS value has been found in classic and scienti®c high schools, as a consequence of the highest school population density. The consumption indexes diversi®ed for the kind of fuels used in the thermal system show

that the consumption of the schools equipped with thermal oil-burning generator is higher. 3.3.2. Electric energy consumptions The consumption data of electric energy in 13 High Schools was analyzed. Data from the technical of®ce of the province of Perugia were integrated with information got in the schools examined. Table 3 shows the main characteristics

Fig. 2. Thermal energy specific consumption's indexes per student: (A) scientific and humane science high schools; (B) technical commercial schools and technical schools for geometers; (C) technical and industrial schools with technical laboratories.

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Table 3 Characteristics of the selected schools and electric consumptions in 1998 School

Type of structure

Volume (m3)

Students

A1 A4 B2 C1 A5 A6 B4 B6 B15 A7 B10 B13 C6

Antique building Antique building Antique building Antique building Reinforced concrete Reinforced concrete Reinforced concrete Reinforced concrete Reinforced concrete Reinforced concrete Reinforced concrete Reinforced concrete Reinforced concrete

6600 11408 24234 13500 13727 8219 30054 20165 9060 11874 7120 15225 26739

311 224 460 612 728 466 597 422 342 389 95 251 982

and and and and and and and and and

plugging plugging plugging plugging plugging prefabricated prefabricated prefabricated prefabricated

construction construction construction construction

of the schools, electric consumptions taken from the ®nal balance in the year 1998, and the absorbed power. For some schools two values of absorbed power were reported. It is a kind of contract ``double use'' that uses two different power levels for the high consumption period (school year) and for the low consumption one (summer period). On the basis of the consumption values, the electric energy speci®c consumption's indexes per volume unit (EV), per student (ES), and per class (EC) were calculated and reported in Table 4 and in Figs. 3 and 4. The consumption values considered in the calculations are the active electric energy [6], measured in (kWh). Table 5 shows the average indexes of the speci®c consumption of electric energy on the basis of the division in building and school typologies. Through the analysis of the energy consumption of the 13 school buildings considered it can be noted that the EV index is particularly high in the schools located in ancient buildings, because of the obsolescence of lighting systems and of the smaller size of the windows. The most recent buildings present an average EV value and the highest ES among the structural

Table 4 Values of electric energy specific consumption indexes School

EV (kWh/m3 per year)

ES (kWh per student)

EC (kWh per class per year)

A1 A4 B2 C1 A5 A6 B4 B6 B15 A7 B10 B13 C6

2.9 2.1 1.5 6.2 2.3 4.1 2.1 4.2 2.1 3.8 1.7 4.4 2.7

63 108 80 137 43 73 107 202 55 117 129 267 73

1315 2424 1832 3000 981 1551 2363 4727 1043 2533 2452 5583 1569

Absorbed power (kW) 20 2025 35 1540 20 30 1525 2440 25 n.a. n.a. 1580 2050

Active energy (kWh) 19726 24244 36650 84000 31388 34117 45665 85080 18769 45596 12262 67000 72180

typologies we have analyzed. All this can be connected to the kind of systems that ensures the lighting standard and to the tools which have a high energy absorption. The highest energy consumptions characterize technical schools and in particular industrial technical schools, for the strong presence of high energy absorption machine-tools and equipments. 3.4. Results of the general analysis Energy consumptions analysis of the high schools of the province of Perugia is similar to data presented in the literature [7]: in the analyzed schools, electric energy represents between 15 and 25%, while heating contributes for up to 80% of the total yearly energy consumption. A correct energy management and upgrade interventions in this ®eld may enable the schools to obtain economic advantages and make larger ®nancial sources available for didactic purposes. After the analysis of the speci®c energy consumption indexes, a sample of 10 high schools was chosen to perform a more complete analysis and to understand their peculiarities. The aim of these technical controls was to complete a ®rst audit of the structures considering speci®c consumptions, higher or lower than average values, in order to:  verify the validity of the methodology and of the parameters used in the preliminary phase of the analysis for a first energy comparison between school buildings;  correlate particular structural and engineering situations to the high consumptions or the good energy ``yield'' [6] of the examined schools;  identify possible improvements to energy management;  identify the school buildings where the energy analysis could be shared with the students. 4. Energy survey in school buildings Even though the examination of the energy indexes are signi®cant, they are not exhaustive for the knowledge of the

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Fig. 3. Electric energy specific consumption's indexes per unit volume: (A) scientific and humane science high schools; (B) technical commercial schools and technical schools for geometers; (C) technical and industrial schools with technical laboratories.

energetic situation of the schools. To re®ne the investigation a more speci®c research in some school buildings was carried out. The preliminary analysis of the energy indexes for every building typology, showed structures with higher and lower consumption. The schools, which had energy indexes far from the mean values, were visited to make an energy survey to determine the main causes of the too high or too low values of energy consumption and to propose possible interventions in the ®eld of rational use of energy.

Schools with a particular low energy consumption were also surveyed to verify the ambient comfort conditions and to determine the best engineering solutions, that could be applied to new projects and new buildings. An energy survey card [5,8] was prepared for the study of the chosen sample, where all the elements related to the ambient context, school typology, structural characteristics of the buildings and the technological systems have been codi®ed. The card has been set according to the basic model

Fig. 4. Electric energy specific consumption's indexes per student: (A) scientific and humane science high schools; (B) technical commercial schools and technical schools for geometers; (C) technical and industrial schools with technical laboratories.

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Table 5 Mean values of electric energy specific consumption indexes Distribution Building typology Antique buildings Reinforced concrete and plugging Reinforced concrete and prefabricated construction Didactic typology A Scientific and humanistic high schools Technical schools for geometers B Technical commercial schools Commercial schools for geometers C Industrial technical schools

EV (kWh/m3 per year)

ES (kWh per student per year)

EC (kWh per class per year)

3.2 2.9 3.1

97 96 146

2143 2133 3034

3.1 1.6

81 104

1761 2142

4.3 2.1

234 81

5155 1703

4.5

105

2284

used in the buildings energy certi®cation practice [8], introducing modi®cations in order to adapt the cards to the peculiarities of the energy parameters of schools. The survey concerning physical and technical characteristics of the systems and of the buildings has sometimes gained a qualitative character, since it has not always been possible to ®nd all the necessary data for the energy diagnosis. The collected data on the ®eld were integrated with those provided by the technical of®ce of the province of Perugia (volume and surface of the buildings, and the energy bills), by the company that manages the heating system (data related to the daily average working hours of the plants), and by the School Buildings Basic Informatory Management of the Public Education Ministry (for some structural data relating to energy consumption). For each of the examined schools a technical report was prepared with the aim of describing the building energy characteristics. In this paper, three case studies, carried out in school buildings chosen from the preliminary examination of the energy consumption indexes and belonging to the three main building typologies are described. 4.1. The ``Franchetti'' Public Technical Industrial High School of CittaÁ di Castello The technical industrial high school ``Franchetti'' is located in the urban centre of CittaÁ di Castello, in a highly populated area of the town. In the school year 1999/2000 612 students, divided in 28 classrooms attended the school and the school population is still increasing. From the preliminary energy consumption analysis, it was shown that the school has the highest speci®c thermal consumption per unit volume among the schools located in antique buildings: this school consumes 2 kg oil per cubic meter, while the yearly energy consumption per student is 44 kg oil. The school was visited to understand its structural conditions and the causes of such a high energy consumption. The general information about the examined school is reported in Table 6.

The school is oriented along a S/E±N/W axis. The presence of other adjacent buildings creates signi®cant shading on the analyzed structure. The building is structured in two different bodies, for both the age and the building technology used. The two buildings are adjacent, linked and connected at different levels and are exclusively used for didactic purposes. The larger building is a historic-monumental structure of the XV century; it is realized with masonry and exterior plaster still in a good state of conservation. The average thickness of the walls is between 60 and 80 cm, but no thermal insulation materials were found, either in the external walls, or under the roof. The average height of the rooms varies from 4 m in the classrooms to 6 m in the corridors. The general conditions of the walls are good (the building was restructured in 1999). The window frames present a wooden framework and double panes; a complete remaking of the frames was realized in 1999 to improve their poor air seal, which caused remarkable heat losses. This section of the building has two ¯oors. Some laboratories, the archives, service and passage rooms and the technological power plants are located on the ground ¯oor. Classrooms, more laboratories and administrative of®ces are located on the ®rst ¯oor. The remaining part of the school structure is located in a building, built in 1992, which has a carrying structure of steel beams and external plugging in prefabricated panels and rustication, with plain roof. The average thickness of the Table 6 Identification card of the school unit School

``Franchetti'' Technical Industrial High School

Location Management Students Classrooms Didactic classrooms Laboratories Training ground

Via S. Francesco, CittaÁ di Castello Technical office province of Perugia 612 28 24 22 No

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Table 7 Technical±structural data of the building Total internal volume Total heated volume Total trampling area Perimetric walls thickness (old side) Perimetric walls thickness (new side) Rooms height (old side) Rooms height (new side)

13500 m3 13500 m3 4500 m2 60±80 cm 25-30 cm 4.00±6.00 m 3.00 m

external walls is 40 cm. These walls are insulated to reduce heat losses. The average height of the rooms is 3 m. The metallic and double glasses frames of the windows have an excellent air seal. The ground ¯oor of the new building is used for didactical activities. Classes, teacher rooms and laboratories occupy the ®rst ¯oor of the building, corresponding to the ground ¯oor of the old wing of the school. On the second ¯oor of the new part, there are more classrooms and laboratories. The corridor of the new wing is connected to the ®rst ¯oor corridor of the old side of the building. Thanks to the recent construction, the general conditions of the structure are good. Technical-structural data of the school is reported in Table 7. The electric energy consumption analysis in the ``Franchetti'' High School is quite interesting, since the school has some high electric absorption equipments. The electric load is high because some auxiliary heaters are present, which cover some de®ciencies of the heating system. In 1996 the technical of®ce of the school installed an automatic system for power factor correction. This allowed to correct the phase displacement of the electric users, now remarkably higher than that allowed by the electric company contract, and caused by the high electric absorption equipments of the laboratories. At present this new electric installation ensures a power factor (cos f) ranging from 0.982 to 0.985. From the analysis of the electric energy consumption in the years 1994±1998 it is clear that the contract made 15 years ago, is no longer suf®cient for the growing needs of the school. The penalty paid for the power surplus, was in that period about one-third of the yearly entire bill. From the data of the preliminary phase of the energy survey and those regarding the working hours of the heating plant, it was possible to verify that the installed thermal power is higher than that indicated in the local authority's data. Two identical methane boilers, coupled in parallel and with a sequential cyclical connection, guarantee the heating load. The characteristics of the boilers (year of construction: 1999; minimum thermal power: 230000 kcal/h; maximum thermal power: 450000 kcal/h) have been collected during the visit to the central heating system. A special thermoelectric boiler produces the hot water for sanitary use. The insulation conditions of the boiler room, of the hot water pipelines and of the thermal generator are good. The heating system is with vertical columns not divided in zones. The heating bodies are cast iron radiators with plain plates in the new wing's rooms, modular cast iron radiators

in the old side of the building and convectors in the laboratory which is the furthest from the heating system. However, the radiators do not work well, because of the low temperature of the water. It is therefore necessary to heat the laboratory with auxiliary heating bodies (heaters). Other auxiliary heaters are located in the old wing. Water delivery temperature is controlled by an external probe, ambient thermostats located in the new wing of the building and a thermostat in the boiler. The heating comfort in the new wing of the building is more than satisfying, while in the old wing the temperatures noticed during winter months are lower than the comfort conditions. From the measurements taken in November 1999, temperature in classrooms was 11 8C at 8:00 a.m. (15 8C at 12:00 p.m.), while it was 8 8C in the corridors (12 8C at 12:00 p.m.). It is therefore necessary an intervention on the plant control system. Since there are no divided thermal zones in the school, the inef®ciency of the old wing heating system is mainly caused by the age and obsolescence of the pipelines in this side of the structure. The remarkable load waste in the old side of the system causes a lower in¯ow of hot water to the heating bodies in the old side of the building and a bigger ¯ow in the new wing, compared to the values calculated in the project. This creates a discomfort condition because of the too high temperature in this side of the structure. Some interventions that could be applied in a short time are: the breaking up of the heating system in two different zones, so that the heating time in the old wing of the building could be extended in the afternoon avoiding the restarting of the system in the new wing; an improvement of the logic of control of the inner temperature in the old wing of the building (ambient thermostatic switches); the installation of thermostatic valves in the most recent classrooms of the structure. 4.2. The ``F.lli Rosselli'' Technical Commercial High School of Castiglione del Lago In the year 2000, 167 students divided into 9 classrooms attended the ``F.lli Rosselli'' Technical Commercial High School which was built in 1980. The building, used just for didactical purpose, is a modern structure in reinforced concrete and external plugging; it is located in the suburban part of Castiglione del Lago. The structure extends itself longitudinally along the N/W±S/E axis. The building is a single bloc, with plane roof. The orientation of the building was settled neither by particular town-planning obligations nor by project attempts aimed at the optimization of the solar irradiation exposure. The surfaces with windows are regularly arranged on the four sides of the building. The main structure of the building is made of reinforced concrete pillars; the external plugging is made up of prefabricated panels. The walls structure is unknown, but from the thinness of the external walls (25±30 cm) the thermal insulation is quite scarce. It was quite common for the school buildings erected in the decade

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1970±1980 to lack thermal insulation thus causing remarkable heat losses through the external walls and the roof. Furthermore, the panels and pillars junctions constitute important thermal bridges because of their large number. From the preliminary energy test on the school heating system we have noticed that the speci®c consumption (IV, IS, IC) are the highest among the buildings with the same structural typology with values that are remarkably above the mean. However, the information about the heating and the thermal control system are qualitative and partial because it was impossible to visit the central heating room. The heat loss towards the outside, connected to the only building elements, is quantitatively very high even though the building has a low volume/surface ratio because of its regular shape. The visible building structure is not in a good condition. The external windows frames present all a metal structure made of steel and single pane; they were never upgraded since the building of the school and present an insuf®cient air seal, because of the poor quality of the material and assembly problems. The glass surfaces are wide (at least two windows) in every classroom and they are located on the S/W exposed side of the building that has a good solar exposure. The high consumptions are caused by the covering technology, in particular by the external frames, which have a very bad seal and by the absence of thermal insulation on the external walls. No data was available about the electric energy consumption of the school. The electric installations go back to the year of the building construction, but the electric and lighting installations of the ground ¯oor were upgraded in 1998. In the above mentioned rooms, high ef®ciency lamps have been installed with thin reeds to direct the light, while in the remaining rooms the lighting installation consists of ceiling light ®xtures with neon. The main energy consumption is constituted by personal computers for didactical and of®ce use (30); television sets (two) and other moving and occasional electric equipments. There are no particular laboratory equipments with high energy consumption. The heating system is controlled remotely by a company, which provides the fuel, the operation, the control and the ordinary and extraordinary maintenance of the system. The boilers are fed with gas oil and they are dated 1980. They have reached such an obsolescence that a renewal is required. Some data about the energy consumption are shown in Table 8. Table 8 System characteristics and energy consumption for the ``Rosselli'' High School Fuel for the heating system Totally installed power Yearly average consumption Yearly average consumption School days per year School hours per day School hours per year

Gas oil 698 (kW) 22839 (MWh) 19.64 (TEP) 144 (day per year) 7 (h per day) 1008 (h)

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From the analysis of the thermal energy consumption data and the system working hours it was found that the installed power of the system is remarkably higher than the design load, with considerable ef®ciency drop of the heat generator, as a consequence of its scarce use. The heating bodies for the classrooms, the of®ces and the corridors are forced convection heat exchangers, whereas the service rooms have cast iron modular radiators. Changes of air are natural (draughts, opening of the windows, etc.) Regarding the thermal control that guarantees the comfort temperature, the three ambient thermostats located in the corridors of the three ¯oors were found to be disconnected. The temperature of the water ¯owing to the heating bodies is regulated by the telecontrol system. It is possible to take action on the fan-coils by means of an electric power station that allows their switching on and off in the classrooms and of®ces. The recorded comfort conditions is lower than the standard for a classroom. The heating plant is generally operated 7 hours/day, but when the school is open in the afternoon, a speci®c request to the province's of®ce is submitted so that the system can work outside of the normal period of operation. The main causes of the thermal energy speci®c high consumptions in the ``Rosselli'' High School can be found in the high heat loss through the not insulated external walls and roof; in the remarkable air passage through the external frames; in the installed power of the heat generator, that is much higher than the requested load; in the obsolescence of the heating system. The energy saving measures that can be proposed for this school can be summed up into two different typologies: small interventions, which can be done in a short time (gasket and double panes installation on the frames, adaptation of the burner's power, the boiler room insulation and the roof insulation); complex interventions, which are more expensive and longer compared to the above-mentioned ones (insulation of the external walls, replacement of the external frames with new ones, replacement of the boilers with high-ef®ciency burners and with a suitable capacity of the requested load, replacement of the fuel, replacement of the heating bodies). 4.3. The ``Giordano Bruno'' Technical High School for Social Activities of Perugia This is an experimental High School, whose didactical activities are divided into three different study curricula: linguistic, technological-scienti®c and sanitary-biologic. In the school year 1999/2000, 928 students, divided in 44 classrooms, attended it and its student population has always grown in the last years. The building, originally the site of a manufacturing industry, was transformed in a school in 1986 and this change brought some necessary modi®cations of the buildings such as the demolition and rebuilding of some parts of the old building.

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The energy survey of building-plants and the discovery of further consumption data have been quite interesting because of its low energy consumption. A student of this school consumes yearly about 27 kg of oil. This is a remarkably below average speci®c consumption value per student compared to other structures of the same building typology (82 kg oil). The unit volume thermal energy consumption data is also meaningful: to heat a cubic meter of the ``Giordano Bruno'' High School 0.97 kg of oil are necessary, while the average value in structures of the same typology is 1.36 kg oil/m3. The structure is located in the urban center of Perugia, in a high building density zone and it extends longitudinally along the N/S direction. The town planning obligations due to the presence of public transportation lines and several other settlements in this area and the original utilization of the structure as an industry let us assume that no speci®c project criterion was followed for the optimal positioning of the structure regarding the solar irradiation. The main body is made of reinforced concrete; the external plugging is realized with solid brick. It was not possible to survey the precise sectional structure of the external walls and the presence of thermal insulation, but many data about the structure of this building was available. The building roof is in many points plain and in other of ``shed'' type (it assures a good daily lighting and it favors a good air exchange in the rooms). The building has two ¯oors and a basement; it has many laboratories, a training ground and an auditorium. Steel and infra-vacuum double glass windows without external shielding constitute the external frame; furthermore there are door windows with metal framework and glass that present in general a good thermal insulation. Only the glass surfaces of the gym's roof are made of metal and single pane with a scarce air seal. The structure is in a general good condition. Considerable results, for the heat loss, the contribution of the thermal conjunctions, in particular the reinforced concrete pillars (one every 4 m in the perimetral walls) and the metal pillar for the rain ¯ow, located in the inner side of the external walls. First of all, the electric energy consumptions have been deduced from the ®nal balance consumption of 1998 provided by the province of Perugia. From the 1998 data it can be determined that the power used was too low compared to the real needs. Even if the energy costs are not available, we assume that a modi®cation of the energy supply contract with an increase of the installed power and the passage to medium utilization is necessary. However, the school has already changed the contract, optimizing the costs of the energy supply. There is no rise in cost for the energy because of the consumed reactive energy in excess. The high cos® value is due to the presence of an automatic power factor correction group. The electric installation is almost new and presents a good ef®ciency. From the summary of the electric load and from the reference values of the electric energy model shown in

Table 9 Electric load summary and electric energy model for the ``Giordano Bruno'' High School Installed power for lighting Installed power for electric appliances Total installed power Furnished power Working hours of the electric appliances per day Days per year of the school utilization Hours per year of utilization Absorbed energy Absorbed power Utilization coefficient

38905 (kW) 61090 (kW) 99995 (kW) 40 (kW) 9 (h per day) 215 (days per year) 1935 (h per year) 72180 (kWh per year) 37 (kW) 92.5 (%)

Table 9, it was assumed that it is necessary to optimize the energy contract to adequate it to the increase in the used power. As regards thermal energy, the yearly average fuel consumption for the heating system operation is 31527 Stm3 of natural gas. The school seems to have an optimal energetic behaviour: the IS index is the lowest among the whole examined construction typologies; the IV index is remarkably below average. The heating system works on average 7 hours/day for a total of 1008 hours per year, while it is impossible to quantify the real working time of the burner (it is a on/off regulation type). The methane boiler has tubes for the smoke and it was built in 1986 with a nominal thermal power equal to 600000 kcal/h (696 kW). The backup boiler (1986) has a nominal thermal power of 200000 kcal/h (232 kW). As the school is often open in the afternoons all week long, the thermal generator is switched off at the end of the morning and switched on according to the different timetables of the activities (about 2 hours/day). An electric water heater, occasionally switched on during the wintertime, produces hot water for the bathrooms. The hot water for the laboratories (kitchens) is directly taken from thermal system boiler and sent to a special insulated tank. The thermal system is centralized in several zones, with four main thermal zones (laboratories, administrative of®ces, classrooms and training ground). The external temperature probes do not work at all and there are no thermostats in the inner rooms. The heating system control is totally inadequate for the real necessity of the school: on the ®rst ¯oor there is a remarkable inner temperature level higher than the levels imposed by the legislation both in the middle seasons and in the winter sunny days. The changes of the air can be only obtained by hand, opening the windows, since the external frame have a good air seal. The comfort is inadequate in the classrooms, where there is often a too high temperature and a bad quality of the air. The heating bodies, however, present a quite good ef®ciency. Discomfort conditions were recorded caused by remarkably low temperature compared with the project's values

U. Desideri, S. Proietti / Energy and Buildings 34 (2002) 1003±1016

both in the training ground and in the adjacent teachers' room, which have a ``shed'' roof without false ceiling and thermal insulation; therefore there is a considerable heat loss through the roof. The heating system, even if it is of recent production, presents lacks caused by the control logic and by the not homogeneous heat supply to the school. The interventions proposed for an energy and economic saving are: the installation of double-pane windows and gaskets, and the ``shed'' roof glass surfaces; the installation of thermostatic valves applied to the classrooms' radiators to recuperate the free heat supply and to improve the comfort in the rooms; the breaking up of the system through the connection of two or more fall-boilers with cyclic connection to improve the system's ef®ciency reducing the lighting hour for every single unit. Among the earlier mentioned interventions, the technical±economic possibility to improve the control system was considered. Thermostatic valves in the 18 classrooms with glass surfaces having a westward exposure should be installed. A discomfort condition was noticed caused by the high inner temperature that derives from the solar exposure, by students presence for long periods of time, by the remarkable rooms height and by the absence of arti®cial ventilation systems. This intervention could save 5104 Stm3 of natural gas, i.e. 15% of the annual total consumption of this school. This represents an energy saving of 116 PET per year and an economic saving of 800 s per year. The initial investment is of 1500 s and the expected payback time is about 5 years, which is acceptable for a public investment. 5. Conclusions This research is the necessary step to start with the effective intervention of energy survey ``shared'' with students, which is a valid formative instrument for young people and, an introduction for future interventions for a rational use of energy and for the diffusion of renewable sources in the school ®eld and in of®ce buildings in general. For the particular examined school group, managed by a local public body, it is possible to accomplish a planned and concrete intervention in the ®eld of energy saving. If all the high schools of the same type of construction had the minimum IV 284 PET per year, 38% of thermal energy could be saved. The same percentage of energy could be saved if all the similar school buildings had the same IS. If the minimum Is could be reached in all the schools disregarding the differences in building type, 359 PET per year could be saved, i.e. 47.6% of the thermal energy. A larger amount of electric energy could be saved if the optimal values of EV and ES could be applied to all the schools: if each school type had the minimum EV, 46% electric energy could be saved. Similarly, if each school type had the mimimum ES, 41% of electric energy could be

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saved. If all the schools had the minimum ES, disregarding the type of building, 27,8 PET per year could be saved, equal to 56%. As a consequence of the energy survey in the schools, energy speci®c consumption indexes, used to study the data in the ®rst stage of the auditing, turned out to be an important instrument to understand the energy consumption structure in a speci®c homogeneous sector. In the light of the obtained results, the speci®c consumption indexes can be assumed as mean parameters. They allow to compare the energy performances of different school buildings, even if some data is lacking. The following stage of our energy survey has validated the used methodology of the preliminary analysis. We have noticed signi®cant faults in the electric and heating plants and in the construction of the buildings, where the speci®c consumption indexes were above mean values. It has also permitted to identify the main causes of the high energy consumptions and the technical and economic interventions for a more rational energy use in the school ®eld, and to identify possible ``pilot'' schools where we could start with the experimental stage of the shared survey. In a further step of the work, it would be important to acquire data to perform a precise energy diagnosis of the school buildings. Moreover, it could be possible to monitor and quantify the energy and economic savings obtained after the effective realization of the interventions. A further stage of our study could examine the diffusion of the use of renewable sources in the school ®eld, studying the technical and economic feasibility of the systems for the exploiting of renewable energy sources (i.e. solar photovoltaic and thermal systems and/or of integration to the existing systems). Schools are generally characterized by wide face and covering surfaces, by wide areas of competence and by occupation time in the central hours of the day factors that are positive for applications of solar energy systems. 6. Definition of terms EV ES EC IV IS IC NPV PET

electric energy specific consumption per unit volume (kWh/m3 per year) electric energy specific consumption per student (kWh per student per year) electric energy specific consumption's index per class (kWh per class per year) thermal energy specific consumption per unit volume (kWh/m3 per year) thermal energy specific consumption per student (kWh per student per year) thermal energy specific consumption per class (kWh per class per year) net present value petroleum equivalent ton

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Acknowledgements The province of Perugia and the Agenzia per l'Energia e l'Ambiente della Provincia di Perugia are gratefully acknowledged for having provided the data necessary for this study. The authorization of the province of Perugia was also necessary to access the schools and their thermal and electric plants. References [1] D. Pitimada, ENEA Activities: rational use of energy, ENEA, Rome, 1990.

[2] Energy and Environment Agency of the province of Perugia, TEACH: Training pupils for Energy Analysis in School Buildings, Proposal for a SAVE action, Perugia, 1990. [3] Ministry of Public Instruction, Public school. A synthesis of data: School year 1999/2000, Rome, 2000. [4] Provincial Education Office of Perugia, Informative Base Management, School year 1999/2000. [5] B. Puttinger, Guideline for implementing energy audits in public buildings, Landes Energie Verein. [6] V. Butala, P. Novak, Energy consumption and potential energy savings in old school buildings, Energy and Buildings 29 (1999) 241± 246. [7] C. Accorona, L. Angelone, G. Funaro, M. Olivetti, G. Perrella, Rational use of energy in schools, ENEA, Rome, 1994. [8] R Recalcati, G. Dall'O', Procedure for buildings energetic certification, Punto Energia, Brescia, 1998.