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Analysis of the energy performance strategies of school buildings site in the Mediterranean climate: A case study the schools of Matera city
Accepted Manuscript Title: Analysis of the energy performance strategies of school buildings site in the Mediterranean climate: A case study the schools of Matera city Authors: Gianluca Rospi, Nicola Cardinale, Francesca Intini, Elisabetta Negro PII: DOI: Reference:
S0378-7788(16)31714-5 http://dx.doi.org/doi:10.1016/j.enbuild.2017.07.018 ENB 7758
To appear in:
ENB
Received date: Revised date: Accepted date:
28-11-2016 1-6-2017 8-7-2017
Please cite this article as: Gianluca Rospi, Nicola Cardinale, Francesca Intini, Elisabetta Negro, Analysis of the energy performance strategies of school buildings site in the Mediterranean climate: A case study the schools of Matera city, Energy and Buildingshttp://dx.doi.org/10.1016/j.enbuild.2017.07.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Analysis of the energy performance strategies of school buildings site in the Mediterranean climate: A case study the schools of Matera city GIANLUCA ROSPI1*, NICOLA CARDINALE1, FRANCESCA INTINI1, ELISABETTA NEGRO1 1
DICEM, Università degli Studi della Basilicata - ITALY
[email protected]
Graphical abstract
Highlights This study analyses the energy performance of eight schools located southern Italy We measured the thermal parameters and the gas consumptions The energy performance was validated by the measurements in situ and analysis in dynamic regime We implemented different energy perfomance strategies for enevelope and system The energy saved and environmental benefits were analyses Abstract Energy consumption of the public building stock represents an important cost of the balance of a state. Moreover, public buildings, in particular schools, should be buildings with elevated comfort levels because student and teachers spend much time in these rooms. The wellness and productive capacity of students and teachers are primarily affected by the comfort inside and air quality of school rooms.
Regarding energy use, school buildings waste much energy because most buildings were constructed before the 1991 and energy saving measures were only implemented in a few schools. This paper analyses the energy performance of eight different schools located in Matera city, southern Italy. The aim of this research is to analyse energy requirement utilizing dynamic analyses with a time step of one hour (using Energy-Plus method). Next, the values of the dynamic analyses were compared to the effective energy consumption. Using the results of this comparison, we validated the numerical model, and then, we analysed different energy auditing actions for these buildings. We included the energy auditing works in three categories: energy restoration of the envelope, of the plant and of both. For each of these categories, we calculated the energy savings. Ultimately, we analysed the environmental benefits of the three different categories in terms of CO 2 reduction. This research confirmed that the dynamic method is the best method to achieve a good energy analysis of these complex buildings. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649956. Key-Words: School buildings, Energy performance buildings, dynamic method, energy auditing, Mediterranean climate, comfort indoor.
1 Introduction The energy saving and efficiency actions in the building sector are a key theme for achieving the environmental targets of the national and EU levels . In the next few years, many public buildings will have to undergo significant retrofits. An important public building stock is constituted of school buildings. Different studies in the literature demonstrate that these buildings have poor indoor air quality and consume a large amount of thermal energy; this is confirmed by the fact that in the last twenty years, no energy saving measures were applied in school buildings during the processes of restoration. Moreover, it was demonstrated that the indoor comfort and indoor air quality in schools are important for ensuring the health and productivity of students and teachers. Over the past few decades, numerous international studies have been performed to address the topic of energy consumption and indoor environmental quality (IEQ) in school buildings. A field survey was conducted to collect, elaborate and analyse data concerning the actual energy consumption of space heating in school buildings of the Province di Torino. The study constructed an energy index that was defined as the ratio of the energy supplied by the heating system to the gross heated volume [1]. In [2], the authors performed functional benchmarking of different schools considering the different operation conditions of school buildings. The authors analysed the results through an intensive literature survey on energy consumption in schools. The literature was analysed to determine if a worldwide comparison among the published data could be established. In [3], the authors present an energy analysis of school buildings of the province of Perugia in central Italy. The study aimed to calculate the main thermal and electric energy consumption indices to evaluate the status of energy consumption and possible interventions to save energy in the school sector. In this paper, two applications of energy auditing in school buildings are presented. In [4], the authors studied a number of contemporary Hellenic school buildings. This study was conducted with a holistic approach consisting of three steps: first, an IEQ investigation, in situ, to reveal related problems and their potential sources; second, an energy audit to collect information on the energy related characteristics of the building; and third, an energy performance assessment. They also investigated the air indoor quality in school rooms. In [5], the energy quality of various schools in Rome was analysed, and different intervention strategies to reduce energy consumption were defined. The authors analysed the envelope, thermal plant and energy consumption, they performed energy retrofit interventions on the envelope and on the plant, and they calculated achievable benefits from the interventions in terms of energy and money saving through a simple payback time analysis (PBT), which is useful to identify priorities for action. In [6], the authors presented the project Educa-RUE. This project focuses on speeding up the implementation of European Directive on Energy Performance in Buildings, EPBD (2002/91/EC) in Member States at the local government level and to ensure its operability within the various national legislations of reference. The project developed a model process, known as the “Educa-RUE method”, to assess possible policies of intervention on educational buildings by promoting the ability of local players to guide and orient initiatives designed to encourage energy savings by means of specific measures and integrated tools. In [7], the energy consumption patterns of eight Portuguese case-study schools were analysed using a methodological approach that integrated quantitative and qualitative data analysis, and in [8], the energy performance of seven schools sited in Germany was studied. In [9], the authors presented an energy audit campaign on 49 school building situated in Lombardy in North Italy. They analysed actual energy consumption for heating, the occupant behaviour and the buildings technical characteristics. This study showed that, for some school buildings, it would be less expensive and more convenient to construct a new building instead of apply energy saving actions. In [10], a study of the indoor comfort of seven Italian schools was conducted. The authors measured the main thermo-physical parameters (temperature, humidity, illuminance, CO2 concentration, etc.), and they asked students to describe their thermo-hygrometric comfort. In [11], the authors proposed a new value of the expectancy factor of the PMV index for the Mediterranean climate. This value was obtained by conducting a combined subjective and objective investigation on approximately 200 Italian classrooms and on more than 4000 students, both in winter and summer. All of the investigated school buildings were non-air conditioned and only ventilated by operable windows. In [12], the author investigated the energetic and economic feasibility of a solar-assisted heating and cooling system (SHC) for use in different types of school buildings and Italian climates. The SHC system under investigation is based on the coupling of evacuated solar collectors with a single-stage LiBr–H2O absorption chiller; auxiliary energy for both heating and cooling is supplied by an electricity-driven reversible heat pump.
In the past, we studied the energy performances of the vernacular architectures of South Italy; this work was published in [13] [14]. In the previously paper four school buildings were analysed in stationary method using Italian energy low [15] This paper analyses the energy performance of eight different school buildings situated in the city of Matera in southern Italy. Matera has a typical Mediterranean climate, with temperate winters and hot summers, as well as a high humidity level. The aim of this research was to perform an energy audit. We conducted different monitoring campaigns in situ to evaluate the thermal conductance of the envelope; then, we evaluated the energy performance by using dynamic simulations (using the Energy Plus method). We estimated the gap between measured and simulated consumption. Finally, we analysed the different energy improvements, both for the envelope and the plant. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649956. 2 Techniques and technologies of the school buildings 2.1 Description of the project In this study, we described the energy diagnosis and different actions for improving the energy savings of eight different high school buildings situated in the city of Matera, southern Italy. The school buildings were built between 1540 and 1992, and these buildings were constructed with different techniques and technologies. Eight schools were analysed: Gymnasium Lyceum "L.G." "E. Duni", Scientific Lyceum "L.S." “D. Alighieri”, Scientific Technical Lyceum "L.S.C." “Pentasuglia”, Technical Institutes "I.T.G." “A. Olivetti”, Technical Institutes "I.T.I.S." "G.B. Pentasuglia", Technical Institutes "I.T.C." "A. Loperfido", Professional Istitutes"I.P.S.S." “I. Morra”, and Music Lyceum "L.M." “E. Duni”. Table 1 shows the principal data (year of construction, volume, total area, floors, etc.) of the school buildings analysed.
School name
Year
Gross volume Total area
Building height
N. classrooms
m3
m2
m
N
N. floors
L.G. “ E.Duni”
1966
6
24,556
5,761
23.00
37
L. S. “D. Alighieri”
1971
4
38,496
7,830
12.00
31
I.T.C. " Loperfido"
1961
5
20,846
5,814
17.70
34
I.T.I.S. “G. B. Pentasuglia”
1987
2
53,282
16,861
10.00
39
L.S.T. “G. B. Pentasuglia”
1992
2
15,118
3,484
8.00
12
I.T.G. “A. Olivetti”
1981
3
29,911
7,178
7.00
28
I.P.S.S. “I. Morra”
1972
4
14,093
3,329
14.00
98
L.M. " E. Duni "
1540
2
5,550
1,500
13.00
20
Table 1 - Principal data of the buildings analysed Because seven of the eight schools were constructed before law 10/91, they have envelopes without air space and thermal insulation. Instead, only L.S.T. “G. B. Pentasuglia” was constructed with a wall made of a double layer of clay interposed by an unventilated air space and plastered on both sides of the masonry with lime plaster and cement. This study was funded in part by the Province of Matera through a special convention and is part of a larger study on the diagnostic efficiency of the public school heritage of the Province of Matera. 3 Methodology
We adopted an integrated approach based on energy analyses in the dynamic regime using the Energy-Plus method [16], monitoring the thermal conductance in situ in accordance with ISO 9869-2014 [17] and monitoring of the energy consumption of heating for four consecutive years (from 2009 to 2012). The research can be divided into three phases. In the first phase, we measured the thermal conductance of the envelope, combustion efficiency of the heat generator and energy consumptions of all of the schools. The measurement of the conductance was performed in accordance with ISO 9869-2014, according to a methodology that has been used by other similar works and published in other papers [18]. We measured the combustion efficiency of heat generators according to the method described by UNI 10389 [19]. In this phase, we also performed a thermographic survey to identify thermal bridges and irregularities of the envelope. In the second phase, we constructed a numerical model in the Energy-Plus platform by inserting the measured in situ values from the first phase. In this phase, we set and validated the numerical model. The numerical model was validated by comparing the deviation the energy consumption simulated with the energy consumption measured. The validation results were good when the percentage of error of the deviation was less than 10 percent. The methodology validation for massive buildings by Energy Plus was presented in [14] and the methodology validation for light enelope by Energy Plus was presented in [20]. In the last phase, some energy performance strategies were proposed, and we calculated the energy savings, CO2 savings and investment payback period of each intervention. 4. Case Studies presentation In the province of Matera, there are 31 school buildings of the second degree, of which 19 are in the municipality of Matera, which is situated in Basilicata, southern Italy. Matera is characterized by a Mediterranean climate and has mild winters and hot summers; the minimum winter temperature is -2 °C, and the maximum summer temperature exceeds 35 °C. Analysing the total gas consumption for heating all of the school buildings, we found that 748578 standard m 3 of gas was consumed; the power consumption of only the school buildings present in the city of Matera was 65% of the total gas consumption. This paper focuses on eight different school buildings located in the city of Matera. The total gas consumption for heating the eight buildings was 314,727 standard m3, (70% of the total gas consumption of Matera schools). Regarding the period of construction of the school buildings, only 7 of the 8 buildings were built after law n.10/91 (the first law on energy savings of buildings) was implemented, whereas all of the other buildings were built between the 1960s and 1980s. The analysed buildings are different both in form and in construction techniques. Table n. 2 summarizes the main technical characteristics (envelope and plant) of the various buildings studied.
School name Construction typology
L.G. E.Duni”
“
Gross volume
Total area
Opaque area
Windows area
m3
m2
m2
m2
Concrete structure, ceilings in brick- concrete and brick 24,556.00 walls plastered
and wall in and ceilings in 38,496.00 brick-cement Structure pillars and beams of reinforced concrete, I.T.C. " reinforced concrete floors 20,846.00 Loperfido" and brick and concrete walls with air gap"
S/V ratio
5,761.00
5,761.00
873.00
0.36
2×305
7,830.00
7,494.00
956.00
0.29
4×227.0 1×147.0
Concrete structure, ceilings brick-cement and 53,282.00 concrete walls
I.T.I.S. “G. B. in Pentasuglia”
5,814.00
6,171.00
777.00
16,861.00 18,253.00 1,880.00
Heating terminals
kW
Structure
L. S. “D. concrete Alighieri”
Installed thermal power
Radiators classrooms, laboratories and offices Radiators classrooms, fan coil units offices
0.42
4×232
Radiators classrooms, laboratories offices
0.59
1×768 3×633.8
Radiators classrooms, laboratories offices
and
and
Structure
in
concrete,
L.S.T. “G. B. ceilings in brick-cement and 15,118.00 Pentasuglia”
3,484.00
2,881.00
158.00
0.32
2×191.9
I.T.G. “A. Olivetti”
Structure and wall in prefabricated panels and 29,911.00 ceilings in brick-cement
7,178.00
6,698.00
1025.00
0.46
2×488.5
I.P.S.S. Morra”
“I.
Structure in concrete, ceilings in brick-cement and 14,093.00 walls in brick face view
3,329.00
3,586.00
1195.00
0.34
2×309.0
L.M. " Duni "
E.
Load-bearing masonry structure, vaulted ceilings in 5,550.00 limestone
1,500.00
595.00
67.00
0.17
1×280
walls with air gaps
Radiators classrooms, fan coil units offices and laboratories Radiators classrooms, laboratories and offices Radiators classrooms, laboratories and offices Radiators classrooms, laboratories and offices
Table 2 - Technical characteristics (envelope and plant) of the various buildings studied 5. First phase: Monitoring campaign and energy diagnosis To ensure a good energy diagnosis, it is necessary to determine the envelope thermal proprieties and thermal parameters of the conditioning plant. The measurement and monitoring activities are essential to achieve a specify energy diagnosis, while also minimizing the error in the next phase of the model construction in the calculation code. In this phase, we measured the technical and technological specific parameters of the school buildings: the surface, volume, window typologies, envelope thickness, roof typologies, and so on. Next, we individuated the thermal bridges and thermal discontinuity of the envelope using an infrared thermal camera. We found the following main thermal bridges in addition to those of form: lack of thermal insulation on the bearing structures, erroneous connections of the window frame to the masonry and erroneous connections of the rolling shutter box to the wall. The figures 1 and 2 present sample images.
Figure 1– A specific section of the ITC “ Loperfido” envelope
Figure 2– A specific section of the L.S. “ D. Alighieri” envelope In the second step, we measured the thermal conductance in situ using a non-invasive methodology described by UNI EN ISO 9869. This standard involves the use of a heat flow meter and four resistance thermometers to estimate the thermal conductance. We mounted the sensors in such a manner to ensure a representative result of the entire wall element. The heat flow meter must be installed on the inner surface of the wall because this side has a more stable temperature, avoiding the proximity of thermal bridges and heat sources. We installed two temperature meters on the inside surface and two on the outside surface of the wall. The measurement campaigns for all of the school buildings were produced in winter because, to minimize the error, the presence of a constant temperature difference between the two sides of the masonry (inside and outside) of approximately 10 °C is essential. The duration of each measurement campaign was ten days, with a duration of 10 minutes. We performed a measurement only if the mean temperature difference found between the outer and inner envelope across all campaigns of measures was between 8 and 9 °C. There were 7200 processed data points from each measurement campaign. After 10 days, we calculated the thermal conductance and thermal transmittance with the “progressive average” or “moving average” method. Using this method, we calculated the thermal conductance from the sampled values of the surface temperature and the heat flux using the following equation: N
q C=
j1
j
[W/m 2 K]
N
(T j1
i, j
- To, j )
where qj is the thermal flux, Ti,j is the indoor surface temperature and T o,j is the outdoor surface temperature. As N increases, the ratio tends to converge to a stationary value and is not influenced by the thermal mass of the wall. The C function converges with oscillations around a horizontal asymptote, with a maximum amplitude of approximately 0.05 W/m²K. To calculate the thermal transmittance, we added the normed indoor and outdoor surface resistances R i (0.13 m2K/W) and Re(0.04 m2K/W) to the value C. We used the following formula:
U
1 1 [W / m2 K ] 1 R Ri Ro C
If the stratigraphy of envelope was known, then the transmittance was calculated in accordance with UNI EN ISO 6946:2008 [21]. Table 3 shows the values of the conductance for the eight analysed buildings for both the opaque shell and transparent one. The transparent envelope was calculated in according to standard UNI EN ISO 10077 1-2 [22].
In the table, the values obtained from ISO 9869 were measured in situ, the values obtained from UNI EN ISO 6946:2008 were calculated because the stratigraphy is noted, and the value obtained from UNI EN ISO 10077 1-2 were calculated using the finite elements method. School name
Opaque vertical envelope C
U
Law limits
Horizontal coverage envelope Calculation typology
U
W/m2K W/m2K W/m2K
L.G. “ E.Duni”
0.48
L. S. “D. 2.04 Alighieri” I.T.C. " 0.31 Loperfido" I.T.I.S. “G. B. 0.22 Pentasuglia” L.S.T. “G. B. 1.69 Pentasuglia” I.T.G. “A. 0.96 Olivetti” I.P.S.S. “I. 1.77 Morra” L.M. " E. Duni "
1.41
Law limits
Transparent envelope
Calculation typology
W/m2K W/m2K
1.54
0.32
ISO 9869
1.50
0.26
2.54
0.32
ISO 9869
2.21
0.26
2.06
0.32
ISO 9869
1.60
0.26
2.54
0.32
ISO 9869
1.51
0.26
0.54
0.32
ISO 9869
1.69
0.26
0.83
0.32
ISO 9869
0.88
0.26
1.36
0.32
ISO 9869
0.85
0.26
0.63
0.32
ISO 9869
1.04
0.26
Law limits
U
Calculation typology
W/m2K W/m2K
UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008
ISO ISO ISO ISO ISO ISO ISO ISO
5.78
1.8
5.78
1.8
5.78
1.8
5.78
1.8
3.10
1.8
4.02
1.8
6.02
1.8
3.15
1.8
UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2
ISO ISO ISO ISO ISO ISO ISO ISO
Table 3 - Values of the conductance for the eight analysed buildings
“A. 977.00 618.00 280.00
Efficiency at 100% load
74%
82%
83%
84%
70%
64%
91%
L.M. " E. Duni "
383.80
I.P.S.S. “I. Morra”
1,075.00 928.00 2,669.40
I.T.G. Olivetti”
L.S.T. “Pentasuglia”
610.00
I.T.C. "Loperfido"
Generator power [kW]
L.G. “E.Duni”
I.T.I.S. “Pentasuglia”
L. S. “D. Alighieri”
Subsequently, we performed a measurement campaign of the combustion efficiency of heat generators according to the method described by UNI 10389 [19] and analysed the bills of heat consumption (gas and/or diesel) for the years 2009, 2010, 2011 and 2012. For the analysed buildings, we show the measured values of the heat generator efficiency in Table 4 and the measured values of the heating energy consumption in Table 5.
97.9%
Table 4 - Efficiency of the heat generator School name
Methane gas Consumption 2009
2010
2011
2012
Average
Sm3/year
Sm3/year
Sm3/year
Sm3/year
Sm3/year
L.G. “ E.Duni”
31,928.00
25,672.00
25,557.00
23,546.00
26,675.75
L. S. “D. Alighieri”
42,195.00
50,522.00
51,606.00
57,519.00
50,460.50
I.T.C. " Loperfido"
39,189.00
37,782.00
37,360.00
33,193.00
36,881.00
I.T.I.S. “G. B. Pentasuglia”
133,959.58
135,994.85
105,833.04
10,3761.05
119,887.13
L.S.T. “G. B. Pentasuglia”
11,961.42
12,143.15
9,449.96
9,264.95
10,704.87
I.T.C.G. “A. Olivetti”
38,947.00
39,197.00
32,481.00
30,409.00
35,258.50
I.P.S.S. “I. Morra”
33,286.00
28,691.00
25,258.00
21,584.00
27,204.75
8,125.00
L.M. " E. Duni "
7,811.00
7,497.00
7,183.00
7,654.00
Table 5 - Gas consumption for the time step 2009 – 2012
Volume
Total dispersing surface
Opaque area
Windows area
UxS opaque envelope
UxS trasparent envelope
UxS envelope
m3
m2
m2
m2
W/K
W/K
W/K
L.G. “ E.Duni”
24,556.00
8,838.84
5,761.00
873.00
9,310.75
5,044.19
14,354.94
L. S. “D. Alighieri”
38,496.00
11,015.00
7,494.00
956.00
18,000.63
5,523.77
23,524.40
I.T.C. " Loperfido"
20,846.00
8,767.00
6,171.00
777.00
11,976.35
4,489.51
16,465.86
I.T.I.S. “G. B. Pentasuglia”
53,282.00
31,419.34
18,253.00
1880.00
50,531.65
4,489.51
61,394.29
L.S.T. “G. B. Pentasuglia”
15,118.00
4,910.85
2,881.00
158.00
1,717.86
486.92
2,204.78
I.T.C.G. “A. Olivetti”
29,911.00
11,989.30
6,698.00
1025.00
5,829.58
4,127.03
9,956.61
I.P.S.S. “I. Morra”
14,093.00
6,261.60
3,586.00
1195.00
3,854.60
7,170.00
11,024.60
L.M. " E. Duni "
5,550.00
2,217.00
2,150.00
67.00
1,091.30
210.78
1,302.08
School name
Table 6 - Main energy performance characteristic of the envelope Finally, we correlated all of the measured values and calculated to date. We analysed the relationship between the product UxS with the gross volume of the buildings, heat loss through the surfaces and energy consumption of heating. The calculation was performed while considering the weighted average of the thermal transmittance for the surface (opaque vertical, horizontal opaque and transparent). Figures 3 and 4 show that the correlation between UxS and the gross volume increases with the volume of the building and heat loss. The slope of the line is higher in the case of the heat loss surface (Figure 4).
Figure 3 -Relationship between UxS and the gross volume
Figure 4 - Relationship between UxS and the heat loss surface Figure 5 shows the relationship between the product U × S and the gas consumption for heating. In this case, the slope of the line is less than that of the previous case in spite of the correlation coefficient being higher than that of the other case.
Figure 5 -Relation between UxS and gas consumption 6. Second phase: Dynamic energy analysis In this step, a numerical model was developed for each of the school buildings analysed. We used the EnergyPlus software to analyse the energy performance. The analysis was performed in the dynamic regime. Before starting the calculation under dynamic conditions, we set the functioning templates of the building (set point system, during of starting and switching off of the plant, internal loads, lighting loads, opening windows, etc.); these values were entered according to the actual data acquired by the staff that maintains the boiler and by the school manager. The processing of the model under dynamic conditions directly determines the consumption of the heating thermal energy; this value, once converted into thermal primary energy, was compared with the actual consumption measured in situ. Table 7 shows a comparison between the measured annual fossil consumption and simulated annual consumption, with the percentage error.
Average Consumption Consumption simulated measured
Percentage error
Sm3/year
Sm3/year
%
L.G. “ E.Duni”
26,675.75
24,782.00
7.10%
L. S. “D. Alighieri”
50,460.50
48,588.00
3.71%
I.T.C. " Loperfido"
36,881.00
33,482.00
9.22%
I.T.I.S. “G. B. Pentasuglia”
119,887.13
117,695.00
1.83%
L.S.T. “G. B. Pentasuglia”
10,704.87
10,528.16
1.65%
I.T.C.G. “A. Olivetti”
35,258.50
34,611.00
1.84%
I.P.S.S. “I. Morra”
27,204.75
28,531.00
-4.88%
L.M. " E. Duni "
7,654.00
7,248.00
5.30%
School name
Table 7 - Comparison between the measured and simulated annual fossil consumption Because the Energy Plus method outputs the value in kWh/year, the conversion procedure to m 3/year was performed with reference to the calorific value to 1 m3 of methane gas, equivalent to approximately 35 MJ (9.7 kWh). Next, by dividing the total value of kWh/year by 9.7, the total value of m3/year was obtained. The low deviation obtained between the simulated fuel consumption and measured consumption is caused by small uncertainties, including the difficulty of estimating the real program operation of the system installation, the approximation of the internal loads and the lack of easy access to schematics of thermal bridges in the numeric code. In this way, we calibrated the numerical models designed in Energy Plus of the school buildings. Next, we analysed the following energy performance strategies: improvement of the envelope and heat plant and the addition of renewable energy systems. 4. Third phase: Energy Performance Strategies All energy improvement actions were conducted using the dynamic method. We hypothesized different energy improvement strategies: energy improvements of the envelope and of the system. The used energy renovation strategies of the envelope were the following: insertion of thermal insulation in the wall, replacement of the windows, and application of thermal insulation in the roof. Alternatively, the energy renovation strategies of the system used were the following: substitution of the old plant with a gas heat pump or with an electric heat pump. Finally, we analysed the school buildings by implementing renewable energy solutions, such as thermal solar and photovoltaic systems.
4.1 Performance of the envelope The energy improvement of the envelope was conducted in such a way as to achieve thermal transmittance values that were in accordance with the limitations imposed by the three Interministral Italian Decrees 26 June 2015: “Decree for minimum requirements: application of the calculation methodology of the energy performance and definition of requirements and minimum requirements for buildings” [23]. This improvement was performed in three successive steps, considering the improvement of the opaque envelope (step 1), replacement of windows frames (step 2) and both solutions of step 1 and 2 (step 3). The intervention on the opaque envelope consists of an inner insulation of flat roofs and walls, constituted of a plasterboard sheet thickness of 10 mm coupled to an insulating layer consisting of panel hemp fibre with λ = 0.030 W/m*K. As shown in Figure 6, the intervention on the windows frames ensured greater primary energy savings (kWh) that were related to the area of intervention. Furthermore, such an intervention, compared to the application of the coat on the facades, is easy to implement and does not require the use of expensive external scaffolding.
Figure 6 - Total primary energy consumption before and after their interventions These improvements provide a total reduction (step 3) of approximately 66.5%, on average, in the consumption of total primary energy.
Figure 7 - Total primary energy consumption before and after combined intervention of opaque and transparent envelope 4.2 Performance of the System Regarding improvements on the system, the adopted solutions are related to the generator system and regulation system. The installation of thermostatic valves benefits from all of the free heat gains because of the variation of the heating flow emitted from the terminals according to the power required by the room.
Improving heating systems was conducted through a heat absorption system that condensed "air to water" gas via a powered pump (methane or LPG), which exploits the air renewable energy. A G.U.E. of 165% allows a reduction of the consumption of natural gas for an equally useful power heat flow and contributes 39.4% of the energy from renewable sources. The table 8 shows the old system’s efficiency, the system efficiency after improvement and the increase obtained. System System efficiency of efficiency old plant new plant Gymnasium Liceo "L.G."Duni" 0.74 1.65 Scientific Liceo "L.S." "D. Alighieri" 0.82 1.65 Technical Institutes "I.T.C""Loperfido" 0.7 1.65 Technical Institutes "I.T.I.S.""Pentasuglia" 0.64 1.65 ScientificTechnical Lyceum "L.S.T."Pentasuglia 0.83 1.65 Technical Institutes "I.T.G" " Olivetti" 0.84 1.65 Professional Istitutes "I.P.S.S"Morra" 0.84 1.65 Music Lyceum "L.M. Duni" 0.978 1.65 Table 8- Old system efficiency and the system efficiency after improvement Institute
Increase of 2.23 2.01 2.36 2.58 1.99 1.96 1.96 1.69
As is shown in Figure 8, the improvement of the plant produce a savings, on average, of 48% of the annual total primary energy consumption
Figure 8 - Total primary energy consumption before and after improving a plant 4.3 Performance of the envelope and plant Table n. 9 summarizes the results for all of the analysed buildings.
School Buildings
Gymnasium "L.G."Duni"
Energy strategy of the envelope
Liceo
Improving opaque envelope Improving transparent envelope Improving plant
Energy consumption kWh 260,865.00
Energy savings kWh 181,844.04 106,155.06 128,305.26
% 69.7% 40.7% 49.2%
Scientific Liceo "L.S." "D. Alighieri"
Technical Institutes "I.T.C""Loperfido"
Technical Institutes "I.T.I.S.""Pentasuglia"
Scientific Technical Liceo "L.S.T."Pentasuglia"
Technical Institutes "I.T.G" " Olivetti"
Professional Istitutes "I.P.S.S"Morra"
Music "L.M. Duni"
Lyceum
Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant
511,450.00
352,440.00
1,238,896.00
110,823.00
364,325.00
300,326.00
76,295.00
218,830.29 242,458.73 218,995.03 85,210.07 237,821.05 401,255.87 445,075.07 234,604.66 88,669.35 219,231.58 266,022.79 303,102.15 482,769.45 351,583.68 756,010.53 867,227.15 929,265.68 42,096.65 3,741.68 66,894.74 42,973.53 86,031.30 285,349.43 215,720.53 187,347.37 287,904.50 327,202.18 37,582.00 26,035.00 154,437.03 237,329.82 39,042.42 3,820.07 15,283.57 30,384.09 20,662.36 22,452.59
83.9% 92.9% 83.9% 32.7% 46.5% 78.5% 87.0% 66.6% 25.2% 62.2% 75.5% 86.0% 39.0% 28.4% 61.0% 70.0% 75.0% 38.0% 3.4% 60.4% 38.8% 77.6% 78.3% 59.2% 51.4% 79.0% 89.8% 12.5% 8.7% 51.4% 79.0% 87.0% 5.0% 20.0% 39.8% 27.1% 29.4%
Table 9 - Results of the analysis The school that achieved the smallest savings is the institute L.S.T “G. B. Pentasuglia” because it is a building that was constructed after Italian Law 10/9, that is, the first Italian law on energy savings. The Music Lyceum ”L.M. Duni” is the school that had the lowest percentage of energy savings after improvements because it is a historical structure characterized by a room with a vaulted roof and a fresco. Although this building has a condensing boiler with a high efficiency and this structure is characterized by a high thermal inertia without thermal insulation, this study shows that the improvement of the envelope produced primary energy savings greater than 70%, with this percentage reaching 83% for L.G. “E. Duni”. The percentage of primary energy savings related to the thermal system is close to 50% for four of the school buildings, and for three schools, the percentage is 60%. Finally, considering the improvement of the plant and envelope, the percentage of primary energy savings exceeds 90% for most of the schools.
Acknowledgements This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649956. References: [1] S. P. Corgnati , V. Corrado, M. Filippi, A method for heating consumption assessment in existing buildings: A field survey concerning 120 Italian schools, Energy and Buildings 40 (2008) 801-809. [2] L. Dias Pereira, D. Raimondo, S. Corgnati, M. Gameiro da Silva, Energy consumptioninschools – A reviewpaper, Renewable and Sustainable Energy Reviews 40 (2014) 911–922. [3] U. Desideri, S. Proietti, Analysis of energy consumption in the high school of the provincie in central Italy, Energy and Buildings 34 (2002) 1003-1016. [4] E. G. Dascalakia, V. G. Sermpetzogloub, Energy performance and indoor environmental quality in Hellenic schools, Energy and Buildings 43 (2011) 718–727. [5] L. de Santoli, F. Fraticelli, F. Fornari, C. Calice, Energy performance assessment and a retrofit strategies in public school buildings in Rome, Energy and Buildings 68 part A (2014) 196-202. [6] U. Desideri, D. Leonardi, L. Arcioni, P. Sdringola, European project Educa-RUE: An example of energy efficiency paths in educational buildings, Energy and Buildings 68 part A (2014) 196-202. [7] P. Lourenc¸ M. Duarte Pinheiro, T. Heitor, From indicators to strategies: Key Performance Strategies forsustainable energy use in Portuguese school buildings, Energy and Buildings 85 (2014) 212-224. [8] Johann Reiss, Energy retrofitting of the school buildings to achieve plus energy and 3-litre building standards, Energy Procedia 48 (2014) 1503-1511. [9] G. Dall'O, L. Sarto, Potential and limits to improve energy efficiency in space heating in existing school buildings in northern Italy, Energy and Buildings 67 (2013) 298-308. [10] V. De Giuli, O. Da Pos, M. De Carli, Indoor environmental quality and pupil perception in Italian primary schools, Building and Environment 56 (2012) 335-345. [11] F. R. D'Ambrosio Alfano, E. Ianniello, B. I. Palella, PMV-PPD and acceptability in naturally ventilated schools, Building and Environment 67 (2013) 129-137. [12] F. Calise, Thermoeconomic analysis and optimization of high efficiency solar heating and cooling systems for different Italian school buildings and climates, Energy and Buildings 42 (2010) 992-1003. [13] Rospi G., Cardinale N., Stazi A., Energy and Microclimatic Performance of Restored Hypogeous Buildings in South Italy: the "Sassi" District of Matera”, Building and Environment 45 Issue 1 (2010) 94-106. [14] G. Rospi, N. Cardinale, P. Stefanizzi, Energy and microclimatic performance of Mediterranean vernacular buildings: The Sassi district of Matera and the Trulli district of Alberobello, Building and Environment 59 (2013) 590-598 [15] G. Rospi, N. Cardinale, Intini F., Cardinale T., Analysisi of Energy consumption of different typologies of school buildings in the city on Matera (Southern Italy), Energy Procedia 82 (2015) 512-518 [16] Energy Plus vers. 8.3, Program Energy Efficiency, Energy Technologies and Renewable Energy, U.S. Deparment of Energy. http://apps1.eere.energy.gov/buildings/energyplus/. [17] Standard ISO 9869-1:2014, “Thermal insulation - Building elements - In situ measurement of thermal resistance and thermal transmittance" [18] G. Rospi, N. Cardinale, P. Stefanizzi, V. Augenti, Thermal performance of a mobile home with light envelope, Building Simulation, 3 (2010) 331-338. [19] Standard UNI 10389-1:2009, “Heat Generators - Flue Gases Analysis And Measurement On Site Of Combustion Efficiency” [20] G. Rospi, N. Catdinale, P. Stefanizzi, V. Augenti, Thermal performance of mobile home with light envelope, Building Simulation 3 Issue 4 (2010) 331-338 [21] Standard UNI EN ISO 6946:2008 , “Building components and building elements -- Thermal resistance and thermal transmittance - Calculation method” [22] Standard UNI EN ISO 10077 1-2, “Thermal performance of windows, doors and shutters -- Calculation of thermal transmittance”
S0378-7788(16)31714-5 http://dx.doi.org/doi:10.1016/j.enbuild.2017.07.018 ENB 7758
To appear in:
ENB
Received date: Revised date: Accepted date:
28-11-2016 1-6-2017 8-7-2017
Please cite this article as: Gianluca Rospi, Nicola Cardinale, Francesca Intini, Elisabetta Negro, Analysis of the energy performance strategies of school buildings site in the Mediterranean climate: A case study the schools of Matera city, Energy and Buildingshttp://dx.doi.org/10.1016/j.enbuild.2017.07.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Analysis of the energy performance strategies of school buildings site in the Mediterranean climate: A case study the schools of Matera city GIANLUCA ROSPI1*, NICOLA CARDINALE1, FRANCESCA INTINI1, ELISABETTA NEGRO1 1
DICEM, Università degli Studi della Basilicata - ITALY
[email protected]
Graphical abstract
Highlights This study analyses the energy performance of eight schools located southern Italy We measured the thermal parameters and the gas consumptions The energy performance was validated by the measurements in situ and analysis in dynamic regime We implemented different energy perfomance strategies for enevelope and system The energy saved and environmental benefits were analyses Abstract Energy consumption of the public building stock represents an important cost of the balance of a state. Moreover, public buildings, in particular schools, should be buildings with elevated comfort levels because student and teachers spend much time in these rooms. The wellness and productive capacity of students and teachers are primarily affected by the comfort inside and air quality of school rooms.
Regarding energy use, school buildings waste much energy because most buildings were constructed before the 1991 and energy saving measures were only implemented in a few schools. This paper analyses the energy performance of eight different schools located in Matera city, southern Italy. The aim of this research is to analyse energy requirement utilizing dynamic analyses with a time step of one hour (using Energy-Plus method). Next, the values of the dynamic analyses were compared to the effective energy consumption. Using the results of this comparison, we validated the numerical model, and then, we analysed different energy auditing actions for these buildings. We included the energy auditing works in three categories: energy restoration of the envelope, of the plant and of both. For each of these categories, we calculated the energy savings. Ultimately, we analysed the environmental benefits of the three different categories in terms of CO 2 reduction. This research confirmed that the dynamic method is the best method to achieve a good energy analysis of these complex buildings. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649956. Key-Words: School buildings, Energy performance buildings, dynamic method, energy auditing, Mediterranean climate, comfort indoor.
1 Introduction The energy saving and efficiency actions in the building sector are a key theme for achieving the environmental targets of the national and EU levels . In the next few years, many public buildings will have to undergo significant retrofits. An important public building stock is constituted of school buildings. Different studies in the literature demonstrate that these buildings have poor indoor air quality and consume a large amount of thermal energy; this is confirmed by the fact that in the last twenty years, no energy saving measures were applied in school buildings during the processes of restoration. Moreover, it was demonstrated that the indoor comfort and indoor air quality in schools are important for ensuring the health and productivity of students and teachers. Over the past few decades, numerous international studies have been performed to address the topic of energy consumption and indoor environmental quality (IEQ) in school buildings. A field survey was conducted to collect, elaborate and analyse data concerning the actual energy consumption of space heating in school buildings of the Province di Torino. The study constructed an energy index that was defined as the ratio of the energy supplied by the heating system to the gross heated volume [1]. In [2], the authors performed functional benchmarking of different schools considering the different operation conditions of school buildings. The authors analysed the results through an intensive literature survey on energy consumption in schools. The literature was analysed to determine if a worldwide comparison among the published data could be established. In [3], the authors present an energy analysis of school buildings of the province of Perugia in central Italy. The study aimed to calculate the main thermal and electric energy consumption indices to evaluate the status of energy consumption and possible interventions to save energy in the school sector. In this paper, two applications of energy auditing in school buildings are presented. In [4], the authors studied a number of contemporary Hellenic school buildings. This study was conducted with a holistic approach consisting of three steps: first, an IEQ investigation, in situ, to reveal related problems and their potential sources; second, an energy audit to collect information on the energy related characteristics of the building; and third, an energy performance assessment. They also investigated the air indoor quality in school rooms. In [5], the energy quality of various schools in Rome was analysed, and different intervention strategies to reduce energy consumption were defined. The authors analysed the envelope, thermal plant and energy consumption, they performed energy retrofit interventions on the envelope and on the plant, and they calculated achievable benefits from the interventions in terms of energy and money saving through a simple payback time analysis (PBT), which is useful to identify priorities for action. In [6], the authors presented the project Educa-RUE. This project focuses on speeding up the implementation of European Directive on Energy Performance in Buildings, EPBD (2002/91/EC) in Member States at the local government level and to ensure its operability within the various national legislations of reference. The project developed a model process, known as the “Educa-RUE method”, to assess possible policies of intervention on educational buildings by promoting the ability of local players to guide and orient initiatives designed to encourage energy savings by means of specific measures and integrated tools. In [7], the energy consumption patterns of eight Portuguese case-study schools were analysed using a methodological approach that integrated quantitative and qualitative data analysis, and in [8], the energy performance of seven schools sited in Germany was studied. In [9], the authors presented an energy audit campaign on 49 school building situated in Lombardy in North Italy. They analysed actual energy consumption for heating, the occupant behaviour and the buildings technical characteristics. This study showed that, for some school buildings, it would be less expensive and more convenient to construct a new building instead of apply energy saving actions. In [10], a study of the indoor comfort of seven Italian schools was conducted. The authors measured the main thermo-physical parameters (temperature, humidity, illuminance, CO2 concentration, etc.), and they asked students to describe their thermo-hygrometric comfort. In [11], the authors proposed a new value of the expectancy factor of the PMV index for the Mediterranean climate. This value was obtained by conducting a combined subjective and objective investigation on approximately 200 Italian classrooms and on more than 4000 students, both in winter and summer. All of the investigated school buildings were non-air conditioned and only ventilated by operable windows. In [12], the author investigated the energetic and economic feasibility of a solar-assisted heating and cooling system (SHC) for use in different types of school buildings and Italian climates. The SHC system under investigation is based on the coupling of evacuated solar collectors with a single-stage LiBr–H2O absorption chiller; auxiliary energy for both heating and cooling is supplied by an electricity-driven reversible heat pump.
In the past, we studied the energy performances of the vernacular architectures of South Italy; this work was published in [13] [14]. In the previously paper four school buildings were analysed in stationary method using Italian energy low [15] This paper analyses the energy performance of eight different school buildings situated in the city of Matera in southern Italy. Matera has a typical Mediterranean climate, with temperate winters and hot summers, as well as a high humidity level. The aim of this research was to perform an energy audit. We conducted different monitoring campaigns in situ to evaluate the thermal conductance of the envelope; then, we evaluated the energy performance by using dynamic simulations (using the Energy Plus method). We estimated the gap between measured and simulated consumption. Finally, we analysed the different energy improvements, both for the envelope and the plant. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649956. 2 Techniques and technologies of the school buildings 2.1 Description of the project In this study, we described the energy diagnosis and different actions for improving the energy savings of eight different high school buildings situated in the city of Matera, southern Italy. The school buildings were built between 1540 and 1992, and these buildings were constructed with different techniques and technologies. Eight schools were analysed: Gymnasium Lyceum "L.G." "E. Duni", Scientific Lyceum "L.S." “D. Alighieri”, Scientific Technical Lyceum "L.S.C." “Pentasuglia”, Technical Institutes "I.T.G." “A. Olivetti”, Technical Institutes "I.T.I.S." "G.B. Pentasuglia", Technical Institutes "I.T.C." "A. Loperfido", Professional Istitutes"I.P.S.S." “I. Morra”, and Music Lyceum "L.M." “E. Duni”. Table 1 shows the principal data (year of construction, volume, total area, floors, etc.) of the school buildings analysed.
School name
Year
Gross volume Total area
Building height
N. classrooms
m3
m2
m
N
N. floors
L.G. “ E.Duni”
1966
6
24,556
5,761
23.00
37
L. S. “D. Alighieri”
1971
4
38,496
7,830
12.00
31
I.T.C. " Loperfido"
1961
5
20,846
5,814
17.70
34
I.T.I.S. “G. B. Pentasuglia”
1987
2
53,282
16,861
10.00
39
L.S.T. “G. B. Pentasuglia”
1992
2
15,118
3,484
8.00
12
I.T.G. “A. Olivetti”
1981
3
29,911
7,178
7.00
28
I.P.S.S. “I. Morra”
1972
4
14,093
3,329
14.00
98
L.M. " E. Duni "
1540
2
5,550
1,500
13.00
20
Table 1 - Principal data of the buildings analysed Because seven of the eight schools were constructed before law 10/91, they have envelopes without air space and thermal insulation. Instead, only L.S.T. “G. B. Pentasuglia” was constructed with a wall made of a double layer of clay interposed by an unventilated air space and plastered on both sides of the masonry with lime plaster and cement. This study was funded in part by the Province of Matera through a special convention and is part of a larger study on the diagnostic efficiency of the public school heritage of the Province of Matera. 3 Methodology
We adopted an integrated approach based on energy analyses in the dynamic regime using the Energy-Plus method [16], monitoring the thermal conductance in situ in accordance with ISO 9869-2014 [17] and monitoring of the energy consumption of heating for four consecutive years (from 2009 to 2012). The research can be divided into three phases. In the first phase, we measured the thermal conductance of the envelope, combustion efficiency of the heat generator and energy consumptions of all of the schools. The measurement of the conductance was performed in accordance with ISO 9869-2014, according to a methodology that has been used by other similar works and published in other papers [18]. We measured the combustion efficiency of heat generators according to the method described by UNI 10389 [19]. In this phase, we also performed a thermographic survey to identify thermal bridges and irregularities of the envelope. In the second phase, we constructed a numerical model in the Energy-Plus platform by inserting the measured in situ values from the first phase. In this phase, we set and validated the numerical model. The numerical model was validated by comparing the deviation the energy consumption simulated with the energy consumption measured. The validation results were good when the percentage of error of the deviation was less than 10 percent. The methodology validation for massive buildings by Energy Plus was presented in [14] and the methodology validation for light enelope by Energy Plus was presented in [20]. In the last phase, some energy performance strategies were proposed, and we calculated the energy savings, CO2 savings and investment payback period of each intervention. 4. Case Studies presentation In the province of Matera, there are 31 school buildings of the second degree, of which 19 are in the municipality of Matera, which is situated in Basilicata, southern Italy. Matera is characterized by a Mediterranean climate and has mild winters and hot summers; the minimum winter temperature is -2 °C, and the maximum summer temperature exceeds 35 °C. Analysing the total gas consumption for heating all of the school buildings, we found that 748578 standard m 3 of gas was consumed; the power consumption of only the school buildings present in the city of Matera was 65% of the total gas consumption. This paper focuses on eight different school buildings located in the city of Matera. The total gas consumption for heating the eight buildings was 314,727 standard m3, (70% of the total gas consumption of Matera schools). Regarding the period of construction of the school buildings, only 7 of the 8 buildings were built after law n.10/91 (the first law on energy savings of buildings) was implemented, whereas all of the other buildings were built between the 1960s and 1980s. The analysed buildings are different both in form and in construction techniques. Table n. 2 summarizes the main technical characteristics (envelope and plant) of the various buildings studied.
School name Construction typology
L.G. E.Duni”
“
Gross volume
Total area
Opaque area
Windows area
m3
m2
m2
m2
Concrete structure, ceilings in brick- concrete and brick 24,556.00 walls plastered
and wall in and ceilings in 38,496.00 brick-cement Structure pillars and beams of reinforced concrete, I.T.C. " reinforced concrete floors 20,846.00 Loperfido" and brick and concrete walls with air gap"
S/V ratio
5,761.00
5,761.00
873.00
0.36
2×305
7,830.00
7,494.00
956.00
0.29
4×227.0 1×147.0
Concrete structure, ceilings brick-cement and 53,282.00 concrete walls
I.T.I.S. “G. B. in Pentasuglia”
5,814.00
6,171.00
777.00
16,861.00 18,253.00 1,880.00
Heating terminals
kW
Structure
L. S. “D. concrete Alighieri”
Installed thermal power
Radiators classrooms, laboratories and offices Radiators classrooms, fan coil units offices
0.42
4×232
Radiators classrooms, laboratories offices
0.59
1×768 3×633.8
Radiators classrooms, laboratories offices
and
and
Structure
in
concrete,
L.S.T. “G. B. ceilings in brick-cement and 15,118.00 Pentasuglia”
3,484.00
2,881.00
158.00
0.32
2×191.9
I.T.G. “A. Olivetti”
Structure and wall in prefabricated panels and 29,911.00 ceilings in brick-cement
7,178.00
6,698.00
1025.00
0.46
2×488.5
I.P.S.S. Morra”
“I.
Structure in concrete, ceilings in brick-cement and 14,093.00 walls in brick face view
3,329.00
3,586.00
1195.00
0.34
2×309.0
L.M. " Duni "
E.
Load-bearing masonry structure, vaulted ceilings in 5,550.00 limestone
1,500.00
595.00
67.00
0.17
1×280
walls with air gaps
Radiators classrooms, fan coil units offices and laboratories Radiators classrooms, laboratories and offices Radiators classrooms, laboratories and offices Radiators classrooms, laboratories and offices
Table 2 - Technical characteristics (envelope and plant) of the various buildings studied 5. First phase: Monitoring campaign and energy diagnosis To ensure a good energy diagnosis, it is necessary to determine the envelope thermal proprieties and thermal parameters of the conditioning plant. The measurement and monitoring activities are essential to achieve a specify energy diagnosis, while also minimizing the error in the next phase of the model construction in the calculation code. In this phase, we measured the technical and technological specific parameters of the school buildings: the surface, volume, window typologies, envelope thickness, roof typologies, and so on. Next, we individuated the thermal bridges and thermal discontinuity of the envelope using an infrared thermal camera. We found the following main thermal bridges in addition to those of form: lack of thermal insulation on the bearing structures, erroneous connections of the window frame to the masonry and erroneous connections of the rolling shutter box to the wall. The figures 1 and 2 present sample images.
Figure 1– A specific section of the ITC “ Loperfido” envelope
Figure 2– A specific section of the L.S. “ D. Alighieri” envelope In the second step, we measured the thermal conductance in situ using a non-invasive methodology described by UNI EN ISO 9869. This standard involves the use of a heat flow meter and four resistance thermometers to estimate the thermal conductance. We mounted the sensors in such a manner to ensure a representative result of the entire wall element. The heat flow meter must be installed on the inner surface of the wall because this side has a more stable temperature, avoiding the proximity of thermal bridges and heat sources. We installed two temperature meters on the inside surface and two on the outside surface of the wall. The measurement campaigns for all of the school buildings were produced in winter because, to minimize the error, the presence of a constant temperature difference between the two sides of the masonry (inside and outside) of approximately 10 °C is essential. The duration of each measurement campaign was ten days, with a duration of 10 minutes. We performed a measurement only if the mean temperature difference found between the outer and inner envelope across all campaigns of measures was between 8 and 9 °C. There were 7200 processed data points from each measurement campaign. After 10 days, we calculated the thermal conductance and thermal transmittance with the “progressive average” or “moving average” method. Using this method, we calculated the thermal conductance from the sampled values of the surface temperature and the heat flux using the following equation: N
q C=
j1
j
[W/m 2 K]
N
(T j1
i, j
- To, j )
where qj is the thermal flux, Ti,j is the indoor surface temperature and T o,j is the outdoor surface temperature. As N increases, the ratio tends to converge to a stationary value and is not influenced by the thermal mass of the wall. The C function converges with oscillations around a horizontal asymptote, with a maximum amplitude of approximately 0.05 W/m²K. To calculate the thermal transmittance, we added the normed indoor and outdoor surface resistances R i (0.13 m2K/W) and Re(0.04 m2K/W) to the value C. We used the following formula:
U
1 1 [W / m2 K ] 1 R Ri Ro C
If the stratigraphy of envelope was known, then the transmittance was calculated in accordance with UNI EN ISO 6946:2008 [21]. Table 3 shows the values of the conductance for the eight analysed buildings for both the opaque shell and transparent one. The transparent envelope was calculated in according to standard UNI EN ISO 10077 1-2 [22].
In the table, the values obtained from ISO 9869 were measured in situ, the values obtained from UNI EN ISO 6946:2008 were calculated because the stratigraphy is noted, and the value obtained from UNI EN ISO 10077 1-2 were calculated using the finite elements method. School name
Opaque vertical envelope C
U
Law limits
Horizontal coverage envelope Calculation typology
U
W/m2K W/m2K W/m2K
L.G. “ E.Duni”
0.48
L. S. “D. 2.04 Alighieri” I.T.C. " 0.31 Loperfido" I.T.I.S. “G. B. 0.22 Pentasuglia” L.S.T. “G. B. 1.69 Pentasuglia” I.T.G. “A. 0.96 Olivetti” I.P.S.S. “I. 1.77 Morra” L.M. " E. Duni "
1.41
Law limits
Transparent envelope
Calculation typology
W/m2K W/m2K
1.54
0.32
ISO 9869
1.50
0.26
2.54
0.32
ISO 9869
2.21
0.26
2.06
0.32
ISO 9869
1.60
0.26
2.54
0.32
ISO 9869
1.51
0.26
0.54
0.32
ISO 9869
1.69
0.26
0.83
0.32
ISO 9869
0.88
0.26
1.36
0.32
ISO 9869
0.85
0.26
0.63
0.32
ISO 9869
1.04
0.26
Law limits
U
Calculation typology
W/m2K W/m2K
UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008 UNI EN 6946:2008
ISO ISO ISO ISO ISO ISO ISO ISO
5.78
1.8
5.78
1.8
5.78
1.8
5.78
1.8
3.10
1.8
4.02
1.8
6.02
1.8
3.15
1.8
UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2 UNI EN 10077-1-2
ISO ISO ISO ISO ISO ISO ISO ISO
Table 3 - Values of the conductance for the eight analysed buildings
“A. 977.00 618.00 280.00
Efficiency at 100% load
74%
82%
83%
84%
70%
64%
91%
L.M. " E. Duni "
383.80
I.P.S.S. “I. Morra”
1,075.00 928.00 2,669.40
I.T.G. Olivetti”
L.S.T. “Pentasuglia”
610.00
I.T.C. "Loperfido"
Generator power [kW]
L.G. “E.Duni”
I.T.I.S. “Pentasuglia”
L. S. “D. Alighieri”
Subsequently, we performed a measurement campaign of the combustion efficiency of heat generators according to the method described by UNI 10389 [19] and analysed the bills of heat consumption (gas and/or diesel) for the years 2009, 2010, 2011 and 2012. For the analysed buildings, we show the measured values of the heat generator efficiency in Table 4 and the measured values of the heating energy consumption in Table 5.
97.9%
Table 4 - Efficiency of the heat generator School name
Methane gas Consumption 2009
2010
2011
2012
Average
Sm3/year
Sm3/year
Sm3/year
Sm3/year
Sm3/year
L.G. “ E.Duni”
31,928.00
25,672.00
25,557.00
23,546.00
26,675.75
L. S. “D. Alighieri”
42,195.00
50,522.00
51,606.00
57,519.00
50,460.50
I.T.C. " Loperfido"
39,189.00
37,782.00
37,360.00
33,193.00
36,881.00
I.T.I.S. “G. B. Pentasuglia”
133,959.58
135,994.85
105,833.04
10,3761.05
119,887.13
L.S.T. “G. B. Pentasuglia”
11,961.42
12,143.15
9,449.96
9,264.95
10,704.87
I.T.C.G. “A. Olivetti”
38,947.00
39,197.00
32,481.00
30,409.00
35,258.50
I.P.S.S. “I. Morra”
33,286.00
28,691.00
25,258.00
21,584.00
27,204.75
8,125.00
L.M. " E. Duni "
7,811.00
7,497.00
7,183.00
7,654.00
Table 5 - Gas consumption for the time step 2009 – 2012
Volume
Total dispersing surface
Opaque area
Windows area
UxS opaque envelope
UxS trasparent envelope
UxS envelope
m3
m2
m2
m2
W/K
W/K
W/K
L.G. “ E.Duni”
24,556.00
8,838.84
5,761.00
873.00
9,310.75
5,044.19
14,354.94
L. S. “D. Alighieri”
38,496.00
11,015.00
7,494.00
956.00
18,000.63
5,523.77
23,524.40
I.T.C. " Loperfido"
20,846.00
8,767.00
6,171.00
777.00
11,976.35
4,489.51
16,465.86
I.T.I.S. “G. B. Pentasuglia”
53,282.00
31,419.34
18,253.00
1880.00
50,531.65
4,489.51
61,394.29
L.S.T. “G. B. Pentasuglia”
15,118.00
4,910.85
2,881.00
158.00
1,717.86
486.92
2,204.78
I.T.C.G. “A. Olivetti”
29,911.00
11,989.30
6,698.00
1025.00
5,829.58
4,127.03
9,956.61
I.P.S.S. “I. Morra”
14,093.00
6,261.60
3,586.00
1195.00
3,854.60
7,170.00
11,024.60
L.M. " E. Duni "
5,550.00
2,217.00
2,150.00
67.00
1,091.30
210.78
1,302.08
School name
Table 6 - Main energy performance characteristic of the envelope Finally, we correlated all of the measured values and calculated to date. We analysed the relationship between the product UxS with the gross volume of the buildings, heat loss through the surfaces and energy consumption of heating. The calculation was performed while considering the weighted average of the thermal transmittance for the surface (opaque vertical, horizontal opaque and transparent). Figures 3 and 4 show that the correlation between UxS and the gross volume increases with the volume of the building and heat loss. The slope of the line is higher in the case of the heat loss surface (Figure 4).
Figure 3 -Relationship between UxS and the gross volume
Figure 4 - Relationship between UxS and the heat loss surface Figure 5 shows the relationship between the product U × S and the gas consumption for heating. In this case, the slope of the line is less than that of the previous case in spite of the correlation coefficient being higher than that of the other case.
Figure 5 -Relation between UxS and gas consumption 6. Second phase: Dynamic energy analysis In this step, a numerical model was developed for each of the school buildings analysed. We used the EnergyPlus software to analyse the energy performance. The analysis was performed in the dynamic regime. Before starting the calculation under dynamic conditions, we set the functioning templates of the building (set point system, during of starting and switching off of the plant, internal loads, lighting loads, opening windows, etc.); these values were entered according to the actual data acquired by the staff that maintains the boiler and by the school manager. The processing of the model under dynamic conditions directly determines the consumption of the heating thermal energy; this value, once converted into thermal primary energy, was compared with the actual consumption measured in situ. Table 7 shows a comparison between the measured annual fossil consumption and simulated annual consumption, with the percentage error.
Average Consumption Consumption simulated measured
Percentage error
Sm3/year
Sm3/year
%
L.G. “ E.Duni”
26,675.75
24,782.00
7.10%
L. S. “D. Alighieri”
50,460.50
48,588.00
3.71%
I.T.C. " Loperfido"
36,881.00
33,482.00
9.22%
I.T.I.S. “G. B. Pentasuglia”
119,887.13
117,695.00
1.83%
L.S.T. “G. B. Pentasuglia”
10,704.87
10,528.16
1.65%
I.T.C.G. “A. Olivetti”
35,258.50
34,611.00
1.84%
I.P.S.S. “I. Morra”
27,204.75
28,531.00
-4.88%
L.M. " E. Duni "
7,654.00
7,248.00
5.30%
School name
Table 7 - Comparison between the measured and simulated annual fossil consumption Because the Energy Plus method outputs the value in kWh/year, the conversion procedure to m 3/year was performed with reference to the calorific value to 1 m3 of methane gas, equivalent to approximately 35 MJ (9.7 kWh). Next, by dividing the total value of kWh/year by 9.7, the total value of m3/year was obtained. The low deviation obtained between the simulated fuel consumption and measured consumption is caused by small uncertainties, including the difficulty of estimating the real program operation of the system installation, the approximation of the internal loads and the lack of easy access to schematics of thermal bridges in the numeric code. In this way, we calibrated the numerical models designed in Energy Plus of the school buildings. Next, we analysed the following energy performance strategies: improvement of the envelope and heat plant and the addition of renewable energy systems. 4. Third phase: Energy Performance Strategies All energy improvement actions were conducted using the dynamic method. We hypothesized different energy improvement strategies: energy improvements of the envelope and of the system. The used energy renovation strategies of the envelope were the following: insertion of thermal insulation in the wall, replacement of the windows, and application of thermal insulation in the roof. Alternatively, the energy renovation strategies of the system used were the following: substitution of the old plant with a gas heat pump or with an electric heat pump. Finally, we analysed the school buildings by implementing renewable energy solutions, such as thermal solar and photovoltaic systems.
4.1 Performance of the envelope The energy improvement of the envelope was conducted in such a way as to achieve thermal transmittance values that were in accordance with the limitations imposed by the three Interministral Italian Decrees 26 June 2015: “Decree for minimum requirements: application of the calculation methodology of the energy performance and definition of requirements and minimum requirements for buildings” [23]. This improvement was performed in three successive steps, considering the improvement of the opaque envelope (step 1), replacement of windows frames (step 2) and both solutions of step 1 and 2 (step 3). The intervention on the opaque envelope consists of an inner insulation of flat roofs and walls, constituted of a plasterboard sheet thickness of 10 mm coupled to an insulating layer consisting of panel hemp fibre with λ = 0.030 W/m*K. As shown in Figure 6, the intervention on the windows frames ensured greater primary energy savings (kWh) that were related to the area of intervention. Furthermore, such an intervention, compared to the application of the coat on the facades, is easy to implement and does not require the use of expensive external scaffolding.
Figure 6 - Total primary energy consumption before and after their interventions These improvements provide a total reduction (step 3) of approximately 66.5%, on average, in the consumption of total primary energy.
Figure 7 - Total primary energy consumption before and after combined intervention of opaque and transparent envelope 4.2 Performance of the System Regarding improvements on the system, the adopted solutions are related to the generator system and regulation system. The installation of thermostatic valves benefits from all of the free heat gains because of the variation of the heating flow emitted from the terminals according to the power required by the room.
Improving heating systems was conducted through a heat absorption system that condensed "air to water" gas via a powered pump (methane or LPG), which exploits the air renewable energy. A G.U.E. of 165% allows a reduction of the consumption of natural gas for an equally useful power heat flow and contributes 39.4% of the energy from renewable sources. The table 8 shows the old system’s efficiency, the system efficiency after improvement and the increase obtained. System System efficiency of efficiency old plant new plant Gymnasium Liceo "L.G."Duni" 0.74 1.65 Scientific Liceo "L.S." "D. Alighieri" 0.82 1.65 Technical Institutes "I.T.C""Loperfido" 0.7 1.65 Technical Institutes "I.T.I.S.""Pentasuglia" 0.64 1.65 ScientificTechnical Lyceum "L.S.T."Pentasuglia 0.83 1.65 Technical Institutes "I.T.G" " Olivetti" 0.84 1.65 Professional Istitutes "I.P.S.S"Morra" 0.84 1.65 Music Lyceum "L.M. Duni" 0.978 1.65 Table 8- Old system efficiency and the system efficiency after improvement Institute
Increase of 2.23 2.01 2.36 2.58 1.99 1.96 1.96 1.69
As is shown in Figure 8, the improvement of the plant produce a savings, on average, of 48% of the annual total primary energy consumption
Figure 8 - Total primary energy consumption before and after improving a plant 4.3 Performance of the envelope and plant Table n. 9 summarizes the results for all of the analysed buildings.
School Buildings
Gymnasium "L.G."Duni"
Energy strategy of the envelope
Liceo
Improving opaque envelope Improving transparent envelope Improving plant
Energy consumption kWh 260,865.00
Energy savings kWh 181,844.04 106,155.06 128,305.26
% 69.7% 40.7% 49.2%
Scientific Liceo "L.S." "D. Alighieri"
Technical Institutes "I.T.C""Loperfido"
Technical Institutes "I.T.I.S.""Pentasuglia"
Scientific Technical Liceo "L.S.T."Pentasuglia"
Technical Institutes "I.T.G" " Olivetti"
Professional Istitutes "I.P.S.S"Morra"
Music "L.M. Duni"
Lyceum
Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant Improving opaque envelope Improving transparent envelope Improving plant Improving opaque envelope and windows Improving envelope and plant
511,450.00
352,440.00
1,238,896.00
110,823.00
364,325.00
300,326.00
76,295.00
218,830.29 242,458.73 218,995.03 85,210.07 237,821.05 401,255.87 445,075.07 234,604.66 88,669.35 219,231.58 266,022.79 303,102.15 482,769.45 351,583.68 756,010.53 867,227.15 929,265.68 42,096.65 3,741.68 66,894.74 42,973.53 86,031.30 285,349.43 215,720.53 187,347.37 287,904.50 327,202.18 37,582.00 26,035.00 154,437.03 237,329.82 39,042.42 3,820.07 15,283.57 30,384.09 20,662.36 22,452.59
83.9% 92.9% 83.9% 32.7% 46.5% 78.5% 87.0% 66.6% 25.2% 62.2% 75.5% 86.0% 39.0% 28.4% 61.0% 70.0% 75.0% 38.0% 3.4% 60.4% 38.8% 77.6% 78.3% 59.2% 51.4% 79.0% 89.8% 12.5% 8.7% 51.4% 79.0% 87.0% 5.0% 20.0% 39.8% 27.1% 29.4%
Table 9 - Results of the analysis The school that achieved the smallest savings is the institute L.S.T “G. B. Pentasuglia” because it is a building that was constructed after Italian Law 10/9, that is, the first Italian law on energy savings. The Music Lyceum ”L.M. Duni” is the school that had the lowest percentage of energy savings after improvements because it is a historical structure characterized by a room with a vaulted roof and a fresco. Although this building has a condensing boiler with a high efficiency and this structure is characterized by a high thermal inertia without thermal insulation, this study shows that the improvement of the envelope produced primary energy savings greater than 70%, with this percentage reaching 83% for L.G. “E. Duni”. The percentage of primary energy savings related to the thermal system is close to 50% for four of the school buildings, and for three schools, the percentage is 60%. Finally, considering the improvement of the plant and envelope, the percentage of primary energy savings exceeds 90% for most of the schools.
Acknowledgements This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649956. References: [1] S. P. Corgnati , V. Corrado, M. Filippi, A method for heating consumption assessment in existing buildings: A field survey concerning 120 Italian schools, Energy and Buildings 40 (2008) 801-809. [2] L. Dias Pereira, D. Raimondo, S. Corgnati, M. Gameiro da Silva, Energy consumptioninschools – A reviewpaper, Renewable and Sustainable Energy Reviews 40 (2014) 911–922. [3] U. Desideri, S. Proietti, Analysis of energy consumption in the high school of the provincie in central Italy, Energy and Buildings 34 (2002) 1003-1016. [4] E. G. Dascalakia, V. G. Sermpetzogloub, Energy performance and indoor environmental quality in Hellenic schools, Energy and Buildings 43 (2011) 718–727. [5] L. de Santoli, F. Fraticelli, F. Fornari, C. Calice, Energy performance assessment and a retrofit strategies in public school buildings in Rome, Energy and Buildings 68 part A (2014) 196-202. [6] U. Desideri, D. Leonardi, L. Arcioni, P. Sdringola, European project Educa-RUE: An example of energy efficiency paths in educational buildings, Energy and Buildings 68 part A (2014) 196-202. [7] P. Lourenc¸ M. Duarte Pinheiro, T. Heitor, From indicators to strategies: Key Performance Strategies forsustainable energy use in Portuguese school buildings, Energy and Buildings 85 (2014) 212-224. [8] Johann Reiss, Energy retrofitting of the school buildings to achieve plus energy and 3-litre building standards, Energy Procedia 48 (2014) 1503-1511. [9] G. Dall'O, L. Sarto, Potential and limits to improve energy efficiency in space heating in existing school buildings in northern Italy, Energy and Buildings 67 (2013) 298-308. [10] V. De Giuli, O. Da Pos, M. De Carli, Indoor environmental quality and pupil perception in Italian primary schools, Building and Environment 56 (2012) 335-345. [11] F. R. D'Ambrosio Alfano, E. Ianniello, B. I. Palella, PMV-PPD and acceptability in naturally ventilated schools, Building and Environment 67 (2013) 129-137. [12] F. Calise, Thermoeconomic analysis and optimization of high efficiency solar heating and cooling systems for different Italian school buildings and climates, Energy and Buildings 42 (2010) 992-1003. [13] Rospi G., Cardinale N., Stazi A., Energy and Microclimatic Performance of Restored Hypogeous Buildings in South Italy: the "Sassi" District of Matera”, Building and Environment 45 Issue 1 (2010) 94-106. [14] G. Rospi, N. Cardinale, P. Stefanizzi, Energy and microclimatic performance of Mediterranean vernacular buildings: The Sassi district of Matera and the Trulli district of Alberobello, Building and Environment 59 (2013) 590-598 [15] G. Rospi, N. Cardinale, Intini F., Cardinale T., Analysisi of Energy consumption of different typologies of school buildings in the city on Matera (Southern Italy), Energy Procedia 82 (2015) 512-518 [16] Energy Plus vers. 8.3, Program Energy Efficiency, Energy Technologies and Renewable Energy, U.S. Deparment of Energy. http://apps1.eere.energy.gov/buildings/energyplus/. [17] Standard ISO 9869-1:2014, “Thermal insulation - Building elements - In situ measurement of thermal resistance and thermal transmittance" [18] G. Rospi, N. Cardinale, P. Stefanizzi, V. Augenti, Thermal performance of a mobile home with light envelope, Building Simulation, 3 (2010) 331-338. [19] Standard UNI 10389-1:2009, “Heat Generators - Flue Gases Analysis And Measurement On Site Of Combustion Efficiency” [20] G. Rospi, N. Catdinale, P. Stefanizzi, V. Augenti, Thermal performance of mobile home with light envelope, Building Simulation 3 Issue 4 (2010) 331-338 [21] Standard UNI EN ISO 6946:2008 , “Building components and building elements -- Thermal resistance and thermal transmittance - Calculation method” [22] Standard UNI EN ISO 10077 1-2, “Thermal performance of windows, doors and shutters -- Calculation of thermal transmittance”