Evaluation of School Building Energy Performance and Classroom Indoor Environment

energies Review Evaluation of School Building Energy Performance and Classroom Indoor Environment Jitka Mohelníková1, Miloslav Novotný1and Pavla Mocová2,* 1Faculty of Civil Engineering, Brno University of Technology, 602 00 Brno, Czech Republic; [email protected].cz (J.M.); novotny[email protected].cz (M.N.) 2Faculty of Forestry and Wood Technology, Mendel University, 613 00 Brno, Czech Republic *Correspondence: [email protected] Received: 21 April 2020; Accepted: 12 May 2020; Published: 15 May 2020   Abstract: Existing building stock represents potential for energy saving renovations. Energy savings and indoor climate comfort are key demands for sustainable building refurbishment. Especially in schools, indoor comfort is an extremely important issue. A case study of energy consumption in selected school buildings in temperate climatic conditions of Central Europe region was performed. The studied buildings are representatives of various school premises constructed throughout the last century. The evaluation was based on data analysis of energy audits. The goal was aimed at assessment of the school building envelopes and their influence on energy consumption. One of the studied schools was selected for detailed evaluation. The school classroom was monitored for indoor thermal and visual environments. The monitoring was performed to compare the current state and renovation scenarios. Results of the evaluation show that the school buildings are highly inefficient even if renovated. Indoor climate in classrooms is largely influenced by windows. Solar gains affect interior thermal stability and daylighting. Thermal insulation quality of building envelopes and efficient solar shading systems appear to be fundamental tasks of school renovation strategies. Keywords: energy performance; energy audits; school buildings; indoor climate 1. Introduction Current trends are aimed at the improvement in building energy performance and sustainability [1,2] . Modern construction methods facilitate more energy conscious buildings compared to old building stocks [ 2 – 4 ]. Newly designed buildings comply with top-level energy efficiency[ 5 , 6 ].Nevertheless,buildingrefurbishmentrepresentsarationalapproachtowardssustainable development [ 7 , 8 ]. Energy conscious renovation became one of the promising ways to reduce carbon dioxide emissions from buildings [ 9 , 10 ]. Existing buildings in the EU region represent massive potentials for energy savings [ 1 , 2 ]. Energy renovation has utmost importance for the residential and public buildings sectors. These buildings exert high energy consumption for heating and ventilation or cooling systems as well as artificial lighting. Especially school buildings have been objects of energy saving interests. Considerable numbers of programs are focused on school buildings performance [ 11 – 13 ]. Zero emissions and high quality of indoor environment were topical tasks of the project “School of the Future”, within the frame of the EU programme [ 14 ]. The aim of the project was to communicate examples of efficient buildings under different European climates. Strategies for energy consumption [ 15 – 21 ] and thermal comfort assessments [ 22 – 26 ] were developed for educational buildings. Energy efficiency, together with indoor climate comfort, are key features of good practice school performances in accordance with sustainable architecture principles [ 27 , 28 ]. Building envelopes play a Energies 2020,13, 2489; doi:10.3390/en13102489 www.mdpi.com/journal/energies Energies 2020,13, 2489 2 of 17 substantial role in the built environment [ 29 , 30 ]. Particularly windows influence indoor thermal and visual comfort [31–33]. The abovementioned overview shows the importance of energy efficiency and indoor climate conscious attitudes [ 34 ] towards educational buildings. A study focused on the assessment of selected representatives of school buildings in temperate climatic conditions was performed to evaluate their energy saving potentials in accordance with recent trends of highly energy efficient schools in Central Europe [35]. 2. Materials and Methods A case study aimed at an analysis of energy consumption in selected school buildings in the Central Europe region was performed. The studied buildings are representatives of various school premises. The evaluation was based on the analysis of data from energy audits for specification of current state of building envelopes and their influence on energy consumption. One of the studied schools was selected for detailed evaluation. The school classroom was monitored for indoor thermal and visual climate. 2.1. Analysis of Energy Audits The selected schools [ 36 ] were studied for their energy consumption. They are representatives of an existing school building stock of construction styles throughout the last century. Many schools are very old and some of them are listed as historically protected premises. Most of them are energy inefficient. Thermal insulation improvements and windows retrofit are required for upgraded efficiency. The case study is focused on analysis of the buildings’ energy performance and renovation potentials. The school buildings were selected in accordance with the building site locality and climatic conditions, (Figure 1and Table 1). The buildings’ construction is commonly represented by solid brick (70%) and ceramic block (18%) masonry systems or reinforced concrete prefabricated technology (12%). Central gas heating is widely used in the schools, while electric heating has minor application. The school buildings’ energy consumption is spent on heating and hot water services (80%), artificial lighting and electric appliances (12%) and auxiliary energy demands (8%). Energies 2020, 13, x FOR PEER REVIEW 2 of 18 Energy efficiency, together with indoor climate comfort, are key features of good practice school performances in accordance with sustainable architecture principles [27,28]. Building envelopes play a substantial role in the built environment [29,30]. Particularly windows influence indoor thermal and visual comfort [31–33]. The abovementioned overview shows the importance of energy efficiency and indoor climate conscious attitudes [34] towards educational buildings. A study focused on the assessment of selected representatives of school buildings in temperate climatic conditions was performed to evaluate their energy saving potentials in accordance with recent trends of highly energy efficient schools in Central Europe [35]. 2. Materials and Methods A case study aimed at an analysis of energy consumption in selected school buildings in the Central Europe region was performed. The studied buildings are representatives of various school premises. The evaluation was based on the analysis of data from energy audits for specification of current state of building envelopes and their influence on energy consumption. One of the studied schools was selected for detailed evaluation. The school classroom was monitored for indoor thermal and visual climate. 2.1. Analysis of Energy Audits The selected schools [36] were studied for their energy consumption. They are representatives of an existing school building stock of construction styles throughout the last century. Many schools are very old and some of them are listed as historically protected premises. Most of them are energy inefficient. Thermal insulation improvements and windows retrofit are required for upgraded efficiency. The case study is focused on analysis of the buildings’ energy performance and renovation potentials. The school buildings were selected in accordance with the building site locality and climatic conditions, (Figure 1 and Table 1). The buildings’ construction is commonly represented by solid brick (70%) and ceramic block (18%) masonry systems or reinforced concrete prefabricated technology (12%). Central gas heating is widely used in the schools, while electric heating has minor application. The school buildings’ energy consumption is spent on heating and hot water services (80%), artificial lighting and electric appliances (12%) and auxiliary energy demands (8%). Figure 1. Map with localities of the studied school buildings 1 to 18, (map: https://geology.com/world/czech-republic-satellite-image.shtml). Figure 1. Map with localities of the studied school buildings 1 to 18, (map: https://geology.com/world/ czech-republic-satellite-image.shtml). Energies 2020,13, 2489 3 of 17 Table 1. Buildings location, geometry and heat losses. Building Year of Construction (Renovation) Locality Building Geometry Building Envelope Altitude [m] Latitude Longitude [◦] Aver. Winter Temperature [◦C] Building Volume [m3] Gross Floor Area/Heated Volume [m−1] Heat Loss [kW] Average U Value [W m−2K−1] 11900 (2000) 248 49.763969 N 17.180405 E 4.1 3264 0.63 90 0.907 21950 210 49.456479 N 17.450230 E 3.9 23,278 0.40 373.1 1.27 31994 272 49.038646 N 17.814872 E 3.9 19,255 0.4 303.6 1.136 41931 272 49.038646 N 17.814872 E 3.9 3448 0.47 61.1 0.954 51890 334 49.458565 N 18.056868 E 3.8 1938 0.574 50.1 0.97 61984 304 49.6819311 N 18.3673219 E 3.7 23,955 0.45 434 1.087 71949 336 49.712716 N 13.204605 E 3.6 3491 0.43 88.7 1.23 81978 387 49.443259 N 13.248114 E 3.7 1471 0.85 61.1 0.95 91937 520 49.7161561 N 13.9473069 E 3.5 7163 0.47 102 0.90 10 1930 440 49.4248869 N 13.8817589 E 3.7 11,427 0.503 276.5 1.05 11 1988 225 50.289161 N 14.824512 E 3.8 5288 0.40 99.4 0.82 12 1960 188 48.9.07468 N 16.775371 E 4.5 4140 0.48 82.6 1.18 13 1929 450 50.129276 N 16.499965 E 3.6 6670 0.40 160.6 1.21 14 1967 179 49.059797 N 17.495850 E 3.6 3326 0.46 78 1.33 15 1980 675 49.908449 N 17.211115 E 3.1 4131 0.68 130 1.02 16 1887 (1962) 378 49.303454 N 14.158029 E 3.7 21,777 0.37 380.6 1.1 17 1980 334 49.820923 N 18.262524 E 3.6 22,423 0.25 424.5 0.76 18 1894 (2014) 280 50.655668 N, 14.724856 E 2.9 17,244 0.24 396 0.72 2.2. School Classroom Thermal and Daylight Evaluation One of the studied buildings was selected for detail evaluations—building 18 (Table 1). The main goal was thermal and daylight assessment of the school classrooms. The school building constructed in 1894 is listed as a historically protected premise (Figure 2) [ 37 ]. The three-storey building has a solid brick masonry and roof truss load-bearing structures. The ground floor is dedicated to the main entrance and school facilities as well as management and administrative departments. Educational rooms are on the first and second floor. Energies 2020, 13, x FOR PEER REVIEW 4 of 18 Figure 2. Historical building of primary school, locality Mimoň, CZ [37]. The school has spacious side lit classrooms. One of them, located on the second floor, was selected for the evaluation. Firstly, the classroom thermal assessment was performed for the current state and compared with renovation scenarios. Secondly, the classroom daylight evaluation was carried out. Daylight illuminance and luminance measurements were taken and completed with a daylight simulation study. 2.2.1. Thermal Evaluation The thermal study was focused on the building facade and its influence on indoor climate. The external wall thermal transmittance and condensation risks were studied. The evaluation was carried out for three variations: • current state: wall with 8 cm of thermal insulation on the interior side; • renovation scenario I: wall with 15 cm of thermal insulation on the interior side; • renovation scenario II: wall with 15 cm of thermal insulation on the exterior surface. The software Teplo [38] was used for the evaluation. The software is intended for fundamental analyses of building constructions like thermal resistance R (m 2 KW −1 ) and U-value (W m −2 K −1 ) calculations, temperature profiles, interstitial condensation analysis and specification of annual balance of condensed and evaporated amount within building constructions in accordance with standard methodology of ISO 6946 and ISO 13788 [39,40] and other standard requirements [41]. Boundary conditions for the thermal evaluation according to [ 41] are following: • design outdoor temperature -13.0 °C, locality—GPS: 50.655668 N, 14.724856 E; • design indoor air temperature 21.0 °C (classroom); • design relative humidity of outdoor air 84.0%; • design relative humidity of indoor air 55%. Two-dimensional temperature distribution of the wall details at window jambs in the current state and design variations with internal and external thermal insulation were simulated using the software Area [38]. The software is dedicated to complex thermal analyses of building construction details for specification of potential thermal bridges in two dimensional stationary heat transfer and water vapour diffusion simulations in accordance with standard methodology of ISO 10211 [42]. A study of the influence of the renovated facade on indoor thermal stability was performed [41,43]. The thermal stability was selected as an indicator of indoor thermal climate. Thermal stability of the classroom was simulated for winter and summer season conditions using the software Stabilita [38]. The internal temperature drop during a heating lapse in winter and summer indoor temperature rise were calculated. The goal of the evaluation is to compare influence of windows on the indoor thermal environment. 2.2.2. Daylight Evaluation Figure 2. Historical building of primary school, locality Mimoˇn, CZ [37]. Energies 2020,13, 2489 4 of 17 The school building maintenance has been limited by design obstructions like many other historical premises. The building was renovated in 2014 under an architectural preservation review. The renovation was mainly aimed at the building envelope. Window and facade retrofit was completed. It was not allowed to change the historical style of the facade and for this reason, external walls were thermally insulated from the interior side. The school has spacious side lit classrooms. One of them, located on the second floor, was selected for the evaluation. Firstly, the classroom thermal assessment was performed for the current state and compared with renovation scenarios. Secondly, the classroom daylight evaluation was carried out. Daylight illuminance and luminance measurements were taken and completed with a daylight simulation study. 2.2.1. Thermal Evaluation The thermal study was focused on the building facade and its influence on indoor climate. The external wall thermal transmittance and condensation risks were studied. The evaluation was carried out for three variations: •current state: wall with 8 cm of thermal insulation on the interior side; •renovation scenario I: wall with 15 cm of thermal insulation on the interior side; •renovation scenario II: wall with 15 cm of thermal insulation on the exterior surface. The software Teplo [ 38 ] was used for the evaluation. The software is intended for fundamental analyses of building constructions like thermal resistance R (m 2 KW −1 ) and U-value (W m −2 K −1 ) calculations, temperature profiles, interstitial condensation analysis and specification of annual balance of condensed and evaporated amount within building constructions in accordance with standard methodology of ISO 6946 and ISO 13788 [39,40] and other standard requirements [41]. Boundary conditions for the thermal evaluation according to [41] are following: •design outdoor temperature −13.0 ◦C, locality—GPS: 50.655668 N, 14.724856 E; •design indoor air temperature 21.0 ◦C (classroom); •design relative humidity of outdoor air 84.0%; •design relative humidity of indoor air 55%. Two-dimensional temperature distribution of the wall details at window jambs in the current state and design variations with internal and external thermal insulation were simulated using the software Area [ 38 ]. The software is dedicated to complex thermal analyses of building construction details for specification of potential thermal bridges in two dimensional stationary heat transfer and water vapour diffusion simulations in accordance with standard methodology of ISO 10211 [42]. A study of the influence of the renovated facade on indoor thermal stability was performed [ 41 , 43 ]. The thermal stability was selected as an indicator of indoor thermal climate. Thermal stability of the classroom was simulated for winter and summer season conditions using the software Stabilita [ 38 ]. The internal temperature drop during a heating lapse in winter and summer indoor temperature rise were calculated. The goal of the evaluation is to compare influence of windows on the indoor thermal environment. 2.2.2. Daylight Evaluation Natural light influences indoor climate and wellbeing. Especially in educational buildings, visual comfort is crucial. Daylight positively affects students’ alertness and health [ 44 ]. Reviews of the importance of daylighting in schools [ 45 , 46 ] show relationships between the occupants’ responses and natural lighting. The positive impact of daylight in classrooms was proven [ 47 , 48 ]. Daylighting in educational buildings has been a topical task of professional projects [ 49 – 51 ]. Extensive surveys of US schools in different climate conditions were performed [ 52 ]. The EU programme [ 53 ] promotes daylight integration for high performance indoor environment in schools. These activities are in agreement Energies 2020,13, 2489 5 of 17 with the main principles of sustainable development [ 54 , 55 ] and architectural design strategies [ 56 – 59 ] as well as standard recommendations [60–62]. Daylight Measurements Daylight illuminance was monitored in the classroom. The intention was to study the classroom visual environment under the most characteristic daylight conditions throughout the year. The measurement time was limited due to the accessibility schedule into the classroom. Measurements were performed without pupils’ occupancy over weekends in March 2017. The classroom is a spacious place of floor area 11.9 × 7.63 m and clearance height 4 m. It has three big windows, of width about 2 m and height 2.5 m (Figures 3and 4). The daylight measurements were taken for a set of sixty points on a working plane. The plane is located 0.85 m over the classroom floor level (Figure 4). The set of points is positioned in distance of 1 m around the room perimeter. Spacing of the points is 1.10 m by 1.126 m. Simultaneously with the interior measurements, the external illuminance was monitored on unshaded horizontal plane outdoors. Sky luminance was also studied. Energies 2020, 13, x FOR PEER REVIEW 5 of 18 Natural light influences indoor climate and wellbeing. Especially in educational buildings, visual comfort is crucial. Daylight positively affects students’ alertness and health [44]. Reviews of the importance of daylighting in schools [45,46] show relationships between the occupants’ responses and natural lighting. The positive impact of daylight in classrooms was proven [47,48]. Daylighting in educational buildings has been a topical task of professional projects [49-51]. Extensive surveys of US schools in different climate conditions were performed [52]. The EU programme [53] promotes daylight integration for high performance indoor environment in schools. These activities are in agreement with the main principles of sustainable development [54,55] and architectural design strategies [56–59] as well as standard recommendations [60-62]. Daylight Measurements Daylight illuminance was monitored in the classroom. The intention was to study the classroom visual environment under the most characteristic daylight conditions throughout the year. The measurement time was limited due to the accessibility schedule into the classroom. Measurements were performed without pupils’ occupancy over weekends in March 2017. The classroom is a spacious place of floor area 11.9 × 7.63 m and clearance height 4 m. It has three big windows, of width about 2 m and height 2.5 m (Figures 3 and 4). The daylight measurements were taken for a set of sixty points on a working plane. The plane is located 0.85 m over the classroom floor level (Figure 4). The set of points is positioned in distance of 1 m around the room perimeter. Spacing of the points is 1.10 m by 1.126 m. Simultaneously with the interior measurements, the external illuminance was monitored on unshaded horizontal plane outdoors. Sky luminance was also studied. The daylight illuminance was measured using two calibrated illuminance meters Testo 545 (calibration 2017). One illuminance meter was taken for interior measurements and the second device measured external horizontal illuminance. Laser rangefinder Bosch GLM 50 C Professional was used to set points on the working plane. Tripods were also used to stabilize the illuminance meter at the required height. The external illuminance sensor was positioned on the roof. The measuring instruments were synchronized. Outdoor and indoor illuminance values were measured at the same time. The illuminance data processing was carried out in MS Excel and Statistica software [63]. Figure 3. View into the classroom [37]. Figure 3. View into the classroom [37]. Energies 2020, 13, x FOR PEER REVIEW 6 of 18 Figure 4. Plan of the classroom with points 1 to 60 on the working plane (0.85 m over the floor). Furthermore, monitoring of the surface luminance was taken in the classroom visual field. Luminance Meter LS-100 Konica Minolta is used for measurements. Daylight Simulations The classroom visual environment was also studied on the basis of daylight simulations. The current state daylighting is compared with designed variations. The design state is represented by renovation scenario II with two variations of window glazing (double or triple glass units). Daylight simulations were run in software Daylight Visualizer [64] for the following parameters: • light reflectance ρ [-] of the classroom surfaces in current state (resp. designed state): floor finishing 0.35 (resp. 0.5), wall surfaces 0.7 (resp. 0.9), ceiling 0.84 (resp. 0.9). • window glass light transmittance τ [-]: double glazed units 0.81, triple glazed units 0.73. • the south-east orientation of the classroom windows (Figure 5). Daylight simulations were run for an annual balance of internal horizontal illuminance under two sky models [65]: • CIE clear sky model to simulate sunlight conditions. • CIE overcast sky model for consideration of the most unfavourable daylight situation. The balance was simulated for the 21st day of every month and daytime 12:00. Finally, the classroom daylighting was also simulated for designed variations and compared with standard requirements according to EN 17037 [61] as follows: • Daylight illuminance simulated for the clear sky model on 21st June, at 12:00 was compared with target illuminance 300 lux. • Daylight factor simulation for the overcast sky model was compared with target daylight factor DT = 2%. Figure 4. Plan of the classroom with points 1 to 60 on the working plane (0.85 m over the floor). Energies 2020,13, 2489 6 of 17 The daylight illuminance was measured using two calibrated illuminance meters Testo 545 (calibration 2017). One illuminance meter was taken for interior measurements and the second device measured external horizontal illuminance. Laser rangefinder Bosch GLM 50 C Professional was used to set points on the working plane. Tripods were also used to stabilize the illuminance meter at the required height. The external illuminance sensor was positioned on the roof. The measuring instruments were synchronized. Outdoor and indoor illuminance values were measured at the same time. The illuminance data processing was carried out in MS Excel and Statistica software [63]. Furthermore, monitoring of the surface luminance was taken in the classroom visual field. Luminance Meter LS-100 Konica Minolta is used for measurements. Daylight Simulations The classroom visual environment was also studied on the basis of daylight simulations. The current state daylighting is compared with designed variations. The design state is represented by renovation scenario II with two variations of window glazing (double or triple glass units). Daylight simulations were run in software Daylight Visualizer [64] for the following parameters: • light reflectance ρ [-] of the classroom surfaces in current state (resp. designed state): floor finishing 0.35 (resp. 0.5), wall surfaces 0.7 (resp. 0.9), ceiling 0.84 (resp. 0.9). •window glass light transmittance τ[-]: double glazed units 0.81, triple glazed units 0.73. •the south-east orientation of the classroom windows (Figure 5). Daylight simulations were run for an annual balance of internal horizontal illuminance under two sky models [65]: •CIE clear sky model to simulate sunlight conditions. •CIE overcast sky model for consideration of the most unfavourable daylight situation. The balance was simulated for the 21st day of every month and daytime 12:00. Finally, the classroom daylighting was also simulated for designed variations and compared with standard requirements according to EN 17037 [61] as follows: • Daylight illuminance simulated for the clear sky model on 21st June, at 12:00 was compared with target illuminance 300 lux. • Daylight factor simulation for the overcast sky model was compared with target daylight factor DT=2%. Energies 2020, 13, x FOR PEER REVIEW 7 of 18 (a) (b) Figure 5. Orientation of windows in the daylight model. (a) Photograph of a part of the school building facade (the classroom windows are on the 2nd floor). (b) Geometric model of the classroom (Daylight Visualizer). 3. Results The above mentioned energy auditing evaluation achieved notable results for the analysis of the school buildings efficiency. Outputs of indoor thermal and daylight evaluations in the selected representative of school classrooms show potential problems in the current state and give an overview about some renovation scenarios. 3.1. Results of the Energy Audits Analysis The analysis of selected school buildings energy audits gives an overview about their envelopes and their influence on heat losses. Total heat transmission and ventilation losses of buildings vary from 61.1 kW to 424.5 kW. Total annual energy consumption in the schools is between 265 and 3305 GJ per year. Percentage of heat transmission losses of their building envelopes are following: • 23.6% to 57.0% of external walls (U = 0.57 to 1.83 W m−2 K−1). • 18.3% to 36.0% of roofs (U = 0.36 to 1.50 W m−2 K−1). • 17.4% to 55.3% of windows (U = 2.30 to 3.50 W m−2 K−1), external doors (U = 3.50 to 6.50 W m−2 K−1). The annual consumption of energy in dependence of the building volume is between 23.7 and 64.7 kWh.m−3 per year and consumption of energy for heating and domestic hot water vary from 19.8 to 61.7 kWh.m−3 per year. The heating energy consumption is quite high in the school buildings compared to demands for low energy buildings (less than 50 kWh/m2 per year) and passive houses (less than 15 kWh/m2 per year) [5] (Figure 6). Figure 6. Comparison of heating energy consumption in studied school buildings 1 to 18. 3.2. Results of the Thermal Evaluation Figure 5. Orientation of windows in the daylight model. ( a ) Photograph of a part of the school building facade (the classroom windows are on the 2nd floor). ( b ) Geometric model of the classroom (Daylight Visualizer). Energies 2020,13, 2489 7 of 17 3. Results The above mentioned energy auditing evaluation achieved notable results for the analysis of the school buildings efficiency. Outputs of indoor thermal and daylight evaluations in the selected representative of school classrooms show potential problems in the current state and give an overview about some renovation scenarios. 3.1. Results of the Energy Audits Analysis The analysis of selected school buildings energy audits gives an overview about their envelopes and their influence on heat losses. Total heat transmission and ventilation losses of buildings vary from 61.1 kW to 424.5 kW. Total annual energy consumption in the schools is between 265 and 3305 GJ per year. Percentage of heat transmission losses of their building envelopes are following: •23.6% to 57.0% of external walls (U =0.57 to 1.83 W m−2K−1). •18.3% to 36.0% of roofs (U =0.36 to 1.50 W m−2K−1). • 17.4% to 55.3% of windows (U =2.30 to 3.50 W m −2 K −1 ), external doors (U =3.50 to 6.50 W m −2 K −1 ). The annual consumption of energy in dependence of the building volume is between 23.7 and 64.7 kWh.m −3 per year and consumption of energy for heating and domestic hot water vary from 19.8 to 61.7 kWh.m −3 per year. The heating energy consumption is quite high in the school buildings compared to demands for low energy buildings (less than 50 kWh/m 2 per year) and passive houses (less than 15 kWh/m2per year) [5] (Figure 6). Energies 2020, 13, x FOR PEER REVIEW 7 of 18 (a) (b) Figure 5. Orientation of windows in the daylight model. (a) Photograph of a part of the school building facade (the classroom windows are on the 2nd floor). (b) Geometric model of the classroom (Daylight Visualizer). 3. Results The above mentioned energy auditing evaluation achieved notable results for the analysis of the school buildings efficiency. Outputs of indoor thermal and daylight evaluations in the selected representative of school classrooms show potential problems in the current state and give an overview about some renovation scenarios. 3.1. Results of the Energy Audits Analysis The analysis of selected school buildings energy audits gives an overview about their envelopes and their influence on heat losses. Total heat transmission and ventilation losses of buildings vary from 61.1 kW to 424.5 kW. Total annual energy consumption in the schools is between 265 and 3305 GJ per year. Percentage of heat transmission losses of their building envelopes are following: • 23.6% to 57.0% of external walls (U = 0.57 to 1.83 W m−2 K−1). • 18.3% to 36.0% of roofs (U = 0.36 to 1.50 W m−2 K−1). • 17.4% to 55.3% of windows (U = 2.30 to 3.50 W m−2 K−1), external doors (U = 3.50 to 6.50 W m−2 K−1). The annual consumption of energy in dependence of the building volume is between 23.7 and 64.7 kWh.m−3 per year and consumption of energy for heating and domestic hot water vary from 19.8 to 61.7 kWh.m−3 per year. The heating energy consumption is quite high in the school buildings compared to demands for low energy buildings (less than 50 kWh/m2 per year) and passive houses (less than 15 kWh/m2 per year) [5] (Figure 6). Figure 6. Comparison of heating energy consumption in studied school buildings 1 to 18. 3.2. Results of the Thermal Evaluation Figure 6. Comparison of heating energy consumption in studied school buildings 1 to 18. 3.2. Results of the Thermal Evaluation Results of the external wall hygro-thermal evaluation are presented in Figure 7. The current wall (U =0.43 W m −2 K −1 ) and renovation scenarios (U =0.29 W m −2 K −1 ) with internal and external thermal insulation were studied. The figure shows schemes of vapour pressure distribution within the wall and specification of potential condensation regions. An annual balance of condensed/evaporated amount inside of the wall is summarized in graphs. It is clear that the interstitial condensation is fully eliminated in the wall with external thermal insulation (renovation scenario II). Energies 2020,13, 2489 8 of 17 Energies 2020, 13, x FOR PEER REVIEW 8 of 18 Results of the external wall hygro-thermal evaluation are presented in Figure 7. The current wall (U = 0.43 W m−2 K−1) and renovation scenarios (U = 0.29 W m−2 K−1) with internal and external thermal insulation were studied. The figure shows schemes of vapour pressure distribution within the wall and specification of potential condensation regions. An annual balance of condensed/evaporated amount inside of the wall is summarized in graphs. It is clear that the interstitial condensation is fully eliminated in the wall with external thermal insulation (renovation scenario II). Vapour pressure distribution (month 11) Annual balance, condensation/evaporation Current state Renovation scenario I Renovation scenario II No condensation occurs in the construction during the model year of the annual balance of condensation/evaporation rate in accordance with ISO 13,788 [40]. Figure 7. Vapour pressure distribution within the external wall and annual balance of condensation/evaporation rate according to ISO 13788 [40]. Simulation outputs of two-dimensional temperature distribution of the window jamb details in the current state and in the two renovation scenarios are shown in Figure 8. It is obvious that the variation of the wall with external thermal insulation represents better temperature distribution and more convenient design solution. Energies 2020,13, 2489 9 of 17 Energies 2020, 13, x FOR PEER REVIEW 9 of 18 Figure 7. Vapour pressure distribution within the external wall and annual balance of condensation/evaporation rate according to ISO 13788 [40]. Simulation outputs of two-dimensional temperature distribution of the window jamb details in the current state and in the two renovation scenarios are shown in Figure 8. It is obvious that the variation of the wall with external thermal insulation represents better temperature distribution and more convenient design solution. Figure 8. Temperature distribution of the external wall detail at the window jamb. Thermal stability of the classroom was evaluated for winter and summer season conditions. The indoor temperature drop during a 24 h heating lapse in winter does not vary significantly when comparing the existing state and two renovation scenarios (Figure 9). It is because of the relatively small facade area compared to the big volume of the classroom. Three large windows of southeast orientation represent massive solar gains and indoor temperature rise in summer seasons (Table 2). It could bring about overheating problems during intensive solar shining periods. Solar gains can affect indoor visual discomfort. For this reason, daylighting in the classroom was also evaluated for clear sky conditions. Figure 8. Temperature distribution of the external wall detail at the window jamb. Thermal stability of the classroom was evaluated for winter and summer season conditions. The indoor temperature drop during a 24 h heating lapse in winter does not vary significantly when comparing the existing state and two renovation scenarios (Figure 9). It is because of the relatively small facade area compared to the big volume of the classroom. Three large windows of southeast orientation represent massive solar gains and indoor temperature rise in summer seasons (Table 2). It could bring about overheating problems during intensive solar shining periods. Solar gains can affect indoor visual discomfort. For this reason, daylighting in the classroom was also evaluated for clear sky conditions. Energies 2020, 13, x FOR PEER REVIEW 10 of 18 Figure 9. Results of assessment of the classroom thermal stability in winter. Table 2. Results of assessment of the classroom thermal stability in summer. Current State Renovated Scenario I, II Total solar transmittance of window g = 0.65 Total solar transmittance of window g = 0.53 Solar gains 2141.64 W Solar gains 1746.26 W Heat gain through facade 4857.30 W Heat gain through façade 3961.7 Heat ventilation loss Heat ventilation loss (for ventilation rate 0.5 h −1 ) −32.78 W (for ventilation rate 0.5 h −1 ) −32.78 W Total heat gain 6966.16 W Total heat gain 5675.24 W Max. indoor temperature rise per day 16.5 °C Max. indoor temperature rise per day 14.7 °C 3.3. Daylight Study Resultss The classroom daylighting was analysed for illuminance and luminance measured data and daylight simulation outputs. 3.3.1. Measured Data Analysis Data from illuminance measurements on the horizontal working plane in the classroom (from Figure 4) are summarized in Figures 10 and 11. The daylight level is reduced with the distance from windows. It is obvious that big differences in illuminance are in Row i close to the window line. The illuminance differences are minimized in the room depth. Higher illuminance values in positions of Line A and B at Row i are influenced due to the glossy whiteboard surface located near the big window (Figure 3). It is also obvious from Figure 11, where illuminance is intensified at points 8, 9 and 10 of Row i. Illuminance at points 2, 6 and 10 is increased because of windows positions. Illuminance difference between window/wall positions is reduced in the room depth—Rows iii to vi. Figure 10. Classroom daylight illuminance—dependence on distance from windows. Figure 9. Results of assessment of the classroom thermal stability in winter. Energies 2020,13, 2489 16 of 17 31. Windows—Making It Clear: Energy, Daylight and Thermal Comfort (NF78). National House Building Council (NHBC) Foundation, 2017. Available online: https://www.buildup.eu/en/practices/publications/ windows-making-it-clear-energy-daylight-and-thermal-comfort-nf78-0 (accessed on 29 April 2020). 32. 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