Upgrading Energy Efficiency For School BuildingsIn Greece

Available online at www.sciencedirect.com

ScienceDirect Procedia Environmental Sciences 38 (2017) 248 – 255

International Conference on Sustainable Synergies from Buildings to the Urban Scale, SBE16

Upgrading Energy Efficiency For School Buildings In Greece Dimitris Al. Katsaprakakisa,*, George Zidianakisa a

Wind Energy and Power Plants Synthesis Laboratory, Department of Mechanical Engineering, Technological Educational Institute of Crete, Estavromenos, Heraklion Crete, 71410, Greece

Abstract This article presents the cumulative experience from the design, the study and the application of energy efficiency technologies in school buildings in Greece, implemented within the frame of a funding action by the European Committee and the Greek State. In total 10 school buildings in Crete, Thessaly, Macedonia and Thrace were studied. All of them were approved for funding. Among the proposed actions both passive measures, to reduce heating and cooling loads, and active systems, to approach maximum Renewable Energy Sources penetration, were involved. Building envelope insulation, replacement of inadequate openings and, in one case, a green roof construction as a pilot application, constitute the implemented passive measures. On the other hand, photovoltaic (PV) panels on roofs, solar combi-system with biomass heaters for the most southern locations (Crete) or single biomass heaters for the northern locations, installation of low energy consumption lighting equipment and introduction of hybrid cooling techniques mainly with the installation of ceiling fans, compose the set of the introduced active systems. The calculation of the heating and cooling loads was executed with the use of TRNSYS software, for both the existing situation and after the proposed passive systems introduction. The operation of the solar combi-systems was arithmetically simulated using annual time series of mean hourly values for the heating loads and the available solar radiation. A software application was developed using LabVIEW. Finally, a fundamental economic analysis was executed for each introduced technology separately, as well as for the whole intervention. The examined buildings energy efficiency is expected to be upgraded at least in category B. Currently, all the proposed works have been integrated. A measuring system for the monitoring of the operation of the introduced technologies has been proposed, accompanied by a user friendly application. This monitoring system will also be exploited demonstratively for the students, as a teaching supporting tool. The measuring of the introduced systems normal operation will provide a reliable evaluation for the initial calculations and the anticipated upgrading of the buildings energy efficiency. © 2017 2017The TheAuthors. Authors. Published by Elsevier © Published by Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of SBE16. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. Keywords: school buildings energy efficiency; solar biomass combi-systems; building envelope insulation; photovoltaic panels on roofs; passive solar systems

* Corresponding author. Tel.: +30-2810-379220; fax: +30-2810-319478. E-mail address: [email protected]

1878-0296 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. doi:10.1016/j.proenv.2017.03.067

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255

1. Introduction Most buildings worldwide exhibit remarkably high specific energy consumption per unit of covered area. Old building envelope constructions, lack of relevant national regulations regarding the building’s energy performance or inadequate application of the existing ones, absence of any production technologies of thermal energy or electricity production from Renewable Energy Sources (R.E.S.) and building users with deficient education on the primary energy sources conservation and the rational use of energy constitute common characteristics and attitudes met even in the widely considered developed countries. An ultimate consequence of the above facts is that the building sector contribution to the overall annual energy consumption globally is approximately estimated at 40%. An effort to rationalize the use of energy in buildings in Europe has begun with the issuance of the European Directives 2002/91/EC and 2010/31/EU on the energy performance of buildings. These directives: x establish a clear cluster of potential passive and active measures, employing a variety of on a case-by-case applicable technologies, towards the energy saving and production from R.E.S. in buildings x introduce the buildings energy efficiency ranking, in terms of the energy consumed, establishing simultaneously clear targets regarding the buildings energy performance. The application of these directives has gradually passed from the central European stage to all the members of the European Union (EU) with the introduction of corresponding national laws. Additionally, focusing on the support of the application of the above directives and, most importantly, on the “energy cultivation” of the European residents, a large number of funding actions have been announced during the last fifteen years, both in a central EU level and in decentralized national funding calls. These calls are targeted on the application of energy saving measures and production from R.E.S. technologies in buildings, favouring, usually, the energy upgrading of buildings open in public and, generally, of buildings accessible to a large number of users or visitors, such as museums, civil buildings, universities and schools. In this way, the demonstration of the introduced energy efficient measures is maximized, contributing, simultaneously, to the cultivation of the public energy conservation attitude. This paper presents the results of the implementation of energy upgrading passive and active measures in ten school buildings in Greece. All the implemented tasks were co-funded by the European Committee and the Greek State, under a specific relevant call posted and executed in the second half of 2011 by the Greek Ministry of Energy and Environment. The basic structure of the call was the introduction of energy efficient measures in school buildings, aiming: x obviously at the energy upgrading of the school buildings, practically the direct and apparent benefit of the implemented measures x at the reduction of the operating cost of the school buildings, relieving, thus, the annual economic balances of the local Municipalities in charge for the maintenance and the economic support of the school buildings operation x at the introduction of a strong and highly effective demonstration tool for the promotion of the energy conservation concept on the young and easily cultivated school ages, investing, thus, in a future generation with deep “energy culture” foundations. Practically, by approaching targets in three different fundamental pylons of a contemporary community, namely the energy conservation, the public economy and the education, the potential added value of the proposed energy upgrading tasks can be enormous. Towards this end, an optimum mixture of interventions for each school building should be selected, configured by the size and the age of the building, as well as the available climate conditions, while all the proposed active systems should be effectively dimensioned. Finally, the secure and trouble-free normal operation of all the introduced systems should be ensured, minimizing the required time consumed from the Municipalities technical staff for their maintenance. A detailed presentation of the work accomplished towards the energy upgrading of the above mentioned ten school buildings, including the initial selection of the buildings’ locations, the parameters adopted for the studies implementation, the passive and active measures introduced, the operating algorithms of the proposed active measures and, finally, the achieved results, is presented in the next sections.

249

250

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255

2. Design parameters 2.1. Selection of school buildings locations A number of school buildings located evenly in all the Greek insular and mainland territory were initially selected and corresponding collaboration proposals were submitted to the Municipalities in charge. The finally selected ten schools were the ones approved by the responsible Municipal Councils. Two of them are located in the island of Crete, in the small towns of Arkalochori and Charakas, two in the city of Larissa, in Thessaly region, one in the town of Naoussa, in Western Macedonia, three of them in Thessaloniki, one in the town of Serres, in Eastern Macedonia and one in the town of Konotini, in Thrace (Fig. 1).

Fig. 1. locations of the upgraded school buildings.

Fig. 2. available global irradiation in Greece.

The geographical latitudes of the schools locations vary between 35 οN to 42οN. This geographical dispersion implies a considerable variation of the available solar irradiation, depicted in Fig. 2 1, and a relevant change on the climate conditions. For example, the minimum monthly averaged temperature in Naoussa is measured 2,3οC, while in Crete it is measured 12.2οC, in both places in January. Additionally, Naoussa also exhibits the minimum total sunshine hours during the annual school season, namely from September to May, measured at 1,507.2, while the maximum value is measured at 1,721.3 hours in Crete. As it will be shown below, this alteration in the climate conditions and the available solar irradiation affects significantly both the energy consumption for the buildings conditioning and the optimum mixture of the proposed energy upgrading interventions. 2.2. Energy consumption and performance before the interventions In the examined school buildings two different forms of energy were consumed before the interventions: diesel oil for space heating and electricity for the remaining loads (lighting, motors, devices etc). Diesel oil still remains in Greece a traditional source of energy consumed for space heating. Only in the early 2010s, with the international Brent prices above 100$ per barrel and a special state tax of almost 30% introduced in all the imported liquid fossil fuels, there was a massive stream in Greece towards alternative heating technologies, substituting diesel oil with electricity or biomass (biomass heaters, heat pumps, heating fireplaces, electric convectors etc). Some of the examined school buildings were not equipped with any type of passive measures, mainly because they were constructed some decades ago (e.g. in the ‘50s or ‘60s) when no Buildings Insulation Regulation or Energy Performance Directive had been introduced in the relevant national legislation. On the other hand, even in cases of new buildings, inadequate construction or the use of low quality products – techniques commonly used by the Contractors in Greece to raise their profit from a State project – has already led to serious operation problems of the buildings envelope, such as the penetration of moisture in the walls and roofs mass, increase of natural ventilation due to bad splicing in the openings frames etc.

251

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255

Additionally, in the examined buildings space heating was produced with conventional hydraulic networks and central heating oil burners, usually old, with low efficiency (at the range of 75%). At the same time, lighting was provided with inefficient incandescent light bulbs or fluorescent lamps for the interior spaces and energy intensive floodlights for the exterior yards (e.g. HQI, sodium-vapor lamps etc). Generally, there were not met any energy efficient equipment or energy saving technologies for the reduction of electricity consumption in any of the buildings under consideration. The common resultant of the above facts was, apparently, the low energy performance of the examined schools. This was revealed by the accomplished energy inspections and the issuance of the relevant energy performance certificates. The results, regarding the operating situation before the implementation of the proposed interventions, are presented in Table 1, according to the energy inspections. Table 1. Energy performance of the examined school buildings in the pre-interventions period. School

Building envelope features*

Specific primary energy consumption (kWh/m2)

Specific primary energy consumption of reference building (kWh/m2)

Energy performance rank

Technical Highschool of Arkalochori, Crete

a

127.8

122.6

C

General Highschool of Charakas, Crete

c

130.7

108.9

C

2nd General Highschool of Larissa

b

221.3

113.9

E

19 Elementary School of Larissa

d

296.3

109.4

F

2nd General Highschool of Naoussa

a

91.3

91.3

C

3rd Elementary School of Peraia, Thessaloniki

a

177.2

104.2

D

2 General Highschool of Michaniona, Thessaloniki

e

443.5

104.2

G

1st Elementary School of Polykastro, Thessaloniki

e

628.5

116.5

G

20th Elementary School of Serres

b

250.7

124.3

E

Technical Highschool of Komotini

f

174.7

128.6

C

th

nd

* a: Insulated envelope, openings with double glazing and metallic frame with no insulation b: Insulated envelope, half openings with double glazing, half with single glazing and metallic frame with no insulation c: No insulation in the building’s envelope, half openings with double glazing, half with single glazing and metallic frame with no insulation d: Insulated, openings with double glazing and metallic frame with no insulation e: No insulation in the building’s envelope, openings with single glazing and metallic frame with no insulation f: Partially insulated, openings with double glazing and metallic frame with no insulation of old technology

3. Proposed measures - dimensioning 3.1. Proposed measures Given the existing conditions of the examined school buildings, a cluster of passive measures, for the reduction of the buildings thermal and cooling loads, and of active systems, for the maximization of the electricity and thermal energy production from R.E.S., were proposed. Specifically, the following passive measures were proposed: x the application of external insulation in the inadequately insulated building envelopes (walls and roofs) x the installation of new windows and doors with double glazing and metallic insulated frame, in cases of existing openings with single glazing x the construction of shading overhangs above south orientation openings, in cases there was no shading protection against direct solar radiation x only in case of the Technical School of Komotini, due the large covered area of the building (around 6,000 m2) and the high amount of students, the installation of a green roof in a specific part of the building’s roof, particularly for demonstration reasons. Furthermore, once the efficient operation of the buildings envelope is ensured with the introduction of adequate passive measures, a number of active systems were proposed, for the reduction of the consumed energy sources and the maximization of the R.E.S. share in the buildings energy balance. The proposed active systems were selected

252

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255

taking into account that they should guarantee, apart from the obviously expected energy efficiency, a reasonable economic feasibility. Aiming to satisfy both these parameters, the following active systems were proposed: x small photovoltaic (PV) stations on the roofs of all the buildings under consideration, aiming at the compensation of the consumed electricity x biomass heaters for space heating, burning locally produced biomass pellets for the school buildings in the mainland Greece (except from Crete) x combi-solar systems for space heating, consisting of selective solar collectors and biomass heaters burning locally produced olive kernel, for the two schools in Crete, focusing to exploit the high available amounts of solar radiation in Southern Greece, even during the winter period x the low cooling loads, due to the restricted operation of the schools during summer, will be faced with the socalled “hybrid-cooling”, namely with the installation of roof fans in the schools classrooms and offices x replacement of all the existing inefficient lighting equipment with LED lamps and floodlights or with fluorescent lamps T5 (instead of the previously installed T8) with electronic transformers and soft starters x installation of central heating compensation systems. The calculation of the electricity production from a PV station was based on the fundamental relevant theory 2. A brief presentation of the combi-solar systems, as a more sophisticated one, is provided in the next sub-section. 3.2. Combi-solar systems Combi-solar systems consist of solar collectors, usually collective or, in colder climates, evacuated tube collectors, as the base thermal energy production unit, thermal storage tanks, usually hot water insulated tanks, and a conventional heater, as the back-up thermal production unit. Combi-solar systems can be considered as the equivalent “hybrid power plants” for thermal energy production, with ultimate scope the maximization of the solar collectors’ contribution for a specific thermal load cover. To this end, the thermal storage is introduced, aiming to store any thermal power production surplus from the solar collectors and provide it to the consumption in cases of thermal production lower than the thermal demand. The system is integrated with a back-up production unit, namely a conventional heater, in order to support inadequate thermal power availability from both the solar collectors and the storage tanks. A typical layout of a combi-solar system is presented in Fig. 3.

Fig. 3. general layout of a combi-solar system.

The successful introduction of a combi-solar system to fulfil a specific thermal demand depends on the following fundamental prerequisites: x the availability of abundant solar radiation; the examined schools in Crete can be considered as ideal cases for the introduction of solar-combi systems for space heating, given the high available solar radiation even during winter

253

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255

x the optimum operating algorithm of the combi-solar system, in order to approach the maximum possible exploitation of the available solar radiation, satisfying at the same time the thermal energy demand x the correct dimensioning procedure, performed with an adequate and accurate operation arithmetic simulation. Fig. 3 presents the layout of a combi-solar system with 15,000 l of water volume total storage capacity, divided in three water tanks of 5,000 l each. In this case the operating algorithm should be developed so as to maintain a storage tank with the highest possible storage temperature. This storage tank will be the “load tank”, since the central heating terminals will be supplied exclusively from this tank. The conventional heater will be also exclusively connected to this load tank. At the same time, the storage temperature of the other two storage tanks should be gradually kept lower from tank to tank, in order to ensure that there will always be a storage tank with the minimum possible storage temperature, to maximize solar energy exploitation even in the early morning hours, when the working medium’s temperature in the primary solar collectors loop is still relatively low. The automatic operation of the combi-solar systems under the above mentioned requirements are satisfied with a central control unit, four circulating pumps (C1 – C4), three motorized valves (V1 – V3), seven temperature sensors (T0, T1, T1΄, …, T3΄) installed as depicted in Fig. 3 and the overall system’s layout presented in the same figure. The optimized operating algorithm is summarized in the following lines: x If T0>T1 then: C1=ΟΝ, V1=open, V2=close, V3=close x If T0T2 then: C1=ΟΝ, V1=close, V2=open, V3=close x If T0T3 then: C1=OFF, V1=close, V2=close, V3=open x If T2΄>T1 then: C2=OΝ x If T3΄>T2 then: C3=OΝ x If T1΄<85oC then: C4=OΝ. Further explanation on the above optimization algorithm is not possible in this article due to space limitations. The dimensioning procedure was based on the arithmetic simulation of the annual operation of the combi-solar system, based on the fundamental theory of solar collectors 3, and an iterative optimization procedure. A relevant software application was developed using NI LabVIEW platform. The full presentation of this methodology requires a whole article by itself. Hopefully, there will be a new manuscript submission in the approximate future. 4. Results 4.1. Heating and cooling loads reduction due to passive measures introduction The introduction of passive measures aims to the reduction of the buildings heating and cooling loads. In Table 2 the heating and cooling loads reduction is presented for four characteristic school buildings, one in Crete (south location), one in Larissa (middle location), one in Thessaloniki (urban location) and one in Komotini (north location), all of them initially inadequately insulated. Table 2. Indicative results of heating and cooling loads calculations before and after the proposed passive measures. School

Charakas, Crete 2

Covered area (m ) Month

Larissa, 19th elementary school

1,196.24 2,482.56 Heating and Cooling load (MWh) Before After Before After

Paionia, Thessaloniki

Komotini

721.68

9,034.49

Before

After

Before

After

72.48

53.89

471.50

388.73

4.44

3.50

211.60

175.15

100.43

74.67

52.19

43.03

4.85

23.42

19.39

Total annual heating load

64.02

45.91

156.54

133.43

Total annual cooling load

18.07

15.71

59.92

45.25

Total annual specific heating load (kWh/m2)

53.52

38.38

63.06

53.75

Total annual specific cooling load (kWh/m2)

15.11

13.13

24.14

18.23

6.15

Heating load annual percentage reduction (%)

28.29

14.76

25.65

17.55

Cooling load annual percentage reduction (%)

13.06

24.48

21.17

17.23

254

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255

The heating and cooling load calculations were thoroughly executed with TRNSYS. In Table 2 it is seen that annual reduction percentages in the range of 13 – 30% are achieved either in heating or cooling loads with the proposed passive measures. Additionally, the effect of the school’s geographical position on the interior space conditioning loads is revealed by comparing the schools in Charakas, Crete (φ = 35ο approximately) and Paionia, Thessaloniki, Central Macedonia (φ = 41ο approximately), namely two buildings with initially no type of insulation. The specific heating load in Paionia is calculated almost twice higher than in Crete. 4.2. Energy performance upgrading In Table 3 characteristic features of the school buildings energy performance upgrading are presented. All the examined buildings are upgraded to the energy performance rank B or higher. Diesel oil consumption is totally eliminated is all cases except from one, that the school Management preferred to maintain the use of diesel oil, mainly because they were not convinced of the adequate and convenient use of a biomass heater. In that case, the diesel oil consumption was reduced with the installation of a new efficient oil burner and the central heating compensation system. This attitude reveals the necessity for the delivery of appropriately designed information campaigns in favour of the use of alternative, locally produced and renewable energy sources for heating, instead of imported fossil fuels. Table 3. Cumulative results of the expected upgrading energy performance of the school buildings. Reduction Reduction PV New primary percentage of percentage of CO2 emission installed energy electricity diesel oil percentage power consumption consumption consumption reduction (%) 2 (kWp) (kWh/m ) (%) (%)

Expected new energy performance rank

Payback period (years)

Arkalochori, Crete

26.31

2.5

100.00

71.43

40.43

B+

18.23

Charakas, Crete

21.14

1.0

100.00

33.62

65.21

A+

21.63

Highschool of Larissa, Thessaly

21.37

8.0

100.00

75.10

54.71

B+

13.08

Elementary School of Larissa, Thessaly

40.48

2.6

100.00

77.34

66.99

B+

16.63

Naoussa, W. Macedonia

23.36

2.5

100.00

77.08

68.72

B

8.82

Peraia, Thessaloniki

12.64

5.0

100.00

88.55

49.52

B

12.27

Michaniona, Thessaloniki

18.06

1.0

20.00

86.44

30.74

B

15.71

Polykastro, Thessaloniki

77.65

5.0

100.00

92.07

86.22

B

22.71

8.23

2.1

100.00

74.68

55.43

B+

17.52

11.72

10.0

100.00

99.41

39.94

B

10.50

Serres, E. Macedonia Komotini, Thrace

The electricity consumption is reduced from 10 to 40% approximately, due to the installation of energy efficient lighting equipment and the PV stations (the produced electricity from the PV station is compensated with the consumed). The nominal power of the PV stations installed varies between 1.0 to 10.0 kWp. The produced electricity from the PV stations will be sold to the local grid under a fixed feed-in-tariff regime. Since all the proposed tasks are funded by the EU, the introduced technologies are not allowed to generate direct incomes. To this end, the nominal power of the installed PV stations was configured aiming to maintain a neutral economic balance between the PV stations equities and the cost of the consumed electricity. Further electricity reduction could be achieved with the installation of additional PV station power, if there was not the above limitation In the cases of the Cretan schools, diesel oil is substituted with combi-solar systems with biomass heaters. The results from the dimensioning optimisation algorithm are presented in Table 4, given the annual heating loads after the passive systems installation. It is seen, that solar collectors final thermal energy percentage contributions of 45% and 58% over the total annual thermal load are achieved.

255

Dimitris Al. Katsaprakakis and George Zidianakis / Procedia Environmental Sciences 38 (2017) 248 – 255 Table 4. Solar combi-systems dimensioning and analysis of the thermal annual energy production. School Annual thermal load (MWh)

Solar panels total installed area (m2)

Biomass heater Thermal nominal power storage (kWth) capacity (l)

Annual final thermal energy production

(MWh)

(%)

(MWh)

(%)

Solar collectors

Biomass heater

Arkalochori, Crete

48.27

106.20

266.80

2 x 5,000

21.74

45.04

26.53

54.96

Charakas, Crete

45.91

129.80

150.80

3 x 5,000

26.86

58.51

19.05

41.49

In Table 3 there is an indicative payback period of the examined projects. Although the achieved payback periods are not so attractive, the strong demonstrative concept of the energy upgrading works should be kept in mind, as well as the significant reduction of the annual operating cost due to energy needs. The latter, combined with the fact that the proposed projects were 100% co-funded by EU and national funds, ensures their economic feasibility. It is also mentioned, for integration reasons, that the approved budgets range from 68,000€ for the school in Naoussa to 616,000€ for the school in Komotini, while the annual operating cost reduction achieved with the energy upgrading tasks range from 5,500€ for the school in Arkalochori, Crete, to 58,600€ for the school in Komotini. A measuring system for the monitoring of the operation of the introduced technologies has been proposed, accompanied by a user friendly application. The monitoring system will collect measurements from fundamental magnitudes (solar radiation, ambient and interior space temperatures, thermal power production from solar collectors and, biomass heaters, electricity consumed and produced by the PV etc), display them in graphs and store for statistical processing. The measuring of the introduced systems normal operation will provide a reliable evaluation for the initial calculations and the anticipated upgrading of the buildings energy performance. This monitoring system will also be exploited demonstratively for the students, as a teaching supporting tool. 5. Conclusions This article presents the integrated proposals for the installation of passive and active energy systems in ten school buildings in Greece, aiming to their energy performance upgrading. Significant reduction of primary energy consumption, CO2 emissions and operating cost of the school buildings are achieved. All the school buildings are upgraded to the energy performance rank B or higher. The presented approach exhibits a strong demonstrative attitude, which is supported with the installation of a monitoring system, capable to be also employed as a teaching tool, contributing, thus, to the cultivation of an energy conservation attitude for the new generation, maybe the most significant achievement of the implemented projects presented in this article. Acknowledgements Sincerely acknowledgments are accredited to the Municipal Councils of Minoan Pediodos, Acharnon – Asterousion, Larissa, Naoussa, Perraia, Paionia, Serres and Komotini for the approval of our proposals, the funding of the initial feasibility studies and the funding call applications and our excellent collaboration. References 1. European Commission Photovoltaic Geographical Information System (PVGIS): http://re.jrc.ec.europa.eu/pvgis/cmaps/eu_cmsaf_hor/G_hor_GR.png (last accessed on 23rd of April 2016). 2. Fragkiadakis IE. Photovoltaic systems. 1st ed. Athens: Ziti; 2006. 3. Duffie JA, Beckman WA. Solar engineering of thermal processes. 4th ed. New York: Wiley; 2013.