Solar active school in Laion (Italy)

Transcription

1 Solar active school in Laion (Italy) Alexandra Troi 1, Stefano Avesani 1, Assunta Napolitano 1, Johann Vonmetz 2, Michael Bergmeister 3 1 Eurac Research, Drususallee 1, Bozen, Italien Tel.: , Fax: alexandra.troi@eurac.edu, Internet: 2 Arch.TV TROJER VONMETZ ARCHITEKTEN - ARCHITETTI, Enzenbergweg, TERLAN (BZ) - Italien Tel.: , Fax.: arch.tv@tin.it 3 INGENIEURTEAM BERGMEISTER GmbH, Eisackstr. 1, Vahrn (BZ) - Italien Tel.: , Fax.: info@bergmeister.it Figure 1: The primary school of Lajon-Ried. 1. Abstract The new primary school built for the Novale village, in the community of Lajon (South Tyrol / Italy), achieves ambitious energy and environmental efficiency goals. For this, the project complies with the criteria of a KlimaHaus Gold +. It became operative in July 2006 and it is the first Passivhaus School in Italy. It won the Best CasaClima award in 2006; through the integration of a photovoltaic plant, the school is also the first public building that in the annual balance produces more energy than it consumes. This matches very well the present orientation of the European Parliament foreseeing that all the buildings built from January 2019 shall be energy autonomous and shall produce more energy on site than they consume. The question of what actually is a

2 zero energy building is presently being discussed in IEA Task 40 (International Energy Agency). The Lajon school is a shining example of a design approach considering in a holistic way all the net zero energy issues as the low net energy needs (through an efficient choice of envelope components both with regards materials and architectural matters), as the high technological system efficiency and as on-site energy production using renewable energy sources. The building offers a net usable area of 625 m 2 and hosts 40 students - in four bright classrooms, a workroom and a multipurpose room - as well as teachers room, training room and other service rooms. The compliances with the Passivhaus standards, the mechanical ventilation with heat recovery as well as the integration of renewable sources as PV plant, heat pump coupled with geothermal probes, solar heat collectors and local raw materials are the points of strength that lead to a zero emission building. Also in terms of costs the building scores well: compared to a quality reference scenario of a new school in South Tyrol after 13 years additional costs to build a KlimaHaus Gold + energetically active school are paid back and money is earned. 2. Building and energy system 2.1 Building Novale s first primary school was built in After a first structural extension in 1980, in 2003 the Municipality decided for a refurbishment and an energy retrofitting of the whole building. Arch.TV won the architectural competition in 2004 with the project of an innovative building and plant system. The final project matches the historical and cultural building background and the fusion with the natural landscape with an high technology energy solutions towards energy efficiency and renewable energy implementation. The project is characterized by three main aspects. Firstly, the school lies on a sloped ground and has hence been built on two levels following this morphological aspect (Figure 2 and Figure 3). This layout realizes a strong interaction between the building and the surrounding.

3 Figure 2: Prospect East [2]. Figure 3: Prospect South [2]. Figure 4: Plan of the second floor [2]. Secondly, the new structure is deeply integrated in the landscape from the aesthetical aspect and the sustainability point of view: local materials have been used taking into account environmental sustainability issues and creating a characteristic South Tyrolean appearance. In particular, Laion quartz rock for the basement, oak for doors and windows frames and plastered masonry for the first floor walls have been used. Interior bearing walls and floors are in heavy concrete. Thirdly, the enhancement of the old energy system and the overall building envelope s thermal performance have been developed towards an energy selfsufficient and productive structure as described in the following paragraph.

4 2.2 The building envelope and the energy system The energy concept is first of all based on the reduction of the energy demand toward a so called passive house. The compact building shape with an S/V ratio of 0.53 m -1 minimizes the outer scattering surfaces. Another structural solution maximizing the users comfort and reducing energy costs is given by a high thermal insulation of the external walls. These have been entirely covered with 20 cm of mineral foam panels, except for the roof where 24 cm wood fibre panels have been used. The mean U-value of the opaque surface is around 0.23 W/m 2 K. Large windows let in light to naturally illuminate the interior spaces and venetian blinds protect from glaring sunlight conditions Orientation has though been selected carefully: While the south facing facade is characterised by an extensive glazed surfaces (128 m 2, on a total surface of 150 m 2 ). the glazed surface facing east is only 16 m 2 and windows facing north cover 36 m 2. Also the main staircase is naturally lighted thanks to 24 m 2 of glass on the roof. The triple coated panes filled with Argon and the window frames in oak model Raicotherm 8 cm wide guarantee an overall high thermal performance of the whole glazed façade: the mean U-value of the transparent surface amounts to 0.78 W/m 2 K. A mechanical ventilation system with heat recovery assures high air quality and comfort for the students, whilst the air-air cross flow heat exchanger recovers energy from the exhaust air and delivers it to the incoming fresh air. With a Blower Door test result of 0.49 air changes per hour the air tightness of the building has been well demonstrated. All these technical solutions have led to a high design energy performance of the envelope, thus low building energy demand is achieved. The realization of an selfsufficient building has been obtained installing equipment with high efficiency rate (heat pump) and renewable energy sources (geothermal probes, solar thermal collectors and solar photovoltaic panels). Residual space heating and domestic hot water demands are covered by an electric heat pump nominal power of 1.83 kw electric and 8.3 kw thermal operating with three ground probes (50 m deep) and by the heat produced from 18 m² of flat plate solar

5 thermal collectors in the facade at first floor. Space heating with radiant floor supports the low energy approach allowing for reduced supply temperature. The major part of the south faced pitched roof 140 m 2 has been covered by silicon polycrystalline photovoltaic panels with an electric peak power of 17.7 kwp. The electric energy production allows to cover the electricity demand of the whole building and to feed into the grid a high amount of energy as shown in the next paragraph. 2.3 Expected energy performance and balances Considering the design values of thermal demand, calculations show a space heating demand from November to March with a peak in January of 2620 kwh/month. The domestic hot water demand follows an average of almost 500 kwh/month. There is no heat demand in the months of July and August as the school is closed. The heat production of solar thermal collectors can basically cover the monthly heat demand for DHW. The heat pump production provides the rest of the thermal load of the building. The monthly values are shown in Figure 5. Figure 5: Monthly design values of heat demand and heat production. Heat demand and heat production values have been simulated with PHPP. Design data for the electric energy demand of the heat pump do not consider the solar collectors heat production as if the heat pump s thermal production had to cover the total heat demand (space heating and DHW). Monthly design values for

6 electricity show that the PV plant production does not cover the total electric demand during January, February, November and December. This trends of design values are reported in Figure 6. Figure 6: Monthly design values of electricity demand and electricity production. PV electricity production has been simulated with RETScreen. Nevertheless, further calculations have been done taking into account the solar collectors production as well. In this case, the total monthly heat demand has been decreased by the solar collectors heat production. The resulting monthly trends show that only in December and January the total electricity demand is not fully covered by the PV production. However, the total energy balance (PV production less electricity demand) is largely positive on a yearly basis both without and with considering solar collectors thermal production. In fact, in the first case the annual overall electricity demand is around kwh/a. The PV plant has an estimated yield of kwh/a. This results in a surplus of electrical energy equal to kwh. In the second case the electric surplus is even bigger and it is equal to kwh. Hence, the school does not only cover its needs, but can annually supply a considerable amount of energy to the grid. 3. Practical experience: costs, benefits and real data 3.1 Real energy performance Bergmeister Eng. is periodically monitoring the overall energy performance of building and energy system in terms of electricity consumption: the amount of

7 electrical kwh delivered to the building from the grid and from the PV plant are read and reported. These values give a first global proof of the school s energy behaviour. The recorded electricity consumption of the building amounted to kwh el /a in 2006, kwh el /a in 2007 and kwh el /a in Differences in real consumption have still to be studied. The related design value is with kwh/a, however, considerably higher than the average real consumption of kwh/a. Furthermore, the PV production was kwh/a in 2007 and kwh/a in 2008, compared to a design value of kwh/a. The whole system s real performance is therefore better than predicted for the first two year, since the electricity consumption halved in 2007 and PV production increased for 8% of the design value. In 2008 an higher energy demand has been observed, but the overall yearly energy balance is still largely positive. 3.2 Costs and benefits Cost and benefit analysis based on real investment costs has been done comparing both design and real data with a reference scenario. This latter was a first design draft of the project: a Casaclima A building (25 kwh/m² space heating demand), without PV plant, with pellets boiler (peak power of 20 kw) instead of the heat pump and geothermal probes. The solar thermal collectors production has not been taken into account in none of the scenarios. The assessments compare yearly operation costs and gains due to the energy performance of the building with the difference of investment between actually realized plants and the reference scenario considered. Firstly, annual energy balances have been determined for each case (Table 1Error! Not a valid bookmark self-reference.). Secondly, operation costs and gains have been calculated (Table 2) and matched with the difference of the initial investment (Table 3). Thirdly, costs differences and net cash flows have been compared (Table 4). Table 1: Energy yearly balances for the cases considered. n.p. means data not available. Design data have been simulated with PHPP (heating part) and RETScreen (PV part).. Real data Design value Reference case kwh/year kwh/year kwh/year kwh/year kwh/year Heat demand Space heating demand 6'477 n.p. n.p. n.p

8 Domestic Hot Water 4'658 n.p. n.p. n.p. 4'658 Total heat demand 11'135 n.p. n.p. n.p Electricity demand Users equipment 1'063 n.p. n.p. n.p. 1'063 Heat pump 4'627 n.p. n.p. n.p. / Total electric demand 5'690 4'665 2'030 7'058 1'063 Electricity production PV energy production 16'471 NoProduction 17'859 17'175 / Table 2: Operation costs and gains for the case considered. Design value Real data 2006 Reference case /year /year /year Costs Total costs for heating 1 / / Total costs for electricity Gains Total euro gains for electricity sold 3 9'183 9'971.8 / Table 3: Costs differences of the technologies used in the real case and in the reference scenario (referring to standard specific energy and cost values). Delta costs (heat pump&geothermal system pellets plant) for heating system 954 PV costs 101'507 Mechanical ventilation overall costs 45'277 Total costs difference 147'738 Table 4: Results of the benefits-costs analysis. ref. case & design data ref. case & average real data Operation costs difference /year 511 1'065 Gains for PV plant /year 9'183 9'998 Net cash flow difference /year 9'694 11'063 Simple pay back period Year In one case the total cost difference has been related to the design energy data, while in the second case real data better energy performance than the design case in term of electricity demand and production have been used. 5. Conclusions 1 Pellets cost = 0.21 /kg [3]; Pellets calorific value = kwh/kg [1] 2 Electricity cost = /kwh for a family with peak power of 3 kw and maximum consumption of kwh/year [5] 3 Incentive tarif = 0.46 /kwh referred to the old ContoEnergia (2006) for PV-energy production, Selling price = /kwh referred to the selling price for PV-energy [4]

9 The presented study case implements design high performance technical solutions: design yearly energy scenario is well verified by monitored values, even if yearly variations in the electricity demand have to be further investigated. Presented design choices are possible reliable answers to global energy problems. Furthermore, the costs/benefits analysis shows a competitive even if not extremely low - simple payback time. By the way, PV plant cost that represent the higher investment cost is nowadays considerably falling due to the market evolution. For these reasons Lajon school is a real example of zero energy building for future realizations towards global sustainability of building sector. 6. References [1]. Project, PELLETS@LAS IEE. Pellets@LAS. [Online] [Cited: ] [2]. Lantschner, Norbert. CasaClima: Il piacere di abitare. Bolzano : Athesia, [3]. CdM. Decreto Legislativo n.115/2008. s.l. : Supplemento ordinario n.196 della Gazzetta Ufficiale n.195 del 21 agosto 2008, [4]. Gestore Servizi Elettrici. GSE. [Online] [Cited: ] %202009%20( ).pdf. [5]. Autorità per l'energia elettrica e il gas. AEEG. [Online] [Cited: ] [6]. Vonmetz, Johann. Una scuola che fa scuola. Ottobre 2007, Casa & Clima n. 9, pp Acknowledgements The authors would like to gratefully thank the Stiftung SüdTiroler Sparkasse for the financial support, Commune of Laion, TBZ (Technisches Bauphzsik Zentrum) dott. Günther Gantioler.