ENERGY DEMAND ANALYSIS AND ENERGY LABELLING OF NEW RESIDENTIAL BUILDINGS IN TUSCANY (ITALY)

Transcription

1 ENERGY DEMAND ANALYSIS AND ENERGY LABELLING OF NEW RESIDENTIAL BUILDINGS IN TUSCANY (ITALY) F. Fantozzi, F. Leccese, G. Salvadori, G. Tuoni Department of Energy L. Poggi Faculty of Engineering, University of Pisa Seventh International Conference on Ecosystems and Sustainable Development 8-10 July 2009 Chianciano Terme, Italy

2 INTRODUCTION For the realization of a new building, in Italy, the prescriptions on the energy consumption reduction to be satisfied are given in: Legislative Decree n. 192/2005; Legislative Decree n. 311/2006; Decree of the Republic President n. 59/2009; (Italian acknowledgements of EPBD European Directive 2002/91/EC on energy performance of buildings). The n. 192 and n. 311 Decrees have introduced limit values for: the primary energy demand of buildings for winter heating; the thermal transmittances of the building envelope components (both opaque and glazed). Recently (April 2009) the n. 59 Decree has introduced limit values for: the primary energy demand of building for summer cooling; the dynamic/periodic thermal transmittances of the building envelope opaque components (defined as indicated in EN ISO 13786). Currently in Italy there isn t a standardized method on a national level for the energy labelling of buildings.

3 AIMS OF THE WORK In this paper, the Authors show the results related to the energy demand evaluation of two new buildings in Tuscany (Italy) and to their energy labelling for space heating and DHW production. The evaluation of the building energy demand during the heating season has to take into account both the energy demand for space heating and that for domestic hot water (DHW) production, according to the European standards EN ISO 13790, EN and Italian standard UNI/TS This analysis has been performed with a critical approach to the use of the standard, pointing out how in very well insulated buildings the energy consumptions can be strongly influenced by the behaviour of the users and hence very different to the calculated demands. In the absence of a unique criterion for the energy labelling on a national level, different labelling criteria suggested by European standards and Italian local administrations have been tested. This analysis has been performed pointing out how the energy label of a building in Italy can vary with the adopted labelling criterion.

4 CASE STUDY DESCRIPTION Location of the buildings The complex of the two studied buildings is currently being realized in the town of Greve in Chianti (Florence, Tuscany region, Italy). Greve in Chianti : Height above sea level = 236 m Latitude = N Degrees-day = 2126 Conventional duration of the heating period = 183 days. (From 15 th of October to 15 th of April)

5 CASE STUDY DESCRIPTION The project of the buildings The two buildings are composed of 4 typologies of flats, differing from each other mainly in dimensional characteristics, exposure and net area. The first is composed of 17 flats distributed on three floors. The second is composed of 8 flats distributed on three floors. D 3 D 2 FLATS TYPOLOGIES A type: duplex-type flats for 4 persons; B type: single flats for 2 persons with independent entrance (external stairs); C type: single flats similar to those of the type B but presenting a larger net area (3 persons); D type: flats similar to those of the B type (2 persons) but having a condominial entrance.

6 CASE STUDY DESCRIPTION The envelope of the buildings The building envelope of both buildings is made of: opaque surfaces, for about 90%; glazed surfaces, for the remaining 10%. Each building is constructed with: a steel structure and panelling with lightened brick blocks with outdoor external insulation, to reduce as much as possible the effect of thermal bridges. The thermal insulation material is polystyrene (mean thickness of 0.1 m, thermal conductivity of W/mK) so as. The glazed surfaces have: triple glass (provided with air spaces) and PVC frames. They allow different opening configurations, so that the indoor natural ventilation conditions could be varied. Both opaque and glazed envelope structures have thermal transmittances lower than the limit values imposed by 192/2005 and 311/2006 Legislative Decrees.

7 ENERGY DEMAND ANALYSIS Useful energy demand for winter heating: evaluation Useful energy demand evaluation for winter heating has been carried out according to the methods proposed in: EN ISO Energy performance of buildings - Calculation of energy use for space heating and cooling (in Italy UNI EN ISO, June 2008); EN Heating systems in buildings - Method for calculation of the design heat load (in Italy UNI EN 12831, December 2006); UNI/TS Prestazioni energetiche degli edifici - Climatizzazione e preparazione acqua calda per usi igienico-sanitari - Parte 1: Fabbisogno di energia termica dell'edificio per la climatizzazione estiva ed invernale (May 2008, in Italian). Energy balance for the building (or flat) Q H =Q T +Q V η G Q G Where: Q H useful energy demand for winter heating; Q T transmission heat losses; Q V ventilation heat losses; Q G heat gains (solar and internal heat gains); η G utilization factor for heat gains; Ventilation heat losses are evaluated by using a fixed number of air change per hour n. The value n =0.3 h -1 is considered to be a standard for residential buildings in UNI/TS In Italy the working-out of several regulations and prescriptions on the ventilation of residential buildings is currently being discussed. Values of n variable between 0.5 h -1 and 0.8 h -1 are proposed as a reference in case of indoor natural ventilation and airing without using controlled mechanical ventilation systems.

8 ENERGY DEMAND ANALYSIS Useful energy demand for winter heating: results By considering flat A1 as a significant example: INPUT DATA gross area =113 m 2 (net area =92.4 m 2 ) gross volume V =403 m 3 ; dispersing surface S =326 m 2 (55% external walls, 20% roof, 17% floor, 8% of glazed surfaces); compactness ratio F = S/V =0.81 m -1 ; indoor air temperature T i = 20 C; outdoor air temperature Te = Tem, (where Tem are the mean monthly values indicated in the Italian standard UNI 10349); number of air change per hour n =0.3, 0.5, 0.8 h -1. Calculation results for: Ventilation (Q V ) and Transmission (Q T ) heat losses n = 0.3 h -1 OUTPUT DATA useful energy demand Q H = MJ/year for n =0.3 h -1 ; useful energy demand Q H = MJ/year for n =0.5 h -1 ; useful energy demand Q H = MJ/year for n =0.8 h -1. n = 0.8 h -1

9 ENERGY DEMAND ANALYSIS Useful energy demand for DHW production: evaluation Useful energy demand evaluation for DHW production has been carried out according to the methods proposed in: UNI/TS Prestazioni energetiche degli edifici - Climatizzazione e preparazione acqua calda per usi igienico-sanitari - Parte 2: Energia primaria e rendimenti per la climatizzazione invernale e per la produzione di acqua calda per usi igienico sanitari (May 2008, in Italian). Energy balance for the building (or flat) Q HW =ρ g W N C P ΔT t Y Where: Q HW useful energy demand for DHW production; ρ water density; g W DHW daily demand per person; N number of building occupants; C P water specific heat; ΔT temperature difference (between cold water collected from the municipal network and heated water); t Y number of days. DHW daily demand per person To calculate Q HW different values of g w have been used. The value g W =36 l/person day is considered to be a standard for a residential buildings with the net area and number of occupants like the reference flat A1 in UNI/TS The value g W =75 l/person day is indicated as a reference value in the Guidelines on Sustainable Building in Tuscany drawn up by the Tuscan Region.

10 ENERGY DEMAND ANALYSIS Useful energy demand for DHW production: results In case of reference flat A1: INPUT DATA number of occupants =4; temperature difference ΔT=25 C (temperature of DHW =40 C, temperature of cold water from the municipal network =15 C); DHW daily demand per person gw=36 and 75 l/person day. OUTPUT DATA useful energy demand Q HW = MJ/year for g W =36 l/person day; useful energy demand Q HW = MJ/year for g W =75 l/person day. From the calculation results, which have been obtained for all the flats, it is well underlined how in high-level-thermal-insulation buildings useful energy demand for DHW production results to be of remarkable importance compared to the overall energy demand. gw = 36 l/person day gw = 75 l/person day Comparison between different energy demands

11 ENERGY DEMAND ANALYSIS Primary energy demand evaluation Characteristics of the Heating and DHW production plants Heat generator: electronic condensation gas boilers, with minimum nominal power of 9.50 kw and with production of DHW. The choice to consider each of the different flats to be provided with an autonomous plant has been imposed by specific requirements of the building firm to comply with the current expectations of the final users. Emission terminals: floor radiant panels provided with modulating adjustable thermostat with pitch of 1 C and with thermally insulated hot water inlet pipes. Overall seasonal mean efficiency for heating: ηr=0.80. Overall seasonal mean efficiency for DHW production: ηw=0.90. Primary energy demand The primary energy demand for space heating (Q R ) and for DHW production (Q W ) for the example flat (A1) have been evaluated respectively as: Q R =Q H /η R MJ/year; Q W =Q HW /η W MJ/year.

12 ENERGY DEMAND ANALYSIS Building energy performance indicators EP R indicator: is defined as the ratio between the primary energy demand for the space heating Q R (kwh/year) and the net area of the building (m 2 ). The determination of the indicators EP R and EP W has been repeated for all the flats being the subject of the energy analysis. EP W indicator: is defined as the ratio between the primary energy demand for DHW production QW (kwh/year) and the net area of the building (m 2 ). The EP R indicator results lower than the limit value for all flats, the maximum value of EP R has been obtained for the flat C5: EP R = 33 kwh/m 2 year In the case of reference flat A1: EP lim =81.8 kwh/m 2 year EP R =31.4 kwh/m 2 year (40% of the EP lim ) EP W =18.3 kwh/m 2 year. The EP R indicator results lower than the value of 50 kwh/m 2 year indicated by the municipal district of Greve in Chianti as limit below which volumetric incentives can be applied.

13 BUILDING ENERGY LABELLING The National Guidelines proposal The energy labelling of buildings is reported in the EN 15217; Labels are marked by letters from A to G (according to a decreasing energy performance); By R R (Energy Performance Regulation Reference) the value according to the law being in force in the country of adoption has been indicated; By R S (Building Stock Reference) the reference value representing the average performance of the existing buildings in the country of adoption has been indicated; In the table the implementation proposal of the energy labelling of buildings in Italy, recently published in the National Guidelines being currently discussed, is also reported.

14 BUILDING ENERGY LABELLING Different Italian energy labelling criteria Examples of type 1 labelling criteria In Italy, in absence of regulations on a national level, different local energy labelling criteria have been developed. At the moment regional labelling procedures, for instance, in Lombardy, Liguria and Emilia-Romagna as well as local ones in the districts of Bolzano, Trento, Vicenza, Reggio Emilia and, finally, in Tuscany, for example, in the towns of Pisa and Pontedera are already activated. All the criteria can be grouped in two categories: 1) that for which the labelling occurs considering only the energy performance indicator EPR, 2) that contemplating the use of the sum of the energy performance indicators EP*=EPR+EPW. Examples of type 2 labelling criteria

15 BUILDING ENERGY LABELLING Energy labelling of the case study buildings Energy labelling of the flats Comparing the energy labels, obtained by using different criteria valid on a local level, significant differences can be detected. For example: the reference flat A1 changes over from label A (National Guidelines criterion [16]) to label B (Lombardy region criterion [17]). On the contrary, using the criterion proposed by the Vicenza district [19], all the examined flats undergo a labels change towards lower energy performance compared to that obtained by [16]. An alternative method to compare the energy performance of different buildings has been introduced in the Guidelines on Sustainable Building in Tuscany, according to the international method Green Building Challenge (GBC), by using the performance indicator k=ep R /EPlim. Energy performance indicator k

16 CONCLUSIVE REMARKS According to the results obtained, the investigated buildings can be considered "low energy consumption buildings". The examined flats show, in fact, energy performance indicators for winter heating EPR lower than 33 kwh/m 2 year, much lower than the respective limit values fixed by Italian regulations. In well-insulated buildings, the energy demand for ventilation and DHW production represent a significant share of the overall winter building energy demand. This share varies with the users behaviour, so that the EPR can be used as a figure of merit for each building, but to achieve remarkable energy saving a conscious use of the energy efficient building is also necessary. The energy labels have been assigned to each of the flats according to different criteria currently used in Italy. Among the labelling criteria considered in this paper, a nonhomogeneity can be pointed out both in the labelling criteria and in the limit values indicated for each label. Such non-homogeneities can lead to the attribution of different energy labels for the same building depending on the criterion adopted. The energy labelling method for buildings, as well as the introduction into the labelling criterion of performance indicators relating to summer air-conditioning, should be, then, standardized on a national level in a short time.