Thermal performance of single family residential building according to the methodology of RCCTE calculation

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1 Thermal performance of single family residential building according to the methodology of RCCTE calculation The influence of climatic conditions in the thermal study of buildings Ricardo Ferreira 1, Gabriel Pita Instituto Superior Técnico, Av. Rovisco Pais Lisboa, Portugal September, 2010 ABSTRACT This article is focused in the Thermal Performance of the Buildings area, particularly for the residential sector. On a first approach, the main concern is the energy scenery in this sector, referring some causes and corrective measures for the energy consumption increase in Portugal in these recent years. This work also approaches the present regulations in the Portuguese Legislation, in the area of thermal performance of buildings, mainly the Decrees 78/2006, 79/3006 and 80/2006, under the European Directive 2002/91/EC. The main objective consists in the evaluation of the possibility of implementing a single family residential building model with a certain architectural structure for the different municipalities of Portugal, without infringing the present RCCTE criteria. After a detailed description of the calculation of the RCCTE methodology, the case studies are based on the requirements to fulfill the regulation, for five single family residential buildings. Despite of the buildings having same architectural structure, not all of them fulfilled the requirements of the regulation, due to the diverse climate conditions existing in Portugal. This fact shows the importance of the climate data to be considered in the thermal studies of buildings, depending on the municipality where they are located. Key-Words: Energy Efficiency, Buildings, Thermal Performance, Residential Sector, RCCTE, Climate Data. INTRODUCTION The buildings define spaces where people spend more than 80% of the time of their lives and should provide adequate comfort and indoor air quality conditions. The energy consumption associated to the satisfaction of these conditions is very important because the building sector is one of the higher consumers of energy in Portugal. In terms of final energy use in households, energy costs are divided into the following proportions: 50% for the hot sanitary water preparation (AQS), 25% for cooling the building and the remaining 25% for lighting and usage of household appliances. In recent times, it is a fact we are facing an increase of energy expenditure on buildings. This increase occurs particularly due to features related to the structure of the existing buildings, such as: insufficient insulation in the opaque elements, influence of thermal bridges in the building external elements, the presence of moisture, low thermal performance of glazing and 1 ricardomiguelferreira@ist.utl.pt

2 Thermal performance of single family residential building according to the methodology of RCCTE calculation doors, lack of adequate sun protection and uncontrolled or inadequate ventilation in the building. In Portugal, the effort to reverse the growing trend of energy consumption in the building sector led to the need of regulating the requirements for thermal comfort and indoor air quality, developing a legislative framework for the thermal performance of buildings, through the reformulation of RSECE 2 and RCCTE 3, the Decrees 79/2006 and 80/2006, respectively, under the European Directive 2002/91/EC. At the same time, the Decree 78/2006 (SEC 4 ) was published, enabling the emission of an energy certificate, which contains information about the thermal conditions of buildings. This article focuses the methodology of the RCCTE calculation, in order to conclude if it is possible to implement a group of single family residential buildings with the same architectural structure on different municipalities of Portugal, in order to establish if the RCCTE criteria can be verified. To achieve the criteria established by RCCTE, the case studies were developed based on thermal studies of buildings for the village of Porto de Lagos, municipality of Portimão; Glória, in Estremoz; Vale de Pardinho, in Alcanena; Donões, in Montalegre, and finally, Souto Côvo, in Lamego, in order to check their thermal performance, according to the climate zone where they belong. METHODOLOGY OF RCCTE CALCULATION In order to meet the parameters set by RCCTE, detailed methods of calculating were developed, focused on the nominal needs for heating (Nic), cooling (Nvc), energy for AQS preparation (Nac) and primary energy (Ntc) (RCCTE, Chapter 2, Article 4, Section 2). The energy parameters above mentioned, cannot exceed the maximum admitted values, corresponding to the nominal energy of heating (Ni) (RCCTE, Chapter 3, Article 5, Section 1), cooling (Nv) (RCCTE, Cap. 3, Article 6, Section 1), AQS preparation (Na) (RCCTE, Chapter 3, Article 7, Section 1) and primary energy (Nt) (RCCTE, Chapter 3, Art. 8, Section 1), otherwise the regulation won t be fulfilled. In this methodology of calculation, it will be only emphasized the main formulas for calculating the energy requirements above, which are dependent of certain parameters. The methodology of calculation of those parameters can be found through the information presented in the RCCTE. 2 Regulamento dos Sistemas Energéticos de Climatização dos Edifícios 3 Regulamento do Comportamento das Características Térmicas de Edifícios 4 Sistema Nacional de Certificação Energética e da Qualidade do Ar Interior nos Edifícios 2

3 Existing Buildings New Buildings Thermal performance of single family residential building according to the methodology of RCCTE calculation Table 1 Methodology of calculation for the main energy requirements of the thermal studies of buildings according to RCCTE Nic Nic = (Q t +Q v Q gu ) (Eq.1) A p FF = ( A ext )+ i τa int i V (Eq.2) Ni Nvc FF 0,5 Ni = 4,5 + 0,0395 GD 0,5 FF 1 Ni = 4,5 + 0, ,037 FF GD 1 FF 1,5 Ni = 4,5 + 0, ,037 FF GD (1,2 0,2 FF) FF 1,5 Nvc = Q g (1 ƞ) A p Ni = 4,05 + 0,06885 GD (Eq.3) Nv V1 (Norte) Nv = 16 kwh/m2. ano V1 (Sul) Nv = 22 kwh/m2. ano V2 (Norte) Nv = 18 kwh/m2. ano V2 (Sul) Nv = 32 kwh/m2. ano V3 (Norte) Nv = 26 kwh/m2. ano V3 (Sul) Nv = 32 kwh/m2. ano Nac Nac = (Q a /ƞ a E solar E ren ) A p (Eq.4) Na N a = 0,081 M AQS n d A p (Eq.5) Ntc Ntc = 0,1. Nic ƞ i. F pui + 0,1. Nvc ƞ v. F puv + Nac. F pua (Eq.6) Nt Nt = 0,9. (0,01. Ni + 0,01. Nv Na) (Eq.7) The single family residential buildings mentioned in the case studies were included in the category of buildings with or without air-conditioning systems under 25 kw of installed power. Their classification is calculated by equation 8 and Table 1 works as rating scale of thermal efficient of buildings. For new buildings, the energy class verified by SCE goes to B- and the buildings cannot have an energy certificate if their energy class was below that. R = Ntc Nt (Eq. 8) Table 1 - Energy class of buildings and limits of their classes Energy Class R A + R 0,25 A 0,25 R 0,50 B 0,50 R 0,75 B 0,75 R 1,00 C 1,00 R 1,50 D 1,50 R 2,00 E 2,00 R 2,50 F 2,50 R 3,00 G R 3,00 Source: (ADENE, 2010) 3

4 Thermal performance of single family residential building according to the methodology of RCCTE calculation CASE STUDIES In the case studies developed for the single family residential buildings, their thermal projects were analyzed in order to verify the RCCTE and quantify their energy performance. The buildings are similar in terms of architectural structure but with different climate data, since every municipality of Portugal has its own records. The figures below correspond to the calculated values of the energy requirements, particularly for Nic, Nvc, Nac, Ntc, their maximum allowed values Ni, Nv, Na, Nt and energy class of buildings included in the villages of Porto de Lagos, Glória, Vale Pardinho, Donões and Souto Côvo, in the municipalities of Portimão, Estremoz, Alcanena Montalegre and Lamego, respectively. Nic Vs. Ni ,24 136,32 125,73 114, ,83 48,44 72,75 62,42 80,24 83,03 Nic Ni 2 Figure 1 - Values of Nic and Ni for buildings under study Nvc Vs. Nv ,51 10, ,41 1, ,27 Nvc Nv Figure 2 - Values of Nvc and Nv for buildings under study 4

5 Ntc / Nt Thermal performance of single family residential building according to the methodology of RCCTE calculation Nac Vs. Na 3 32,27 32,27 32,27 32,27 32, ,65 14,56 15,06 16,67 16,55 Nac Na 1 Figure 3 - Values of Nac and Na for buildings under study Ntc Vs. Nt 6,00 4,99 5,30 5,27 5,77 5,73 5,62 5,13 4,00 3,16 3,64 3,00 2,00 2,22 Ntc Nt 1,00 Figure4 - Values of Ntc and Nt for buildings under study Energy Class of Buildings 1,20 1,00 1,01 0,91 0,80 0,60 0,69 0,60 0,44 0,40 0,20 Figure 5 - Energy class for buildings under study The following set of figures corresponds to the verification of the thermal projects of the same buildings, except the building located in Portimão, with the aim of obtaining an upgraded energy class, equal to A. In the thermal studies, the changes focus the addition or changing of equipment and details of construction, so the buildings can be able to upgrade their energy 5

6 Thermal performance of single family residential building according to the methodology of RCCTE calculation performance. In Table 2, the changes already referred in the thermal studies are briefly presented below. Table 2 - Addition or changing of equipment and construction details for the buildings in order to verify the RCCTE and obtain an energy class equal to A Location of the building Addition or changing of equipment and construction details Glória, Estremoz Replacement of water boiler for condensation boiler wall as support equipment for AQS preparation. Vale Pardinho, Alcanena Replacement of water boiler for condensation boiler wall as support equipment for AQS preparation. Isolation of ground floor slab. Donões, Montalegre Isolation of ground floor slab. Addition of three heat pumps with 9000 BTU / hr in rooms + 2 heat pumps with BTU / hr in the living-room and kitchen. Souto Côvo, Lamego Isolation of ground floor slab. Addition of three heat pumps with 9000 BTU / hr in rooms + 2 heat pumps with BTU / hr in the living-room and kitchen. 16 Nic Vs. Ni 147, ,83 48,44 72,75 62,42 64,77 89,94 112,74 95,17 124,52 Nic Ni 2 Figure 6 - Values of Nic and Ni, after verification of thermal studies of buildings Nvc Vs. Nv ,51 10, ,41 1, ,27 Nvc Nv Figure 7 - Values of Nvc and Nv, after verification of thermal studies of buildings 6

7 Ntc / Nt Thermal performance of single family residential building according to the methodology of RCCTE calculation Nac Vs. Na 3 32,27 32,27 32,27 32,27 32, ,65 16,67 16,55 Nac Na 1 5,39 5,89 Figure 8 - Values of Nac and Na, after verification of thermal studies of buildings Ntc Vs. Nt 6,00 4,99 5,30 5,33 5,83 5,71 4,00 3,00 2,00 2,22 2,37 2,40 2,35 2,24 Ntc Nt 1,00 Figure 9 - Values of Ntc and Nt, after verification of thermal studies of buildings Energy Class of Buildings 0,50 0,40 0,44 0,45 0,45 0,40 0,39 0,30 0,20 0,10 Figure 10 - Energy class of buildings after verification of their thermal studies 7

8 Thermal performance of single family residential building according to the methodology of RCCTE calculation RESULTS EXPLANATION In Figure 1, the buildings in the municipalities of Montalegre and Lamego do not present the requirements of the regulation, since Nic > Ni. In Figure 2, the highest value obtained relates to the building in the municipality of Estremoz (10,12 kwh/m 2.year). However, all values obtained for Nvc are far from their maximum allowed values (Nv). In Figure 3, the energy used for AQS preparation is lower in the buildings in the south of Portugal (Portimão and Estremoz), compared to the buildings in the north of the country (Montalegre and Lamego). The Figure 4 represents the values of Ntc and their maximum allowed values (Nt), influenced by the results verified in Figures 1, 2 and 3. As the buildings included in the municipalities of Montalegre and Lamego cannot present the requirements of the RCCTE at the level of Nic, the Ntc values are affected by this occurrence, causing Ntc > Nt. Thus, the thermal studies of these two buildings have to be reviewed in order to comply with the RCCTE regulation. In Figure 5, the building insert in the municipality of Portimão has energy class equal to A, the buildings in the municipalities of Estremoz and Alcanena have energy class equal to B, the building in Montalegre has energy class equal to B- and energy class C for the building located in Lamego. After verifying the thermal studies of the buildings above mentioned, in order to upgrade energy class at the level of A, in Figure 6, all buildings comply with the regulation in terms of Nic as Nic < Nt. By comparing Figures 1 and 6, the values of Nic come down in the buildings in Alcanena, Montalegre and Lamego. Comparing Figures 2 and 7, it appears that there are no changes in the values of Nvc and Nv, since the revision of the thermal studies focus the Nic and not the Nvc needs. Comparing Figures 3 and 8, there is a clear reduction in Nac values for the buildings of Estremoz and Alcanena. Figure 9 presents the Ntc values and their maximum allowed values (Nt) after the revision of the thermal studies of buildings. Due to the influence of the data presented in Figures 6, 7 and 8, there is a clear reduction of Ntc compared to Figure 4. Finally, Figure 10 shows that the addition of equipment and construction solutions for the buildings under study, turn plausible the possibility of achieving energy class equals to A. CONCLUSIONS The main conclusion of this work shows that not all buildings with a certain architectural establishment can be implemented on the several municipalities of Portugal, due to the diverse climate conditions of the country. Thus, the climate data considered in thermal studies should be one of the major concerns of the thermal buildings performance. The diversity of climate conditions influences directly the amount of energy supplied to buildings in terms of heating needs (Nic), cooling needs (Nvc) and energy for AQS preparation. This fact can be seen on the energy class obtained for the building in Porto de Lagos, Portimão (A) and the building in Donões, Montalegre (C). 8

9 Thermal performance of single family residential building according to the methodology of RCCTE calculation Although the two case studies vary only in the climate data, the amounts of energy spent on the building of Montalegre are much higher than the building in Portimão, as Montalegre has a longer duration of the heating season and a higher number of degree-days (7.7 months, 2820ºC.day) compared to Portimão (5.3 months, 940ºC.day), which attests the severity of the climate in Montalegre. Another climate detail that influences the thermal performance of buildings is related to the energy demand for AQS preparation. From Figure 3, it is possible to see that there are lower costs with AQS preparation in the south of Portugal (Portimão and Estremoz), compared to the northern municipalities (Montalegre and Lamego). This occurrence is explained by the fact that there are greater amounts of solar radiation available in the south of Portugal, which allows a better usage of solar radiation by solar thermal collectors systems placed on the roof of buildings. In Figure 8, there is a decrease of energy costs with AQS preparation in the municipalities of Estremoz and Alcanena, due to the usage of condensing boiler wall as a support system for solar collectors with high yield (partial yield at 30% - 97%), minimizing energy losses. In this context, the solar thermal collectors system represents a useful solution in the energy rationalization, particularly in the period of cooling season due to an increased availability of solar radiation. Other conclusions attained represent the degree of isolation from the outside elements that buildings should have in order to minimize excessive energy gains or losses. In order to minimize such energy gains and losses, buildings must introduce constructive solutions. This way, they can achieve a higher level of energy conservation. In this work, the quality and quantity of insulation used in diverse elements was a concern in areas as walls, roof, ground floor, columns, beams and doors and windows. Despite the constructive solutions presented in the heating season, the energy gains resulting from the glazing and internal are not sufficient to offset the needs with heating (Nic). On the other hand, the energy waste involving Nvc is much lower when compared to Nic because of the insertion of constructive solutions exclusively dedicated to the minimization of non-useful energy gains, such as the shading caused by flap coverage at the roof top and the existence of systems that protect the glazing from direct sunlight like blinds. The systems described, coupled with the power of natural ventilation, can solve many of the problems related to overheating in the buildings. Figure 10 presents the allocation of energy class equal to A after the introduction of constructive solutions or equipment, which affects the acclimatization or minimization of energy losses in the buildings. In the building located in the municipality of Estremoz, the review of its thermal studies to achieve energy class A is focused on the replacement of the water boiler for condensing boiler wall due to the reasons already mentioned. In the building located in the municipality of Alcanena, the review of its thermal studies to improve their class energy, involves the introduction of condensing boiler wall to replace the water boiler and the constructive solution of insulation in the ground floor slab. With the isolation of the ground floor, the building can keep more energy, allowing less spending on heating. The RCCTE regulations do not consider the existence of thermal requirements for floors with directly contact to the ground, so, this situation should be reviewed in a future RCCTE revision because like it was demonstrated, there is a clear energy loss by the insufficient insulation of the floor slab, harming the energy performance of buildings. 9

10 Thermal performance of single family residential building according to the methodology of RCCTE calculation In the buildings included in the municipalities of Montalegre and Lamego, as they are similar in terms of their thermal behavior, the solutions for changing their energy class involve the insulation of the ground floor slab (advantages explained in the preceding paragraph) and by placing heat pumps for acclimatization. In these cases, there were chosen equipments with high COP (coefficient of performance), using three heat pumps with rated power of 9000 BTU / hr in the bedrooms and two heat pumps with rated power of 18,000 BTU / hr in the living-room and kitchen. In terms of cooling, the heat pumps have a COP between 3.21 and The solutions mentioned, combined with the characteristics of the thermal insulation of the buildings, provide a dramatic reduction in energy loss with Nic and a favorable influence in their energy class as shown in Figure 10, providing the best thermal performance comparing to the other buildings. Despite of the technical solutions adopted to improve the thermal efficiency, the parameter based on rationalization of energy by the habitants of these buildings implies a change in their behavior, adopting measures that enable a better use of energy without changing the environmental comfort in buildings. As a conclusion, there is an unquestionable need of these occupants to live in a symbiosis of constructive solutions and good practices of energy saving, in order to minimize the energy waste resulting from the residential sector. BIBLIOGRAPHICAL REFERENCES Camelo, S., Santos, C., Ramalho, A., Horta, C., Gonçalves, H., Maldonado, E., (2006). Manual de apoio à aplicação do RCCTE. INETI. Decreto-Lei n.º 78/2006 de 4 de Abril. Sistema Nacional de Certificação Energética e da Qualidade do Ar Interior nos Edifícios (SCE). Decreto-Lei n.º 79/2006 de 4 de Abril. Regulamento dos Sistemas Energéticos de Climatização em Edifícios (RSECE). Decreto-Lei n.º 80/2006 de 4 de Abril. Regulamento das Características de Comportamento Térmico dos Edifícios (RCCTE) DGGE, (2002). Eficiência Energética nos Edifícios. Direcção Geral de Energia - Ministério da Economia. ISBN: Directiva Comunitária 2002/91/CE de 16 de Dezembro de Desempenho Energético dos Edifícios. Ferreira, M., (2009). A Eficiência Energética na Reabilitação de Edifícios. Dissertação de Mestrado em Engenharia do Ambiente na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa. Isolani, P., (2008). Eficiência Energética em Edifícios Residenciais. Intelligent Energy Europe. Oliveira, I., (2003). Poupar Energia e Proteger o Ambiente. DECO PROTESTE. ISBN: