Influence of Degradation and Service Life of Construction Materials on the Embodied Energy and the Energy Requirements of Buildings

Influence of Degradation and Service Life of Construction Materials on the Embodied Energy and the Energy Requirements of Buildings Carol Monticelli 1 Fulvio Re Cecconi 2 Giorgio Pansa 3 Andrea Giovanni Mainini 4 ABSTRACT The construction of buildings and their operation have extensive direct and indirect impacts on the environment during the life cycle. Designers and builders face a unique challenge in attempting to meet the requirements of either new and renovated facilities that provide accessibility and security but also offer a healthy and productive working environment whilst minimizing their environmental impact. Methods to evaluate the environmental sustainability of buildings and those to measure operational energy efficiency often do not take into account the decay in performance of building materials over time. Results of ongoing research conducted at the Politecnico di Milano, Dept. BEST, are presented on the influence of the degradation of construction materials and their service life on the energy performance over the building life cycle. Focus was made on determining the embodied energy (ISO 14040) of building construction practices and maintenance, and the energy requirement (ISO 13790) for both heating and cooling. Studies were conducted on two different types of building: a 16 storey tower and a single-unit dwelling. Six types of building envelope were considered: five typical Italian brick masonry walls and one light-weight solution. For each of these wall systems and building types, standard methods were used to calculate the embodied energy for the selected solutions and the energy requirements over a building service life of 60 years. Monte-Carlo simulation was used to take into account the degradation of the thermal insulation over time, and thus to determine if and how building type and building envelope technology were sensitive to this degradation. KEYWORDS Life Cycle Assessment, Energy performance, Thermal insulation degradation. 1 Dept. of Building, Environment, Science and Technology of the Politecnico di Milano, Milano, ITALY, carol.monticelli@polimi.it 2 Dept. of Building, Environment, Science and Technology (BEST) of the Politecnico di Milano, Milano, ITALY, fulvio.rececconi@polimi.it 3 Dept. of Building, Environment, Science and Technology (BEST) of the Politecnico di Milano, Milano, ITALY, giorgio.pansa@mail.polimi.it 4 Dept. of Building, Environment, Science and Technology (BEST) of the Politecnico di Milano, Milano, ITALY, andreagiovanni.mainini@mail.polimi.it

Carol Monticelli, Fulvio Re Cecconi, Giorgio Pansa and Andrea Giovanni Mainini 1 INTRODUCTION An important goal for the building sector is to design sustainable buildings, considering not only the construction process, but also the operational, maintenance and disposal phases. Durability of building materials and components should be considered from the first phases of the design, since their selection directly affects the environmental impact of the construction. Total energy use during the life cycle of buildings is a growing research field, on one hand, and the aging and degradation processes of building components are object of theoretical and experimental studies, in order to define the durability of building materials and components, on the other hand. Researches on the environmental performance of building materials show how material choice may affect embodied energy in houses with a defined life time [Thormark 2006, Gustavsson et al. 2006, Monticelli 2006] and how the service life of materials affects the results [Junnila and Horvarth 2003]. There are also various studies focusing on the environmental impact of whole buildings: Scheuer et al. [2003] assessed a six-storey-building with a life time of 75 years, using LCA; Peuportier [2001] compared the life cycle analysis of three single-family houses with a service life of 80 years; Ortiz et al. [2009] apply the LCA approach to a typical Spanish house with a projected 50-year life span. Adalberth [1997] tried to propose a method about the calculation of energy use during life cycle of buildings taking into account energy associated to maintenance works. To summarize, lot of studies evaluate the environmental impact of buildings, from cradle to grave, considering the energy burdens and, in few cases [Thormark 2006], also the recycling potential of materials. Only the study of Haapio and Viitaniemi [2008] shows how durability of building components affects service life of buildings and how components and building service life together affect the environmental impact in a life cycle analysis. The Building Envelope Life Cycle Assessment Management Project tried to define a technique to predict the remaining service life of building envelope components and a procedure to optimize their maintenance [Lacasse et al. 1997]. In order to predict maintenance scheduling results from studies about building materials performance over time are very important because they give useful indication in order to quantify the maintenance cycles and their impacts in the LCA. 2 AIM OF THE STUDY In order to evaluate the environmental compatibility of buildings and to measure operational energy efficiency, taking into account the maintenance and the durability, exist different methods, but often they do not take into account performance decay of building materials over time. The aim of this study was to investigate how different building envelope solutions and different building types affect environmental assessment over the whole building life cycle. In addition, the influence of the degradation of construction materials and of their service life on the energy performance over the building life cycle was analyzed. Focus was made on determining the embodied energy of building construction and maintenance (following the standard series for the LCA ISO 14040:2006), and the energy requirement for both heating and cooling (following the standard ISO 13790:2008). 3 REFERENCE CASES Two different types of buildings were analyzed: 1. a single-family house (the shape factor defined as Gross Area of Heat Loss Elements / Gross Building Conditioned Volume A/V is 0.90), 2. a 16 storey tower (A/V = 0.375). Both analyzed building have the same type of basement system, roof system, windows, heating and cooling plants. The differences are related to the different solutions of building envelope investigated (for both types of buildings): five typical Italian brick masonry walls and one light weight solution. Totally 12 case studies were analyzed. The external walls covering types, designed to have the same thermal transmittance (U-value =0,33 W/(m 2 K)), are: A. external thermal insulation render system on single leaf brickwork cavity wall; B. cement rendered lightweight brickwork outer leaf, insulation, gypsum rendered brickwork inner leaf; C. dense solid brickwork outer leaf, insulation, gypsum rendered brickwork inner leaf; D. ventilated wall, an external thermal insulation brick masonry wall externally covered in brick hollow flat blocks, and assembled by means 2 XII DBMC, Porto, PORTUGAL, 2011

Influence of Degradation and Service Life of Construction Materials on the Total Energy of suspension devices and mechanical style fixings; E. single leaf brickwork cavity wall with cement rendering; F. dry assembled light weight solution with thermal insulation and external aluminum slabs. The thermal insulation material used was mineral wool. The walls thickness is different, consequently each conditioned area of the case studies is different. In the evaluation of the embodied energy of buildings the input of the main structural system, of the internal walls and, for the tower, of the 16 floors were omitted: structure, foundations and floors surely would generate a big difference of the involved embodied energy between the single houses and the towers types, but they do not affect the comparison of different envelope technologies on the same building. Figure 1. The 12 case studies: two buildings with six different external wall types. The system limits of the energy computation in the life cycle analysis were the production phase and the operational phase, considering the maintenance cycles. Contributions of transportation from the industry to the building site, building site itself and end-of-life phase were excluded. In order to compare easily the environmental impact of the pre-operational phase with that of the service life, the synthetic indicator Energy consumption were used: a. Embodied Energy EE (MJ/kg) in order to quantify the energy for building materials and component production (including all working processes, from extraction of raw materials up to the packaging ready to leave the factory, and feedstock); b. Non renewable Energy required for the heating and cooling of the building, for the maintenance in the service life. 4 METHOD The total embodied energy of building construction practices and maintenance, over the life cycle, was calculated and compared with the total energy requirement for both heating and cooling. The method used for the energy life cycle analysis follows the procedures in accordance with standardization ISO 14040. The assumed life time was 60 years. At first, the dimensions of the two buildings, the structure of the six external walls covering types, than the quantities of the used building materials and also their thermal proprieties, in order to quantify the buildings energy requirement during the operation, were calculated. The second step dealt with the quantification of the embodied energy of each building subsystem (basement, external walls, windows and roof were considered); their addition has generated the amount of total embodied energy of the case studies. The mass of materials and component (kg/m 2 ) and the areas of the buildings systems were necessary in order to define the total embodied energy of the buildings. Practically the embodied energy was XII DBMC, Porto, PORTUGAL, 2011 3

Carol Monticelli, Fulvio Re Cecconi, Giorgio Pansa and Andrea Giovanni Mainini defined on one square meter of each building system at first, then multiplied by their areas and normalized on the square meters of the usable floor area. Data on embodied energy (MJ/kg) were collected from the English database ICE Version 1.6a [2008]. The third step dealt with the calculation of the energy need for heating (Q H ) and for cooling (Q C ) to maintain the intended temperature conditions (20 C in winter, 26 C in summer) in each building during the year. The energy for operation was calculated using the procedure of the national standard UNI/TS 11300-1:2008 (the Italian version of ISO 13790:2008). Buildings were located in Milan, considering climatic data from UNI 10349:1994. The dispersion due to ventilation and the solar heat gains through windows, optical properties of the glazing, shading effects from awnings and internal heating from other sources were considered in this evaluation. The infrared radiation s contribution to the wall thermal exchange was taken into account, together with solar heat gains over opaque elements (considering a solar absorption coefficient across of 0,6). Thermal bridges in the buildings were calculated according to ISO 14683:2007: those between pillars and those related to internal walls have been neglected. The contribution of the ground has been defined according to ISO 13370:2007 and the thermal capacity according to ISO 13786:2007 (calculating internal areal heat capacity for each building element). In both buildings, following thermal transmittances were considered: slab-onground U-value = 0,204 W/(m 2 K) for single-family house and 0,183 W/(m 2 K) for 16 storey house, roof U-value = 0,30 W/(m 2 K), windows U-value = 1,685 W/(m 2 K), external walls U-value = 0,33 W/(m 2 K). The efficiency of the technical building system for heating (gas methane) and for cooling (electrical heat pump) were also taken into consideration to easily evaluate the delivered energy. The first resulted in a value of energy efficiency η = 0,79, and the second in a value of performance coefficient COP= 2,5. In order to evaluate the primary energy consumptions, total primary energy factors have been assumed: 1 for the fossil fuel (heating season) and 2,18 for the electrical carrier (summer season). The relative consumption of lighting and hot water production was not taken into consideration. The results have been related to the conditioned area, in terms of energy performance indicator [kwh/m 2 ]. The fourth step involved the investigation on the maintenance, calculated for each material and component as embodied energy time s interval/60 years. Maintenance intervals were assigned to each component in the six types of building envelope and based on the maintenance codes obtained from English data into HAPM [1996]. Two main kind of maintenance actions were assumed: standard operation on the façade component and replacement. The replacement is scheduled as follow: every 15 years the internal plaster of all different envelopes is replaced; every 15 years for the Env. A (replacement of external thermal insulation render system); every 40 years for the Env. B (replacement of the external plaster, in this case the insulation is not substituted over the period of analisys, being between the brick leafs); no other replacement for Env. C; every 40 years for the Env. D (replacement of the brick hollow flat blocks, the insulation layer, the suspension devices and mechanical style fixings); every 40 years for the Env. E (replacement of external plaster); every 15 years (replacement of the external aluminum composite panels), every 30 years (replacement of the plasterboards) and every 40 years (replacement of the whole building component) for the Env. F. The data for the embodied energy of the new materials were extracted from ICE again. It has to be underlined that the performance of the building materials was considered constant in this phase, neglecting the materials aging and thermal degradation. After these four steps the obtained results allowed the comparison between the embodied energies of the different life cycle phases of the two buildings, in order to demonstrate their incidence on the total energy amount. The last step was the investigation of the influence of degradation on embodied energy. Building components and materials degradation influences the environmental assessment of building because it changes both energy demands for winter heating and summer cooling over time and energy for maintenance phase. In order to take into account the influence of degradation on energy demands some simplifying assumptions were made, the most important are: degradation was taken into account only for façade; although this may not seem realistic, the choice is due to the fact that research focused on façade components and not on roofs or windows; 4 XII DBMC, Porto, PORTUGAL, 2011

Influence of Degradation and Service Life of Construction Materials on the Total Energy degradation of thermal resistance happens only on the insulation layer of façade components; although this is not true, it has to be considered that in components under analysis more than 90% of thermal resistance is due to the thermal resistance of the insulation layer. Energy demands were calculated according to these simplifying assumptions taking into account also the influence of degradation and of actual humidity and temperature of the insulation layer using the equation (1) in ISO 10456. The ISO equation was adapted to the case studies as follows: Where: is the design value of thermal conductivity; is the actual value of thermal conductivity; takes into account temperature difference between test condition when measured and the actual in use temperature (T in Celsius degrees); takes into account humidity difference between test condition when measured and the actual in use humidity (ψ in kg/kg of air); takes into account the degradation over time (A in years). is is Assumption of different values of temperature T 2 and humidity ψ 2 were made according to the different position of the insulation layer in the façade component: for example the inner the layer the lower the temperature T 2 due to the lower effect of solar radiation. Both T 2 and ψ 2 were assumed constant during the heating or cooling period. The influence of degradation on energy for the maintenance phase was also simplified by the assumption that degradation will only change the frequencies of maintenance operations and not the type. Service life of façade components was estimated using the factor method (ISO 15686-1) starting from reference service life used in step four. At the end of step five a Monte Carlo simulation was carried out in order to measure possible errors in thermal conductivity calculations and in service life estimations. 5 RESULTS OF THE ENERGY ASSESSMENT OF BUILDINGS 5.1 Pre-construction Phase and Embodied Energy of Buildings The embodied energy EE for each of six external wall types has been compared: the envelope solution F shows the highest EE value (1410,07 MJ for a envelope m 2 ), due to the external surface system (aluminium has an high EE value), and the solution B has the lowest EE value (820,28 MJ for a m 2 of envelope). Solution B involves less quantities of materials than the other brick wall type. The differences in both groups of cases studies are between the EE starting values of the envelope types, because the EE values of the other building systems is constant. The great difference between the EE results of the two building types (normalized on a m 2 of the conditionated area) is due to the form factor A/V: the tower has a more compact shape than the single family house, so its EE/m 2 of conditioned space is lower than the second one. 5.2 Operational Phase The amount of total primary energy for heating and cooling during the year in the single family houses is in the range of 103 and 113 kwh/m 2 y; the one in the towers is in the range of 69 and 78 kwh/m 2 y. The differences of results between the tower and the single family houses are due to the shape factor. Although they have the same external wall solutions, the lower A/V ratio determines a thermal losses reduction. In both groups of cases strong differences in conductive thermal losses are also influenced by thermal bridges that, in accordance with UNI EN ISO 14683:2008, depends on XII DBMC, Porto, PORTUGAL, 2011 5

Carol Monticelli, Fulvio Re Cecconi, Giorgio Pansa and Andrea Giovanni Mainini building external wall type. The percentage of thermal bridges influence on thermal losses varies from 8 to 27%. In every group of case, from A to F, of the single family house and the storey tower, the conditioned area are are different, even if the external dimension of the building are the same for every case in both groups, because of the use of different external walls type with different tickness. In the figure 2 emerges the amount of the energy involved in the pre-operational phase and the energy demand for heating and cooling. Figure 2. Case studies: comparison and ratio (e.g. 1:2,86 for the 1A) between the values of embodied energy EE and primary energy PE requirement in 60 years, normalized by the net usable floor area. Comparing both groups of case studies and taking into account the maintenance contribution, the calculated energy needs are totally different in the whole life cycle. Both of building types assume the highest value of energy with the solution F, during a lifetime of 60 years, (fig. 3), just the opposite scenario than the previous phase: the durability of the components, and besides the maintenance with components substitution, affect the results. The lightweight solution F has an high EE value and it allows a lower energy requirement for heating and cooling in buildings than other solutions, thanks to the thickness of the insulation slab. Considering the materials service life, this solution needs more scheduled maitenance than the other solutions over the 60 years. The EE for the maitenance defines the final high energy amount (fig. 3). An other consideration: if only the pre-operational phase is considered, both of building types with the solution B have the lowest EE, because of the lower EE of the involved materials (compared with the other brick work walls). If the operational phase is taken into account, the single family house with the solution F consumes less energy than the other ones, just as the solution A between the 16 storey tower case studies. At least if the maintenance phase is taken into account, the single family house with the solution E has totally the less energy consumption than the other ones, just as solution A between the 16 storey tower case studies. Figure 3. Affection of maintenance schedules in a life time of 60 years of the single family house. Taking into account the difference of energy consumption between the most efficient case (in terms of energy) and the worst one, the envelope type choice affects the results and the energy consumption. For example, in the single family house the choice of the solution E generates an energy consumption of 31.600,95 MJ/m 2, equivalent to 8778,042 kwh/m 2 and to 146 kwh/m 2 y. In the same building type the solution F generates a consumption of 33.816,62 MJ/m 2, equivalent to 9393,5 kwh/m 2 and to 156,5 kwh/m 2 y. The difference of 10,5 kwh/m 2 y is quite comparable to the primary energy heating demand of a class A new house (in Milan). 6 XII DBMC, Porto, PORTUGAL, 2011

Influence of Degradation and Service Life of Construction Materials on the Total Energy Table 1. Results of the energy assessment of the houses 1 and of the towers 2 (life exp. of 60 years). LCA phases Unit 1A 1B 1C 1D 1E 1F EE production MJ/m 2 S u 7.993,56 7.809,93 8.066,31 8.176,21 7.954,82 8.401,51 Operational E MJ/m 2 S u 22.891,13 24.327,25 24.499,02 23.347,74 23.513,19 22.298,62 EE maintenance MJ/m 2 S u 871,99 133,54 103,03 406,05 132,93 3.116,50 Tot. Energy/60 MJ/m 2 S u 31.756,69 32.270,72 32.668,36 31.930,01 31.600,95 33.816,62 LCA phases Unit 2A 2B 2C 2D 2E 2F EE production MJ/m 2 S u 1.199,71 1.113,03 1.236,60 1.277,20 1.181,26 1.399,62 Operational E MJ/m 2 S u 14.678,81 15.503,04 15.612,86 15.051,72 16.321,02 15.650,88 EE maintenance MJ/m 2 S u 360,70 54,59 43,10 164,14 54,81 1.333,06 Tot. Energy/60 MJ/m 2 S u 16.239,22 16.670,67 16.892,56 16.493,06 17.557,09 18.383,55 5.3 Influence of Building Components and Material Degradation on Environmental Assessment As an example of the analysis done on all façade components, the case 1A single family house is presented. The Monte Carlo simulation was performed using the following input values for conversion of thermal conductivity (ISO 10456): f t = GaussNormal(0.0048; 0.0005333), f ψ = GaussNormal(4;1), f a = GaussNormal(0.0123577; 0.0041192). The estimated service life of the external insulation layer was cumputed using the following equation: ESL = GaussNormal(15; 5) 1 1 GaussNormal(1; 0.133) 1 GaussNormal(1; 0.133) GaussNormal(1; 0.133) 1 This means that RSl, C, E and F factors were assumed as probability density functions in order to take into account possible errors in estimating their value. Results of the simulation are presented in Table 2, where it is readable the minimum value, maximum value and mean value of the probability distribution function of total energy. Table 2. Results of the MC simulation Total energy [MJ/m 2 ] - case 1A - single family house. Min Max Mean 5% 10% 15% 20% 25% 30% 35% 40% %tile 23862 45% 50% 55% 30960 60% 65% 70% 75% 80% 85% 90% 95% 24333 24045 24077 24101 24123 24141 24157 24172 24191 24209 24227 24248 24270 24295 24327 24363 24409 24469 24579 24893 6 CONCLUSION The six building envelopes in the two different building typologies affect results of total energy computation over the life cycle. Differences in results (fig. 4) between the two groups of case studies are directly related with the shape factor, while differences into each group are related to building envelopes type because some technical solutions are more sensitive than others to aging and to environmental conditions, i.e. humidity and temperature. Further are the continuous line (result of the effect of the degradation of materials on the total energy computation) and the corresponding dotted line (deterministic evaluation result of the total energy without the aging of materials), more important is the consideration of the materials aging in the energy demand computation over the service life. In addition, more inclinated is the continuous line, more these solutions are subjected to a possibility of error in the aging effects evaluation. This is especially true for some envelope solutions. For example, the light weight solution F, with a thicker insulation layer than the others, and the solution A, with the external thermal insulation render system, are more subjected to aging effects and to humidity and temperature variations. XII DBMC, Porto, PORTUGAL, 2011 7

Carol Monticelli, Fulvio Re Cecconi, Giorgio Pansa and Andrea Giovanni Mainini Figure 4. Results of the total energy consumption scenario with the Monte Carlo analysis. ACKNOWLEDGMENTS The framework of the present work is the research Energy to build, energy to live. Energetically and environmental optimization of brick work envelope types coordinated by prof. A. Campioli, dept. BEST, funded by ANDIL, the Italian Brick Development Association. REFERENCES Adalberth, K. 1997, Energy use during the Life Cycle of Buildings: a Method, Building and Environment, 32[4], pp. 317-20. Gustavsson, L. & Sathre, R. 2006, Variability in energy and carbon dioxide balances of wood and concrete building materials, Building and Environment, 41[7], pp. 940-51. Hammond, G.P., Jones, C.I. 2008, Inventory of Carbon & Energy (ICE) Version 1.6a, Sustainable Energy Research Team (SERT), Dept. of mechanical Engineering, University of Bath. Haapio, A. & Viitaniema, P. 2008, Environmental effect of structural solutions and building materials to a building, Environmental Impact Assessment Review, 28, pp. 587-600. HAPM (Housing Association Property Mutual) 1996, Component Life Manual (4th edition), E & F.N. Spon, London, Junnila, S., Horvarth, A. 2003, Life cycle environmental effects of an office building, Journal of Infrastructurel systems, 9[4], pp. 157-66. Lacasse, M.A., Vanier, D.J. & Kyle B.R. 1997, Towards integration of service life and asset management tools for building envelope systems, in Proc. 7 th Conference on Building Science and Technology: Durability of buildings Design, Maintenance, Codes and Practice, Toronto, 20-12 may 1997, pp. 153-57. Monticelli, C. 2006, Environmental profile and Building Process. LCA application to experimental dry external wall Construction System, in Proc. 23rd Int. Conference on Passive and Low Energy Architecture PLEA 2006, Swiss, Geneva, 12-15 september 2006, vol.2, pp. 1023-28. Peuportier, B. 2001, Life cycle assessment applied to the comparative evaluation of single family houses in the French context, Energy and Buildings, 33[5], pp.443-50. Scheuer, C., Keoleian, GA., Reppe, P. 2003, Life cycle energy and environmental performance of a new university building: modelling challenges and design implications, International Journal for Energy and Buildings, 35[10], pp.1049-64. Thormark, C. 2006, The effect of material choice on the total energy need and recycling potential of a building, Building and Environment, 41, 1019-26. 8 XII DBMC, Porto, PORTUGAL, 2011