MED GREEN FORUM: Mediterranean Green Buildings & Renewable Energy 26-28 August 2015, Florence, Italy
EVALUATION OF THERMAL PERFORMANCE, ENVIRONMENTAL IMPACT AND COST EFFECTIVENESS OF AN XLAM COMPONENT FOR RETROFITTING IN EXISTING BUILDING Tiziano Dalla Moraa, Alessandro Righia, Fabio Perona, Piercarlo Romagnonib a
Università I.U.A.V. di Venezia,
[email protected] Tel.041 2571483, Fax: 041 2571485
Abstract Renovation and retrofitting of residential buildings is a subject of strong awareness in Italy: the most part of the existing building stock is completely inappropriate in terms of structural rigidity in the event of earthquakes and in respect of the objectives of energy efficiency set by the European law. This research presents the design of an innovative system of structural reinforcement using CLT (Cross Laminated Timber) technology based on materials with environmental compatibility: an xlam panel comes attached by a metal structure into the outside or inside layer of the external wall of existing building; the stratigraphy also includes the insertion of the insulation, the net of new systems (hydraulic and thermal) and also the new window frames. The new component is studied for modularization and standardization to ensure simplicity and speed of installation, low cost of pure proving and assembly. The research focused on aspects relating to building physics and sustainability in construction in order to optimize the choice of materials: analysis on performance were conducted and simulations were performed on various kinds of insulation materials in order to find the best possible configuration in terms of thermal performance, environmental impact and cost effectiveness. The results were verified with the construction of a prototype that has been check with a thermal test. Finally, with the obtained data it has been verified the renovation of a case study with different measures of intervention.
Keywords: italian residential buildings, structural reinforcement, energy renovation, CLT technology, thermal performance, environmental impact and cost effectiveness
Introduction In Italy the seismic events in recent years (Molise in 2002, L'Aquila in 2009, Emilia in 2012) have highlighted the total inadequacy of the existing buildings in earthquake case and consequently the need for action to address this criticality. Moreover 92% of Italian residential stock was built before 2001, but the first legislation that imposes technical criteria of anti-seismic construction was enacted on 2003. The research develops and deepens the application of a particular structural xlam panel connected to existing masonry: wood in fact has excellent characteristics such as light weight, mechanical strength and thermal insulation; as well xlam technology has demonstrated the capacity on stress distribution both in the vertical than in horizontal direction even in the presence of openings. A Xlam panel shows a great ratio between strength and specific weight compared to other common materials such as masonry or concrete and also it presents a better hard-set and anti-seismic behavior than a wood frame structure. The proposed technological system is composed as follows: a metal structure is fixed at the slab level or in the existent masonry for providing flexural rigidity and it’s connected to xlam panel by wooden curb which transfers shear stresses coming from the building (Figure 1).
Figure 1 - Panel and curb connection to slab level.
2
The different kind of insulating materials have been proposed in order to improve the thermal resistance and to optimize the hygrometric behavior of the panel. This study focused also on the environmental impacts (Carbon Footprint and Embodied Energy) of each proposed material and, at the end, the economic feasibility was evaluated for the proposed combination of layers and products. The main objective is to identify the best combination that could be able to achieve all benchmarks of the research reducing energy consumption and lowering CO2 emissions and being cost-effective in case of retrofitting. 1. Methodology The research work was planned and followed a precise strategic line for checking the type of intervention and the performances of the technological component, applying on a single external wall and comparing all aspects of analysis. The first phase has seen the construction of a matrix in which elements were selected introducing a code for xlam (K), insulation (X1expanded polystyrene EPS, X2 mineral wool, X3 aerogel), selected between the best sellers in market, and a brick masonry (Ya), in order to verify the performances with a test in a prototype and with simulations in a real case study; some specific characteristics have been identified to carry out the analysis: for example, values of thickness, thermal conductivity, specific heat, steam resistance, environmental impacts (LCA), supply and laying costs. Then four combinations of different stratigraphy of the various elements were identified; these combinations became the object of all analysis and simulations (Figure 2). Each combination is identified by the real possibility of intervention in the existent masonry building and by adopting the technological system in Xlam. The Italian legislation on historic facades protection, the level of damage and decay of the building, the location and condition of the site at urban level affect the positioning of the panel (see code K in Table 1) outside or inside the existing masonry wall and, as consequence, the internal or external application of insulation (X). The obtained combinations, matrix allow to understand what is the more favorable stratification between the various ones in the Italian building stock. It is also possible to control the performances of the intervention in an existing building. This research shows the analysis developed on this new component and its combination of material: in a first phase by numerical simulation mathematical model and then a thermal characterization by test in a prototype.
Figure 2 - Possible kind of combinations
2. Simulation and analysis on panel 2.1. Thermal analysis Because of its fiber orientations and porosity, wood can be considered a poor heat conductor. Since the thermal conductivity (λ) dependent on the presence of air and water within the wood, the value is strongly tied to considered wooden species and establishing a percentage of moisture content of 20% values are fluctuating between 0.10 and 0.20 W/(mK). The masonry walls instead have different features because the stratigraphy is composed by different materials, age and manufacturing, and also it’s influenced by the geographic area and the type of construction. However, the thermal properties values are obtained from the UNI TS 11300-1 database which lists the most useful configurations and obtained thermal transmittance is a U value between 1.4 and 0.7 W/(m2K). Table 1 - Minimum insulation thickness to achieve U = 0.34 W/m2K Insulation thickness (m) for Ya wall X3
expanded polystyrene (EPS)
0,055
X5
mineral wool
0,068
X6
aerogel
0,021
The proposed insulating materials are different because of their origin, vegetable, mineral, synthetic and composite. The main objective was to identify the thickness of each insulation for obtaining the minimum U values of the wall according to current national regulation (Italian Regulation Dlgs. 192/2005, i.e. 0.34 W/m2K for a Italian climate zone E corresponding to Venice area), and also that to obtain a lower thickness than the value of 0.1 m, corresponding to the interspace created by the metal structure for holding the xlam panel up. The most important result is that all proposed insulation allow thickness below 0.07 m (Table 1Table 1). Examples concern a selection of masonry with the combination XKY, tested with all types of masonry and selected insulation.
3
2.2. Environmental Impact The goal was to investigate the impact of the elements in the xlam technological panel. The analysis have been focused on various insulating selected (Y) so as to obtain the values of the Embodied Energy measured in MJ/kg (Table 2) and to identify those with less impact at equal equivalent transmittance. Table 2 - Embodied Energy values for insulation specific weight (kg/m3)
weight kg/m2
embodied energy (MJ)
(MJ*kg)
X3
expanded polystyrene (EPS)
0,10
37,00
4
101,50
386,60
X5
mineral wool
0,12
100,00
12
16,80
197,65
X6
aerogel
0,04
120,00
5
53,00
243,18
thickness (m)
The same study was also conducted on the brick masonry (X) and on the xlam panel, obtaining a value of 672 MJ. Therefore the insertion of the technological element in xlam with the insulation hypothesis provided an absolute value of Embodied Energy ranging between 700 and 1300 MJ. Afterwards investigations have focused on wood panel and insulation for the calculation of LCA of all materials by software simulations: using the method Impact 2002+v2.11 the four impact categories (Table 3) and their values have been obtained, including the Embodied Energy expressed in resources category. Table 3 - Impact categories Impact category
X3
X5
X6
Human health
DALY
5,21E-06
2,15E-05
3,65E-06
Ecosystem quality
PDF*m2*yr
3,93E-01
2,61E+00
4,39E-01
Climate change
kg CO2 eq
1,12E+01
1,68E+01
2,61E+00
Resources
MJ primary
3,43E+02
2,23E+02
2,64E+02
Calculation has allowed a comparison of the results obtained for Embodied Energy using the database (ICE) and the results are reliable and comparable because the database of the University of Bath allows a tolerance of approximately ± 30%. Finally CO2equivalent value was derived indicating the extent of the GWP (Global Warming Potential) of greenhouse gases, or rather their global warming potential for each selected material (Table 4). Table 4 - IPCC 2007 impacts
Kg CO2 eq
X3
X5
X6
13,255
17,830
3,370
A comparison between the production process of packages according to the method 2007 IPCC (Intergovernmental Panel on Climate Change) has been analyzed: an unit value is attributed on-base percentage to the material with higher CO2 equivalent and the remaining values were get consequently. Some materials such as aerogels and expanded polystyrene have low impacts since in the first case the material used is little amount, while the second has low harm values for global warming. 2.3. Outcomes on panel and simulation on a brick masonry In reference to methodology definition and based on the data of the various analyses, it is possible to order obtained information and to make a summary for configuring the kind of base panel and for applying it to a case study. The best combination of existing masonry, xlam panel and insulation is given precisely by the last variable: in fact the proposed xlam panel is given by structural calculation and its characteristics are broadly similar in the actual market, the kind of masonry might change depending on the building, and selected insulations have different properties and performances. The choice has been made taking as objective the minimization of heat loss, environmental impacts and intervention costs (Table 5). A further constraint has added due to the size of the structure for fixing the existing masonry and to the passage of system net: from the previous analysis it has made that it could take advantage of 10 cm of thickness on the gap in the inner side of the panel in correspondence of structure or exploit the external side with a gap of 10 cm at least for plumping thickness. Table 5 - Outcomes for insulation after thermal, impact and economic analysis λ [ W/(m K)]
φ [h]
supply [€/ m3]
laying [ €/ m2]
EE [MJ]
CF [kgCO2eq]
X3 - EPS
0,035
19,96
110,00
39,00
386,60
13,255
X5 - mineral wool
0,040
19,82
150,00
70,00
197,65
17,83
X6 - aerogel
0,013
0,33
430,00
90,00
243,18
3,37
The type of insulation that better meets the demands and benchmarks for minimizing thermal, economic and environmental is aerogel (X6), then polyurethane foam EPS (X3) and mineral wool (X5). Aerogel represents the best balance, but it shows significant results only in thermal and impact behavior, even if today its costs are prohibitive; polyurethane foam and mineral wool give similar thermal performances, but the first material is cheaper because of its market deployment, and the second show
4
a low environmental impact in embodied energy value. This selection was the basis for all further analysis of technology nodes and the types of masonry. After insulation choosing and locating, the four combinations matrix was verified in order to control the formation of condensation and the heat flow in thermal bridges and to provide data to other areas of the research (functional, seismic, structural one) or rather the design and sizing of the technological element and the architectural and functional conformations in case of application on residential buildings.
Figure 3 - Test on a X5KYa combination
First of all it was made a 3D model of different kind of masonry, selected from the most spread in Italian building stock from 1950. These performances allow to understand the best combination depending on the position of the insulation, according the four combinations explained in methodology. The result leads to the concept of an external "coat" (KXY), which, in addition to isolate, allows the complete precast of the panel and a fast installation on site, with related economic benefits (Figure 3). About the intervention on the internal side of the existing masonry, it was adopted the same disposition with a mirrored stratigraphy compared to the outside one. The thermal performance about transmittance are performing and in order to remedy the condensation two states of vapor barriers were introduced sealing the xlam and insulation package. To illustrate the procedure this paper presents the results about a selection of three significant elements: panel xlam (K), mineral wool insulation (X5) and plastered masonry on solid brick (Ya). This stratigraphy has been chosen because it shows the worst values of temperature and humidity between those obtained with the combinations and with the selected materials, and also it has been studied since this type in fact it is the most widespread type of masonry in Italian building stock and it’s the same of the case study. 2.4. Characterization and test on a prototype connected to a brick masonry Since the architectural design the building envelope is made thinking not only to aesthetic but also to performance (in particular to thermal type), an hygrothermic test was carried out using a hotbox with thermal guard (Figure 4).
Figure 4 - Hotbox schema: 1 Metering box; 2 Hot room with guard; 3 Cold room; 4 Prototype
5
A prototype of the technology has been built using a xlam panel (1m * 0,8m * 0,12m) that has been applied to a brick masonry and, according to the combination XYK, tests were performed using two insulation, mineral wool and polyurethane foam EPS. The device allowed the characterization of the thermal behavior of the inhomogeneous structure by calculating, in conditions of steady-state, the thermal transmittance (U), and the thermal resistance (R). The measurement equipment is able to maintain a constant temperature difference between the faces of the sample for a period of time sufficiently long to permit to determine the stationary state of the thermal flow and consequent as to allow to perform all the measurements with the required accuracy. The prototype was placed between a hot room (20°C) and a cold room (at -5°C), subsequently a metering box was applied where the electrical resistances dissipate a measurable power. Applying a series of thermocouples on the inner and outer surfaces of each stratification of the prototype, it was assessed by measuring the heat flow difference of the temperatures on the walls. In this case the test lasted three days to reach the stationarity of the thermal flow and it return very similar values of thermal transmittance to those derived from simulations, with a standard deviation of 0,5%. 3. Application on retrofitting a case study The obtained data from analysis of materials and from test on built component were verified on a case study that would need to energetic and seismic refurbishment. It is a multifamily building of Fifties located in Venice, composed of five levels, with entrance on the ground floor, three levels with 6 residential units and boxes in the last level. The structure is reinforced concrete with masonry envelope made by hollow brick without insulation and single-glazed windows; a high temperature traditional boiler constitutes the central heating system for heating and domestic hot water (DHW) providing, with that has radiators as terminals in the individual apartments. The energy performance are therefore very low but it’s similar in the majority of existing buildings of the period that also represent a serious structural problem for the safety and seismic (Table 6). Table 6 - Case study characteristics Building typology Location Climatic zone Heating degree days: Gross volume Heated area Dispersing area Glazing area Floor net height Footprint area on ground S/V
multifamily Venice E 2.345 1806,71 475,92 1068,16 53,30304 2,7 185 0,591
m3 m2 m2 m2 m m2
3.1. Three possible scenario analysis The aim of the analysis is to apply the technological system in xlam so as to achieve the minimum requirements of energy performance set by Italian law. Increasing complexity and degree of improvement and investment, three scenarios were created with possible measures in the building in order to compare the results from the point of view of reduction of energy needs, environmental impact and cost-effectiveness (Figure 5).
Figure 5 - Measures schema and identification fo possible scenario
6
After simulation, some considerations are presented (Table 7). In case #1 heating system doesn’t change and intervention is the installation of the technological system in xlam inserting mineral wool as insulation, like in the X5KYa combination; also all existing windows are replaced with with a low-energy double layer ones, according to Italian law requirements. The energy requirement drops to 121.607 kWh/m²a, so a Italian energy E class; the total cost of the intervention is equal to about € 150’000,000. Compared with the previous case, in the case #2 the generator is replaced and a condensing boiler is installed, maintaining existing terminals in order to not disrupt the existing situation. Obviously the energy performance improve and cost increase: energy need amounted to 107.833 kWh/m²a, D class, and the total cost is about 200’000,000 €. Finally, the case #3 is designed like a standard intervention for improving energy in a multifamily building: in the external envelope windows are replaced with low-emissivity glass and a insulation “coat” in mineral wool is placed. Technologies measures consist in the installation of a condensing boiler and a system of solar panels for DHW and photovoltaic panels. With the same overall cost of the intervention of the case #2, energy improvement needs 84.400 kWh/m²a, in C class, thus reaching the benchmark of 87.975 kWh / m²a, required by energetic Italian law. Table 7 - Energetic performances Case #0
Case #1
Case #2
Case #3
EPi - Total heating need
kWh/m²a
153,601
83,388
74,359
76,044
EPacs - Total acs need
kWh/m²a
37,875
38,219
33,475
8,356
Epgl – Global energy need
kWh/m²a
191,476
121,607
107,833
84,400
F
E
D
C
50,225
31,831
20,745
17,440
Energy Class KgCO2/m2a
CO2 emissions
The environmental impacts in the proposals are interesting and express the same concepts in thermal analysis: between the traditional intervention of retrofitting and the insertion of the xlam component, the reduction of greenhouse gases emissions are equivalent and in any case they have decreased compared to the existing situation. Moreover Embodied Energy calculation (Table 8) of each intervention on the external envelope shows that the mineral wool coat has values which are four times less of the new component, precisely because the last case presents the use of a structural wood panel. Table 8 - Embodied Energy calculation Material Case #2
thickness (m)
specific weight (kg/m3)
weight kg/m2
embodied energy (MJ)
(MJ*kg)
Plasterborad
0,02
2000
40
1,00
40,00
Mineral wool
0,10
100,00
10
16,80
168,00
Xlam panel
0,10
480
48
14,00
total embodied energy
Case #3
672,00 880,00
Plasterborad
0,02
2000
40
1,00
40,00
Mineral wool
0,10
100,00
10
16,80
168,00
total embodied energy
208,00
By comparing the costs and benefits of interventions, it’s significant the cost savings of energy needs, compared to the current € 8,201.62 per year: in all three scenarios, the costs are almost halved, with a maximum reduction of 44% in case #3 due to renewable energy contribution. Counting the costs, deductions and actualized savings, the payback time remains very high, about 50 to 60 years. However, all scenarios can take advantage by national tax relief of 65% and 50%, allowing to write off the cost of the intervention in 10 years and consequently significantly reduce the time to return in 30 to 40 years (Table 9). Table 9 - Measure cost and time return Cost and measure
Case #1
Case #2
Cost for whole system (xlam + mineral wool)
€ 136.424,00
€ 136.424,00
Cost for windows replacement
€ 13.325,76
€ 13.325,76
Cost for mineral wool insulation
Case #3
€ 42.000,00 € 70.000,00
Cost for condensation boiler substitution
€ 70.000,00
Cost for photovoltaic system
€ 86.400,00
Cost for solar thermal system
€ 18.400,00
Total without tax relief
€ 149.749,76
€ 219.749,76
€ 216.800,00
Total with tax relief
€
97.337,34
€ 142.837,34
€ 127.960,00
Cost of energy bills annual
€
5.208,47
€
€
4.618,79
3.615,09
7 Time return without tax relief
-50 years
-61 years
-47 years
Time return with tax relief
-33 years
-40 years
-28 years
3.2. Outcomes on different scenario In brief the xlam system installation gives a very good result, improving energy efficiency and safety in case of earthquake (case #1). However it can see that this technology is very effective and convenient only if it is combined with other measures: in fact, comparing the results of the intervention target on energy efficiency (case #3), the investment is similar although the needs reduction is considerably higher, but the cost of energy bills would still half. So this new technological system (like in case #2) aims to seismic and static requalification of Italians buildings and also can be the drivers of the whole building improvements with energy, aesthetic (with the façade design) and functional measures, reducing the overall costs with also tax relief. 4. Conclusions Therefore, the research has achieved several objectives regarding environmental, economic and energy issues. The panel with new technological system allows to achieve good results in terms of thermal performance of selected insulations, which exceed the normative standard for efficiency in existing buildings. Furthermore it is a versatile system because it allows different solutions to reduce size and heaviness and different kind of assembly configurations within and outside of the building according to the needs and constraints. The analysis of environmental impacts returns low values due to the use of natural materials (wood, mineral wool), to the low mass (aerogel) or an optimized production chain (polyurethane). The thermal tests on the prototype of masonry and xlam proved and validated the simulated values and return the behavior of an existing masonry subjected to insulation and connected to xlam panel, obtaining a null condensation. The scenarios of the case study demonstrate the economic feasibility and the convenience of the component only if inserted in a program of general redevelopment and retrofitting of the building. Further research can be extended to several different scientific areas; with regard to buildings physics analysis of the thermal points could be strictly deepened, or it could expand the research to various residential typologies in order to obtain output from buildings with different s/v index and with different number of residential units, trying to reach the objective of an anti-seismic building and simultaneously a NZEB (nearly Zero Energy Building), a building capable of a balance between energy consumed and energy produced close to zero. Therefore, research has achieved several objectives regarding to environmental and energy issues: the proposed technological system allows different solutions and assembly configurations, designed to reduce size and weight but always ensuring the minimum law requirement: the combinations set for insulation allows in fact comparable performances and variations according to existing building typology to intervene on. References UNI TS 11300 - Normativa tecnica di riferimento sul risparmio energetico e la certificazione energetica degli edifici D.Lgs.192/2005 e s.m. - Attuazione della direttiva 2002/91/CE relativa al rendimento energetico nell'edilizia DPR 59/09 – Norme attuative del D.Lgs.192/2005 UNI EN ISO 6946/2008 - Componenti ed elementi per l’edilizia. Resistenza termica e trasmittanza termica. Metodo di calcolo UNI 13788:2003 - Prestazione igrotermica dei componenti e degli elementi per edilizia; verifica condensa interstiziale UNI EN ISO 14683/2008 - Ponti termici, consente di calcolare il valore della trasmittanza termica lineica Ψk; calcolare i flussi termici attraverso metodi semplificati in corrispondenza alle giunzioni tra elementi di edifici, ma non si applica a ponti termici associati ai telai di porte e finestre o a facciate continue UNI EN ISO 10211/2011 - Ponti termici, calcolo flusso termico bidimensionale e tridimensionale ISO 140400 - Passaggi per lo sviluppo della procedura del Life Cycle Assessment ISO 14040:2006 Environmental Management – Life Cycle Assessment – Principles and Framework e ISO 14044:2006 Environmental Management – Life Cycle Assessment – Requirements and Guidelines ISO EN 9001 - Sistemi qualità - Modello per l’assicurazione della qualità nella progettazione, sviluppo, fabbricazione installazione ed assistenza Dl 83/2012 (Art. 11) - Detrazioni per interventi di ristrutturazione e di efficientamento energetico Dl 63/2013(Art. 14) - Detrazioni fiscali per interventi di efficienza energetica ASTM C-236, 1993. Standard Test Method for Steady-State Thermal Performance of Building Assemblies by Means of a guarded Hot Box. ASTM C-1199, 1999. Standard Test Method for Measuring the Steady-State Thermal Trasmittance of Fenestration Systems Using Hot Box Methods. UNI EN ISO 8990. Determinazione delle proprietà di trasmissione termica in regime stazionario: metodo della doppia camera calibrata e della doppia camera con anello di guardia. M. Zobec, M. Colombari, F. Peron, P. Romagnoni, Hot box tests for building envelope condensation assessment, Proceedings of th 3rd European Conference on Energy Performance & Indoor Climate in Buildings, Lyon (F), 23 -26 October 2002
