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Experimental and numerical thermal analysis of a balcony board with integrated glass fibre reinforced polymer GFRP elements
Energy and Buildings 39 (2007) 76–81 www.elsevier.com/locate/enbuild
Experimental and numerical thermal analysis of a balcony board with integrated glass fibre reinforced polymer GFRP elements Karim Ghazi Wakili *, Hans Simmler, Thomas Frank Swiss Federal Laboratories for Materials Testing and Research (Empa), CH-8600 Duebendorf, Switzerland Received 30 March 2006; received in revised form 3 May 2006; accepted 4 May 2006
Abstract The thermal behaviour of a balcony board with integrated glass fibre reinforced plastic (GFRP) elements replacing the compression reinforcement rods, is investigated by means of measurement as well as numerical analysis. For this reason a specimen consisting of an externally insulated brick wall and a representative part of a balcony is tested under a steady state temperature gradient of 30 K in a guarded hot box. Additionally to the normative requirements, temperature sensors are placed on critical sites within the construction, prior to the pouring of cement, to help the verification of the numerical analysis carried out simultaneously. Measured and calculated results are compared and some numerical parameter studies are carried out to quantify the advantage of glass fibre reinforced plastic elements over conventional balcony boards from a thermal point of view. # 2006 Elsevier B.V. All rights reserved. Keywords: Balcony board; Thermal analysis; Linear thermal transmittance; Reinforcement rods; Hot box
1. Introduction From the point of view of energy saving and the problem of moisture condensation at inner surfaces, a balcony board represents generally one of the weakest elements of the whole building envelope. This is due to the fact that a balcony board penetrates the building envelope and by doing so connects the internal with the external environment. In other words it results in a thermal bridge which can be quantified by an additional heat loss and by a reduction of the temperature at the inner corners such as the floor wall and more dramatically the ceiling wall junctions. This may cause mould growth and condensation problems if adequate measures are not taken. A number of thermal bridge catalogues [1–4] assume for the conventional reinforced concrete balcony board a homogeneous slab (Fig. 1) to which a thermal conductivity of 1.80–2.0 W/(m K) is attributed which is higher than 1.0 W/(m K), the value for cement mortar, homogenising hereby the effect of the metallic reinforcement. This is an admissible approximation and the steel reinforcements need not to be modelled explicitly when calculating a two- or three-dimensional temperature distribution.
* Corresponding author. Tel.: +41 44 823 4763; fax: +41 44 423 4009. E-mail address: [email protected] (K. Ghazi Wakili). 0378-7788/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2006.05.002
This is not the case when the balcony board is interrupted by a thermal break, e.g. insulation material, and the two halves are interconnected by means of tensile, compression and shear steel rods fulfilling the compulsory static requirements (Fig. 2). Hence, the diameter and the number of these rods per length of the balcony board have to be known and taken into consideration to determine the additional heat loss as well as the temperature reduction at the inner corners. The remaining reinforcement rods which do not cross the thermal break can be considered implicitly as mentioned above. The present paper reports on the experimental and numerical investigation of a newly developed balcony board with a thermal break incorporating glass fibre reinforced polymer GFRP elements. These are meant to reduce the additional heat loss by replacing the compression steel rods and enabling a reduction in the diameter of the tensile steel rods without deteriorating the static strength of the board. For this purpose a representative size of the above balcony board was built into an externally insulated brick wall with an undisturbed U-value of 0.20 W/(m K). The whole wall with the balcony board was put into a guarded hot box and submitted to an air to air temperature gradient of approximately 30 K. The measured steady state (equilibrium) temperatures at critical sites of the detail were compared to calculated values obtained by means of a three-dimensional numerical analysis of an appropriate model. Based on the comparison of the results of the two methods a
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
77
Fig. 1. Model of a conventional balcony board (a continuous steel reinforced concrete slab).
Fig. 2. Model of a balcony board interrupted by a thermal break.
numerical parameter study was carried out to compare different variations of the investigated system with other more conventional types of balcony boards.
An overview of the thermocouple positions is given in Fig. 4. Subsequently, cement was poured into the formwork. In a second stage a brick wall was built up and the balcony board described above was placed at mid height as shown in Fig. 5a and b where the dimensions are indicated as well. A layer of 10 mm of inner rendering was applied to the warm side of the brick wall and the whole specimen was held in a conditioned room at 20 8C and 50% relative humidity for a period of 3 months to achieve equilibrium moisture content. Subsequently, an insulation layer of 160 mm of expanded polystyrene was added to the outer side of the wall. Further thermocouples were placed between the brick wall and the insulation layer (Fig. 4) to support the verification of the numerical analysis. A layer of
2. Experimental set up The specimen used for the measurement in the guarded hot box was built in two stages. At a first stage a representative part of the balcony board including the GFRP elements was assembled within a wooden formwork. Fig. 3 shows the thermal break, the reinforcement steel rods (tensile and shear) and some of the thermocouples. The latter were fixed with glue on critical sites on both the cold and the warm side of the system.
Fig. 3. Thermal break, GFRP elements, the steel rods and the embedded thermocouples prior to the pouring of cement.
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K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
3. Numerical analysis
Fig. 4. Position of the thermocouples (number and nomenclature in Table 2).
10 mm of outer rendering was applied to the outer surface of the insulation. The specimen was built into the hot box after an additional week in the mentioned climatic condition. This enabled the outer rendering to reach equilibrium moisture content too. A complete description of the hot box apparatus used for the present study is given in both [5,6]. In order to accommodate the horizontal dimensions of the balcony board, an additional insulation frame was put around the specimen and the baffles were driven back on both sides to guarantee a sufficient uniformity of the air flow velocity, i.e. uniformity of heat transfer coefficients.
The numerical analysis was carried out by TRISCO1, a program to calculate the three-dimensional steady state temperature distribution and heat transfer in a rectangular grid [7]. Details of the model used to simulate the hot box measurement are given as well in Fig. 4. The thermal conductivities of the materials and the imposed boundary conditions on both sides of the specimen are summarized in Table 1. The equivalent value of the perforated brick leq,brick was determined by a preliminary two-dimensional thermal analysis of the undisturbed homogeneous wall using the thermal conductivity of the bulk clay (l = 0.445 W/(m K) according to its density of r = 1680 kg/m3) and the perforation geometry (Fig. 6). The equivalent thermal conductivity for the different air layers was calculated automatically in an iterative procedure by the calculation program in accordance to the CEN standard [8]. The calculations were done by choosing an appropriate grid [9] resulting in approximately 360,000 nodes for the three-dimensional and 14,000 nodes for the preliminary two-dimensional calculation. The additional thermal heat loss, in other words the linear thermal transmittance C due to the thermal bridges, was calculated according to ref. [10]. In order to compare this system of balcony board with conventional balconies the following two systems were also analysed numerically. First, an ordinary balcony with a continuous concrete slab (Fig. 1) representing the most common and conventional case was analysed and its linear thermal
Fig. 5. Wall prior to being externally insulated with balcony board: (a) view from the room side and (b) view from the cold side (sizes in mm). Table 1 Thermal conductivity of the materials and the imposed boundary conditions on both sides of the specimen for the numerical calculations Material
Thermal conductivity (W/(m K))
Material
Thermal conductivity (W/(m K))
Brick (leq,brick) Brick (bulk) Outer rendering Wall insulation Concrete Stainless steel Flooring Floor insulation
0.254 0.445 0.87 0.040 1.80 25.0 1.50 0.034
Thermal break Inner rendering Mortar Acoustic insulation GFRP* Insulation frame Air layers
0.040 0.70 1.0 0.029 0.40 0.035 CEN rules [8]
Boundary conditions
Air temperature (8C)
Heat transfer coefficient (W/(m2 K))
Cold side Room side
8.0 +22.1
10.0 7.7
*
Measured by means of a heat flow meter apparatus at Empa.
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
79
Fig. 6. The perforated brick: (a) perforation geometry and (b) the respective model for the preliminary two-dimensional calculation (because of symmetry only the half brick was modelled).
transmittance determined. Second, a balcony with a concrete slab interrupted by a thermal break was modelled, the two concrete parts being interconnected by steel bars with diameters dimensioned to be statically equivalent to the investigated system (Fig. 2). The linear thermal transmittance of this system was determined as well. 4. Results and discussions An evaluation of the experimental and the numerical thermal analysis of the specimen is done by comparing measured and calculated temperatures. A summary hereof is given in Table 2. Having in mind that a model assumes ideal thermal contact between different materials, a homogeneous value of the heat transfer coefficient over the surface on both sides of the wall and a rectangular shape for the steel rods (maintaining the cross-section), the correspondence between measurement and calculation can be judged as quite satisfactory. Further evidence for the good agreement between calculated and measured results is given in Fig. 7a and b where the temperature distribution on the room side surface of the wall is represented as an infrared picture and a calculated diagram, respectively. The temperature step between two adjacent grey shades is 0.1 K
for both pictures. It is not the value of the temperature itself but the differences occurring on the surface that is important as the infrared camera has always a shift. The rising warm air flow during the shooting of the infrared picture is clearly detectable at the lower part of Fig. 7a but does not appear in Fig. 7b as fluid dynamics are not included in the mentioned calculation program. Based on these results two variations of the investigated balcony board system were analysed numerically by adjusting the above model (Table 3). These together with the investigated system represent three balcony boards with three different static strengths. For comparison of the thermal behaviour equivalent balcony boards without GFRP elements were analyzed too. Here, equivalent is meant in the static sense, i.e. capable of bearing the same loads. The major parameter being the total cross-section of each type of the steel rods (tensile, shear and compression). Table 3 shows the respective cross-sections through the thermal break for all six systems. Finally, the conventional balcony board without thermal break was also analyzed numerically representing the most unfavourable case from a thermal point of view. A summary of the linear thermal transmittances of the investigated systems are given in Table 3 and compared to the
Table 2 Summary of the measured and calculated temperature values at different sites Thermocouples number and nomenclature (for position, see Fig. 2) Air temperature room side Air temperature cold side GFRP cold side (KE1, KE2, KE3 and KE4) GFRP room side (WE1, WE2, WE3 and WE4) Thermal break cold side (KD1, KD2, KD3 and KD4) Thermal break room side (WD1, WD2, WD3 and WD4) Tensile rod/thermal break cold side (KS1, KS2 and KS3) Tensile rod/thermal break room side (WS1, WS2 and WS3) In the concrete slab cold side (KB1, KB2 and KK1) in the concrete slab room side (WB1, WB2 and WK1) Between brick wall and insulation (UD1, UD2, UD3 and UD4) Wall surface, cold side (KO1, KO2,KO3, KO4, KO5, KO6, KO7 and KO8) Wall surface, room side (WO1, WO2,WO3, WO4, WO5, WO6, WO7 and WO8) a
Damaged thermocouple.
Measured temperature (8C)
Calculated temperature (8C)
8.0 +22.1 a
16.9 5.6 17.7 4.2 16.6 7.4 19.6 18.4
4.9 17.1 5.8 17.7 4.7 17.1 7.5 19.6 17.7
5.0 17.1 5.6 17.5 4.9 16.4 7.7 20.5 17.6
4.9 17.0 5.8 17.7 – – – – 17.6
7.5 7.6
7.5 7.9
7.7 7.9
7.6 7.9
21.4 21.0
21.4 21.1
21.4 20.9
21.0 21.0
8.0 +22.1 4.7 < u < 3.7 15.5 < u < 16.5 5.0 < u < 4.5 16.5 < u < 17.5 3.5 < u < 2.5 15.5 < u < 16.0 7.6 < u < 7.8 19.8 < u < 21.0 17.2 < u < 17.6 7.4 < u <
7.3
20.9 < u < 21.2
80
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
Fig. 7. Temperature distribution on the room side of the wall: (a) infrared picture and (b) three-dimensional steady state calculation. Table 3 Calculated results of the numerical analysis for all the investigated balcony systems (the main system being the measured one)
The design value of the shear load resistance is 41.1, 73.0 and 132.8 kN/m for Variation 1, Main system and Variation 2, respectively. The values for the bending resistance in the same order are 12.3, 49.1 and 85.4 kNm/m.
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
transmittance values of the conventional concrete slab and the slab with a thermal break, respectively. 5. Conclusions A novel system of thermally interrupted balcony boards containing glass fibre reinforced elements analyzed both experimentally and numerically resulted to be a thermally more favourable solution than its statically equivalent conventional boards. This was achieved by using the glass fibre reinforced plastic elements which replace the compression rods and simultaneously allow a reduction of the diameter of the tensile rods, which in turn reduces the additional heat loss, i.e. the linear thermal transmittance of the whole building detail. Acknowledgments The authors thank Rene´ Menet for building the test specimen, Stefan Carl and Rudi Blessing for the execution of the hot box measurement. The authorization for publication of the measured and calculated data given by SFS Locher AG Switzerland is greatly acknowledged.
81
References [1] Minimising Thermal Bridging in New Dwellings, Chapter 14, Good Practice Guide 174, British Department of the Environment, Best Practice Programme, 1996. [2] Wa¨rmebru¨ckenkatalog, energieschweiz, Swiss Federal Office of Energy, Bern, 2003, pp. 20–23 (in German). [3] EUROKOBRA, Computer Based Atlas of Building Details, EMPA and Swiss Federal Office of Energy, 2002. [4] Th.-E. Re´gle, Re´glementation Thermique, CSTB, 2000 (in French). [5] T. Nussbaumer, R. Bundi, C. Tanner, H. Muehlebach, Thermal analysis of a wooden door system with integrated vacuum insulation panels, Energy and Buildings 37 (2005) 1107–1113. [6] T. Nussbaumer, K. Ghazi Wakili, C. Tanner, Experimental and numerical investigation of the thermal performance of a protected vacuuminsulation system applied to a concrete wall, Applied Energy 83 (2006) 841–855. [7] TRISCO, 3D Steady State Heat Transfer Computer Program, Physibel, 9990 Maldegem, Belgium, Version 10.0w, 2003. [8] EN ISO 10077-2, Thermal performance of windows, doors and shutters— calculation of thermal transmittance, part 2. Numerical methods for frames, 2003. [9] EN ISO 10211-1, Thermal bridges in building construction—heat flows and surface temperatures, part 1. General calculation methods, 1996. [10] EN ISO 10211-2, Thermal bridges in building construction—heat flows and surface temperatures, part 2. Linear thermal bridges, 2001.
Experimental and numerical thermal analysis of a balcony board with integrated glass fibre reinforced polymer GFRP elements Karim Ghazi Wakili *, Hans Simmler, Thomas Frank Swiss Federal Laboratories for Materials Testing and Research (Empa), CH-8600 Duebendorf, Switzerland Received 30 March 2006; received in revised form 3 May 2006; accepted 4 May 2006
Abstract The thermal behaviour of a balcony board with integrated glass fibre reinforced plastic (GFRP) elements replacing the compression reinforcement rods, is investigated by means of measurement as well as numerical analysis. For this reason a specimen consisting of an externally insulated brick wall and a representative part of a balcony is tested under a steady state temperature gradient of 30 K in a guarded hot box. Additionally to the normative requirements, temperature sensors are placed on critical sites within the construction, prior to the pouring of cement, to help the verification of the numerical analysis carried out simultaneously. Measured and calculated results are compared and some numerical parameter studies are carried out to quantify the advantage of glass fibre reinforced plastic elements over conventional balcony boards from a thermal point of view. # 2006 Elsevier B.V. All rights reserved. Keywords: Balcony board; Thermal analysis; Linear thermal transmittance; Reinforcement rods; Hot box
1. Introduction From the point of view of energy saving and the problem of moisture condensation at inner surfaces, a balcony board represents generally one of the weakest elements of the whole building envelope. This is due to the fact that a balcony board penetrates the building envelope and by doing so connects the internal with the external environment. In other words it results in a thermal bridge which can be quantified by an additional heat loss and by a reduction of the temperature at the inner corners such as the floor wall and more dramatically the ceiling wall junctions. This may cause mould growth and condensation problems if adequate measures are not taken. A number of thermal bridge catalogues [1–4] assume for the conventional reinforced concrete balcony board a homogeneous slab (Fig. 1) to which a thermal conductivity of 1.80–2.0 W/(m K) is attributed which is higher than 1.0 W/(m K), the value for cement mortar, homogenising hereby the effect of the metallic reinforcement. This is an admissible approximation and the steel reinforcements need not to be modelled explicitly when calculating a two- or three-dimensional temperature distribution.
* Corresponding author. Tel.: +41 44 823 4763; fax: +41 44 423 4009. E-mail address: [email protected] (K. Ghazi Wakili). 0378-7788/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2006.05.002
This is not the case when the balcony board is interrupted by a thermal break, e.g. insulation material, and the two halves are interconnected by means of tensile, compression and shear steel rods fulfilling the compulsory static requirements (Fig. 2). Hence, the diameter and the number of these rods per length of the balcony board have to be known and taken into consideration to determine the additional heat loss as well as the temperature reduction at the inner corners. The remaining reinforcement rods which do not cross the thermal break can be considered implicitly as mentioned above. The present paper reports on the experimental and numerical investigation of a newly developed balcony board with a thermal break incorporating glass fibre reinforced polymer GFRP elements. These are meant to reduce the additional heat loss by replacing the compression steel rods and enabling a reduction in the diameter of the tensile steel rods without deteriorating the static strength of the board. For this purpose a representative size of the above balcony board was built into an externally insulated brick wall with an undisturbed U-value of 0.20 W/(m K). The whole wall with the balcony board was put into a guarded hot box and submitted to an air to air temperature gradient of approximately 30 K. The measured steady state (equilibrium) temperatures at critical sites of the detail were compared to calculated values obtained by means of a three-dimensional numerical analysis of an appropriate model. Based on the comparison of the results of the two methods a
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
77
Fig. 1. Model of a conventional balcony board (a continuous steel reinforced concrete slab).
Fig. 2. Model of a balcony board interrupted by a thermal break.
numerical parameter study was carried out to compare different variations of the investigated system with other more conventional types of balcony boards.
An overview of the thermocouple positions is given in Fig. 4. Subsequently, cement was poured into the formwork. In a second stage a brick wall was built up and the balcony board described above was placed at mid height as shown in Fig. 5a and b where the dimensions are indicated as well. A layer of 10 mm of inner rendering was applied to the warm side of the brick wall and the whole specimen was held in a conditioned room at 20 8C and 50% relative humidity for a period of 3 months to achieve equilibrium moisture content. Subsequently, an insulation layer of 160 mm of expanded polystyrene was added to the outer side of the wall. Further thermocouples were placed between the brick wall and the insulation layer (Fig. 4) to support the verification of the numerical analysis. A layer of
2. Experimental set up The specimen used for the measurement in the guarded hot box was built in two stages. At a first stage a representative part of the balcony board including the GFRP elements was assembled within a wooden formwork. Fig. 3 shows the thermal break, the reinforcement steel rods (tensile and shear) and some of the thermocouples. The latter were fixed with glue on critical sites on both the cold and the warm side of the system.
Fig. 3. Thermal break, GFRP elements, the steel rods and the embedded thermocouples prior to the pouring of cement.
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K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
3. Numerical analysis
Fig. 4. Position of the thermocouples (number and nomenclature in Table 2).
10 mm of outer rendering was applied to the outer surface of the insulation. The specimen was built into the hot box after an additional week in the mentioned climatic condition. This enabled the outer rendering to reach equilibrium moisture content too. A complete description of the hot box apparatus used for the present study is given in both [5,6]. In order to accommodate the horizontal dimensions of the balcony board, an additional insulation frame was put around the specimen and the baffles were driven back on both sides to guarantee a sufficient uniformity of the air flow velocity, i.e. uniformity of heat transfer coefficients.
The numerical analysis was carried out by TRISCO1, a program to calculate the three-dimensional steady state temperature distribution and heat transfer in a rectangular grid [7]. Details of the model used to simulate the hot box measurement are given as well in Fig. 4. The thermal conductivities of the materials and the imposed boundary conditions on both sides of the specimen are summarized in Table 1. The equivalent value of the perforated brick leq,brick was determined by a preliminary two-dimensional thermal analysis of the undisturbed homogeneous wall using the thermal conductivity of the bulk clay (l = 0.445 W/(m K) according to its density of r = 1680 kg/m3) and the perforation geometry (Fig. 6). The equivalent thermal conductivity for the different air layers was calculated automatically in an iterative procedure by the calculation program in accordance to the CEN standard [8]. The calculations were done by choosing an appropriate grid [9] resulting in approximately 360,000 nodes for the three-dimensional and 14,000 nodes for the preliminary two-dimensional calculation. The additional thermal heat loss, in other words the linear thermal transmittance C due to the thermal bridges, was calculated according to ref. [10]. In order to compare this system of balcony board with conventional balconies the following two systems were also analysed numerically. First, an ordinary balcony with a continuous concrete slab (Fig. 1) representing the most common and conventional case was analysed and its linear thermal
Fig. 5. Wall prior to being externally insulated with balcony board: (a) view from the room side and (b) view from the cold side (sizes in mm). Table 1 Thermal conductivity of the materials and the imposed boundary conditions on both sides of the specimen for the numerical calculations Material
Thermal conductivity (W/(m K))
Material
Thermal conductivity (W/(m K))
Brick (leq,brick) Brick (bulk) Outer rendering Wall insulation Concrete Stainless steel Flooring Floor insulation
0.254 0.445 0.87 0.040 1.80 25.0 1.50 0.034
Thermal break Inner rendering Mortar Acoustic insulation GFRP* Insulation frame Air layers
0.040 0.70 1.0 0.029 0.40 0.035 CEN rules [8]
Boundary conditions
Air temperature (8C)
Heat transfer coefficient (W/(m2 K))
Cold side Room side
8.0 +22.1
10.0 7.7
*
Measured by means of a heat flow meter apparatus at Empa.
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
79
Fig. 6. The perforated brick: (a) perforation geometry and (b) the respective model for the preliminary two-dimensional calculation (because of symmetry only the half brick was modelled).
transmittance determined. Second, a balcony with a concrete slab interrupted by a thermal break was modelled, the two concrete parts being interconnected by steel bars with diameters dimensioned to be statically equivalent to the investigated system (Fig. 2). The linear thermal transmittance of this system was determined as well. 4. Results and discussions An evaluation of the experimental and the numerical thermal analysis of the specimen is done by comparing measured and calculated temperatures. A summary hereof is given in Table 2. Having in mind that a model assumes ideal thermal contact between different materials, a homogeneous value of the heat transfer coefficient over the surface on both sides of the wall and a rectangular shape for the steel rods (maintaining the cross-section), the correspondence between measurement and calculation can be judged as quite satisfactory. Further evidence for the good agreement between calculated and measured results is given in Fig. 7a and b where the temperature distribution on the room side surface of the wall is represented as an infrared picture and a calculated diagram, respectively. The temperature step between two adjacent grey shades is 0.1 K
for both pictures. It is not the value of the temperature itself but the differences occurring on the surface that is important as the infrared camera has always a shift. The rising warm air flow during the shooting of the infrared picture is clearly detectable at the lower part of Fig. 7a but does not appear in Fig. 7b as fluid dynamics are not included in the mentioned calculation program. Based on these results two variations of the investigated balcony board system were analysed numerically by adjusting the above model (Table 3). These together with the investigated system represent three balcony boards with three different static strengths. For comparison of the thermal behaviour equivalent balcony boards without GFRP elements were analyzed too. Here, equivalent is meant in the static sense, i.e. capable of bearing the same loads. The major parameter being the total cross-section of each type of the steel rods (tensile, shear and compression). Table 3 shows the respective cross-sections through the thermal break for all six systems. Finally, the conventional balcony board without thermal break was also analyzed numerically representing the most unfavourable case from a thermal point of view. A summary of the linear thermal transmittances of the investigated systems are given in Table 3 and compared to the
Table 2 Summary of the measured and calculated temperature values at different sites Thermocouples number and nomenclature (for position, see Fig. 2) Air temperature room side Air temperature cold side GFRP cold side (KE1, KE2, KE3 and KE4) GFRP room side (WE1, WE2, WE3 and WE4) Thermal break cold side (KD1, KD2, KD3 and KD4) Thermal break room side (WD1, WD2, WD3 and WD4) Tensile rod/thermal break cold side (KS1, KS2 and KS3) Tensile rod/thermal break room side (WS1, WS2 and WS3) In the concrete slab cold side (KB1, KB2 and KK1) in the concrete slab room side (WB1, WB2 and WK1) Between brick wall and insulation (UD1, UD2, UD3 and UD4) Wall surface, cold side (KO1, KO2,KO3, KO4, KO5, KO6, KO7 and KO8) Wall surface, room side (WO1, WO2,WO3, WO4, WO5, WO6, WO7 and WO8) a
Damaged thermocouple.
Measured temperature (8C)
Calculated temperature (8C)
8.0 +22.1 a
16.9 5.6 17.7 4.2 16.6 7.4 19.6 18.4
4.9 17.1 5.8 17.7 4.7 17.1 7.5 19.6 17.7
5.0 17.1 5.6 17.5 4.9 16.4 7.7 20.5 17.6
4.9 17.0 5.8 17.7 – – – – 17.6
7.5 7.6
7.5 7.9
7.7 7.9
7.6 7.9
21.4 21.0
21.4 21.1
21.4 20.9
21.0 21.0
8.0 +22.1 4.7 < u < 3.7 15.5 < u < 16.5 5.0 < u < 4.5 16.5 < u < 17.5 3.5 < u < 2.5 15.5 < u < 16.0 7.6 < u < 7.8 19.8 < u < 21.0 17.2 < u < 17.6 7.4 < u <
7.3
20.9 < u < 21.2
80
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
Fig. 7. Temperature distribution on the room side of the wall: (a) infrared picture and (b) three-dimensional steady state calculation. Table 3 Calculated results of the numerical analysis for all the investigated balcony systems (the main system being the measured one)
The design value of the shear load resistance is 41.1, 73.0 and 132.8 kN/m for Variation 1, Main system and Variation 2, respectively. The values for the bending resistance in the same order are 12.3, 49.1 and 85.4 kNm/m.
K. Ghazi Wakili et al. / Energy and Buildings 39 (2007) 76–81
transmittance values of the conventional concrete slab and the slab with a thermal break, respectively. 5. Conclusions A novel system of thermally interrupted balcony boards containing glass fibre reinforced elements analyzed both experimentally and numerically resulted to be a thermally more favourable solution than its statically equivalent conventional boards. This was achieved by using the glass fibre reinforced plastic elements which replace the compression rods and simultaneously allow a reduction of the diameter of the tensile rods, which in turn reduces the additional heat loss, i.e. the linear thermal transmittance of the whole building detail. Acknowledgments The authors thank Rene´ Menet for building the test specimen, Stefan Carl and Rudi Blessing for the execution of the hot box measurement. The authorization for publication of the measured and calculated data given by SFS Locher AG Switzerland is greatly acknowledged.
81
References [1] Minimising Thermal Bridging in New Dwellings, Chapter 14, Good Practice Guide 174, British Department of the Environment, Best Practice Programme, 1996. [2] Wa¨rmebru¨ckenkatalog, energieschweiz, Swiss Federal Office of Energy, Bern, 2003, pp. 20–23 (in German). [3] EUROKOBRA, Computer Based Atlas of Building Details, EMPA and Swiss Federal Office of Energy, 2002. [4] Th.-E. Re´gle, Re´glementation Thermique, CSTB, 2000 (in French). [5] T. Nussbaumer, R. Bundi, C. Tanner, H. Muehlebach, Thermal analysis of a wooden door system with integrated vacuum insulation panels, Energy and Buildings 37 (2005) 1107–1113. [6] T. Nussbaumer, K. Ghazi Wakili, C. Tanner, Experimental and numerical investigation of the thermal performance of a protected vacuuminsulation system applied to a concrete wall, Applied Energy 83 (2006) 841–855. [7] TRISCO, 3D Steady State Heat Transfer Computer Program, Physibel, 9990 Maldegem, Belgium, Version 10.0w, 2003. [8] EN ISO 10077-2, Thermal performance of windows, doors and shutters— calculation of thermal transmittance, part 2. Numerical methods for frames, 2003. [9] EN ISO 10211-1, Thermal bridges in building construction—heat flows and surface temperatures, part 1. General calculation methods, 1996. [10] EN ISO 10211-2, Thermal bridges in building construction—heat flows and surface temperatures, part 2. Linear thermal bridges, 2001.