A numerical and experimental study of thermal transmittance of window systems

A NUMERICAL AND EXPERIMENTAL STUDY OF THERMAL TRANSMITTANCE OF WINDOW SYSTEMS ZHOU XU (M.ENG, NUS) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgement The author would like to thank Professor Chou Siaw Kiang for his guidance in the research Aung Khant for his assistance in the hot box instrumentation and calibration and the FLUENT simulations Yeo Khee Ho for his help in the hot box operation and many other aspects Chen Fangzhi for his advice on the hot box modification and sharing of tested thermal resistance of characterization panels His family for their support and faith in the author i Table of Contents Acknowledgement . i Table of Contents ii Summary . v List of Tables vii List of Figures viii Nomenclature x CHAPTER INTRODUCTION 1.1 Background information . 1.2 Singapore building sector 1.3 Purpose and objectives 1.4 Organization of thesis CHAPTER LITERATURE REVIEW . 2.1 Thermal transmittance . 2.2 Window frame . 2.3 Singapore ETTV . CHAPTER RESEARCH METHODOLOGY . 12 3.1 Thermal transmittance of window . 12 3.1.1 Overall area-weighted U-value . 12 3.1.2 Centre-of-glass U-value 13 3.1.3 Indoor surface heat transfer coefficient 14 3.1.4 Outdoor surface heat transfer coefficient . 16 3.1.5 Frame U-value 17 3.1.6 Frame cavity . 17 3.2 WINDOW/THERM simulation 18 3.2.1 Software 18 3.2.2 Frame profiles . 19 3.2.3 Glazing units . 23 3.2.4 Environmental conditions . 24 3.2.5 Indoor surface heat transfer coefficient for frame 26 3.3 FLUENT simulation 27 ii 3.3.1 Software 27 3.3.2 Window model . 27 3.3.3 Indoor surface heat transfer coefficient 31 3.4 Guarded hot box 31 3.4.1 Introduction of guarded hot box . 31 3.4.2 Heat balance in the hot box 34 3.4.3 Metering box wall loss and flanking loss calibration . 36 CHAPTER SIMULATION RESULTS AND DISCUSSION . 38 4.1 Centre-of-glass U-value 38 4.2 Frame U-value . 43 4.3 Overall U-value . 46 4.3.1 40S with single glazing . 46 4.3.2 45DS with double glazing units 48 4.3.3 50TT with double glazing units 53 4.4 Application in ETTV calculation 58 4.5 Surface heat transfer coefficient 61 4.5.1 Grid independence test . 61 4.5.2 Indoor convective surface heat transfer coefficient 61 CHAPTER HOT BOX ENHANCEMENT AND CALIBRATION . 63 5.1 Hot box modification and preparation 63 5.1.1 Metering box temperature control 63 5.1.2 Airflow control and measurement 65 5.1.3 Fans . 69 5.1.4 Other temperature measurement . 70 5.1.5 Characterization panel 71 5.1.6 Data logging . 72 5.1.7 Risk control . 74 5.2 Metering box wall loss and flanking loss calibration 75 CHAPTER HOT BOX TEST PROCEDURE . 78 6.1 Installation of window system . 78 6.2 Test conditions 78 iii 6.3 Stabilization and test times 79 6.4 Test data acquisition and completion 82 6.5 Calculation of thermal transmittance (U-value) 82 CHAPTER EXPERIMENTAL UNCERTAINTY ESTIMATE . 84 CHAPTER CONCLUSION . 87 8.1 Overall U-value and ETTV . 87 8.2 Guarded Hot Box 88 8.3 Recommendation . 88 Bibliography . 89 Appendices 91 Appendix A: Selected window products of AVA Globle . 91 Appendix B: Singapore weather statistics . 93 Appendix C: Position diagram of sensors . 95 Appendix D: Specifics of test specimen mounting in Surround panel . 97 Appendix E: Example calibration data 98 Appendix F: Effective conductivity – unventilated frame cavities . 100 iv Summary Highly glazed buildings are the trend in today’s architecture, but the glazing system is a weak barrier from the thermal point of view. The heat gain through window is a primary source of the cooling loads in air-conditioned buildings in the hot and humid climate of Singapore. The thermal transmittance (U-value) is currently used in the calculation of the ETTV, which is a primary criterion in the energy performance standard adopted by the Building and Construction Authority of Singapore. However, the window U-value used in the ETTV calculation is the centre-of-glass U-value of the glazing unit alone, while it should be the overall U-value of the whole window system including the centre area of the glazing unit, the edge area of the glazing unit, and the window frame. A numerical study has been undertaken on the thermal transmittance of window systems. The computations indicate that the overall U-value of common single glazing aluminium windows is to 11% higher than the centre-of-glass U-value. For common double glazing aluminium windows without thermal break and with thermally broken aluminium frames, the overall U-values are 17 to 112% and to 57% higher than the corresponding centre-of-glass U-values, respectively. The use of these overall U-values instead of the centre-of-glass U-values would enable a more accurate estimate of the energy performance of building envelopes in the standard. v In the current work, correlations have been obtained to allow building designers to easily convert the centre-of-glass U-values to the overall U-values for common window systems in Singapore. The range of environmental conditions simulated corresponds to the conditions in Singapore, which are completely different from the winter conditions in which the labelled properties are measured in North America and Europe. A Guarded Hot Box facility has been constructed in compliance with standards 1363 and 1199 of the American Society of Testing and Materials (ASTM). While the instrumentation and calibration of the instrument have been completed, the hot box is pending ASTM certification. The U-values obtained by computations will be verified with the hot box testing in later work. vi List of Tables Table 1: Thermal conductivity and emissivity of selected materials 19 Table 2: Description of selected glazing units 24 Table 3: Variation range of outdoor temperature and wind velocity 25 Table 4: Design parameters of Guard Chamber and Metering Chamber . 34 Table 5: Design parameters of Climatic Chamber 34 Table 6: Centre-of-glass U-value of Single Glazing in W/(m2.K) 38 Table 7: Centre-of-glass U-value of Double Glazing in W/(m2.K) 39 Table 8: Centre-of-glass U-value of Double Glazing Low-E 0.6 in W/(m2.K) 39 Table 9: Centre-of-glass U-value of Double Glazing Low-E 0.4 in W/(m2.K) 40 Table 10: Centre-of-glass U-value of Double Glazing Low-E 0.2 in W/(m2.K) 40 Table 11: Centre-of-glass U-value of Double Glazing Low-E 0.1 in W/(m2.K) 41 Table 12: Centre-of-glass U-value of Double Glazing Low-E 0.05 in W/(m2.K) 41 Table 13: U-value of frame 40S in W/(m2.K) . 44 Table 14: U-value of frame 45DS in W/(m2.K) 44 Table 15: U-value of frame 50TT in W/(m2.K) 45 Table 16: Average increase of overall U-value for window 40S+Single glazing 48 Table 17: Average increase of overall U-value for windows with 45DS and double glazing units 52 Table 18: Average increase of overall U-value for windows with 50TT and double glazing units 57 Table 19: Reference building envelope characteristics 59 Table 20: Reference building ETTV comparison . 60 Table 21: Grid independence test results 61 Table 22: Indoor convective surface heat transfer coefficient for aluminium window 62 Table 23: Metering side data logger connection information . 73 Table 24: Climatic side data logger connection information 73 Table 25: Metering box wall loss and flanking loss calibration matrix 77 Table 26: Base scenario of hot box simulation conditions . 79 Table 27: Constant time determination table 81 vii List of Figures Figure 1: Extrusion profile of frame 40S 21 Figure 2: Extrusion profile of frame 45DS . 22 Figure 3: Extrusion profile of frame 50TT . 23 Figure 4: Gambit simulation model 28 Figure 5: Boundary definition in Gambit 28 Figure 6: Drawing of casement window 29 Figure 7: Drawing of casement window 29 Figure 8: Drawing of awning window 30 Figure 9: Drawing of sliding window . 30 Figure 10: Exterior view of Hot Box 33 Figure 11: Interior view of Hot Box . 33 Figure 12: Comparison of Centre-of-glass U-value for the selected glazing units . 43 Figure 13: Comparison of Frame U-value 46 Figure 14: Comparison of Centre-of-glass and Overall U-value of 40S+Single glazing at different environmental conditions . 47 Figure 15: Comparison of Centre-of-glass and Overall U-value of 45DS+Double Glazing at different environmental conditions . 49 Figure 16: Comparison of Centre-of-glass and Overall U-value of 45DS+Double Glazing Low-E 0.6 at different environmental conditions . 49 Figure 17: Comparison of Centre-of-glass and Overall U-value of 45DS+Double Glazing Low-E 0.4 at different environmental conditions . 50 Figure 18: Comparison of Centre-of-glass and Overall U-value of 45DS+Double Glazing Low-E 0.2 at different environmental conditions . 50 Figure 19: Comparison of Centre-of-glass and Overall U-value of 45DS+Double Glazing Low-E 0.1 at different environmental conditions . 51 Figure 20: Comparison of Centre-of-glass and Overall U-value of 45DS+Double Glazing Low-E 0.05 at different environmental conditions . 51 Figure 21: Comparison of Centre-of-glass and Overall U-value of 50TT+Double Glazing at different environmental conditions . 54 Figure 22: Comparison of Centre-of-glass and Overall U-value of 50TT+Double Glazing Low-E 0.6 at different environmental conditions . 54 Figure 23: Comparison of Centre-of-glass and Overall U-value of 50TT+Double Glazing Low-E 0.4 at different environmental conditions . 55 Figure 24: Comparison of Centre-of-glass and Overall U-value of 50TT+Double Glazing Low-E 0.2 at different environmental conditions . 55 Figure 25: Comparison of Centre-of-glass and Overall U-value of 50TT+Double Glazing Low-E 0.1 at different environmental conditions . 56 viii Figure 26: Comparison of Centre-of-glass and Overall U-value of 50TT+Double Glazing Low-E 0.05 at different environmental conditions . 56 Figure 27: Straight wire heaters in the Metering Box . 64 Figure 28: Photo of the fans inside the metering box 65 Figure 29: Air circulation in hot box 67 Figure 30: Air curtain temperature and velocity sensors in Metering Box . 68 Figure 31: Air curtain temperature and velocity sensors in Climatic Box . 69 Figure 32: Self-made T-type thermocouples 70 Figure 33: Thermocouple calibration setup 71 Figure 34: Characterization panel . 72 Figure 35: Overheating proof device 75 Figure 36: Metering box wall loss and flanking loss (W) versus thermopile output (mV) . 76 ix Bibliography 1. Local heat transfer coefficients for a flush-mounted glazing unit. A. Schrey, R.A. Fraser, P.F. de Abreu. s.l. : ASHRAE Transactions 104 (1) 1207-1221, 1998. 2. Effects of glass plate curvature on the U-factor of sealed insulated glazing units. M.A. Bernier, B. Bourret. s.l. : ASHRAE Transactions 103 (1) 270-277, 1997. 3. Thermal performance of advanced glazing materials. M.G. Hutchins, W.J. Platzer. s.l. : Renewable Energy (1) 540-545. 4. Thermal performance of complex fenestration systems. Elmahdy, S.C. Carpenter and A.H. 1179-1186, s.l. : ASHRAE Transactions, Vol. 100. 5. Calculating the heat transfer coefficient of frame profiles with internal cavities. others, Peter A. Noyé and. s.l. : Nordic Journal of Building Physics, 2004, Vol. 3. 6. S. Svendsen, K. Duer, and P. Noyé. Calculating the heat transfer coefficient of frame profiles in aluminium. s.l. : Lyngby: Department of Buildings and Energy, Technical University of Denmark, 2000. 7. Natural convection at an indoor glazing surface. Cristian Cuevas, Adelqui Fissore. s.l. : Building and Environment, 2004, Vol. 39. 8. Frame and spacer effects on window U-value. S.C. Carpenter, A.G. McGowan. 604608, s.l. : ASHRAE Transactions, 1989, Vol. 95. 9. The Significance of bolts in the thermal performance of curtain-wall frames for glazed facades. B. Griffith, E. Finlayson, M. Yazdanian, and D. Arasteh. 1063-1069, s.l. : ASHRAE Transactions, 1998, Vol. 104. 10. Three-dimensional heat transfer effects in building components. McGowan, S.C. Carpenter and A. 1070-1076, s.l. : ASHRAE Transations, 1998, Vol. 104. 11. Standaert, P. Thermal evaluation of window frames by the finite difference method. Proceeding of windows in building design and maintenance. Stockholm : Swedish Council for Building Research, 1984. 12. Gustavsen, A. Heat transfer in window frames with internal cavities. s.l. : Department of Building and Construction Engineering, Norwegian University of Science and Technology, 2001. 89 13. Natural convection effects in three-dimensional window frames with internal cavities. A. Gustavsen, B.T. Griffith, and D. Arasteh. 527-537, s.l. : ASHRAE Transactions, 2001, Vol. 107. 14. Two-dimensional natural convection over the isothermal indoor fenestration surface finite element numerical solution. Goss, D. Curcija and W.P. 274-287, s.l. : ASHRAE Transactions, 1993, Vol. 99. 15. An ETTV-based approach to improving the energy performance of commercial buildings. Chou, K.J. Chua and S.K. s.l. : Energy and Buildings, 2009. 16. Standardization, International Organization for. ISO 15099 Thermal Performance of Windows, Doors and Shading Devices - Detailed Calculations. s.l. : ISO, 2002. 17. ASHRAE. 2009 ASHRAE Handbook - Fundamentals. Atlanta : s.n., 2009. 18. Good Industry Practices - Aluminium Window. s.l. : Singapore Building and Construction Authority. 19. Lawrence Berkeley National Laboratory. THERM 6.3 / WINDOW 6.3 NFRC Simulation Manual. 2010. 20. CEN. Building components and building elements - Thermal resistance and thermal transmittance - Calculation method (ISO 6949:2007). 2007. 21. ASTM. ASTM 1363: Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus. 2005. 90 Appendices Appendix A: Selected window products of AVA Globle 91 92 Appendix B: Singapore weather statistics TEMPERATURE (°C) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Period of Record Mean Daily 30.1 31.1 31.6 31.7 31.6 31.3 30.9 30.9 30.9 31.1 30.6 29.9 Maximum Mean Daily 23.3 23.6 23.9 24.4 24.8 24.7 24.5 24.4 24.2 24.0 23.7 23.4 Minimum 24-hr Mean 1929 - 1941 1948 - 2009 ( 75 yrs) 25.9 26.5 26.9 27.3 27.7 27.7 27.4 27.3 27.1 27.0 26.4 25.9 34 34.3 35.0 36 35.8 35.4 35 17 34.2 34.3 34.6 34.2 33.8 Highest 31 15 26 19 01 25 1991 17 15 29 26 02 Temperature 1979 2009 1998 1983 2005 1985 17 1986 2000 2002 2000 1948 1997 1929 - 1941 1948 - 2009 ( 75 yrs) 19.4 19.7 20.2 20.7 21.2 20.8 19.7 20.2 20.7 20.6 20.6 Lowest 21.1 30,31 23 14 16 04 19 06 30 20 10 02 Temperature sev 1934 1951 2000 1979 1989 1952 1976 1929 1933 1952 1964 93 SURFACE WIND Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Period of Record Mean Wind N/NE N/NE N/NE Variable S/SE S/SE S/SE S/SE S/SE Variable Variable N/NE Direction Mean Daily Wind Speed (m/s) Highest 10 minutes Mean Wind Speed (m/s) 1935 - 1941 1948 - 2008 ( 68 yrs) 2.4 2.4 1.8 12.2 12.4 14.2 17 1986 1977 1986 1.3 13.4 11 1981 1.3 1.6 1.9 1.9 1.6 13.9 12.4 15.4 13.9 13.9 20 19 1976 1978 1975 1979 1980 1.3 1.3 1.8 12.4 26 1976 13.8 10 1976 11.1 17 1981 1975 - 2009 (35 yrs) Source: Singapore National Environment Agency 94 Appendix C: Position diagram of sensors Metering side: Panel surface 101 102 103 104 105 106 107 108 109 Guard box air 201 205 204 206 202 208 207 209 203 Baffle surface 210 211 212 213 214 215 Baffle-to-specimen air-curtain temperature 301 302 303 304 305 306 307 308 309 95 Baffle-to-specimen air-curtain velocity 220 219 217 218 Climatic side: Baffle surface 201 204 206 202 203 205 Panel surface 109 108 107 112 111 110 115 114 113 Baffle-to-specimen air-curtain temperature 207 208 209 210 211 212 213 214 215 Baffle-to-specimen air-curtain velocity 216 217 218 219 220 96 Appendix D: Specifics of test specimen mounting in Surround panel Surround panel is the characterization panel with an aperture at the centre to accommodate the test specimen. Surround panel should be constructed the same way as the characterization panel so that the thermal conductivity of the characterization panel tested can be applied to the surround panel. And the additional requirements are as the followings: - - - - The surround panel aperture shall fit the specimen snugly (which is positioned at the centre of the surround panel) If the fenestration system does not fill the opening in the surround panel completely, the space between the surround panel and the fenestration system shall be filled with material of similar thermal conductance and thickness to that of the surround panel If the test specimen is of very high mass and framing is required to support the specimen, then the thermal bridge effects must be minimized by keeping the framing members away from the specimen aperture and away from the point of contact of the metering walls All potential air leakage sites must be sealed with non-metallic tape or caulking, or both, as close to the hot side as possible to minimize or eliminate air leakage between the hot side and cold side chambers A test specimen with primary and secondary components (such as a storm window) shall be sealed at the hot side of each component Weep holes/slots located on the cold side shall be sealed on the cold side Perimeter joints between the test specimen and the surround panel shall be sealed on both sides of the wall. In no case shall the tape or caulk cover more than 13 mm (0.5 in.) of the test specimen frame or edge 97 Appendix E: Example calibration data Vf If 21 (V) (A) Time 09:06:27 09:16:27 09:26:27 09:36:27 09:46:27 09:56:27 10:06:27 10:16:27 10:26:27 10:36:27 10:46:27 10:56:27 11:06:27 11:16:27 11:26:27 11:36:27 11:46:27 11:56:27 12:06:27 12:16:27 12:26:27 12:36:27 12:46:27 12:56:27 13:06:27 13:16:27 13:26:27 13:36:27 13:46:27 13:56:27 14:06:27 14:16:27 14:26:27 14:36:27 14:46:27 14:56:27 15:06:27 15:16:27 15:26:27 15:36:27 Tsp1 43.77 43.75 43.73 43.72 43.68 43.70 43.68 43.66 43.63 43.62 43.59 43.57 43.53 43.50 43.50 43.49 43.47 43.44 43.40 43.39 43.39 43.31 43.29 43.29 43.29 43.23 43.23 43.17 43.18 43.14 43.15 43.11 43.08 43.06 43.02 43.00 42.99 42.97 43.00 42.99 Vh Ih Tsp2 26.42 26.38 26.34 26.27 26.22 26.18 26.13 26.09 26.04 26.00 25.97 25.91 25.88 25.84 25.80 25.76 25.75 25.73 25.69 25.64 25.66 25.60 25.61 25.60 25.56 25.57 25.52 25.55 25.52 25.55 25.52 25.50 25.53 25.51 25.49 25.48 25.46 25.48 25.48 25.48 0 To Ti 43.81 43.82 43.76 43.77 43.77 43.76 43.73 43.69 43.69 43.68 43.63 43.58 43.53 43.54 43.50 43.46 43.44 43.41 43.44 43.39 43.39 43.36 43.33 43.33 43.32 43.24 43.26 43.25 43.20 43.21 43.18 43.15 43.10 43.07 43.05 43.04 43.03 43.00 42.99 43.03 25.68 25.66 25.58 25.55 25.51 25.45 25.39 25.37 25.31 25.28 25.24 25.18 25.16 25.12 25.06 25.03 25.02 25.01 24.99 24.91 24.94 24.91 24.90 24.89 24.87 24.85 24.85 24.84 24.82 24.82 24.80 24.83 24.82 24.79 24.78 24.79 24.79 24.79 24.78 24.79 E -0.01469 -0.01473 -0.01477 -0.0148 -0.01483 -0.01486 -0.01488 -0.0149 -0.01491 -0.01492 -0.01494 -0.01494 -0.01495 -0.01496 -0.01496 -0.01496 -0.01496 -0.01496 -0.01496 -0.01496 -0.01496 -0.01495 -0.01494 -0.01494 -0.01493 -0.01492 -0.0149 -0.01489 -0.01487 -0.01486 -0.01485 -0.01483 -0.01482 -0.01481 -0.0148 -0.01479 -0.01477 -0.01476 -0.01476 -0.01475 98 15:46:27 15:56:27 16:06:27 16:16:27 16:26:27 16:36:27 16:46:27 16:56:27 17:06:27 17:16:27 17:26:27 17:36:27 17:46:27 17:56:27 42.94 42.98 42.94 42.88 42.88 42.88 42.86 42.87 42.87 42.82 42.81 42.83 42.85 42.84 25.49 25.47 25.45 25.44 25.44 25.44 25.44 25.45 25.45 25.45 25.44 25.45 25.42 25.44 43.00 42.96 42.95 42.95 42.94 42.91 42.90 42.90 42.86 42.86 42.86 42.81 42.82 42.81 24.78 24.76 24.77 24.77 24.76 24.76 24.76 24.75 24.74 24.75 24.74 24.74 24.71 24.73 -0.01473 -0.01473 -0.01472 -0.01471 -0.0147 -0.0147 -0.01469 -0.01468 -0.01467 -0.01467 -0.01466 -0.01466 -0.01465 -0.01465 99 Appendix F: Effective conductivity – unventilated frame cavities A frame cavity shall be treated as though it contains an opaque solid which is assigned an effective conductivity. This effective conductivity accounts for both radiative and convective heat transfer and shall be determined as follows. ݇௘௙௙ = (ℎ௖ + ℎ௥ ). ݀ where keff is the effective conductivity; hc is the convective heat transfer coefficient; hr is the radiative heat transfer coefficient (hr=0 in the case when detailed radiation procedure is used); d is the thickness or width of the air cavity in the direction of heat flow. The convective heat transfer coefficient, hc, is calculated from the Nusselt number, Nu, which can be determined from various correlations, depending on aspect ratio, orientation and direction of heat flow. ℎ௖ = ܰ‫ݑ‬ ݇௔௜௥ ݀ There are three different cases to be considered, depending on whether the heat flow is upward, downward, or horizontal. 1. Heat flow downward ܰ‫ = ݑ‬1.0 2. Heat flow upward This situation is inherently unstable and will yield a Nusselt number that is dependent on the height-to-width aspect ratio, Lv/Lh, where Lv and Lh are the largest cavity dimensions in the vertical and horizontal directions. 100 a) For ௅ೡ ௅೓ < 1convection is restricted by wall friction, and b) For < ௅ೡ ௅೓ ܰ‫ = ݑ‬1.0 < the Nusselt number is calculated according to the method given by where ݇1 = 1.4 ݇2 = ሾ‫ݔ‬ሿା = ܴܽଵ/ଷ 450.5 ‫ ݔ‬+ |‫|ݔ‬ Racrit is a critical Rayleigh number, which is found by least squares regression of tabulated values. Ra is the Rayleigh number for the air cavity: ௅ c) For ௅ ೡ > the Nusselt number is: ೓ 3. Horizontal heat flow 101 a) For ௅ೡ ௅೓ < 0.5 the Nusselt number is: where Ra is Raleigh number and is defined as: ௅ b) For ௅ ೡ > the following correlation, also the maximum Nu is gives as: ೓ ௅ c) For 0.5 < ௅ ೡ < the Nusselt number is found using a linear interpolation between the ೓ endpoints of (a) and (b) above. For jamb frame sections, frame cavities are oriented vertically and therefore the height of the cavity is in the direction normal to the plane of the cross section. For these cavities it is assumed that heat flow is always in horizontal direction with Lv/Lh > 5. The temperatures Thot and Tcold are not known in advance, so it is necessary to estimate them. From previous experience it is recommended to apply Thot=10°C and Tcold=0°C. However, after the simulation is done, it is necessary to update these temperatures from the results of the previous run. This procedure shall be repeated until values of Thot-Tcold 102 from two consecutive runs are within 1°C. Also, it is important to inspect the direction of heat flow after the initial run, because if the direction of the bulk of heat flow is different than initially specified, it will need to be corrected for the next run. For unventilated irregularly shaped frame cavity, the geometry shall be converted into equivalent rectangular cavity according to the procedure in ISO 10077. For these cavities, the following procedure shall be used to determine which surfaces belong to vertical and horizontal surfaces of equivalent rectangular cavity. If the shortest distance between two opposite surfaces is smaller than mm then the frame cavity shall be split at this "throat" region. Also: a) any surface whose normal is between 315° and 45° a is left vertical surface b) any surface whose normal is between 45° and 135° a is bottom horizontal surface c) any surface whose normal is between 135° and 225° a is right vertical surface d) any surface whose normal is between 225° and 315° a is top horizontal surface Temperatures of equivalent vertical and horizontal surfaces shall be calculated as the mean of the surface temperatures according to the classification shown above. The direction of heat flow shall be determined from the temperature difference between vertical and horizontal surfaces of the equivalent cavity. The following rule shall be used: a) heat flow is horizontal if the absolute value of the temperature difference between vertical cavity surfaces is larger than between horizontal the cavity surfaces; b) heat flow is vertical heat flow up if absolute temperature difference between horizontal cavity surfaces is larger than between vertical cavity surfaces and temperature difference between the top horizontal cavity surface and bottom horizontal cavity surface is negative; c) heat flow is vertical, heat flow down if absolute temperature difference between horizontal cavity surfaces is larger than between vertical cavity surfaces and temperature difference between the top horizontal cavity surface and bottom horizontal cavity surface is positive. 4. Radiant heat flow 103 The radiative heat transfer coefficient hr shall be calculated using: where: Above notation assumes radiant heat flow in the horizontal direction. If the heat flow direction is vertical then the inverse of the ratio Lh/Lv shall be used (i.e., Lv/Lh). 104 [...]... measurement of glazing surface temperatures Bernier and Bourret [2] experimentally studied the effects of glass plate curvature due to barometric pressure and gas space temperature variations on the thermal transmittance of sealed glazing units Hutchins and Platzer [3] measured the thermal performance of advanced glazing materials for windows Carpenter and Elmahdy [4] studied the thermal performance for... simulated with glazing and spacer, not with an insulation panel to find the frame U-value Griffith et al [9] and Carpenter and McGowan [10] studied heat transfer in curtain wall aluminium frames They found that a two-dimensional calculation programme gives accurate results when appropriate calculation procedures are applied Standaert [11] studied the U-value of an aluminium frame with internal cavities,... simulated in WINDOW 6 Frame and edge effects are simulated in THERM 6 and then imported into WINDOW 6 So WINDOW 6 can calculate the thermal properties of the whole window system 3.2.2 Frame profiles Three frame profiles have been created based on the literature and real window product investigation The unanimous majority of the window frames in Singapore are made of aluminium alloys Singapore Building and. .. procedure adapted to our GHB and test environment Chapter 7 presents the method to calculate the experimental uncertainty of the GHB testing Chapter 8 concludes the thesis with the findings from numerical simulations and the progress of the BHB modification and calibration 5 CHAPTER 2 LITERATURE REVIEW 2.1 Thermal transmittance The thermal transmittance, or U-value, of a window is the rate of heat transfer... is necessary to apply a more detailed radiation exchange model than described in the preEN ISO 10077-2 standard, which can be ISO standard Svendsen et al [6] carried out similar research and found that division of air cavities also affects the U-value, but not as much as the change of radiation model 7 Cuevas and Fissore [7] developed correlations for calculation of the convective heat transfer coefficient...Nomenclature ‫ :ܣ‬Area of heat flow, m2 ‫ܣ‬௖௚ : Centre -of- glass area, m2 ‫ܣ‬௘௚ : Edge -of- glass area, m2 ‫ܣ‬௙ : Frame area, m2 ‫ܣ‬௣௙ : Projected window system area, m2 As: Projected area of test specimen (same as open area in surround panel), m2 Asp: Area of surround panel, m2 Csp: Thermal conductance of the surround panel, W/(m2.K) Cp: Thermal conductance, W/(m2.K) ݀௚ : Glass thickness, m... fenestration systems) , and radiation transmission through and between fenestration and indoor/outdoor environment and between glazing layers Solar radiation absorbed will contribute to the temperature driven heat transfer However, solar radiation is not accounted for in U-value calculation in this study Thermal transmittance, or U-value, which measures the rate of heat transfer through fenestration systems, is... Cavities are separated by “throat” of 5mm However, if Nusselt number . edge area of the glazing unit, and the window frame. A numerical study has been undertaken on the thermal transmittance of window systems. The computations indicate that the overall U-value of. to barometric pressure and gas space temperature variations on the thermal transmittance of sealed glazing units. Hutchins and Platzer [3] measured the thermal performance of advanced glazing. between measured and calculated thermal transmittance values. Two typical frame profiles in aluminium and PVC with internal cavities were investigated. The thermal transmittance was determined