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Mohamed Zedan - State of The Art in the Use of Thermal Insulation in Building


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Mohamed Zedan - State of The Art in the Use of Thermal Insulation in Building

  1. 1. State of the Art in the Use of Thermal Insulation in Building Walls and Roofs (Part I) By Prof. Mohamed Fouad Zedan Department of Mechanical Engineering King Saud University, Riyadh, KSA Copyright - Al-Sanea/Zedan ; 2012 1
  2. 2. Objectives and Topics Covered1. Importance of thermal insulation2. Best location of insulation layer in building envelopes for different AC operation modes (continuous/intermittent).3. Optimum thickness of insulation for buildings in the central region of Saudi Arabia (generally applicable to most of the gulf region).4. Effect of wall orientation and economic parameters on optimum thickness of insulation with emphasis on the effect of future projected electricity tariff. Copyright - Al-Sanea/Zedan ; 2012 2
  3. 3. TOPIC-1Importance of Thermal Insulationa. Energy Conservation in Buildings Energy consumed by AC is about 2/3 of energy consumed in buildings in KSA. Transmission load through walls and roofs of residential buildings is about 2/3 of AC load. Accordingly, substantial energy savings can be achieved by increasing the R-value of building envelope by applying thermal insulation. Copyright - Al-Sanea/Zedan ; 2012 3
  4. 4. Importance of Thermal Insulation- cont.b. Improved Thermal Comfort Lower indoor air temperature Lower indoor surface temperature (less radiation effects) Lower indoor surface temperature fluctuations Copyright - Al-Sanea/Zedan ; 2012 4
  5. 5. Importance of Thermal Insulation- cont.c. Reduces size and maintenance cost of AC equipmentd. Increases time lag and improve load leveling on the electric grid (smaller peak load and higher valley)e. Reduces global warming , protects the environment, etc.f. Reduces dependence on operating AC equipment in moderate climatesg. Protects building envelope, preserves furniture, and reduces condensation risk.h. Reduces transmission of sound Copyright - Al-Sanea/Zedan ; 2012 5
  6. 6. Drawbacks of Using Thermal Insulationa. Installing insulation adds to overall cost What is the pay-back period?b. Insulation layer makes walls thicker Copyright - Al-Sanea/Zedan ; 2012 6
  7. 7. TOPIC-2Effect of Insulation Location in Walls a. Under Steady Periodic Conditions b. Under Initial transient Conditions These conditions are related to the AC operation mode Copyright - Al-Sanea/Zedan ; 2012 7
  8. 8. Modes of Operation of AC Systems  Modes of operation of AC systems:  Continuously operating mode.  Intermittently operating mode.  Former would generally give rise to steady periodic conditions, whereas latter is associated with initial transient behavior.  Literature reveals lack of detailed and systematic studies that investigate effect of insulation location within building envelope with regard to AC operating mode. Copyright - Al-Sanea/Zedan ; 2012 8
  9. 9. Effect of Insulation Location in Walls understeady periodic conditions (continuouslyoperating AC) Study is made under the assumptions:  Insulation layer thickness is fixed.  Representative days for July and January.  Riyadh climatic conditions.  Fixed indoor air temperature: 25 C in July and 21C in January Study is made using a validated computer model Copyright - Al-Sanea/Zedan ; 2012 9
  10. 10. Model: Definition sketch of composite wall Copyright - Al-Sanea/Zedan ; 2012 10
  11. 11. Thermal properties of wall materials.Material k (W/m.K) ρ (kg.m3) c (J/kg.K)HWHCB (200mm) 1.05 1105 840HWHCB (150mm) 0.96 1362 840HWHCB (100mm) 0.81 1618 840Molded polystyrene 0.036 20 1215Cement plaster 0.72 1865 840 Copyright - Al-Sanea/Zedan ; 2012 11
  12. 12. Validation: Periodic heat conduction in three-layered wall Indoor Outdoor 15-cm 5-cm 10-cm HWHCB MP HWHCB x• Outside surface is exposed to periodicvariation in boundary conditions.• Indoor air temperature is kept constant at 25oCwith hi = 8.23 W/m2.K. Copyright - Al-Sanea/Zedan ; 2012 12
  13. 13. Validation: Comparison of temperature distribution acrosswall at various times as obtained from finite-volume andsemi-analytic solutions; July, west face. Copyright - Al-Sanea/Zedan ; 2012 13
  14. 14. Validation: Comparison of variation of transmission load tospace obtained from numerical model and semi-analyticsolutions; July, west face. Copyright - Al-Sanea/Zedan ; 2012 14
  15. 15. Wall Configurations used in the investigation:Wall I with inside insulation Copyright - Al-Sanea/Zedan ; 2012
  16. 16. Wall II with outside insulation Copyright - Al-Sanea/Zedan ; 2012 16
  17. 17. Temperature Distribution Across Wall I (inner insulation)  Representative day in July.  Wall is facing west.  Variations are shown in next figure at different times of day. Copyright - Al-Sanea/Zedan ; 2012 17
  18. 18. Temperature distribution across wall I at different times; July,facing west. Copyright - Al-Sanea/Zedan ; 2012 18
  19. 19. Results indicate: Temperature variation is smooth across each layer with discontinuities in gradients at interfaces because of different conductivities. Steepest change in temperature occurs in insulation layer. Copyright - Al-Sanea/Zedan ; 2012 19
  20. 20. Temperature Variation Across Wall II(outer insulation) Copyright - Al-Sanea/Zedan ; 2012 20
  21. 21. Results indicate:• Again, most of temperature drop occurs in insulation layer near outside surface.• This leads to much smaller temperature drop across concrete block and consequently smaller temperature fluctuation at inner surface of this wall compared to case of inside insulation.• Temperature at outside surface is generally higher in present case due to accumulation of heat in outside plaster layer. Copyright - Al-Sanea/Zedan ; 2012 21
  22. 22. Transmission Load Variation with Time Copyright - Al-Sanea/Zedan ; 2012 22
  23. 23. Results indicate:  Peak transmission load is higher and minimum load is lower (hence amplitude of load fluctuation is bigger) in case of inside insulation.  Difference in peak loads is about 14%, e.g. 14% smaller capacity AC equipment with outside insulation.  Above result is generally valid for all wall orientations and in both summer and winter.  Mean transmission load appears to be essentially the same for walls with inside and outside insulation. Copyright - Al-Sanea/Zedan ; 2012 23
  24. 24. Daily Transmission Loads Copyright - Al-Sanea/Zedan ; 2012 24
  25. 25. Effects of wall orientationResults indicate: Daily mean cooling loads in summer for east and west faces are 15% higher than those for north and south faces. Daily mean heating load in winter for north face is 18% higher than those for east and west faces. Daily mean heating load in winter for south face is 39% lower than those for east and west faces. Copyright - Al-Sanea/Zedan ; 2012 25
  26. 26. Summary Insulation layer has minimal effect on mean daily cooling and heating loads, with slight advantage for outside insulation in summer and inside insulation in winter. Outside insulation gives smaller amplitude of load fluctuation and smaller peak load in both summer and winter for all wall orientations. Copyright - Al-Sanea/Zedan ; 2012 26
  27. 27.  Outside insulation slightly increases time lag in summer, compared to inside insulation, and has practically same effect on time lag in winter. More detailed results can be found in: S.A. Al-Sanea and M.F. Zedan, “Effect of insulation location on thermal performance of building walls under steady periodic conditions”, International Journal of Ambient Energy., Vol. 22 (2), pp. 59-72, 2001. Copyright - Al-Sanea/Zedan ; 2012 27
  28. 28. Effect of Insulation Location in Walls under Initial Transient Conditions (intermittently operating AC) Copyright - Al-Sanea/Zedan ; 2012 28
  29. 29. Initial Transient Thermal Response  Initial transient stage arises when AC system is switched on after relatively long period of shutdown and prior to attaining steady periodic conditions again.  Initial transient stage may last for number of hours or even days depending on initial temperature distribution, thermal mass of wall, and location of insulation layer. Copyright - Al-Sanea/Zedan ; 2012 29
  30. 30.  Most important of these applications is use of room air conditioners such as window and split units. These units are normally switched on when room is occupied and off when it is not. AC of such rooms is quite problematic because of thermal radiation from walls, especially if AC system has been off for few hours. Copyright - Al-Sanea/Zedan ; 2012 30
  31. 31. Validation: Comparison of temp variation with time atvarious interfaces in 1st cycle as obtained from finite-volume and semi-analytic solutions; July, west face. Copyright - Al-Sanea/Zedan ; 2012 31
  32. 32. Validation: Comparison of variation of transmission load withtime in 1st cycle as obtained from finite-volume and semi-analyticsolutions; July, west face. Copyright - Al-Sanea/Zedan ; 2012 32
  33. 33. Temperature Distribution Across Wall I (innerinsulation)  West facing wall, July  Initial temperature is uniform at 37.2oC (daily mean outdoor air temperature).  Calculations start at t = 0 (midnight).  Distributions are shown later at different times during 1st cycle, and compared with those under steady periodic conditions. Copyright - Al-Sanea/Zedan ; 2012 33
  34. 34. Temperature distribution across wall I at different times in 1stcycle; July, facing west. Copyright - Al-Sanea/Zedan ; 2012 34
  35. 35. Temperature distribution across wall I at different times insteady periodic state; July, facing west. Copyright - Al-Sanea/Zedan ; 2012 35
  36. 36. Results indicate: Initial transient effect diminishes rather fast for case of inside insulation and steady periodic state is practically reached after about 5 hours. Fast change of inner surface temperature to value close to indoor design temperature reduces occupant discomfort (due to radiation exchange) and reduces energy consumption. Copyright - Al-Sanea/Zedan ; 2012 36
  37. 37. Temperature Variation Across Wall II (outer insulation)First Cycle: Copyright - Al-Sanea/Zedan ; 2012 37
  38. 38. Steady periodic state Copyright - Al-Sanea/Zedan ; 2012 38
  39. 39. Results indicate: Most of temperature drop occurs within insulation layer near outside surface. Concrete block with its large thermal mass on inside is responsible for slower temperature drop at inside surface. This leads to thermal discomfort and increased energy consumption. Initially stored energy in concrete block is essentially trapped and prevented by insulation from dissipating to outside. Copyright - Al-Sanea/Zedan ; 2012 39
  40. 40.  This is reflected by positive temperature gradients across whole concrete block at all times during 1st cycle; heat is transferred mainly to inside. Compared with steady periodic response, present results of outside insulation show that transient effects persist much longer compared to case of inside insulation. Heat dissipated from concrete block is passed mostly to inner space, increasing transmission load. Copyright - Al-Sanea/Zedan ; 2012 40
  41. 41. Inside-Surface Temperature Variation  Inside-surface temperature variation with time for walls I and II are compared in next figure under initial transient and steady periodic conditions.  Inner surface temperature drops much faster in case of inside insulation (curve 4) reaching steady periodic state (curve 5) after about 5 hours.  Temperature drops at much slower rate for case of outside insulation (curve 1); it does not reach steady periodic state until after about two cycles (48 hours). Copyright - Al-Sanea/Zedan ; 2012 41
  42. 42. Inside-surface temp variation with time. Copyright - Al-Sanea/Zedan ; 2012 42
  43. 43. Transmission Load Variation with Time  Space heat gain and its variation with time are compared in next figure for cases with inside and outside insulation under initial transient and steady periodic conditions.  Transmission load variation with time shows similar trend to that of inner surface temperature (presented earlier) because it is proportional to difference between inner surface and indoor air temperatures. Copyright - Al-Sanea/Zedan ; 2012 43
  44. 44.  Instantaneous transmission load for outside insulation is more than five-fold higher than that for inside insulation during early hours in 1st cycle. It is concluded that energy consumption by AC during initial transient stage is much less when placing insulation on inside. Besides, better comfort level is achieved faster with inside insulation mainly because of reduced radiation effects. Copyright - Al-Sanea/Zedan ; 2012 44
  45. 45. Variation of transmission load with time under transient andsteady-periodic conditions for cases of inside and outsideinsulation; July, west facing wall. Copyright - Al-Sanea/Zedan ; 2012 45
  46. 46. Daily Transmission Loads Daily transmission loads into space during 1st 24 hours of operation for cases of inside and outside insulation and for various wall orientations in July and January are presented in next figure and are compared with those under steady periodic conditions. It is seen that daily cooling and heating loads are much smaller for inside insulation and for all orientations during 1st 24 hours. Copyright - Al-Sanea/Zedan ; 2012 46
  47. 47.  Energy savings in first 24 hours is about 66% in July and 64% in January by placing insulation on inside; savings would be much bigger for shorter durations. Effect of wall orientation is relatively smaller for outside insulation since heat gain or loss in 1st cycle comes mainly from energy stored in wall which is independent of wall orientation in present investigation. Copyright - Al-Sanea/Zedan ; 2012 47
  48. 48. Daily transmission loads during 1st cycle. Copyright - Al-Sanea/Zedan ; 2012 48
  49. 49. Daily transmission loads during steady periodic state. Copyright - Al-Sanea/Zedan ; 2012 49
  50. 50. Summary Under conditions of present study, inner surface temperature drops relatively very fast and conditions reach steady periodic state after very short time (5 hours) for case of inside insulation. For case of outside insulation, inner surface temperature drops much slower and wall needs more than two full cycles (48 hours) to reach steady periodic conditions. Copyright - Al-Sanea/Zedan ; 2012 50
  51. 51.  Placing insulation on inside gives instantaneous load that is 20% of that for outside insulation during first few hours in transient process. Duration of transient process (which leads to steady periodic state) and thus period of thermal discomfort due to radiation exchange is much shorter for inside insulation. Copyright - Al-Sanea/Zedan ; 2012 51
  52. 52.  Average heat transmission over first 24-h period of AC operation with inside insulation is about one- third of that with outside insulation. It is recommended that for spaces where AC system is switched on and off intermittently, insulation should be placed on inside. This is usually the case in applications that utilize room air conditioners, such as window and split units. Copyright - Al-Sanea/Zedan ; 2012 52
  53. 53.  It is suggested that future studies should be carried out to investigate effects of using different initial temperature distributions and different times of operating AC system. More detailed results can be found in: S.A. Al-Sanea and M.F. Zedan, “Effect of insulation location on initial transient thermal response of building walls”, Journal of Thermal Env. & Bldg. Sci., Vol. 24, pp. 275-300, 2001. Copyright - Al-Sanea/Zedan ; 2012 53
  54. 54. TOPIC-3 Determination of Optimum Insulation Thickness Copyright - Al-Sanea/Zedan ; 2012 54
  55. 55. What is optimum insulation thickness? Optimum insulation thickness (Lopt) is thickness that gives minimum total cost. Total cost (ctot) comprises cost of insulation material and its installation, plus present worth of energy consumption cost due to transmission part of AC load over lifetime of building. Copyright - Al-Sanea/Zedan ; 2012 55
  56. 56. Typical cost versus insulation thickness. Copyright - Al-Sanea/Zedan ; 2012 56
  57. 57. Economic Model Total cost per unit area of wall/roof is: ctot = cins + cad + cenr = Lins ci + cad + Ce PWF Lins is insulation thickness, ci is cost of insulation material per unit volume, Ce is current yearly total cost of energy (SR/m2.year) and PWF is present worth factor accounting for inflation and discount rates. Copyright - Al-Sanea/Zedan ; 2012 57
  58. 58. In case rd  ri ,  m  1 r    1 r   PWF   i  1  i  r  r   1 r    d i   d    mIn case rd = ri , PWF  1 rdri inflation rate in energy cost,rd discount ratem expected lifetime of building (years) Copyright - Al-Sanea/Zedan ; 2012 58
  59. 59. Current Yearly Total Cost of Energy (Ce)  Ce = Etot ce ce is current electric charge ($/kWh)  Yearly total electric energy consumption is: Etot = Ec + Eh  For vapor-compression cooling, electric energy consumption Ec is: Ec = Q g / pc Q g heat gain per unit area per year, pc coef. of performance Copyright - Al-Sanea/Zedan ; 2012 59
  60. 60.  For heat-pump heating, electric energy consumption Eh = Ql / pf ; pf is performance factor Economic Parameters are:  Cost of insulation material, ci  Cost of installation of insulation, cad  Cost of electricity, ce  Lifetime of building, m (years)  AC performance factors,  Discount and inflation rates, rd and ri Copyright - Al-Sanea/Zedan ; 2012 60
  61. 61. TOPIC-4 Effect of Wall Orientation and Economic Parameters on Optimum Insulation Thickness Copyright - Al-Sanea/Zedan ; 2012 61
  62. 62. Nominal values of parameters used in economicmodel. ci cad ce pc pf m rd ri ($/m3) ($/m2) ($/kWh) (years) * * 0.0317 3 4 30 0.07 0.04*Cost depends on insulation material;details are given later. Copyright - Al-Sanea/Zedan ; 2012 62
  63. 63. Properties of materials and costs of insulation materialsand their installation. Material k  c Mat. c. Inst. c. (W/m.K) (kg/m3) (J/kg.K) ($/m3) ($/m2) HWHCB (200 mm) 1.05 1105 840 - - Plaster board 0.17 800 1090 - - Cement plaster 0.72 1865 840 - - Polystyrene (molded) 0.036 20 1215 42.67 1.60 Polystyrene (extruded) 0.032 26 1215 69.33 1.60 Polystyrene (injected) 0.032 20 1215 50.67 1.60 Rock wool 0.042 30 837 48.00 1.60 Glass fiber 0.038 24 837 45.33 1.60 Polyurethane (board) 0.024 30 1590 138.67 1.60 Copyright - Al-Sanea/Zedan ; 2012 63
  64. 64. Schematic of wall structure used in this investigation Plaster board (12.5 mm) Cement plaster (25 mm) Molded polystyrene Insulation (optimized) HWHCB (200 mm) Inside Outside Copyright - Al-Sanea/Zedan ; 2012 64
  65. 65. Effect of Wall Orientation on Total Cost andOptimum Insulation Thickness Total cost is shown versus Lins in next figure using molded polystyrene. Total cost comprises cost of insulation material and its installation plus present value of cost of energy spent to remove transmission loads over lifetime of building. Total cost curve shows minimum value that corresponds to Lopt. Copyright - Al-Sanea/Zedan ; 2012 65
  66. 66. Total cost versus insulation thickness for molded polystyreneshowing effect of wall orientation. Copyright - Al-Sanea/Zedan ; 2012 66
  67. 67. Effect of wall orientation on total cost and optimuminsulation thickness using molded polystyrene. Wall orientation Min. total cost Optimum ($/m2) thickness (cm) South 9.74 8.75 North 9.88 8.88 East 10.14 9.20 West 10.19 9.25 Copyright - Al-Sanea/Zedan ; 2012 67
  68. 68. Effect of Economic Parameters on Total Cost andOptimum Insulation Thickness Parametric study is carried out to investigate effect of varying values of economic parameters (from their nominal settings) on total cost and Lopt. Costs of insulations, electricity, etc. can vary appreciably with time; therefore, this sensitivity study is warranted. Copyright - Al-Sanea/Zedan ; 2012 68
  69. 69.  Study is done by using molded polystyrene and for west facing wall. Only one factor is changed at a time while keeping rest at nominal values. Changes investigated cover rather wide, though still practical, range of economic parameters. It is found that total cost and Lopt are quite sensitive to these changes; however, trends obtained are as expected. Copyright - Al-Sanea/Zedan ; 2012 69
  70. 70. Effect of insulation cost Copyright - Al-Sanea/Zedan ; 2012 70
  71. 71. Effect of electricity cost Copyright - Al-Sanea/Zedan ; 2012 71
  72. 72. Effect of AC equipment performance: pc and pf Copyright - Al-Sanea/Zedan ; 2012 72
  73. 73. Effect of building lifetime Copyright - Al-Sanea/Zedan ; 2012 73
  74. 74. Effect of discount rate Copyright - Al-Sanea/Zedan ; 2012 74
  75. 75. Effect of inflation rate Copyright - Al-Sanea/Zedan ; 2012 75
  76. 76. Summary Wall orientation has significant effect on thermal behavior but relatively smaller effect on total cost and Lopt. South facing wall is most favorite and gives about 12% lower yearly transmission load and 5% lower total cost compared to least favorite orientation which is west wall. Total cost and Lopt are sensitive to changes in economic parameters. Copyright - Al-Sanea/Zedan ; 2012 76
  77. 77.  Lopt is found to increase with cost of electricity, building lifetime and inflation rate; and decrease with cost of insulation material, coefficient of performance of AC equipment and discount rate. More detailed results can be found in: S.A. Al-Sanea and M.F. Zedan, “Optimum insulation thickness for building walls in a hot-dry climate”, International Journal of Ambient Energy, Vol. 23, No. 3, pp. 115-126, 2002. Copyright - Al-Sanea/Zedan ; 2012 77
  78. 78. THANK YOUCopyright - Al-Sanea/Zedan ; 2012 78