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# Thermal Dynamics and Heat Transfer

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ICC has developed these training modules in order to help people understand the science behind cool roofing and heat transfer management within buildings.

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### Thermal Dynamics and Heat Transfer

1. 1. ASTEC Training Program Copyright 2007 Insulating Coatings Corporation
2. 2. Training Program 1. The Concept of Heat 2. Heat Transfer (I) 3. Heat Transfer (II) 4. Processes in Radiation 5. Term Definitions 6. ASTEC – Thermal Properties 7. ASTEC – The Total Solution
3. 3. Module 1 Thermodynamics The Concept of Heat (Thermodynamics) Module 1
4. 4. Module 1 Thermodynamics Thermodynamics: 1. Energy is always conserved; it is never lost. 2. Heat always travels from a “hot” region to a “colder” region. Therefore, the issue is: • Flow of Heat • Heat Flow •Heat Transfer
5. 5. Module 1 Thermodynamics Heat Transfer Radiation ~ Electromagnetic Waves Conduction ~ Molecule Movement Convection ~ Air Current
6. 6. Module 1 Thermodynamics Heat Transfer Modes • Conduction Heat transfer for conduction and for convection is directly • Convection proportional to the driving temperature differential. • Radiation Double the difference to double the heat transfer rate ( T1 – T2 )
7. 7. Module 1 Thermodynamics Heat Transfer Modes • Conduction Heat transfer by radiation is proportional to the fourth • Convection power of the temperature difference ( T14 – T24 ). • Radiation Small changes in temperature can create relatively large changes in radiation heat transfer rates.
8. 8. Module 2 Heat Transfer (I) Heat Transfer (I) (Modes / Electromagnetics) Module 2
9. 9. Module 2 Heat Transfer (I) Heat Flows Only by… •Conduction Intensity of conduction •Convection Amount of convection •Radiation Rate of radiation [reflectivity, absorption, and transmissivity]
10. 10. Module 2 Heat Transfer (I) CONDUCTION •Direct heat flow through matter resulting from a physical contact. • Transmission of heat by molecular motion.
11. 11. Module 2 Heat Transfer (I) CONVECTION •Transfer or transportation of heat which is within a gas or liquid. “Free convection” “Forced convection”
12. 12. Module 2 Heat Transfer (I) RADIATION •Transmission through space of energy by means of electromagnetic rays of varying wavelengths (λ)and cycles (Hertz).
13. 13. Module 2 Heat Transfer (I) Wavelength, λ (μ m) for c = 3 x 108 m/s
14. 14. Module 2 Heat Transfer (I)
15. 15. Module 2 Heat Transfer (I) Terminology G Irradiation (solar/thermal radiation) Radiant flux incident per unit area W/m2 ε Emissivity (thermal radiation) Rate of radiation emanating from Numeric the surface of an object compared to the rate of radiation emanating from a “black body”
16. 16. Module 2 Heat Transfer (I) Terminology ρ (Radiant) reflectance (Numeric) Ratio of reflected radiant flux ρG to incident radiant flux α (Radiant) absorptance (Numeric) Ratio of absorbed radiant flux αG to incident radiant flux τ (Radiant) transmittance (Numeric) Ratio of transmitted radiant flux τG to incident radiant flux
17. 17. Module 3 Heat Transfer (II) Heat Transfer (II) (Electromagnetics and Infrared Energy) Module 3
18. 18. Module 3 Heat Transfer (II) RADIATION The sun radiates energy to the earth through 93 million miles of space by means of rays of many different wavelengths. 186,286 miles/sec or 300,000 km/sec
19. 19. Module 3 Heat Transfer (II) SOLAR RADIATION SPECTRUM Infrared (Heat rays) Very Low Frequency • NIR 0.75 to 3 Low Frequency • MIR 3 to 6 Medium Frequency • FIR 6 to 15 High Frequency • XIR 15 to 1000 Very High Frequency Ultra High Frequency Visible rays Ultraviolet rays Super High Frequency X rays Extra High Frequency Gamma Rays Cosmic Rays
20. 20. Module 3 Heat Transfer (II) SOLAR RADIATION SPECTRUM Radiation Spectrum Infrared rays Visible rays Ultraviolet rays 0.76 to 100 μ m 0.75 to 0.4 μ m 0.4 micron to 100 A (feels warm) (visible light) (causes sunburn)
21. 21. Module 3 Heat Transfer (II) Radiation Intensity • The closer to the sun a body is, the more rays it will intercept. • Closer to the sun, the intensity can be so great that we could not survive.
22. 22. Module 3 Heat Transfer (II) Radiation Exposure • A 7 story building is exposed to more radiation on the walls than on the roof. • A single story building receives 70% of it’s radiation on the roof.
23. 23. Module 3 Heat Transfer (II) Radiation: Solar and Thermal •Solar •Emanating from the sun •High energy content •Short wavelength, High frequency •Thermal •Emanating from every object in the universe •Low energy content •Long wavelength, Low frequency
24. 24. Module 3 Heat Transfer (II) Every Exposed Surface …Of every object …In the universe …With a temperature …Above absolute zero …Gives off infrared rays …In varying amounts
25. 25. Module 3 Heat Transfer (II) Absolute Zero
26. 26. Module 3 Heat Transfer (II) Absolute Zero
27. 27. Module 3 Heat Transfer (II) ABSOLUTE ZERO
28. 28. Module 3 Heat Transfer (II) Everything Above Absolute Zero… Radiates Energy in the form of infrared heat rays.
29. 29. Module 3 Heat Transfer (II) Infrared (thermal) heat rays travel… •Away from every point on the surface. •In a straight line. •In any direction. •With the greatest intensity perpendicular to the surface. •With the least intensity parallel with the receiving surface (zero intensity).
30. 30. Module 3 Heat Transfer (II) The radiation from a metal roof, a concrete surface or other opaque material originates within a few microns of the surface; hence emissivity (the rate of radiation emitted by a given surface) is a function of the surface state of a material rather than of its bulk properties. For this reason, the emissivity of a coated or painted surface is characteristic of the coating rather than of the underlying surface.
31. 31. Module 4 Processes in Radiation Processes in Radiation (ρ, α, τ, and ε) Module 4
32. 32. Module 4 Processes in Radiation Reflectivity Absorptivity Transmissivity
33. 33. Module 4 Processes in Radiation What’s a Black Body? •A theoretical body •With properties such that… •It will absorb all (100%) radiation falling on its surface •Reflecting and transmitting none •But it will emit radiation depending on its absolute temperature.
34. 34. Module 4 Processes in Radiation Black Body Radiation •Allows no convection •Reflects no radiation In-coming irradiation •Transmits no radiation (energy) Emits radiation Absorbs all radiation (depending on its (energy converts to heat) absolute temperature) (Absorptivity) + (Reflectivity) + τ (Transmissivity) = 1
35. 35. Module 4 Processes in Radiation Black Body Radiation (Absorptivity) + (Reflectivity) + τ (Transmissivity) = 1 A+R+T=1 Since there is no Reflectivity R=0 & Since there is no Transmissivity T=0 Then Absoptivity must equal one A=1
36. 36. Module 4 Processes in Radiation Black Body Radiation •No Reflectivity In-coming irradiation •No Transmissivity (G) •No Convection Absorbs all radiation Emits ( ε ) all radiation (energy converts to heat) If all in-coming G (energy) is absorbed, then all in-coming G (energy) is emitted, therefore ε = 1 Kirchoff’s Identity
37. 37. Module 4 Processes in Radiation Emissivity ( ε ) • The rate at which radiant heat energy is emitted by a given surface. • “The ratio of the thermal radiation from unit area of a surface to the radiation from unit area of a full emitter (black body) at the same temperature” • It is a physical property… just like weight, color, shape, etc. • All materials have an emissivity ranging from zero to one (100%).
38. 38. Module 4 Processes in Radiation Emissivity ( ε ) • The rate of radiation emanating from a surface. (the emissivity of an object’s surface is related to the ability of that surface to absorb heat rays.) • Total Emissive Power of a Black Body: Eb = σT4
39. 39. Module 4 Processes in Radiation Total Emissive Power of a Black Body Eb = σT4 q = quantity of heat ( J ) Joule ( 1 J = 1 Watt/s ) σ = Stefan – Boltzmann Sigma: a constant = constant 0.1714 x 10-8 Btu/h-ft2 or 5.669 x 10-8 W/m2 T = temperature K˚ or temperature R˚ K˚ = Celsius ˚ + 273.15˚ or R ˚ = Fahrenheit ˚ + 459.7˚
40. 40. Module 4 Processes in Radiation Common Power Units 1 watt = 3.412 Btu/hr 1 Watt/s = 1 Joule 1 Btu/s = 1.055 Watts 1 Cal/s = 4.19 Watts 1 Ft-lb./s = 1.36 Watts 1 Btu = 1050 Joules 1 Joule = 0.2389 Cal 1 Cal = 4.186 Joules
41. 41. Module 4 Processes in Radiation Grey Body Radiation •A grey body is a non-ideal emitter or an imperfect radiator. •A grey body will: •absorb some of the energy it will receive. •reflect some of the energy it will receive. •emit the energy it absorbs. •A grey body is opaque: τ = 0
42. 42. Module 4 Processes in Radiation Model of a Grey Body Radiation In-coming irradiation (G) Reflected energy Absorbs all radiation (energy converts to heat) Emitted ( ε ) energy Convected energy
43. 43. Module 4 Processes in Radiation Grey Body Radiation (Absorptivity) + (Reflectivity) + τ (Transmissivity) = 1 A+R+T=1 Since there is no Transmissivity T=0 then Reflectivity + Absorptivity = 1 A+R=1 Since there is Reflectivity R=>0 then Absorptivity must be: A=<0 therefore Emissivity must be less than 1 ε=<1
44. 44. Module 4 Processes in Radiation Emissive Power of a Grey Body •Real surfaces emit less radiation than ideal “black body” surface. •The ratio of actual emissive power [E] to the emissive power of a black body at the same temperature [Eb] is called the emissivity. •It is defined by ε = E/Eb
45. 45. Module 4 Processes in Radiation Energy Economics •Office worker requires 200 ft2 •Salary: \$30,000/yr •Value of services: \$150/ ft2 •Cost of Energy: \$2.25/ ft2 (1985 \$)
46. 46. Module 5 Term Definitions Term Definitions (Physics) Module 5
47. 47. Module 5 Term Definitions Definitions of Terms •Absorptivity •British Thermal Unit (Btu) •Conductance (C factor) •Conductivity (K factor) •Emissivity •Reflectivity •Resistance (R factor) •U Factor
48. 48. Module 5 Term Definitions Absorptivity • The fraction of thermal radiation incident on a surface which is absorbed.
49. 49. Module 5 Term Definitions British Thermal Unit • The amount of heat needed to raise the temperature of 1lb. Water 1 degree Fahrenheit. Conductance (C Factor) • The rate of heat flow in Watts per square meter Kelvin (W/m2K) of any material whether homogeneous or non-homogeneous.
50. 50. Module 5 Term Definitions Conductivity (k Factor) • Thermal conductivity, k, is the rate of conduction heat transfer per unit area for a temperature gradient of 1˚ C/m ( or 1˚ F/ft). •The units for k are W/(m ˚C) *or Btu/(h ft ˚F)+. •Thermal conductivity (k) measures the rate of heat transfer through a material from face to face. Calculate for any material by multiplying the thickness in meters by the appropriate k value.
51. 51. Module 5 Term Definitions Emissivity • Ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature. Reflectivity • The fraction of thermal radiation incident on a surface which is reflected.
52. 52. Module 5 Term Definitions Resistance (R Factor) • Resistance to heat flow is the reciprocal of C, k, or U: • 1/C, 1/k, 1/U •The smaller the C, k, or U factor fraction, and the larger the R factor, the better the insulation against heat transfer by conduction.
53. 53. Module 5 Term Definitions U Factor • The rate of heat flow or “overall coefficient of heat transmission” in Btus in one hour through one sq. ft. area of the entire depth of ceiling, roof, wall, or floor, including insulation if any, which will result from a 1˚ F temperature difference between the air inside and the air outside.
54. 54. Module 6 ASTEC Thermal Properties ASTEC Thermal Properties Module 6
55. 55. Module 6 ASTEC Thermal Properties ASTEC Thermal Properties Reflectivity: 86.9%
56. 56. Module 6 ASTEC Thermal Properties ASTEC Thermal Properties Absorptivity: 13.1%
57. 57. Module 6 ASTEC Thermal Properties ASTEC Thermal Properties Emissivity: 90.1%
58. 58. Module 7 ASTEC The Total Solution ASTEC The Total Solution Module 7
59. 59. Module 7 ASTEC The Total Solution Heat Transfer • The best way to reduce heat transfer: Prevent it from entering the building. • The best wat to manage heat transfer: Re-emit it quickly.
60. 60. Module 7 ASTEC The Total Solution Customer Requirements • Energy saving radiant heat barrier •Reduced heat transfer •Better heat management •Reduced cooling load •Protection against ultra-violet degradation • Long lasting waterproofing protection
61. 61. Module 7 ASTEC The Total Solution Customer Requirements • Roof structural integrity • No chipping, no cracking, no flaking • Corrosion control • Environmentally friendly products • Economical solutions •Attractive and clean finish •Long life cycle
62. 62. Module 7 ASTEC The Total Solution Customer Requirements • Low installation cost • Brand name recognition • Low roof maintenance • Product warranty • Labor warranty • Increased roof longevity
63. 63. Module 7 ASTEC The Total Solution Meeting Customer’s Needs • ASTEC is more than a mere coating: •Exterior Radiant Insulation & Finish System • ASTEC greatly reduces radiant heat transfer: •High solar reflectivity of 0.87 • ASTEC efficiently manages heat transfer •High thermal emissivity of .91
64. 64. Module 7 ASTEC The Total Solution Meeting Customer’s Needs ASTEC’s radiant heat barrier… • Reduces surface temperatures by as much as 20˚ C • Reflects between 80% and 87% or radiant heat (p = 0.80 to 0.87) • Limits radiant heat absorption between 15% and 20% (α = 0.14 to 0.20) • Reduces energy consumption by as much as 40%
65. 65. Module 7 ASTEC The Total Solution Meeting Customer’s Needs • ASTEC’s high density ceramic components: • Resists ultra-violet degradation • Maintains its color • ASTEC products are water based •ASTEC provides an aesthetic architectural appearance.
66. 66. Module 7 ASTEC The Total Solution Meeting Customer’s Needs • ASTEC’s metal primer seal inhibits corrosion and prevents oxidation from air and humidity. • ASTEC’s waterproofing membrane retains its flexibility and monolithic structural integrity.
67. 67. Module 7 ASTEC The Total Solution Meeting Customer’s Needs • ASTEC’s lower surface temperature provides: • Thermal shock protection • Longer roof life cycle • ASTEC is a world leader • Applied on structures in more than 30 countries.
68. 68. Module 7 ASTEC The Total Solution Meeting Customer’s Needs • ASTEC is easy to maintain and easy to repair •Ten (10) year warranty •ASTEC is applied by trained and authorized applicators only •Astec Dealers offer an optional “certified” roof maintenance program
69. 69. Module 7 ASTEC The Total Solution Cost Analysis / Financial Benefits • Cost effective installation •Low cost maintenance •Easy do-it-yourself repair •Energy Conservation
70. 70. Module 7 ASTEC The Total Solution Cost Analysis / Financial Benefits • Lower roof repair cost • Longer roof life • Environmentally friendly materials • Fire safe products: self extinguishing • Sound attenuation features • Mildew resistant qualities
71. 71. Module 7 ASTEC The Total Solution ASTEC Strengths • Over 20 year proven performance •Over 300 million square feet of applied products • Fully tested in independent laboratories • Accepted, approved and specified by several government agencies in various countries. •ISO 9001 – 2000 Registered Manufacturing
72. 72. Module 7 ASTEC The Total Solution ASTEC Strengths • Prestigious client references •Industrial sector •Commercial sector •Petrochemical sector •Residential Sector •Military sector • All marketing claims are scientifically substantiated
73. 73. Module 7 ASTEC The Total Solution ASTEC Strengths • All dealers are professionally trained • ASTEC Dealers have full time dedicated staff • Labor and Product warranty • Worldwide leadership and international recognition
74. 74. Module 7 ASTEC The Total Solution Next Steps • Check our references • Verify our claims • Compare us with the competition • Contact your local ASTEC Dealer for a free estimate