8. Radiation %26 Solar

7/29/2019 8. Radiation %26 Solar

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Heat transfer mechanisms

Heat exchange from the body


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Title

Heat exchange from the body Radiant heat & the building enclosure


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region frequency wavelength comments

ultraviolet

waves1 - 3 PHz 100 - 280 nm

ultraviolet C (UVC), most

energetic & damaging to tissue,

filtered out by several hundred

metres of stratospheric ozone

layer, blocked by window glass

0 .94 - 1 PHz 280 - 315 nm

ultraviolet B (UVB),

causes most skin damage, mostly

blocked by ozone layer, dense

clouds & window glass

750 - 935 THz 315 - 400 nm

ultraviolet A (UVA), less absorbed

by atmosphere, penetrates glass

& deep into tissue but less

damaging, causes fluorescent

materials to emit light (black

light), used in tanning salons,

causes fading of colours


visible

light672 - 750 THz 400 - 446 nm violet

600 - 672 THz 446 - 500 nm blue

519 - 600 THz 500 - 578 nm green

507 - 519 THz 578 - 590 nm yellow

484 - 507 THz 592 - 620 nm orange

429 - 484 THz 620 - 700 nm red


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infrared

waves215 - 425 THz 0.7 - 1.4m

near (colour, photo, solar

or reflected) IR, closest to visible

range, can record on film, TV

remote controls, fibre optics,

passes through window glass

100 - 215 THz 1.4 - 3.0m short wavelength IR

40 - 100 THz 3.0 - 8.0 mmid (intermediate)

wavelength IR

20 - 40 THz 8.0 - 15 mlong wavelength IR,

blocked by window glass

0.3 - 20 THz 15 - 1,000 m

far (thermal) IR, type of

radiation felt as heat,

blocked by window glass,

produced in heat lamps


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WAVELENGTH (nm)

ENERGY

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

blackbody radiation (at sun)

radiation outside atmosphere

radiation at earths surface


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Impact of solar radiation

on buildings

through apertures


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Solar Heat Gain Factors (W/m2) 48N latitude

Clear, cloudless day, including direct, diffuse and reflected radiation (20% ground reflectance) through single-glazing (Tg = 0.87).

On the 21st day of each month indicated.

North-facing vertical surface

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

5 52 111 57

6 39 112 146 116 42

7 23 49 73 93 78 53 24

8 4 24 44 64 83 90 86 69 46 25 4

9 24 42 60 79 93 98 96 84 63 44 25 16

10 37 54 72 90 103 108 106 95 75 56 38 30

11 45 61 79 97 109 114 112 102 82 64 46 38

noon 48 63 81 99 111 116 114 104 84 66 48 41

13 45 61 79 97 109 114 112 102 82 64 46 38

14 37 54 72 90 103 108 106 95 75 56 38 30

15 24 42 60 79 93 98 96 84 63 44 25 16

16 4 24 44 64 83 90 86 69 46 25 4

17 23 49 73 93 78 53 24

18 39 112 146 116 42

19 52 111 57

East-facing vertical surface


5 122 228 129

6 337 504 534 492 316

7 10 458 628 668 667 653 598 403 11

8 90 470 644 690 689 678 675 665 602 439 90

9 371 530 609 621 611 600 601 605 581 508 363 272

10 333 415 460 466 458 450 453 453 444 403 328 286

11 166 205 232 245 249 248 249 247 230 203 165 146

noon 5 1 68 86 106 120 126 124 113 91 71 53 44

13 45 61 79 97 109 114 112 102 82 64 46 38

14 37 54 72 90 103 108 106 95 75 56 38 30

15 24 42 60 79 93 98 96 84 63 44 25 16

16 4 24 44 64 79 84 81 69 46 25 4

17 22 45 61 67 63 49 2318 19 38 46 40 21

19 8 17 9

Extracted from ASHRAE Solar Intensity & Solar Heat Gain Factor tables.

15 24 42 60 79 93 98 96 84 63 44 25 16

16 4 24 44 64 83 90 86 69 46 25 4

17 23 49 73 93 78 53 24

18 39 112 146 116 42

19 52 111 57



5 122 228 129

6 337 504 534 492 316

7 10 458 628 668 667 653 598 403 11

8 90 470 644 690 689 678 675 665 602 439 90

9 371 530 609 621 611 600 601 605 581 508 363 272

10 333 415 460 466 458 450 453 453 444 403 328 286

11 166 205 232 245 249 248 249 247 230 203 165 146

noon 51 68 86 106 120 126 124 113 91 71 53 44

13 45 61 79 97 109 114 112 102 82 64 46 38

14 37 54 72 90 103 108 106 95 75 56 38 3015 24 42 60 79 93 98 96 84 63 44 25 16

16 4 24 44 64 79 84 81 69 46 25 4

17 22 45 61 67 63 49 23

18 19 38 46 40 21

19 8 17 9

South-facing vertical surface


5 8 17 9

6 20 38 46 40 22

7 71 56 66 72 69 59 66 3

8 63 259 257 173 120 107 119 168 244 242 62

9 406 488 449 335 243 208 237 323 430 466 394 316

10 615 653 596 472 366 319 356 456 573 628 602 563

11 734 755 689 558 447 396 435 539 664 729 720 694

noon 772 790 720 587 474 423 462 568 695 763 758 734

13 734 755 689 558 447 396 435 539 664 729 720 694

14 615 653 596 472 366 319 356 456 573 628 602 563

15 406 488 449 335 243 208 237 323 430 466 394 316

16 63 259 257 173 120 107 119 168 244 242 62

17 71 56 66 72 69 59 66 3

18 20 38 46 40 22

19 8 17 9


on opaque surfaces

Solar radiation which strikes theopaque exterior surfaces of a

building cladding typicallyresults in heating of the surface.

Predicting the exact amount ofheating which occurs or the

temperature rise is complicatedby many factors.


on opaque surfaces


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Factors influencing surface temperature rise

Ambient air temperature

determines heat loss/gain to environment by conduction and convection

Mean radiant temperature of surroundings

dependent on temperature of nearby objects and sky

impacts heat loss/gain by radiation

Air movement

impacts heat loss/gain by convection

Absorption characteristics of surface

determined primarily by colour/texture/material

determines proportions of energy absorbed, reflected, or transmitted

Construction of assembly beneath the surface cladding

determines heat transfer by conduction into the assembly

thermal mass provides short-term energy storage

The most common technique for determining the temperature

rise makes use of the concept of a Sol-Air temperature, which isdefined as the fictitious exterior air temperature resulting inidentical heat flows to the actual situation.

The difference between the Sol-Air temperature and the actualexterior air temperature know as Sol-Air Excess Temperature

can be calculated from the Solar Intensities, depending onlatitude, month, time of day and orientation of the surface.

This Sol-Air Excess Temperature can be thought of as the rise intemperature of the surface caused by th e solar radiation.

Determining temperature rise

SolAir Excess Temperature (SolAir Temperature minus Air Temperature) (C) 48N latitude

Values in table below are calculated from preceeding ASHRAE Solar Intensity & Solar Heat Gain Factor tables.

North-facing vertical surface


5 3 7 3

6 2 7 9 7 3

7 1 3 4 6 5 3 1

8 1 3 4 5 5 5 4 3 1

9 1 3 4 5 6 6 6 5 4 3 1 1

10 2 3 4 5 6 6 6 6 4 3 2 2

11 3 4 5 6 7 7 7 6 5 4 3 2

noon 3 4 5 6 7 7 7 6 5 4 3 2

13 3 4 5 6 7 7 7 6 5 4 3 2

14 2 3 4 5 6 6 6 6 4 3 2 2

15 1 3 4 5 6 6 6 5 4 3 1 1

16 1 3 4 5 5 5 4 3 1

17 1 3 4 6 5 3 1

18 2 7 9 7 3

19 3 7 3

Clear, cloudless day, including direct, diffuse and reflected radiation (20% ground reflectance), on the 21st of each month indicated.

Vertical surfaces: Tsa - Tair= (/h0) I Horizontal surfaces: Tsa - Tair= (/h0) I 4C

Incident short wave solar intensity I = 1.15 x SHGF from preceding table (factor of 1.15 removes 0.87 glazing factor).

Values are for dark-coloured surfaces (/h0 = 0.052); for light-coloured surfaces (/h0 = 0.026), divide by 2).

15 1 3 4 5 6 6 6 5 4 3 1 1

16 1 3 4 5 5 5 4 3 1

17 1 3 4 6 5 3 1

18 2 7 9 7 3

19 3 7 3



5 7 14 8

6 20 30 32 29 19

7 1 27 38 40 40 39 36 24 1

8 5 28 39 41 41 41 40 40 36 26 5

9 22 32 36 37 37 36 36 36 35 30 22 16

10 20 25 28 28 27 27 27 27 27 24 20 17

11 10 12 14 15 15 15 15 15 14 12 10 9

noon 3 4 5 6 7 8 7 7 5 4 3 313 3 4 5 6 7 7 7 6 5 4 3 2

14 2 3 4 5 6 6 6 6 4 3 2 2

15 1 3 4 5 6 6 6 5 4 3 1 1

16 0 1 3 4 5 5 5 4 3 1 0

17 1 3 4 4 4 3 1

18 1 2 3 2 1

19 0 1 1

South-facing vertical surface


5 1

6 1 2 3 2 1

7 4 3 4 4 4 4 4

8 4 15 15 10 7 6 7 10 15 14 4

9 24 29 27 20 15 12 14 19 26 28 24 19

10 37 39 36 28 22 19 21 27 34 38 36 34

11 44 45 41 33 27 24 26 32 40 44 43 42

noon 46 47 43 35 28 25 28 34 42 46 45 44

13 44 45 41 33 27 24 26 32 40 44 43 42

14 37 39 36 28 22 19 21 27 34 38 36 34

15 24 29 27 20 15 12 14 19 26 28 24 19

16 4 15 15 10 7 6 7 10 15 14 4

17 4 3 4 4 4 4 418 1 2 3 2 1

19 1


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8. Radiation %26 Solar

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