8. Radiation %26 Solar
Transcript of 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
region frequency wavelength comments
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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region frequency wavelength comments
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
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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
East-facing vertical surface
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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
Impact of solar radiation
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.
Impact of solar radiation
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
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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
East-facing vertical surface
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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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