Solar Radiation
WORKSHOP IN
THE PRACTICAL ASPECTS OF
SOLAR SPACE AND DOMESTIC WATER HEATING SYSTEMS
FOR
RESIDENTIAL BUILDINGS
MODULE 5
SOLAR RADIATION
SOLAR ENERGY APPLICATIONS LABORATORY
COLORADO STATE UNIVERSITY
FORT COLLINS, COLORADO
NOVEMBER, 1978
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
GLOSSARY OF TERMS
INTRODUCTION
OBJECTIVE
UNITS
VARIABILITY OF SOLAR ENERGY ON THE EARTH'S SURFACE
SOLAR CONSTANT
THE SOLAR SPECTRUM
ENERGY REACHING EARTH
.
.
.
.
.
.
.
MONTHLY VARIATIONS
DAILY VARIATIONS
HOURLY VARIATIONS
EFFECT OF SURFACE TILT
EFFECTS OF COLLECTOR ORIENTATION
DETERMINATION OF DUE SOUTH
SOLAR DATA FOR SYSTEM DESIGN
REFERENCES
.
.
.
LIST OF FIGURES
Figure
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
Page
Useful Spectrum of Solar Energy for Space
Heating and Cooling Systems
5-5
Atmospheric Effects on Solar Radiation Reaching
Earth
5-5
Energy Intercepted by a Unit-Width Horizontal
Surface
5-7
Monthly Variation of Average Daily Radiation on a
Horizontal Surface, Boulder, Colorado
. . .
5-7
Hourly Record of Clear Day Radiation on a Horizontal
Surface at Fort Collins, Colorado .
.
.
.
5-10
Effect of Tilting the Collector on Energy
Intercepted
5-10
Variation of the Angle of Incoming Radiation with
Season and Collector Tile to Maximize Winter
Collection
5-12
Shadow Diagram on a Horizontal Surface Showing the
Passage of the Sun Across the Sky and the
Determination of Due South, March 23, 1976,
Fort Collins, Colorado
5-13
5-9
Mean Daily Solar Radiation (Langleys), January
.
5-17
5-10
Mean Daily Solar Radiation (Langleys), February
.
5-17
5-11
Mean Daily Solar Radiation (Langleys), March .
.
5-18
5-12
Mean Daily Solar Radiation (Langleys), April .
.
5-18
5-13
Mean Daily Solar Radiation (Langleys), May
.
.
5-19
5-14
Mean Daily Solar Radiation (Langleys), June
.
.
5-19
5-15
Mean Daily Solar Radiation (Langleys), July
.
.
5-20
5-16
Mean Daily Solar Radiation (Langleys), August
.
5-20
5-17
Mean Daily Solar Radiation (Langleys), September
.
5-21
5-18
Mean Daily Solar Radiation (Langleys), October
.
5-21
5-19
Mean Daily Solar Radiation (Langleys), November
.
5-22
LIST OF TABLES
C
Table
Page
5-1
Energy Units
5-2
5-2
Energy Conversion Factors
5-3
5-3
Monthly Variations in Energy on a Horizontal
Surface Selected Cities
5-8
5-4
Mean Daily Solar Radiation (Langleys)
5-5
Monthly Averages of Daily Radiation on South Facing
Surfaces of Several Tilts for Several Sites
B t u
in Colorado ( 2
)
Ft -day
V
.
.
.
5-14
5-22
5-iv
GLOSSARY OF TERMS
beam radiation
See "direct radiation"
Btu
British Thermal Unit - the amount of heat
required to raise the temperature of one
pound of water one degree Fahrenheit
calorie
The amount of heat required to raise the
temperature of one gram of water one degree
Centigrade
diffuse radiation
Radiation that has been scattered in passing
through the atmosphere
direct radiation
Radiation received by a surface directly from
the region of the solar disc
infrared radiation
Non-visible radiation just beyond the red
end of the visible spectrum
insolation
Solar radiation that is received by a surface
latitude
angular distance, measured in degrees, north
or south from the equator
northern hemisphere
Half of the Earth north of the equator
ozone layer
A layer in the upper atmosphere comprised
primarily of the gas ozone (0 3 )
ultraviolet radiation
visible radiation
Non-visible radiation with short wavelengths
just beyond the violet end of the visible
spectrum
radiation that is perceptible by the eye
INTRODUCTION
Solar energy starts, of course, with the sun.
The sun is a huge
nuclear fusion reactor located at an average distance of 93 million
miles from earth.
It has a surface temperature of about 10,800°F, and
gives off energy continuously in the form of radiation.
The use of the
energy which reaches earth for heating is what this course is all
about.
In this module you will learn about the way the energy given
off by the sun is altered before it reaches the earth and the amount of
energy that reaches earth.
OBJECTIVE
The objective of this module is to present the factors which affect
the availability of solar radiation of the earth's surface, At the
end of this module the trainee should be able to:
1.
Recognize the amount of solar radiation available on the
earth's surface on a clear day.
2.
Recognize seasonal variations in solar radiation
3.
Recognize daily variations in solar radiation
4.
Differentiate between beam and diffuse radiation
5.
Estimate the amount of solar energy reaching a collector
surface.
6.
Recognize the various units used to measure solar energy
7.
Given conversion factors, convert solar radiation from
one set of units to another
8.
Select the data needed for planning a solar system.
UNITS
The intensity of solar energy is expressed in several different
2
units.
In this manual one unit will consistently be used, Btu/ft .
However, you will often encounter other units in the literature, and
it is therefore advantageous to be able to convert from one unit to
another.
Units commonly found are listed in Table 5-1.
Table 5-1
Energy Units
Abbreviation
Unit
Energy Density
Btu/ft
KJ/m
2
British Thermal Units per square foot
2
Kilojoules per square meter
2
Langley (cal/cm )
calories per square centimeter
Power
2
Btu/ft -hr
2
British Thermal Units per square foot
per hour
KJ/m *hr
Kilojoules per square meter per hour
Langley/min
calories per square centimeter per
minute
W/m
2
Watts per square meter
Table 5-2 gives conversion factors from one set of units to another.
An example will show the use of this table.
The Climatic Atlas of the
United States lists the annual average daily solar radiation for
Table 5-2
Energy Conversion Factors
To Convert into Btu/ft
2
To Convert into Btu/ft
Multiply
Multiply
3.69
Langleys
KJ/m
2
221
2
KJ/m -hr
W/m
.088
2
Boulder, Colorado as 367 Langleys per day.
hr
By
Langleys/min
.088
2
.316
To convert Langleys/day to
2
Btu/(ft *day) multiply by the conversion factor (3.69) in Table 5-2 to
2
change Langleys to Btu/ft .
367
L a n g 1 e y s
day
x 3.69
= 1354
'
Langley "
Btu
f t 2
d a y
VARIABILITY OF SOLAR ENERGY ON THE EARTH'S SURFACE
SOLAR CONSTANT
The intensity of the sun's energy on a surface varies with distance
from the sun.
At the average earth-sun distance, out in space, the
intensity of solar energy has been determined to be 428 Btu/(ft
with a variability of about three percent.
is called the "solar constant".
2
hr)
2
The value of 428 Btu/(ft *hr)
Due to the earth's elliptical orbit
around the sun, the distance from the earth to the sun changes during
the year so that the energy reaching the outer atmosphere of the earth
2
varies from 410 to 440 Btu/ft *hr.
In addition to the variability in
solar radiation that reaches the outer atmosphere around earth due to
seasons, there are very large variations in the amount of solar energy
available at a particular location on the earth's surface.
Radiation
reaching the earth's surface is of primary interest to terrestrial
applications and the intensity will vary considerably with latitude
season of the year, and local weather conditions.
THE SOLAR SPECTRUM
The radiation from the sun can be separated into three major
energy regions.
The high frequency (short wave length) energy in the
radiation spectrum is labeled "ultraviolet" or "UV" and is detected by
the human body primarily in terms of sunburn.
The medium frequency
energy radiation band in the solar spectrum is the visible band.
The
low frequency (long wave length) radiation band is the "infrared" or
"IR" region.
The amount of ultraviolet energy in the solar spectrum
is small, essentially negligible in terms of useful heating effect.
The visible band comprises about 47 to 48 percent of useful radiation
for heating and the "near" infrared band makes up the balance.
illustration of the solar spectrum is shown in Figure 5-1.
An
The in-
tensity will vary with latitude, elevation and time of year because the
amount of radiation that is absorbed and scattered by the atmosphere
depends on the thickness of the atmosphere through which solar radiation
must penetrate.
ENERGY REACHING EARTH
The energy reaching earth is less than the "outer space" intensity.
There are a number of factors that cause this reduction as illustrated
in Figure 5-2.
Some of the energy is reflected back into outer space
Wavelengh,
Figure 5-1.
(
)
Useful Spectrum of Solar Energy for Space
Heating and Cooling Systems
Reflection
Upper
Atmosphere
Atmosphere
Direct
(Absorption)
Dust
(Scattering)
Clouds
(Scattering and
Absorption)
Diffuse
Earth's
Figure 5-2.
Surface
Atmospheric Effects on Solar Radiation Reaching
Earth
by the top of the atmosphere, much as light is reflected from a
mirror.
Still more is reflected from the tops of clouds.
As much as
30 percent of the incoming radiation can be reflected in this manner.
A portion of the radiation is absorbed by chemical constituents in
the atmosphere.
The ozone layer absorbs much of the ultraviolet
radiation, and carbon dioxide, oxygen, and water vapor also absorb
radiation.
Some of the radiation is scattered by dust and clouds.
Radiation that is received from the solar disc is called "direct
radiation", that is, the sun's rays have not been scattered in passing
through the atmosphere.
Solar radiation received elsewhere is called
"diffuse radiation" because it has been scattered by clouds or other
particles.
On a "clear" day most of the energy reaches earth as direct
radiation, but on a cloudy overcast day, a large portion or all of
the solar radiation at a particular location on earth may be diffuse.
MONTHLY VARIATIONS
Solar energy on a horizontal surface at any location on earth, if
averaged over a month, shows a month-to-month variation.
This is due
to earth's rotation about the sun and to seasonal changes in weather,
which affect the cloud cover.
In the winter the sun is lower in the sky
than in the summer, and the resultant larger incident angle between the
sun and earth's a line perpendicular to a horizontal surface reduces the
amount of radiation Intercepted by the earth's surface, as shown in
Figure 5-3.
Figure 5-3-a shows the energy intercepted by a unit width
horizontal surface when the sun is at a low angle as it is in winter.
In Figure 5-3-b, the sun is shown at a higher angle, say during the
summer months, and a larger amount of energy is intercepted.
SOLAR R A D I A T I O N
(a) LOW SUN ANGLE, WINTER
4 " R A D I A T I O N U N I T S " INTERCEPTED
Figure 5-3.
(b) H I G H SUN ANGLE,
SUMMER
6 "RADIATION
U N I T S " INTERCEPTED
Energy Intercepted by a Unit-Width Horizontal Surface
The monthly variation in solar radiation incident on a horizontal
surface is shown in Figure 5-4 for Boulder, Colorado.
There is approxi-
mately twice as much radiation during June and July compared to December
and January.
Figure 5-4.
Monthly Variation of Average Daily Radiation on a Horizontal
Surface, Boulder, Colorado (From the Climatic Atlas of the
United States)
Monthly variations for some other cities are listed in Table 5-3
The variations for Chicago from December to June is about 6 times, and
for Washington it is about a factor of 3.
Other cities in the U . S .
exhibit variations similar to those shown in Figure 5-4.
Table 5-3
Monthly Variations in Energy on a Horizontal
Surface
2
Selected Cities, (U.S.)(Btu/ft -day)
December
City
Chicago, Illinois
Tucson, Arizona
Washington, D.C.
Miami, Florida
Fairbanks, Alaska
Los Angeles, California
March
June
September
280
835
1685
1152
1122
1987
2582
2098
611
1266
1818
1380
1163
1800
1958
1619
22
784
1855
622
887
1730
2193
1851
DAILY VARIATIONS
The total amount of solar radiation reaching a horizontal surface
on earth varies from day to day, primarily because of atmospheric
phenomena.
Clouds, dust, and other particulate matter in the atmosphere
cause variations in radiation absorption and scatter.
Daily variations
are large, and may range from zero useful heating energy to 2000 to
2
2500 Btu/(ft -day).
The values shown in Figure 5-4 are typical for the
Colorado Front Range region.
HOURLY VARIATIONS
Hourly variations in available solar energy at a given location
are principally due to the earth's rotation although cloudiness can
have significant effects.
Early morning sun is at a very low angle and
the solar rays must pass through a large thickness of atmosphere.
intensity of the energy received is therefore low.
The
The hourly peak in
radiation occurs at noon, when the sun is at the highest angle and is
passing through the minimum thickness of the atmosphere. Since winter
days are shorter than summer days, the period during which solar energy
can be collected varies with season.
The solar intensity on a horizontal surface, measured in Fort Collins,
Colorado is shown in Figure 5-5.
data were obtained on clear days.
breaks in the curves.
The smooth curves indicate that these
The presence of clouds would result in
Note the higher intensity and longer period of
measurable radiation during a summer month as opposed to a winter month.
EFFECT OF SURFACE TILT
Discussion so far has concerned only the radiation on a horizontal
surface.
In fact, when designing a solar collector, it is advantageous
to tilt the collector so that it is perpendicular to the sun's rays.
Figure 5-6 illustrates the increase in energy intercepted by a collector
when it is tilted with respect to a horizontal plane.
The maximum
amount of energy that can be intercepted by a plane surface is when
the surface is perpendicular to the sun's rays as shown in
Figure 5-6(b).
When the collector is tilted at any other angle the
amount of energy intercepted is reduced as shown in Figure 5-6(c).
Time of Day
Figure 5-5.
Hourly Record of Clear Day Radiation on a Horizontal
Surface at Fort Collins, Colorado (Data from Solar
House I)
Energy Intercepted
by a Horizontal
Surface
Figure 5-6.
Effect of Tilting the Collector on Energy Intercepted.
Maximum energy would be intercepted by a collector if the plane
surface were to track the sun across the sky so that the rays would
always be perpendicular to the plane.
This would mean both following
the sun as it moved from east to west during the day and changing the
collector tilt from day to day.
Tracking can be accomplished but is
not considered practical for collectors in residential solar heating
systems.
Since tracking is impractical, a compromise is to tilt the collector
so that it is roughly perpendicular to the sun's rays at solar noon
during the months when maximum heat collection is desired.
The best
angle for a given location depends on the time of year, since the
sun moves across the sky at a lower angle in the winter than in the
summer.
For heating purposes, maximum collection is desired during the
coldest part of the heating season.
During this season, from about
October until March, the sun's angle varies from 5 degrees to 23 degrees
below a line drawn at an angle from the perpendicular equal to the
latitude of the location (Figure 5-7-a).
To maximize collection during
the heating season a good compromise is to tilt the collector at an
angle of about latitude plus 15 degrees.
This is illustrated in
Figure 5-7-b.
In the northern hemisphere the collector should be tilted to the
south; the opposite is true in the southern hemisphere.
To maximize
summer collection the collector can be tilted to latitude minus 15 degrees.
If both summer and winter collection are desired, a good compromise is to
tilt the collector to an angle equal to the latitude.
September 21
March 21
June 21
Collector
- Latitude
Angle
Hori;
(a) December 21, Sun 23° below Lat. Angle from Perpendicular
(b) Collector Tilted at Latitude
June 21, Sun 2 3 ° above Lat. Angle from Perpendicular
+ 15° Maximizes Winter
September 21 and March 21, Sun at Lat. Angle from
Collection.
Perpendicular
Figure 5-7.
(a)
Variation of the Angle of Incoming Radiation
with Season
(b)
Collector Tilt to Maximize Winter Collection
EFFECTS OF COLLECTOR ORIENTATION
Since the maximum intensity of direct radiation occurs at noon
when the sun is due south (northern hemisphere), the collectors should
face directly south.
If this is not practical because of building
considerations, a variation of 15 degrees east or west of due south can
be tolerated without serious effect on the total energy collected. An
orientation 15 degrees east of south will advance the time of peak
collection one hour; an orientation 15 degrees west of south will delay
the peak one hour.
In some cases a designer can take advantage of the
change in peak collection.
If, for example, the collectors are partially
shaded in the later afternoon, facing the collectors east of south would
increase daily energy collection.
DETERMINATION OF DUE SOUTH
The effect of the passage of the sun across the sky during the day
is shown in Figure 5-8.
Such a shadow diagram can be used to determine
due south for collector orientation.
shadows lies due east-west.
A line joining the tips of the
By drawing a perpendicular to this line the
north-south line is determined.
Note the deviation of true north from
magnetic north as determined with a compass.
( a ) Equipment Set-up
Figure 5-8.
(b) Resultant Sun-track Diagram
Magnetic North Shown
Shadow Diagram on a Horizontal Surface Showing the Passage
of the Sun Across the Sky and the Determination of Due
South, March 23, 1976, Fort Collins, Colorado
SOLAR DATA FOR SYSTEM DESIGN
Solar heating and cooling systems can be sized on the basis of
monthly average daily radiation on a horizontal surface.
Tabular values
are listed for each month in Table 5-4, for many cities in the United
States.
The yearly average daily radiation for the cities is also
included in the table.
Because the data for specific locations are
Table 5-4.
MONTHS
STATE AND STATIONS
ALASKA, Annette
Barrow
Bethel
Fairbanks
Mataruska
ARIZONA, Page
Phoenix
Tucson
ARKANSAS. L i t t l e Rock
CALIFORNIA. Davis
Fresno
Inyokern (China Lake)
LaJolla
Los Angeles W A S
Los Angeles WBO
Riverside
Santa Maria
Soda Springs
COLORADO, Boulder
Grand J u n c t i o n
Grand Lake (Granby)
O . C . , Washington ( C . O . )
American U n i v e r s i t y
Silver Hill
FLORIDA. Apalachicola
B e l l e Isle
Gainesville
Miami A i r p o r t
Tallahassee
Tampa
GEORGIA, A t l a n t a
Griffin
HAWAII. Honolulu
Mauna Loa Obs.
P e a r l Harbor
IDAHO, Boise
Twin F a l l s
I L L I N O I S , Chicago
Lemont
INDIANA. I n d i a n a p o l i s
IOWA, Ames
KANSAS. Dodge C i t y
Manhattan
KENTUCKY, Le«ington
LOUISIANA, Lake Charles
New Orleans
Shreveport
MAINE, Caribour
Portland
MASSACHUSETTS, Amherst
Blue H i l l
Boston
Cambridge
E a s t Wareham
Lynn
MICHIGAN, E a s t Lansing
S a u l t S t e . Marie
MINNESOTA, S t . Cloud
MISSOURI, Columbus ( C . O . )
U n i v e r s i t y of Missouri
Mean Daily Solar Radiation (Langleys)
FEB MAR
63
1
38
16
32
*x>
301
315
IB8
174
IW
306
244
!'S
243
275
263
2?3
201
227
212
174
158
177
m
267
349
274
327
2li)
234
363
522
359
133
163
96
170
144
174
255
192
172
245
2H
232
133
152
116
I5J
129
153
140
118
121
130
168
173
166
APR MAY
364
|236
380
1180
444
282
21.3
376
1242
356
~i2i>
6l8
526
636
540
655
'353 446
390
528
'-4J7
452
1412 ,562
683
• 302 '397 457
•331 ,470
515
327 !436
483
• 36/ '78 541
i 346 .482
552
1316 374
551
:268 U o i
460
I 324 . a x
546
313 1423 ' 512
411
! 266 !344
398
I 231 1322
.247 ;342
438
" 367 1441
535
j 330 '412
ItJ
' 34 3 4 2 7 517
|415 389
540
311 423
499
• 391 474 539
.290 .380
488
• 295 '385 522
1422 1516
559
: 576 680
689
• 400 487 529
<85
1 236 ^343
240 .'355
462
• 147 '227 331
242 V O
402
213 316
396
' 25J 1326
4UJ
316 418
528
264 34!
4:3
263 357
480
• 306 - 397 481
412
' I V ) J Jb
446
'292 '384
400
I 231 ,364
: 235 ,352 409
•
' • (300
' m
jia
1 194 290 350
| 235 ,323 400
218 1305
385
1 209 1300 394
2IU juy
jiy
225 :356
416
1 260 ' 368 426
251 • 340 434
' 248 {324 | 429
1115
38
108
71
92
' J42"
409
' 391
260
257
JAN
JUN
438
528
454
504
13fi 462
' 695 707
724 739
729 699
523 559
625 694
647 702
772 819
506 487
572 596
555 584
623 6&>
635 694
615 691
460 525
615 708
552 652
551 494
510
467
513 555
•m
603
V,\
483 464
579 521
553 532
547 521
596 574
533 562
570 577
617 615
*
727
573 566
1 585 636
552 592
424 458
506 553
488 543
400 M l
568 650
551
527
581 628
591
555
4411
449
558 557
4 76 470
539
514
514
431
51(1
469
445 483
476
420
508
452
549
454
54/
483
557
523
535
496
574
530
560
501
437
513
457
61
JUL
AUG
SEP
OCT
4 38 341
429 255
376 252
4 34 317
409 314
680 596
658 613
626 588
556 518
682 612
682 621
772 729
497 464
641 581
651 581
673 618
680 613
760 681
520 439
676 595
600 505
536 446
496 440
511 457
529 511
488 461
438 483
532 505
50 P 542
534 494
532 w a
556 522
615 612
703 642
598 567
670 576
602 540
473 403
540 498
541 I 4go
43b 4 fi 0
642 592
531 526
617 563
526 511
417 416
578 528
508 448
561 488
258
115
202
180
198
516
566
570
439
493
510
635
389
503
500
531
524
510
412
514
4/6
375
364
391
456
400
418
440
122
41
115
82
Iftfl
402
449
442
343
,34 7
376
467
320
373
362
40/
419
357
310
373
361
299
278
293
413
366
347
384
452
41b
435
573
602
539
4bU
432
313
398
405
367
493
410
494
449
303
414
336
383
400
344
368
50/
560
466
301
286
20/
275
293
274
380
292
357
402
357
354
212
2/8
502
486
482
495
528
b4U
573
557
574
583
344
334
367
365
341
373
322
366
453
417
266
235
253
258
241
255
216
237
322
324
*
—
449
411
464
436
432
466
472
486
522
509
•
—
*
—
NOV
DEC
Ann'l
59
41
a
22
6
IS
243
281
305
187
148
161
300
221
241
?34
270
252
1B2
182
212
184
166
141
156
262
291
233
316
230
300
211
201
371
481
343
124
131
76
138
132
143
234
156
174
250
198
205
107
137
124
135
115
124
140
107
108
96
124
158
M6
243
206
233
224
J24
498
520
518
385
411
450
568
380
463
436
483
481
4 59
36/
456
41 /
356
333
35/
444
39/
410
451
*
44
26
38
310
344
356
244
222
M
363
277
289
281
319
313
248
222
260
234
211
192
202
^J U
300
353
292
356
264
283
426
504
386
IU2
176
120
165
177
la;
285
227
245
300
Vi
254
111
157
152
162
136
164
163
135
136
105
146
225
177
453
396
413
516
484
395
378
273
352
345
345
447
371
411
418
347
400
316
350
—
328
301
322
322
317
311
333
348
380
365
STATE AND STATIONS
MONTANA. Glasgow
Great F a l l s
Summit
NEBRASKA, L i n c o l n
North Qmaha
NEVADA. E l y
Las Vegas
NEW J E R S E Y . Seabrook
NEW HAMPSHIRE, Mt. Washington
NEW MEXICO, Albuquerque
NEW YORK. Ithaca
New York Central Park
Sayville
Schenectady
Upton
NORTH CAROLINA, Greensboro
Hatteras
Raleigh
NORTH DAKOTA, Bismarck
OHIO, C l e v e l a n d
Columbus
Put-in-Bay
OKLAHOMA, Oklahoma C i t y
Stillwater
OREGON, A s t o r i a
CorvalIis
Medford
PENNSYLVANIA, P i t t s b u r g h
S t a t e College
RHODE ISLAND, Newport
SOUTH CAROLINA, Charleston
SOUTH DAKOTA, Rapid C i t y
TENNESSEE, N a s h v i l l e
Oak Ridge
TEXAS, B r o w n s v i l l e
El Paso
F o r t Worth
Midland
San Antonio
UTAH, Flaming Gorge
S a l t Lake C i t y
VIRGINIA, Mt. Weather
WASHINGTON, North Head
F r i d a y Harbor
Prosser
Pullman
U n i v e r s i t y of Washington
Seattle-Tacoma
Spokane
WISCONSIN, Madison
WYOMING, Lander
Laramie
INLAND STATIONS
Canton I s l a n d
San J u a n , P . R .
Swan I s l a n d
Wake I s l a n d
NOTES:
*
--I
t
{
Langley
MONTHS
JAN
FEB
154 258
140 232
122 162
188 259
193 299
236 339
277 384
157 227
117 218
303 386
116 194
130 199
160 249
130 200
155 232
200 276
238 317
235 302
157 250
125 183
128 200
126 204
251 319
205 289
90 162
•
89
116 215
94 169
133 201
155 232
252 314
183 277
149 228
161 239
297 341
333 430
250 320
283 358
279 347
238 298
163 256
172 274
•
16'
8/ 157
K7
222
121 205
67 126
75 139
119 204
148 220
226 « 4
216 290
588
404
442
4 38
626
481
496
51B
MAR
APR
HAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
knn' 1
385
366
268
350
365
468
519
318
238
511
272
290
335
273
339
354
426
466
434
414
416
463
563
621
403
568
528
462
494
516
625
702
482
605
583
493
544
546
712
748
52/
645
6 39
560
568
568
64/
675
509
531
532
510
484
519
618
627
455
410
407
354
396
410
bit!
551
385
26/
264
216
296
298
J94
429
278
154
154
102
199
204
281
318
192
388
366
312
363
379
aby
509
339
356
303
291
302
409
390
270
26?
336
216
295
334
384
400
322
331
402
547
427
4 76
417
443
354
338
257
274
351
304
245
265
321
313
45?
424
618
334
369
415
338
428
469
569
466
44 7
286
391
386
494
454
375
406
482
317
380
405
512
482
4 32
450
456
654
488
550
445
522
47$
414
432
418
521
462
364
403
4 74
394
548
608
686
440
432
494
413
502
531
635
494
550
502
4?l
468
536
504
492
517
592
429
456
477
551
532
503
518
564
7l4
562
611
541
565
570
508
509
514
616
558
445
503
563
466
587
554
726
SOI
470
565
448
573
564
652
564
590
562
562
544
615
600
469
570
652
491
518
527
564
585
551
551
610
72$
651
617
612
650
621
525
437
578
680
653
461
511
596
514
678
643
683 626
515 4 b J
459 389
543 462
441 397
543 4 75
544 485
625 562
535 476
617 516
562 494
542 477
561 487
610 593
596 545
539 461
676 bbB
698 605
497 409
511 444
513 455
520 bOl
590 541
530 473
526 4 78
627 568
666 640
613 593
608 574
639 585
599 538
620 551
510 430
486 436
586 507
707 604
699 562
496 435
566 452
665 556
534 452
651 586
606 636
554
346
331
385
299
391
406
471
379
390
278
422
382
487
455
354
39/
447
339
358
377
4U4
435
403
416
475
i/6
503
522
493
425
446
375
321
351
458
410
299
324
404
348
4/2
438
4 38
231
242
289
218
293
VI
358
307
272
289
286
275
377
354
209
2Jb
279
207
256
271
J JU
315
308
318
411
460
403
396
398
352
Jib
281
205
194
274
U b
170
188
225
241
Jb4
324
334
I2U
147
186
128
182
24 J
282
235
161
141
l/b
144
291
269
111
144
149
118
149
176
286
204
208
213
296
372
306
325
295
262
2U4
202
122
10'
136
146
93
104
131
145
2J9
229
116
112
76
159
170
Zla
258
140
96
276
9b
115
142
104
146
19/
214
199
124
115
I 29
109
240
209
79
BU
93
77
JIB
139
"225"
158
150
163
263
"313"
245
275
256
215
~T46~
168
77
75
100
96"
59
64
75
115
19b
186
634
580
615
577
604
622
646
627
561
519
625
642
540
536
544
656
640
531
53
587
651
460
457
525
600
411
304
482
579
411
382
421
•
•
*
*
—
550
639
588
629
—
597
540
591
623
*
*
Denotes o n l y one year of data f o r the month -- no means computed
No data f o r the month ( o r incomplete data f o r the y e a r )
Barrow i s in darkness during the w i n t e r months
Madison data f t e r 1957 not used due to exposure i n f l u e n c e
R i v e r s i d e data p r i o r to March 1952 not used - Instrumental d i s c r e p a n c i e s
is
the u n i t used to denote one gram c a l o r i c per square c e n t i m e t e r .
•
—
512
JU^
298
352
282
355
mi
443
—
369
335
J4(T
332
436
405
301
—
389
280
318
338
404
392
355
364
442
536
445
466
442
426
394
350
320
399
372
272
300
361
324
443
408
597
512
526
560
limited, and estimates for adjacent areas are necessary, it is convenient
to arrange a graphical presentation of the distributions of the monthly
average daily radiation iso-intensity lines on a map of the United States,
as shown in Figures 5-9 through 5-20.
The sizing techniques to be used in this workshop require a knowledge
of the monthly average solar radiation incident on a one square foot
surface set at the tilt of the particular collector.
The calculation
to convert the radiation on a horizontal surface to that on a tilted
surface is lengthy, complicated, and time consuming.
The details of
the calculation are given in References [8] and [9].
To simplify the
sizing process these calculations have been done for several sites in
Colorado and for several common collector tilts.
presented in Table 5-5.
The results are
Also included in this table is T
average ambient temperature, also needed for system sizing.
the monthly
The
radiation data for collector tilts presented are:
T.
Horizontal - this is the raw data and would be useful in roof
pond passive designs (see Module 11)
2.
Tilt equal to latitude - this would be useful in sizing systems
heating domestic hot water only (see Module 6)
3.
Tilt equal to latitude plus 15° - this would be useful for space
heating systems (See Modules 8 and 9)
4.
Vertical - this would be useful in passive direct gain and
mass wall applications (see Module 11)
For locations which are not close to one of the sites given it
may be necessary to use some judgement in selecting site data.
The
criteria should be similar weather with regard to cloud cover and
roughly similar latitude.
The selection of appropriate solar data
is most difficult in mountainous regions where cloud cover may vary
over short distances.
It may be more appropriate for a mountainous site
in Colorado to use Grand Lake data even though some other site may be
geographically closer.
For locations between two data sites it may be
appropriate to use linear interpolation (or averaging) of the data.
MEAN DAILY SOLAR RADIATION
. JANUARY
Figure 5-9.
(Langleys)
\
Mean Daily Solar Radiation (Langleys), January
MEAN DAILY SOLAR RADIATION
(Langleys)"
Figure 5-11.
Mean Daily Solar Radiation (Langleys), March
Figure 5-13.
Mean Daily Solar Radiation (Langleys), May
Figure 5-15.
Mean Daily Solar Radiation (Langleys), July
Figure 5-17. Mean Daily Solar Radiation (Langleys), September
MEAN DAILY SOLAR RADIATION
7
_L»
~ - - NOVEMBER.
Figure 5-19.
-... . . ' 7 ' ^ . . '
* •
'.
'
•
"*/•
"
\
Mean Daily Solar Radiation (Langleys), November
..r^FAN "DAILY
, i
L a n g "ley
•
\
SOLAR
RADIATION
(Langleys)
DECEMBER—'
i
I
; ^
I;/
, ' IIn
• I
:i i! ^\
:
.
.
S
-»•*-.
r
l
'
i
' . . > 1
I
q ^ /f y ' ^ ^ V
, . ,
'
I
1
V
v i
„....!..
I
,
I
_! — ,», , , . r
!
"''I-
w
O1
1
—
1
^ " I I T T ' f i f i f c **
. :
*
o
Table 5-5.
Monthly Averages of Daily Radiation on South Facing Surfaces of Several Tilts for Several Sites
B t u
in Colorado ( 2
)
Ft day
City
MAY
JUNE
JULY
AUG
SEPT
32
34
37
48
57
66
73
72
63
54
41
36
Horizontal 740
Latitude
1358
Lat.+15°
1450
Vertical
1355
987
1495
1537
1318
1478
1877
1833
1375
1695
1720
1593
1003
1695
1526
1339
759
1934
1644
1392
750
1518
1746
1670
1168
1142
1633
1655
1379
818
1432
1521
1392
671
1302
1409
1344
F
Grand Lake
(Granby)
LAT = 40.2°
1916
1667
1418
780
1617
1568
1400
843
30
32
37
48
57
66
73
72
63
52
39
32
1245
1992
2057
1685
1606
2024
2008
1450
1912
1988
1816
1126
2145
1931
1673
858
2409
2024
1710
819
2332
2006
1679
840
2182
2145
1876
1047
1820
2148
2046
1398
1363
2004
2064
1691
965
1747
1864
1707
803
1614
1768
1693
27
32
41
52
61
72
77
75
66
54
39
30
Horizontal 854
Latitude
1584
Lat.+15°
1701
Vertical
1583
1196
1869
1920
1648
1582
2002
1969
1456
1962
2040
1844
1130
2226
2003
1725
910
2605
2292
1824
862
2469
2271
1778
894
2138
2095
1839
1055
1845
2174
2085
1423
1391
2040
2085
1726
968
1731
1847
1687
796
1582
1723
1630
16
19
Horizontal 781
Latitude
1471
Lat.+15°
1574
Vertical
1473
1154
1839
1392
1639
Ta°F
Ta°F
Pueblo
LAT = 38.2
JAN
Horizontal 940
Latitude
1824
Lat.+l5°
1975
Vertical
1813
Ta°F
Grand Junction
LAT. = 39.1°
DEC
APR
F
Denver
LAT. = 39.4°
NOV
MAR
V
Boulder
LAT = 40.0°
OCT
FEB
Collector
Tilt
Horizontal
Latitude
Lat.+15°
Vertical
25
32
43
50
55
54
46
37
27
18
1558
1996
1868
1428
1887
1960
1793
1113
2034
1837
1586
876
2328
1956
1623
844
2211
1912
1664
864
1860
1304
1620
960
1754
2074
1969
1375
1330
1990
2055
1690
862
1554
1647
1513
678
1333
1444
1382
30
34
39
52
61
70
77
75
66
54
41
34
1002
1890
2042
2092
1297
2018
2091
1784
1643
2072
2023
1469
2005
2195
1885
1125
2218
1996
1708
855
2468
2073
1740
803
2 37
2068
1719
849
2207
2147
1898
1012
1857
2157
2047
1382
1452
2119
2168
1764
1083
1951
2088
1905
881
1777
1907
1846
cn
ro
co
REFERENCES
1.
Jessup, E., "A Brief History of the Solar Radiation Program",
Report and Recommendations of the Solar Energy Data Workshop,
November 29-30, 1973. Report No. NSF-RA-N-74-062, NOAA,
September 1974.
2.
Liu, B.Y.H. and Jordan, R.C., "A Rational Procedure for Predicting
a Long-Term Average Performance of Flat-Plate Collectors",
Solar Energy, Vol. 17, No. 2, 1963.
3.
Liu, B.Y.H. and Jordan, R.C., The Interrelationship and Characteristic Distribution of Direct, Diffuse, and Total Solar Radiation.
Solar Energy, Vol. 4, No. 3, pp. 1-19, 1960.
4.
Duffie, J.A. and Beckman, W.A., Solar Energy Thermal Processes,
John Wiley and Sons, New York, New York, 1974.
5.
Liu, B.Y.H., and Jordan, R.C., (1977), "Availability of Solar
Energy for Flat-Plate Solar Heat Collectors", Chapter V , Applications of Solar Energy for Heating and Cooling of Buildings.
ASHRAE GRP 170 edited by Jordan and Liu, ASHRAE, Inc., N.Y.,
N.Y.
6.
Klein, S.A., Beckman, W.A., and Duffie, J.A., "A Design
Procedure for Solar Heating Systems". Presented by International
Solar Energy Society Meeting, Los Angeles, California, July/
August 1975.
7.
National Bureau of Standards, Intermediate Minimum Property
Standards for Solar Heating and Domestic Hot Water Systems.
Report No. NBSIR 77-1226, March 1977.
8.
Beckman, W.A., Klein, S.A. and Duffie, J.A., Solar Heating
Design by the f-chart Method, John Wiley and Sons, New York,
N . Y . , 1977.
9.
Solar Energy Applications Laboratory, Colorado State University,
Solar Heating and Cooling of Residential Buildings, Design of
Systems, (Available from U.S. Government Printing Office,
Stock No. 003-011-00084-4).