Environmental Engineering Reference
In-Depth Information
With the day angle
day of the year
number of days of the year
y'
= 360
°
•
the solar declination becomes:
δ
(
y
') = {0.3948 - 23.2559
•
cos(
y
'+9.1°) - 0.3915
•
cos(2
y
'+5.4°) -
0.1764
•
cos(3
•
y
'+105.2°)}°
(2.14)
and the equation of time
eqt
(
y
') = [0.0066 + 7.3525
•
cos(
y
'+85.9°) + 9.9359
•
cos(2
•
y
'+108.9°) + 0.3387
•
cos(3
•
y
'+105.2°)]min
(2.15)
is calculated. With the
Local time
, the
Time zone
(e.g. Greenwich mean time
GMT = 0, Central European Time CET = 1 h, Pacific Standard Time PST
= -8 h) and the longitude
λ
, the mean local time MLT becomes:
MLT = Local time - Time zone + 4
•
λ
•
min/°
(2.16)
Adding the equation of time
eqt
to the mean local time
MLT
provides the
Solar
time
:
Solar time = MLT +
eqt
(2.17)
With the latitude
ϕ
of the location and the hour angle
ω
:
ω
= (12.00 h - Solar time)
•
15°/h
(2.18)
the angle of solar altitude (sun height)
γ
S
and angle of solar azimuth
α
S
become:
γ
S
= arcsin(cos
ω
•
cos
ϕ
•
cos
δ
+ sin
ϕ
•
sin
δ
)
(2.19)
{
sin
S
•
sin
S
-
sin
δ
180
°
- arccos
if Solar time 12.00 h
cos
S
•
cos
S
=
sin
S
•
sin
S
-
sin
δ
180
°
+ arccos
if Solar time > 12.00 h
cos
S
•
cos
(2.20)
