Civil Engineering Reference
In-Depth Information
Steady-state Models
Simple steady-state models (Duffie and Beckman, 2006) calculate the
efficiency of the solar collector as a function of the inlet fluid temperature,
thetotalincidentradiation,andtheambienttemperature.Thesecond-order
efficiency curve for a glazed solar thermal collector is
(2.35)
where
A
c
is the collector area (m
2
);
C
1
is the first-order loss coefficient,
dependent of fluid temperature (Wm
−2
K
−1
);
C
2
is the second-order loss
coefficient, dependent of fluid temperature (Wm
−2
K
−2
);
Q
u
is the useful
power output of the collector (W);
T
i
is the inlet temperature of the fluid
in the collector (K);
η
is the efficiency of the solar collector; and
η
0
is the
intercept of the collector efficiency curve.
Quasi-dynamic Models
Quasi-dynamic models account for the losses due to the wind speed, sky
temperature,aswellastheequivalentthermalcapacityofthecollectorwhen
determining the useful energy output of the collectors (Fischer
etal.
, 2004).
(2.36)
where
C
3
is the wind speed loss coefficient (Jm
−3
K
−1
);
C
4
is the longwave
radiation loss coefficient;
C
5
is the equivalent thermal capacity of the
collector (Jm
−2
K
−1
);
C
6
is the wind dependence of zero loss coefficient
(sm
−1
);
E
L
is the longwave radiation (Wm
−2
);
F
(
τα
) is the zero loss
coefficient;
G
b
isthebeamincidentsolarradiation(Wm
−2
);
G
d
isthediffuse
incident solar radiation (Wm
−2
);
K
b
(
θ
) is the incident angle modifier for
beam solar radiation;
K
d
is the incident angle modifier for diffuse solar
radiation; and
θ
is the angle of incidence.
These models have two advantages: easy coupling with other component
models of the solar system and short computation times. They also have
the disadvantage of overestimating the potential of solar collectors during
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