Civil Engineering Reference
In-Depth Information
fluctuating periods of solar radiation (Schnieders, 1997). Another drawback
is that the coefficients
C
1
to
C
6
are not usually provided by manufacturers
and can only be determined experimentally, while coefficients for stationary
models are usually provided with manufacturers' certification test results.
Dynamic Models
Dynamic models require a more complex implementation than steady-state
models, but are generally more accurate if the appropriate inputs are used.
For these models, the dynamic thermal behavior of each component of the
collector (i.e., the cover, absorber, fluid) and the energy exchanges between
them are modeled to predict the temperature output of the solar collector.
These dynamic models have shown good performance and low error. One
of the first dynamic models for solar collectors was presented by Kamminga
(1985); it takes into account all the elements of the collector. The
transparent cover, absorber, and fluid flow are considered separately. Each
equation reflects the energy balance on every element. From this model,
Schnieders (1997) proposed a model for a vacuum flat plate (using a lumped
transfer coefficient for radiation transfer between the glass cover and the
absorber).
- Glass cover
(2.37)
- Absorber
(2.38)
- Fluid
(2.39)
where is the fluid heat capacity per unit area (Jm
−2
K
−1
); is the glass
coverheatcapacityperunitarea(Jm
−2
K
−1
); istheabsorberheatcapacity
per unit area (Jm
−2
K
−1
);
h
g_a
is the heat transfer coefficient glass-exterior
(Wm
−2
K
−1
);
h
g_p
is the heat transfer coefficient glass-absorber (Wm
−2
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