Environmental Engineering Reference
In-Depth Information
Description
The heating system is made up of:
a field of air solar collectors
a stone bed seasonal storage
a thermal regulation
Solar Collector
The single pass air solar collector was retained due to the simplicity of its realization and
to its low cost. It also allows us to reach average seasonal temperatures largely higher than
that required by the substrate. The selected thermal model is that of Hottel-Whiller-Bliss [3]
which was used successfully in the majority of the simulation cases of solar systems.
According to this model, the instantaneous efficiency η of the solar collector can be written
according to the inlet temperature of the fluid T i :
( )
)
]
[
(
η
=
F
'
τα
U
T
T
/
I
(1)
l
i
o
a
The exit temperature of the fluid is calculated by carrying out a total energy balance
between the entry and the exit of the solar collector:
T
=
T
+
q
/(
m
C
)
(2)
s
i
c
c
p
with:
q =
I
a
(3)
c
where:
m : surface mass flow rate of the liquid
C
: specific heat of the liquid
p
F and
F are dependent with respect to the following relation:
The coefficients
[
{
}
]
F
=
(
m
C
)
/
U
1
exp
U
F
'
/(
m
C
)
(4)
R
c
p
l
l
c
p
Heat Storage in the Packed Bed
The storage unit is an isolated space containing a stone bed crossed by air coming from
the solar collector. The collected heat results leads an increase of stones temperature. It is a
sensible heat storage. Hence, temperatures are only function of time and distance covered
according to the direction of the air flow.
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