Civil Engineering Reference
In-Depth Information
In the previous equations,
i
is the outermost layer (e.g., PV module) and
j
is the innermost layer (e.g., inner glass) of the
N
-layer assembly (for this
example,
N
= 2),
i,j
= 1,2…
N
;
A
PV
photovoltaic module area (m
2
);
m
mass
flow rate (kgs
−1
);
c
p
specific heat capacity (Jkg
−1
K
−1
);
α
j
solar absorbance
of layer
j
;
τ
i,j
solar transmittance through layers
i
to
j
; front (toward
outside) solar reflectance from layers
i
to
j
; back (toward inside) solar
reflectance from layers
i
to
j
;
T
b
,
T
rm
surface temperature of the inner
glass and room air temperature, respectively (K);
T
ch
,n
−1
,
T
ch
,n
average
heat removal fluid temperature of the (
n
− 1)-th control volume and the
n
-th control volume, respectively (K);
U
ch
, convective conductances due
to heat removal fluid (Wm
−2
K
−1
);
U
r
radiative conductance between PV
panel and inner glass (Wm
−2
K
−1
); and
U
a
,
U
rm
combined (radiative and
convective) conductance between, PV and ambient environment and, inner
glass and room, respectively (Wm
−2
K
−1
).
Alternatively, an
approximate analytical solution may be obtained for a
control volume in a BIPV/T or PV/T open loop air system
as follows,
assuming the average convective heat transfer coefficient
h
ch
corresponds
to conductances
U
ch
and . Note that the convective coefficient
h
ch
is an
average for both cavity surfaces (in reality it will generally be higher on the
upper surface).
The average channel air temperature
T
ch
is determined from a differential
analysis, which finds the air temperature as a function of distance
x
along
the flow path. It is assumed that the air speed is constant, and the, air
is drawn by a fan (as fresh air or connected to a heat exchanger or an
air-to-water heat pump). The actual air temperature
T
ch
(
x
) is then used to
Search WWH ::
Custom Search