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of the absorber plate and PV cells on the performances were examined. The results
showed that the Model I collector has the lowest performance under similar operational
conditions. Other collectors achieved comparable thermal and electrical yields, among
which the Model III collector requires the least fan power, followed by Models II and IV.
The impact of air flow induced by buoyancy and heat transfer through a verti-
cal channel heated from one side by the PV module on the PV/T performance was
investigated numerically and experimentally by Moshfegh and Sanberg (1998) and
Sanberg and Moshfegh (2002). The study reports that the induced velocity increases
the heat flux non-uniformly inside the duct and its impact depends on the exit size and
design. More analysis and modeling on passively cooled PV/T air systems continue to
appear (Tiwari et al., 2006; Tiwari and Sodha, 2006; Naphon, 2005; Garg et al., 1994;
Tripanagnostopoulos et al., 2006) and a substantial amount of research has been specif-
ically carried out (Brinkworth and Sandberg, 2006; Benemann et al., 2001; Hodge
and Gibbons, 2004; Pottler et al., 1999; Tiggelbeck et al., 1993; Tonui et al., 2007;
Tripanagnostopoulos, 2007) to improve heat transfer to the air of both buoyancy-
driven and forced air flow systems. Their studies were focused generally on channel
geometry, creation of more turbulence in the flow channel and increasing the convective
heat transfer surface area in the channel. Most of these studies used simulation models
for their experimental work where the PV module was simulated by a heated foil.
Similar to the liquid collectors, various types of solar air systems exist and an
overview has been given by Hastings and Morck (2000). The main concepts on air-
cooled PV/T systems were presented in the works of Kern and Russel (1978), Hendrie
(1979), Florschuetz (1979), Raghuraman (1981) and Cox and Raghuraman (1985).
The exclusive theoretical aspects of PV/T systems with air as the heat extraction fluid
are detailed by Bhargava et al. (1991), Prakash (1994) and Sopian et al. (1996).
5.2.3 Ventilated PV with heat recovery
In general, for building integrated photovoltaic panels, to ensure the modules are not
overheated, the ambient air is circulated by thermosiphoning beneath or at the rear
end of the PV panel, which is commonly referred to as “ventilated PV.''
If this waste heat can be harvested and be used for secondary purposes, it functions
as a PV/T collector, providing additional benefits:
(i)
A PV-facade may limit the thermal losses in a building by infiltration. Also the
PV facade has the advantage of shielding the building from solar irradiance,
thereby reducing the cooling load. Hence, such facades are especially useful for
retrofitting poorly insulated existing offices.
(ii)
If there is no demand for the generated heat, then air collectors and PV-facades
can use their buoyancy induced pressure difference to assist the ventilation.
(iii)
Facade integration of PV has additional cost incentives of substituting expensive
facade cladding materials.
However, the ventilated PV-façade may contribute to the building's cooling load
in hot summer, which is not desirable. To overcome this issue, a desiccant cooling
cycle can be employed which can be energized with an additional collector. It is a
novel open driven system introduced by Li et al. (2006), in which the required room
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