A validated model of naturally ventilated PV cladding

A simplified method has been derived for use in the estimation of the flow rate in naturally ventilated PV cladding for buildings. The method is based on a one-dimensional ‘loop analysis’ in which the buoyancy forces are balanced by the pressure drops due to friction. Wind effects at the entrance and exit are also taken into account. The procedure yields the mass flow rate and temperature rise directly by the solution of a simple cubic equation and therefore is straightforward and simple enough to be put on a spreadsheet. This methodology allows the designer to explore various potential PV configurations at little expense and hence to focus on those designs which warrant further detailed analysis, perhaps coupled to a full building simulation package. In this paper, the fundamental theory behind the loop analysis is described. The hypothesis tested is that the form and values for the friction factors and internal heat transfer coefficients for the buoyancy driven case are the same as those for forced convection in ducts. Next, the experimental rig is discussed with which the first validation exercises are carried out for the no-wind case, using an emulation of the simple single stack PV cladding arrangement. The two key parameters are identified using the measurement error weighted least squares linear regression. Overall excellent agreement between the modelled and measured mass flow rates is seen; the hypothesis is therefore valid. A general model is then derived to describe the thermal behaviour of building-integrated PV with natural ventilation cooling for use in a wide variety of design and validation exercises.