Statistical analysis of factors affecting the flow characteristics and thermal efficiency of a building integrated thermal (bit) solar collector

Abstract

Previous research has identified four factors (array geometry, manifold to riser channel ratio, flow direction in manifold, and the mass flow rate) which will influence the distribution of internal fluid flow within a solar thermal collector. In this study, a two level full factorial (2k) experiment was designed in order to statistically rank their impact and also to identify any significant interactions between these factors. The thermal efficiency of the array, calculated by means of a fluid and heat transfer analysis was taken to be the experiment response. During the heat transfer analysis we approximated the fin efficiency of a BIT collector using the finite difference method which considered the heat losses through the structural ribs of the collector. A statistical analysis of the results revealed that all four main effects had a statistical influence on thermal efficiency of the array at 5 per cent significance level. The main effects ranked from highest to lowest in impact were found to be; geometry, manifold to riser fluid channel diameter, mass flow rate, and the direction of flow in the manifolds. Additionally, two secondary interactions were found to have a statistical influence on the experiment response; the array geometry and the direction of flow in the manifold followed by the array geometry and the ratio of manifold to fluid channel diameter. As the geometry of the BIT collector will vary from customer to customer due to its custom nature, these results indicate that the design of a BIT system should consider the effects of flow distribution. Finally, our numerical analysis of the fin efficiency revealed an approximate 5% drop due to additional heat losses through the structural ribs.