Gwilym T. Still and Terry H. Thomas
11th International Rainwater Catchment Systems Conference, Texcoco, Mexico, 2003
Guttering is the most common method for conveying rainwater from the capture surface normally a roof) to storage. The cost of such gutters is a relatively small fraction of the total system cost (typically under 20%) but guttering failure accounts for much loss in RWH system performance. The optimum gutter may be defined as that which minimises the system cost per litre of water captured. There are a series of gutter variables within the control of the installer, including: gutter shape, slope, width and position relative to the roof edge.
This paper focuses on an analysis of the sizing and positioning of gutters, based on several sources, including rainfall data from the humid tropics and experiments undertaken by the DTU at the University of Warwick and in Sri Lanka. For domestic RWH applications, it was found that relatively small gutters (around 5 to 8cm wide), if hung accurately, offer high performance. Typically an economically optimum gutter would intercept and convey only 90-95% of roof run-off to the cistern. Indeed, it appears that gutters are often oversized in practice. The use of a dual slope can improve the performance of guttering.
Having concluded the technical analysis, rules of thumb and tabulated recommendations are presented, suitable for application by rainwater harvesting practitioners.
Keywords: Guttering; economic; optimisation.