Effect of Different Roof Materials on Energy Savings and Carbon Dioxide Reductions for Rainwater Harvesting Systems

The rapid requirement to reduce treated water consumption has necessitated action in finding alternate sources to be taken throughout the nation. One of the actions taken by the Malaysian government is the promotion of rainwater harvesting techniques. Rainwater harvesting systems not only provide water savings to users, but with proper implementation reduce the amount of energy consumed which is required to treat water to make suitable for consumption and its carbon dioxide emissions. Many developers intend to implement the system however lack of design tool that will help to identify the total amount of savings provided by the system with the effect of using different roofing materials across different tank sizes. The aim of this paper is to design a tool that analyses the effect of utilizing different roof materials on the total water and energy savings, and carbon dioxide emission reduction on hourly water demands and rainfall values via mass balance calculations. The scope will cover commercial buildings; offices, hospitals and hotels. Based on the findings, slate tiles with a run-off coefficient of 0.9 are found to be the best roof material which can provide energy savings and carbon dioxide emission reductions of 2870 MJ and 830 kg in offices, 9925 MJ and 2875 kg in hospitals and 5629 MJ and 1631 kg in hotels with a payback period of 20, 13 and 16 years respectively when using a large tank that accommodates 5 times the total demand of the specific building