Economical viability analysis of an innovative gravity‐driven rainwater harvesting system for a commercial office building.

Gravity‐driven rainwater harvesting (RWH) system showcases a promising alternative solution to reduce energy consumption in rainwater recycling. However, the economic efficiency is one of the most concerns with regard to the adoption of this green infrastructure. In this study, a commercial official building has a rooftop area of 1600 m2 and with 560 inhabitants was assumed to apply two configurations of RWH system (i.e., gravity system and pressure system), and comparative study was conducted to evaluate the economic performance of two RWH systems. The potential water saving quantity of the RWH system was simulated based on a daily water balance model and their expected economic efficiency were discussed in terms of benefit cost ratio and net present value. Results shown that only when the building height is higher than 102 m or the property rent is less than 0.4 CNY (China Yuan) per square metre per day, can make the gravity system economically attractive. This study provides an innovative approach to utilize roof rainwater in a more low‐energy mode; it is of great significance to promote building energy‐saving and carbon reduction. [ABSTRACT FROM AUTHOR]