Abstract : Traditional water supply methods mostly employ a combination of ground-level and rooftop water tanks, constant pressure water supply, or variable frequency constant pressure water supply. However, all of these require ground-level water tanks, often resulting in a waste of municipal water resources and secondary water pollution. This paper introduces the transformation of residential secondary water supply systems using variable frequency constant pressure direct water supply equipment. This not only solves the pollution problem of secondary water supply but also significantly saves energy, achieving good economic benefits. Keywords : Variable frequency drive, environmental protection, energy saving 1 Overview Generally, urban pipe network water pressure only guarantees water supply for users in buildings with three floors or less. All other upper floors must have their water pressure increased to meet user needs. Most water supply methods use a combination of ground-level and rooftop water tanks. Daily domestic water consumption often varies over time, with significant seasonal and diurnal differences. The height of the water tower affects the water pressure supplied to users. Furthermore, the use of ground-level and rooftop water tanks easily leads to secondary water pollution and water quality degradation. With the development of power electronics technology, variable frequency speed control technology has been widely used in automatic constant pressure water supply, such as constant pressure water supply equipment and variable frequency constant pressure water supply equipment. However, they all rely on primary water supply (equipped with a low-level water tank), resulting in primary water pollution and wasted water pressure energy. 2. Secondary Water Supply Equipment System Retrofit and Environmental Protection Most of the buildings managed by our company use a secondary water supply system with ground-level and roof-level water tanks. This system consists of a pump controller in the pump room, water pumps, and water supply pipes. The water flow direction is: municipal water flows into the ground-level water tank, is pressurized by the pumps, and then supplied to the roof-level water tank, from which it supplies water to the users on each floor. The water supply characteristic is that all the tap water is put into the water tank, the original pressure becomes zero, and then it has to be repressurized from zero, resulting in wasted energy. [b][align=center]For details, please click: Application of Variable Frequency Drives in Constant Pressure Water Supply Systems - Retrofit of Secondary Water Supply Systems[/align][/b]