I. Overview

With the development of frequency conversion & speed regulation technology and the continuous improvement of people's requirements for drinking water varieties, frequency conversion water supply equipment has been widely used in domestic water and fire-fighting water supply systems of multi-storey residence communities and high-rise buildings. Frequency conversion water supply equipment generally has the characteristics of low equipment investment, stable and reliable system operation, small floor space, electricity- and water-saving, high degree of automation, and convenient operation and control. If it fails to save energy, it will waste electricity. Based on our years of practical experience, the application and control methods of several frequency conversion water supply systems are introduced as follows for reference by peers and users in design, transformation and selection.

II. One-to-two frequency conversion water supply mode

This equipment is often used in practical applications. The system consists of a water pump unit, a cyclic soft-start frequency conversion cabinet, a pressure instrument, and a pipeline system. The frequency conversion cabinet is composed of a frequency conversion speed regulator, a constant pressure water supply controller, and low-voltage electrical appliances. The system generally selects 2-3 pumps of the same model . Take 3 pumps as an example. The working conditions of the system are as follows:

Usually a pump is used for frequency conversion water supply. When the water supply is insufficient with one pump, the first pump is switched to power frequency operation, and then the frequency counter soft-starts the second pump. If the flow is not enough, the second pump is switched to power frequency operation. The frequency conversion cabinet then soft-starts the third pump. If the water consumption decreases, the power frequency pumps are stopped in the order of the pump starting until the last pump supplies the water with frequency conversion and constant pressure.

In addition, the system has the function of changing pumps regularly. If a pump runs continuously for more than 24 hours, the frequency conversion cabinet can automatically stop the pump and switch to the next pump to continue frequency conversion operation. The pump replacement time is set by the program and can be adjusted at any time as required. This can balance the running time of each pump, extend the lifecycle of the overall pump set, and prevent individual pumps from rusting due to long periods of non-operation.

When the frequency-conversion water supply system is in the condition of small or zero flow, such as the low water consumption at night, the water consumption in the system is very small. At this time, the pump runs at a low flow rate, which will greatly reduce the efficiency of the pump and cannot achieve the purpose of energy saving. The greater the power of the pump, the more electricity is used. For example, for the domestic water system of a multi-storey residence communities of 300-1000 households or a small high-rise residential building group of about 600 households (within 12 floors), the main domestic pump power is generally about 15KW, and the zero flow frequency P0 of the system is generally 25.00 - 35.00Hz. Therefore, when the flow rate is small at night, the frequency-conversion water supply efficiency of the main pump will be reduced.

This involves the power-saving problem of the water-supply system when the flow is small. Generally, 4 solutions can be adopted:   A. Variable-frequency main pump + power-frequency auxiliary pump;   B. Variable-frequency main pump + power-frequency auxiliary pump + air pressure tank;   C. Variable-frequency main pump + air pressure tank;   D.  Variable-frequency main pump + Variable-frequency auxiliary pump. From the perspective of technological investment, the fourth option is more appropriate. This option is based on the original Variable-frequency main pump and equipped with 1-2 small pumps dedicated to Variable-frequency water supply at night or when the flow is small at ordinary times. Generally, the flow rate of the small pump is 3- 6 M³ / H, the more residential households, the larger flow rate may be appropriately selected. The small-sized pump power is generally 1.5-3kw and the lift of the small pump varies with the main pump, or slightly lower.

III. Parameter setting of Yuanxin inverter    

IV. Advantages of Yuanxin inverter control

A) The domestic & fire-fighting pump set rotates regularly, and the fire pump will not be rusted due to long-term idling or poor management of the fire pump, and the set is always in the best working condition. 

B) A set of fire pumps can be basically saved with combination of domestic pumps and fire pumps, which facilitates equipment management and maintenance.     

C) The equipment has a high degree of automation, the water supply is stable and reliable, and the water is free of secondary pollution.      

D) The water pump soft-starst and stops, with no impact and overpressure hazard. No water hammer occurs.      

E) Reliable operation. The soft start of the pump is realized by the frequency converter, so that the water pump can realize the impact-free switching from the power frequency to the frequency conversion, to prevent the impact of the pipe network, and avoid the pressure of the pipe network from exceeding the limit and the pipe rupture.        

F) Perfect self-protection function: If a pump fails, it will actively send out an alarm message and start the backup pump at the same time to maintain the water supply balance. In case of failure of the automatic control system, the user can directly operate the manual system to ensure the water supply.        

V. Onsite pictures