Water Supply Modes of Variable Frequency Water Supply Equipment

Based on water supply characteristics, the variable-speed water supply modes of variable frequency water supply equipment are divided into two categories: constant-pressure variable-flow water supply and variable-pressure variable-flow water supply.

Constant-pressure variable-flow water supply refers to a mode where the water supply pressure remains constant at all times even when the water consumption flow rate changes. Variable-pressure variable-flow water supply refers to a mode where the water supply pressure rises as the flow rate increases.

Let the flow resistance characteristic equation of the water supply pipeline be:H=H0+AQ2In the formula:

· H = water supply head

· H0 = water supply height (m)

· Q = water supply flow rate (m³/h)

A = coefficient, which varies with the pipeline and the unit system used

The ideal water supply characteristic of variable-pressure variable-flow water supply H=f(Q) should conform to Formula (1). Water supply based on this characteristic can ensure a constant pressure at the end of the water supply pipeline under any flow rate.

In practice, it is difficult to derive the flow resistance characteristic equation (1) of the water supply pipeline during both the building design and operation phases, and thus it is impossible to realize the variable-pressure variable-flow water supply that follows the ideal law (expressed by Formula (1)). In addition, the ideal variable-pressure variable-flow water supply of the variable frequency water supply equipment must be tailored to a specific water supply pipeline, and has no universality. Therefore, the ideal variable-pressure variable-flow water supply has little practical value under normal circumstances. At present, none of the general variable frequency speed-regulating water supply systems (equipment) are designed according to the ideal variable-pressure variable-flow water supply characteristics.

The practical variable-pressure variable-flow water supply equipment is designed in such a way that the water supply pressure rises in steps as the flow rate increases. For multi-pump parallel constant-pressure water supply, the specific scheme is that the system is designed for variable frequency constant-pressure water supply, and the constant pressure value rises in steps with the number of pumps put into operation. The step value for each pump when it is put into operation can be set as required. This makes it possible for the stepped water supply H-Q characteristic to approximate the ideal variable-pressure variable-flow H-Q characteristic, thereby achieving excellent energy-saving effects. This variable-pressure variable-flow water supply mode is named quasi-variable-pressure variable-flow water supply.

This quasi-variable-pressure variable-flow water supply control mode features universality and practicability, and has been applied in variable frequency water supply systems or equipment at home and abroad. For example, the frequency converter produced by a certain company can realize the function of quasi-variable-pressure variable-flow water supply when operating according to the PFC application macro.