Water supply control of deep well submersible pump

Temperature difference control method is adopted for deep well submersible pump. Since the water outlet temperature of the evaporator must not be too low in the heating condition of the heat pump unit, a temperature sensor is set on the backwater pipe of the deep well pump and the setting temperature is TJH. When the backwater temperature at the water source side of the well is greater than TJH value, the controller of the deep well pump sends the signal of reducing current frequency to the frequency converter, and the frequency converter reduces the frequency of the input power, the revolution of the deep well pump decreases correspondingly, and the water supply of the pump, shaft power and motor input power also decrease accordingly, thus achieving the purpose of energy saving. When the backwater temperature of the water source side is lower than the TJH value, the frequency increase regulation is adopted.

Pump speed control principle

Changing the speed of shenyang water pump can change the performance of the pump, so as to achieve the purpose of adjusting the operating point. According to the law of similarity, when the same pump operates at different speeds, the relationship between flow rate, head, shaft power and rotation speed of the pump can be expressed as follows:

Q/Qe = n/ne (1)

H/He = (n/ne) 2 (2)

P = (n/ne/Pe) three (3)

Type:

Ne -- rated speed of pump, r/min; N -- speed, r/min, under actual operating conditions;

Qe -- flow rate of pump at rated speed, m3/h; Q -- flow rate under actual operating condition, m3/h;

He -- head of pump at rated speed, m; H -- head under actual operating condition, m;

Pe -- rated speed of the pump power, kw; P -- power under actual operating condition, kw.

Equation (1) and equation (2) can be obtained

H1/Q12= H2/Q22=k (4), that is, H=kQ2 (5).

Equation (5) is a quadratic parabola with the coordinate origin as the vertex. Each point on the line has similar working conditions. According to the law of similarity, when the rotation speed before and after the pump changes, the pump efficiency remains unchanged. Therefore, from the perspective of energy conservation, usually use the method of changing the speed of the pump to change the working point of the pump, try to make it work in the high efficiency range.

Determination of frequency conversion range of water pump

When the load of heat pump unit changes, the water supply of deep well pump also changes. The water supply of the deep well pump is between (Qmin ~ Qe), that is, the frequency conversion range of the deep well pump (nmin ~ ne). The minimum flow required by the heat pump unit is 40 m3/h (equipment requirement), that is, the minimum water supply of the deep well pump. Then, the minimum speed of the deep well pump is:

Nmin = Qmin/ Qe×ne=40/160×2900=725 RPM

Frequency conversion range of deep well pump in winter heating condition: 725 RPM ~ 2900 RPM

Water supply and power consumption of deep well pump at different frequency

The frequency conversion water supply equipment of deep well pump adopts HT microcomputer to control frequency conversion speed regulating water supply equipment, of which the frequency converter model is (vfd-f, 45KW/60HP, 460HP, 3phase). After the frequency conversion of the deep-well pump, the measured water supply and electricity consumption of the deep-well pump at different frequencies can be obtained: when the frequency of power input decreases, the water supply and electricity consumption of the submersible pump in the deep-well shenyang gradually decrease. When the frequency decreases from 45hz to 30hz, the water supply of deep-well pump decreases from 122m3/h to 54m3/h, and the water supply decreases by 23.75% and 66.25% respectively compared with the rated speed. However, the input power decreased from 26.2kw to 8.9kw, decreasing by 29.1% and 75.9% respectively compared with the rated speed. It can be seen that energy saving effect is quite obvious. But when the frequency drops to 20hz, although the deep well pump is still running, the water supply is close to zero due to insufficient head.