Shanxi deep well pump using temperature difference control method

Because the heat pump unit must ensure that the outlet water temperature of the evaporator cannot be too low under the heating condition, a temperature sensor is set on the return pipe of Shanxi deep well pump, and the set temperature is tjh. When the return water temperature on the water source side of the well is greater than tjh value, the deep well pump controller sends a signal to the frequency converter to reduce the current frequency. The frequency converter reduces the frequency of the input power supply, and the number of revolutions of the Shanxi deep well pump is correspondingly reduced. The water supply, shaft power and motor input power are also reduced, thus achieving the purpose of energy saving. When the return water temperature on the water source side is lower than the tjh value, the frequency is increased and adjusted.
Water pump variable speed regulation principle
Changing the speed of the submersible 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 is running at different speeds, the relationship between the flow rate, head, shaft power and speed of the pump can be expressed by the following formula:
Q/Qe = n/ne (1)
H/He= (n/ne)2 (2)
P/Pe= (n/ne)3 (3)
Where:
ne -- rated speed of water pump, r/min;n -- speed under actual operating conditions, r/min;
Qe -- Flow rate at rated speed of water pump, m3/h;Q -- Flow rate under actual operating conditions, m3/h;
He -- lift at rated speed of the pump, m;H -- lift under actual operating conditions, m;
Pe -- power at rated speed of water pump, kw;P -- power under actual operating conditions, kw.
From equation (1) and equation (2), we have
H1/Q12 = H2/Q22 = k (4), I .e., H = kQ2 (5)
(5) The formula is a quadratic parabola with the coordinate origin as the vertex. Each point on the line has similar working conditions. It is known from the similarity law that when the speed of the pump changes before and after, the efficiency of the pump remains unchanged, so the parabola under similar working conditions is also called the equal efficiency curve. Therefore, from the perspective of energy saving, the method of changing the speed of the water pump is usually used to change the working condition of the water pump, so as to make it work in the high efficiency range.
Determination of Frequency Conversion Range of Water Pump
When the load of the heat pump unit changes, the water supply of the deep well pump also changes. The water supply of the deep well pump is between (Qmin ~ Qe), I .e. the frequency conversion range (nmin ~ ne) of the deep well pump, and the minimum flow rate required by the heat pump unit is 40 m 3/h (equipment requirement), I .e. the minimum water supply of the deep well pump, then the minimum rotation speed of the deep well pump is: nmin = Qmin/ Qe×ne = 40/160 × 2900=725 r/min
Frequency conversion range of deep well pump under heating condition in winter: 725 r/min ~ 2900 r/min
Water supply and power consumption of deep well pump under different frequencies
Shanxi deep well pump frequency conversion water supply equipment adopts HT microcomputer control frequency conversion speed regulation 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 results of the water supply and power consumption of the deep well pump at different frequencies can be obtained: when the frequency of the power input decreases, the water supply and power consumption of the deep well submersible pump also decreases gradually. When the frequency of 45hz down to 30hz, the deep well pump water supply from 122 m3/h down to 54 m3/h, compared with the rated speed of the water supply decreased by 23.75, 66.25. The input power is reduced from 26.2kw to 8.9kw, which is 29.1% and 75.9% respectively compared with the input power at the rated speed. Thus, the energy saving effect is quite obvious. However, when the frequency drops to 20hz, although the deep well pump is still running, the water supply is close to zero due to insufficient lift.