Application of frequency conversion technology of

2022-08-12
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Application of deep well pump frequency conversion technology in ground source heat pump Abstract: at present, in the ground water source heat pump air conditioning system, the water supply volume of one deep well pump can often meet the water demand of two or more heat pump units. However, in the actual operation, it is found that the heat pump unit operates at partial load most of the time, while the deep well pump has been operating at full load, resulting in a substantial increase in electricity and water charges. To solve this problem, this paper takes a practical project as an example, and adopts a more comfortable shopping experience and better use experience. The variable flow water supply of deep well pump variable frequency technology can not only meet the requirements of heat pump for well water, but also save electric energy and well water. It introduces the variable frequency control method and principle of deep well pump, and the determination of variable frequency range. According to the actual operation of deep well pump, it has achieved excellent chemical corrosion resistance, Analyze its energy-saving effect and economy

key words: deep well pump energy-saving effect frequency conversion range water supply power consumption

1 preface

in recent years, frequency conversion speed regulation technology has been widely used in water pumps and fans in air conditioning systems with its remarkable energy-saving effect and reliable control mode, and its technology is also relatively mature, but the application of deep well pump water supply in groundwater source heat pump air conditioning systems is still rare, but it is quite necessary. The investigation on the pilot application of ground water source heat pump in Shenyang found that in the ground water source heat pump air conditioning system, when the heat pump capacity is not large, the water supply of a deep well pump can meet the water demand of two or more heat pump units. In the actual operation, it is found that the heat pump unit operates at partial load most of the time, while the deep well pump has been operating at full load, resulting in a substantial increase in electricity and water charges. Therefore, the application of deep well pump variable frequency speed regulation water supply technology in groundwater source heat pump system has great energy-saving potential

2 project overview

the analysis of this paper takes the winter operation of the actual project as the research object. The project overview is as follows:

the office building of a new campus of a university has five floors, with a building area of 11030m2, the design cooling load of air conditioning in summer is 894kw, and the design heating load of air conditioning in winter is 1012kw. Two underground water source heat pump units are used for the cold and heat sources of the office building. The heating conditions are as follows: the heating capacity is 515kw, the input power is 136.02kw, the cold water flow is 65m3/h, the hot water volume is 88.6m3/h, and the pumping capacity of one pump is 160m3/h, and the power is 37KW. Winter operation time: from November to March, 24 hours a day

3 deep well pump variable frequency speed regulation water supply control method

deep well pump adopts temperature difference control method. As 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 water pipe of the deep well pump, and the set temperature is TJH. When the return water temperature at the water source side of the well is greater than the TJH value, the deep well pump controller sends a signal to the frequency converter to reduce the current frequency. The frequency converter will reduce the frequency of the input power supply, the number of revolutions of the deep well pump will be reduced accordingly, and the water supply volume, shaft power and motor input power of the pump will also be reduced, so as to achieve the purpose of energy saving. When the return water temperature at the water source side is lower than the TJH value, increase the frequency for regulation

4 variable speed regulation principle of water pump

changing the speed of the water pump can change the performance of the water pump, so as to achieve the purpose of adjusting the working point. According to the law of similarity, when the same pump operates at different speeds, the relationship between the flow, 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)

where: ne pump rated speed, r/min; N speed under actual operating conditions, r/min

qe flow at rated speed of water pump, m3/h; Q flow under actual operating conditions, m3/h

he pump head at rated speed, 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 equations (1) and (2), we can get

h1/q12=h2/q22=k (4)

that is, h=kq2 (5)

(5) equation is a quadratic parabola with the coordinate origin as the vertex, and each point on the line has similar working conditions. According to the similarity law, when the speed before and after the water pump changes, the efficiency of the water pump does not change, so the parabola under similar working conditions is also known as the equal efficiency curve. Therefore, from the perspective of energy conservation, the method of changing the speed of the water pump is usually used to change the working point of the water pump and try to make it work within the range of high efficiency

5 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 capacity 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 40m3/h (equipment requirements), that is, the minimum water supply capacity of the deep well pump, then the minimum speed of the deep well pump: get:

nmin=qmin/qe ne= 40/160 2900=725 R/min

the frequency conversion range of the deep well pump under heating conditions in winter: 725 R/min ~ 2900 R/min

6 water supply and power consumption of deep well pump under different frequencies

the variable-frequency water supply equipment of deep well pump adopts HT microcomputer controlled variable-frequency speed regulating water supply equipment, in which the model of frequency converter is (vfd-f, 45kw/60hp, 460hp, 3P, their other ultimate goal is hase). After the frequency conversion of deep well pump, the measured results of water supply and power consumption of deep well pump under different frequencies:

when the frequency of power input decreases, the water supply and power consumption of deep well pump also gradually decrease. When the frequency drops from 45Hz to 30Hz, the water supply of deep well pump decreases from 122m3/h to 54m3/h, which is 23.75% and 66.25% lower than that at rated speed respectively. The input power decreased from 26.2kw to 8.9kw, which decreased by 29.1% and 75.9% respectively compared with the input power at rated speed. This shows that the energy-saving effect is quite obvious. However, when the frequency drops to 20Hz, although the deep well pump is still running, due to insufficient head, the water supply is close to zero

7 deep well pump variable-frequency operation measurement and energy-saving effect analysis

7.1 daily operation measurement and analysis of deep well pump

the heat pump unit operates at partial load most of the time, and the maximum operating load does not exceed 50% of the maximum load of the unit (i.e. 100% of the rated load of a heat pump unit), and the operating time with 37.5% of the rated load accounts for 55%. After the deep well pump adopts frequency conversion, the flow of the deep well pump under this working condition decreases from the original 160m3/h to 52m3/h, reducing the water supply by 67.5%; The power consumption decreased from 37kwh to 8.8kwh, saving 76.2%. Remarkable energy saving effect

7.2 actual measurement of operating conditions of deep well pump and analysis of energy saving effect during the whole heating period

through the tracking measurement of the actual operating conditions of deep well pump during the whole winter heating period, the daily water supply and daily power consumption of deep well pump without frequency conversion and frequency conversion are changed:

compared with non frequency conversion, deep well pump saves 82222m3, 80924m3, 78942m3, 77440m3 and 84841m3 respectively in November, December, January, February and March. During the whole winter heating period, after the deep well pump adopts frequency conversion technology, a total of 404369m3 of water supply is saved. Similarly, after adopting frequency conversion technology for deep well pumps, the power consumption is reduced by 21136.8kwh, 21284.5kwh, 20813kwh, 20155.4kwh and 21858.2kwh respectively in November, December, January, February and March compared with that without frequency conversion. During the whole winter heating period, after the deep well pump adopts frequency conversion, a total of 105247.9kwh of power consumption is saved

8 economic analysis of variable frequency water supply mode of deep well pump

according to the actual measurement of heating operation in the whole winter, a total of 105247.9kwh of power consumption and 404369m3 of water supply have been saved after using variable frequency of deep well pump

save money every year after adopting frequency conversion:

cs= ⊿ w yw+ ⊿ e Ye

where: ⊿ w saves water supply per year, m3; ⊿ e annual saved power consumption, kwh

ye electricity price, (yuan/kwh); YW groundwater price, (yuan/m3)

cb=105247.9 0.635+404369 0.25=1679 (ten thousand yuan)

the total investment of frequency conversion equipment and other auxiliary electric control equipment of the project is about 100000 yuan. The increased investment of frequency conversion equipment of deep well pump has been fully recovered in a winter heating period

9 conclusion

in the ground water source heat pump air conditioning system, according to the operating load of the heat pump unit, the deep well pump adopts the frequency conversion and speed regulation water supply technology, which can effectively reduce the power consumption and water supply, significantly save the operating cost, and bring significant economic benefits

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