Application of Deep Well Pump Frequency Conversion Technology in Groundwater Source Heat Pump

Abstract: At present, in ground-source heat pump air-conditioning systems, the volume of water normally supplied by a deep well pump can meet the required water quantity of two or more heat pump units. However, in actual operation, it has been found that heat pump units are operating at partial load most of the time while deep-well pumps have been operating at full capacity, resulting in a substantial increase in electricity bills and water bills. To solve this problem, this paper takes practical engineering as an example. The variable-volume water supply using deep well pump frequency conversion technology not only meets the requirement of heat pump for well water but also saves electric energy and well water. The variable frequency control method and principle of deep well pump, Determine, and based on the measured results of deep well pump operation, analyze its energy-saving effect and economy. Keywords: Deep well pump Energy saving effect Variable frequency range Water supply Power consumption 1 Introduction In recent years, the frequency control technology with its significant energy-saving effect and reliable control of air-conditioning systems in the pump and fan more applications, and its technology More mature, but groundwater source heat pump air conditioning system in deep well pump water supply applications, is still rare, but it is quite necessary. A pilot survey of the groundwater source heat pump application in Shenyang found that in the groundwater source heat pump air conditioning system, when the heat pump capacity is not large, the water supply of the deep well pump can meet the required water quantity of two or more heat pump units. During the actual operation, it was found that the heat pump unit was under partial load most of the time while the deep well pump had been operating at full capacity. As a result, the electricity bill and water bill were greatly increased. Therefore, deep well pump frequency conversion water supply technology in groundwater source heat pump system has great potential for energy saving. 2 Project Overview This paper analyzes the winter operation of the actual project for the study, the project profile is as follows: a new campus campus five floors, construction area of ​​11030m2, the summer air conditioning design cooling load of 894kw, winter air conditioning design heat load of 1012kw. The office building uses two underground water source heat pump units for heating and cooling. The heating conditions are: heating capacity 515kw, input power 136.02kw, cold water flow 65m3 / h, hot water volume 88.6m3 / h, pump pumping capacity 160m3 / h , Power 37kw. Winter Runtime: November to March, 24 hours a day. 3 deep well pump frequency control water supply method Deep well pump adopts temperature difference control method. As the heat pump unit in the heating conditions, we must ensure that the evaporator water temperature can not be too low, so deep well pump backwater pipe temperature sensor set temperature tjh. When the backwater temperature at the well water source side is greater than tjh, the deep well pump controller sends down the current frequency signal to the inverter to reduce the frequency of the input power, the corresponding reduction of the number of revolutions of the deep well pump, the pump water supply, the shaft power and the motor input The power will also be reduced, so as to achieve the purpose of energy saving. When the water side of the backwater temperature is lower than tjh value, the frequency adjustment. 4 pump speed adjustment principle Change the pump speed, you can change the performance of the pump, so as to achieve the purpose of adjusting the operating point. According to the similar law, for the same pump running at different speeds, the pump flow, head, shaft power and speed of the relationship can be expressed as follows: Q / Qe = n / ne (1) ) 2 (2) P / Pe = (n / ne) 3 (3) Where: ne-- pump rated speed, r / min; n-- speed under actual operating conditions, r / min; M3 / h; Q - flow rate under actual operating conditions, m3 / h; He - lift at rated speed of the pump, in m; H - lift in actual operating conditions, m ; Pe-- pump rated speed power, kw; P-- actual operating conditions of power, kw. From (1) and (2), we can get H1 / Q12 = H2 / Q22 = k (4) That is H = kQ2 (5) The formula (5) is the quadratic parabola whose vertex Point with similar conditions, known by a similar law, when the pump speed changes before and after the same, the pump efficiency remains unchanged, so the similar conditions parabolic efficiency is also called the equivalent curve. Therefore, from the energy point of view, usually by changing the pump speed method to change the pump operating point, try to make it work in a high efficiency range. 5 determine the pump frequency range When the heat pump load changes, the deep well pump water supply also will change. Deep well pump water supply (Qmin ~ Qe), that is, deep well pump frequency range (nmin ~ ne), shown in Figure 1. The minimum flow rate required for the heat pump unit is 40m3 / h (equipment requirement), which is the minimum water supply for the deep well pump, then the minimum speed of the deep well pump is: nmin = Qmin / Qe × ne = 40/160 × 2900 = 725 rpm / Sub-heating conditions in winter deep well pump frequency conversion range: 725 rev / min ~ 2900 r / min.