Pipeline direct drinking water supply system and control method thereof

Abstract

The embodiment of the application discloses a pipeline direct drinking water supply system and a control method thereof, the system comprises a water supply pump, a PLC controller and a plurality of water supply subareas, the PLC controller collects a constant pressure point pressure feedback value P in real time through a pressure sensor A, if it is detected that P f , the water supply pump is controlled to work at a frequency increasing and speed increasing mode; if it is detected that P d , the water supply pump is controlled to work at a frequency decreasing and speed decreasing mode, a pressure compensation is performed on a pressure stabilizing tank, and if P f , the water supply pump is controlled to continuously work at a frequency decreasing mode until a shutdown and hibernation state. The application is started from the purpose of guaranteeing water use of the most unfavorable subarea, analyzes and calculates pipeline impedance characteristics of the most unfavorable path, describes pressure head change of a control pressure point caused by variable pressure control of a constant pressure point, and gives a pressure operation interval of the variable pressure control, so as to satisfy normal water use of the subarea.

Description

Technical Field

[0001] This invention relates to the field of piped drinking water technology, and in particular to a piped drinking water supply system and its control method. Background Technology

[0002] Currently, piped drinking water generally adopts a variable frequency constant pressure water supply method, and the pressure feedback point for constant pressure control is set at the outlet of the water supply pump.

[0003] like Figure 1 The figure shows the characteristic curves of the pipeline network and pump for variable frequency constant pressure water supply.

[0004] Curve 1 is the pipeline characteristic curve, and its starting point H0 is the static head, which is the height difference that the water supply needs to lift.

[0005] Curve A is the performance curve of the water supply pump at the motor input current frequency f0. The flow rate corresponding to the intersection of curve A and the pipeline characteristic curve 1 is the design flow rate Q. s The corresponding head H s As a constant pressure line.

[0006] Constant pressure water supply determines the constant pressure value by using the total head required for maximum hourly consumption. However, the maximum hourly consumption and its required water pressure only occupy a portion of the daily water supply time, while the average hourly consumption and minimum flow rate have a longer duration.

[0007] During the system design phase, the design flow rate is generally taken to equal the maximum usage. This is to ensure that the design flow rate Q... s To meet the water supply pressure requirements, with Q s The corresponding pressure value H s This is a constant pressure line. The outlet of the water supply pump is a constant pressure point. The PLC controls the frequency converter to adjust the pump speed based on the difference between the data collected by the pressure sensor at the constant pressure point and the target value, so that the pressure at the constant pressure point is maintained at a constant pressure, thus achieving the purpose of constant pressure water supply. The operating frequency of the water supply pump is a cluster of curves centered at A, in the interval between A' and A”.

[0008] The flow rate at a certain moment is Q i Its corresponding head is H i H S –H i The difference is the residual head, which represents the extra energy consumed by the water pump to maintain constant pressure, and can also lead to overpressure in the water supply. Constant pressure water supply systems, designed to meet peak water demand in terms of pressure and flow, neglect changes in head loss due to flow variations in the pipeline, resulting in significant waste of excess head during off-peak periods. If the system operates at low flow rates for extended periods, it can lead to high energy consumption, low efficiency, and overheating of the water pump.

[0009] Especially for long distance water supply pipe network, the impedance S of water supply pump to the most unfavorable point is large, and the pipe resistance loss formula is ΔP=SQ 2 Therefore, the pipe network pressure fluctuation is more affected by the flow, and the water supply overpressure amplitude is larger during the low flow and low water consumption peak. At present, a stable pressure tank is generally connected in parallel at the outlet of the water supply pump. Since the adjustable capacity of the stable pressure tank is small, the output pressure drops quickly, and the constant pressure control is sensitive to the pressure fluctuation. The water pump will be in a high frequency operation state for a long time in order to maintain the constant pressure. SUMMARY

[0010] The technical problem to be solved by the embodiments of the present application is to provide a pipe direct drinking water supply system and a control method thereof, so as to reduce the energy consumption of the water supply pump, improve the efficiency, and relieve the water supply overpressure phenomenon.

[0011] In order to solve the above technical problems, the embodiments of the present application provide a pipe direct drinking water supply system, which comprises a water supply pump, a frequency converter, a stable pressure tank, a PLC controller and a plurality of water supply subareas. The water supply pump supplies water to the water supply riser of the plurality of water supply subareas through a water supply main pipe. A pressure sensor A is arranged at a constant pressure point of the water supply pump. A remote pressure gauge is arranged at a control pressure point of a most unfavorable subarea in the water supply subarea.

[0012] The most unfavorable subarea is a water supply subarea with the largest height difference between the subarea entrance plane and the water supply pump outlet plane,

[0013] The water supply pump is initially in a shutdown hibernation state. The PLC controller collects a constant pressure point pressure feedback value P in real time through the pressure sensor A. If it is detected that P f , the water supply pump is controlled to work by increasing frequency and speed through the frequency converter; if it is detected that P≥H d , the water supply pump is controlled to work by decreasing frequency and speed through the frequency converter, and the stable pressure tank is controlled to supplement pressure. If it is always P>H f during the process of decreasing frequency, the water supply pump is controlled to continuously decrease frequency until the shutdown hibernation state.

[0014] H f is the service lift of the pipe direct drinking water supply system, and H d is the dynamic lift of the pipe direct drinking water supply system.

[0015] Further, the service lift H f and the dynamic lift H d satisfy:

[0016] H f =H j +h0, H d =h0+(P1-P2).

[0017] P1 is the pressure head of the constant pressure point after the pump, P2 is the residual pressure head of the control pressure point, H jStatic head is the difference between the plane of the partition entrance and the plane of the outlet of the water supply pump, h0 is the minimum service head, and the minimum service head is the lowest static water pressure required at the pressure control point.

[0018] Correspondingly, the embodiment of the present application also provides a control method of the pipeline direct drinking water supply system, comprising:

[0019] Step 1: initializing the service head H of the pipeline direct drinking water system f and the dynamic head H d , collecting the pressure feedback value P of the pressure control point at the outlet position of the water supply pump of the pipeline direct drinking water system;

[0020] Step 2: controlling the water supply pump to be in a stop and hibernation state;

[0021] Step 3: if P < H f is detected, the water supply pump is controlled to work at a higher frequency;

[0022] Step 4: if P >= H d is detected, the water supply pump is controlled to work at a lower frequency, the pressure compensation tank is compensated, and if P > H f is detected during the process of the lower frequency, the water supply pump is controlled to continuously work at a lower frequency until the stop and hibernation state.

[0023] Further, the service head H f and the dynamic head H d satisfy:

[0024] H f = H j +h0, H d =h0+(P1-P2);

[0025] P1 is the pressure head of the pressure control point after the pump, P2 is the residual pressure head of the pressure control point, H j is the static head, the static head is the difference between the plane of the partition entrance and the plane of the outlet of the water supply pump, and h0 is the minimum service head, which is the lowest static water pressure required at the pressure control point.

[0026] The present application has the following beneficial effects:

[0027] 1. For the pipeline direct drinking water system of an office building, the present application has a certain tolerance to water supply pressure landslide, and the water supply pump can work at a lower frequency to the hibernation state during a long period of time of low water consumption and night small flow.

[0028] 2. For a long-distance park-type pipeline direct drinking water system, the pipe network impedance becomes larger, and the dynamic head is higher, so that the present application does not have to waste a large amount of excess head in order to maintain a higher dynamic head, and also relieves the problem of water supply overpressure. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a traditional variable frequency constant pressure water supply pipe network-pump characteristic curve diagram.

[0030] Figure 2 is a typical pipe direct drinking water supply system pipe network system diagram of the prior art.

[0031] Figure 3 is an equivalent impedance model schematic diagram of the most unfavorable path of the water supply system of the embodiment of the application.

[0032] Figure 4 is a flow schematic diagram of the control method of the pipe direct drinking water supply system of the embodiment of the application.

[0033] Figure 5 is a pipe network-pump characteristic curve diagram of the embodiment of the application.

[0034] Figure 6 is a water supply pump pressure operation interval schematic diagram of the embodiment of the application.

[0035] Figure 7 is a water supply pump operation frequency range schematic diagram of the embodiment of the application.

[0036] Figure 8 is a flow analysis diagram of the pressure control point under any working condition of the embodiment of the application.

[0037] Figure 9 is a residual pressure head schematic diagram of the pressure control point under any working condition of the embodiment of the application.

[0038] BRIEF DESCRIPTION OF DRAWINGS

[0039] Direct drinking water machine room 10, water supply pump 11, constant pressure point 12, pressure sensor 13, remote pressure gauge 14, pressure control point 15, S1 and S2 represent pipe impedance;

[0040] Water supply partition 20, water supply riser 21, water supply main pipe 22, partition backwater pipe 23, partition water supply pressure reducing valve 24. DETAILED DESCRIPTION

[0041] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict, and the application will be further described in detail below in combination with the drawings and specific embodiments.

[0042] The application can be applied to office building pipe direct drinking water systems, long-distance park type pipe direct drinking water systems, etc. Figure 2 As shown in the figure, it is a typical pipe direct drinking water supply system diagram covering multiple buildings (backwater pipe network is not drawn).

[0043] The water supply pump supplies water to the water supply riser of multiple buildings through a water supply main pipe, and the water supply riser of each building is divided into multiple water supply sub-zones by vertical zoning.

[0044] The present application defines:

[0045] The most unfavorable sub-zone: the water supply sub-zone with the largest height difference between the sub-zone entrance plane and the water supply pump outlet plane.

[0046] The most unfavorable path: the pipe path composed of the pipe section between the water supply pump outlet and the entrance of the most unfavorable sub-zone. Further, the sub-zone entrance particularly refers to the position before the sub-zone pressure reducing valve, that is, the most unfavorable path does not include the sub-zone pressure reducing valve.

[0047] The above most unfavorable path is taken as the control object of the variable frequency variable pressure water supply method of the present application, and the following parameters are defined.

[0048] Static head: H j , the height difference between the sub-zone entrance plane and the water supply pump outlet plane.

[0049] Minimum service water head: h0, the minimum static water pressure required by the sub-zone entrance.

[0050] Service head: H f , the static head plus the minimum service water head, that is, f H j +h0.

[0051] Dynamic head: H d , the service head considering the pipe resistance loss.

[0052] Please refer to Figures 2-3 , the pipe direct drinking water supply system of the embodiment of the present application comprises a water supply pump, a frequency converter, a pressure stabilizing tank, a PLC controller and multiple water supply sub-zones, the water supply pump supplies water to the water supply riser of the multiple water supply sub-zones through a water supply main pipe, a pressure sensor A is arranged at the constant pressure point of the water supply pump, the sub-zone entrance of the most unfavorable sub-zone in the water supply sub-zone is the pressure control point, and a remote pressure gauge is arranged at the pressure control point.

[0053] The water supply pump is initially in a shutdown hibernation state, the PLC controller collects the constant pressure point pressure feedback value P in real time through the pressure sensor A, if P f is detected, the water supply pump is controlled to work at a higher frequency and speed; if P d is detected, the water supply pump is controlled to work at a lower frequency and speed, the pressure stabilizing tank is controlled to supplement pressure, and if P f is always greater than H f during the frequency reduction process, the water supply pump is controlled to continuously reduce the frequency until the shutdown hibernation state.

[0054] Among them, H f is the service head of the pipe direct drinking water supply system, and Hd The dynamic head of the direct drinking water supply system.

[0055] As an embodiment, the service head H f and the dynamic head H d satisfy:

[0056] H f = H j +h0, H d =h0+(P1-P2);

[0057] P1 is the pressure head of the fixed pressure point after the pump, P2 is the residual pressure head of the pressure control point, H j is the static head, the static head is the height difference between the partition entrance plane and the outlet plane of the water supply pump, h0 is the minimum service water head, the minimum service water head is the lowest static water pressure required at the pressure control point.

[0058] The pipe network characteristic curve of the present application refers to the pipe characteristic curve of the most unfavorable path.

[0059] The sum of the flow resistances of all the series pipe sections of the most unfavorable pipe is the total resistance of the pipe network system. According to the theory of fluid mechanics, the flow resistance is expressed as:

[0060] △P=SQ 2 ;

[0061] In order to maintain the pipe flow, the energy (head) required by the pipe flow is equal to the flow resistance. Therefore, the formula is the expression of the pipe network characteristic curve:

[0062] H=△P=SQ 2 ;

[0063] H is the energy (head) required by the pipe flow. S is the pipe impedance, which is related to the geometric size of the pipe network, the friction coefficient along the way, and the local resistance coefficient. When these factors are once determined and remain unchanged, S is a constant. The above formula can obtain that the curve relationship between the head and the flow is a quadratic parabola.

[0064] The static head of the present application:

[0065] The pipe network characteristic curve is:

[0066] H=H j +SQ 2 .

[0067] The service head of the present application:

[0068] In order to ensure the normal water use and pressure safety of each water use point of the building, the water supply partition has a pressure design interval. Among them, the partition entrance needs to meet the minimum service pressure requirement. The static head H jAdd the minimum service water head (h0), which is the service lift H f , the pipe network characteristic curve is translated upward, and the pipe network characteristic curve is expressed as:

[0069] H = H f + SQ 2

[0070] Wherein, H f = H j +h0.

[0071] The dynamic lift of the present application:

[0072] The greater the flow, the greater the flow resistance of the pipeline. The pipe network characteristic curve corresponding to the design flow Q s , that is, the dynamic lift H d .

[0073] The pipe network-pump characteristic curve described in the present application is shown in the following figure: Figure 5

[0074] Curve 1, the most unfavorable pipeline characteristic curve with static lift H j as the starting point.

[0075] Curve 2, the most unfavorable pipeline characteristic curve with service lift H f as the starting point considering the minimum service water head (h0). The water supply system must meet the requirement of the minimum service water head (h0) of the partition. The control method of the water supply pump of the present application adopts this curve, and its expression is: H = H f + SQ 2 . Point O is the point on curve 2 with flow Q s .

[0076] Curve A, the performance curve of the water supply pump passing through point O. Point O is the working point of the pump supplying water at the design flow, and the corresponding lift is the dynamic lift H d .

[0077] As Figure 6 , the constant pressure point is the outlet position of the water supply pump, and it is also the pressure feedback point of the input PLC. The pressure control point is the end of the most unfavorable path (i.e. the inlet of the most unfavorable partition). The pressure control of the constant pressure point of the present application is not constant pressure control, but interval pressure control between the service lift H f and the dynamic lift H d , as shown in the shaded part of the figure. Curve 1 is the pipe network characteristic curve with static lift as the starting point without considering the minimum service water head (h0). Curve 2 is the pipe network characteristic curve with service lift H f as the starting point considering the minimum service water head (h0), and curve A is the performance curve of the water supply pump at the design flow Q s ​The intersection point of the water supply pump performance curve and curve 2 and curve A corresponds to the dynamic lift H d . Curve B is the performance curve of the water supply pump at the minimum working frequency for maintaining the service lift H f .

[0078] The larger the scale and the longer the distance of the direct drinking water pipe network, the greater the impedance S from the constant pressure point to the pressure control point, and the greater the difference between the dynamic lift H d and the service lift H f , that is, the pressure interval increases.

[0079] The running frequency range of the water supply pump of the present application is as shown in Figure 7 :

[0080] When the pressure of the constant pressure point reaches the dynamic lift H d , the water supply pump reduces the frequency and speed; when the pressure of the constant pressure point is lower than the service lift H f , the water supply pump increases the frequency and speed or restarts until the feedback point pressure reaches H d . In the case of a pressure stabilizing tank connected in parallel at the outlet of the water supply pump, although the pressure output of the pressure stabilizing tank is fast and the pressure stabilizing time is short, since the present application adopts interval pressure control, the interference of pressure fluctuation can be eliminated to a certain extent, and even the frequency can be reduced to the shutdown hibernation state, such as Figure 7 , the running curve of the water supply pump of the present application is the curve cluster falling in the light color shaded part in the figure.

[0081] In the constant pressure water supply system provided with a pressure stabilizing tank, since the adjustable capacity of the pressure stabilizing tank is small and the pressure drop is fast, and the constant pressure control is very sensitive to pressure fluctuation, the water supply pump will be in a high frequency running state for a long time in order to maintain the constant pressure, such as the dark color shaded part in the figure is the running frequency range of the pump in the constant pressure water supply.

[0082] Compared with the above, the water supply pump adopting the technical solution of the present application is not in a high frequency running state for a long time, and the pump body will not be hot, and can be in a shutdown hibernation state during low flow and no water use. Specifically embodied as:

[0083] For the direct drinking water pipe system of an office building, the present application has a certain tolerance to water supply pressure drop, and during the low water use valley and the long period of night low flow, the water supply pump can reduce the frequency to the hibernation state.

[0084] For a long distance park type direct drinking water pipe system, the pipe network impedance increases, and the dynamic lift is higher, and the present application does not have to waste a lot of excess head in order to maintain a high dynamic lift, and also relieves the water supply overpressure problem.

[0085] The present application selects the service lift H f as the low pressure line of the running frequency interval of the water supply pump.

[0086] Depend on Figure 6 As shown, the pressure at the constant pressure point is always greater than the service head H. f And H f The minimum service head requirement that the water supply pump needs to provide is the lowest head required for the most unfavorable zone when the flow rate is zero.

[0087] like Figure 8 The flow rate at a certain moment is Q i The water supply pump needs to provide a head of H. i If the constant pressure point pressure is less than H at this time i ,like Figure 8 The shaded region, assuming it to be H i0 H i0 <H i On the network characteristic curve (curve 1) starting from the static head, the head H output by the water supply pump is... i0 The available traffic is Q. i0 That is, under the above operating conditions, although the head output by the water supply pump is less than the dynamic head required to make the most unfavorable zone reach the minimum service head, it can still provide sufficient flow for this zone.

[0088] like Figure 9 Traffic Q i Point O is located on characteristic curve 1, with static head as the starting point, and its corresponding head is H. j0 H i0 and H j0 The difference between these values ​​represents the actual remaining pressure head at the inlet of the most unfavorable zone under the aforementioned operating conditions. This pressure head is not significantly different from the service head h0, and its effectiveness in water supply has been well verified in engineering practice. Furthermore, the pressure-reducing valves of the zones after the pressure control point automatically reduce their resistance as the pressure head before the valve decreases, thereby maximizing the maintenance of the minimum required service head.

[0089] Please refer to Figure 4 The control method for the piped drinking water supply system of this invention includes:

[0090] Step 1: Initialize the service head H of the piped drinking water system f and driving head H d (In this field, the unit is generally pressure or head), collect the pressure feedback value P of the constant pressure point at the outlet of the water supply pump of the piped drinking water system;

[0091] Step 2: Control the water supply pump to be in a shutdown and sleep state;

[0092] Step 3: If P < H is detected f Then, the water supply pump will be controlled to operate at a higher frequency.

[0093] Step 4: If P≥H is detected d, then control the water supply pump to reduce frequency, and the pressure tank to supplement pressure, if P>H f , then control the water supply pump to reduce frequency continuously until the stoppage of the sleep state.

[0094] The pipe network characteristic curve adopted by the present application is a quadratic parabola, and the static lift and the service lift are both determined values: the static lift is the elevation difference between the entrance of the most unfavorable subarea and the water supply pump; the service lift is expressed as: static lift + minimum service water head, i.e. f H j + SQ S 2 .

[0095] The dynamic lift needs to be determined by actual measurement and calculation, and the method is as follows.

[0096] As Figure 3 , the constant pressure point is at the outlet of the water supply pump, and the pressure control point is at the entrance of the subarea with the highest static lift. The present application sets the pressure control point at the entrance of the subarea, obtains the characteristic curve (H-Q characteristic curve) of the pipe section between the constant pressure point and the pressure control point through calculation, thereby describes the change of the pressure head of the pressure control point caused by the variable pressure control of the constant pressure point, and gives the pressure operation interval of the variable pressure control to meet the normal water use of the subarea.

[0097] The pressure head of the constant pressure point is used not only to lift the potential energy of the elevation difference, but also to consume part of the flow resistance loss. The pressure head difference between the two points is equal to the sum of the elevation difference and the resistance loss:

[0098] P1-P2=H j + SQ s 2

[0099] In the above formula, P1 is the pressure head of the constant pressure point after the pump, P2 is the residual pressure head of the pressure control point, H j is the static lift, i.e. the elevation difference, Q s is the design flow, and SQ s 2 is the pipe resistance loss.

[0100] Under the design flow Q s , the data of P1 and P2 are collected, and the resistance loss is obtained through the above formula:

[0101] SQ s 2 = P1-P2-H j

[0102] The target pipe network characteristic curve of the present application is the curve with the service lift H f as the starting point, so:

[0103] H d = H f + SQ S 2

[0104] And: H f = H j + h0

[0105] So: H d = H j + h0 + SQ s 2

[0106] = H j + h0 + P1 - P2 - H j

[0107] = h0 + (P1 - P2)

[0108] The value of H d is obtained above, and the parameters required for the frequency and voltage control of the application have been obtained.

[0109] The pipe impedance is obtained from the foregoing equation:

[0110]

[0111] The pipe characteristic curve equation of the most unfavorable path is obtained by substituting the target curve expression:

[0112]

[0113] This equation is the target pipe characteristic curve (curve 2) in the application. Figure 5

[0114] For a garden-type direct drinking water system covering multiple buildings, it is difficult to give an accurate pipe network hydraulic model. The application starts from the purpose of ensuring the most unfavorable subarea water use, analyzes and calculates the pipe impedance characteristics of the most unfavorable path, obtains the characteristic curve, describes the pressure head change of the pressure control point caused by the variable voltage control of the pressure point, and gives the pressure operation interval of the variable voltage control to meet the normal water use of the subarea.

[0115] Although embodiments of the application have been shown and described, it is to be understood that the application is not limited to the details of the foregoing embodiments, and that various changes, modifications, substitutions and alterations can be made thereto without departing from the spirit and scope of the application as defined in the appended claims and its equivalents.​

Claims

1. A piped direct drinking water supply system, comprising a water supply pump, a frequency converter, a pressure stabilizing tank, a PLC controller, and multiple water supply zones, wherein the water supply pump supplies water to the water supply risers of the multiple water supply zones through a main water supply pipe, and a pressure sensor A is installed at the pressure stabilization point of the water supply pump, characterized in that, The control pressure point is located at the entrance of the most unfavorable subarea in the water supply subarea, and a remote pressure gauge is arranged at the control pressure point, The most unfavorable subarea is the water supply subarea with the largest height difference between the entrance plane of the subarea and the outlet plane of the water supply pump, The water supply pump is initially in a stopped and dormant state. The PLC controller collects the pressure feedback value P at the constant pressure point in real time through pressure sensor A. If P < H is detected... f Then, the water supply pump is controlled by a frequency converter to increase its frequency and speed; if P≥H is detected... d Then, the frequency converter controls the water supply pump to reduce its frequency and speed, and the pressure tank replenishes the pressure. During the frequency reduction process, if P>H remains constant... f Then the water supply pump will be controlled to continuously reduce its frequency until it stops and enters a sleep state; wherein H f is the service head of the direct-piping drinking water supply system, H d is the dynamic head of the direct-piping drinking water supply system; Service head H f And dynamic head H d Satisfies: H f = H j + h0,H d = h0+(P1- P2); P1 is the pressure head of the post-pump constant pressure point, P2 is the residual pressure head of the pressure control point, H j is the static lift, the static lift is the height difference between the partition inlet plane and the outlet plane of the water supply pump, h0 is the minimum service water head, the minimum service water head is the lowest static water pressure required at the pressure control point.

2. The control method of the direct drinking water supply system of the pipe according to claim 1, characterized by, Comprise: Step 1: initialize the service head H of the direct drinking water pipeline system f and the dynamic head H d Collect the constant pressure point pressure feedback value P of the outlet position of the water supply pump of the direct drinking water pipeline system; Step 2: control the water supply pump to be in a shutdown dormant state; Step 3: If P < H is detected f then control the water supply pump to increase the frequency of operation; Step 4: If P≥H is detected d , then the water supply pump is controlled to reduce the frequency, and the pressure compensation tank is compensated. If P>H is detected during the frequency reduction process f , then the water supply pump is controlled to continue to reduce the frequency until it stops and enters the hibernation state. Service head H f And dynamic head H d Satisfies: H f = H j + h0,H d = h0+(P1- P2); P1 is the pressure head of the post-pump constant pressure point, P2 is the residual pressure head of the pressure control point, H j is the static lift, the static lift is the height difference between the partition inlet plane and the outlet plane of the water supply pump, h0 is the minimum service water head, the minimum service water head is the lowest static water pressure required at the pressure control point.

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