PUMP DEVICE

Abstract

 The present invention relates to a pump apparatus which can be suitably used as a water supply apparatus for supplying water to a building. The pump apparatus includes: a pump (2); a motor (3) configured to drive the pump (2); a driver (20) for driving of the motor (3) at variable speed; and a controller (40) configured to control the driver (20) so as to start the pump when the discharge-side pressure of the pump (2) decreases to a predetermined starting pressure and to keep the discharge-side pressure equal to a target pressure on a target pressure control curve. The controller (40) determines a lowest value PL of the discharge-side pressure after the pump (2) is started, calculates a difference ΔP1 between the lowest value PL and a predetermined lower limit Pz of the discharge-side pressure, and corrects the target pressure control curve R based on the difference ΔP1.

Description

Technical Field

[0001] The present invention relates to a pump apparatus for delivering a liquid, and more particularly to a pump apparatus which is suitable for use as a water supply apparatus for supplying water to a building.

Background Art

[0002] Pump apparatuses are widely used as water supply apparatuses for supplying water to buildings. FIG. 1 is a schematic view showing a typical water supply apparatus. As shown in FIG. 1, a water supply apparatus 100 has a suction inlet which is coupled via an introduction pipe 5 to a water main pipe 4 or a not-shown water reservoir. The water supply apparatus 100 has a discharge outlet which is coupled to a water supply pipe 7. This water supply pipe 7 communicates with water outlet devices (e.g., faucets) on each floor of a building. The water supply apparatus 100 is configured to pressurize water from the water main pipe 4 or the water reservoir and supplies the water to the water outlet devices of the building.

[0003] The water supply apparatus 100, in which a suction side of a pump is directly coupled to the water main pipe 4 via the introduction pipe 5, includes a pump 2, a motor 3 as a drive source for driving the pump 2, an inverter 20 as a driver for driving the motor 3 at variable speed, a backflow prevention device 25 provided at a suction side of the pump 2, a pressure sensor 21 provided at a suction side of the backflow prevention device 25, a check valve 22 provided at a discharge side of the pump 2, and a pressure sensor 26, a flow switch 24 and a pressure tank 28 which are provided at a discharge side of the check valve 22. These components are housed in a cabinet 30 of the water supply apparatus 100. There also exists a type of water supply apparatus which is not provided with such a cabinet 30.

[0004] A bypass pipe 8 for supplying water solely by the water pressure of the water main pipe 4 is provided between the introduction pipe 5 and the water supply pipe 7. The bypass pipe 8 is provided with a check valve 23. In this embodiment, the water supply apparatus 100 has two parallel-arranged sets of pumps 2, motors 3, check valves 22, and flow switches 24. It is also possible to provide one set or three or more sets of pumps, motors, check valves, and flow switches. In a direct-coupling type of water supply apparatus, the suction side of the pump 2 is coupled to the water main pipe 4, as shown in FIG. 1, while in a water-reservoir type of water supply apparatus, the suction side of the pump 2 is coupled to a water reservoir via the introduction pipe 5. Such a water-reservoir type of water supply apparatus is not provided with the backflow prevention device 25, the suction-side pressure sensor 21, and the bypass pipe 8 shown in FIG. 1.

[0005] The check valve 22, which is attached to a discharge pipe 32 coupled to a discharge port of the pump 2, is a valve for preventing a backflow of the water when the pump 2 is stopped. The flow switch 24 is a flow-rate detector which detects a decrease in a flow rate of water, flowing in the discharge pipe 32, to a certain value. The pressure sensor 26 is a water-pressure measuring device for measuring a discharge-side pressure (i.e., a back pressure applied to the water supply apparatus 100). The pressure tank 28 is a pressure holding device for holding the discharge-side pressure during stoppage of the pump 2.

[0006] The water supply apparatus 100 includes a controller 35 for controlling water supply operations. The inverter 20, the flow switch 24, the pressure sensor 21, and the pressure sensor 26 are coupled to the controller 35 via signal lines, respectively. When the flow switch 24 detects that the flow rate of water has decreased to a predetermined value, the controller 35 instructs the inverter 20 to temporarily increase the speed of the pump 2 to accumulate the pressure in the pressure tank 28, and then stops the operation of the pump 2. When the discharge-side pressure (i.e., the pressure of water in the discharge pipe 32) decreases to a predetermined starting pressure, the controller 35 instructs the inverter 20 to start the operation of the pump 2. The starting pressure, which is a trigger for starting the pump 2, is stored in the controller 35 in advance.

[0007] As the water is used in the building while the pump 2 is not in operation, the discharge-side pressure of the pump 2 decreases. When the discharge-side pressure, i.e., an output value of the pressure sensor 26, decreases to the predetermined starting pressure, the controller 35 starts the pump 2. When the pump 2 is in operation, constant estimated terminal pressure control is performed based on the output value of the pressure sensor 26.

[0008] When the use of water in the building is stopped, the flow rate of water discharged from the pump 2 decreases. If a decrease in the flow rate of water to a predetermined value is detected by the flow switch 24, the flow switch 24 sends a detection signal to the controller 35. Upon receiving this detection signal, the controller 35 instructs the inverter 20 to increase the rotational speed of the pump 2 until the discharge-side pressure reaches a predetermined stop pressure, and then stops the pump 2.

[0009] In the constant estimated terminal pressure control, the pressure of water in the water outlet device is controlled to be kept constant by appropriately changing a target pressure in accordance with a loss due to resistance in the water supply pipe in the building. FIG. 2 is a diagram showing pump performance curves for illustrating an example of the constant estimated terminal pressure control. In FIG. 2, horizontal axis indicates the flow rate of water, and vertical axis indicates discharging pressure, i.e., head.

[0010] In FIG. 2, PA represents a discharge-side pressure of the pump 2 at a maximum flow rate, and PB represents a discharge-side pressure of the pump 2 when the pump 2 is in a shut-off operation (i.e., at zero flow rate). A curve indicated by a symbol N_MAX is a performance curve of the pump 2 as obtained when the pump 2 is operated at a rotational speed N_MAX which achieves the pressure PA, and a curve indicated by a symbol N_MIN is a performance curve of the pump 2 as obtained when the pump 2 is operated at a rotational speed (a shut-off rotational speed) N_MIN which achieves the pressure PB. A target pressure control curve R is determined based on the sum of a maximum head for the building, a pressure necessary to use the water outlet devices, and a loss in pipe which is dependent on the flow rate. The target pressure control curve R is used for performing the constant estimated terminal pressure control, and is generally a quadratic curve. The target pressure control curve R represents a relationship between discharge flow rate of the pump 2 and target pressure of the pump 2. The pump 2 is operated at an operating point which is a point of intersection between a performance curve N and the target pressure control curve R.

[0011] In the constant estimated terminal pressure control, the rotational speed of the pump 2 is controlled in consideration of the pipe resistance (indicated by the target pressure control curve R) that varies depending on the flow rate of water. Specifically, the rotational speed of the pump 2 is controlled based on the output value of the pressure sensor 26 so that the discharge-side pressure of the pump 2 varies along the target pressure control curve R. When the flow rate is low, the pipe resistance is low, and therefore a lower power is needed to operate the pump 2. As a result, an energy-saving operation is realized.

[0012] When the pump 2 is in operation, the discharge-side pressure of the pump 2 is controlled between PA and PB. Therefore, the pump 2 is driven at rotational speed of not less than N_MIN during a steady operation. In a case where the pressure PB is set to be equal to the pressure PA in FIG. 2, the controller 35 performs a constant discharge pressure control. In this case, the controller 35 controls the rotational speed of the pump 2 so that the discharge-side pressure of the pump 2 is kept at PA (= PB).

Citation List

Patent Literature

[0013] Patent document 1: International Publication No. WO 2012/099242

Summary of Invention

Technical Problem

[0014] The above-described target pressure control curve R is established with some margin so that water can be supplied at a sufficient pressure to the water outlet device (e.g., faucet) in the building. In some cases, however, a high water supply pressure may not be necessary so long as the flow rate of water at an actually necessary level is ensured. In view of this, the patent document 1 has proposed a water supply apparatus which can operate a pump at a lower rotational speed while ensuring a necessary flow rate. According to the patent document 1, a plurality of target pressure control curves are stored in advance in a controller, and the pump is controlled based on one of the target pressure control curves. Therefore, an energy-saving operation can be achieved by selecting an optimum one from the prepared target pressure control curves.

[0015] However, the water supply apparatus described in the patent document 1 is designed to manually select one from the target pressure control curves and manually switch from one target pressure control curve to another, and is not configured to automatically select one from the target pressure control curves and automatically switch from one target pressure control curve to another. Moreover, since one target pressure control curve to be used is selected from the target pressure control curves that have been stored in the controller, it is not possible to adjust the target pressure control curve itself according to an operating situation of the water supply apparatus. The operating situation of the water supply apparatus can vary depending on time of a day. For example, in a school, the use of water rapidly increases during a break, whereas water is hardly used during the night. In this manner, the operating situation of the water supply apparatus may vary depending on time of a day or other factors. Therefore, there is a demand for optimization of the target pressure control curve. Further, the optimization of the target pressure control curve is also desirable in order to achieve more efficient energy saving.

[0016] The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide a pump apparatus which can automatically determine an optimum target pressure control curve in accordance with an operating situation.

Solution to Problem

[0017] In order to achieve the object, according to one aspect of the present invention, there is provided a pump apparatus comprising: a pump; a motor configured to drive the pump; a driver configured to drive the motor at variable speed; a pressure sensor configured to measure a discharge-side pressure of the pump; and a controller configured to control the driver so as to start the pump when the discharge-side pressure decreases to a predetermined starting pressure and to keep the discharge-side pressure equal to a target pressure on a target pressure control curve. The controller is configured to determine a lowest value of the discharge-side pressure after the pump is started, calculate a difference between the lowest value and a predetermined lower limit of the discharge-side pressure, and correct the target pressure control curve based on the difference.

[0018] In a preferred aspect of the present invention, if the lowest value is larger than the lower limit, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a lower head side based on the difference.

[0019] In a preferred aspect of the present invention, if the lowest value is larger than the lower limit, the controller corrects the target pressure control curve by subtracting the difference from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

[0020] In a preferred aspect of the present invention, if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a higher head side based on the difference.

[0021] In a preferred aspect of the present invention, if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by adding the difference to a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

[0022] In a preferred aspect of the present invention, the controller calculates the difference every time the pump is started to thereby obtain a plurality of differences, and correct the target pressure control curve based on the plurality of differences.

[0023] In a preferred aspect of the present invention, the controller calculates an average of the plurality of differences, and corrects the target pressure control curve based on the average of the plurality of differences.

[0024] In a preferred aspect of the present invention, the controller calculates the difference every time the pump is started during a predetermined period of time to thereby obtain a plurality of differences.

[0025] In a preferred aspect of the present invention, the controller calculates the difference every time the pump is started until the number of starting operations of the pump reaches a predetermined number of times to thereby obtain a plurality of differences.

[0026] In a preferred aspect of the present invention, the controller calculates the difference every time the pump is started, on the condition that the lowest value is larger than the lower limit, to thereby obtain a plurality of differences.

[0027] In a preferred aspect of the present invention, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a lower head side based on an average of the plurality of differences.

[0028] In a preferred aspect of the present invention, the controller corrects the target pressure control curve by subtracting the average of the plurality of differences from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

[0029] In a preferred aspect of the present invention, if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve based on the difference between the lowest value and the lower limit.

[0030] In a preferred aspect of the present invention, if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a higher head side based on the difference between the lowest value and the lower limit.

[0031] In a preferred aspect of the present invention, if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by adding the difference between the lowest value and the lower limit to a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

[0032] In a preferred aspect of the present invention, the controller is configured to calculate the difference every time the pump is started during a predetermined period of time to thereby obtain a plurality of differences, calculate a first average, which is an average of differences among the plurality of differences which are obtained when the lowest value is larger than the lower limit, calculate a second average, which is an average of differences among the plurality of differences which are obtained when the lowest value is smaller than the lower limit, calculate a correction value by subtracting the second average from the first average, and correct the target pressure control curve by subtracting the correction value from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

[0033] In a preferred aspect of the present invention, the controller is configured to calculate the difference every time the pump is started until the number of starting operations of the pump reaches a predetermined number of times to thereby obtain a plurality of differences, calculate a first average, which is an average of differences among the plurality of differences which are obtained when the lowest value is larger than the lower limit, calculate a second average, which is an average of differences among the plurality of differences which are obtained when the lowest value is smaller than the lower limit, calculate a correction value by subtracting the second average from the first average, and correct the target pressure control curve by subtracting the correction value from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

[0034] In a preferred aspect of the present invention, the controller determines the lowest value which is a local minimum value of the discharge-side pressure that appears first after the pump is started.

[0035] In a preferred aspect of the present invention, the controller determines the lowest value after the discharge-side pressure has stabilized.

[0036] In a preferred aspect of the present invention, the controller corrects the target pressure control curve after the discharge-side pressure has stabilized.

[0037] In a preferred aspect of the present invention, the controller determines that the discharge-side pressure has stabilized if the discharge-side pressure has continued to be higher than a predetermined reference value for a predetermined monitoring time.

[0038] In a preferred aspect of the present invention, the controller gradually switches the target pressure control curve from a current one to a corrected target pressure control curve.

[0039] In a preferred aspect of the present invention, the controller gradually switches the target pressure control curve from a current one to a corrected target pressure control curve over a predetermined transition time.

[0040] In a preferred aspect of the present invention, the controller gradually switches the target pressure control curve from a current one to a corrected target pressure control curve at a predetermined rate of change.

[0041] In a preferred aspect of the present invention, the lower limit is determined by adding a pressure loss, occurring at a water outlet device located at a highest position from the pump apparatus, to a head between the pump apparatus and the water outlet device.

[0042] According to another aspect of the present invention, there is provided a controller for controlling an operation of a pump such that the pump is started when a discharge-side pressure of the pump decreases to a predetermined starting pressure and the discharge-side pressure is kept equal to a target pressure on a target pressure control curve. The controller is configured to determine a lowest value of the discharge-side pressure after the pump is started, calculate a difference between the lowest value and a predetermined lower limit of the discharge-side pressure, and correct the target pressure control curve based on the difference.

[0043] In a preferred aspect of the present invention, the controller is configured to calculate the difference every time the pump is started to thereby obtain a plurality of differences, and correct the target pressure control curve based on the plurality of differences.

Advantageous Effects of Invention

[0044] According to the present invention, the target pressure control curve can be automatically corrected based on the difference between the lowest value of the discharge-side pressure, measured after the pump is started, and the predetermined lower limit of the discharge-side pressure. Therefore, an optimum target pressure control curve for an operating situation of the pump can be obtained.

Brief Description of Drawings

[0045] 

FIG. 1 is a schematic view showing a typical water supply apparatus;

FIG. 2 is a diagraph showing pump performance curves for illustrating an example of constant estimated terminal pressure control;

FIG. 3 is a schematic view showing a water supply apparatus as an example of a pump apparatus according to an embodiment of the present invention;

FIG. 4 is a diagram showing a target pressure control curve according to an embodiment of the present invention;

FIG. 5 is a graph showing a temporal change in a discharge-side pressure measured by a pressure sensor;

FIG. 6 is a graph showing a target pressure control curve as corrected toward a lower head side;

FIG. 7 is a graph showing another example of a corrected target pressure control curve;

FIG. 8 is a graph showing another example of a temporal change in the discharge-side pressure measured by the pressure sensor;

FIG. 9 is a graph showing another example of a target pressure control curve as corrected toward a higher head side;

FIG. 10 is a graph showing a dead zone in which a correction of a target pressure control curve is not permitted;

FIG. 11 is a flow chart showing a pump control operation performed by a controller;

FIG. 12 is a flow chart showing another pump control operation performed by the controller;

FIG. 13 is a schematic view of a pump apparatus according to another embodiment of the present invention;

FIG. 14 is a plan view of the pump apparatus shown in FIG. 13;

FIG. 15A is a side view of a guide cover;

FIG. 15B is a diagram of the guide cover of FIG. 15A as viewed from below; and

FIG. 16 is a diagram showing an exemplary construction of the controller (or controlling device).

Description of Embodiments

[0046] Embodiments of the present invention will now be described with reference to the drawings. FIG. 3 is a schematic view showing a water supply apparatus as an example of a pump apparatus according to an embodiment of the present invention. A water supply apparatus 1 shown in FIG. 3 has the same construction as the water supply apparatus 100 shown in FIG. 1 except for a controller 40, and hence duplicate descriptions thereof are omitted. FIG. 4 is a diagram showing a target pressure control curve according to an embodiment of the present invention. In FIG. 4, vertical axis indicates the discharge-side pressure (head) of the pump 2, and horizontal axis indicates the flow rate of water discharged from the pump 2.

[0047] In FIG. 4, PA represents a discharge-side pressure of the pump 2 at a maximum flow rate, and PB represents a discharge-side pressure of the pump 2 when the pump is in a shut-off operation (i.e., at zero flow rate). A curve indicated by symbol N_MAX is a performance curve of the pump 2 as obtained when the pump 2 is operated at a rotational speed N_MAX which can achieve the pressure PA at the maximum flow rate, and a curve indicated by symbol N_MIN is a performance curve of the pump 2 as obtained when the pump 2 is operated at a rotational speed (a shut-off rotational speed) N_MIN which can achieve the pressure PB at zero flow rate. The target pressure control curve R is determined based on the sum of a maximum head for the building, a pressure necessary to use the water outlet devices, and a loss in pipe which is dependent on the flow rate. The target pressure control curve R is used for performing the constant estimated terminal pressure control, and is generally a quadratic curve. The target pressure control curve R represents a relationship between the discharge flow rate of the pump 2 and the target pressure of the pump 2. The pump 2 is operated at an operating point which is a point of intersection between the performance curve N and the target pressure control curve R.

[0048] A symbol Ps shown in FIG. 4 is a starting pressure which is a threshold value for starting the pump 2. In this embodiment, for example, the starting pressure Ps is set between the pressure PB and the pressure PA. The controller 40 starts the pump 2 if the discharge-side pressure, measured by the pressure sensor 26, decreases to the starting pressure Ps. A symbol Pz shown in FIG. 4 is a minimum discharge-side pressure (head) required by a user, i.e., a lower limit of the discharge-side pressure. This lower limit Pz is determined by adding a pressure loss, occurring at a water outlet device located at the highest position from the water supply apparatus 1, to a pressure necessary to pump up water to that water outlet device. The lower limit Pz is stored in advance in the controller 40. The lower limit Pz may be changed according to usage conditions (usage environment) of the water supply apparatus. The target pressure PB at the shut-off operation (hereinafter referred to as shut-off target pressure) is set to a value larger than the lower limit Pz so that the discharge pressure of the water supply apparatus 1 does not become lower than the lower limit Pz.

[0049] FIG. 5 is a graph showing a temporal change in the discharge-side pressure measured by the pressure sensor 26 (i.e., a pressure-varying curve). If a decrease in the flow rate of water to a predetermined value is detected by the flow switch 24 (time t1), the rotational speed of the pump 2 is increased temporarily to accumulate pressure in the pressure tank 28, and then the pump 2 is stopped (time t2). If water is used through the water outlet device while the pump 2 is not in operation, the discharge-side pressure decreases rapidly. Thus, the pump 2 is started if the discharge-side pressure reaches the starting pressure Ps (time t3). Even after the pump 2 is started, the discharge-side pressure continues to decrease, because it takes a certain time for the pump 2 to increase its rotational speed. For this reason, after the pump 2 is started, the discharge-side pressure decreases for a very short period of time, and then begins to increase (time t4).

[0050] As shown in FIG. 5, although the discharge-side pressure varies relatively greatly for a while due to a hunting phenomenon immediately after the pump 2 is started, a range of change in the discharge-side pressure decreases with time, and the discharge-side pressure stabilizes at an approximately constant value (time t5). The range of change herein refers to a difference between a target pressure and a local minimum value of the discharge-side pressure and a difference between a target pressure and a local maximum value of the discharge-side pressure. The stabilized discharge-side pressure is equal to or slightly higher than the shut-off target pressure PB.

[0051] After the pump 2 is started, the controller 40 determines a lowest value PL of the discharge-side pressure as follows. The lowest value PL is a value of the discharge-side pressure at the point in time (time t4) at which the change in the discharge-side pressure (represented by a slope of a tangential line to the pressure-varying curve) turns from a downward trend (negative) to an upward trend (positive) for the first time. In other words, the lowest value PL is a local minimum value of the discharge-side pressure that appears first after the pump 2 is started. The controller 40 compares the determined lowest value PL with the lower limit Pz, and calculates a difference ΔP1 (which is an absolute value) between the lowest value PL and the lower limit Pz. If the lowest value PL is larger than the lower limit Pz, i.e., if the discharge-side pressure has not decreased to the lower limit Pz after the pump 2 is started, the controller 40 subtracts the difference ΔP1 from the shut-off target pressure PB on the target pressure control curve R, thereby moving (or shifting) the target pressure control curve R toward a lower head side (lower pressure side). The target pressure control curve R is corrected based on the difference ΔP1 in this manner, and the operation of the pump 2 is controlled based on the corrected target pressure control curve.

[0052] The controller 40 may determine whether or not the discharge-side pressure has stabilized after the pump 2 is started, and may determine the lowest value PL after the discharge-side pressure has stabilized (time t5). More specifically, the controller 40 compares the discharge-side pressure, measured by the pressure sensor 26, with a predetermined reference value and, if the discharge-side pressure has continued to be higher than the reference value for a predetermined monitoring time tc, the controller 40 determines that the discharge-side pressure has stabilized. The predetermined reference value may be equal to or smaller than the current shut-off target pressure PB. The predetermined reference value is preferably smaller than the current shut-off target pressure PB in order for the controller 40 to more quickly determine whether the discharge-side pressure has stabilized.

[0053] FIG. 6 is a graph showing a corrected target pressure control curve R'. The controller 40 calculates a new shut-off target pressure PB' by subtracting the difference ΔP1 from the current shut-off target pressure PB, and determines the new target pressure control curve R' by connecting, with a quadratic curve, a point specified by the zero flow rate and the shut-off target pressure PB' and a point specified by the maximum flow rate Q_MAX and the corresponding pressure PA in a coordinate system of FIG. 6. As a result of such a correction, the current target pressure control curve R almost entirely moves (or shifts) toward the lower head side.

[0054] The fact that the lowest value PL is larger than the lower limit Pz indicates that a satisfactory water supply operation can be achieved even if the discharging pressure of the pump 2 is lowered. Therefore, by correcting the current target pressure control curve R toward the lower head side, the energy-saving operation can be achieved.

[0055] As shown in FIG. 7, it is also possible to correct the current target pressure control curve R by parallel translating the entirety of the target pressure control curve R toward the lower head side by the difference ΔP1.

[0056] In order to avoid a rapid change in the discharging pressure of the pump 2, it is preferred to gradually switch from the current target pressure control curve R to the new target pressure control curve R'. For example, the current target pressure control curve R may be slowly switched to the new target pressure control curve R' over a predetermined transition time (e.g., 10 seconds), or the current target pressure control curve R may be slowly switched to the new target pressure control curve R' at a predetermined rate of change.

[0057] FIG. 8 is a graph showing a temporal change in the discharge-side pressure in a case where the lowest value PL is lower than the lower limit Pz. In this case, the controller 40 corrects the target pressure control curve R toward a higher head side (higher pressure side) by adding a difference ΔP2 (which is an absolute value) between the lowest value PL and the lower limit Pz to the shut-off target pressure PB on the target pressure control curve R. FIG. 9 is a graph showing the corrected target pressure control curve R'. As shown in FIG. 9, the current target pressure control curve R almost entirely shifts toward the higher head side.

[0058] The lower limit Pz is the minimum water supply pressure required for the water supply apparatus 1. If the water supply pressure is lower than the lower limit Pz, water may not be supplied to the entirety of the building. Therefore, if the lowest value PL is smaller than the lower limit Pz, the controller 40 corrects the current target pressure control curve R toward the higher head side to ensure a sufficient water supply pressure. In this manner, the controller 40 can ensure a sufficient water supply pressure according to the operating situation of the pump 2 even when performing the energy-saving operation.

[0059] After determining the lowest value PL or simultaneously with the determination of the lowest value PL, the controller 40 corrects the target pressure control curve based on the following determination results. If the lowest value PL is larger than the lower limit Pz (PL > Pz) and if the lowest value PL is smaller than the lower limit Pz (PL < Pz), the controller 40 corrects the current target pressure control curve R in the above-described manner. On the other hand, if the lowest value PL is equal to the lower limit Pz (PL = Pz), the controller 40 does not correct the current target pressure control curve R.

[0060] The target pressure control curve greatly affects the discharging pressure of the pump 2. Thus, frequent correction of the target pressure control curve R can make the discharging pressure of the pump 2 unstable. In view of this, a dead zone may be provided for the lowest value PL in order to avoid the frequent correction (switching) of the target pressure control curve R.

[0061] FIG. 10 is a graph showing a dead zone in which the correction of the target pressure control curve R is not permitted. A dead zone DZ is set for the lowest value PL of the discharge-side pressure which is determined after the pump 2 is started. If the lowest value PL is in the dead zone DZ, the controller 40 does not correct the target pressure control curve R. In the example illustrated in FIG. 10, a lower limit of the dead zone DZ is Pz, and an upper limit is "Pz + P_add". The controller 40 does not correct the target pressure control curve R when the lowest value PL is not more than "Pz + P_add" and not less than Pz. With the dead zone DZ established as described above, frequent correction (switching) of the target pressure control curve R can be avoided, and stable water supply can be realized.

[0062] As shown in FIG. 10, the dead zone DZ is preferably not lower than the lower limit Pz of the discharge-side pressure. This is because, if the dead zone DZ is set to be lower than the lower limit Pz, the water supply apparatus 1 may not be able to supply water to the entirety of the building. In some usage environments of the water supply apparatus 1, the dead zone DZ may include the lower limit Pz.

[0063] After determining the lowest value PL or simultaneously with the determination of the lowest value PL in the above-described manner, the controller 40 corrects the target pressure control curve based on the difference ΔP1 or ΔP2 between the lowest value PL and the lower limit Pz. Such correction of the target pressure control curve makes it possible to obtain the optimum target pressure control curve suitable for the operating situation of the pump while achieving the energy-saving operation.

[0064] FIG. 11 is a flow chart showing a pump control operation performed by the controller 40. Upon turning-on a power switch of the water supply apparatus 1, the pump control is started with use of an initial target pressure control curve which is stored in advance in the controller 40. The controller 40 determines whether or not the pump 2 is rotating and, if the pump 2 is rotating, determines whether or not the pump 2 has just been started. If the pump 2 has just been started, the controller 40 determines whether or not the discharge-side pressure has reached a first local minimum value. If it is determined that the discharge-side pressure has reached the first local minimum value, the controller 40 determines the lowest value PL which is the first local minimum value. Thereafter, the controller 40 determines whether or not the above-described correction of the target pressure control curve R is necessary or not. In the case where the target pressure control curve R is to be corrected, the controller 40 determines whether or not the discharge-side pressure has stabilized, and slowly switches (changes) from the current target pressure control curve R to the corrected target pressure control curve R'. Upon completion of the switching to the corrected target pressure control curve R', the controller 40 controls the pump 2 based on the corrected target pressure control curve R'.

[0065] FIG. 12 is a flow chart showing another pump control operation performed by the controller 40. This flow chart is the same as the above-described flow chart shown in FIG. 11 from the step of turning on the power switch to the step of determining whether the pump 2 has just been started. If the pump 2 has just been started, the controller 40 determines whether or not the discharge-side pressure has stabilized and, if the discharge-side pressure has stabilized, the controller 40 determines the lowest value PL.

[0066] The controller 40 does not correct the target pressure control curve R if the lowest value PL is either equal to the lower limit Pz or in the dead zone DZ. If the lowest value PL is neither equal to the lower limit Pz nor in the dead zone DZ, the controller 40 corrects the target pressure control curve R. When correcting the target pressure control curve R, the controller 40 slowly switches (changes) from the current target pressure control curve R to the corrected target pressure control curve R'. After the correction of the target pressure control curve, the controller 40 controls the pump 2 based on the corrected target pressure control curve R'.

[0067] In order to avoid frequent correction (switching) of the target pressure control curve, instead of or in addition to providing the above-described dead zone DZ, the target pressure control curve R may be corrected after the pump 2 is started several times. For example, even if the controller 40 has determined to correct the target pressure control curve R each time the pump 2 is started, the controller 40 may not perform the correction, despite such determination results. Instead, the controller 40 may record (or store) one or more differences between the lowest value PL and a predetermined lower limit of the discharge-side pressure, and may correct the target pressure control curve based on the recorded results. More specifically, if the lowest value PL is larger than the lower limit Pz, the controller 40 stores the difference ΔP1 between the lowest value PL and the lower limit Pz without correcting the target pressure control curve R. On the condition that (or so long as) the lowest value PL is larger than the lower limit Pz, the controller 40 calculates and stores the difference ΔP1 every time the pump 2 is started, thereby obtaining and storing a plurality of differences ΔP1. Further, the controller 40 calculates an average of the stored differences ΔP1, and corrects the target pressure control curve R by subtracting the average of the differences ΔP1 from the target pressure PB, at which the pump shut-off operation is performed, on the target pressure control curve R. The above-described calculation and storage of the difference ΔP1 is repeated until the number of starting operations of the pump 2 reaches a predetermined number of times. If the lowest value PL is smaller than the lower limit Pz, the controller 40 may immediately correct the target pressure control curve R by adding the difference ΔP2 between the lowest value PL and the lower limit Pz to the target pressure PB as discussed above. In this manner, if the lowest value PL is larger than the lower limit Pz, the difference ΔP1 is stored as discussed above. If the lowest value PL is smaller than the lower limit Pz and the difference ΔP2 is calculated, the correction of the target pressure control curve may immediately be performed exceptionally as described above. Such an exceptional correction based on the difference ΔP2 may be performed even if no difference ΔP1 has been stored or even if one or more differences ΔP1 have been stored. With this operation, in case the water failure is likely to occur as a result of the shift of the target pressure control curve toward the lower head side, the target pressure control curve can be switched to a higher-head pressure control curve, which enables stable supply of water.

[0068] Instead of the above-described embodiment, it is also possible to correct the target pressure control curve R after a predetermined period of time has elapsed. More specifically, so long as the lowest value PL is larger than the lower limit Pz, the controller 40 stores the difference ΔP1 between the lowest value PL and the lower limit Pz, without correcting the target pressure control curve R, every time the pump 2 is started during the predetermined period of time, thereby obtaining and storing a plurality of differences ΔP1. Further, the controller 40 calculates the average of the stored differences ΔP1, and corrects the target pressure control curve R by subtracting the average of the differences ΔP1 from the target pressure PB, at which the pump shut-off operation is performed, on the target pressure control curve R. If the lowest value PL is smaller than the lower limit Pz, the controller 40 may immediately correct the target pressure control curve R by adding the difference ΔP2 between the lowest value PL and the lower limit Pz to the target pressure PB as described above.

[0069] The predetermined period of time is, for example, set to 24 hours. In this case, the target pressure control curve R is corrected based on a previous day's operating situation of the pump 2. Correction of the target pressure control curve R is performed only once a day, and therefore frequent changes in the water supply pressure can be avoided.

[0070] If the pump 2 has been started only once until the predetermined period of time has elapsed, the target pressure control curve R may be corrected using the difference that is calculated when the pump is started only once. If the pump 2 has never been started during the predetermined period of time, i.e., if the pump 2 has been kept in operation or has been kept stopped, the target pressure control curve R may not be corrected.

[0071] It is also possible to correct the target pressure control curve R based on all of the differences ΔP1, ΔP2 that have been calculated during the predetermined period of time, regardless of whether the lowest value PL is larger or smaller than the lower limit Pz. Further, it is also possible to correct the target pressure control curve R based on averages of all of these differences ΔP1, ΔP2. More specifically, the controller 40 stores the difference ΔP1 or ΔP2 between the lowest value PL and the lower limit Pz every time the pump 2 is started during the predetermined period of time, thereby obtaining and storing a plurality of differences ΔP1, ΔP2. The controller 40 calculates a first average (absolute value), which is an average of the differences ΔP1 that have been obtained in the cases where the lowest value PL is larger than the lower limit Pz, and a second average (absolute value), which is an average of the differences ΔP2 that have been obtained in the cases where the lowest value PL is smaller than the lower limit Pz. Further, the controller 40 calculates a correction value by subtracting the second average from the first average, and corrects the target pressure control curve R by subtracting the correction value from the target pressure PB, at which the pump shut-off operation is performed, on the target pressure control curve R. The correction value is a positive value or a negative value. Specifically, the correction value is a positive value when the first average is larger than the second average, whereas the correction value is a negative value when the first average is smaller than the second average. Accordingly, the target pressure control curve R is corrected toward either the lower head side or the higher head side by subtracting the correction value from the target pressure PB.

[0072] In the above-described embodiment, the controller 40 corrects the target pressure control curve R based on the averages of the differences ΔP1, ΔP2 calculated during the predetermined period of time. In another embodiment, the controller 40 may repeat the calculation and the storage of the differences ΔP1, ΔP2 until the number of starting operations of the pump 2 reaches a predetermined number of times, and may correct the target pressure control curve R based on averages of all the stored differences ΔP1, ΔP2 in accordance with the above-described manner.

[0073] While the pump apparatus of the present invention is applied to the water supply apparatus in the above-described embodiments, the present invention can also be applied to a pump apparatus other than a water supply apparatus. For example, the present invention can be applied to an integrated pump apparatus in which an inverter is secured to a side surface of a motor as shown in FIG. 13. FIG. 13 is a schematic view of a pump apparatus according to another embodiment of the present invention. In FIG. 13, the same reference numerals are used for those components which correspond to the components shown in FIG. 3.

[0074] This pump apparatus includes a pump 2 for delivering a liquid, a motor 3 coupled to the pump 2, an inverter 20 as a driver for driving the motor 3 at variable speed, and two support members 44 coupling the inverter 20 to the motor 3. The inverter 20 is disposed adjacent to the motor 3, and a controller 40 is disposed in the inverter 20. The depiction of the check valve 22, the flow switch 24 and the pressure tank 28, shown in FIG. 3, is omitted from FIG. 13.

[0075] The pump 2 is driven by the motor 3, and sucks a liquid through a suction port 2a, pressurizes the liquid and discharges the liquid through a discharge port 2b. The pump 2 may be a centrifugal pump, while other types of pump can also be used.

[0076] FIG. 14 is a plan view of the pump apparatus shown in FIG. 13. A cooling fan 43 is disposed at the top of the motor 3 and is coupled to a rotating shaft 10 of the motor 3. Thus, the cooling fan 43 is configured to rotate together with the rotating shaft 10 of the motor 3. The cooling fan 43 is a centrifugal fan that expels a gas radially outwardly. A guide cover 45 covering the cooling fan 43 is provided on the motor 3. This guide cover 45 functions to guide a flow of the gas, generated by the rotation of the cooling fan 43, toward the inverter 20. In FIG. 14, the guide cover 45 is depicted by imaginary line.

[0077] FIG. 15A is a side view of the guide cover 45, and FIG. 15B is a diagram of the guide cover 45 of FIG. 15A as viewed from below. The guide cover 45 includes a flat portion 45a having gas-intake openings (air-intake openings) 45c, and a side portion 45b which is in a U-shape when viewed from below. As the cooling fan 43 rotates, an ambient gas (generally air) flows through the gas intake openings 45c into the guide cover 45, and flows along the side portion 45b of the guide cover 45 and is sent to the inverter 20. As shown in FIG. 14, a gap is formed between the guide cover 45 and the motor 3 when they are viewed in an axial direction of the motor 3. A part of the gas flow, generated by the rotation of the cooling fan 43, passes through the gap to flow on a peripheral surface of the motor 3, thereby cooling the motor 3.

[0078] The two support members 44 are located at a distance from each other, so that a space, which serves as a flow passage for the gas flow sent from the cooling fan 43, is formed between these support members 44. The inverter 20 is cooled by the gas flow moving on an outer surface of the inverter 20. The gas flow, moving in the space between the motor 3 and the inverter 20, can also cool the motor 3.

[0079] A pressure sensor 26 is disposed in the discharge port 2b of the pump 2. This pressure sensor 26 measures the discharge-side pressure of the pump 2, and sends a measured value to the controller 40. As in the above-described embodiments, the controller 40 determines the lowest value PL of the discharge-side pressure after the pump 2 is started, calculates the difference between the lowest value PL and the predetermined lower limit Pz, and corrects the target pressure control curve based on the difference.

[0080] FIG. 16 is a diagram showing an exemplary construction of the controller (or controlling device) 40 shown in FIGS. 3 and 13. While FIG. 16 shows a water supply apparatus, the construction of the controller 40 shown in FIG. 16 can also be applied to the controller 40 shown in FIG. 13.

[0081] As shown in FIG. 16, the controller (controlling device) 40 includes a setting section 46, a storage section 47, an arithmetic section 48, a display section 49, an I/O section 50, and an operation panel 51. The setting section 46 and the display section 49 are provided on the operation panel 51.

[0082] The operation panel 51 includes the setting section 46 and the display section 49, and also includes e.g., a switch, an input confirmation buzzer and an input confirmation display, and functions as a human interface. Various set values for creating the target pressure control curve R, such as the discharge-side pressure PB of the pump 2 (i.e., at zero flow rate) when performing the shut-off operation, the discharge-side pressure PA of the pump 2 at the maximum flow rate, etc. are inputted through the setting section 46. Further, various set values for correcting the target pressure control curve R are also inputted through the setting section 46. These set values for correcting the target pressure control curve R include the lower limit Pz of the discharge-side pressure determined by adding a pressure loss, occurring at a water outlet device located at the highest position from the water supply apparatus 1, to the pressure necessary for the water supply apparatus 1 to pump up the water to that water outlet device, the pattern of change in the pressure-varying curve (i.e., the pattern of change in the slope of a tangential line from negative to positive) for setting the timing for determining the lowest value PL of the discharge-side pressure after the pump 2 is started, the time tc for monitoring the pressure change, the monitoring time (predetermined period of time) for setting the timing of correction of the target pressure control curve R, the frequency and the time of storing the difference between the lowest value PL and the lower limit Pz, set values of the dead zone for the lower limit Pz, and the transition time or the rate of change to be used when switching the target pressure control curve R. These data inputted through the setting section 46 are stored in the storage section 47. In another embodiment, the operation panel 51 may be provided with an operation-panel arithmetic section using a CPU. The operation panel 51 of this type can perform data communication between the setting section 46/display section 49 and the arithmetic section 48 via the I/O section 50.

[0083] The display section 49 serves as a human interface, and displays various data, such as set values, stored in the storage section 47. The display section 49 further displays the current operating situation (operating conditions) of the pump 2, such as the operation or stoppage of the pump 2, the operational frequency, the electric current, the discharge pressure, the inflow pressure (in the case of direct-coupling water supply), a water reservoir alarm, etc.

[0084] A memory, such as RAM, may be used as the storage section 47. Information stored in the storage section 47 include a control program for executing a control process as shown by the flow chart of FIG. 11 or 12, and various data, such as data on the results of calculations (the lowest value PL of the discharge-side pressure, the difference between the lowest value PL and the lower limit Pz, the operating time, an integration value, etc.) performed in the arithmetic section 48, pressure values (discharge pressure, inflow pressure), data inputted by the setting section 46, and data inputted or outputted by the I/O section 50.

[0085] A port may be used as the I/O section 50. The I/O section 50 receives the output value of the discharge-side pressure sensor 26 and the signal from the flow switch 24, and sends them to the arithmetic section 48. The I/O section 50 also performs signal input and signal output in communication.

[0086] A CPU may be used as the arithmetic section 48. Based on the program and the various data stored in the storage section 47, and based on the signal inputted from the I/O section 50, the arithmetic section 48 performs the determination of the lowest value PL, the calculation of the differences, the measurement of time (operating time, stoppage time), an integration calculation (integrated value), processing of communication data, calculation of target pressures, calculation of a frequency command value, the correction of the target pressure control curve, etc. The output of the arithmetic section 48 is inputted into the I/O section 50.

[0087] The I/O section 50 and the inverter 20 are coupled to each other by a communication device, such as RS 485. Set values, a frequency command value, and control signals such as a start/stop signal (operation/stop signal) are sent from the I/O section 50 to the inverter 20, while signals of the operating situation (operating condition), such as an actual frequency value and an electric current value, are sequentially sent from the inverter 20 to the I/O section 50.

[0088] An analog signal and/or a digital signal can be used as a control signal to be transmitted between the I/O section 50 and the inverter 20. For example, an analog signal can be used e.g., for a rotational frequency, and a digital signal can be used e.g., for an operation/stop command.

[0089] The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.

Industrial Applicability

[0090] The present invention is applicable to a pump apparatus which is suitable for use as a water supply apparatus for supplying water to a building.

Reference Signs List

[0091] 

1, 100

water supply apparatus

2

pump

3

motor

8

bypass pipe

10

rotating shaft

20

inverter

21

pressure sensor

22, 23

check valve

24

flow switch

25

backflow prevention device

26

pressure sensor

28

pressure tank

35, 40

controller

43

cooling fan

44

support member

45

guide cover

46

setting section

47

storage section

48

arithmetic section

49

display section

50

I/O section

51

operation panel

Claims

1. A pump apparatus comprising:

a pump;

a motor configured to drive the pump;

a driver configured to drive the motor at variable speed;

a pressure sensor configured to measure a discharge-side pressure of the pump; and

a controller configured to control the driver so as to start the pump when the discharge-side pressure decreases to a predetermined starting pressure and to keep the discharge-side pressure equal to a target pressure on a target pressure control curve,

wherein the controller is configured to

determine a lowest value of the discharge-side pressure after the pump is started,

calculate a difference between the lowest value and a predetermined lower limit of the discharge-side pressure, and

correct the target pressure control curve based on the difference.

2. The pump apparatus according to claim 1, wherein if the lowest value is larger than the lower limit, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a lower head side based on the difference.

3. The pump apparatus according to claim 2, wherein if the lowest value is larger than the lower limit, the controller corrects the target pressure control curve by subtracting the difference from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

4. The pump apparatus according to any one of claims 1 to 3, wherein if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a higher head side based on the difference.

5. The pump apparatus according to claim 4, wherein if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by adding the difference to a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

6. The pump apparatus according to claim 1, wherein the controller calculates the difference every time the pump is started to thereby obtain a plurality of differences, and correct the target pressure control curve based on the plurality of differences.

7. The pump apparatus according to claim 6, wherein the controller calculates an average of the plurality of differences, and corrects the target pressure control curve based on the average of the plurality of differences.

8. The pump apparatus according to claim 6 or 7, wherein the controller calculates the difference every time the pump is started during a predetermined period of time to thereby obtain a plurality of differences.

9. The pump apparatus according to any one of claims 6 to 8, wherein the controller calculates the difference every time the pump is started until the number of starting operations of the pump reaches a predetermined number of times to thereby obtain a plurality of differences.

10. The pump apparatus according to any one of claims 6 to 9, wherein the controller calculates the difference every time the pump is started, on the condition that the lowest value is larger than the lower limit, to thereby obtain a plurality of differences.

11. The pump apparatus according to claim 10, wherein the controller corrects the target pressure control curve by shifting the target pressure control curve toward a lower head side based on an average of the plurality of differences.

12. The pump apparatus according to claim 11, wherein the controller corrects the target pressure control curve by subtracting the average of the plurality of differences from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

13. The pump apparatus according to claim 11 or 12, wherein if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve based on the difference between the lowest value and the lower limit.

14. The pump apparatus according to claim 13, wherein if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by shifting the target pressure control curve toward a higher head side based on the difference between the lowest value and the lower limit.

15. The pump apparatus according to claim 14, wherein if the lowest value is smaller than the lower limit, the controller corrects the target pressure control curve by adding the difference between the lowest value and the lower limit to a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

16. The pump apparatus according to claim 6 or 7, wherein the controller is configured to
calculate the difference every time the pump is started during a predetermined period of time to thereby obtain a plurality of differences,
calculate a first average, which is an average of differences among the plurality of differences which are obtained when the lowest value is larger than the lower limit,
calculate a second average, which is an average of differences among the plurality of differences which are obtained when the lowest value is smaller than the lower limit,
calculate a correction value by subtracting the second average from the first average, and
correct the target pressure control curve by subtracting the correction value from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

17. The pump apparatus according to claim 6 or 7, wherein the controller is configured to
calculate the difference every time the pump is started until the number of starting operations of the pump reaches a predetermined number of times to thereby obtain a plurality of differences,
calculate a first average, which is an average of differences among the plurality of differences which are obtained when the lowest value is larger than the lower limit,
calculate a second average, which is an average of differences among the plurality of differences which are obtained when the lowest value is smaller than the lower limit,
calculate a correction value by subtracting the second average from the first average, and
correct the target pressure control curve by subtracting the correction value from a target pressure, at which a pump shut-off operation is performed, on the target pressure control curve.

18. The pump apparatus according to any one of claims 1 to 17, wherein the controller determines the lowest value which is a local minimum value of the discharge-side pressure that appears first after the pump is started.

19. The pump apparatus according to any one of claims 1 to 18, wherein the controller determines the lowest value after the discharge-side pressure has stabilized.

20. The pump apparatus according to any one of claims 1 to 19, wherein the controller corrects the target pressure control curve after the discharge-side pressure has stabilized.

21. The pump apparatus according to claim 19 or 20, wherein the controller determines that the discharge-side pressure has stabilized if the discharge-side pressure has continued to be higher than a predetermined reference value for a predetermined monitoring time.

22. The pump apparatus according to any one of claims 1 to 21, wherein the controller gradually switches the target pressure control curve from a current one to a corrected target pressure control curve.

23. The pump apparatus according to claim 22, wherein the controller gradually switches the target pressure control curve from a current one to a corrected target pressure control curve over a predetermined transition time.

24. The pump apparatus according to claim 22, wherein the controller gradually switches the target pressure control curve from a current one to a corrected target pressure control curve at a predetermined rate of change.

25. The pump apparatus according to any one of claim 1 or 24, wherein the lower limit is determined by adding a pressure loss, occurring at a water outlet device located at a highest position from the pump apparatus, to a head between the pump apparatus and the water outlet device.

26. A controller for controlling an operation of a pump such that the pump is started when a discharge-side pressure of the pump decreases to a predetermined starting pressure and the discharge-side pressure is kept equal to a target pressure on a target pressure control curve, the controller being configured to
determine a lowest value of the discharge-side pressure after the pump is started,
calculate a difference between the lowest value and a predetermined lower limit of the discharge-side pressure, and
correct the target pressure control curve based on the difference.

27. The controller according to claim 26, wherein the controller is configured to calculate the difference every time the pump is started to thereby obtain a plurality of differences, and correct the target pressure control curve based on the plurality of differences.

Drawing