WO2010092238A1 - Energy efficiency observer - Google Patents

Abstract

The invention concerns a pump monitoring arrangement comprising means for receiving measurement data comprising at least a frequency component from a sensor into the memory of a computer device. The invention is characterized in that the arrangement further comprises computing means for determining the motor slip and estimating the torque of the pump from the dynamic measurement information. Also a method and a computer program product are disclosed.

Description

ENERGY EFFICIENCY OBSERVER

TECHNICAL FIELD OF INVENTION

The invention relates to an arrangement and method for analyzing operation of a flow generating device, e.g. a centrifugal pump.

BACKGROUND OF THE INVENTION

Numerous methods and arrangements for monitoring energy efficiency of various devices, e.g. pumps, are known in the art.

WO 2003/084022 discloses an energy management system and method. The system comprises at least one device that controllably consumes energy. The system further comprises a sensing and controlling device for sensing and controlling energy delivered to the energy consuming device. Information from the energy consuming devices is transmitted to a back-end server using a data communication network. The information may be accessed through a user interface of a terminal device.

US 2006/0142961 discloses an enterprise energy management system. The system includes a database including information relating to pieces of energy consuming equipment located at a site. A server is programmed to calculate an expected energy consumption profile and to notify a user if actual energy consumption exceeds the expected energy consumption.

US 2002/0178047 discloses an energy management and corrective method utilizing a computer system and energy sensors. The method comprises the steps of monitoring energy usage at an energy consuming first facility and saving information regarding recording energy usage at the facility; establishing a historical base-line energy usage at the first facility based on the saved information of energy usage; comparing historical base-line energy usage to current energy usage at the first facility; determining excessive energy usage based on the comparison of historical base-line energy usage to current energy usage at the first facility; reporting a recommended corrective action for excessive energy usage and providing an electronic purchase ordering link to purchase a supply needed to perform the corrective action.

U.S. patent US6260004 discloses a pump operation diagnosis method in process control plant. The method involves comparing process data point acquired from process variable of pump with predefined best efficiency point of pump. The disclosure further teaches an apparatus and a method for diagnosing rotating equipment commonly used in the factory and process control industry. The apparatus and method are intended for use in assisting a maintenance engineer in the diagnosis of turbines, compressors, fans, blowers and pumps. The apparatus and method are based on the comparison of the current pump signature curves resulting from the acquisition of process variables from sensors monitoring the current condition of the pump and the original or previous pump performance curve from prior monitoring or knowledge of the pump geometry, installation effects and properties of the pumped process liquid.

Pumps are very seldom manufactured to meet a certain specification. The design specifications are generally calculated so as to satisfy a maximum flow rate with plenty of margin of the flow rate. Thus, the energy efficiency of a pump may not be optimal for the purpose where the pump is actually used. The energy efficiency of a pump may be optimized e.g. by controlling the rotational speed of a motor pump using an inverter.

The energy optimization arrangements of prior art typically need to be installed permanently as part of the system whose optimization is desired. Typically, a relatively large number of sensors need to be installed in the system. Some of the installation operations may require lengthy maintenance break for the pump. The installation work may also require some special permissions, e.g. for performing electrical installations. In general, the analysis and optimization systems tend to be rather complex and expensive. Therefore, they are not often utilized as the cost of acquiring and installing the measurement and optimization system may be higher than the savings that may be expected from the use of the measurement and optimization system.

OBJECT OF THE INVENTION

The object of the present invention is to provide an arrangement, a method and/or a computer program for facilitating efficient and simple measurement of the approximate power consumption of a centrifugal pump by means of a simple- to-install and/or simple-to-use measurement arrangement.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by determining the motor slip and torque of a centrifugal pump from measurement data whose frequency spectrum comprises peaks that correlate with rotating speed of the pump and calculating power consumption and flow rate estimates based on the measurement data.

An aspect of the invention is a measuring arrangement for a pump, the arrangement comprising means for receiving measurement information comprising at least a frequency and optionally an amplitude component from a sensor into the memory of a computer device. The invention is characterized in that the arrangement comprises computing means, e.g. a processor, memory and computer executable program code, for determining the motor slip of the pump from the measurement information and for estimating torque of the motor by comparing the motor slip with motor characteristics data.

The measurement information may be e.g. dynamic pressure measurement data, pump vibration data or data from an optical sensor

In an embodiment, the sensor may be an acoustic sensor. The acoustic sensor may be the microphone of a cellular phone. The computing means may comprise the processor and/or memory of the cellular phone.

The collection frequency of the measurement information may be e.g. at least 50, 100, 500 or 1000Hz.

The motor characteristics data may comprise e.g. the rated torque curve of the motor.

The arrangement may further comprise computing means for estimating flow rate of the pump based on the estimated torque of the motor using pump characteristics data, e.g. the shaft power to flow rate curve of the pump.

The arrangement may yet further comprise computing means for estimating pump head based on the estimated flow rate of the pump using pump characteristics data, e.g. the flow rate to pump head curve of the pump.

The arrangement may still yet further comprise computing means for estimating the inflow pressure of the pump based on the measured outflow pressure and estimated pump head.

The arrangement may still yet further comprise computing means for estimating the current (i.e. present) energy efficiency of the pump based on estimated shaft power and head power. (The head power = delta p x Q). Head power is pump hydraulic power without losses.

The computer device of the arrangement may comprise communication means for exchanging information with some second computer device e.g. a server computer. The computer device of the arrangement may for example receive from a second computer device motor characteristics data, e.g. torque curve of the motor, pump characteristics data, e.g. flow rate to pump head curve or shaft power to flow rate curve of the pump, and/or medium characteristics data, e.g. viscosity of the fluid being pumped. The computer device may also send measurement data, motor slip data and/or any other data obtainable from the measurement data to the second computer device.

Another aspect of the invention is a method for calculating pump motor slip and estimating torque, the method comprising the step of receiving measurement data comprising at least frequency and optionally amplitude components from a sensor means to a computer device, the step of determining the motor slip of the pump from the measurement information and the step of estimating torque of the motor by comparing the motor slip with motor characteristics data..

Yet another aspect of the invention is a computer readable medium comprising computer program product for calculating pump motor slip and estimating torque, the computer program comprising computer executable instructions for receiving measurement information comprising at least frequency and optionally amplitude components from a sensor means to the computer, instructions for determining the motor slip of the pump from the measurement information and instructions for estimating torque of the motor by comparing the motor slip with motor characteristics data.. Some embodiments of the invention are described herein, and further applications and adaptations of the invention will be apparent to those of ordinary skill in the art.

BRIEF DESCRIPTION OF DRAWINGS

In the following, the invention is described in greater detail with reference to the accompanying drawings in which:

Figure 1a shows an overview of the pump efficiency measurement arrangement according to an embodiment of the present invention,

Figure 1 b shows an overview of the pump efficiency measurement arrangement according to another embodiment of the present invention, Figure 2 shows an exemplary method of determining motor slip and pump operating data according to an embodiment of the present invention,

Figure 3 shows another exemplary embodiment of the method of the present invention and

Figure 4 shows exemplary (fictitious) reporting data that may be produced according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1a depicts an exemplary measuring arrangement according to an embodiment of the present invention.

The arrangement comprises a computer 100 which suitably comprises a processor, memory, input and output devices and some network communication means. In an embodiment, the computer may be a portable computer, e.g. a laptop or a smart phone. Suitably, the computer further comprises a storage device 101 , e.g. a hard disk. The computer facilitates the measurement of at least the outlet 104 pressure of the centrifugal pump 102 using dynamic pressure sensor 105. The pressure measuring point comprising a pressure measurement sensor 105 is provided on the pressure side of the pump, e.g. in the flange sheet or in the outlet of the spiral case below the flange. Optionally, also the inlet 103 pressure may be measured using sensor 109. Also optionally, the temperature of the pump case or the medium flowing in the pump may be measured using a temperature sensor 106. The additional sensors may improve the accuracy of the measurements and calculations that are based on the measurements.

The computer 100 is suitably connectable to a second computer 107, e.g. a server computer, using some data communication means 108, e.g. a wireless network adapter, that enables the computer to exchange information with another computer, e.g. the server computer 107 over a network, e.g. a TCP/IP network, e.g. internet. At least part of the network may be a wireless network, e.g. a WLAN network or GSM / 3G cellular telecommunications network.

The unsmoothed signal of the pressure measurement sensor 105 is scanned with suitable resolution into the memory of a computer 100. The signal to be scanned may be e.g. an analogue signal having current of e.g. 4 ... 20 mA. The analogue signal is converted into a digital signal prior to storing it into the memory of the computer.

The computer is adapted to determine from the stored measurement data the pressure as well as the frequency of the pressure pulsation.

In the embodiment shown herein, there is no compelling need for any other measuring means such as flow measurement means or electric or mechanical measurement means. The objects of the invention are typically achievable e.g. with the single pressure sensor 105. However, additional sensors, e.g. inlet pressure sensor 109 and temperature sensor 106 may be used when practical. The computer receiving the measurement data is equipped with suitable software that is capable of analyzing the measurement data using some programming logic and data available from other sources. In a preferred embodiment, the software comprises means for receiving pump, motor and/or medium (fluid) characteristics data from the server computer 107 over the data communications network 108. The characteristics data may comprise e.g. torque curve of the motor, the "shaft power to flow rate" curve of the pump, the "pump head to flow rate" curve of the pump and/or the "viscosity to temperature" curve of the medium.

The pump whose operation is being analyzed, is operating essentially at a constant frequency. The frequency (rotating speed) of the impeller of the pump may be altered by altering the frequency of the alternating electric current operating the motor (not shown in figure) of the pump. The electric motor in this embodiment is an asynchronous motor. In order to determine the slip of the motor operating the pump according to an embodiment of the invention, the information about the frequency of the alternating electric current needs to be input to the computer 100 of the measurement arrangement.

Figure 1 b depicts another exemplary measuring arrangement according to an embodiment of the present invention. Reference numerals 100, 101 , 107 and 108 refer to similar components as in figure 1 a. In the shown embodiment, an optical measuring device 112 emitting a laser beam and sensing the periodically reflected laser beam is used for measuring the actual rotating speed of the motor 110 that is coupled with a centrifugal pump 111. Suitably, the optical measuring device is a hand-held device or a device that is easily attachable to a suitable measuring position, e.g. so that the laser beam points to the fan of the motor. The rotating speed of the motor is obtained from the rotating speed of the fan 114 of the motor towards which the laser beam 113 of the measuring device 112 is pointed. The reflection from each blade of the rotating fan produces a pulse that is observable by the measuring device 112. Once the number of blades of the fan 114 is known, e.g. from the technical specification of the motor, it is trivial to calculate the rotating speed of the motor and the frequency of the impeller of the pump.

In an embodiment, the functionality and computing means of computer 100 and storage 101 may be integrated e.g. in the measuring device 112 which may connect with the server computer 107 directly using e.g. some suitable wireless communication means, e.g. WLAN, GPRS or 3G communication network. In an embodiment, the optical sensor device 112 comprises means for entering e.g. the motor type or other motor identifying information or number of blades of the fan for subsequent or later transfer to computer 100 and/or server 107.

An advantage of the embodiment shown in figure 1 b is the ease of obtaining the rotation frequency information from the motor without any permanent sensor installation or calibration work at all. It is sufficient to just point the laser beam 113 at the fan and determine the number of blades of the fan. This together with the suitable computing means allows quick and effortless analysis of the energy efficiency of the pump 111.

Figure 2 shows exemplary method of estimating 200 pump efficiency based on the dynamic pressure measurement data according to an embodiment of the invention. As a first step 201 , some measurement data, e.g. dynamic pressure measurement data is collected from the pump using a pressure sensor (105 in figure 1). In another embodiment, measurement data may be input from an optical sensor (112 in figure 1 b). Then, a frequency spectrum is formed from the measurement data 202 and impeller blade peak frequency is identified 203 from the frequency spectrum. Now the impeller frequency may be calculated 204 if the number of impeller blades is known. Such information is available e.g. from data provided by the manufacturer of the pump. If a measuring arrangement of figure 1 b is used, the impeller frequency is derived from the rotating speed measured using the optical measuring device (112 in figure 1 b) instead of performing the steps 201 , 202 and 203.

Next, the motor slip is calculated 205. The motor slip is the difference between the measured impeller frequency and the synchronous rotating frequency of the motor. Next, the torque of the motor is estimated 206 by placing the estimated impeller frequency of the pump to the torque curve (see 310 in figure 3 for more details) of the motor.

In the following, an example about determining the shaft power is provided.

With an exact resolution of the pressure pulsation samples, the influence of the individual impeller blades (impulse entry, pressure points) on the measured pressure signal is obviously visible. The peaks caused by the impeller blades can be identified from the pulsation frequency spectrum e.g. by using some suitable filtering (e.g., band pass filtering).

The slip/backlash ("s" in the following equations) may be determined by comparing this pulsation frequency with the stator frequency.

f J blade^' P

J stator

CO**"* blade

J f stator

Equation 1

Kloss'sche equation, which is known to a person skilled in the art, describes the connection between the speed and torque of an asynchronous motor. The equation results as a curve such as one shown as 313 in Figure 3. The curve may be used for determining the dependence between the slip and the load of the motor. The curve is typically available from the manufacturer of the motor. The trend of the number of revolutions and torque characteristics can be assumed to be linear in the area between the nominal operating point and synchronous speed of the motor. Therefore the following equations may be applied for calculating the shaft power of the motor.

M_N -(H₀ -H)

M =

Equation 2

P₂ = ω-M = 2 - π -f - — M

P

Equation 3

Combining equations 2 and 3 results as the following equation:

p __p f - (n_o -n) _ p r2^Γ2N_r (_Λ 2N

Based on the characteristics data of the asynchronous motor and pump (obtainable e.g. from the plate affixed to the motor and from the knowledge of the number of impeller blades of the pump), as well as the measured frequency of the blade impulses in the pressure signal, the wave rating of the motor can be determined:

p __p Count_blade

2N

Equation 4

In the following an example about use of Equation 4 is provided using information from a fictitious data plate of an 11 kW IEC standard motor: 293^ - 60 — (3000 mm¹)² -3000 mm^{1 3}^

P₂ = U Λ0³W : :⁶ , , = 9,9 Λ0³W

2920 mm^"1 -300OmIn^"1 -(2920 mm¹)²

In step 207, the shaft power obtained in step 206 is applied to estimate the flow rate and pump head of the pump by using pump characteristics data. The pump characteristics data comprise "shaft power to flow rate" and "pump head to flow rate" curves that are typically available from the manufacturer of the pump. For an example about these curves, see diagrams 320 and 330 in figure 3 and their description. Once the flow rate and pump head have been estimated, the efficiency of the pump may be calculated 208 and the method is thus complete 209. In a preferred embodiment, the method of figure 2 is repeated e.g. continuously over a period of time, e.g. hours, days or weeks to produce a volume of data that is sufficient e.g. for producing a report about the usage profile and efficiency of the pump. One such exemplary report is depicted in figure 4.

Figure 3 depicts an embodiment of the method of the invention with the help of exemplary measurement data and motor and pump characteristics curves. The measurement arrangement of an embodiment produces dynamic pressure measurement data of which a frequency spectrum 300 having a frequency 302 and amplitude component 301 is formed. The spectrum has a clearly identifiable peak 303 at frequency f, 304. This frequency indicates the pulsations caused by the impeller blades of the pump. The rotating frequency of the impeller may be calculated from the frequency f, 304. If the impeller has "n" blades, the rotating frequency of the impeller is f, / n and the rotating speed n, (rpm) is 60^* f , / n.

Now that the actual rotating speed n, is known, it can be applied into the torque curve 313 of the motor characteristics data of the pump. The torque data has a torque 312 and rotating speed 314 components. The torque of the motor is thus function of the rotating speed of the motor. The manufacturer of the motor provides "rated synchronous rotating speed" figure n_r which is the rotating speed of the motor when no load is applied on the shaft. The torque 316 of the shaft under current operating conditions can be obtained by placing the actual rotating speed n, 315 onto the torque curve 313. The shaft power may now be calculated using formula P_s = ω^* M.

Once the shaft power P_s has been calculated, flow rate Q 326 can be estimated using the "shaft power to flow rate" curve 324 (available e.g. from pump manufacturer) that is presented in P 322 and Q 321 coordinates. The estimated shaft power P, is placed 325 on the curve 324 to obtain the estimated flow rate Q, 326. Next, the pump head H₁ 336 can be obtained by placing 335 the Q₁ value onto the "pump head to flow rate" curve 334 that lies in coordinates comprising Flow rate Q 331 and Head H 332. Further, the inlet pressure of the pump may now be calculated using formula P₁=P₂-H where the P₂ is the measured outlet pressure.

The operating point 335 typically has a range of optimal values on the curve 334. If the measured operating point 335 is not within the optimal range, it may mean that e.g. unnecessary wear or even a failure of the pump is to be anticipated because of the non-optimal operating point.

Finally, the pump efficiency factor η may be calculated using formula η = P_H / P_s wherein P_H = delta p^* Q .

Figure 4 depicts exemplary reports that may be made available using the data created using the method and arrangement of an embodiment of the invention.

Chart 400 shows shaft power consumption divided into five percentage categories 401. Each category is represented by a bar 403a-e. For example, bar 403a shows how many hours 402 the pump has been operating at less than 20% power. The chart 410 shows in similar manner the actual flow rate of the pump divided into five percentage categories 411. For example, bar 413a shows how many hours 412 the pump has been operating producing less than 20% of maximum flow rate.

The chart 420 shows the actual efficiency of the pump divided into five percentage categories 421. For example, bar 423a shows how many hours 422 the pump has been operating with efficiency rate less than 20%.

As demonstrated by the embodiments described herein, the various embodiments of the invention provide some significant advantages over prior art. Most importantly, the invention provides a simple-to-install and simple-to-use arrangement for determining useful data, e.g. the energy efficiency about a centrifugal pump, and determining the operating point of the pump. In some embodiments, the inventive idea described herein may also be used for determining possible reason for the failure of a pump. The method and arrangement are capable of providing measurement and analysis data of sufficient quality even in the simplest embodiments which employ only one dynamic pressure sensor or an optical sensor.

In addition to centrifugal pumps handling liquids, the inventive idea of the present invention may also be applicable to other flow generating devices, e.g. fans and compressors, operated by an electric motor.

In some embodiments, the actual motor speed may be acquired using sensors other than a dynamic pressure sensor that measures the pressure pulsation. For example any of the following sensors may be used:

- a magnet arranged e.g. on the shaft of the motor, e.g., in the area of the coupling between the motor and the pump - a slip reel - a well-known means of determining slip of an asynchronous motor, - a vibration sensor that produces vibration data that correlates with the rotation speed of the pump, or

- an optical sensor that observes e.g. the rotating speed of the fan of the motor.

In one preferred embodiment, an acoustic sensor, e.g. the microphone of a cellular phone, that records the sound of the pump and/or motor to be observed, is used for measuring the actual motor speed. At least part of the software required for analyzing the measured signal may reside in the memory of the cellular phone and it may be executed by the processor of the cellular phone. Use of such commonplace consumer device contributes to the simplicity of observing the pump efficiency, the simplicity of the measurement process being one of the objects of the invention.

To a person skilled in the art, the foregoing exemplary embodiments illustrate the model presented in this application whereby it is possible to design different methods and arrangements, which in obvious ways to the expert, utilize the inventive idea presented in this application.

Claims

1. A measuring arrangement for a pump (102) comprising means for receiving measurement information comprising at least a frequency component from a sensor means (105, 1 12) into the memory of a computer device (100), characterized in that the arrangement comprises computing means for determining the motor (1 10) slip of the pump (102) from the measurement information and computing means for estimating torque of the motor by comparing the motor slip with motor characteristics data.

2. An arrangement according to claim 1 , characterized in that said measurement information comprises at least one of the following: pressure measurement data, pump vibration data or data from an optical sensor.

3. An arrangement according to claim 1 , characterized in that said sensor means comprise an acoustic sensor.

4. An arrangement according to claim 3, characterized in that said acoustic sensor is the microphone of a cellular phone and the computing means comprises the processor and/or memory of the cellular phone.

5. An arrangement according to claim 1 , characterized in that the collection frequency of said measurement information is at least 100 Hz.

6. An arrangement according to claim 1 , characterized in that said arrangement comprises computing means for estimating flow rate of said pump based on said estimated torque of said motor using pump characteristics data.

7. An arrangement according to claim 6, characterized in that said arrangement comprises computing means for estimating pump head based on said estimated flow rate of said pump using pump characteristics data.

8. An arrangement according to claim 7, characterized in that said arrangement comprises computing means for estimating the energy efficiency of the pump based on estimated shaft power and head power.

9. An arrangement according to any of claims 1-8, characterized in that said arrangement comprises computing means for exchanging information with a second computer 107, the information comprising at least one of the following: motor characteristics data, pump characteristics data, and medium characteristics data.

10. A method for calculating pump motor slip and for estimating torque, characterized in that the method comprises the step of receiving measurement information comprising at least a frequency component from a sensor to a computer device, the step of determining the motor slip of the pump from the measurement information and the step of estimating the torque of the motor by comparing the motor slip with motor characteristics data.

11. A computer readable medium comprising a computer program product for calculating pump motor slip and for estimating torque, characterized in that the program comprises computer executable instructions for receiving measurement information comprising at least a frequency components from a sensor to the computer, for determining the motor slip of the pump from the measurement information and for estimating torque of the motor by comparing the motor slip with motor characteristics data.