2012年10月26日星期五
Delano-Earlimart Irrigation District Variable Frequency Drive Study
TABLE OF CONTENTS
Page
LIST OF FIGURES ............................................................................................................ iii
LIST OF TABLES .............................................................................................................. iv
BACKGROUND ................................................................................................................ 1
Project Objectives .................................................................................................... 1
Variable Frequency Drive (VFD) Concept ............................................................... 2
Benefits of VFDs ..................................................................................................... 3
Pump Station D-12 Configuration ............................................................................ 4
Theoretical Energy Savings...................................................................................... 5
Background of VFDs and Payback .......................................................................... 8
Performing an Economic Analysis ................................................................ 8
Key Definitions ............................................................................................ 8
SITE INVESTIGATIONS .................................................................................................. 11
Data Evaluation Procedure ...................................................................................... 14
Highlights of the Monitoring .................................................................................... 15
DISCUSSION..................................................................................................................... 19
Actual Acre-Feet Pumped and Historical Water Deliveries ....................................... 19
Managing the VFD Operation .................................................................................. 19
DEVELOPMENT OF GENERALIZED RECOMMENDATIONS FOR VFD
INSTALLATIONS ........................................................................................................... 20
ENHANCEMENT OF THE PRESENT VFD OPERATION ............................................ 21
CONCLUSIONS .............................................................................................................. 22
REFERENCES ................................................................................................................. 23
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ATTACHMENTS: STATION D-12
Attachment A: DEID and SCE Data....................................................................... A-1
Attachment B: Actual Pump Operation - Data Logger (6/02/94-10/25/94) ............. B-1
Attachment C: Data Logger Summary (Hours, kWH, AF/day) ............................... C-1
Attachment D: Ideal Pump Sequencing to Meet CFS Demand (9/1/91-8/31/93) ..... D-1
Attachment E: Historical Pump Sequencing Based on Pumping Hours (9/1/91-
8/31/93).......................................................................................... E-1
Attachment F: Pump Selection Criteria .................................................................. F-1
Attachment G Estimating the Payback ................................................................... G-1
Attachment H: Requirements for AC VFD Installations .......................................... H-1
Attachment I: Site Photos ..................................................................................... I-1
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Delano-Earlimart Irrigation District
Variable Frequency Drive Study
LIST OF FIGURES
Page
Figure 1. Delano-Earlimart Irrigation District - CEC Project location map ................... 1
Figure 2. Diagram of VFD concept. ............................................................................. 3
Figure 3. Pumping station layout. ................................................................................. 5
Figure 4. Key measurement points at Station D-12 Pump #3. ....................................... 13
Figure 5. Discharge head and TDH versus GPM for D-12 Pump 3 (6/02/95-
10/26/94)...................................................................................................... 16
Figure 6. Input kW to motor versus GPM for D-12 Pump 3 (6/02/94-10/26/94). ......... 17
Figure 7. kW/AF versus GPM for D-12 Pump 3 (6/02/94-10/26/94). ........................... 17
Figure 8. Pumping plant efficiency versus flow rate for D-12 Pump 3 (6/02/94-
10/26/94)...................................................................................................... 18
Figure 9. Pumping plant efficiency versus RPM for D-12 Pump 3 (6/02/94-10/26/94). . 18
ATTACHMENTS
Figure D.1. Generation of D12 pump curve with existing pump.
Figure D.2. Generation of D12 pump curve with new pump.
Figure E.1. CFS pumped vs. cumulative days (9/91-8/92).
Figure E.2. CFS pumped vs. cumulative days (9/92-8/93).
Figure I.1. Station D12. Pumps for the detailed study.
Figure I.2. Control panel for VFD at Station D12.
Figure I.3. Datalogger provided by SCE for data acquisition at Station D12.
Figure I.4. Flow meter and pressure sensor (above and to the right of the flow meter) used
at Station D12 for data collection. The discharge pipe is for the VFD.
Figure I.5. Shaft RPM measurement device for the VFD pump at Station D12.
Figure I.6. Overflow stand at Station D12 to which the VFD was attached. The VFD
maintains a constant water level in the stand, below the overflow pipe seen on
the right hand side.
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Delano-Earlimart Irrigation District
Variable Frequency Drive Study
LIST OF TABLES
Page
Table 1. Comparison of payback analysis (based on 9/1/91-8/31/93 data)................. 6
Table 2. Table summary of kWH consumed based on ideal and historical
sequencing from 9/1/91 to 8/31/93. ............................................................ 7
Table 3. Sensor inventory used in data acquisition.................................................... 12
Table 4. Comparison of variable to constant speed drive pump at D-12 Pump #3. .... 15
ATTACHMENTS
Table A.1. Daily water deliveries from DEID.
Table A.2. Historical hours of operation recorded by DEID.
Table B.1. Selected instantaneous data from data logger (4 times per day) with total
dynamic head (TDH), water horsepower (WHp), and efficiencies.
Table C.1. Summary of data recorded by datalogger.
Table D.1. Determination of ideal input power with existing pump.
Table D.2. Ideal sequencing without VFD.
Table D.3. Ideal sequencing with VFD and existing pump.
Table D.4. Ideal input power with existing pump.
Table D.5. Determination of ideal input power with new pump.
Table D.6. Ideal sequencing with new pump and VFD.
Table D.7. Ideal input power with new pump.
Table E.1. Historical pumping hours for Station D-12 (9/1/91-8/31/93).
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BACKGROUND
This report was conducted to study the pump station operation at Delano-Earlimart Irrigation
District (DEID) after the installation of a variable frequency drive (VFD) control. The district is
currently involved with the California Energy Commission’s low-interest loan program for the
installation of VFD units on their pump stations near Delano, California.
Delano-Earlimart Irrigation District is a special water district organized under Division 11 of the
California Water Code and encompasses 56,500 acres in Southern Tulare County and Northern
Kern County. DEID has 18 individual pumping stations. DEID installed VFDs on key pumps at
three different plants (D-3, D-12, and D-14). See Figure 1 for a description of the project
location.
Highway 99
Earlimart
Road 192
Avenue 24
County Line Road
PS 3 PS 12 PS 14
Delano
North
Figure 1. Delano-Earlimart Irrigation District - CEC Project location map.
Project Objectives
In order to develop specific recommendations on the operation and use of the VFDs, a detailed
evaluation was performed on Pump Station 12. This project had the following specific objectives:
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• Estimate 1991-1993 energy savings and payback period for going to VFD based on
ideal pump sequencing and historical (actual) pump sequencing.
• Collect data regarding existing pump operation at Station D-12.
• Examine current VFD performance and compare it to single speed hydraulic tests
conducted by Southern California Edison.
• Develop guidelines for pump sequencing and choosing which pump to automate with
VFD.
Variable Frequency Drive (VFD) Concept
Variable frequency drives (VFDs) were incorporated into key pumps at pumping stations and
were intended to be capable of varying the flow of a pump. The objective is to minimize wasted
energy at the pumping station associated with pumping water to meet customer water demand.
The VFD system used at Station D-12 consists of four basic components:
• Pump and motor set
• Variable frequency drive
• Process controller
• Level sensor
Figure 2 shows how each of the components are connected and used. The desired set point is
established and is typically lower than the historical operation level for the TDH. The value is
lower because the water is not required to spill as was done historically.
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Process controller Level sensor provides
provides output signal signal proportional
based on relationship to water level
between target set point
and level signal Shielded cable
Process
Controller Desired
water level
Speed
signal
Water-cooled
enclosure
VFD STANDPIPE
Valve
(keep open)
Speed of pump directly
proportional to speed signal Pump
Figure 2. Diagram of VFD concept.
The VFD system automatically maintained a desired water level in the discharge standpipe. The
lower set point has the potential to lower the energy consumption of the pumping station slightly.
Maintenance of the set point was accomplished by mounting a water level sensor inside the
standpipe that works in conjunction with a process controller. The process controller generates a
signal that controls the output of the VFD on one of the pumps. Because the speed of the pump
can be varied, this VFD pump may also be referred to as an adjustable speed drive (ASD) pump.
This pump, used by itself or in conjunction with any other pump, provides full flow variability up
to the capacity of the plant. With this control, the objective of reducing wasted energy
consumption can be met.
Benefits of VFDs
Using the VFD has the following benefits:
• Conserves energy by reducing pump speed to produce lower flow.
• Eliminates the need for the flow control valve at the pump station; thus, generates
reductions in amount of energy used by the pump.
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• Provides cost-saving benefits, such as reduced electrical and mechanical maintenance.
• Improves reliability and pump-control strategies.
Pump Station D-12 Configuration
Pumping Station D-12 consists of two sets of pumps. One set of pumps supplies water to the
lateral pipeline system for the water users, and pumps conveying water to another reservoir. This
study is based on data at Station D-12 for which DEID retrofitted the panel for Pump 3 at Station
D- 12 for VFD control (see Fig. 3). The overall pumping plant efficiencies were provided by
Southern California Edison (SCE) from single speed hydraulic tests.
The station under evaluation consists of four pumps connected in parallel with a common output
manifold hooked to a standpipe, approximately 30 feet tall. This standpipe has an overflow pipe
which returns excess water to a common sump. By turning on a combination of pumps to fill this
standpipe to overflow level, a variable and uninterrupted flow of water to the pipeline system for
the customer is attained.
For example, water demand for a specific day might be 8.7 cubic feet per second (cfs):
This demand would be met by turning on the 6.1 cfs pump and the
2.9 cfs pump, thereby producing 9.0 cfs. The standpipe fills to
overflow height and the excess 0.3 cfs is returned to the sump.
Energy is wasted by pumping excess water to the overflow.
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(variable flow)
5.7 cfs 6.1 cfs 2.9 cfs 2.1 cfs
#4 25 Hp #3 25 Hp #2 15 Hp #1 15 Hp
VFD
Controller
Overall Pumping Plant Efficiency
(from SCE single-speed Pump #3
hydraulic tests):
25 Hp #4: 59.1%
25 Hp #3: 62.5%
15 Hp #2: 54.4%
15 Hp #1: 41.6%
Standpipe
VFD Controller Cabinet Temperature
Transformer Cabinet Temperature
Figure 3. Pumping station layout.
Theoretical Energy Savings
Estimates were made by ITRC for Stations D-3, D-12, and D-14 based on water demand and
pumping hours from 9/1/91 to 8/31/93. The following focuses only on the savings at Station D-
12. Table 1 illustrates two methods of payback analysis.
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Table 1. Comparison of payback analysis (based on 9/1/91-8/31/93 data).
IDEAL SEQUENCING HISTORICAL SEQUENCING
CFS Used CFS Demand CFS Demand
kW Consumed kW/pump based on an ideal kW/pump rating directly from
pump seq. to fulfill CFS SCE
Pumps 1-4 are sequenced so that
the CFS capacity per pump
(SCE) is then totaled to
meet CFS demand.
Overspill? some overspill unknown
Pumping Hours 24 hrs/day basis actual recorded pumping hrs
EXISTING NEW EXISTING NEW
PUMP PUMP PUMP PUMP
Annual kWH without VFD 128,802 128,802 115,415 115,415
Annual kWH with VFD 109,698 93,377 104,764 96,095
Annual kWH Savings 19,104 35,425 10,651 19,320
Annual Savings $ 2,177 $ 4,038 $ 1,214 $ 2,203
($.114/kWH)
VFD Cost + pump
(if applicable) $18,342 $ 23,342 $18,342 $ 23,342
Simple 8.4 5.9 15.1 10.6
Payback (years)
Table 1 indicates that the actual pumping hours (historical) were significantly less than the ideal
situation that should have occurred to achieve a predetermined flow rate. This was based on the
lower annual kWH without the VFD. This means that the CFS demand was not met, and the
customer received less water than the recorded CFS deliveries. Thus, Table 1 shows that savings
are highly sensitive to how the pumps are sequenced.
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Table 2. Table summary of kWH consumed based on ideal and historical sequencing from
9/1/91 to 8/31/93.
PUMPING STATION: D-12 (Pumps 1-4)
Monthly Average
kWH kWH/AF
Ideal Historical Ideal Historical
With Without Without With Without Without
VFD VFD VFD VFD VFD VFD
AF Existing New Existing New
Date Demand Pump Pump Pump Pump
Sep-91 267 9,758 7,227 12,931 11,782 27.1 27.1 48.5 44.2
Oct-91 287 10,540 7,724 13,927 13,362 26.9 26.9 48.5 46.5
Nov-91 355 12,871 8,920 16,277 14,214 25.1 25.1 45.9 40.0
Dec-91 0 0 0 0 0 0.0 0.0 0.0 0.0
Jan-92 0 0 0 0 0 0.0 0.0 0.0 0.0
Feb-92 20 1,146 1,181 1,181 1,033 58.7 58.7 58.7 51.3
Mar-92 7 498 590 590 517 80.7 80.7 80.7 70.6
Apr-92 448 16,061 14,034 18,494 16,625 31.3 31.3 41.3 37.1
May-92 525 17,641 15,924 19,790 16,451 30.3 30.3 37.7 31.3
Jun-92 597 21,708 18,917 23,916 17,798 31.7 31.7 40.1 29.8
Jul-92 365 13,381 10,948 15,643 14,697 30.0 30.0 42.9 40.3
Aug-92 188 7,734 6,606 9,586 8,331 35.2 35.2 51.1 44.4
Subtotals 3,059 111,338 92,072 132,336 114,810
Ave. 36.4 30.1 43.3 37.5
Sep-92 124 5,551 5,067 7,584 5,873 44.9 41.0 61.4 47.6
Oct-92 75 3,939 4,249 5,201 4,759 31.9 34.4 42.1 38.5
Nov-92 42 1,867 1,877 2,606 659 15.1 15.2 21.1 5.3
Dec-92 0 0 0 0 0 0.0 0.0 0.0 0.0
Jan-93 0 0 0 0 0 0.0 0.0 0.0 0.0
Feb-93 21 1,161 1,181 1,181 517 9.4 9.6 9.6 4.2
Mar-93 44 2,254 2,165 2,518 1,841 18.3 17.5 20.4 14.9
Apr-93 304 11,220 10,222 13,330 12,867 90.9 82.8 107.9 104.2
May-93 549 19,631 16,811 22,646 22,405 159.0 136.1 183.4 181.4
Jun-93 695 24,727 21,421 27,024 26,539 200.2 173.4 218.8 214.9
Jul-93 765 27,657 24,200 30,233 28,278 223.9 196.0 244.8 229.0
Aug-93 280 10,050 7,490 12,945 12,281 81.4 60.6 104.8 99.4
Subtotals 2900 108,057 94,681 125,268 116,020
Ave. 37.3 32.6 43.2 40.0
2 Yr Totals 5959 219,395 186,753 257,604 230,830
Yrly Ave 2980 109,698 93,377 128,802 115,415 36.8 31.3 43.2 38.7
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Background of VFDs and Payback
Perceived or actual improved energy efficiency is undoubtedly the greatest stimulus towards the
use of VFDs, but it is not the only one. It is the connection between energy efficiency and better
process control which often fuels the interest in VFDs (Process Engineering, 1994). The VFD
controller can be used to modify an existing, single speed motor operation, as at DEID.
Performing an Economic Analysis. Variable speed systems have the potential to save energy in
many installations. However, they do not necessarily save money. The total cost of equipment
and life cycle should always be analyzed for applications. The estimates of energy savings must
account for the hours of operation of various speeds, the pump TDH and flow rate at those
speeds, and the total pumping plant efficiency at those speeds. In general, the pump impeller and
motor efficiencies are considerable lower at low RPMs than at higher RPMs. This drop in
efficiency will reduce the payback efficiency.
As part of the work done at DEID for the CEC, the ITRC developed two sets of guidelines for
new installations. One is related to the selection of the proper pump to automate with a VFD; the
other guideline relates to the computation of annual savings in power. These are included in a
subsequent section of this report.
Key Definitions. The following are the key definitions for this report:
Affinity laws. These are the relationships between speed ratios, pressure ratios, and
horsepower ratios for centrifugal pump applications:
Q1 N1 H 1 N 1 2 hp1 N 1 3
; ;
Q2 N2 H2 N 2 hp2 N 2
(1)
Q flow (GPM) , N speed (RPM) ; H head (ft ) ; hp horsepower
** It should be noted that the affinity laws are only used to develop a new pump
curve for different RPMs. The actual HP used by the pump when changing RPMs
will depend on where the system curve intersects the pump curve. In determining
power savings, the system curve must be taken into account.
Pump curve. A graph showing the relationship between TDH (total dynamic head) and
flow rate at a single RPM. The efficiency of the impeller is also shown at key flow
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rates. In general, as the flow rate increases, the TDH delivered by the pump
decreases. The curve will be different at each RPM.
System curve. A graph showing the relationship between the TDH required by an
irrigation system and the flow rate through the system. As the flow rate through
the system increases, the TDH required increases. For most cases, the pump curve
will only intersect the system curve at one point (this assumes one RPM of the
pump).
Head. This refers to pressure given in units of feet of water column or pounds per square
inch (PSI).
Static head. The static head is the elevation change between the source water level and
the discharge point. The pump must deliver a TDH greater than the static head
before water will begin to flow.
Friction. The friction is the pressure loss due to the friction of the water moving against
the pipe and fittings.
Drawdown. The drop in the source water level once pumping starts.
Discharge pressure. The pressure (head) at the discharge point. For example, a sprinkler
may have a discharge pressure of 50-60 psi. An open pipe has a discharge
pressure of 0 psi.
Total Dynamic Head (TDH). The TDH is the pressure that the system will impose on the
pump at a particular flow rate. This is simply a sum of the static head, the friction,
drawdown, and the discharge pressure. On the type of pump stations analyzed at
DEID, the TDH remains relatively constant through the range of flow rates. This
is because the static head is the greatest component in the TDH. The piping
system is of a large diameter and short in length, so there is very little friction loss.
Also, there is no drawdown. In other words, the system curve is fairly flat
(horizontal).
Pumping plant efficiency. This is the efficiency of the complete pumping plant, including
the VFD panel, the motor, and the impeller/bowl assembly. It is computed as:
Water Horsepower
PPE = x 100
Input Horsepower
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where
GPM * TDH
Water Horsepower = 3960
with TDH measured in feet of pressure, and
Input Horsepower = measured at the meter
Maximum GPM. The maximum actual flow rate (gallons per minute) developed by the
pump. This was obtained from SCE (Southern California Edison) single speed
pump tests.
Operating scenario. This is the percent time at a certain flow rate.
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SITE INVESTIGATIONS
The examination of the DEID VFD applications concentrated around one site - D12. An initial
meeting was held with DEID personnel, employees from Turnipseed Electric of Delano (which
installed the equipment), and SCE energy specialists. At that time, several items of interest were
defined:
• Since the efficiency of the pump itself had not been considered, it was determined that
more information about the pump characteristics was needed.
• The actual payback of the unit was a primary concern of DEID.
• This project provided SCE with an opportunity to examine the details of operation of
a VFD for a whole irrigation season.
After that meeting, the pumps were evaluated for flow rate, TDH, and efficiency. SCE also
arranged for the installation of a complete data collection and remote monitoring system at plant
D12. SCE contracted with Severson Company, Inc. for the installation of equipment and
software. The ITRC specified what equipment was needed, and the required accuracy of that
equipment. The ITRC also participated in the installation of the equipment. SCE arranged for
the ITRC to obtain the data from Severson. Table 3 is a listing of the primary components of the
data collection system. Data was recorded in 15 minute intervals. Operations for 3 months
(6/2/94-10/26/94) were used in this study.
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Table 3. Sensor inventory used in data acquisition.
DATA COLLECTION UNITS EQUIPMENT/NOTES
Data logger Campbell Scientific Model 21 XL
with Modem and Cellular Phone Interface
Sample Rate: for this project, 1 per
second
Flow Pump 3 GPM Flow meter
(VFD) Model: LP-3 Serial: 934923
Size: 12"
Pulse: 10pps @ 3000 GPM
Pipe size calibration: 11.938"
Calibration ratio:
New pipe Area 144.1 in2
Ratio = =
Calibration Area 11.9 in2
= 1.287:1
Therefore:
Pulse 10 pps @ 3000 x 1.287 GPM
= 10 pps @ 3861 GPM
Motor Speed Pump 3 RPM Pulse
Power Pumps 1 - 4 kW Error in Pump 3 (VFD): 1.5%
(1.6 % Efficiency offset)
Pump Pressure Pump 3 ft Pressure Transducer Omega
Model: PX 615 Serial: 413292
Range: 30 psi Error: 1%
Current Loop Installation
Input: 10-30v Output: 4-20 Ma
Temperature Into Pump 3 oC Type "T" Thermocouple
Out of Pump 3
VFD
Transformer
Water Level Above ft Pressure Transducer IP-DC
Transducer Model: 5PSI6
Differential PTX 165-0857
Figure 4 shows the location of the data collection components used for this study. The critical
dimensions of the measurement points are also shown.
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11'- 2" Flow Meter
10'- 2" Pressure Transducer
D
E A
B
A
F
Standpipe
A
SECTION A-A C A Flow meter
Area
B Pump pressure transducer
144.1 sq. in.
C Water height transducer
D Motor air temperature out
E Motor air temperature in
F Motor RPM pick-up
Figure 4. Key measurement points at Station D-12 Pump #3.
The purpose of collecting data is to evaluate VFD pump operation and performance. VFD
performance and its comparison to values generated from SCE single speed pump tests are
represented in the form of graphs:
• Discharge head and Total Dynamic Head (TDH) vs. GPM.
• kW to motor vs. GPM.
• kWH/AF vs. GPM.
• VFD panel efficiency vs. kW to motor.
• Pumping Plant Efficiency (PPE) vs. GPM.
• Pumping Plant Efficiency (PPE) vs. RPM.
To compare the VFD pump operation and performance to that of the constant speed drive pumps,
values generated from SCE single-speed pump tests were designated as data points on the Pump
#3 curves.
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Data Evaluation Procedure
The following information regarding Station D-12 was gathered:
1. Water delivery records and hours of pump operation from DEID:
a. Historical (9/1/91-8/31/93)
b. With VFD (current)
2. Data from data logger:
a. Pumping hours and kilowatts (kW) consumed for each pump.
b. Pump #3 (VFD)
- Flow rate (GPM)
- Speed (RPM).
- Water pressure (ft).
- kW into VFD panel, kW into motor.
- Temperatures
3. Single speed pump hydraulic tests from Southern California Edison (SCE).
4. Estimated cost of VFD conversion from contractor.
Observations and Results were represented by:
1. Estimated 1991-1993 energy savings based on:
a. Ideal pump sequencing
b. Historical (recorded) pump sequencing
2. Actual operation of the chosen VFD Pump (#3) is represented by:
a. Graphs of GPM, RPM, and water pressure versus time. (6/2/94-10/2/94)
b. Average operating flow rate, pumping plant efficiency, and kWH/AF.
3. Comparison of VFD performance to that of SCE single speed pump tests:
a. Pumping Plant Efficiency (PPE) vs. GPM.
b. PPE vs. RPM.
c. VFD panel efficiency vs. kW to motor.
d. kW to motor vs. GPM.
e. Discharge head and TDH vs. GPM.
f. kWH/AF vs. GPM.
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Highlights of the Monitoring
Attachment B includes current operation of Station D-12 from 6/02/94 to 10/26/94 (see Table
B.1). Key factors to look at regarding the VFD pump (#3) were flow rate (GPM), speed (RPM),
and water pressure (P1) (see Figs. B.1-B.21).
DEID selected the proper pump for VFD conversion based upon the following summary:
Table 4. Comparison of variable to constant speed drive pump at D-12 Pump #3.
Constant Speed Drive Variable Frequency
Drive
SCE test existing operation
(8/10/93) (6/02/94-10/26/94)
Average Range
Discharge Head, ft 16.4 15.3 11.0 - 15.8
Total Dynamic Head, ft 20.5 21.8 18.8 - 34.2
% of Maximum GPM 100 72 25 - 100
Flow Rate, GPM 2735 1994 675 - 2725
Speed, RPM 1184 1046 780 - 1183
kW input to motor 16.9 11.2 6.6 - 16.2
kW input to VFD Panel -- 11.3 6.9 - 16.6
kW per Acre-Ft 34 34.9 30.1 - 57.9
VFD Panel Efficiency % -- 98 94 - 99
Overall Pumping Plant
Efficiency (PPE) % 62.5 62.0 35.0 - 71.0
One of the questions regarding a VFD operation related to what the average flow rate would be.
At D-12, the average operating flow rate was 72% of the maximum capacity.
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The following figures represent current VFD pump performance. SCE test values for Pump 1
through 4 are designated with an "X" and labeled as P-1, P-2, P-3, and P-4. The ITRC included
some additional factors in the computation of the VFD, such as column friction.
The discharge head of the VFD pump should remain fairly constant if the pump is operated
properly. In this piping system, there is very little difference in friction with flow rate changes,
since the pipes have a large diameter and are short in length. In Figure 5, the discharge head can
be seen to remain fairly constant, but suddenly drops off near 2,600 GPM. This occurs because
the pump is at 100% RPM, and the flow rate leaving the standpipe is greater than the pump
capacity -- the water level in the stand drops (i.e., the discharge pressure of the pump drops).
Another example of this is seen in Figure B.4 (Attachment B) where the pump was at maximum
flow rate while the pressure continued to drop.
26
24
TDH
22
P-2 P-4
P-3
P-1 X X X
20
X
18
Discharge Head P-4 P-3
P-2
P-1 X X
16
X
X
14
12
10
8
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
Flow Rate (GPM)
Note: X is SCE test data (8/10/93),
for Pumps 1-4 Fig
ure 5. Discharge head and TDH versus GPM for D-12 Pump 3 (6/02/94-10/26/94).
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18
P-4 P-3
17
X X
16
15
14
13
12
11
10
P-2
X
9
P-1
X
8
7
6
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
Flow Rate (GPM)
Note: X is SCE test data (8/10/93)
Figure 6. Input kW to motor versus GPM for D-12 Pump 3 (6/02/94-10/26/94).
60.00
56.00
52.00
P-1
48.00 X
44.00
P-2
40.00
X
P-4
36.00 X
P-3
X
32.00
28.00
24.00
20.00
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
Flow Rate (GPM)
Note: X is SCE test data (8/10/93) Fig
ure 7. kW/AF versus GPM for D-12 Pump 3 (6/02/94-10/26/94).
CEC - DEID VFD Report 17 Irrigation Training and Research Center
----------------------- Page 24-----------------------
80
70
60
50
40
30
20
10
0
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
Flow Rate (GPM)
Note: X is SCE test data (8/10/93)
Figure 8. Pumping plant efficiency versus flow rate for D-12 Pump 3 (6/02/94-10/26/94).
80
70
P-3 X
60
50
40
30
20
10
0
600 700 800 900 1000 1100 1200
Speed (RPM)
Note: X is SCE test data (8/10/93)
Figure 9. Pumping plant efficiency versus RPM for D-12 Pump 3 (6/02/94-10/26/94).
CEC - DEID VFD Report 18 Irrigation Training and Research Center
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DISCUSSION
The following observations were made.
Actual Acre-Ft Pumped and Historical Water Deliveries
The acre-ft pumped and recorded by the data logger (Tables C.1.1-C.2.2) closely matched DEID
historical daily water deliveries (Tables A.1.1-A.1.2) for the months of June and July 1994.. This
supports the reliability of using the collected data values for determining current pump
performance and estimating energy savings.
Managing the VFD Operation
In several cases the data shows that the VFD pump reached its maximum capacity at 1,184 rpm,
and the water level in the stand continued to drop significantly. For example, in Fig. B.4
(Attachment B), Pump #3 is operated at the maximum RPM of 1,183 RPM from 6/29/94 to
7/2/94. That problem can be solved if another pump is turned on to supplement the VFD flow
rate. Remote monitoring and/or automation of all of the pumps at the station provide a simple
remedy.
From 8/22/94 - 10/26/94 (Figs. B.12 - B.21), there were no significant fluctuations in water
pressure. The VFD pump covered a wide range of operating flow rates from 700 GPM to 2725
GPM.
The pump chosen for VFD was the proper pump to automate. It was the correct size (see
Guideline #1 in the next section), and it had a reasonably good efficiency (62%).
CEC - DEID VFD Report 19 Irrigation Training and Research Center
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DEVELOPMENT OF GENERALIZED
RECOMMENDATIONS FOR VFD INSTALLATIONS
As a result of the work at DEID, three sets of guidelines were developed for the CEC so that it
can assist others with the proper selection of VFD pumps.
Guideline #1 - An explanation of which pump should be controlled by a VFD if more than
1 pump exists at a site, and what characteristics that pump should have (see
Attachment F)
Guideline #2 - The recommended procedure for estimating the annual cost (payback)
which will occur if a VFD is to be installed (see Attachment G).
Guideline #3 - The proper hardware that should be used in a new installation (see
Attachment H).
CEC - DEID VFD Report 20 Irrigation Training and Research Center
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ENHANCEMENT OF THE PRESENT VFD OPERATION
The following recommendations have been given to DEID regarding the VFD installation at D-
12:
1. Renovate the existing VFD pump with a new impeller/bowl assembly. The ITRC has worked
with DEID and various pump manufacturers to locate a suitable pump. This included the
development of written pump specifications by the ITRC. DEID is presently in the process of
locating a suitable pump. DEID has found that care must be taken with some pump company
employees - in spite of written specifications, they may recommend the incorrect pump for an
installation, and may be unfamiliar with their own products and how they can be applied in
VFD installations.
2. Install remote monitoring of the location. This will enable district staff to know the status of
water deliveries and pump operation without having to physically visit the site. It will enhance
the district's ability to provide more flexible deliveries (see next item).
3. Allow farmers to personally operate their turnouts. They should be required to request water
deliveries in advance, so that the district can determine if there will be sufficient capacity.
However, an automated and remotely monitored installation will allow them to shut off
without giving advance notice. This concept was explained by the ITRC and the DEID
manager to the board members at an informal meeting.
4. Automate the three other pumps at the D-12 overflow stand. They would be constant speed,
but a Programmable Logic Controller, PLC (the same one as is presently used to control the
VFD), can be used to automatically turn the pumps on and off as the flow rate demand from
the VFD approaches the maximum or minimum limits. This is a standard type of operation for
most municipal systems.
CEC - DEID VFD Report 21 Irrigation Training and Research Center
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CONCLUSIONS
The following are the main conclusions or results from this project:
1. The payback period is longer than was anticipated in the loan application. The computations
on the original loan application did not account for the irrigation system curve. VFD
controller specialists may not be familiar with pump and irrigation system characteristics,
which are key items in estimating payback periods.
2. In order for a VFD installation to minimize the payback period, it is important to consider the
pump and motor efficiencies. In the D-12 case, a different pump will reduce energy
consumption and also improve the payback period. Care must be taken when working with
pump suppliers, as many are unfamiliar with VFD requirements.
3. As a result of experiences on this projects, specifications were developed for the proper initial
estimate of payback periods, and for required VFD equipment.
4. The VFD application is capable of providing the district with significant secondary energy
savings (not quantified in this report) related to less travel by operations staff and improved
on-farm irrigation efficiency through better flexibility in turning water on and off at the farm
level.
5. Having a VFD control can guarantee a stable water level at the discharge as long as (i) the
controller has the correct logic, (ii) the pump curve is not intersected by the system curve in
more than one point, and (iii) the flow rate being withdrawn from the stand does not exceed
the flow rate capacity of the pumps which are activated. Regarding the last point, it is
apparent that it is very valuable to automate all of the pumps at a station, and to have remote
monitoring.
CEC - DEID VFD Report 22 Irrigation Training and Research Center
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REFERENCES
1. Albern, William F. 1986. Variable flow pumping. ASHRAE Journal 28: 34-6.
2. Gibson, Ian H. 1994. Variable-speed drives as flow control elements. ISA Transactions 33:
165-169.
3. Floway Pumps. Turbine Data Handbook. 1992.
4. Lambeth, Jeff and Jerry Houston. 1991. Adjustable Frequency Drives Save Energy. Water
Environment and Technology 3: 42-6.
5. Process Engineering. 1994. Variable driving conditions. Vol. 74: 18-22.
6. Stefanides, E. J., ed. 1991. New pumps get power stingy. Design News 47: 86-8.
7. Vaillencourt, R.R. 1994. Simple solutions to VSD measures. Energy Engineering.
Vol. 91(1): 45-59.
CEC - DEID VFD Report 23 Irrigation Training and Research Center
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Attachment A
----------------------- Page 31-----------------------
DEID and SCE Data
----------------------- Page 32-----------------------
Attachment B
Actual Pump Operation, TDH Calculation
----------------------- Page 33-----------------------
Attachment C
Data Logger Summary (Hrs, kWH, AF/day)
----------------------- Page 34-----------------------
Attachment D
----------------------- Page 35-----------------------
Ideal Pump Sequencing
----------------------- Page 36-----------------------
Attachment E
Historical Pump Sequencing, Savings Calculation
----------------------- Page 37-----------------------
----------------------- Page 38-----------------------
Attachment F
Pump Selection Criteria
----------------------- Page 39-----------------------
----------------------- Page 40-----------------------
Attachment G
Estimating the Payback
----------------------- Page 41-----------------------
----------------------- Page 42-----------------------
Attachment H
Requirements of VFD Installations
----------------------- Page 43-----------------------
----------------------- Page 44-----------------------
Attachment I
Site Photos
----------------------- Page 45-----------------------
Figure I.1. Station D12. Pumps for the detailed study.
Figure I.2. Control panel for VFD at Station D12.
----------------------- Page 46-----------------------
Figure I.3. Datalogger provided by SCE for data acquisition at Station D12.
----------------------- Page 47-----------------------
Figure I.4. Flow meter and pressure sensor (above and to the right of the flow meter) used at
Station D12 for data collection. The discharge pipe is for the VFD.
Figure I.5. Shaft RPM measurement device for the VFD pump at Station D12.
----------------------- Page 48-----------------------
Figure I.6. Overflow stand at Station D12 to which the VFD was attached. The VFD
maintains a constant water level in the stand, below the overflow pipe seen on the
right hand side.
----------------------- Page 49-----------------------
Attachment F
Pump Selection Criteria
1. The pump to automate with a VFD (in a location with multiple pumps supplying the same
pipeline) is the smallest which will meet both of the following criteria:
a. (Flow Rate of the VFD pump
+ Sum of the flow rates of all the smaller pumps)
must be greater than or equal to
(The flow rate of the next bigger pump)
i.e., (QVFD + [sum of all Qsmaller pumps])>= QNext bigger pump
b. No larger pump flow can exceed the combined flow of all pumps which are smaller
than it (including the VFD at full speed).
2. There is generally little or no energy savings associated with converting to VFD control
for more than one pump at an installation.
----------------------- Page 50-----------------------
Attachment G
Estimating the Payback
for an
Electrical VFD (Variable Frequency Drive) Application
in a Pumping Plant Which Presently Spills Excess Pumpage
1. Estimating the maximum potential savings.
An estimate of savings requires an estimate of the historical amounts of spilled water. If,
for example, the spilled water is 5% of the total pumped water, then the maximum KW-Hr
savings can be:
Max. KW-Hr savings = .05 x Annual KW-Hr
If pumping amounts vary significantly from year to year, an average of three years of data
should be used.
The savings may be somewhat less than this (if the VFD operation puts the pump into a
less efficient operating range) or somewhat more than this (if the new controlled water
level is lower than the previous spill level). An examination of pump efficiencies may
show the greatest savings possible can be obtained by simply improving the efficiencies of
existing pumps.
a. The following information is necessary in most cases:
- Monthly power bills or pump test data providing KW-Hr per Acre-Foot (AF)
pumped for each pump
- Monthly hours of operation per pump
- Monthly water deliveries (as opposed to pumped amounts)
- Pump test data, providing Acre-Feet (AF) pumped per hour of operation for each
pump
----------------------- Page 51-----------------------
b. Compute AF pumped per month for each pump
AF
AF = hour x Hours of operation
c. From district delivery records, determine the total AF delivered to users (plus seepage
and conveyance losses) supplied by the pumping station, by month
d. Sum the monthly totals
e. For each water year, find the % spilled
AF Pumped - AF Delivered
% Spilled = x 100
AF Pumped
f. Compute the total KW-Hr savings possible
% Spilled
Annual KW-Hr savings possible = 100 x (Ann. KW-Hr consumed)
2. Estimating KW-Hr which would have been consumed if one of the pumps had been
converted to VFD.
This second step should serve as a check on the first step, in which the "possible" savings
were computed. By doing this computation, the effect of the overall pump efficiency of
the selected VFD-controlled pump is accounted for.
Again, use historical data to make these "what-if" computations.
a. Estimate the AF which will be pumped by the VFD unit
(Hours) x GPM
AF =
5428
where
Hours = The total hours per year that water is delivered from the pump
station (the VFD will operate continuously)
GPM = 67% of the maximum GPM of the pump with the VFD controller
(the actual percentage can be determined with a detailed analysis, but it
is probably not warranted. The 67% provides a weighted average for a
----------------------- Page 52-----------------------
typical condition, accounting for the KW-Hr consumed at various flow
rates)
b. Estimate the annual KW-Hrs which would be used by the VFD
GPM x TDH x 0.0188 x Hours
Kw-HrsVFD =
Efficiency/100
where
TDH = The total dynamic head of the pump, in feet.
Efficiency = The total efficiency of the pump (generally in the range of 40 -
70), which depends upon:
Panel Efficiency (Panel) -about 97
Motor Efficiency (Motor) - depends upon motor size and model;
typically somewhere between 85 - 93
Impeller Efficiency (Impeller) - the efficiency of the impeller and
bowls. The Impeller Efficiency to use will occur at a flow rate
of about 67% of the maximum flow rate
Losses (Losses) - a measure of the losses which occur due to
bearings; typically about 98 on a short lift.
Panel x Motor x Impeller x Losses
Efficiency = 106
c. Estimate the annual KW-Hrs used by the other pumps at the station.
1. Estimate the AF delivered by the other pumps
AFother = (Total AF delivered to users plus conv. losses) - AFVFD
2. Compute the average pump efficiency (Effother) for the other (non-VFD) pumps.
The information from individual pumps will come from a pump test. Ideally, the
average efficiency should be determined by taking a weighted average after
considering the KW and the Hours of each pump, as anticipated after the VFD is
installed. In practice, a simple average may be sufficient because the pumps with
----------------------- Page 53-----------------------
the lowest KW will be cycled on and off more often than the larger pumps, so
they will have more hours of operation than the larger KW pumps.
3. Make the final KW-Hr computation for the other pumps
TDH x 102 x AFother
KW-Hrother = Effother
d. Find the total annual KW-Hrs to be used by all pumps
Total KW-Hr = KW-Hrother + Kw-HrsVFD
e. Compute the total KW-Hr savings possible
Annual KW-Hr savings possible = (KW-Hr actually consumed - Total KW-Hr)
----------------------- Page 54-----------------------
Attachment H
Requirements for AC VFD (Variable Frequency Drive) Installations
Nov. 1994
Farm Energy Assistance Program
California Energy Commission
The installer shall supply the VFD controller, and also be responsible for the turn-key installation
and all other electronics related to the sensor, motor, and controls.
NEMA Standards Publication No. ICS 7 shall be adhered to. All electrical codes must be met or
exceeded.
The features listed below are required for the CEC loan program because their absence in VFD
installations has contributed to problems or failures. They are complimentary to many standard
protective features; they shall not replace more stringent or protective features which are required
by various codes, standards, and specifications.
Features required for the VFD panel
• Space heater for winter to prevent condensation
• Weatherproof and dust/insect-proof enclosure
• Fluorescent light (external mounting)
• Water cooling heat exchanger for the panel, with a water filter having automatic flushing
----------------------- Page 55-----------------------
• GFI receptacle (external mounting)
• Speed potentiometer and starter for manual control
• Remote Terminal Unit (RTU) containing a PID process controller, with communication port
for either radio or phone. Radio or phone must be specified.
• Message Display of Operational Parameters and System Faults.
• HOA switch(es).
• Shading of the panel from direct sunlight.
Automation
• The RTU must automate both the VFD and the other pumps which operate in parallel
with the VFD.
Conditioning of incoming power.
• A self-contained control power transformer must be supplied to feed the GFI, controls, and
light. The RTU must have an isolated, conditioned power supply and battery backup.
• Harmonic filters must be provided for each leg of incoming power of the VFD.
• If the VFD is to be installed on an ungrounded Delta system, then a 3 phase, Delta to WYE
isolation transformer, electrostatically shielded, should be installed before the VFD with the
WYE grounded with an individual grounding rod.
• The contractor shall specify in the bid (1) the maximum overvoltage and undervoltage prior to
trip, (2) maximum overcurrent capacity prior to trip, and (3) maximum transient protection.
Lightning Protection
Recommendations of the NEMA Standard No. ICS7 shall be followed.
----------------------- Page 56-----------------------
Voltage and Current Distortion back to the line.
The performance specified in IEEE 519 shall be met or exceeded. The contractor must specify
the degree of harmonic control provided, after consultation with the local electrical utility.
Performance must be verified after installation by an independent instrumentation contractor or
the local utility. Such performance verification must be arranged by the contractor.
Sensors
The water level sensor shall be calibrated to within 0.2' of the water level in a stand, and shall
have an accuracy better than plus or minus 0.1 feet.
Control
Water levels must be controlled within plus or minus 0.5 feet of the target depth.
Other
Radio frequency interference filters shall be provided.
Warranty
The installation shall have a two year warranty on all parts and labor, beginning on the date of
satisfactory operation.
----------------------- Page 57-----------------------
Attachment I
Site Photos
----------------------- Page 58-----------------------
Figure I.1. Station D12. Pumps for the detailed study.
Figure I.2. Control panel for VFD at Station D12.
----------------------- Page 59-----------------------
Figure I.3. Datalogger provided by SCE for data acquisition at Station D12.
Figure I.4. Flow meter and pressure sensor (above and to the right of the flow meter) used at
Station D12 for data collection. The discharge pipe is for the VFD.
----------------------- Page 60-----------------------
Figure I.5. Shaft RPM measurement device for the VFD pump at Station D12.
Figure I.6. Overflow stand at Station d12 to which the VFD was attached. The VFD
maintains a constant water level in the stand, below the overflow pipe seen on the
right hand side.
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