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Design & Engineering Services Milking Pulsation Stop Control - Energy Savings Assessment ET 07.07 Final Report Prepared by: Design & Engineering Services Customer Service Business Unit Southern California Edison Company June 26, 2009

Milking Pulsation Stop Control - Energy Savings Assessment...Milking Pulsation Stop Control - Energy Savings Assessment ET 07.07 Southern California Edison Page 1 Design & Engineering

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Page 1: Milking Pulsation Stop Control - Energy Savings Assessment...Milking Pulsation Stop Control - Energy Savings Assessment ET 07.07 Southern California Edison Page 1 Design & Engineering

Design & Engineering Services

Milking Pulsation Stop Control - Energy Savings Assessment ET 07.07 Final Report

Prepared by:

Design & Engineering Services Customer Service Business Unit Southern California Edison Company June 26, 2009

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Southern California Edison Design & Energy Services June 26, 2009June 26, 2009

Acknowledgements

Southern California Edison’s Design & Engineering Services (D&ES) group is responsible for this project. It was developed as part of Southern California Edison’s Emerging Technology program under internal project number ET 07.07. D&ES project manager Paul M. Williams, P.E. conducted this technology evaluation with overall guidance and management from Henry Lau, Ph.D., P.E. For more information on this project, contact [email protected].

SCE contracted with EnSave, Inc. and specific acknowledgement extended to Ed Sengle at EnSave, Inc. for conducting this project and to Ravi Parikh for assisting in the project implementation.

Special thanks to Rob Leal and Aaron Martinez of Performance Dairy Service in Tulare, CA, Ed Martin of Martine’s Dairy Service in Fresno, CA, and Stan Brown of BECO Dairy Automation, Inc. in Hanford, CA for their help in providing technical information and locating test sites.

Disclaimer

This report was prepared by Southern California Edison (SCE) and funded by California utility customers under the auspices of the California Public Utilities Commission. Reproduction or distribution of the whole or any part of the contents of this document without the express written permission of SCE is prohibited. This work was performed with reasonable care and in accordance with professional standards. However, neither SCE nor any entity performing the work pursuant to SCE’s authority make any warranty or representation, expressed or implied, with regard to this report, the merchantability or fitness for a particular purpose of the results of the work, or any analyses, or conclusions contained in this report. The results reflected in the work are generally representative of operating conditions; however, the results in any other situation may vary depending upon particular operating conditions.

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ABBREVIATIONS AND ACRONYMS “Hg Inches of Mercury

ASABE American Society of Agricultural and Biological Engineers

ASAE American Society of Agricultural Engineers (new name is ASABE)

BHP Brake Horsepower

CFM Cubic Feet per Minute

CSV Comma Separated Value (a computer file format)

CT Current Transformer

EHP Electric Horsepower

ET Emerging Technology

FT3 Cubic Foot

HP Horsepower

ID Inside Diameter

kW Kilowatt

kWh Kilowatt-Hour

MDL MicroDataLogger®

Min Minute

MU Milking Unit

PG&E Pacific Gas and Electric Company

PSC Pulsation Stop Control

SCE Southern California Edison Company

VFD Variable Frequency Drive

VSD Variable Speed Drive

W Watt

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FIGURES Figure 1. Milking Unit or Milking Assembly (Source: BECO Dairy

Automation) ...............................................................3 Figure 2. Pulsator Liner Cycle (Left – Liner Closed, Right – Liner

Open)........................................................................4 Figure 3. MicroDataLogger Portable Data Acquisition Unit .............10 Figure 4. AC Watthour Transducers (WattNode™) .......................11 Figure 5 MDL Pulse Input Adapter for Pulse Measurements ..........11 Figure 6 Dent Data Logging.....................................................12 Figure 7. Typical Data logger Traces for Vacuum Pump and

Pulsator Power Supply (Dairy Farm 1) showing transition from continuous pulsation to Interrupted pulsation..................................................................17

Figure 8 Dairy Farm 1 Power Trace...........................................28 Figure 9 Dairy Farm 2 Power Trace...........................................29 Figure 10 Dairy Farm 3 Power Trace..........................................30 Figure 11 Dairy Farm 4 Power Trace..........................................31 Figure 12 Dairy Farm 5 Power Trace..........................................32 Figure 13 Dairy Farm 6 Power Trace..........................................33

TABLES Table 1. Dairy Farm Information..............................................15 Table 2. Milk Parlor & Vacuum System Information.....................16 Table 3. Vacuum Pump Power Reduction due to Airflow

Reduction from PSC Use.............................................18 Table 4. Pulsator Power Supply Power Reduction from PSC Use....18 Table 5. Combined Power Reduction from PSC Use.....................18 Table 6. Vacuum Pump Motor Loading (PSC is Turned Off) ..........20 Table 7. Energy Savings from Vacuum Airflow Reduction due to

PSC.........................................................................20 Table 8. Energy Savings from Pulsation Power Supply due to

PSC.........................................................................21 Table 9. Combined Energy Savings due to PSC ..........................21 Table 10. Vacuum Pump Power Reduction from VFD Use...............39

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EQUATIONS Equation 1. Recommended Milk Vacuum Pump Capacity ...................5 Equation 2 Annual Energy Savings...............................................23 Equation 3 Demand Reduction ....................................................23

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CONTENTS EXECUTIVE SUMMARY _______________________________________________ 1

INTRODUCTION ____________________________________________________ 3 Project Goals and Objectives....................................................3 General Dairy Farm Milking Information ....................................3 Vacuum System.....................................................................4 Pulsation Stop Control Information ...........................................5 Dairy Farm Market Information ................................................6

Incremental Measure Unit Cost............................................6 Energy Savings Predictions ......................................................7

Effective Useful Life ...........................................................8

TECHNICAL APPROACH _____________________________________________ 9 Methodology..........................................................................9

Selection of Dairy Farm Sites ..............................................9 Inspection of dairy farm sites and milking system

equipment...................................................................9 Selecting data logger system equipment.............................10 Installing the Data Logger System .....................................12 Testing data logger system installation...............................12 Pulsation Stop Controls Testing Plan ..................................13 Data Logger Collected Values............................................13 Reviewing field data ........................................................14

RESULTS ________________________________________________________ 15 Data Analysis ......................................................................16 Discussion...........................................................................19

Comparison of Predicted versus Test Data Results................19 Test Dairy Farms Demand Reduction..................................19 Test Dairy Farms Energy Savings ......................................20 Vacuum Pump Without PSC Results Compared with Another

Study .......................................................................22

CONCLUSION____________________________________________________ 23 Suggested Calculation Methods for Utilities Considering

Adding PSC as an Energy Efficiency Measure ..................23 Suggestions for Electric Utility Future Studies......................24

REFERENCES _____________________________________________________ 26

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APPENDICES _____________________________________________________ 27

APPENDIX A – DAIRY FARM SUMMARY SHEETS ___________________________ 27 Dairy Farm 1 – 50 Stall Carousel .......................................28 Dairy Farm 2 – Double 23 Herringbone...............................29 Dairy Farm 3 – Double 35 Parallel......................................30 Dairy Farm 4 – Double 32 Herringbone...............................31 Dairy Farm 5 – 80 Stall Carousel .......................................32 Dairy Farm 6 – Double 6 Herringbone ................................33

APPENDIX B – “BACK-OF-ENVELOPE” ESTIMATE OF VACUUM PUMP ENERGY SAVINGS ____________________________________________ 34

APPENDIX C – HISTORICAL MILKING VACUUM SYSTEMS ENERGY EFFICIENCY IMPROVEMENTS FROM 1995 TO 1997 ________________________ 36

APPENDIX D – ENERGY SAVINGS WITH AND WITHOUT VSD __________________ 39

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EXECUTIVE SUMMARY The objective of this project is to measure the amount of electrical energy and demand savings potential from the vacuum pump motor and pulsation system power supply when using the Pulsation Stop Control (PSC) device in the dairy farm industry. The study was initiated to potentially incentivize the PSC device within the dairy farm equipment. Six dairy farms in Southern California were selected for the study.

Pulsators provide the physical massaging action necessary when milking cows. PSC is the feature that automatically shuts off these pulsators on individual milking units during the time that they are not attached to the cow. In recent years, PSC has become available as part of either an automatic detacher system or a pulsation monitoring system. The feature can also be implemented as a standalone retrofit to existing automatic detacher systems. This project was selected in order to understand if the energy savings associated with PSC are consistent and substantial enough to offer rebates in the future.

One farm was selected and monitored to verify the methodology and establish an initial energy savings estimate. After monitoring the first dairy farm, five additional farms were selected and monitored across a range of sizes and farm/parlor configurations. All farms selected had pulsation monitoring systems, which allowed the PSC feature to be easily enabled or disabled with a simple software setting. This minimized required technician time and lowered potential for disrupting milking operations.

Power was measured from the vacuum pump motor and pulsator power supply using a measured time between 1 - 5 minutes, depending on the how long the loggers were scheduled to run and how much available memory the loggers had. The default configuration on all farms was with the PSC feature enabled. Data was collected for a minimum of one week with the PSC feature enabled and one week with the feature disabled. (Actual durations varied depending on when a technician could be scheduled to make the switch between the two modes.) Average power (kW) data was summarized for each milking period, with wash-up times removed (pulsators are typically always on and vacuum pumps run at full speed during wash-up). Energy (kWh) data was calculated by multiplying average power (kW) by the overall average milking times.

The results showed energy savings in line with predicted values. All six farms showed consistent pulsator power supply power savings, averaging 48.5%, or 9.3 W/milking unit. Four of the six farms showed consistent vacuum pump motor power savings, averaging 19.4% or 17.4 W/milking unit. The other two farms showed much smaller vacuum pump motor power savings which made their data become suspect. Further review of their data revealed that their lack of energy savings were, likely, related to having vacuum pump sizing and vacuum pressure control hardware issues. With appropriate modifications, it is believed that these two farms can achieve savings in line with the other four farms. Overall annual energy (kWh) savings per milking unit was 143 kWh for all six farms and the savings increased to 177 kWh for the four farms without the suspected smaller savings farms. No other studies are known to have measured energy savings associated with PSC in the past, so there is no meaningful basis for comparison of our results.

As other energy savings measures associated with milk harvesting approach market saturation, PSC offers a new measure that is not yet in widespread use. While payback on automatic detacher systems or pulsation monitoring systems are quite long if based on energy savings alone, there are numerous other benefits associated with these measures that make them cost effective. These can include labor savings, improved cow health, enhanced equipment life, and improved parlor efficiency.

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One recommendation is to define detailed specifications for the PSC measure. These specifications would ensure that any inhibitors to achieving the expected energy savings, such as those identified as suspect reasons that caused the smaller energy savings on the two farms in this report, would be addressed prior to issuing the rebate. These recommendations could also include a detailed review of the offerings of manufacturers not included in the original study.

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INTRODUCTION PROJECT GOALS AND OBJECTIVES The goal of this project is to quantify the amount of electrical energy saved and demand reduced by using pulsation stop control, which stops pulsation unit operation after the milking unit is detached from the cow during the milking process at a dairy farm milking barn. This energy efficiency assessment information may be used to help develop incentives paid by electric utilities to dairy farm customers to offset part of the cost of purchasing pulsation stop control equipment.

GENERAL DAIRY FARM MILKING INFORMATION On modern dairy farms, milking is performed by a milking unit or milking assembly (see Figure 1) that consists of a milking claw, four rubber liners, and metal shells or housings surrounding each liner. The claw is a collection point for the milk and is connected to a milk tube through which vacuum is applied to the claw and milk flows down to the collection header. The liner is the part that is attached to each teat and extracts the milk from the cow.

FIGURE 1. MILKING UNIT OR MILKING ASSEMBLY (SOURCE: BECO DAIRY AUTOMATION)

Milk cannot simply be sucked from the cow by applying vacuum to the liner/claw assembly. Instead, a massaging action is required, where the teat is periodically exposed to vacuum and then allowed to rest. This is where the shell comes in; it is connected to a different vacuum line. The essential massaging action is accomplished by periodically applying the vacuum, and then atmospheric pressure to the shell space between the shell and liner. When the vacuum is applied to the shell space, the liner relaxes from the teat (vacuum pressure now being the same on both

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sides of the liner), the vacuum from the claw is exposed to the teat, and milk flows. When the shell is vented (atmospheric pressure is applied), the liner collapses, the teat is no longer under vacuum and it is allowed to rest in preparation for the next massaging cycle, thus milking pulsation.

The device that controls the vacuum to the shells is called a pulsator. Typically, this is a three-port electric solenoid valve, connected to a vacuum source, atmospheric air, and tubes going to the milking unit. The solenoid receives its signal from a controller that sets the amount of time the shell space is exposed to the vacuum and the amount of time it is vented, see Figure 2. These times can be set to optimize milking performance.

FIGURE 2. PULSATOR LINER CYCLE (LEFT – LINER CLOSED, RIGHT – LINER OPEN)

Each milking unit is actually connected to three vacuum hoses: one connecting the claw to the milk line which carries away the milk, and two connecting pulsators to shells/liners (one to two of four shells and one to the other two shells). The reason there are two sets of shells is because the front two teats are connected to one pulsator and the back two teats are connected to another. The pulsation action is synchronized so that when the front teats are being milked the back ones are resting and visa versa.

VACUUM SYSTEM A milking barn will typically have one vacuum system with one to two vacuum pumps. If two pumps are installed, often one is used during milking and the other used as a backup and may be used during washup. Alternatively, the pumps may be sequenced, where every few days the milking operation is switched from one pump to the other. The vacuum system provides vacuum to both the milk hoses and the pulsator hoses. The air flow through the milk hoses is fairly constant during milking, as there is typically a small vent in each claw that allows a small amount of airflow to enter, promoting good milk flow to the milk line. When the milking unit is not connected to the cow, the liners’ connection hoses drape down the sides of the claw and are pinched off, reducing the amount of airflow entering the liners’ open ends and passing through the claw and going into the vacuum system. However, as the liners are attached or detached from the cow, there is a momentary surge of air into the vacuum system. Similarly, if a liner is poorly attached or if the cow kicks off the milking unit, there can also be a large inflow of air.

This fluctuation in airflow causes a corresponding fluctuation in vacuum pressure on all other milking units connected to the system, unless a pressure control system is installed. Steady vacuum pressure is critical to safe, efficient milking: too high a

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vacuum can injure the teat and/or the udder, and too low a pressure can allow backflow of milk into the teat causing mastitis (inflammation of the teat or udder). Typical milking pressure is 13.5 “Hg of vacuum with pressure fluctuations limited to no more than ±0.6 “Hg.

In the past, this pressure fluctuation problem was addressed by using a fixed speed vacuum pump sized large enough to handle the maximum airflow rate case, along with a vacuum pressure valve with a pressure sensor/controller. The valve was installed near the milk receiver tank. During times of low airflow demand by the milking system, the sensor would detect the vacuum pressure becoming too strong and would open the valve and allow a large amount of makeup air to enter the system, maintaining the vacuum pressure at the desired levels. When the milking system had high airflow demand, the sensor would sense vacuum pressure becoming too weak and would throttle back the valve, allowing less makeup air into the system, thus keeping vacuum pressure steady.

This control system was effective, but was very energy intensive, because the vacuum pump was always operating at maximum airflow and speed even though the milking system only required that airflow for a very small percentage of the milking time.

Modern milking vacuum systems are sized according to a specification of the American Society of Agricultural and Biological Engineers (ASAE S518.2)1. Equation 1 shows the recommended basic pump capacity required for modern, well-designed milking systems.

EQUATION 1. RECOMMENDED MILK VACUUM PUMP CAPACITY

C = (35 + 3n) cfm (cubic feet per minute)

Where:

C = Vacuum Pump volumetric flow rate in cfm

n = Number of milking units

This represents the flow rate required when the pump is operating at full speed. The Variable Speed Drive (VSD) controls the actual speed of the pump, as necessary.

PULSATION STOP CONTROL INFORMATION Each time the pulsator goes through its cycle, it evacuates and then vents the volume contained in between the shell and the liner, and in the hose between the pulsator and the shell. While this flow is intermittent and fairly small for each milking unit, when multiplied by many milking units it represents a significant fraction of the total airflow into the vacuum system.

When the milking unit is not attached to the cow, the pulsators are still in operation even though they are not serving any useful purpose. This accounts for a significant percentage of time both prior to milking (cow entry into stall, udder cleaning, massage, milk squirt inspection, and wipe-off/health check) and after milking (teat dip and exit from the stall). In batch style parlors with two sides (parallel or herringbone) there is also significant wait time while some cows wait to be milked on one side or wait for other cows to finish milking on the other side. In carousel style parlors (where the cow enters a moving circle platform at the one o’clock position and then rides around to the twelve o’clock unloading position, there is wait time

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while the stall returns to the unload position. In all, the milking unit can sit idle for well over half the overall milking time.

The focus of this study is to document the potential energy savings associated with stopping the pulsator operation during all times that the milking unit is not attached to the cow. This feature will be referred to as the Pulsation Stop Control (PSC).

Using the PSC has the potential to save energy and demand in two electrical consuming systems. The first system is the power supply for the pulsation units which convert the 120 voltage to a lower 24 volts to energize the solenoid inside each pulsation unit. When the PSC allows the individual pulsation units to be de-energized when the MU is detached, fewer pulsation units are operating at the same time; and less energy is required at the pulsator power supply. The second system is the vacuum pump system. When fewer pulsation units are operating, less atmospheric air enters the vacuum piping system, and less air needs to be pumped out by the vacuum pump and the pump motor uses less energy.

In order to realize the vacuum pump energy savings, the parlor must have a VSD with pressure feedback control on its vacuum pump; otherwise the reduction in airflow will not result in any reduction in energy usage with a fixed speed vacuum pump.

In addition, there must be a way to detect when the milking unit is not attached to the cow. Fortunately, many modern dairies already have a milk flow sensor as part of an automatic detacher system. This system shuts off the claw vacuum and pulls the milking unit away from under the cow when it detects that milk flow has fallen below a minimum value. Without automatic detachers, an operator must watch the many milking units, decide when milk flow has ended, and manually remove the milking unit. A majority of Southern California dairies have automatic detachers.

DAIRY FARM MARKET INFORMATION Depending on the manufacturer, the PSC feature can be installed in three basic ways: as part of the automatic detacher system itself, as part of a third party retrofit or as part of a pulsation monitoring system. In all cases, the system signals to shutoff the pulsators from the milk flow sensor, either directly or indirectly.

If PSC is installed as part of an automatic detacher system, or as a retrofit, it could potentially provide the following additional benefits:

Extended liner life, and

Extended pulsator life due to less operation time.

INCREMENTAL MEASURE UNIT COST Costs for these options vary widely depending on what make and model of detacher system is currently installed on the dairy farm. One manufacturer estimated the cost difference between a basic detacher system without PSC and a more advanced system with PSC to be around $250 per milking unit.

If PSC is installed as part of a Pulsation Monitoring System, the following benefits would be provided, in addition to those mentioned above:

Continuous monitoring for proper operation of pulsators:

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Proper operation means that the pulsator fully expands and contracts the liner/shell quickly and remains in each milk and rest phase for the specified times for each cycle.

If pulsators aren’t operating properly, cows could be harmed, milk times could increase, and overall milk yield could decrease.

Without a continuous monitoring system, pulsators are checked only periodically (usually monthly); these checks can often miss intermittent pulsation problems for weeks.

Continuous monitoring and recording of milking times and milking sequence, help to identify health problems or understand and optimize overall parlor operations.

To install a pulsation monitoring system, which has many more features in addition to the PSC option, can cost between $500 and $1500 per milking stall or per milking unit depending on how sophisticated the system is. It is estimated that less than 5% of farms in Southern California currently have such systems installed. Most installations, to date, have been retrofit installations, where the pulsation monitoring system was added to an existing parlor that already had automatic detachers and associated milk flow sensors.

The PSC feature is now available from the major dairy equipment manufacturers (BECO, Delaval, Westfalia-Surge, and Boumatic). Also, other equipment installers have expressed interest in offering retrofit solutions.

ENERGY SAVINGS PREDICTIONS One way of predicting potential energy savings associated with PSC, is to perform an analysis based on the physical configuration of the pulsators and milking units. For each pulsation cycle, the vacuum system must evacuate the volume of two hoses and four liner/shell assemblies for each milking unit. (Evacuate means to reduce from atmospheric pressure to the working pressure of the vacuum system at the pump.) A typical system will have 9/32 inch inside diameter (ID) pulsator hoses, each about 8 feet long, liner/shell space internal volumes of 8 cubic inches, a pulsation rate of 60 cycles per minute, and a working vacuum level at the pump of 13.5” Hg vacuum. Using these values, along with an assumption that the vacuum pump provides about 24 cfm/hp, and that pulsators are turned off 50% of the time, a predicted vacuum pump savings of 1.07 kW would be expected for a 50 milking unit dairy (about 0.021 kW/MU). Details of this calculation are shown in Appendix B.

Another method of predicting energy savings can be made by reviewing Equation 1 and ASAE S518S in more detail as it recommends milking vacuum pump system airflow rates. The 3 cfm per milking unit is actually made up of the following:

1 cfm per milking unit for incremental component of effective vacuum reserve

Pulsator consumption of 1 cfm per milking unit.

Claw air admission of 0.35 cfm per milking unit.

All multiplied by a factor of 1.2 - 1.3 to cover system leakage, regulation loss, frictional losses, and pump wear.

It is expected that the pulsators alone should account for about 1.25 cfm per milking unit. As an example, for a 50 milking unit dairy, the recommended capacity would be 35 + 3(50) = 185 cfm, with the pulsators accounting for about 50(1.25 cfm) = 63

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cfm, or about 34% of the total capacity. If it is further assumed that the pulsators are turned off for 50% of the milking time, then a reasonable estimate of the vacuum pump percentage savings would be 50% of 34% or about 17% savings.

In addition to the vacuum pump savings, there are also expected energy savings associated with actuating the pulsator solenoid by the low voltage power supply. Without specific information on the solenoids’ electrical energy consumption, it is difficult to estimate this savings up front, however, it should be directly proportional to the ratio of time the pulsators are stopped, or about 50% savings.

EFFECTIVE USEFUL LIFE Pulsation monitoring systems are new to the market and no data exists on their useful life. However these systems, as well as simplified PSC-only systems, are or would be made up of fairly common electric components, so an effective useful life in excess of 10 years would be expected.

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TECHNICAL APPROACH METHODOLOGY This section captures the methodology used to measure electrical energy and demand savings from the vacuum pump motor and pulsation system power supply when a pulsation unit 1) is turned off by the pulsation stop control (PSC) when the milking unit is not attached versus 2) allowing the pulsation unit to operate all the time during the milking period.

Summary of Major Testing Protocol Steps

1. Selection of dairy farm sites

2. Inspection of dairy farm sites and milking system equipment

3. Selecting data logger system equipment

4. Installing data logger system

5. Testing data logger system installation

6. Testing milking system with and without PSC

7. Reviewing field data

8. Removing data logging equipment

SELECTION OF DAIRY FARM SITES Dairy farm test sites needed to have the following key criteria:

1. A milking system with existing PSC that could be changed to stop or not stop the pulsation units.

2. A vacuum pump system using a VSD with pressure feedback controls.

This selection criteria was used to: 1) eliminate time delay associated with purchasing new PSC equipment and installation, 2) reduce project costs for installing new PSC equipment, and 3) without vacuum pump VSD, there would be no energy and demand savings potential.

INSPECTION OF DAIRY FARM SITES AND MILKING SYSTEM EQUIPMENT How did we determine the study sites?

• Number of milking units

• Number of milkings per day

• Total hours of milking per day

• Did they have milking controls that allowed PSC?

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• Who was the manufacturer of the milking controls?

• Were there locations and space to install data logging system equipment?

• Type of milking parlor

SELECTING DATA LOGGER SYSTEM EQUIPMENT Two data logging systems were used during the study; one was the MicroDataLogger (MDL) based system used on five diary farms and the Dent-based system used on one dairy farm.

The MDL System Description;

• Data logger was MicroDataLogger® unit

• Pulse Input Adapter

• Watthour transducers were WattNode™ units

• Current transformers

• Voltage connections

• MDL Software

MicroDataLogger® Portable Data Acquisition Unit information:

FIGURE 3. MICRODATALOGGER PORTABLE DATA ACQUISITION UNIT

Architectural Energy Corporation makes the MicroDataLogger® portable data acquisition system in a battery or line-powered, four-channel data logger and hand-held meter that records time-series data from many sensors or transducers.

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Electrical Power Measurement

The alternating current (AC) Watthour Transducers (WattNode™) used split-core current transformers (CT) and voltage taps to measure true root mean square (RMS) AC and electrical demand (kW). Output signals are pulses in proportion to demand. WattNode is small in size and can fit either inside or outside electrical panels. Models are available for 3-phase “Wye” and 3-phase “Delta” configurations, for voltages from 120 VAC to 480 VAC, 50 to 60 Hz.

FIGURE 4. AC WATTHOUR TRANSDUCERS (WATTNODE™)

Two different WattNode models were used in the field study. Model WNA-3Y-480-P was used on three-phase power electrical circuits, and Model 3Y-208-P was used on single-phase circuits.

For each power measurement, one WattNode was used. The output pulses were sent to a separate MDL pulse adapters, and were connected to one channel of the MDL. The WattNode units were provided by Architectural Energy Corporation

FIGURE 5 MDL PULSE INPUT ADAPTER FOR PULSE MEASUREMENTS

The Pulse Input Adapter connects sensors with pulse power meters and outputs to the MDL. The adapter is compatible with the WattNode® unit. The MDL Pulse Input Adapter, Pulse Count #3-80 (Part # S-UCA-M006), is used to receive pulses from the WattNode and is made by Architectural Energy Corporation.

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MDL Software

DataManager, version 5.2, software was used to program the MDL, monitor the data, retrieve the data, and analyze the data to produce kWh and kW values. This software is also made by Architectural Energy Corporation.

Dent Brand Data Logging Equipment Description

• DataLogger: Dent Instruments Elite Pro

• Current Transformers: Pacific Science & Technology C150A

FIGURE 6 DENT DATA LOGGING

For Dairy Farm 6, Dent® brand loggers were used, while all other farms used MicroDataLogger® brand loggers. Logger sampling was set to average over 1, 3 or 5-minute intervals.

INSTALLING THE DATA LOGGER SYSTEM Data loggers were installed on both the vacuum pump motor(s) and the pulsator power supply circuits. The vacuum pump motors required three-phase power and the pulsation power supplies required single-phase power. The pulsator solenoids were actuated with a 24-volt signal from the pulsation power supply units (transformers). The power supply input power and vacuum pump motor energy were monitored by the data logger system.

TESTING DATA LOGGER SYSTEM INSTALLATION At each test site, the data logger system was installed and checked for a day to verify that they were working properly before any testing started.

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PULSATION STOP CONTROLS TESTING PLAN Each farm was monitored in its “normal” state (PSC feature enabled) for at least a week. The farms were then switched over (PSC feature disabled) and monitored for at least one week. Depending on the availability of the technicians who switched over the PSC feature, and the schedule for evaluating additional farms, the farms were sometimes monitored for additional time after they were switched back to their normal state (PSC feature enabled).

Note: When the PSC feature is enabled the pulsators are stopped during idle times when the milking unit is detached; when the PSC feature is disabled, the pulsators are on during idle times.

DATA LOGGER COLLECTED VALUES The data logger system and equipment were configured to measure the following:

• Vacuum pump motor average demand (kW)

• Pulsation power supply average demand (kW)

The data logger system was configured to record the following information:

• MDL serial number (example 3087)

• Assigned test site name identify (example Jones Dairy)

• Start recording date and time

• End recording date and time

• Recording sample time (typical each 3 or 5 minutes)

• Number of data recordings made (15,850)

• Logger status information (logging, push button stop)

• Logger channel names (max 4 channels)

• Plug-in channel module identification information (Pulse Count #80).

• Channel described names (vacuum pump 1, pulsation power East, pulsation power West)

• Channel unit (kW)

• Each reading included the data and time the data was recorded (mm/dd/yyyy hh:mm).

The data logger software was used to configure the data logger, start the logger, retrieve the recorded information, and do basic demand and energy calculations. The software also allowed the viewing of graphs, printing, and exporting comma separated value (CSV) data files to Excel.

The dairy test sites usually required using three or four data logger channels. Using sampling rates of three to five minutes, the data logger could record from 55 to 76 days before the storage memory was to capacity. The 55 to 76 days usually allowed enough time for the service technician to schedule trips to the dairy to enable or disable the PSC feature during the data logger recording period.

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REVIEWING FIELD DATA Reviewing of field test data values was completed before the data logging system was removed from the dairy test sites.

If adjustments to the data logging system or milking system were needed, they were made and the field tests were repeated. The field data was again reviewed. This was repeated until actuate field data was collected.

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RESULTS In selecting farm sites for evaluation, milking systems from multiple manufacturers were investigated. However, only one pulsation monitoring system, BECO PulsNexus, had an easy way to enable or disable the PSC feature for our study. The other milking systems did not allow the PSC feature to be easily enabled or disabled. Instead, a technician would have to make a hardware modification every time a switchover was needed during the test on each pulsator module (one pulsator module is associated with each milking unit). This would have been extremely time consuming to the project and unacceptably disruptive and risky to the milking operations. Thus, all farms in the evaluation used the BECO PulsNexus pulsation monitoring system.

There was an attempt to include a range of parlor sizes. However, since pulsation monitoring systems are more likely to be installed on larger farms, the evaluation included mostly farms toward the larger side of the size range (over 1,000 cows), even for Southern California, with the exception of Dairy Farm 6, a university teaching dairy having a small herd.

An initial “proof of concept” farm was selected and evaluated (Dairy Farm 1). Based on positive results, an additional five farms were selected for evaluation.

Most farms, again with the exception of Dairy Farm 6, had fairly long milking times. Milking times shown in Table 2 are per milking, not per day and do not include the wash cycle. With two milkings per day and wash cycles of about one hour after each milking, some of the farms were approaching continuous operation.

The evaluation included 2 carousel style parlors, three herringbones and one parallel parlor. Basic dairy information is summarized in Tables 1 and 2.

TABLE 1. DAIRY FARM INFORMATION

FARM NAME COUNTY PARLOR TYPE SERVICE AREA DATA LOGGERS

Dairy Farm 1 Tulare 50 Stall Carousel SCE MDL

Dairy Farm 2 Tulare Double 23 Herringbone SCE MDL

Dairy Farm 3 Tulare Double 35 Parallel SCE MDL

Dairy Farm 4 Tulare Double 32 Herringbone SCE MDL

Dairy Farm 5 Fresno 80 Stall Carousel PGE MDL

Dairy Farm 6 Fresno Double 6 Herringbone PGE Dent

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TABLE 2. MILK PARLOR & VACUUM SYSTEM INFORMATION

FARM NAME

# OF

VACUUM

PUMPS

EACH

VACUUM

PUMP

MOTOR

HP

# OF

PULSATION

POWER

SUPPLIES

# OF

MILKING

UNITS MILKINGS

PER DAY

AVERAGE

TIME PER

MILKING

(HOURS) TEST DATES

Dairy Farm 1 1 20 (note 3) 50 2 7.75 12/6/07 to 1/2/08

Dairy Farm 2 1 20 4 46 2 9.58 5/26/08 to 6/15/08

Dairy Farm 3 2

(note 1) 20 4 70 2 9.62 10/20/08 to 11/2/08

Dairy Farm 4 2

(note 2) 20 4 64 2 10.41 10/13/08 to 11/2/08

Dairy Farm 5 2

(note 1) 20 4 80 2 9.27 10/19/08 to 11/5/08

Dairy Farm 6

2 (note 1) 7.5 (note 3) 12 2 4 10/20/08 to 12/03/08

Note 1 – Only one vacuum pump operated during milking.

Note 2 – Alternating vacuum pumps used for milking, but only one is used during any given milking.

Note 3 – Number of pulsation power supply units was not recorded.

DATA ANALYSIS Figure 7 shows a typical data logger electrical demand kW trace for both the vacuum pump and the pulsator power supply (transformer). On all farms there is always a very clear change on the pulsator trace when the PSC feature is enabled or disabled. In this particular example, the switch is from PSC-disabled to PSC-enabled and it occurs around 9:30 am on 12/24/07. The vacuum pump difference is not as distinct, but is clearly evident.

For Dairy Farm 3, see Figure 10 in the appendix, the graph of vacuum pump power does not show as distinct a change from one mode to the other, and the summarized data reflects a savings that is noticeably smaller than the other farms. This issue is further addressed in the Discussion section of this report.

For Dairy Farm 6, see Figure 13 in the appendix, the graph of the vacuum pump power clearly shows a difference between modes, however when summarized, the difference is not nearly as large as was observed on the other farms. This issue is also further addressed in the Discussion section.

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0

2

4

6

8

10

kW

Vacuum Pump

0.0

0.2

0.4

0.6

0.8

1.0

12/23 12:00 12/24 00:00 12/24 12:00 12/25 00:00 12/25 12:00 12/26 00:00

kW

Date, 2007

Pulsation Tran

FIGURE 7. TYPICAL DATA LOGGER TRACES FOR VACUUM PUMP AND PULSATOR POWER SUPPLY (DAIRY FARM 1) SHOWING TRANSITION FROM CONTINUOUS PULSATION TO INTERRUPTED PULSATION

For each milking cycle, the data from the start of milking to the start of wash-up was captured and summarized. The average kW values for each milking were averaged for each mode (PSC-enabled and PSC-disabled), and reported in Table 3, Table 4, and Table 5. The energy use during wash-up was not included in the analysis.

As is evident in Figure 7, during the washup times at the end of each milking period, both the vacuum pump and the pulsators were drawing maximum power, regardless of whether the milking was performed with PSC enabled or disabled.

Initially, the energy (kWh) values instead of the average power (kW) values were summarized. However, on some farms, the milking times varied measurably between the two modes. This resulted in differences in kWh significantly higher than the differences in kW. We believe this essentially overestimates the savings associated with PSC, since there is no reason why the milking time should be affected whatsoever by whether the PSC feature is enabled or disabled.

Further analysis showed that the differences in milking times were driven by a few specific milking operating conditions which seemed to be randomly scattered between the two modes, and did not correspond to the changeover from one PSC mode to another.

Ideally, the variability in milking times would be averaged out over time and an analysis of power (kW) and energy (kWh) would yield identical results. However, for the finite time over which the study was performed, it was decided that it was most accurate to base the analysis on kW values, and then calculate energy savings by using overall average milking times.

Washup

PSC change

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The data was normalized by milking unit to allow reasonable side-by-side comparisons between dairies of different size and configuration.

TABLE 3. VACUUM PUMP POWER REDUCTION DUE TO AIRFLOW REDUCTION FROM PSC USE

FARM NAME

NO. OF

MILKING

UNITS

(MU)

AVG. POWER

PSC

DISABLED

(KW)

AVG. POWER

PSC

DISABLED

(KW/MU)

AVG. POWER

PSC

ENABLED

(KW)

AVG. POWER

PSC

ENABLED

(KW/MU)

POWER

REDUCTION

(KW/MU)

POWER

REDUCTION

(%)

Dairy Farm 1 50 3.96 0.0791 3.11 0.0622 0.0169 21.3%

Dairy Farm 2 46 4.01 0.0871 3.13 0.0681 0.0190 21.8%

Dairy Farm 3 70 9.61 0.1373 9.21 0.1315 0.0058 4.2%

Dairy Farm 4 64 5.63 0.0880 4.70 0.0734 0.0146 16.6%

Dairy Farm 5 80 8.44 0.1056 6.92 0.0865 0.0190 18.0%

Dairy Farm 6 12 1.02 0.0851 0.96 0.0801 0.0050 5.9%

Overall Average: 0.0134 14.6%

Overall Average w/o Dairy Farms 3 & 6: 0.0174 19.4%

TABLE 4. PULSATOR POWER SUPPLY POWER REDUCTION FROM PSC USE

FARM NAME

NO. OF

MILKING

UNITS

(MU)

AVG. POWER

PSC

DISABLED

(KW)

AVG. POWER

PSC

DISABLED

(KW/MU)

AVG. POWER

PSC

ENABLED

(KW)

AVG. POWER

PSC

ENABLED

(KW/MU)

POWER

REDUCTION

(KW/MU)

POWER

REDUCTION

(%)

Dairy Farm 1 50 0.87 0.0174 0.46 0.0091 0.0083 47.7%

Dairy Farm 2 46 0.88 0.0191 0.40 0.0087 0.0103 54.2%

Dairy Farm 3 70 1.35 0.0193 0.78 0.0111 0.0081 42.3%

Dairy Farm 4 64 1.24 0.0193 0.73 0.0115 0.0079 40.8%

Dairy Farm 5 80 1.56 0.0195 0.85 0.0106 0.0089 45.7%

Dairy Farm 6 12 0.25 0.0208 0.10 0.0083 0.0125 60.3%

Overall Average: 0.0093 48.5%

TABLE 5. COMBINED POWER REDUCTION FROM PSC USE

FARM NAME

NO. OF

MILKING

UNITS

(MU)

AVG. POWER

PSC

DISABLED

(KW)

AVG. POWER

PSC

DISABLED

(KW/MU)

AVG. POWER

PSC

ENABLED

(KW)

AVG. POWER

PSC

ENABLED

(KW/MU)

POWER

REDUCTION

(KW/MU)

POWER

REDUCTION

(%)

Dairy Farm 1 50 4.83 0.0965 3.57 0.0713 0.0252 26.1%

Dairy Farm 2 46 4.88 0.1062 3.54 0.0769 0.0293 27.6%

Dairy Farm 3 70 10.96 0.1566 9.99 0.1427 0.0139 8.9%

Dairy Farm 4 64 6.87 0.1074 5.43 0.0849 0.0225 20.9%

Dairy Farm 5 80 10.00 0.1250 7.77 0.0971 0.0279 22.3%

Dairy Farm 6 12 1.27 0.1059 1.06 0.0883 0.0176 16.6%

Overall Average: 0.0227 20.4%

Overall Average w/o Dairy Farms 3 & 6: 0.0262 24.2%

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DISCUSSION

COMPARISON OF PREDICTED VERSUS TEST DATA RESULTS Overall, the test results were in line with the predicted savings listed in the Energy Savings Prediction section.

The vacuum pump motors’ predicted savings resulted in a value of 0.021 kW/MU for a 50-milking unit dairy. This was fairly close to the value listed in Table 3, 0.169 kW/MU, that was observed for Dairy 1, which was also a 50 milking unit dairy. Similarly, vacuum pump motor demand reduction ranged from 4.2% to 21.8%, versus the predicted 17% as discussed earlier.

The pulsator power supply tested reduction ranged from 40.8% to 60.3% using Table 4, versus the earlier predicted value of 50%.

This is a fairly good agreement given the rough nature of the initial predictions, and serves as a valuable “sanity check” that the test results are reasonable.

TEST DAIRY FARMS DEMAND REDUCTION The demand reduction due to the vacuum pump motor accounted for the larger portion of the combined demand reduction. Table 3, Table 4, and Table 5 values for all test farms show the vacuum pump contributed about 59% (= 0.0134/0.0227 kW/MU) while the pulsator power supplies contributed about 41% (= 0.0093/0.0227 kW/MU) demand reduction.

There were two farms that showed suspect data, Dairy Farms 3 and 6, and did not seem to realize the expected vacuum pump demand reduction. There are two separate reasons for this.

First, Dairy Farm 3 has a type of vacuum pressure control for the vacuum pump VSD system that was different from the other 5 dairies. Dairy Farm 3 uses a vacuum pressure sensor that allows unwanted/unneeded air to enter the vacuum system. The other farms simply have a vacuum pressure sensor/controller unit that does not allow air to enter the vacuum system. Without even considering the effects of PSC, Dairy Farm 3 looks unusual in that its initial power use (kW/milking unit) is significantly higher than the other farms (see Table 3). The farm starts out with higher than normal airflow, and doesn’t save very much when PSC is added. These observations can be explained by the nature of their vacuum pressure control system allowing unneeded air into the vacuum system. Any excess air entering the vacuum system results in more energy being consumed by the vacuum pump motor.

Second, Dairy Farm 6 has a vacuum pump VSD control system similar to the other farms, and its initial power use (kW/milking unit) is also very similar to the other farms. In this case, the vacuum pump is simply running so far below its normal capacity and pump revolution per minute (RPM) speed that it is unable to operate efficiently. Table 6 shows the vacuum pump motor percent load factor based on the motor size. Dairy Farm 6 is clearly the most under-loaded. For vacuum pumps, power is roughly a linear function of speed at constant pressure, so this would correspond to a speed signal out of the VSD of 16% of 60 Hz or 10 Hz, which may be approaching the practical lower limit of the VSD and is likely in a region where motor efficiency significantly degrades. Without further investigating the detailed layout

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and control of this dairy’s vacuum system, we think this explanation is consistent with the observations.

TABLE 6. VACUUM PUMP MOTOR LOADING (PSC IS TURNED OFF)

FARM NAME

MOTOR AVG. INPUT POWER

(KW)

MOTOR INPUT

ELECTRIC -HORSE-POWER

(EHP)

ASSUMED

MOTOR

EFFICIENCY

(EPACT)

MOTOR

OUTPUT

BRAKE HORSE

POWER (BHP) MOTOR

SIZE (HP) MOTOR LOAD

FACTOR %

Dairy Farm 1 3.96 5.30 91.0% 4.83 20 24.1%

Dairy Farm 2 4.01 5.37 91.0% 4.89 20 24.4%

Dairy Farm 3 9.61 12.89 91.0% 11.72 20 58.6%

Dairy Farm 4 5.63 7.55 91.0% 6.87 20 34.4%

Dairy Farm 5 8.44 11.32 91.0% 10.30 20 51.5%

Dairy Farm 6 1.02 1.37 89.5% 12.3 7.5 16.3%

Based on the above considerations, Tables 3 and 5 report overall averages, as well as averages with Dairy Farms 3 & 6 excluded, with the former being a conservative estimate of potential power reductions and the latter being an estimate assuming “best practices” in terms of vacuum system sizing and control.

After the two exceptions are removed, values from Tables 3, 4, & 5 show the demand reduction portion from the vacuum pump accounts for about 66% (0.0174 / 0.262 kW/MU) and pulsation power supply part accounts for about 34% (0.0093/0.0262 kW/MU) of the combined power reduction.

TEST DAIRY FARMS ENERGY SAVINGS TABLE 7. ENERGY SAVINGS FROM VACUUM AIRFLOW REDUCTION DUE TO PSC

FARM NAME SAVINGS

(KW/MU)

AVG. MILK

TIME

(HOURS) MILKINGS

/DAY ENERGY SAVINGS

(KWH/DAY/MU) ENERGY SAVINGS

(KWH/YEAR/MU)

COST SAVINGS

@ $0.10/KWH

($/YEAR/MU)

Dairy Farm 1 0.0169 7.90 2 0.267 97 $9.74

Dairy Farm 2 0.0190 9.57 2 0.364 133 $13.27

Dairy Farm 3 0.0058 9.61 2 0.111 41 $4.06

Dairy Farm 4 0.0146 10.41 2 0.304 111 $11.08

Dairy Farm 5 0.0190 9.27 2 0.353 129 $12.87

Dairy Farm 6 0.0125 3.79 2 0.038 14 $1.4

Overall Average: 87 $8.74

Overall Average w/o Dairy Farms 3 & 6: 117 $11.74

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TABLE 8. ENERGY SAVINGS FROM PULSATION POWER SUPPLY DUE TO PSC

FARM NAME SAVINGS

(KW/MU)

AVG. MILK

TIME

(HOURS) MILKINGS

/DAY ENERGY SAVINGS

(KWH/DAY/MU) ENERGY SAVINGS

(KWH/YEAR/MU)

COST SAVINGS

@ $0.10 KWH

($/YEAR/MU)

Dairy Farm 1 .0083 7.90 2 0.131 48 $4.78

Dairy Farm 2 0.0103 9.57 2 0.198 72 $7.22

Dairy Farm 3 0.0081 9.61 2 0.157 57 $5.71

Dairy Farm 4 0.0079 10.41 2 0.164 60 $5.99

Dairy Farm 5 0.0089 9.27 2 0.165 60 $6.01

Dairy Farm 6 0.0125 3.79 2 0.095 35 3.47

Overall Average: 55 $5.53

TABLE 9. COMBINED ENERGY SAVINGS DUE TO PSC

FARM NAME SAVINGS

(KW/MU)

AVG. MILK

TIME

(HOURS) MILKINGS

/DAY ENERGY SAVINGS

(KWH/DAY/MU) ENERGY SAVINGS

(KWH/YEAR/MU)

COST SAVINGS

@ $0.10/KWH

($/YEAR/MU)

Dairy Farm 1 0.0252 7.90 2 0.398 145 $14.53

Dairy Farm 2 0.0293 9.57 2 0.561 205 $20.49

Dairy Farm 3 0.0139 9.61 2 0.268 98 $9.78

Dairy Farm 4 0.0225 10.41 2 0.468 171 $17.07

Dairy Farm 5 0.0279 9.27 2 0.517 189 $18.88

Dairy Farm 6 0.0176 3.79 2 0.133 49 $4.86

Overall Average: 143 $14.27

Overall Average w/o Dairy Farms 3 & 6: 177 $17.74

Table 7, Table 8, and Table 9 report energy savings based on an overall average milking time for each farm. As discussed earlier, overall averages are calculated with and without the farms having suspect data.

The PSC overall annual energy savings were 143 kWh per milking unit for all test farms and 177 kWh per milking unit excluding the two farms with suspected data. These energy savings result in cost savings of $14.27 and $17.74 per milking unit respectively, assuming an electricity rate of $0.10/kWh. If all farms are included, the vacuum pump motor accounted for 61% (61% = 87/143 kWh/MU) of the savings and 41% attributable to the pulsator power supply. Excluding the two farms with suspected data, the vacuum pump motor accounted for 66% (66%= 117 /177 kWh/MU) of the savings and the pulsation power supply portion is 34% (34% = 100%-66%). It was unexpected that the pulsators power supply would account for such a large percent of the overall savings.

It would be useful to measure the “operational efficiency” of the milking operations. For a carousel, this is how far around the rotation the average cow goes before it is finished milking as a percentage of the total time on the carousel. For a parallel or

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herringbone design, it is how much time does the cow stand in the stall with the milking unit attached as a percentage of the total time in the stall. Clearly, farms that are more efficient, have less idle time, and thus the savings associated with PSC are less. There was no easy way to measure this, but it is useful to note that the highest percentage pulsator savings occurred on Dairy Farm 6, which is a teaching university dairy and the smallest with the least automated operation.

VACUUM PUMP WITHOUT PSC RESULTS COMPARED WITH ANOTHER STUDY As a validation against existing literature in this area, power use values were compared to a 2003 study by Sanford2. The Sanford study reported only the vacuum pump motor power and not the pulsation unit power. Sanford’s study was based on four farms with vacuum pump VSDs in the Midwestern US ranging from 12 to 32 milking units without PSC. Vacuum pump motor power use during milking ranged from 0.109 kW/MU to 0.292 kW/MU.

The farms in the current study, with PSC off, have vacuum pump motor power in the range of 0.079 to 0.137 kW/MU as shown in Table 3. Thus, even including the farm with the highest energy use (dairy farm 3), these large California farms are quite efficient compared to the Sanford study.

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CONCLUSION There is potential energy savings and demand reductions when the PSC equipment is part of a dairy farm vacuum milking system if:

1. A VFD is used with a vacuum pressure feedback control system, and

2. The vacuum pressure sensor is not part of an apparatus that allows air to enter the vacuum system.

SUGGESTED CALCULATION METHODS FOR UTILITIES CONSIDERING ADDING PSC AS AN ENERGY EFFICIENCY MEASURE

The results of this study clearly suggest the PSC control does have the potential to increase the energy efficiency of a dairy farm milking system. Equation 2 and Equation 3 below are suggested methods for calculating the annual energy savings and demand reduction based on these results if they were included in an electric utility incentive program.

EQUATION 2 ANNUAL ENERGY SAVINGS

Annual Energy Savings (kWh) = (Average demand reduction per MU) x (Average hours per milking period) x (Number of milkings/day) x (365 days per year) x (Number of MU per dairy)

= (0.0262 kW/MU) x (8 hrs/milking period) x (2 milkings/day) x (365 days/year) x (number of MU per dairy)

= (153 x number of MU) kWh

EQUATION 3 DEMAND REDUCTION

Demand Reduction (kW) = (average demand reduction per MU) X (number of MUs) = (0.0262 kW/MU) x (number of MUs) kW

Basing Equation 2 and Equation 3 on the number of milking units allows for a simple yet accurate calculation of energy savings and demand reduction. This is useful because most farmers readily know the number of milking units they have, and vendors can easily communicate rebate information to customers when it is based on the number of milking units. In addition, using the number of milking units is easier for utilities to design their incentive programs and also for verification during the audit phase.

In Equation 2 and Equation 3, the average demand reduction per MU was taken from Table 5 without including the two farms with the suspected data. The value for average hours per milking period was calculated by averaging the recorded milking shown in Table 7, Table 8, and Table 9 excluding Dairy Farm 6, because this farm is a teaching university and does not represent a true dairy production operation.

Note: These milking times do not, and should not, include the wash cycle.) This value was 9.4 hours, but it is likely somewhat higher than the stated average, since

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the farms in the study were all large, highly automated farms. Therefore a more conservative value of 8 hours was chosen, which also corresponds to a typical workday. A further study may be necessary to determine the appropriate value for a given area.

In some cases, the number of milking units might not be known. For example, in an assessment of the likely impact of offering PSC as an energy efficiency measure, in a given geographical area, it is more likely that the only data available would be the number of cows/farm. In that case, the number of milking units can be estimated by dividing the number of cows by four, and by the hours per milking period. The value of four comes from the fact that about 4 cows pass through each milking stall each hour.

All dairy farms in this study milked two times per day, but some milked three times per day. Virtually all modern dairies manage their herd so they are milking year-round, or 365 days/year. It is worth noting, that in fact each individual cow is typically only milked about 300 days per year and is “dry” for about 65 days. However, farmers stagger their breeding cycles so that on any given day, the number of milking cows is roughly constant. This implies that when we speak of “number of cows” we really mean “average number of cows milked each day”. The total number of cows in the herd will be larger by about 20%. In this study, we specifically did not record the number of cows being milked, out of concerns that farmers consider this information confidential.

As an example for a sample calculation, a 1000 cow dairy, milking 8 hours/milking period would be estimated to have (1000 cows) / (4 cows/hr/MU) / 8 hours = about 32 milking units.

Equation 2 would then yield an annual energy savings of 4900 kWh (4900 kWh = 153 kWh/MU x 32 MU).

Equation 3 would then yield a demand reduction of 0.84 kW (0.84 kW= 0.0262 kW/MU X 32 MU).

The above sample calculation used these dairy farm assumptions. If a deemed incentive measure is considered by an electric utility, the following basic California dairy farm values are suggested;

• Average number of milking cows on a dairy farm: 1000

• Average number of cows milked per hour at one milking station: 4 cows per hour per MU

• Average number of hours for each milking period: 8-hour milking period

• Average number of times a cow is milked each day: 2 milkings per day

• Number of days per year the cow is milked: 365 days per year

SUGGESTIONS FOR ELECTRIC UTILITY FUTURE STUDIES 1. A future study may be needed to establish the average hours per milking period

for California. It is likely the hours will vary in different parts of the state.

2. A future study may be needed to understand the actual percentage of milking units operating at the same time during the milking period. A higher percentage may reduce energy savings and a lower percentage may increase energy savings.

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3. There may be other variables that need future studies to support selecting the values used to estimate energy savings and demand reduction from using this EE control.

4. A market penetration study is warranted to understand how many farms do not yet have the PSC feature installed.

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REFERENCES 1ASAE S518.2 Milking Machine Installations – Construction and Performance.

2Sanford, S. A. 2003. “Milking System Air Consumption When Using a Variable Speed Vacuum Pump.” 2003 ASAE Annual International Meeting, Las Vegas, NV.

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APPENDICES

APPENDIX A – DAIRY FARM SUMMARY SHEETS This section contains information on individual farms and observations taken from the data logger traces.

One general observation is that the pulsator power supply traces clearly show the transition between PSC modes, while on the vacuum pump motor traces, the transition is more subtle and harder to detect.

Another observation is that when the PSC feature is engaged, the graph of pulsator power supply is noisy (changes rapidly up and down). This is due to the cow loading and unloading of each side of a two sided parlor. Depending on the relative timing of the two sides of the parlor, pulsator use can go from nearly all pulsators being off to all pulsators being on. For a carousel, there are still rapid changes in pulsator power since some cow’s milk for longer periods of time than others, however the number of pulsators in use at any given time is much more constant and the graphs, as expected, are much less noisy.

Finally, all farms in the study turned all the pulsators on during wash up, in both PSC-enabled and PSC-disabled mode. In all but two cases, the vacuum pump motor goes to full speed (or at least higher speed) during wash up.

Individual farm observations are discussed in the following pages.

Note: The Monitored Date Ranges in the following pages refer to the dates over which data was analyzed. In some cases, the dataset containing the raw data may exceed these ranges. In some cases this was because the farm was being monitored while equipment was being repaired, and in others, the number of monitored days simply exceeded what was necessary for the analysis.

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DAIRY FARM 1 – 50 STALL CAROUSEL

0

1

2

3

4

5

6

7

8

9

10

kW

Vacuum Pump

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

12/16 12:00 12/16 18:00 12/17 00:00 12/17 06:00 12/17 12:00 12/17 18:00 12/18 00:00 12/18 06:00 12/18 12:00 12/18 18:00

kW

Date, 2007

Pulsation Tran

Washup

PSC Change

FIGURE 8 DAIRY FARM 1 POWER TRACE

This was the study’s most efficient farm (lowest kW/MU).

This farm has a large difference in vacuum pump power between milking and wash up.

Switchover occurred midway through a milking; data for this milking was excluded from analysis.

Monitored Date Range: 12/06/07 to 1/02/08

Switch Date: PSC enabled to disabled: 12/17/07

PSC disabled to enabled: 12/24/07

Sampling Interval: 1 minute.

The data logger used two channels to collect field measurements: one for the vacuum pump motor and two for pulsation power supplies.

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DAIRY FARM 2 – DOUBLE 23 HERRINGBONE

1

2

3

4

5

kW

Vacuum Pump

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

06/04 13:00 06/05 01:00 06/05 13:00 06/06 01:00 06/06 13:00

kW

Date, 2008

Pulsation Tran

Washup

PSC Change

FIGURE 9 DAIRY FARM 2 POWER TRACE

Milking vacuum pump DOES NOT run during wash up. This was because the dairy farmer’s normal operation was to have the milking vacuum pump turned off and to use a different vacuum pump during wash up.

Changeover made partway into 06/05 morning milking. This milking was excluded from results (not counted as either PSC-on or PSC-off).

When PSC is disabled, pulsators stay on all the time, even after wash up. This may not be a problem because they stayed on during the PSC disable test period. As seen above, when the PSC is enabled the pulsation unit energy consumption drops to zero after wash up and at the start of the next milking period.

Monitored Date Range: 5/26/08 to 6/15/08

Switch Date: PSC enabled to disabled: 6/5/08

Sampling interval: 2 minutes.

The data logger used two channels to collect field measurements: one for the vacuum pump motor and two for pulsation power supplies.

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DAIRY FARM 3 – DOUBLE 35 PARALLEL

0

5

10

kW

Vacuum Pump 1

0.00

0.01

0.02

0.03

kW

Vacuum Pump 2

0.2

0.4

0.6

kW

Pulsation 1

0.2

0.4

0.6

10/26 13:00 10/27 01:00 10/27 13:00 10/28 01:00 10/28 13:00

kW

Date, 2008

Pulsation 2

Washup

PSC Change

FIGURE 10 DAIRY FARM 3 POWER TRACE

Prior to 10/20/08, the vacuum pump trace was “unusual,” slightly and more variable than later. This data was not used in the analysis.

Prior to collecting the final data, this farm ran without a working VSD.

Switchover occurred midway through a milking; data for this milking was excluded from analysis.

The vacuum pump used for milking is not used during wash up. A second vacuum pump comes on during the wash up period, but only for a very short time.

When PSC is disabled, pulsators stay on all the time, even after wash up. This may not be a problem because they stayed on during the PSC disable test period. As seen above, when the PSC is enabled the pulsation unit energy consumption drops to zero after wash up and at the start of the next milking period.

Monitored Date Range: 10/20/08 to 11/02/08

Switch Date: PSC disabled to enabled: 10/27/08

Sampling interval: 5 minutes.

The data logger used four channels to collect field measurements: one and two for each vacuum pump motor, three for half of pulsation power supplies, and four for the other half.

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DAIRY FARM 4 – DOUBLE 32 HERRINGBONE

0

5

10

kW

Vacuum Pump 1

0

5

10

kW

Vacuum Pump 2

0.0

0.2

0.4

0.6

kW

Pulsation East

0.0

0.1

0.2

0.3

0.4

0.5

0.6

10/19/08 10/20/08 10/21/08 10/22/08

kW

Date

Pulsation West

PSC change Washup

FIGURE 11 DAIRY FARM 4 POWER TRACE

Longest milk time dairy (10.41 hours). (With wash up is included, it is nearly a continuous milking operation.)

Switchover occurred midway through the 10/20/08 milking; data for this milking was excluded from analysis.

Monitored Date Range: 10/13/08 to 11/02/08

Switch Dates: PSC enabled to disabled: 10/20/08

PSC disabled to enabled: 10/27/08

Sampling interval: 5 minutes.

The data logger used four channels to collect field measurement: one and two for each vacuum pump motor, three for half of pulsation power supplies, and four for the other half.

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DAIRY FARM 5 – 80 STALL CAROUSEL

0

5

10

kW

Vacuum Pump 1

0.0

0.2

0.4

0.6

0.8

kW

Pulsation 1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

10/27 13:00 10/28 01:00 10/28 13:00 10/29 01:00 10/29 13:00

kW

Date, 2008

Pulsation 2

Washup

PSC change

FIGURE 12 DAIRY FARM 5 POWER TRACE

Largest dairy (80 stalls), and had the least difference between the vacuum pump power during milking and during wash up.

Each milking period includes an interruption roughly in the middle of the period. This was confirmed to be a meal break time.

Monitored Date Range: 10/19/08 to 11/05/08

Switch Dates: PSC enabled to disabled: 10/28/08

Sampling interval: 5 minutes.

The data logger used three channels to collect field measurements: one for the vacuum pump motor, two for half of pulsation power supplies, and three for the other half.

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DAIRY FARM 6 – DOUBLE 6 HERRINGBONE

TIME

11/03/08

18:40:00

11/04/08

08:00:00

14:40:00

21:20:00

11/05/08

10:40:00

11/05/08

0

0.5

1.0

1.5

2.0

Cha

n 5

Avg

. KW

Vacuum Pump, 12.3.08.dat

11/03/08 - 11/05/08

DENT Instruments ELOG 2006

Washup

TIME

11/03/08

18:40:00

11/04/08

08:00:00

14:40:00

21:20:00

11/05/08

10:40:00

11/05/08

0

0.0

0.1

0.1

0.2

0.2

0.3

Cha

n 1

Avg

. KW

Pulsation, 12.3.08.dat

11/03/08 - 11/05/08

DENT Instruments ELOG 2006

PSC Change

FIGURE 13 DAIRY FARM 6 POWER TRACE

This farm used the Dent data logging instruments, so the data manipulation software was different (graphs had to be created and pasted separately). Pulsation and vacuum pump data is in two different datasets, which are not synchronized (need to manually select date ranges to be in sync.)

There is some sort of cycle that occurs prior to starting to milk. This was excluded from the analysis.

This is the university dairy, and by far the smallest operation.

Monitored Date Range: 10/20/08 to 12/03/08

Switch Dates: PSC enabled to disabled: 11/04/08

PSC disabled to enabled: 11/22/08

Sampling interval: 2 minutes.

Two data loggers were used to collect field measurements: one for the vacuum pump motor and other for pulsation power supplies.

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APPENDIX B – “BACK-OF-ENVELOPE” ESTIMATE OF VACUUM PUMP ENERGY SAVINGS

To estimate the potential energy savings associated with PSC, a “back-of-envelope” analysis was performed based on the physical configuration of the pulsators and milking units.

The hose connecting the pulsator and the milking unit is typically about 8 feet long with and internal diameter of 9/32”, resulting in an internal volume of:

Pi / 4 * (9/32 in)2 * (8 ft )(12 in/ft) = 5.96 in3 / hose

Internal volume of the liner/shell space is estimated at 8 in3.

Each milking unit has 4 liner/shell assemblies and two hoses, resulting in a total volume for each milking unit of:

2 hoses * (5.96 in3/hose) + 4 liner/shells * (8 in3/liner/shell) = 44 in3 MU

The density of air at atmospheric conditions is 0.075 lbm/ft3. So the mass of air within this volume is:

(0.075 lbm/ft3) * (44 in3/MU) / (1728 in3/ft3) = 0.00191 lbm/MU

The vacuum level of the system is 13.5 “Hg. Atmospheric pressure is 29.9 “Hg. The absolute pressure of the vacuum system is:

29.9 “Hg – 13.5 “Hg = 16.4” Hg

The density of air at vacuum conditions is:

(0.075 lbm/ft3) * (16.4 “Hg / 29.9 “Hg) = 0.041 lbm/ft3

After the volume is evacuated, the mass of the air in the volume is:

(0.041 lbm/ft3) * (44 in3/MU) / (1728 in3/ft3) = 0.00105 lbm/MU

The mass of air that must normally be moved by the vacuum system is:

0.00191 lbm/MU – 0.00105 lbm/MU = 0.00086 lbm/MU

Assuming the dairy has 50 milking units, the pulsators cycle 60 times per minute, and with PSC enabled the pulsators are off 50% of the time, then the mass flow rate of air that no longer needs to be moved by the vacuum system is:

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(0.00086 lbm/MU/cycle) * (60 cycles/min) * (50 MU) * 50% = 1.29 lbm/min

The corresponding volumetric flow rate at vacuum conditions is:

(1.29 lbm/min) / (0.041 lbm/ft3) = 31.5 ft3/min or cfm

For vacuum pumps in the size range serving a 50 MU dairy, a vacuum pump efficiency of 24 cfm/bhp can be assumed, making the expected horsepower savings:

(31.5 cfm) / (24 cfm/bhp) = 1.31 bhp

Assuming a motor efficiency of 91%, then the expected power savings during milking is:

(1.31 bhp) / (0.91) *(0.746 kW/hp) = 1.07 kW (or 0.021 kW/MU)

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APPENDIX C – HISTORICAL MILKING VACUUM SYSTEMS ENERGY EFFICIENCY IMPROVEMENTS FROM 1995 TO 1997

A recap of past California Dairy farm milking vacuum systems, based on size and energy consumption, has decreased per milking unit since 1995.

Before 1995, the typical California dairy farm milking system had installed about one horsepower (HP) of vacuum pump motor for each milking unit (MU). The vacuum pump ran at a constant speed and load. If a milking system had 50 MUs, then there would typically be 50 HP of vacuum pump motor capacity running.

In 1996 a new test to evaluate the milking system performance was developed by the University of California Extension Service in collaboration with the National Mastitis Council. Using this test, they were able to demonstrate that relocating the pressure control valve closer to the milking units resulted in needing only half the vacuum pump HP and energy to milk the same number of cows.

Previously, the valve was typically mounted farther away from the MU. Sanitary constraints dictated that the closest the valve could be to the milking units was in the vacuum pipeline leading from the milk receiver back to the vacuum pump. With moving the valve closer to the milk receiver tank, a 50 MU barn would then only need a 25 HP vacuum pump. The vacuum pump and motor were still running at a constant speed and load. There were many cases when the dairy had two vacuum motors running in 1995 and then they were able to turn off one vacuum pump motor and still meet the milking vacuum air needs. Farms then only needed 0.5 HP per MU to milk the same number of cows. This was a 50% energy savings and demand reduction compared to 1995 milking system.

In 1997 variable frequency drives (VFD) were introduced to the California dairy farm industry. Instead of running the vacuum pump at a constant speed and load all the time, the VFD, with pressure feedback controls, would slow down and speed up the vacuum pump to match the demand of the milking units. Field measurements show the VFD saved 50% of the energy when compared to constant speed vacuum pumps having the same MU and milking the same number of cows. The vacuum VFD systems were still installed with 0.5 HP per MU, but they only used 0.25 HP per MU. The two changes combined resulted in a system that only required 25% of the energy to milk the same number of cows when compared to 1995 system. (50% x 50% = 25% energy use, or 75% savings compared to the 1995 system.)

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Note: Double-click this page to view or print the entire linked report.

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Note: Double-click this page to view or print the entire linked report.

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APPENDIX D – ENERGY SAVINGS WITH AND WITHOUT VSD

As part of this study, there was an opportunity to measure the actual savings associated with the vacuum pump with and without a VSD control. During the time that data loggers were installed, Dairy Farm 3 had to run without a VSD while a replacement part was installed. The energy savings associated with the VSD only (not including pulsation interruption) was 44%. More details are included in Error! Reference source not found..

TABLE 10. VACUUM PUMP POWER REDUCTION FROM VFD USE

FARM NAME

NO. OF

MILKING

UNITS

(MU)

AVG. POWER

WITHOUT

VSD (KW)

AVG. POWER

WITHOUT

VSD

(KW/MU)

AVG. POWER

WITH VSD

(KW)

AVG. POWER WITH

VSD

(KW/MU)

POWER

REDUCTION

(KW/MU)

POWER

REDUCTION

(%)

Dairy Farm 3 70 17.85 0.255 9.99 0.143 0.112 44%