CompleteGuide_102005REV

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Dairy FarmEnergy Management

Guide

California

Milk CoolingMilk Harvest

Lighting

Air Circulation

& VentilationWater Systems

General Info Milk Cooling

Compressed Air

Washing &Water Heating


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Dairy Farm Energy Management Guide ii

Table of Contents

Introduction .. vi

Milk_Harvest 1Purpose 1

Equipment.. 2Energy Utilization Indices (EUIs).. 7Energy Conservation Measures (ECMs). 8Operator Level Checks . 16Glossary of Milk Harvest Terms .. 19

Milk Cooling .. 22Purpose and Cooling Standards . 22Equipment .. 25Energy Utilization Indices (EUIs) .... 37Energy Conservation Measures (ECMs) .... 37Operator Level Checks...... 40Glossary of Milk Cooling Terms.47

Lighting 49Purpose.... 49Dairy Farm Task Lighting... 50Visually Intensive Task Lighting.53Livestock Handling Lighting 58General Lighting... 61Energy Utilization Indices (EUIs)...... 62Energy Conservation Measures (ECMs) 63Operator Level Checks64Glossary of Lighting Terms.65

Air Circulation and Ventilation.. 68Purpose and Design 70Heat Stress Reduction.... 70Energy Utilization Indices (EUIs) .. 79Energy Conservation Measures (ECMs) .... 80Operator Level Checks .. 81Glossary of Air Circulation and Ventilation Terms.. 82

Washing and Water Heating...85Purpose, Requirements.. 87Equipment. 87Energy Utilization Indices (EUIs) . 89Energy Conservation Measures (ECMs) . 90

Vacuum Level Required for Washing . 97Operator Level Checks. 105Glossary of Washing and Water Heating Terms.. 108


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Dairy Farm Energy Management Guide iii

Water Systems 110Purpose .... 110Water Supply ... 111Water Usage .... 111System Design .... 114Intermediate Water Storage .. 118Equipment .... 119Energy Utilization Indices (EUIs) .. 120Energy Conservation Measures (ECMs) .... 120Operator Level Checks .. 123Glossary of Water System Terms .... 124

Compressed Air 125Purpose and Design Factors 125Equipment .. 126Energy Utilization Indices (EUIs) .. 130Energy Conservation Measures (ECMs) .... 131Operator Level Checks .. 135Glossary of Compressed Air Terms .... 139

General Information.. 140Energy Efficient Electric Motors ... 140Gas-Fired Absorption Heat Pumps .. 145Temperature Monitoring .... 147Understanding Pump Curves ... 149Variable Frequency Drives .... 152

References...159


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Dairy Farm Energy Management Guide iv

Southern California Edison February 2004

Prepared for: Southern California EdisonPrepared by:

Dr. David C. Ludington, Eric L. Johnson, James A. Kowalski, Anne L. MageDLtech, Inc.Ithaca, New YorkTel: (607) 266-6401Fax: (607) 266-7037Email: [email protected] A. PetersonNortheast Agriculture Technology CorporationIthaca, New YorkTel: (607) 266-9007Fax: (607) 266-9008Email: [email protected]

Important :

These materials are meant to examine dairy farm energy management, to clarify and illustrate typical situations, andmust be appropriately adapted to individual circumstances. Moreover, the materials are not intended to provide legaladvice or establish legal standards of reasonable behavior.


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Dairy Farm Energy Management Guide v

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Dairy Farm Energy Management Guide vi

(return to: Table_of_Contents) Introduction

The American dairy farmer manages a highly efficient food production system. Yet he/shecontinues to seek ways to become more efficient, because that is the only way to remaincompetitive. This guidebook provides a comprehensive study of energy utilization on a

modern California dairy farm, including discussions of techniques to effectively manageenergy costs.

The goal of this guideline is to increase the understanding of how electric energy is used,provide a measure for comparison, and explore available opportunities for conservation ona modern dairy farm. Electricity is not purchased as a direct end use commodity, but ratherfor the results that can be produced thru conversion to useful light, heat or power. Byincreasing the awareness for how electric energy is transformed to an end use andinvestigation of options for conservation, better energy related management decisions canbe achieved to increase profitability.

Opportunities for significant energy savings exist that allow dairymen options to bettercontrol their energy costs. For example, adding a variable speed drive (VSD) to a vacuumpump will reduce energy use by 50% or more, with no loss of milking system performance.

Although not all options for energy savings available are this dramatic, their cumulativeimpact can help improve dairy farm profitability.

The first, least cost way to approach saving energy is to carefully maintain existingequipment at peak operating efficiency. Worn, poorly maintained equipment uses moreenergy while not meeting original performance specifications. When equipment needs tobe replaced, select the highest efficiency equipment available. The pressures of increasingenergy costs drive the advancement of energy saving technologies. Newer, more efficientequipment is always being developed. Take time to analyze the specifications and makethe most cost effective choices.

The guide focuses on 7 major electric energy use categories found on California dairies,they include:

1. Milk Harvest2. Milk Cooling3. Lighting4. Circulation & Ventilation5. Washing & Water Heating6. Water Systems7. Compressed Air Systems

The pie chart on the following page shows the distribution of electric energy use on arepresentative diary farm in California. Washing and water heating is not shown becausefossil fuel is primarily used to heat water.

The overall impact of each area of energy use is also represented in the chart.


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Dairy Farm Energy Management Guide vii

Electric Energy Use on a Representative

California Dairy Farm

Water Systems

8%

Air Circulation

10% Lighting

13%Compressed Air

4%

Milk Cooling

27%

Miscellaneous

2%Waste Handling

24%

Milk Harvest

12%

The individual sections of the guide offer a comprehensive examination of

Purpose and function of energy use for that category. Description and discussion of typical equipment employed. Development of an Energy Utilization Index (EUI) to

provide a benchmark for comparison of energy use. Describe and explain Energy Conservation Measures (ECM) that can be

implemented to use energy more effectively.

Provide a series of basic field testing procedures and measures that can be used tomaintain equipment at peak operating efficiency.

Energy Utilization Indices (EUIs) were developed to provide a measurement of howefficiently electrical energy is being utilized on the dairy farm. Values are commonlyexpressed in terms of kWh per cow-year, or kWh per hundredweight of milk cooled. EUIsprovide a management and evaluation tool that can be used for comparison of energy usepatterns on a specific dairy in relation to energy use on a representative group of dairies.

EUIs are useful for determining the overall efficiency of electrical energy use on a dairyfarm as well as individual processes or equipment. They provide a benchmark to indicatewhether energy use is in line with that on other farms. They can also offer insight on howelectrical energy is used, identify areas of excessive energy use, provide an indication ofeffectiveness from implementing energy conservation measures and to distinguish theimpact from adopting new technologies.

The following summary of EUIs for typical California dairies will provide you with typicalenergy use ranges for each of the major operations on the farm. They can serve as aguide to help you begin to make the most cost effective energy choices.


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Dairy Farm Energy Management Guide viii

Overall Farm EUI Typical Farm EUIs vary greatly depending on farm size, method ofhousing and milk harvest, utilization of energy conserving technology and extent to whichenvironmental factors (lighting, ventilation/air circulation, waste and material handling) aremodified through the use of electric technologies.

EUIs have been found to range from as low a 300-400 kWh per cow-year, to over 1500

kWh per cow-year. The lower values are found on large freestall, milking parlor dairiesthat use: High-efficiency milk cooling systems variable speed drive vacuum and perhaps milk pumps heat recovery, as this effects milk cooling high-efficiency lighting limited application of air circulation equipment less complicated waste handling systems efficient water heating (for electric water heating) efficient farmstead layouts effective cost control methods.

Farms with high EUIs generally indicate: smaller production units lower production efficiencies older, less efficient equipment

Larger Farm EUI values can also be attributed to: implementation of complex, integrated waste handling systems to comply with

current or future environmental regulations

extensive use of air circulation to reduce heat stress and maintain milkproduction levels

adoption of Long Day Lighting photoperiod manipulation to reduce seasonalvariations to milk production.

limited management focus on energy related issues.

On a dairy farm, however, careful thought needs to be given to each opportunity to saveenergy. Some energy conservation measures can save energy, but at a cost higher thanthe value of the energy saved. In the area of ventilation and air circulation, energy savingsmeasures could result in lower ventilation performance and greater animal discomfort. Insuch cases the dollars saved on energy could be insignificant when compared to the costof lost milk production.

The first, least cost way to save energy is to carefully maintain equipment at peak operatingefficiency. Worn, poorly maintained equipment uses more energy while not meetingoriginal performance specifications. When equipment is replaced, try to get the highestefficiency equipment available. However, sometimes the extra cost of higher efficiencyexceeds the payback realized from lower energy use. Take time to analyze thespecifications and make the most cost effective choices.


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Dairy Farm Energy Management Guide ix

Some of the basic processes found on dairy farms are discussed in more detail in aGeneral Information section. These include energy efficient electric motors, gas-firedabsorption heat pumps, heat exchangers, temperature monitoring, understanding pumpcurves, and variable frequency drives.

(return to top of Introduction: Introduction)(return to Table of Contents: Table_of_Contents)


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Dairy Farm Energy Management Guide 1

(return to: Table_of_Contents) 1. Milk Harvest

Section Contents: Purpose Equipment Vacuum pump

Energy Utilization Indices (EUIs) Energy Conservation Measures (ECMs) Operator Level Checks Glossary

Purpose Milk Harvest

The milk harvesting system is the most important technology used on a modern dairy andaccumulates more hours of use than any other piece of equipment. Careful design,

selection, installation, maintenance of this equipment is critical to optimal performance,efficiency and quality of milk harvest.

The milking process is responsible for quickly and efficiently harvesting the milk producedby the dairy herd 2 or 3 or more times per day, 365 days per year. A significant amount ofenergy must be expended to extract milk from the dairy cow and transport the milk to on-farm storage. The milking system is an assembly of separate components that areconnected together thru electrical and piping systems to perform the task above.

The centerpiece of the milking system is the vacuum pump and is the primary electricalenergy user. The vacuum pump operates whenever milking or washing the milking

equipment takes place, and on large modern dairies this can be 24-hour a day, 7-day aweek. Total energy used by the vacuum pump can comprise 26% of all electrical energyused on California dairies.

The vacuum pump produces a negative pressure to facilitate removal of milk from the cowand provides air movement that assists milk flow from the claw to the receiver. Presentlythere are four main types of vacuum pumps that are in use:

1. Sliding vane rotary pump2. Water-ring3. Rotary lobe type pump

4. Turbine

Each type of vacuum pump offers different advantages and drawbacks that require carefulconsideration when selecting. They also vary in their energy use characteristics and theiradaptability to energy conserving measures that should be taken into account.

(return to top of section: Milk_Harvest)


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Equipment - Vacuum Pumps

Sliding Vane Rotary Pump

The rotary vane vacuum pump is perhaps the oldest and most efficient type still being usedfor milking systems. This pump uses sliding vanes set in slots in a rotating shaft. With

centrifugal force, the vanes are forced outward against the housing. Oil lubrication forms aseal between the vanes edge and housing. Figure 1-1 below shows a cross section of thevane pump. Note that the center of rotation of the rotor is not at the center of the housing.

As the shaft and vanes rotate through one revolution, the volume between two adjoiningvanes varies from near zero to a maximum volume and back to near zero. Where thevolume in increasing, the air is sucked into the pump through the inlet. When the volume isdecreasing, the air is compressed and squeezed out of the pump into the outlet.

Figure 1-1. Sliding vane vacuum pump (Masport Vacuum Pump)

Lubrication of the sliding vane pump is crucial. This includes the vanes and the two endbearings. Two oiling systems are used. One could be termed passive and the other type isactive. The passive type would be a drip system where the oil rate is dependent on thevacuum inside the pump. When vacuum levels are low, say during the washing cycle,lubrication may be reduced. This may be during a time when lubrication is most needed. Toovercome this deficiency, a positive oiling system has been introduced.

Unfortunately, some of the oil used for lubrication becomes atomized and entrained in theair stream discharged from the pump. This is unacceptable if the oil is discharged to theatmosphere. Oil reclaimers were added to the exhaust to remove oil mist from the air. Thisoil can be re-used. However, some oil still escapes, often coating the ground andsurrounding surfaces.

OILER

OILER CROSS

ROTOR & SHAFTINCLUDES BEARINGS &

WING

OILER BRACKET

SEAL

PULLEY

END CAP

BALL BEARING (2)

BEAR COLLAR (2)

SCREW

PULLEY END

SET SCREWKEY

HOUSING


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Water Ring

The water ring or water seal vacuum pump is quite similar to the vane pump in principal butmuch different in operation. Instead of the sliding vanes pressing against the pumphousing, this rotor has rigid blades and the outer seal between these blades and the insideof the housing is a ring of water. These pumps are quiet and no oil is needed. The cross

section in Figure 1-2 shows the same offset between the center of the rotor and center ofthe housing.

Water becomes entrained in the exhaust air. This water must be removed before the air isdischarged to the environment. The recovered water can be either (1) disposed of andmake-up water added to the system or (2) recycled through a cooling device and returnedto the vacuum pump reservoir. Because of contamination of the water with milk and aircontaminants, this water must be changed periodically.

Figure 1-2. Water ring vacuum pump (Siemens)

The simplicity of the Seimens pump, alongwith its superior design characteristics,

ensure greater reliability and lower

maintenance expenses. I - The all stainless

steel rotor is cast with short, rigid blades,further strengthened by reinforcing rings at

both ends and a full length tapered hub. 2-

The design of the discharge and suctionports has an important impact on the

efficient operation of any water sealed

pump. The ports on the Seimens pump are

designed to compensate for motor size, and

vacuum levels required, through its

specially patented variable discharge portdesign. 3 & 4 Two flat port plates enclose

the rotor in axial direction. The clearances,maintained by separate thrust bearings,

keep the rotor in a properly centered

position.


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Rotary Lobe (blower) Pump

A more recently introduced vacuum pump is the rotary lobe that was first used as a blowerto deliver air, as the name implies, rather than developing a partial vacuum on the inletside. This pump has two rotating ductile iron shafts with two lobes on each shaft. An endview of the "shaft" resembles a figure eight. See Figure 1-3. These two shafts (impellers)

rotate in opposite directions with a pair of timing gears to maintain proper orientationbetween them. See cut away view in Figure 1-3. Because there is no contact between therotating impellers and the cast iron housing, no lubrication is needed in the pump. Thetiming gears at each end of the pump are generally lubricated with an oil bath and splashmethod. Seals prevent oil from entering the pump; thus, the discharge air from the pump isoil free. Close tolerances between the two impellers and the housing give high efficiencyand allow the pumps to develop vacuums up to 15 inches Hg.

Figure 1-3. Blower (lobe) vacuum pump (Kaeser Compressors, Inc.)

The high temperatures in the pump may cause milk, for instance, to dry on the internalsurfaces. Periodically this pump should be cleaned to maintain good performance. This isdone by admitting water on the inlet side. (Follow manufacturers recommendations).

Turbine

The turbine vacuum pump is the only one currently in use that is not a positivedisplacement pump. The turbine operates like a centrifugal pump or fan by using the massand momentum of the air to create a vacuum. Turbine vacuum pumps feature a high

temperature discharge that is free of oil. The turbine pump is the least efficient with anefficiency about half that for a vane or rotary lobe pump.

The turbine pump housing and turbine (impeller) are both made of aluminum. The impellerhas the characteristic shape of a turbine blade. See Figure 1-4. The rpm of the turbine ishigher than the other vacuum pumps with speeds up to 5,000 rpm listed in the literature.With two outboard bearings and no internal lubrication, the discharge air is clear of oil.Because of greater clearance between the turbine and housing, one might think that thecapacity would decrease faster with increasing vacuum than the vane pump. This does notseem to be the case.


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Figure 1-4. Turbine vacuum pump

Table 1-2 shows the distribution of vacuum pump types in California. The survey wasconducted by the University of California Cooperative Extension. Since the introduction ofthe variable speed drive for vacuum pumps there may have been a shift from water

Table 1-2 Distribution of Vacuum Pump Types

37% Oil vane25% Lobe/Blower27% Water Ring

9% Turbine2% Did not know

Source: UCCE Survey of 1997 of vacuum pump types Appendix E

ring to lobe/blower and from oil vane to lobe/blower because of the concern for oil beingdischarged into the environment.

In 1993 tests were conducted on various types of vacuum pumps as selected dairy farms inNew York State. The tests were conducted to measure the efficiency of the vacuum pumpsin terms of air delivery [cubic feet per minute (ASME)] per kiloWatt of input power while

operated at various vacuum level under farm conditions. The results of these test arepresented in Figure 1-5.


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Figure 1-5. A Review of Vacuum Pump Technology (David C. Ludington, Stanley A.Weeks)

The efficiency of all pump types decreases as the vacuum level was increased. Thisindicates that more efficient operation can be gained by operated at the lowest possiblevacuum level at the vacuum pump. This means operating that the lowest vacuum level atthe milking unit and minimizing the drop in vacuum between the milking unit and thevacuum pump.

Vacuum Pump Sizing

Correctly sizing the vacuum pump for the dairy allows the pump to meet the vacuum needsof the milking center during normal operation and washing and control energy operatingcosts. Current sizing guidelines (ASAE Standard S518.2 Feb03, Milking MachineInstallations Construction and Performance.) recommends the following:

Basic reserve of 35 cfm Incremental allowance of 3 cfm per milking unit Additional allowances for ancillary equipment such as milk meters, vacuum operated

automatic take-offs, etc.


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Providing vacuum pump capacity in excess of this guideline increases capital costs forequipment and life cycle energy operating costs. Oversized vacuum pumps are commonlyfound in existing installations for a number of reasons. Previous guidelines have specifiedpump capacities of up to 10 cfm per milking unit. Some current installations are also inexcess of this guideline with the belief that the extra vacuum capacity is needed to ensurean adequate wash.

The Washing and WaterHeatingsection of this guidebook provides instructions for tuningthe CIP process for effective cleaning and a vacuum demand that is less than is required tomeet the minimum effective reserve for milking.


Milk Harvest Energy Utilization Indices (EUIs)

The major energy user in the process of milk harvest is the vacuum pump. Delivery of acontinuous stable vacuum supply to each individual milker unit is critical to the milk harvestprocess.

Conventional vacuum systems relied on vacuum pumps that operated at full capacity and avacuum regulator to control airflow thru the milking system. Although effective at providingadequate milking vacuum, a large portion of the total vacuum pump capacity is neverutilized and is vented to the atmosphere by the regulator.

EUIs for conventional vacuum systems can easily range from 70 to 100 kWh per cow-yearand represent a significant portion of total electrical use. The conventional vacuum system

offered little if any means of controlling energy use.

Introduction of the variable speed drive (VSD) technology for controlling vacuum in amilking system has allowed for a dramatic reduction in energy use, while still producingequivalent vacuum stability. The VSD is able to adjust the rate of air removal from themilking system, by changing the speed of the vacuum pump motor; to equal the rate air isadmitted to the system at a given vacuum level. All of the energy used to move air throughthe conventional vacuum regulator is saved.

The EUIs achieved by VSD equipped vacuum pumps are reduced to 25 to 50 kWh percow-year. Energy operating costs are reduced by up to 60 % by running the vacuum pump

at reduced speeds.



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Milk Harvest Energy Conservation Measures (ECMs)

Efficiency of Vacuum Pump

When purchasing a vacuum pump buy the pump that:

has the highest relative efficiency (see Figure 1-5), that can be driven by a variable frequency drive, and do not oversize the vacuum pump.

Variable Frequency Drive for the Vacuum Pump

(Photo Courtesy of DeLaval) (Westfalia-Surge)

Figure 1-6. Variable frequency drive and drive installed on vacuum pump

Conventionally, vacuum pumps had operated at constant speed removing air from themilking system at a rate of 7 to 10 cubic feet per minute (cfm) per milking unit primarily toinsure good washing. Research in 1982 showed that the actual airflow was below 3.6cfm/unit 99 percent of the time. The difference between the air removed by the vacuumpump and what actually leaked into the system was admitted through a regulator. Therewas a common misperception that a larger vacuum pump capacity with greater horsepowerwas necessary to provide stabile vacuum levels and to insure proper cleaning.

Today there is a technology that can reduce the energy used by up to 60 percent. Thistechnology is called a variable frequency drive (VFD). The VFD is electrically installed

between the motor on the vacuum pump and the switch that currently controls the motor. Asecond device that monitors the vacuum level is installed in the vacuum line. This devicesends an electrical signal to the VFD that varies with vacuum level. The VFD comparesthis signal with the set point. As the actual vacuum level differs from the set point, thespeed of the motor/vacuum pump is changed to compensate for the change in vacuumlevel. If the vacuum is too low the motor will go faster and if the vacuum is too high themotor will be slowed. With a VFD, the air removed by the vacuum pump equals the airentering the milking system and there is not need for a conventional regulator.


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Advantages of Using a VFD:

Save Energy and Dollars The system can have a payback of less than 2 years.The savings depend on the hours the vacuum pump operates per day and the

amount the vacuum pump is oversized. Energy saving can be estimated by thefollowing:

Annual savings (kWh) = [Horsepower of presentvacuum pump 0.25 x no. ofmilking units] x 0.9 x Hours of operation per day x 365

Noise Reduction - The noise level can be reduced by many decibels.

Vacuum Pump Lasts Longer. The reduced RPMs of the vacuum pump reduceswear.

Stable Vacuum - With good design and proper installation, vacuum stability can bebetter than with a conventional regulator.

Figure 1-7. VFD vacuum pumps on California dairy


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Applications

Additional factors to consider for VFD application on the following types of vacuum pumps.

Sliding Vane Rotary Pump

The rotary vane pump is one of the most efficient vacuum pumps in use. Most vane pumpswork well on variable frequency drive - vacuum regulation with minimal efficiency loss atreduced speeds. Some vane pumps begin to rattle at low speeds because reducedcentrifugal force is not strong enough to hold the vanes firmly against the pump housing.Some vanes may actually move away from the housing and then move back producing arattle. Some vane pumps have springs in the rotor that force the vanes out against thehousing. These pump can be operated at a lower rpm without the rattle.

Special attention should be directed to the oiling system on the vane pump. Failure of anoiling jet can cause rapid failure of the pump. Oil discharge from the exhaust is one of thebiggest drawbacks to the vane pump. Oil reclaimers minimize the amount of oil discharged

but some oil vapors are still emitted. This oil vapor tends to condense and precipitate outof the air stream after it has exited the exhaust system, causing an oil film to form in thevicinity of the discharge. Water vapor is also present in the exhaust air. Oil reclaimers tendto condense and accumulate this water. Oil reclaimers need to be drained of waterregularly. The application of a variable speed vacuum regulator greatly improves theeffectiveness of the oil reclaimer and virtually eliminates the oily residue in the vicinity of thedischarge. The variable speed vacuum regulator also greatly increase the amount of wateraccumulated by the oil reclaimer.

When a vane pump is plumbed to a system as a backup to a main pump, extreme careshould be taken that no vacuum from the system and the main pump feeds back to thevane backup pump. Vacuum applied to a vane pump while it is not running will cause theoiling system to fill the pump with oil. A vane pump so filled will not start or run should itever be needed. Most slide type isolation valves leak too much air to prevent the pumpfrom filling with oil. A vent should be installed between the slide valve and the vane pumpto vent any air leakage past the slide valve. Care should be taken that gravity will not fillthe pump with oil either.

Rotary Lobe Type Pump

The rotary lobe pump is also a very efficient vacuum pump that works very well withvariable frequency vacuum regulation. The efficiency of the rotary lobe pump tends todecrease slightly faster at lower speeds than vane pumps. This is because the amount ofslip air through the close tolerances of the pump stays the same as the delivered airdecreases.

A 10 hp rotary lobe pump tested on a dynamometer required 2 hp input power to develop 4cfm at 14 inches of mercury. Since the discharge air is free from oil, heat recovery can beinstalled to reclaim heat from the discharge air. This reclaimed heat can be used topreheat water or it can be used for space heating.


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Water Ring Vacuum Pumps

The centrifugal nature of the ring of water limits the ability of the water ring pump to operatewith a variable speed regulator. Once the centrifugal force is insufficient to overcome thevacuum, the water ring distorts. This distorted ring can cause very high torquerequirements and overloaded motors, as water must be squeezed out of the rotor where

the ring is too thick.

The water ring pump also has a lower efficiency than the vane or rotary lobe pumps. Thecapacity and efficiency of the water ring pump varies with the supply water temperature andtherefore can exhibit wide performance fluctuations throughout the year. The low efficiencyand inability to operate with a variable speed vacuum regulator severely limits theopportunity for energy conservation with water ring pumps.

Turbine Vacuum Pumps

The turbine vacuum pump is the only one currently in use that is not a positive

displacement pump. The turbine operates like a centrifugal pump or fan by using the massand momentum of the air to create a vacuum. Turbine vacuum pumps feature a hightemperature discharge that is free of oil. The turbine pump is the least efficient with anefficiency about half that for a vane or rotary lobe pump.

Energy conservation measures with a turbine pump are limited to recovering waste heat forwater or space heating. The low efficiency has deterred attempts to apply a variable speedvacuum regulator to the turbine pump. There is a real concern that the high slip of acentrifugal pump will cause rapid overheating if the turbine pump is operated at a reducedspeed.

Regulator Location and Efficiency on Conventional Vacuum Systems

Conventional vacuum systems incorporate a vacuum pump operating at a fixedspeed/airflow, a vacuum regulator and a load. The load consists of the air admitted by thecomponents that make up the milking system including milking units, pulsators, claws,other device that admits air during operation and air leaks. To maintain a set vacuum level,the vacuum pump must remove air from the milking system at the same rate as air is beingadmitted

Since the air admitted is dynamic and the pump out rate is constant, a vacuum regulator isnecessary to admit the difference between the pump capacity and the air load. The typicalvacuum regulator is a mechanical device that adjusts the rate of air admission into thesystem. The vacuum regulator provides airflow into the system so that the sum of the airadmitted by the milking system plus the air admitted through the regulator exactly matchesthe fixed airflow at the vacuum pump.

When the air load is low, the regulator must admit nearly the entire pump capacity. Whenthe load increases the regulator must close and admit less air. The difference in vacuumlevel that occurs between the regulator in the fully open - full flow state and fully closedstate will be greater than zero. This is an inherent attribute of mechanical vacuum


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regulators. The National Mastitis Council (NMC) has established that a vacuum drop of 0.6inches of mercury below the stable vacuum level is acceptable to allow the regulator toclose.

To illustrate this, consider the following example. A water tank that has a constant out flowwith a float controlled input valve to maintain the water level in the tank. When the water

out flow is increased to a new gpm, the level of water in the tank will decrease. Loweringthe float and further opening the input valve. The new level of water in the tank will be thatpoint where the float valve is opened far enough to again balance the outflow. This newlevel will be lower than the original level because of the interval that occurs betweenopening of the input valve and establishing new outflow.

Regulator efficiency, as determined by the NMC test, measures how close to fully closedthe regulator is by the time the vacuum level drops to 0.6 inches of mercury below the setpoint. Regulators that fully close and admit no air before the vacuum level drops to 0.6inches of mercury below the set point are considered 100% efficient. Regulators that havenot fully closed at 0.6 inches of mercury below the set point are less than 100% efficient.

Regulator efficiency is determined by measuring the system airflow reserve at 0.6 inches ofmercury below the set point with the regulator operating (Effective Reserve) and dividingthis by the system airflow reserve at 0.6 inches of mercury below the set point with theregulator forced closed (Manual Reserve).

The location of the vacuum regulator has a significant impact on the regulator efficiencyand subsequently, the vacuum system efficiency. It has been common practice to locatethe regulator away from the receiver to minimize the noise in the milking parlor and to allowthe regulator to draw cleaner air that is freer of cow hair and dirt.

Installing the regulator in locations away from the receiver introduce losses that decreaseefficiency. Frictional head loss is the reduction of vacuum level due to the friction of theairflow within the pipe. Frictional head loss increases both with increased airflow and withincreasing resistance of the pipe. Long lengths of small diameter pipe with many elbowsand other fittings will have much higher resistance to airflow than a short length of largediameter pipe with no fittings. Frictional head loss between the regulator and the receivercauses the vacuum level at the receiver to be lower than the vacuum level at the regulator.

During periods of low airflow at the receiver, such as normal milking or group changes,there is little airflow between the receiver and the regulator. This low airflow causesminimal vacuum drop between the regulator and the receiver. In contrast, during periods ofhigh airflow at the receiver, such as unit attachment or unit fall off, there is a large airflowbetween the receiver and the regulator. This high airflow causes a larger vacuum dropbetween the regulator and the receiver.

The vacuum difference between the regulator and the receiver is then dependent on howmuch air is flowing through the receiver. A regulator that requires 0.6 inches of mercurybelow the set point to close fully will only achieve 100% regulator efficiency when thevacuum level is the same at the receiver as is at the regulator.

Consider what would happen to this regulator if there were a vacuum drop between theregulator and the receiver of 0.2 inches of mercury during peak airflow. By the time the


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regulator has dropped 0.4 inches below set point, the receiver has dropped the full 0.6inches. The regulator will still be admitting air to the system even though the receivervacuum drop exceeds the 0.6 inches of mercury standard. To improve the efficiency of theregulator it is necessary to reduce frictional head loss between the regulator and receiver.This is best accomplished by locating the regulator as close to the receiver as possible,thereby minimizing the resistance of the pipe between the regulator and receiver.

In addition to improving the vacuum regulation at the receiver, improving the regulatorefficiency also has a substantial energy saving potential. Minimum standards for effectivereserve are directed towards ensuring that the load (air flow) never, or very rarely exceedsthe vacuum pump capacity. Systems with low regulator efficiencies require more pumpcapacity to achieve the minimum effective reserve standard. A 20 hp pump operating witha 95% efficient regulator will have a higher effective reserve than a 30 hp pump with a 60%efficient regulator. High regulator efficiencies indicate the effective reserve and manualreserve are very close, and high volumes of air are not being introduced at the regulatorand pumped through the system.

Relocation of the vacuum regulator to provide better regulator efficiencies can allow beltsheave ratios to be reduced to slow the pump down and lighten the load on the motor andsave energy. A smaller vacuum pump and motor could also be used if conditions allow.

Improving regulator efficiency has the potential to save considerable money. Dairies payfor manual reserve in energy costs, oversized pumps, larger air lines and greaterinstallation costs. The return from that investment is the effective reserve. It is thereforehighly desirable to keep the effective reserve as close to the manual reserve as possible.This can only be accomplished with high regulator efficiency.

Variable Speed Vacuum Regulation

As was noted in the previous section, it is necessary for the air inflow rate of the vacuumsystem to exactly match the pump out rate of the vacuum pump in order to maintain thedesired vacuum level. When a pump operates at fixed speed and flow rate, this balancingof the inflow and pump out rate is accomplished by a vacuum regulator.

An alternative method of balancing the inflow rate with the pump out rate is to regulate thespeed of the vacuum pump. So that the pump out rate exactly matches the vacuum loadinflow rate. This control method eliminates the need to admit extra air through a regulator.

The energy savings attainable by implementing a variable frequency drive vacuumregulator are significant. Reducing the pump out rate by 50% reduces energy consumedby 50%. A typical milking system averages approximately hp of vacuum demand foreach milking unit. Using the current pump-sizing standard of 35 cfm plus 3 cfm per milkingunit to assure adequate reserve results in potential energy savings of 30 to 50%.

Consider the following example for a double 24-milking parlor. The pump size at 35 cfmplus 3 cfm per unit results in a 179 cfm pump. At 10 cfm per hp the smallest pump for thisparlor would be 20 hp. During operation the average vacuum demand of this parlor wouldbe equivalent to 12 hp or 120cfm.


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A conventional system with a vacuum regulator would supply 120 cfm of air to operate themilker system by having the regulator admit 80 cfm of air to balance the pump capacity of200 cfm. By applying a variable speed vacuum regulator, the average electrical demandand energy use for this parlor would be equivalent to 12 hp for a 40% savings. Olderstandards required even more vacuum capacity and systems with 10 cfm per milking unit

are commonly found on older parlors. Energy savings on these older systems can be ashigh as 80%.

Variable speed drive vacuum regulators consist of a sensing element, a controller, and avariable frequency motor drive. The sensing element is an electronic vacuum transducerthat converts the vacuum signal into an electrical signal for processing by the controller.The controller is a microprocessor-based computer that monitors the vacuum level signalfrom the transducer and determines the appropriate speed to operate the vacuum pump inorder to maintain the desired vacuum level. The controller contains the operator interfacewhere vacuum level settings and tuning parameters are adjusted.

The variable frequency motor drive is a device that converts standard line voltage at 60 Hzto a variable frequency and variable voltage output to drive a 3 phase induction motor. Byreducing the frequency and voltage supplied to the motor, the speed and the powerconsumed by the motor will be reduced. For a vacuum system, a motor running on a 30 Hzsupply will run at half its rated speed and will consume half of the normal energy. For moreinformation on variable frequency drives see the VFD section of this guidebook.

As with conventional, mechanical regulators, placement of the sensing element of avariable speed regulator is very important. The sensing element of a variable speedregulator consists of an electronic vacuum transducer and any plumbing needed to connectthe transducer to the vacuum system near the receiver. The sensing element should belocated as close to the receiver as possible noting the following limitations:

Vacuum lines carrying air away from the receiver typically get contaminated withwater, CIP residue, milk foam, and other contaminants. These contaminants mayaffect the sensing element and reduce the sensitivity of the vacuum regulator.Residue of CIP agents and milk can form a crust on the diaphragm of thetransducer, permanently reducing the sensitivity and accuracy of the transducer.

It is therefore recommended that the transducer be located a short distance from thevacuum line with a sensing tube from the transducer to the vacuum line. Thissensing tube should automatically drain any contaminants that may enter. Thereshould be no sags or other liquid traps that would inhibit the draining of the tube.

For short distances (less than 10 feet) a inch vacuum hose is adequate forconnecting the transducer to the vacuum line. For distances over 10 feet, inchpipe is recommended. PVC pipe works well for this sensing tube. A short inchvacuum hose connects the transducer to this sensing pipe. All points in this sensingtube must slope downwards towards an automatic drain, or back into the vacuumline.


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High velocity air in the vicinity of the sensing element interface causes turbulencethat can cause small errors in the vacuum readings at the transducer. Anyprotuberance into the airline causes turbulence. To minimize this turbulence, inserthose barbs or pipe adapters into the main airline as shallow as possible and squareto the main airline wall. Angled or very deep set fittings cause higher turbulence atthe end of the fitting and will result in vacuum reading errors, particularly at high

airflows.

For milking systems with two receivers, the main air lines that supply each receivershould be bridged together with the same size pipe as the main air lines. Thesensing point should then be inserted in the center of this bridge line. This line willexperience much lower air velocities and will provide a very accurate and responsivevacuum reading at the transducer.

The electronic control of a variable speed vacuum regulator does not require that thevacuum level drop in order to achieve full capacity. Therefore the regulator efficiency of avariable speed system should not be less than 100%. The electronic controller maintains

the vacuum level exactly at set point until the pump is running full speed. A variable speedvacuum control is capable of regulating vacuum level more precisely than a top qualitymechanical regulator.

High-speed acceleration and deceleration along with proper tuning assure that transientdemand fluctuations are quickly corrected for during the milking phase. Due to these highspeed acceleration and deceleration capabilities, the electronic controller of a variablespeed regulator should allow the vacuum pump to respond to fluctuations more slowlyduring the washing. Thereby minimizing stress on the pump, motor, belts, and VFDtransistors during air injected CIP cleaning when large vacuum demand fluctuations arenormal.



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Operator Level Checks Milk Harvest

Vacuum System

Vacuum Level

1. Check vacuum level with a quality gauge that is independent of any variable speedvacuum sensor. This gauge should be permanently mounted near the receiver orshould be easily connected to a test port near the receiver. Gauges permanentlyinstalled can suffer shortened life from contamination by moisture and residue carryover from the receiver and trap. Use of a test port valve to isolate the gauge exceptduring periodic vacuum level checks will reduce this contamination.

2. Vacuum levels that have drifted from desired value cause performance changes,efficiency changes, and herd health changes.

High vacuum levels cause injury to cow, higher air flow, higher power

requirements by the vacuum pump, and reduced vacuum pump capacity.

Low vacuum levels cause slow milk out and can cause health problems ifthere is inadequate collapsing of the liner during the rest phase of pulsation.

Variable Speed Vacuum Pump Operating Speed

1. Motor running faster than normal. Check for leaks; i.e. cracked pipes, joints, split liners, leaking gaskets on filter,

trap, receiver, milk line. Check for loose pump belts. This requires higher motor speed to reach the

same pump speed. Check system vacuum level. High system vacuum will cause higher pump

speed.

2. Motor running slower than normal.

This can cause performance problems if the cause of the low pump speed isplugged air vents or malfunctioning pulsators.

Check system vacuum level. Low system vacuum will cause lower pumpspeed.

3. Motor speed is erratic.

Variable speed vacuum sensor fouled or sensor line plugged or leaking. Split liner, cracked or disconnected pulsator tube, or faulty pulsator admitting

excessive air in cycles.


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Vacuum Pump Temperature

1. The vacuum pump temperature should be measured near the end of milking usingan infrared thermometer or adhesive temperature strip.

2. Small changes in end of milking temperature are normal when the ambient air

temperature changes.

3. A significant temperature rise usually indicates that service is required.

Check the system vacuum. Higher vacuum levels will cause higher pumptemperatures.

Check for exhaust restrictions. A restricted exhaust will cause higher pumptemperatures.

For rotary vane pumps, check that the oiling system is functioning properly. For lobe blower pumps, high temperatures can indicate a lubrication problem or

that the pump needs cleaning.

Vacuum Pump Motor Temperature

1. The vacuum pump motor temperature should be measured near the end of milkingusing an infrared thermometer or adhesive temperature strip.

2. High motor temperatures can indicate a high load on the motor or a problem with thesupply voltage to the motor.

The causes of high pump temperature will likely cause a rise in motortemperature as well.

Imbalanced or low line voltage and imbalanced motor currents will cause arise in motor temperature without a rise in pump temperature.

Cleaning Rotary Lobe Vacuum Pumps

Rotary lobe pumps accumulate residue from milk foam and wash chemicals on the rotorsduring normal operation. This accumulation must be removed periodically to maintain thetolerances in the pump. Pumps that have not been cleaned as required run hot and requiremore input power because of the friction of this accumulation.

Rotary lobe pumps are cleaned by introducing soap and water to the inlet of the pumpwhile the pump is running. Care should be taken to prevent a slug of water from enteringthe pump as this can destroy the pump. Allow the pump to run for a while after washing todry the rotors. Some milking equipment companies have introduced automatic controls toautomatically wash the pump on a regular basis.


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Other subcomponents in the milking system include:

Pulsation system Milking units Automatic detachers Milk transfer pumps Milk meters

Vacuum, milk, wash and pulsation lines Vacuum regulators and controllers Backflush systems Numerous configurations of milking stalls (herringbone, parallel, flat barns, swing,

tandem, and rotary parlors).

These components are low energy users compared to the vacuum pump. However, properoperation of these components is critical to the success of milk harvest.



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Glossary of Milk Harvest Terms

Air Injector: A device that allows the controlled, cyclic admission of air during cleaning andsanitizing to produce slug flow conditions.

Clean-in-Place (CIP): The capacity to clean the milking system by circulating appropriate

solutions through it without disassembly.

Distribution Tank: An air vessel or chamber, in the main airline between the vacuumpump or interceptor and the sanitary trap, which acts as a manifold for other pipelines.

Effective Reserve: Air flow rate, measured with all teatcups plugged and operating, thatcan be admitted at or near the receiver in pipeline milking machines to induce a vacuumdrop of 0.6" of Hg below the working vacuum level in the receiver. An indication of thereserve pump capacity actually available to maintain system vacuum when extra air isadmitted. (Based on the assumption that a vacuum drop of 0.6" has little or no effect onmilking performance and that I sufficient to allow the regulator to close

Manual Reserve: The air flow rate measured at the same position and conditions as foreffective reserve except that the regulator is disabled. This is the reserve pump capacityavailable, if the regulator could close completely at 0.6"below the working vacuum level, tomaintain the system vacuum when extra air is admitted through units during milking.

Milkline: A pipeline which carries milk and air during milking and has the dual function ofproviding milking vacuum and conveying milk to a receiver.

Milk Meter: A device between the cluster and milkline for measuring a cows milk yields ineither mass or volume.

Pulsator: A device for producing cyclic pressure changes.

Pulsator airline: The vacuum line connecting the main airline to the pulsators.

Pulsator Controller: A mechanism to operate pulsators, either integral with a singlePulsator (self-contained Pulsator) or system controlling several pulsators.

Receiver: A collecting vessel under vacuum that receives milk from one or moremilklines or milk transfer lines and feeds the receiver milk pump.

Receiver Milk Pump: A pump for removing milk under vacuum in the receiver, moving themilk through filters and inline cooling systems, and discharging to atmospheric pressure ina storage tank, refrigerated or non-refrigerated.

Regulator: An automatic valve designed to maintain a steady vacuum in a milkingsystem.Regulator Efficiency: The effective reserve expressed as a % of the manual reserve(ER/MR). Should be maintained at 90% and above.


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Sanitary Trap: The vessel between the milk system and the air system to preventmovement of liquid from one to the other.

Vacuum Pump: An air pump which produces vacuum in the system.

Variable Frequency Drive: VFD is a device that is installed on the motor of the

vacuum pump. The VFD controls the motor/pump speed to maintain a vacuum level setpoint. As vacuum level differs from the set point, the speed of the motor/pump is changedto compensate for the change in vacuum level. With a VFD, air removed by the pumpequals the air entering the milking system, and the vacuum regulator is eliminated. Energysavings are realized by not moving air thru the system that was admitted by the vacuumregulator.

Wash Pipeline: A pipeline which, during the CIP process, carries cleaning anddisinfectant solutions from the wash sink to the milkline. The wash pipeline is not usually inuse during milking.

(return to top of section: Milk_Harvest)(return to Table of Contents: Table_of_Contents)


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(return to: Table_of_Contents) 2. Milk CoolingSection Contents

Purpose and Cooling Standards Equipment

Energy Utilization Indices (EUIs) Energy Conservation Measures (ECMs) Operator Level Checks Glossary

Purpose and Cooling Standards Milk Cooling

The cooling process of milk produced on California dairy farms consumes the largestportion (30%) of total electrical energy used. The cooling of milk immediately after milkingis vital to maintaining high quality levels until processed for fluid consumption or used tomanufacture other dairy products.

The Grade A Pasteurized Milk Ordinance, 2001 Revision states:

Raw milk for pasteurization shall be cooled to 10C (50F) or less within 4 hour or less, ofthe commencement of the first milking, and to 7C (45F) or less within two (2) hours afterthe completion of milking. Provided, that the blend temperature after the first milk andsubsequent milkings does not exceed 10C (50F). [www.cfsan.fda.gov/~ear/pmo01-3.html]

The 3-A Sanitary Standards for Farm Milk Cooling and Holding Tanks, Number 13-10 is asecond standard that deals with cooling milk on dairy farms. Section E1.1 deals withcooling. This standard states:

Cool the product to 50F (10C) or less within 4 hours or less of the commencement of thefirst milking and to 40 F (4.4 C) or less within 2 hours after the completion of milking.Provided, that the blend temperature after the first milking and subsequent milkings doesnot exceed 50 F (10 C).

In California the milk temperature must be cooled to 50F prior to pickup. However, milkthat is shipped out of state must be cooled to 45F. Since there is some uncertainty aboutfinal destination of the milk that leaves the farm, most CA dairy farmers cool their milk to45F. For the purposes in this Dairy Farm Guidebook, the assumption will be made thatmilk will be cooled to 45F and the blend temperature, where applicable, will not exceed50F

Since milk harvested from the dairy cow is typically 99 F and will be stored at 45 F, thetemperature must be reduced 54 F. To reach this temperature roughly 50 Btu of heat


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must be removed per pound of milk. [Assumes the specific heat of milk to be 0.93 Btu/lb,F] Some of this heat may be lost as the milk travels from the cow to the cooling system.The amount of heat lost will depend on the milking system and the ambient air temperature.Because there is a possibility that no heat may be lost due to high ambient airtemperatures, the cooling system should be designed to remove all this heat.

Two types of milk cooling systems are used on California dairy farms. They are:Direct expansion refers to a system where the evaporator plates are incorporated in thelower portion of the storage tank in direct contact with the milk. Liquid refrigerant boils[expanding] inside the evaporator thus the name direct expansion. Milk cooling takesplace within the tank. One or more agitators move the milk over the evaporator plates forcooling. There is a limit to the size of refrigerated milk cooling and storage tanks due tostructural issues. There is also a limit to the refrigerated surface area. The ability toremove heat from the milk fast enough [Btu/hr] to meet cooling requirements with high milkloading rates is not possible without reducing evaporator surface temperature to the pointwhere freezing of milk may occur. This is particularly challenging when milk temperaturesapproach 38 F. Agitating warm milk for long periods of time can also be detrimental to

milk quality.

Generally, this milk cooling system cannot cool the milk as fast as the milk enters the tank.There must be time between milkings such that the cooling system can catch-up and coolthe milk to 45 F. With cows being milk up to 22 hours per day, this cooling system cannotbe used.

Instant cooling is where the milk cooling is completed external to the storage tank or siloand then pumped into storage. An intermediate cooling fluid, such as chilled water from anice builder or a glycol-water mixture from a chiller is used to cool milk rapidly in a heatexchanger rather than direct expansion. Theoretically there is no limit to the surface areain a heat exchanger, only economical and practical limits.

The trend towards larger milking herds, greater milk production per cow and larger moreefficient milking parlors [cows per hours] has increased milk flow rate [gal/hr], with largevolumes of milk to be cooled within a 24 hour period. The instant cooling system is notlimited by the amount of surface cooling area in the storage tank or silo. This is the mostcommon cooling system on larger California farms in spite of slightly less efficiency due tolower evaporator temperatures and pumping energy required to move the intermediary fluidthru the heat exchangers.

Refrigeration Cycle

A mechanical refrigeration cycle is nearly always used to either cool the milk directly orindirectly via an intermediate cooling fluid. The basic mechanical refrigeration system isshown in Figure 2-1. The system consists of a motor driven compressor that compressesthe cold refrigerant gas returning from the evaporator so that the refrigerant can becondensed at high temperature. The high pressure - high temperature gas from thecompressor flows to the condenser where the refrigerant is de-superheated and condensedby transferring heat to a cooling medium, usually air and/or water. The high- pressureliquid from the condenser will be a few degrees warmer than the cooling medium. This


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liquid is then metered thru a thermostatic expansion valve into the low- pressure evaporatorthat is in contact with milk (direct expansion), water (ice builder) or glycol-water solution in achiller. Here the liquid refrigerant boils at low pressure and temperature absorbing heatfrom the milk, water or glycol-water. The low-pressure vapor is removed from theevaporator by the compressor where the vapor is again compressed and the cycle iscompleted.

Figure 2-1. Schematic of a Mechanical Refrigeration System

The efficiency of a refrigeration system is given in terms of an EER [Energy EfficiencyRatio] where the units are Btu (cooling effect) per Watthour of energy input. There aremany factors that impact EER. One factor deals with the relationship between the highside and low side pressure. EER will decrease as the difference between these twopressures increases. To maximize EER the low side pressure needs to be kept as high aspossible and the high side pressure kept at low as possible. These factors need to beconsidered when selecting the refrigeration equipment. Other factors will be discussedlater.

An assortment of energy conserving measures exists to improve the overall efficiency ofmilk cooling systems. More discussion of their application will be presented later.

(return to top of section: Milk_Cooling)


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Equipment Milk Cooling

Compressors

The most common refrigeration compressor found on dairy farms today is the reciprocating.

Reciprocating compressors can be either open type, hermetic or accessible hermetic. Theopen type has the drive unit external to the compressor. Power would generally betransmitted from the drive unit [motor] to the compressor by V-belts. The hermetic type hasthe compressor and motor in a common sealed housing. The seal is generally a weld. SeeFigure 2-2. The motor operates in a low- pressure atmosphere of the refrigerant.

Figure 2-2. Hermetically sealed reciprocating compressor (Copeland)

The accessible hermetic unit is similar except the housing is bolted together in a single unitrather than welded. The motor and compressor are accessible. See Figure 2-3. In somecases the low pressure - low temperature refrigerant passes over the motor.

Figure 2-3. Accessible reciprocating compressor (Copeland)


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Condensers, Air- and Water-Cooled

The purpose of the condenser is to desuperheat and condense the refrigerant gas byremoving the sensible superheat, the latent heat of condensation and sensible heat tosubcool the liquid. There are two major types of condensers; air-cooled and water-cooled.If the condenser is an integral part with the compressor on a common platform, the unit is

called a condensing unit. Condensers may also be mounted remote of the compressor.

The air-cooled units are similar to a car radiator. The refrigerant gas flows through finnedtubing and air is moved over the fins perpendicular to the tubing to remove heat from thegas. The contact time between the air and the fins is short. The capacity of an air-cooledcondenser is determined by the area of the fins, the velocity of the air across the fins, and amean temperature difference between the air and refrigerant. Air-cooled condensers canbe either an integral part with the compressor on a common platform or remove. Anexample of a remote air-cooled condenser is show in Figure 2-4 as installed on a dairyfarm.

Figure 2-4. Remote air-cooled condenser

A water-cooled condenser operates under the same principles as an air-cooled condenserexcept water is the coolant. Water-cooled condensers are generally smaller in size andoffer a higher EER than air-cooled condensers. There are several reasons.

The heat transfer coefficient [Btu/ft2, F, hr] between the metal surface of the exchanger andwater is greater than that for air. This coefficient describes the heat transfer [Btu/hr] foreach square foot of surface area and the mean temperature difference [F] between therefrigerant gas and the cooling media. This means that for the same temperaturedifference, the surface area of a water-cooled condenser will be smaller than the air-cooledcondenser. This generally means the size or footprint is less. This also means that thetemperature difference can be smaller with the same surface area, which helps maintain ahigher EER.


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Water is a better carrier of heat than air. On an equal volume basis, water will absorb3,500 times as much heat (Btu) for the same rise in temperature. This means that a muchgreater volume of air is required than water to remove the same amount of heat from thecondensing refrigerant.

The airflow in an air-cooled condenser is perpendicular to the flow of refrigerant. This

reduces the contact time between the air and the condenser surface thus requiring greaterface area. This is not true in a water-cooled condenser.

Water-cooled shell and tube condensers are commonly used on dairy farms. A crosssection of such a heat exchanger is shown in Figure 2-5 along with a complete unit. Theunit shown has a removable core for cleaning. Generally the cooling water flows throughthe tubes and the condensing refrigerant gas is in the shell. The unit shown is a 2 tubepasses with baffles in the shell to reduce short-circuiting and increase turbulence of therefrigerant. Condensed refrigerant collects in the bottom of the shell.

Figure 2-5. Example of a shell and tube water-cooled condenser (StandardRefrigeration)

An assembly of a compressor and condenser plus associated controls and equipment iscall a condensing unit. Three condensing units are shown in Figure 2-6. These units havea water-cooled condenser mounted underneath an accessible hermetic compressor. Thewater pipe connections can be seen on the end of the condenser. The flow of waterthrough the water-cooled condenser is generally controlled by pressure controlled watervalve.


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Figure 2-6. Water-cooled condensing units with accessible hermetic compressors

The flow control valve can be seen between the right end of the water cooled condenserand the galvanized water pipe. The control is connected to the high-pressure side of thecompressor. The purpose is to maintain a constant head pressure.

Thermostatic Expansion Valve [TEV]

This type of expansion device is often used on refrigeration system for milk cooling. Thedevice functions as a restrictor and flow regulator. There is considerable pressure dropacross this restriction separating the high-pressure side condenser from the low sideevaporator. The refrigerant flow through the TEV is controlled such that the refrigerant gas

leaving the evaporator will have a few degrees of superheat. This insures that no liquidrefrigerant enters the compressor. [The sensing bulb for the TEV is identified in Figure 2-1.] The sensing bulb contains a small amount of refrigerant, the same refrigerant as in thecooling system, so the pressure in the bulb is the same as the pressure in the return pipefrom the evaporator. The sensing tube provides feedback to the TEV.

Evaporator

The evaporator is that section of the refrigeration system where the liquid refrigerantevaporates or boils at low pressure and temperature, absorbing heat from the surroundings

space. For milk cooling, the evaporator may be a part of the bottom of the milkcooling/storage tank [direct expansion] or a chiller, where an intermediary fluid, such aswater or a water-glycol solution, is employed to transport heat from the milk in a plate heatexchanger to the evaporator of the mechanical refrigeration system.


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Direct Expansion

This system cools the milk directly in the milk storage tank. The lower section of the tank isthe evaporator. There is a chance that the milk can be frozen at the evaporator if theevaporator temperature is too low and there is insufficient mixing of the milk that allows themilk to remain in contact with the evaporator too long.

Indirect or Instant Cooling: Here an intermediary fluid, such as water or a water-glycolsolution, is employed to transport heat from the milk to the evaporator. The chiller generallyworks in conjunction with a dual stage plate cooler. Well water is used in the first stage ofthe plate cooler to reduce milk temperature to within 5F of input water temperature. Thechiller provides 28-34 F water propylene glycol solution to the second stage of the platecooler. When milk enters the second stage of the plate cooler, chilled solution from thechiller instantly cools the milk to 38 F. The milk enters the bulk tank or silo completelycooled.

Generally, instant chilled water/glycol cooling systems are slightly less efficient than direct

expansion systems. The reason for the lower efficiency is the lower suction pressure toachieve lower evaporator temperatures inherent to instant cooling systems and thepumping energy required to move the water/glycol thru the heat exchanger. The lowertemperatures and short heat transfer period along with pumping energy cause the instantcooling system to use more energy per hundredweight than a direct expansion system.

A schematic diagram of an instant cooling system using a one-pump (coupled) system isshown in Figure 2-7.

Figure 2-7. Instant milk cooling system with a coupled, one pump system

Having a single circulation pump requires careful sizing of the evaporator chiller and milkplate heat exchanger because each will have the same flow rate [gpm]. The two heatexchangers [evaporator and milk cooler] are coupled. Manufacturers of plate heatexchangers usually recommend that the coolant flow rate be 2 to 3 times the flow rate ofproduct being cooled.


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A better practice may be a decoupled system where two pumps are used, one for theevaporator and a second for the plate heat exchanger. Such a system is shown in Figure2-8. Here the two pumps can be sized individually to optimize the performance

Precooler

Warm

Milk

ColdMilk

FinalCooler

ColdWater

WarmWater

Compressor

Chiller

Evaporator

Condenser

Glycol -Water

Pump 2

Water-GlycolStorage

Pump1

Return Water-Glycol

Figure 2-8. Instant milk cooling system with decoupled, two pump, system

of the evaporator/chiller section and the final plate heat exchanger. With this system thereis also an opportunity to have two feedback control loops; one to maintain the correcttemperature of the water-glycol storage and second to achieve proper temperature of thecooled milk.

The evaporator on a cooling system could be the cooling plates in a falling film chiller.Examples of a falling film chiller and a single plate are shown in Figures 2-9 and 2-10. Thefalling film chiller consists of a series of plates arranged vertically, the number of platesbeing determined by the required cooling capacity. These plates can be seen in Figure 2-9.

(Photo courtesy of DeLaval)

Figure 2-9. Falling film chiller showing vertical plates and a view of a plate


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The warmed water/glycol solution from the plate cooler enters the top of the chiller cabinetand empties into a distribution pan, which is suppose to evenly disperses the solution overthe vertical cooling plates. Achieving this can be a challenge. A thin layer (film) of solutioncascades (falls), thus the name falling film chiller, down each side of the refrigerated plateand falls into an insulated reservoir located the base of the unit, where it will be returned tothe plate heat exchanger. Falling film chillers are generally associated with coupled

systems, one circulating pump.

Generally two plates would be connected to a single condensing unit. Referring to Figure2-10, the six white (frost covered) pipes are attached to six vertical plates. Each pipe isserved by a thermostatic expansion valve with the sensing bulb attached to the exit pipefrom that same plate [liquid refrigerant enters at the bottom and gas exits at the top of theplate]. The three drier/filters each serve one condensing unit and two plates.

Figure 2-10. Falling film chillers showing refrigerant connections

There are alternative evaporators that generally associated with a decoupled coolingsystem. For this arrangement the water-glycol would be stored in a separate tank. Twotypes will be presented. These units have a much smaller foot print that the falling filmchiller

The first is a chiller barrels. A chiller barrel can be different shapes and sizes. An exampleis shown in Figure 2-11.

3 electric solenoid valves

3 refrigerant driers

6 thermostatic ex ansion valves

6 sensin bulbs

2 chillers


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Figure 2-11. Chiller Barrels (TX from Standard Refrigeration Co.)

This chiller barrel is similar in constructed to a shell & tube heat exchanger discussedearlier as a water cooled condenser. This chiller does not have to be coupled to the milkplate heat exchanger so that both units need not be sized to function at the rated capacitywith the same coolant flow rate (gpm). .

A second alternative is the brazed heat exchanger. These units are similar in function tothe single pass plate heat exchangers used to cool milk that will be discussed next.

However, these units do not have gaskets between the plates and they cannot be opened,the unit is welded shut. An example of a brazed heat exchanger is shown in Figure 2-12.

Figure 2-12. Brazed plate heat exchanger; a complete unit and an expanded view (FlatPlate)

Because of their design these units are more compact and have a smaller foot print thaneither falling film or chiller barrels. These units can be used for direct expansion. Thebarrel chillers and the brazen heat exchangers are more likely to be used on the decoupled

system. The system pictured in Figure 2-13 is a decoupled system with barrel chillers andscroll compressors. The diagram in Figure 2-14 shows the decoupled - two pumps system.


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Figure 2-13. Decoupled or two pump system (Kool Way by WestfaliaSurge)

Figure 2-14. Flow diagram for Kool Way by WestfaliaSurge

CHILLER BARRELS

SIGHTGLASS

PROCESSPUMP

CIRCULATIONPUMPACCUMULATOR

AIR-COOLEDCONDENSER

LIQUIDLINE DRYER

PROCESSSUPPLY

FLOW SAFETYSWITCH

REFRIGERANTBALL VALVE

SOLENODVALVE

TEMPERATURESENSOR

PROCESSRETURN

COMPRESSOR


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The circulation pump operates whenever the refrigeration system is operating. Therefrigeration system is controlled by the temperature of the LowTemp tank. The processpump runs continuously with no feedback control.

Milk Cooling Heat Exchangers

The heat exchangers used for cooling milk are made of stainless steel and are designed tobe opened for cleaning. A well-water-cooled heat exchanger that partially cools the milkprior to entering a direct expansion cooling system or an instant cooler has been availablefor over 20 years. Today this energy conservation measure [ECM] is standard equipmenton larger farms. For instant milk cooling systems this precooler is the first section of alarger plate heat exchanger with final cooling occurring in the second section.

Well Water Partial Cooling

The use of a well water-cooled plate or shell & tube heat exchanger to precool milk prior to

the milk entering a refrigerated milk tank or a final plate heat exchanger is common.Earlier, shell & tube or double tube heat exchangers were commonly used. More recentlyplate type heat exchangers have become dominant.

There are three major configurations of a plate heat exchanger. The configuration shownin Figure 2-15 is a single pass unit. Here the two fluids are in contact [on either side of aplate] as the fluids make one pass between the plates.

Product Out

Single PassWater Out

Product In

Water In

Figure 2-15. SinglePass plate heat exchanger

The flow pattern in Figure 2-15 is a counterflow configuration, the coolant and milk flow inopposite directions, the cold water input is next to the cool milk out. All heat plateexchanger should be installed with counterflow. This flow pattern has a higher meantemperature difference and a greater effectiveness than parallel flow.


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A dual or double pass heat exchanger is more effective than a single pass unit. Here theproduct makes two passes so that the product is in contact with the coolant twice as long,assuming all other factors are equal. See Figure 2-16.

Water Out

Product In Product Out

Water In

Product

Drain

Dual Pass

Figure 2-16. Dual pass plate heat exchanger

The comparison between single and dual pass plate heat exchangers is shown in Figure 2-

17. The graph shows the relationship between the number of plates and the expectedtemperature drop in the milk with single and dual pass plate heat exchangers. The ratio oflow rate between the milk and cooling water was 1:1. There are three data points for thesingle pass unit. A linear projection of those three data points was made to estimate thetemperature drop for a single pass exchanger unit with more plates. Two data points areplotted for a dual pass unit. If both types had 32 plates, the expected drop in temperaturefor the single pass unit would be 25 F and slightly over number of plates and temperaturedrop 28 F for a dual pass unit. For the same number of plates, a dual pass is moreeffective that a single pass.

16

18

20

22

24

26

2830

32

34

10 15 20 25 30 35 40

Number of Plates

TemperatureDrop,

F

Single Pass, actual

Single Pass, projected

Dual Pass

Figure 2-17. Relationship between number of plates and temperature drop

The third configuration for a plate heat exchanger is the two-stage. Figure 2-18 shows theflow configuration for this unit. This unit is equivalent to two single pass units jointedtogether. One section is used for precooling with well water and the second section is forfinal cooling with chilled water or glycol-water solution. This unit is common on Californiadairy farms.


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Water Out

Product In Product Out

Chilled

Water In

Product

Drain

Two Stage

Water In Chilled

Water Out

Figure 2-18. Two stage; well water precooler and chilled water or water-glycol finalcooling)

The effectiveness of a heat exchanger is also dependent on the ratio of flow [gpm] betweenthe product and the cooling media. A higher coolant flow rate provides a greater meantemperature difference between the milk and coolant and a higher coolant velocity between

the plates that increases the heat transfer coefficient. Most manufacturers recommend atleast a ratio of 2, water flow twice the milk flow.

The data for the graphs shown in Figure 2-19 were taken from manufacturers literature todemonstrate the impact of coolant flow on the exit milk temperature. The milk flow from themilk pump on a receiver is intermittent. When the level of milk in the receiver reaches theupper probe, the pump starts. The milk flow could be at least 25 gpm for a few secondsand then stop for perhaps a minute. Tests on two conventional receiver pumps in a doubleparlor showed that the average milk flow rate during milking was about 12 gpm. Bothreceiver pumps operated 26 percent of the time, meaning that the average flow rate of milkwhen a pump was operating was 44 gpm. To achieve a recommended flow ratio of 2, the

chilled coolant flow rate while the milk pump was operating must be 88 gpm which difficultto achieve on a dairy farm.

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Coolant Flow Rate, gpm

MilkExitTemperature,

F

Tci = 55F

Tci = 65F

Tci = 75F

Figure 2-19. Impact of coolant flow rate on exit milk temperature for three coolant

temperatures (Tci), inlet milk temperature = 98F, intermittent milk flow = 35 gpm,coolant flow while milk pump is operating, low flow between cycles.



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Milk Cooling Energy Utilization Indices (EUIs)

The EUI for milk cooling with a well maintained cooling system and no energy conservationmeasures averages between 0.8 and 1.2 kWh/cwt [hundred weight] of milk cooled. Thereare two EMCs that can be employed. They will be described in the next section. As ECMsare added, the EUI will decrease. Partial cooling the milk with a well water precooler will

save 0.2 to 0.3 kWh per cwt milk cooled. Installing a variable frequency drive will lower theEUI an additional 0.2 kWh per cwt milk cooled. The actual reduction in energy use will bedependent on well water temperature, water flow and the effectiveness of the VFD toreduce the milk flow through the heat exchanger.


Milk Cooling Energy Conservation Measures (ECMs)

There are several measures that can be implemented that will reduce the energyconsumed to cool milk. Some of these were mentioned above.

Precoolers

Well water-cooled heat exchangers partially cool milk prior to the milk entering therefrigerated storage tank or a second heat exchanger for instant cooling. This practice wasdiscussed earlier because the practice has been widely accepted and in manyareas has achieved 100 percent market penetration.

Variable Frequency Drives [VFD] For Milk Pumps

As stated earlier, under conventional practice, the flow rate (gpm) of milk from a receiver isnot uniform. The flow of milk during milking from the milk pump will vary from zero to 25 -50 gpm. In a milking parlor with two milk pumps, the pumps may operate 10 to 25 percentof the time while the cows on one side of a parlor are being milked. This means that thereis no milk flowing through the heat exchanger 75 to 90 percent of the time and the flowduring the other 10 to 20 percent of the time will be high. This is not an efficient way tooperate a heat exchanger. On the well water or chilled water-glycol side of the heatexchanger the flow needs to be 50 to 100 gpm for that 10 to 20 percent of the time. This tois difficult.

To help alleviate this problem, a variable frequency drive can be applied to the milk pump.The concept here is to slow down the flow of milk from the receiver so that the milk pumpoperates a higher percentage of the time. This means the flow of milk through the heat

Milk cooling system EUI, kWh/cwt cooledConventional 1.2 0.8Well water precooler 0.9 0.6Well water precooler with VFD onreceiver pump

0.7 0.4


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exchanger will be lower and more continuous. Both factors improve the effectiveness ofthe heat exchanger.

Control for the variable frequency drive is generally a series of magnetic reed switchesmounted inside a hollow stainless steel pipe [probe] mounted vertically near the center ofthe receiver through the Plexiglas cover. Depending on the length of the probe, two to four

reed switches are positioned along the probe at appropriate locations. Stainless steelfloats that hold a magnet fit around the probe and are held positioned along the probe atthe same location as the reed switches. The floats are held in place by clips on either sideof the float. When the float with a magnet floats up to the reed switch the switch eithercloses or opens depending on the logic being used. When the float leaves the switch theswitch returns to its initial position.

Using a binary code, the frequency output from the VFD and thus the speed [rpm] of thereceiver pump can be controlled by which reed switches are closed [one] and which onesare open [zero]. The VFD can be programmed to provide different speeds depending onthe position of the floats. When the top reed switch is activated the VFD generally goes to

60 Hz for full speed of the milk pump. When the lowest switch is activated as the milk risesin the receiver, the pump will start at the lowest preset speed giving the lowest milk flow.The goal is to have the pump operate at the lowest speed for the greatest percentage ofthe time.

One needs to be careful when setting this lowest speed. Nearly all receiver milk pumps arecentrifugal [variable delivery, delivery varies with total head and rpm] as opposed topositive displacement pumps where delivery is nearly linear with speed and within reasonunaffected by discharge pressure. Centrifugal pumps experience shut-off head. At acertain combination of total head [pressure] and pump rpm, the flow from the pump stops.The total head is the sum of the suction head, between 12 and 15 inches of Hg, anddischarge head that includes the vertical height to the discharge point or height of milk in asilo, the pressure loss in the filter, the friction of the heat exchanger and piping.

The curves shown in Figure 2-20 illustrate the performance of a 4-blade impeller milkreceiver pump driven at different speed with a VFD. A vacuum of 13 inch Hg wasmaintained in the receiver. The pump had considerably different characteristics duringspeeding up and slowing down. With 13 inch of vacuum the shut off head occurred at 42Hz, or 2,400 rpm for a motor rated at 3,450 rpm.

The first seven data points in Figure 2-20 are plotted on the graph in Figure 2-21. Thesensitivity of the pumping rate to pump speed is significant. When speeding up, a changein pump speed of 10 Hz or about 600 rpm made little difference in flow rate. However,when the pump was being slowed down by the VFD, the flow rate decreased from 14 to 0.6gpm for the same change of 600 rpm. Setting the preset speeds on a VFD for any milkpump must be done with care.


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Figure 2-20 Characteristics of a 4 Blade Impeller Milk Pump with a VFD

Another issue that should be considered is the agitation of the milk inside the milk pump atlower speeds. When the pump is operating at full speed (the impeller was turning at 3,450rpm) the delivery rate was about 20 gpm. For every gallon of milk delivered the impellerturned 172 times. At low speed the delivery was less than 4 gpm but the speed was 2,400rpm. Now the impeller turned 600 times per gallon or more that three times the agitation.The impact of this additional agitation has never been studied.

0

2

4

6

8

10

12

14

16

40 42 44 46 48 50 52 54

Pump Speed, VFD Frequency, Hz

MilkFlowRate,gp

Speeding Up

Slow ing Dow n

Figure 2-21 Enlargement of a Portion of Figure 2-20

0

5

10

15

20

25

35 40 45 50 55 60 65

Milk Pump Speed, VFD Frequency, Hz

FlowRate,gpm

Speeding Up

Slow ing Dow n


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Scroll Compressors

Two new classes of compressors, the scroll and discus are now being introduced for milkcooling on dairy farms. These new compressors are both more efficient. The scrollcompressor utilizes two identical scrolls, one fixed and the second rotating within the fixedscroll. Because the scroll compressors operate in a circular motion, have fewer moving

parts and no intake or discharge valves, there is less vibration and less noise.

Figure 2-22. Scroll Compressor (Copeland)

A study comparing a scroll compressor with a reciprocating hermetically sealed compressoron a direct

Documents

CompleteGuide_102005REV