DISCLOSURE

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS GUIDEBOOK WAS PREPARED BY THE IRC. NEITHER THE IRC, NOR ANY PERSON ACTING ON BEHALF OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS, OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS OR SIMILAR ITEM DISCLOSED IN THIS GUIDEBOOK, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THE CONTENTS OF THIS GUIDEBOOK IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF THE IRC OR ANY IRC REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM THE USE OF THE CONTENTS OF THIS GUIDEBOOK OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS GUIDEBOOK.

THIS REPORT IS A COPYRIGHTED PUBLICATION AND ITS CONTENTS SHALL NOT BE REPRODUCED OR DISTRIBUTED WITHOUT PRIOR WRITTEN PERMISSION FROM THE IRC.

ORGANIZATION(S) THAT PREPARED THIS REPORT – INDUSTRIAL REFRIGERATION CONSORTIUM (IRC) AT THE UNIVERSITY OF WISCONSIN-

MADISON

FOREWORD

Industrial refrigeration is essential for the production of many food products

consumed in the world today. Although it is an inherently energy-intensive

process, careful application of engineering principles in design and operation can

lead to significant improvements in both capacity and efficiency.

Energy is a fundamental commodity that fuels and sustains the growth and

prosperity of mankind. As demand increases and the finite energy resources of

our planet are depleted, the value of energy in the future will continue to

increase. In the U.S. today, the true cost of energy is not reflected in the price to

consumers, though many other countries have moved to price the commodity in

accordance with its value. In any case, energy prices in the U.S. are increasing

faster than inflation and one can reasonably expect the cost of energy to

continue rising in the future as finite energy reserves deplete. This trend is

driving end-users to improve the efficiency of energy intensive operations such

as industrial refrigeration systems.

This Guidebook is intended to provide refrigeration plant operators, engineers,

and managers with the information they need to improve the energy efficiency of

their industrial refrigeration systems. This Guidebook is intended to be a "desk

reference" to help those responsible for refrigeration systems achieve these

improvements. Much of our focus on preparing this Guidebook has been on

uncovering and presenting proven approaches that result in improvements in

refrigeration system capacity and energy efficiency. We have also dedicated

considerable space to discussing the barriers that commonly block

implementation of the efficiency improvement strategies presented.

Understanding these barriers is a first step toward removing them and clearing a

path for success.

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Industrial Refrigeration Energy Efficiency Guidebook iv

The contents of the Guidebook are included in seven chapters.

• Chapter 1 – Introduction

The rationale for pursuing energy efficiency improvements is presented

and discussed in Chapter 1.

• Chapter 2 – Overview of Systems and Equipment In this chapter, we review the operation and performance characteristics

of major energy consumers in industrial refrigeration systems. We also

review common arrangements of industrial refrigeration systems.

• Chapter 3 – Evaluating Refrigeration System Performance Because industrial refrigeration systems tend to be “one-of-a-kind”

systems, it is difficult to know whether or not a particular system is

efficient. In Chapter 3, we present principles and guidelines for

characterizing the baseline performance or efficiency of a refrigeration

system. The baseline then serves as a measure of comparison for post-

implementation performance.

• Chapter 4 – High-Side Efficiency Improvements

In Chapter 4, we focus our attention to the high-pressure side of industrial

refrigeration systems and look for strategies that provide efficiency

improvements. The chapter covers both operational issues such as head

pressure control as well as design issues that include condenser selection

and piping.

• Chapter 5 – Low-Side Efficiency Improvements In Chapter 5, we consider the low-pressure side of systems and present

techniques to improve the efficiency of systems. Again, the chapter

covers both operational issues and design issues.

• Chapter 6 – Compressors Because compressors are the major energy consumer in industrial

refrigeration systems, many consider them the “heart of the plant.” It is for

this reason that we elected to dedicate an entire chapter to compressors.

Our coverage includes both reciprocating and screw (single and twin)

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Industrial Refrigeration Energy Efficiency Guidebook v

compressor technologies. Considerations for efficient selection and

operation are presented and discussed.

• Chapter 7 – Other Considerations Not every energy efficiency improvement tactic can be neatly categorized

as a “high-side” or “low-side” opportunity. In Chapter 7, we present other

opportunities that can result in appreciable energy improvement benefits

to systems.

Hard work and attention to detail are keys for successfully realizing energy

efficiency improvements. Safety should always be THE prime consideration in

the pursuit of any changes aimed at improving refrigeration system operations.

Utilize the opportunity for refrigeration system energy efficiency improvements to

revisit safety best practices in the design and operation of your refrigeration

systems. Manage these changes in the context of your own plant’s safety

program and reap the rewards of a safer more efficient refrigeration system.

One final note: This Guidebook includes photos, illustrations, and performance

data from various industrial refrigeration equipment manufacturers. We

appreciate their cooperation and permission to re-publish their materials. In

general, we have tried to provide balance by including materials from a range of

equipment manufacturer’s but in some cases, a specific company’s illustrations

were selected as the best material available to illustrate the points being made in

the text. The use of this information should not be construed as an endorsement

of any particular product or manufacturer.

Douglas T. Reindl, Ph.D., P.E.

Todd B. Jekel, Ph.D., P.E.

James S. Elleson, P.E.

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Industrial Refrigeration Energy Efficiency Guidebook vi

ACKNOWLEDGEMENTS

Many people and organizations were instrumental in providing input, support, and background for the development of this Guidebook. First, we would like to acknowledge all of the end-users and industry experts whose shoulders we stand upon in our efforts to continually improve the efficiency, safety, and operability of industrial refrigeration systems. Their willingness to “be the first” has enabled us to bring you the proven principles and practices that achieve efficient refrigeration systems.

We also would like to acknowledge a number of individuals that have unselfishly given of their time and talent to provide careful review of draft manuscripts. Those that have contributed in this regard include: Adam Batcheller, Tony Chihak, and Mike Haller of Wells’ Dairy, Bob Gansler of Xcel Energy, Tony Lundell of Tropicana Products, Don Stroud of Kraft Foods, and Bob Terrell of Alliant Energy. Their insightful comments and suggestions have improved the content and presentation of the Guidebook immeasurably. We would also like to thank James Denkmann for his direct and indirect contributions. He dedicated significant amounts of time discussing, reviewing, and commenting on draft versions of this Guidebook, and the quality of the final product has been assuredly enhanced by his input.

This Guidebook has been funded by Members of the Industrial Refrigeration Consortium and without their support, its preparation would not have been possible. At the time of the printing of this Guidebook, Members of the IRC include: Alliant Energy, CF Industries, General Mills, Kraft Foods, Nor-Am Cold Storage, OSHA, Sargento Foods, Schoep’s Ice Cream, Tropicana Products, US EPA, Wells’ Dairy, and Xcel Energy. Your commitment to excellence and your collaborative support are a model for our industry.

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TABLE OF CONTENTS

1 Introduction.............................................................................................................1-1 1.1 Overview.....................................................................................................1-1 1.2 Steps to Improving Energy Efficiency.........................................................1-4 1.3 Barriers to Improving Energy Efficiency .....................................................1-6 1.4 Guidebook Organization.............................................................................1-7 1.5 References .................................................................................................1-8

2 Overview of Systems and Equipment ....................................................................2-9 2.1 Compressor Technologies..........................................................................2-9

2.1.1 Reciprocating Compressors ...............................................................2-9 2.1.1.1 Principle of operation ....................................................................2-10 2.1.1.2 Capacity control ............................................................................2-11

2.1.2 Screw Compressors .........................................................................2-11 2.1.2.1 Types (single, twin, fixed Vi, variable Vi) ......................................2-12 2.1.2.2 Principle of operation ....................................................................2-14 2.1.2.3 Capacity control ............................................................................2-20 2.1.2.4 Oil cooling .....................................................................................2-23

2.1.3 Other Compressor Types (rotary vane, centrifugal) .........................2-27 2.1.4 Ratings .............................................................................................2-28

2.2 Condensers ..............................................................................................2-33 2.2.1 Air-Cooled Condensers ....................................................................2-34 2.2.2 Water-Cooled Condensers ...............................................................2-35 2.2.3 Evaporative Condensers ..................................................................2-36

2.2.3.1 Factors influencing condenser performance.................................2-39 2.2.3.2 Condenser capacity control ..........................................................2-41 2.2.3.3 Fan types and arrangements........................................................2-41 2.2.3.4 Condenser efficiency characteristics ............................................2-44

2.3 Evaporators ..............................................................................................2-44 2.3.1.1 Factors influencing evaporator performance ................................2-48 2.3.1.2 Capacity control ............................................................................2-50

2.4 Single Stage Compression Systems ........................................................2-50 2.4.1 Direct-Expansion ..............................................................................2-50 2.4.2 Gravity Flooded ................................................................................2-52

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2.4.3 Liquid Overfeed ................................................................................2-55 2.5 Multi-Stage Compression Systems ..........................................................2-59

2.5.1 Single Temperature Level ................................................................2-60 2.5.2 Multiple Temperature Level ..............................................................2-63

2.6 References ...............................................................................................2-66 3 Evaluating Refrigeration System Performance ....................................................3-67

3.1 Goals for Performance Evaluation............................................................3-67 3.2 Measures of Performance ........................................................................3-67

3.2.1 Efficiency ..........................................................................................3-68 3.2.2 Capacity............................................................................................3-68 3.2.3 Annual Energy Cost..........................................................................3-69 3.2.4 Normalized Energy Cost...................................................................3-69

3.3 Factors Influencing System Performance.................................................3-69 3.3.1 Loads................................................................................................3-69 3.3.2 Weather ............................................................................................3-72 3.3.3 Operating Parameters ......................................................................3-72 3.3.4 Design and Operating Procedures ...................................................3-72 3.3.5 Equipment Performance...................................................................3-73

3.4 Normalizing Performance Data ................................................................3-73 3.4.1 Identifying Normalization Factors .....................................................3-74 3.4.2 Normalization Example.....................................................................3-75

3.5 Performance Evaluation Techniques........................................................3-79 3.5.1 Billing Analysis..................................................................................3-80

3.5.1.1 Assemble data ..............................................................................3-80 3.5.1.2 Remove non-refrigeration energy use ..........................................3-80 3.5.1.3 Identify patterns in variation..........................................................3-81

3.5.2 Compressor HP/ton Analysis............................................................3-81 3.5.3 Bin Analysis ......................................................................................3-82

3.5.3.1 Bin weather data...........................................................................3-82 3.5.3.2 Bin energy calculations.................................................................3-82

3.5.4 Component Models ..........................................................................3-85 3.5.5 Field Measurements .........................................................................3-86

3.5.5.1 Pressure and temperature measurement .....................................3-87 3.5.5.2 Wet-bulb temperature measurement ............................................3-87 3.5.5.3 True power measurement.............................................................3-87

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Industrial Refrigeration Energy Efficiency Guidebook x

3.6 Benchmarking...........................................................................................3-88 3.7 Benchmarking Example............................................................................3-91 3.8 References ...............................................................................................3-93

4 High-Side Efficiency Improvements .....................................................................4-95 4.1 Floating Head Pressure............................................................................4-95

4.1.1 Effects of Lowering Head Pressure ..................................................4-95 4.1.2 Condenser Control Strategies ..........................................................4-99 4.1.3 Constraints to Lowering Head Pressure.........................................4-101

4.2 Evaporative Condenser Selection & Operation ......................................4-105 4.2.1 Condenser Sizing Alternatives .......................................................4-105 4.2.2 Operating Strategies.......................................................................4-113 4.2.3 Water Treatment.............................................................................4-117

4.2.3.1 Scale control ...............................................................................4-118 4.2.3.2 Corrosion control ........................................................................4-120 4.2.3.3 Biological growth control.............................................................4-121

4.3 High-Side Piping Considerations............................................................4-122 4.3.1 Discharge Gas Line Piping .............................................................4-123 4.3.2 Liquid Drain Piping (legs and mains) ..............................................4-123 4.3.3 Equalizer Line.................................................................................4-124

4.4 Purgers ...................................................................................................4-130 4.5 Summary ................................................................................................4-132 4.6 References .............................................................................................4-132

5 Low-Side Efficiency Improvements ....................................................................5-135 5.1 Raising Suction Pressure .......................................................................5-135

5.1.1 Effects and Benefits of Raising Suction Pressure ..........................5-136 5.1.2 Constraints to Raising Suction Pressure ........................................5-138

5.1.2.1 Compressor motor size...............................................................5-139 5.1.2.2 Oil separator size........................................................................5-139 5.1.2.3 Suction line pressure drop ..........................................................5-139 5.1.2.4 Vessels .......................................................................................5-139 5.1.2.5 Valve sizes..................................................................................5-140

5.2 Break-Out Suction Levels.......................................................................5-140 5.3 Reduce Suction Line Pressure Drop ......................................................5-140

5.3.1 Dry-Suction Piping..........................................................................5-142 5.3.2 Wet- or Protected-Suction Piping ...................................................5-142

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5.4 Improved Evaporator Defrosting.............................................................5-143 5.4.1 Hot Gas – Pressure and Duration ..................................................5-144 5.4.2 Defrost Sequencing and Controls...................................................5-145 5.4.3 Defrost Piping and Valve Configurations........................................5-147

5.4.3.1 Defrost relief regulators ..............................................................5-147 5.4.3.2 Liquid drainers ............................................................................5-148

5.4.4 Other Considerations......................................................................5-148 5.5 Thermal Energy Storage ........................................................................5-149 5.6 Subcooling..............................................................................................5-150 5.7 Gas Pumping..........................................................................................5-153 5.8 References .............................................................................................5-159

6 Compressors ......................................................................................................6-161 6.1 Reciprocating Compressors ...................................................................6-161 6.2 Screw Compressors ...............................................................................6-164

6.2.1 Variable Ratio Influences................................................................6-164 6.2.2 Oil Cooling Comparison..................................................................6-170

6.3 Compressor Sequencing & Operation....................................................6-172 6.4 Screw Compressor Selection Considerations ........................................6-176 6.5 References .............................................................................................6-179

7 Other Considerations .........................................................................................7-181 7.1 Multi-Stage Compression Systems ........................................................7-181 7.2 Economized Systems.............................................................................7-186 7.3 Intercooler Pressure Reset.....................................................................7-186 7.4 Maintenance-Related Issues..................................................................7-188 7.5 Load Management/Reduction ................................................................7-189

7.5.1 Envelope.........................................................................................7-189 7.5.2 Infiltration ........................................................................................7-190 7.5.3 Internal loads ..................................................................................7-193 7.5.4 Defrost ............................................................................................7-193

7.6 Heat Recovery........................................................................................7-195 7.7 Suction Gas Desuperheating..................................................................7-203 7.8 References .............................................................................................7-207

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LIST OF FIGURES Figure 1-1: Geographic census regions in the US .........................................................1-3 Figure 1-2: Energy efficiency improvement process flow chart......................................1-5 Figure 2-1: Reciprocating compressor installation. ......................................................2-10 Figure 2-2: Schematic of a reciprocating compressor..................................................2-11 Figure 2-3: Screw compressor installation. ..................................................................2-12 Figure 2-4: Main components of single-screw compressor..........................................2-13 Figure 2-5: Main components for a twin-screw compressor. .......................................2-13 Figure 2-6: Twin-screw rotors along with the compressor housing..............................2-14 Figure 2-7: Single-screw compressor during the intake process. ................................2-15 Figure 2-8: Single-screw compressor during the compression process ......................2-15 Figure 2-9: Screw compressor during the discharge process......................................2-16 Figure 2-10: Volume ratio illustration for a screw compressor. ....................................2-17 Figure 2-11: Compression and volume ratios for fixed suction pressure variable volume

ratio screw compressor operating at 0°F suction. ................................................2-18 Figure 2-12: Single-screw at minimum volume ratio ....................................................2-19 Figure 2-13: Single-screw at maximum volume ratio ...................................................2-20 Figure 2-14: Capacity control slide valve at part-load operation ..................................2-21 Figure 2-15: Capacity control slide valve at minimum load..........................................2-22 Figure 2-16: Adiabatic efficiency characteristics for varable speed compressors........2-23 Figure 2-17: Compressor equipped with liquid injection oil cooling .............................2-25 Figure 2-18: Fluid cooler oil cooling arrangement........................................................2-26 Figure 2-19: Thermosiphon oil cooling arrangement. ..................................................2-27 Figure 2-20: Screw compressor capacity & volume flow rate over range conditions...2-29 Figure 2-21: Screw compressor power over range of conditions.................................2-29 Figure 2-22: Screw compressor efficiency over range of conditions............................2-30 Figure 2-23: Pressure-enthalpy diagram for effects of subcooling & superheat. .........2-32 Figure 2-24: Screw compressor performance data over a range of condensing

temperatures and part load ratios. .......................................................................2-33 Figure 2-25: Schematic of an air-cooled condenser. ...................................................2-34 Figure 2-26: Air-cooled condenser on an industrial refrigeration system.....................2-35 Figure 2-27: Schematic of a water-cooled condenser..................................................2-35 Figure 2-28: Schematic of an evaporative condenser including water-side.................2-37 Figure 2-29: Field installation of an induced-draft evaporative condenser...................2-39

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Figure 2-30: Influence of outdoor air wet-bulb and refrigerant temperature on condenser capacity. ...............................................................................................................2-40

Figure 2-31: Forced-draft evaporative condenser with two-stage axial fans................2-42 Figure 2-32: Forced-draft evaporative condenser with centrifugal fans .......................2-42 Figure 2-33: Induced-draft evaporative condenser with axial fan ................................2-43 Figure 2-34: Schematic of a flooded liquid chiller ........................................................2-45 Figure 2-35: Photo showing a flooded liquid chiller in service. ....................................2-45 Figure 2-36: Packaged flooded plate-type fluid chiller .................................................2-46 Figure 2-37: Plate-finned air-cooling evaporator..........................................................2-47 Figure 2-38: Influence of coil rows and velocity on nominal coil unit capacity. ............2-49 Figure 2-39: Influence of coil fin density on nominal coil unit capacity.........................2-49 Figure 2-40: Single stage vapor compression system direct-expansion evaporators..2-51 Figure 2-41: Single stage compression system flooded evaporators. .........................2-53 Figure 2-42: Floor-mounted flooded air evaporator. ....................................................2-54 Figure 2-43: Single stage compression mechanically-pumped overfeed system. .......2-56 Figure 2-44: Examples of liquid refrigerant pumps. .....................................................2-57 Figure 2-45: Single stage compression gas-pumped liquid overfed system................2-58 Figure 2-46: Single temperature level two-stage compression system with single stage

liquid expansion. ..................................................................................................2-60 Figure 2-47: Two-stage compression, single temperature level system with two-stages of

direct liquid expansion..........................................................................................2-63 Figure 2-48: Two temperature level, two-stage compression with two-stages of direct

liquid expansion. ..................................................................................................2-64 Figure 2-49: Two temperature level, two-stage compression system with indirect liquid

expansion.............................................................................................................2-65 Figure 3-1: Example energy use data. ........................................................................3-71 Figure 3-2: Energy cost and cost per unit. ...................................................................3-71 Figure 3-3: Example monthly energy use. ..................................................................3-75 Figure 3-4: Monthly energy use vs. production. ..........................................................3-76 Figure 3-5: Monthly energy use vs. wet-bulb temperature..........................................3-76 Figure 3-6: Energy use normalized for production. .....................................................3-77 Figure 3-7: Normalized energy use vs. wet-bulb temperature. ...................................3-78 Figure 3-8: Measured and predicted energy use. .......................................................3-78 Figure 3-9: Refrigerated warehouse normalized energy use. .....................................3-92 Figure 4-1: Relationship between compressor, condenser, and system power required

for a fixed outside air condition over a range of condensing temperatures..........4-97

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Figure 4-2: Relationship between compressor, condenser, and system power required for a centrifugal fan condenser.............................................................................4-98

Figure 4-3: Trend of screw compressor capacity and oil cooling load as a function of condensing temperature. .....................................................................................4-99

Figure 4-4: System energy consumption effects with an evaporative condenser designed for 85°F [29°C] condensing temperature............................................................4-108

Figure 4-5: Heat rejection factors for Vilter evaporative condensers .........................4-110 Figure 4-6: Heat rejection factors for Imeco evaporative condensers........................4-111 Figure 4-7: Nominal condenser capacities.................................................................4-113 Figure 4-8: Energy performance of condenser fan control strategy alternatives .......4-116 Figure 4-9: Forced-draft centrifugal fan condenser with a desuperheater. ................4-119 Figure 4-10: High-side piping illustrating parallel evaporative condensers with a high

pressure receiver in a surge arrangement .........................................................4-125 Figure 4-11: High-pressure receiver connections. ....................................................4-125 Figure 4-12: Equalizer line sizes for a 0.1 psi maximum pressure drop. ..................4-129 Figure 4-13: Equalizer line sizes for a 0.02 psi maximum pressure drop. ................4-129 Figure 4-14: Purger installation photo .......................................................................4-130 Figure 5-1: System efficiency as a function of TD for air cooling evaporator. ............5-138 Figure 5-2: Change in specific volume relative to saturation temperature (dv/dT).....5-141 Figure 5-3: Seasonal variation in outdoor air humidity ratio.......................................5-146 Figure 5-4: Schematic of flooded load fed with saturated high-pressure liquid..........5-151 Figure 5-5: Schematic of flooded load fed with subcooled high-pressure liquid. .......5-152 Figure 5-6: Relative capacity for a liquid suction heat exchanger..............................5-153 Figure 5-7: Illustration of a simple gas-pumped system.............................................5-154 Figure 5-8: Illustration of a simple mechanically-pumped refrigeration system. ........5-154 Figure 5-9: Typical open-drive liquid refrigerant pump curve.....................................5-155 Figure 5-10: Mechanical pump horsepower per ton for range of recirculation rates..5-156 Figure 5-11: Compressor horsepower per ton associated with gas-driven pumping for a

range of recirculation rates.................................................................................5-157 Figure 5-12: Energy penalty associated with gas-driven vs. mechanical pumping....5-158 Figure 6-1: Full-load efficiency for a 12 cylinder reciprocating compressor. ..............6-162 Figure 6-2: Part-load characteristics for a reciprocating compressor.........................6-163 Figure 6-3: Influence of volume ratio on full-load compressor efficiency at 0°F [-18°C]

saturated suction temperature. ..........................................................................6-165 Figure 6-4: Influence of volume ratio on full-load compressor efficiency at a 20°F

saturated suction temperature. ..........................................................................6-166

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Figure 6-5: Influence of volume ratio on full-load compressor efficiency at a -20°F saturated suction temperature. ..........................................................................6-167

Figure 6-6: Compressor part-load efficiency fixed volume ratio compressors. ..........6-168 Figure 6-7: Fixed and variable volume ratio full-load efficiency characteristics. ........6-169 Figure 6-8: Fixed (Vi = 2.2 and 3.0) and variable volume ratio full-load efficiency

characteristics at 0°F saturated suction temperature. ........................................6-170 Figure 6-9: Performance comparison between a variable volume ratio screw and

reciprocating compressors including system effects ..........................................6-173 Figure 6-10: Performance comparison for equally sized variable volume ratio screw

compressors including system effects................................................................6-174 Figure 6-11: Performance comparison for unequally sized variable volume ratio screw

compressors including system effects................................................................6-175 Figure 6-12: Frequency analysis of theoretical condensing temperatures for an

evaporatively condensed industrial refrigeration system in Madison, WI...........6-178 Figure 7-1: Influence of compression & liquid expansion on efficiency......................7-183 Figure 7-2: Comparison of single- and two-stage compression systems with condensing

and intermediate pressures for a -45°F booster suction temperature. ...............7-184 Figure 7-3: Comparison of single- and two-stage compression systems with condensing

and intermediate pressures for a -28°F booster suction temperature. ...............7-184 Figure 7-4: Comparison of single- and two-stage compression systems with condensing

and intermediate pressures for a -10°F booster suction temperature. ...............7-185 Figure 7-5: Compressor power (booster and high stage) variation with intercooler

pressure over a range of head pressures. .........................................................7-187 Figure 7-6: Pressure-enthalpy diagrams for R-22 showing typical compression

processes from a 0°F saturated suction temperature. .......................................7-196 Figure 7-7: Pressure-enthalpy diagrams for ammonia showing typical compression

processes from a 0°F saturated suction temperature. .......................................7-197 Figure 7-8: Illustration showing proportions of thermal energy in a high pressure

ammonia stream. ...............................................................................................7-199 Figure 7-9: Usable heat recovery for thermosiphon oil cooled screw compressor. ...7-200 Figure 7-10: Thermosiphon oil cooled screw compressor discharge temperature

variation with head pressure. .............................................................................7-201 Figure 7-11: Hot water flow rate over a range of condensing temperatures. .............7-203 Figure 7-12: Net refrigeration capacity loss due to superheat (useful). .....................7-205 Figure 7-13: Net refrigeration capacity loss due to superheat (non-useful). ..............7-205

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LIST OF TABLES Table 1-1: Regional electricity consumption for SIC 20 .................................................1-3 Table 3-1: Example of dry bulb bin temperature data for Madison, WI.......................3-83 Table 3-2: Example of wet-bulb bin temperature data for Madison, WI. .....................3-84 Table 3-3: Bin analysis summary. ...............................................................................3-85 Table 3-4: General benchmarking data requirements..................................................3-90 Table 3-5: Additional information by facility type.........................................................3-91 Table 3-6: Summary of warehouse data. ....................................................................3-92 Table 4-1: Condenser fan control strategy map.........................................................4-100 Table 4-2: Design weather conditions........................................................................4-106 Table 4-3: Condenser fan control strategy map.........................................................4-115 Table 4-4: Equalizer line size recommendations .......................................................4-128 Table 4-5: Equalizer line size recommendations .......................................................4-128 Table 5-1: Impact of raising suction pressure on compressor performance. .............5-137 Table 5-2: Suction valve train size effect compressor performance & energy cost. ..5-142 Table 6-1: Oil cooling comparison for twin-screw compressors.................................6-171 Table 6-2: Fixed volume ratio screw compressor selection ranges. ..........................6-177 Table 7-1: Minimum envelope performance for temperature-controlled spaces........7-190 Table 7-2: Envelope thermal performance for temperature-controlled spaces ..........7-190 Table 7-3: Discharge temperature comparison for ideal compression processes. ....7-198 Table 7-4: Head pressure penalties for screw compressor operation........................7-202

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