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

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2 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

3 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.

4 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 postimplementation 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) iv

5 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. v

6 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. vi

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8 TABLE OF CONTENTS 1 Introduction Overview Steps to Improving Energy Efficiency Barriers to Improving Energy Efficiency Guidebook Organization References Overview of Systems and Equipment Compressor Technologies Reciprocating Compressors Principle of operation Capacity control Screw Compressors Types (single, twin, fixed Vi, variable Vi) Principle of operation Capacity control Oil cooling Other Compressor Types (rotary vane, centrifugal) Ratings Condensers Air-Cooled Condensers Water-Cooled Condensers Evaporative Condensers Factors influencing condenser performance Condenser capacity control Fan types and arrangements Condenser efficiency characteristics Evaporators Factors influencing evaporator performance Capacity control Single Stage Compression Systems Direct-Expansion Gravity Flooded viii

9 2.4.3 Liquid Overfeed Multi-Stage Compression Systems Single Temperature Level Multiple Temperature Level References Evaluating Refrigeration System Performance Goals for Performance Evaluation Measures of Performance Efficiency Capacity Annual Energy Cost Normalized Energy Cost Factors Influencing System Performance Loads Weather Operating Parameters Design and Operating Procedures Equipment Performance Normalizing Performance Data Identifying Normalization Factors Normalization Example Performance Evaluation Techniques Billing Analysis Assemble data Remove non-refrigeration energy use Identify patterns in variation Compressor HP/ton Analysis Bin Analysis Bin weather data Bin energy calculations Component Models Field Measurements Pressure and temperature measurement Wet-bulb temperature measurement True power measurement ix

10 3.6 Benchmarking Benchmarking Example References High-Side Efficiency Improvements Floating Head Pressure Effects of Lowering Head Pressure Condenser Control Strategies Constraints to Lowering Head Pressure Evaporative Condenser Selection & Operation Condenser Sizing Alternatives Operating Strategies Water Treatment Scale control Corrosion control Biological growth control High-Side Piping Considerations Discharge Gas Line Piping Liquid Drain Piping (legs and mains) Equalizer Line Purgers Summary References Low-Side Efficiency Improvements Raising Suction Pressure Effects and Benefits of Raising Suction Pressure Constraints to Raising Suction Pressure Compressor motor size Oil separator size Suction line pressure drop Vessels Valve sizes Break-Out Suction Levels Reduce Suction Line Pressure Drop Dry-Suction Piping Wet- or Protected-Suction Piping x

11 5.4 Improved Evaporator Defrosting Hot Gas Pressure and Duration Defrost Sequencing and Controls Defrost Piping and Valve Configurations Defrost relief regulators Liquid drainers Other Considerations Thermal Energy Storage Subcooling Gas Pumping References Compressors Reciprocating Compressors Screw Compressors Variable Ratio Influences Oil Cooling Comparison Compressor Sequencing & Operation Screw Compressor Selection Considerations References Other Considerations Multi-Stage Compression Systems Economized Systems Intercooler Pressure Reset Maintenance-Related Issues Load Management/Reduction Envelope Infiltration Internal loads Defrost Heat Recovery Suction Gas Desuperheating References xi

12 LIST OF FIGURES Figure 1-1: Geographic census regions in the US Figure 1-2: Energy efficiency improvement process flow chart Figure 2-1: Reciprocating compressor installation Figure 2-2: Schematic of a reciprocating compressor Figure 2-3: Screw compressor installation Figure 2-4: Main components of single-screw compressor Figure 2-5: Main components for a twin-screw compressor Figure 2-6: Twin-screw rotors along with the compressor housing Figure 2-7: Single-screw compressor during the intake process Figure 2-8: Single-screw compressor during the compression process Figure 2-9: Screw compressor during the discharge process Figure 2-10: Volume ratio illustration for a screw compressor Figure 2-11: Compression and volume ratios for fixed suction pressure variable volume ratio screw compressor operating at 0 F suction Figure 2-12: Single-screw at minimum volume ratio Figure 2-13: Single-screw at maximum volume ratio Figure 2-14: Capacity control slide valve at part-load operation Figure 2-15: Capacity control slide valve at minimum load Figure 2-16: Adiabatic efficiency characteristics for varable speed compressors Figure 2-17: Compressor equipped with liquid injection oil cooling Figure 2-18: Fluid cooler oil cooling arrangement Figure 2-19: Thermosiphon oil cooling arrangement Figure 2-20: Screw compressor capacity & volume flow rate over range conditions Figure 2-21: Screw compressor power over range of conditions Figure 2-22: Screw compressor efficiency over range of conditions Figure 2-23: Pressure-enthalpy diagram for effects of subcooling & superheat Figure 2-24: Screw compressor performance data over a range of condensing temperatures and part load ratios Figure 2-25: Schematic of an air-cooled condenser Figure 2-26: Air-cooled condenser on an industrial refrigeration system Figure 2-27: Schematic of a water-cooled condenser Figure 2-28: Schematic of an evaporative condenser including water-side Figure 2-29: Field installation of an induced-draft evaporative condenser xii

13 Figure 2-30: Influence of outdoor air wet-bulb and refrigerant temperature on condenser capacity Figure 2-31: Forced-draft evaporative condenser with two-stage axial fans Figure 2-32: Forced-draft evaporative condenser with centrifugal fans Figure 2-33: Induced-draft evaporative condenser with axial fan Figure 2-34: Schematic of a flooded liquid chiller Figure 2-35: Photo showing a flooded liquid chiller in service Figure 2-36: Packaged flooded plate-type fluid chiller Figure 2-37: Plate-finned air-cooling evaporator Figure 2-38: Influence of coil rows and velocity on nominal coil unit capacity Figure 2-39: Influence of coil fin density on nominal coil unit capacity Figure 2-40: Single stage vapor compression system direct-expansion evaporators Figure 2-41: Single stage compression system flooded evaporators Figure 2-42: Floor-mounted flooded air evaporator Figure 2-43: Single stage compression mechanically-pumped overfeed system Figure 2-44: Examples of liquid refrigerant pumps Figure 2-45: Single stage compression gas-pumped liquid overfed system Figure 2-46: Single temperature level two-stage compression system with single stage liquid expansion Figure 2-47: Two-stage compression, single temperature level system with two-stages of direct liquid expansion Figure 2-48: Two temperature level, two-stage compression with two-stages of direct liquid expansion Figure 2-49: Two temperature level, two-stage compression system with indirect liquid expansion Figure 3-1: Example energy use data Figure 3-2: Energy cost and cost per unit Figure 3-3: Example monthly energy use Figure 3-4: Monthly energy use vs. production Figure 3-5: Monthly energy use vs. wet-bulb temperature Figure 3-6: Energy use normalized for production Figure 3-7: Normalized energy use vs. wet-bulb temperature Figure 3-8: Measured and predicted energy use Figure 3-9: Refrigerated warehouse normalized energy use Figure 4-1: Relationship between compressor, condenser, and system power required for a fixed outside air condition over a range of condensing temperatures xiii

14 Figure 4-2: Relationship between compressor, condenser, and system power required for a centrifugal fan condenser Figure 4-3: Trend of screw compressor capacity and oil cooling load as a function of condensing temperature Figure 4-4: System energy consumption effects with an evaporative condenser designed for 85 F [29 C] condensing temperature Figure 4-5: Heat rejection factors for Vilter evaporative condensers Figure 4-6: Heat rejection factors for Imeco evaporative condensers Figure 4-7: Nominal condenser capacities Figure 4-8: Energy performance of condenser fan control strategy alternatives Figure 4-9: Forced-draft centrifugal fan condenser with a desuperheater Figure 4-10: High-side piping illustrating parallel evaporative condensers with a high pressure receiver in a surge arrangement Figure 4-11: High-pressure receiver connections Figure 4-12: Equalizer line sizes for a 0.1 psi maximum pressure drop Figure 4-13: Equalizer line sizes for a 0.02 psi maximum pressure drop Figure 4-14: Purger installation photo Figure 5-1: System efficiency as a function of TD for air cooling evaporator Figure 5-2: Change in specific volume relative to saturation temperature (dv/dt) Figure 5-3: Seasonal variation in outdoor air humidity ratio Figure 5-4: Schematic of flooded load fed with saturated high-pressure liquid Figure 5-5: Schematic of flooded load fed with subcooled high-pressure liquid Figure 5-6: Relative capacity for a liquid suction heat exchanger Figure 5-7: Illustration of a simple gas-pumped system Figure 5-8: Illustration of a simple mechanically-pumped refrigeration system Figure 5-9: Typical open-drive liquid refrigerant pump curve Figure 5-10: Mechanical pump horsepower per ton for range of recirculation rates Figure 5-11: Compressor horsepower per ton associated with gas-driven pumping for a range of recirculation rates Figure 5-12: Energy penalty associated with gas-driven vs. mechanical pumping Figure 6-1: Full-load efficiency for a 12 cylinder reciprocating compressor Figure 6-2: Part-load characteristics for a reciprocating compressor Figure 6-3: Influence of volume ratio on full-load compressor efficiency at 0 F [-18 C] saturated suction temperature Figure 6-4: Influence of volume ratio on full-load compressor efficiency at a 20 F saturated suction temperature xiv

15 Figure 6-5: Influence of volume ratio on full-load compressor efficiency at a -20 F saturated suction temperature Figure 6-6: Compressor part-load efficiency fixed volume ratio compressors Figure 6-7: Fixed and variable volume ratio full-load efficiency characteristics Figure 6-8: Fixed (Vi = 2.2 and 3.0) and variable volume ratio full-load efficiency characteristics at 0 F saturated suction temperature Figure 6-9: Performance comparison between a variable volume ratio screw and reciprocating compressors including system effects Figure 6-10: Performance comparison for equally sized variable volume ratio screw compressors including system effects Figure 6-11: Performance comparison for unequally sized variable volume ratio screw compressors including system effects Figure 6-12: Frequency analysis of theoretical condensing temperatures for an evaporatively condensed industrial refrigeration system in Madison, WI Figure 7-1: Influence of compression & liquid expansion on efficiency Figure 7-2: Comparison of single- and two-stage compression systems with condensing and intermediate pressures for a -45 F booster suction temperature Figure 7-3: Comparison of single- and two-stage compression systems with condensing and intermediate pressures for a -28 F booster suction temperature Figure 7-4: Comparison of single- and two-stage compression systems with condensing and intermediate pressures for a -10 F booster suction temperature Figure 7-5: Compressor power (booster and high stage) variation with intercooler pressure over a range of head pressures Figure 7-6: Pressure-enthalpy diagrams for R-22 showing typical compression processes from a 0 F saturated suction temperature Figure 7-7: Pressure-enthalpy diagrams for ammonia showing typical compression processes from a 0 F saturated suction temperature Figure 7-8: Illustration showing proportions of thermal energy in a high pressure ammonia stream Figure 7-9: Usable heat recovery for thermosiphon oil cooled screw compressor Figure 7-10: Thermosiphon oil cooled screw compressor discharge temperature variation with head pressure Figure 7-11: Hot water flow rate over a range of condensing temperatures Figure 7-12: Net refrigeration capacity loss due to superheat (useful) Figure 7-13: Net refrigeration capacity loss due to superheat (non-useful) xv

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

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