Evaporative Cooling Design Guidelines
Course No: M06-014
Credit: 6 PDH
A. Bhatia
Continuing Education and Development, Inc. 22 Stonewall Court Woodcliff Lake, NJ 07677
P: (877) 322-5800 [email protected]
Energy Conservation and Management Division Energy, Minerals and Natural Resources Department
= HEAT + AIR + WATER = COOLING
EVAPORATIVE COOLING DESIGN GUIDELINES MANUAL
FOR
NEW MEXICO SCHOOLS
AND COMMERCIAL BUILDINGS
Evaporative Cooling Design Guidelines Manual
Author:
J. D. Palmer, P.E., C.E.M. NRG Engineering
Contract Manager:
Harold Trujillo, P.E., Bureau Chief New Mexico EMNRD Energy Conservation and Management Division
Funded By:
United States Department of Energy
AND
New Mexico Energy Minerals and Natural Resources Department Energy Conservation and Management Division www.emnrd.state.nm.us/
December 2002
ii Evaporative Cooling Design Guidelines Manual
EVAPORATIVE COOLING DESIGN GUIDELINES MANUAL
FOR NEW MEXICO SCHOOLS AND COMMERCIAL BUILDINGS
Principal Investigator:
James D. Palmer, P.E., C.E.M.
NRG Engineering 2626 Central Ave. SW Albuquerque, New Mexico 87104
iii Evaporative Cooling Design Guidelines Manual
This report by NRG Engineering is funded by the New Mexico Energy Minerals and Natural Resources Department, 1220 South St. Francis Drive, Santa Fe, New Mexico 87505.
NOTICE: This report was prepared as an account of work sponsored by an agency of the State of New Mexico. Neither the State of New Mexico nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the State of New Mexico or any agency thereof.
ACKNOWLEDGEMENTS
NRG Engineering would like to acknowledge the contributions and assistance of the New Mexico Energy Minerals and Natural Resources Department, the referenced authors, the manufacturers and the reviewers that provided input and feedback during the development this project. Their assistance was an important contribution to this endeavor.
Those include the following individuals and companies
Harold Trujillo, P.E., State of New Mexico EMNRD – ECMD Michael McDiarmid, P.E., State of New Mexico EMNRD – ECMD Robert Foster, P.E., Evaporative Cooling Institute, Las Cruces, NM Jim Coupland, P.E., Coupland Engineering, Taos, NM Pat Sedillo, P.E., Mechanical Consultant, Albuquerque, NM David Robertson, P.E., Albuquerque Public Schools Ray J. Alfini, P.E., Alfini Construction, Phoenix, AZ. John Vitacco, Rio Rancho Public Schools Tim Fultz, TK Marketing, Albuquerque, NM The Trane Company, Albuquerque Sales District Munters Corp., Evaporative Cooling Division AdobeAir, Inc., Phoenix, AZ Spec-Air, Inc., Canutillo, TX
iv Evaporative Cooling Design Guidelines Manual
EVAPORATIVE COOLING DESIGN GUIDELINES MANUAL FOR NEW MEXICO SCHOOLS AND COMMERCIAL BUILDINGS
TABLE OF CONTENTS PREFACE...... IX EXECUTIVE SUMMARY ...... 1 INTRODUCTION...... 3 How Evaporative Cooling Works...... 3 Types of Cooling Systems ...... 3 Utility Costs ...... 4 A Natural Resource...... 4 Advantage New Mexico ...... 5
PART I: EVAPORATIVE COOLING DESIGN...... 7 SYSTEM TYPES...... 7 Background...... 7 Direct evaporative cooling...... 8 Indirect Evaporative Cooling...... 10 Combination Systems ...... 14 Cooling Tower "Free Cooling"...... 15 Evaporative Media Types ...... 17 Psychrometrics...... 19 Environmental Considerations...... 24 System Problems and Solutions...... 28 APPLICATIONS...... 29 Comfort Cooling ...... 29 Process Cooling ...... 31 Humidification ...... 31 PERFORMANCE AND ENERGY CONSUMPTION...... 32 Evaporative Air Cooling...... 32 Refrigerated Air Conditioning ...... 33 Mixing EAC and Refrigerated Air:...... 33 Water Consumption ...... 34 Comfort and Energy Consumption Comparisons...... 37 Commissioning of Evaporative Cooling Systems ...... 38 EAC SYSTEM SIZING ...... 40 Typical EAC System Sizing: ...... 40 Wet-bulb Depression ...... 40 Yardsticks for EAC Sizing: ...... 42 Manufacturers Catalog Data ...... 43 SYSTEM CONTROLS ...... 45 EAC Thermostats:...... 45 v Evaporative Cooling Design Guidelines Manual
Relief Air Dampers...... 46 Fan Speed and Pump Switches ...... 46 Solids Buildup Control ...... 46 Bio-Growth Control...... 49 AIR QUALITY...... 50 Outdoor and Indoor Air Quality ...... 50 ASHRAE Comfort Window ...... 52 Importance of Relief Air Dampers ...... 54 Outside Air Requirements...... 55 Humidity Control...... 56 Legionella, Mold and Corrosion Considerations...... 56 SUPPLY AIR DISTRIBUTION ...... 58 Heat Loss ...... 58 EAC Ductwork and Air Diffusers...... 60 Static Pressure and Other Considerations...... 61 ECONOMICS ...... 63 Life Cycle Cost Analysis ...... 63 Comfort vs. Cost ...... 64 Operation Expense...... 64 Maintenance Considerations:...... 65 RELIABILITY ...... 66 Weather Related Issues...... 66 Comparison to Refrigerated Cooling...... 66 System Replacement Considerations...... 67 Corrosion Control ...... 67 Availability of EAC Parts ...... 67
PART II: MAINTENANCE AND OPERATIONS ...... 70 SUMMER START-UP...... 71 Cleaning the Sump and Water Distribution System ...... 73 WINTER SHUTDOWN...... 74 CONTROLS...... 75 PERIODIC MAINTENANCE REQUIREMENTS...... 76 EAC TUNING FOR PEAK PERFORMANCE ...... 77 At the EAC unit ...... 77 Air Distribution System...... 78 Other Tips ...... 79 TROUBLESHOOTING ...... 80 GLOSSARY ...... 84 CONVERSIONS FACTORS...... 91 INDEX ...... 93 FOOTNOTES...... 97
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APPENDIX A ……...……………………………………….. Separate Volume
APPENDIX B ……...……………………………………….. Separate Volume
LIST OF FIGURES
FIGURE 1: COMPARATIVE ELECTRICITY ANNUAL USE FOR A DIRECT EAC AND REFRIGERATED AIR .1 FIGURE 3: DIRECT EAC SCHEMATIC ...... 9 FIGURE 4: TYPICAL WETTED ASPEN PAD COOLER ...... 10 FIGURE 5: IEAC PERFORMANCE...... 11 FIGURE 6: INDIRECT COOLER SCHEMATIC ...... 12 FIGURE 7: AIR-TO-AIR HEAT EXCHANGER INDIRECT + DIRECT EAC...... 12 FIGURE 8: HEAT RECOVERY PERFORMANCE...... 14 FIGURE 9: COMBINATION EVAPORATIVE AND REFRIGERATED COOLING SYSTEM SCHEMATIC...... 15 FIGURE 10: WATER COIL INDIRECT EAC SCHEMATIC...... 16 FIGURE 11: “FREE COOLING” EVAPORATIVE AND REFRIGERATED COMBINATION SYSTEM...... 16 FIGURE 12: DIRECT EAC EFFECTIVENESS FOR RIGID MEDIA...... 18 FIGURE 13: PSYCHROMETRIC CHART...... 19 FIGURE 14: SIMPLIFIED EVAPORATIVE AIR-CONDITIONING PROCESS ...... 20 FIGURE 14: ADIABATIC COOLING PROCESS ...... 21 FIGURE 15: EAC COOLING ...... 22 FIGURE 16: SENSIBLE COOLING PROCESS...... 22 FIGURE 17: TYPICAL EVAPORATIVE COOLING COMFORT ZONE AND MONTHLY HOURS ...... 23 FIGURE 18: TYPICAL REFRIGERATED COOLING COMFORT ZONE AND MONTHLY HOURS...... 24 FIGURE 19: QUICK REFERENCE CHART FOR WATER QUALITY ...... 47 FIGURE 20: FILTRATION EFFICIENCY FOR VARIOUS PARTICLE SIZES FOR 12” RIGID EAC MEDIA.... 51 FIGURE 21: EAC RELIEF THROUGH ATTIC...... 55 FIGURE 22: SEASONAL DAMPER TYPICAL LOCATIONS ...... 59
=
Lesson : HEAT + AIR + WATER = COOLING
vii Evaporative Cooling Design Guidelines Manual
LIST OF TABLES
TABLE 1: LEAVING AIR TEMPERATURE CHART ...... 13 TABLE 2: EAC WATER USE MODEL...... 25 TABLE 3: EAC WATER USE ESTIMATES...... 27 TABLE 6: ENERGY AND COMFORT COMPARISON ...... 38 TABLE 8: EAC EFFECTIVENESS COMPARISON...... 41 TABLE 7: RECOMMENDED DIRECT EAC AIR CHANGE RATES FOR COMFORT COOLING ...... 42 TABLE 9: RELATION BETWEEN WET-BULB TEMPERATURES AND EFFECTIVENESS ...... 43 TABLE 10: LCC COMPARISONS ...... 63
=
Lesson :
HEAT + AIR + WATER = COOLING
viii Evaporative Cooling Design Guidelines Manual
PREFACE This Evaporative Cooling Design Guidelines Manual for New Mexico Schools and Commercial Buildings was prepared for the New Mexico State Energy Minerals and Natural Resources Department, Energy Conservation and Management Division (EMNRD-ECMD). EMNRD’s goal is to conserve energy, design schools that are comfortable, and also save money for educational benefits.
The purpose of this manual is to inform and educate New Mexico’s building owners and school administrators, their staff, and facilities maintenance personnel, and their facility design teams about the proper application, control, maintenance, and comfort expectations of evaporative cooling in New Mexico schools and commercial buildings. This manual is intended to be used as a tool for the design of successful and efficient evaporative cooling systems and will allow engineers to specify and design evaporative cooling systems with confidence. This manual is also intended as an overview of evaporative cooling principles and equipment for the non-technical reader, with technical terms shown in bold print and defined in the glossary. Review of this manual may suggest design features that may be used to improve the economy of operation, comfort, reliability appearance, serviceability, and service life of evaporative cooling systems.
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EXECUTIVE SUMMARY
Electricity is used for many parts of a buildings operation; the largest uses are lighting and air conditioning. Building energy can be saved and pollution decreased while utility expenditures are minimized if energy conservation measures are incorporated into the design, maintenance and operation of a facility. Energy costs will surpass the installed cost of heating and cooling equipment many times over during the life of a typical building. It is important that the design decisions that define a building’s lifetime energy use account for the operations cost of a particular system.
The pie charts in Figure 1 reflect typical percentages used by all the electrical equipment in a conventional New Mexico school. This comparison is for a direct evaporative cooler using rigid media and a self-contained rooftop refrigeration unit with an EER = 10. The electricity used for air conditioning is the sum of the space cooling (sump pump for and EAC; compressor and condenser for refrigerated A/C) and the ventilation fans. The cooling totals 27% of the total utility use for evaporative cooling and 33% of the total utility use for refrigerated cooling.
DIRECT EVAPORATIVE COOLING REFRIGERATED AIR CONDITIONING
Figure 1: Comparative Electricity Annual Use for a Direct EAC and Refrigerated Air
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The benefits of using evaporative cooling in New Mexico are usually perceived in terms of economy of operation. Operating cost is an important factor when utility budgets are a major consideration. However, there are other compelling reasons that make evaporative cooling a smart choice. These include: