Evaporative Air Conditioning Handbook, 2nd Edition - Dr John R. Watt

EVAPORATIVE AIR CONDITIONING HANDBOOK

EVAPORATIVE AIR CONDITIONING HANDBOOK Second Edition

Dr. John R. Watt with the assistance of Richard L. Koral Loren W. Crow Alfred Greenberg

KAPARCHIEF

CHAPMAN & HALL New York

London

First published 1986 by Chapman and Hall 29 West 35 Street, New York, N.Y. 10001 Published in Great Britain by Chapman and Hall Ltd II New Fetter Lane, London EC4P 4EE ©

1986 Chapman and Hall

All Rights Reserved. No part of this book may be reprinted, or reproduced or utilized in any form or by any electronic, mechanical or other means, not known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers.

Library of Congress Cataloging-in-Publication Data Watt, John R. Evaporative air conditioning handbook. Rev. ed. of: Evaporative air conditioning. 1st ed. 1963. Bibliography: p. Includes index. \. Air conditioning. I. Watt, John R. Evaporative air conditioning. 1963. II. Title. 697.9 86-17172 TH7687.W3 1986 ISBN-13 :978-1-4612-9387-3 e-ISBN-13:978-1-4613-2259-7 DOLlO.IO07/978-1-4613-2259-7

PREFACE TO THE 1963 EDITION Air conditioning boosts man's efficiency no less than his comfort. Air-conditioned homes, offices, and factories unmistakably raise human productivity and reduce absenteeism, turnover, mistakes, accidents and grievances, especially in summer. Accordingly, many employers every year cool workrooms and offices to raise summer profits. Employees in turn find cool homes enhancing not only comfort and prestige but also personal efficiency and income. With such economic impetus, low-cost summer cooling must irresistibly spread to all kinds of occupied buildings. Refrigeration provides our best cooling, serving well where people are closely spaced in well-constructed, shaded, and insulated structures. However, its first and operating costs bar it from our hottest commercial, industrial, and residential buildings. Fortunately, evaporative cooling is an economical substitute in many regions. First used in Southwest homes and businesses and in textile mills, it soon invaded other fields and climates. In 1946, six firms produced 200,000 evaporative coolers; in 1958, 25 firms produced 1,250,000, despite the phenomenal sale of refrigerating window air conditioners. Though clearly secondary to refrigeration, evaporative cooling is 60 to 80 percent cheaper to buy and operate. Thus, it is economical for moderate income groups and climates where summers are short. Moreover, it cheaply cools hot, thinly constructed mills, factories, workshops, foundries, powerhouses, farm buildings, canneries, etc., where refrigerated cooling is prohibitively expensive. However, because evaporative cooling is the product of small regional companies, it is little known nationally. As our second-best form of comfort cooling and as the only cooling economical for many industrial plants, it deserves wider understanding. This book attempts to supply it.

PREFACE TO THE 1986 EDITION In the 23 years following the original edition, evaporative cooling sales suffered badly as refrigerative air conditioning became inexpensive enough to displace it. The latter provided greater comfort and independence from weather conditions, quieter and less drafty cooling, and easier incorporation into most heating systems. Its installations also were often more sightly. Evaporative cooling. declined most in rich and prestige-conscious Southern California, where refrigerative cooling better excluded regional smog. Several manufacturers and hundreds of dealers left the field. However, arid and less prosperous Arizona, Nevada, New Mexico, Colorado, Texas, and Utah maintained steady markets where manufacturers and dealers survived v

vi / Preface the incursions of refrigerative cooling. The markets were saved by the area's massive population growth and oppressive heat, which forces almost everyone to purchase cooling. Meanwhile, little decline occurred in the use of large evaporative cooling. The increasing need to promote worker productivity by cooling large industrial buildings helped sell big, versatile, spray-type air washers that could evaporatively cool when the weather permitted, refrigeratively cool when it did not, and also heat, ventilate, and control humidity. Because of their flexibility they spread nationwide into thousands of factories, mills, processing and atomic and chemical plants as far outside historic evaporative-cooling areas as Detroit itself. Such fields as smelting, metalworking, food processing, dry-cleaning, laundering, and power generating needed simple cooling with massive ventilation. Smaller evaporative cooling units, using pads wet by sprays or "water slingers," met their needs. Then, revolutionary Munters rigid·.pad_media appeared. Made of mUltiple strong, corrugated cellulose or glass-fiber sheets cemented together, they were long-lasting, self-cleaning, and highly effective. They made possible big, simple, troublefree coolers that replaced many air washers. In 1973, precipitous increases in energy costs began. These handicapped refrigerative cooling far more than they did evaporative. Accordingly, evaporative cooling is enjoying a vigorous comeback. New small manufacturers are appearing; established producers and dealers are expanding. Insiders estimate that the 1973- 80 growth exceeded to percent per year; many expect sales of small coolers to grow 30 percent yearly in the 1980s. The sale of rigid-media devices is nearly explosive. Similarly boosted, indirect evaporative coolers, which cool air without wetting it, are spreading widely as precoolers for ordinary evaporative or refrigerative cooling. So combined, they cut operating costs immensely and provide cooling that serves well in areas of moderate humidity. That promises to spread evaporative cooling into many new regions. Evaporative cooling today is also helping save refrigerative power costs. Millions of tons of small- and medium-sized air conditioning and commercial refrigeration have air-cooled condensers with low hot-weather efficiency. Many now boost summer economy with devices that evaporatively precool outdoor air entering those condensers. Even so, rising power costs ahead may well sideline many refrigerative window units and small central systems. If so, direct evaporative cooling must assume orphan cooling loads in the drier regions, indirect evaporative cooling following suit in damper climates, staged with direct evaporative cooling or small-scale refrigeration. Admittedly, refrigeration usually produces better all-around comfort. However, in its growing climatic ranges, evaporative cooling enjoys strong monetary advantages: • • • • • •

Much lower equipment and installation costs Much lower operating and power costs Much lower maintenance costs Much greater ventilating effect, if needed Better air distribution without ducts Usually lower outdoor noise levels

In today's world of climbing energy, material and labor expense, cost advantages seem likely to dominate 'many cooling markets for years to come. So evaporative cooling has a rosy future.

Preface I

vii

Looking Ahead The market for evaporative cooling is enormous and growing, boosted by new housing construction and ever-climbing power costs. According to the Census Bureau's "Characteristics of New Housing: 1982," 66 percent of new housing starts that year included air conditioning, a percentage that has increased yearly since 1977. That suggests Americans increasingly consider cooling a necessity. With about 1,730,000 new housing starts in 1985, new homes with cooling approached 1,300,000. With interest rates falling significantly that year, counting replacements and retrofits in existing homes, cooling sales could quadruple in the next decade. Besides these sales will be those of very large systems to commercial and industrial markets. In spite of collapsing oil prices after 1984, power costs continue to rise. Not only do power companies burn less oil than natural gas and coal, but also many are amortizing inordinate outlays for atomic plants, including abandoned ones. Moreover, most completed atomic plants operate more expensively and have more frequent shutdowns than conventional plants. Each one completed also increases the company capital-base against which legally allowable charges are levied. Upward pricing is inevitable for another reason; growing summer cooling loads are unbalancing yearly power demands, forcing utilities to expand their plants at increasing material, labor, and equipment costs, although excess capacity exists during the other seasons. Because of rising power costs, population movements to the sunny states, and the growing geographical mobility of staged indirect evaporative systems, the market share of evaporative cooling is growing steadily and should continue to do so in the foreseeable future. As the staged equipment becomes better known, better packaged (Arvin Industries leads the way here), and mass-produced, its sales should mushroom, replacing much whole-system refrigeration in many climatic regions and fields. Solarized equipment may make a significant contribution. The September-October 1984 issue of Solar Engineering and Contracting listed firms already offering solarized equipment. Three manufactured indirect or staged evaporative coolers, two made photovoltaic powered direct coolers, and one offered similar evaporative precoolers for refrigeration condensers. The anticipated rise in solar-cell cost-efficiency will encourage such firms in the same way that 40 percent federal income tax credits and some state tax credits did through 1985, by subsidizing the solar components in products. Though lapsed, such tax credits generally favored low-cost over high-cost combined installations and thus favored evaporative over refrigerative equipment. If there are future versions of such tax credits, they will likely be similar. Tosummarize, strong economic trends encourage the spread of cooling to improve human productivity and comfort. Ample reason exists for such cooling to be as economical as possible, in both power consumption and life cycle. Evaporative cooling seemingly leads all competitors in both respects. John R. Watt Atlanta, Ga. June, 1986

TABLE OF CONTENTS PREFACE

............................................... v

Man's Need for Cooling, Evaporative Cooling Origins, Its Early Southwest Boom and Uses, Temporary Decline, Recent Revival, New Types and Purposes, Economic Advantages Today, Growing Markets Ahead, Solar Connections.

I. INTRODUCTION ......................................... 01 Evaporative Cooling Types, Long Scientific Neglect, Aid to Industrial Productivity, Coming Triumphs, Omissions, Abbreviations, Metric Equivalents.

II. HISTORY OF EVAPORATIVE

COOLING .................. 05

Primitive Evaporative Cooling, Modern Evaporative Cooling, Eastern Types and History, Western Types and Development, Typical Indirect System Cooling Towers, An Early Plate-Type Indirect Cooler, Early Drip Coolers, Mass Production Begins, Historical Importance, The Industry Consolidates, Industry Achievements, Review Questions.

III. THEORY OF DIRECT EVAPORATIVE

COOLING . ......... 12

Heat and Mass Transfer, Sensible and Latent Heat, Adiabatic Saturation, Limits of Direct Evaporative Cooling, Humidity Measurement, Dry-Bulb and Wet-Bulb Temperatures, Psychrometric Charts, Other Psychrometric Properties, Psychrometric Processes, Ideal Evaporative Cooling, Ordinary Evaporative Cooling, Saturating Efficiency, Evaporative Cooling Process in Rooms, Washed-Air Discharge Outdoors, Indoor Relative Humidity, Review Questions.

IV. COMFORT ASPECTS OF AIR CONDITIONING ........... 26 The Organic Thermodynamics of Comfort, Heat Dissipated by People, The Body's Means of Heat Dissipation, Bodily Governing Factors, Organic Temperature Controls and Limits, Architectural and Psychological Factors, The Effect of Building Size and Mass upon Indoor Comfort, Effective Temperatures and Comfort Zones, Comfort Charts, Limited Pertinence, Comfort Chart Adaption to Other Conditions, An Evaporative Cooling Comfort Zone, A Proposed Evaporative Cooling Comfort Chart, Nomograph for Rapid Calculating of Evaporative Cooling Results, Recommended Summer Indoor Conditions, Adjustment for Radiant Heat, Permissible Relative Humidities, Permissible Air Motion with Evaporative Cooling, Fresh Air Requirements, Air Cleaning, Review Questions.

ix

x / Table of Contents

V. GEOGRAPHIC RANGE AND EVAPORATIVE

COOLING .. 43

Other Factors Than Humidity, Traditional Design Temperatures, Coincident Dry- and Wet-Bulb Temperatures, Use of Diurnal Temperature Swings, U.S. Evaporative Cooling Coincident Design Temperatures, Selected Canadian Cooling Coincident Design Temperatures, Climatic Considerations and the Need for Cooling, International Comparative Weather Data, International Direct Evaporative Cooling Applicability, Achieving Comfort, Process Path Vectors, Wet-Bulb Temperatures that Permit Vectors to Achieve Comfort Zones, Indirect Coolers and Geographic Range, Review Questions.

VI. DRIP-TYPE DIRECT EVAPORATIVE

COOLERS ........... 90

Cabinet Design, Fans and Motors, Motor Ratings, Pad-Holders, Pad Materials, Water Distribution Systems, Recirculating Pumps, Pad Thickness and Density, Air Velocity in Pads, Water Flow in Pads, Review Questions.

VII. DRIP COOLER PROGRESS .. .......................... . 107 Pad Sagging, Pad Clogging, Pad Scaling, Bleed-Off and Blow-Down, Chemical Water Treatment, Pad Deterioration, Odor Problems, Corrosion Resistance, Galvanized Steel Coolers, Stainless Steel Coolers, Pressure Molded Plastic Coolers, Another Molded Plastic Cooler, Fiber Glass Coolers, Composite Australian Coolers, Exaggerated U.S. Performance Data, Controls, Idealized Drip Cooler Controls, Solar Connections, Solar Drip Coolers, Solar Tax Credits, Review Questions.

VIII. OTHER SMALL EVAPORATIVE

COOLERS .............. 131

Portable Drip Coolers, Spot Coolers, Exhaust-Type Window-Pad Coolers, The New Roller Pad Coolers, Automobile Evaporative Coolers, Modern Vehicular Coolers, The Fog Chamber Coolers, A New Small Rotary Drum Cooler, Outdoor Fog-Type Cooling, Small Rigid-Media Coolers, Solar-Powered Small Coolers, The Future, Review Questions.

IX. COMMERCIAL DIRECT EVAPORATIVE

COOLERS ...... 146

Slinger-Type Coolers, Adaptability, The Saturation Pads or "Filters," Pad Wetting Devices and Problems, Pump-and-Nozzle Pad Spraying, Air-Cleaning Effect, The Proper Name for Such Coolers, Cooling Effect, Cooler Construction and Materials, Advantages and Disadvantages, Rotary Pad Evaporative Coolers, The Rotors, Antiscaling and Anticlogging Features, Rotary Cooler Advantages and Disadvantages, Rotary Drum Coolers, Review Questions.

X. COMBINED EVAPORATIVE

COOLING SySTEMS ....... 163

"Add-On" Systems, Duct Size Problems, Add-On System Changeover, "Piggy-Back" Units, A Residential Unit, "Make-up Air" Units, A Heat Recirculation Method, The Future, Review Questions.

XI. AIR-WASHER

EVAPORATIVE

COOLERS ................ 174

Commercial Air Washers, Construction, Heating-Cooling Coils, Airflow, Spray Arrangements, Nozzles, Other Aspects, New

Table of Contents / xi

Developments, Cooling Performance, Advantages and Disadvantages, Cell-Type Air Washers, Construction, Capillary Cells, Wetting Devices, Air Cleaning Effect, Evaporative Cooling Performance, Trends, Review Questions.

XII. THE RIGID-MEDIA COOLERS .......................... 185 The New Materials, Rigid-Media Performance, Large Rigid-Media Coolers, Large Cooler Uses, Exhaust-Type Coolers, Small RigidMedia Coolers, Add-On Pads, Vertical Counter-Flow Coolers, Review Questions.

XIII. INDUSTRIAL PLANT COOLING ........................ . 200 Industrial Trends, True Costs of Industrial Cooling, The Cooling Opportunity, Refrigerative Factory Cooling, Ventilative Cooling, Circulating Fans, Evaporative Cooling versus Ventilative Cooling, Industrial Evaporative Cooling, Space or Room or Area Cooling, Central Station Systems, Spot or Person Cooling, Spot Cooling Outlets, Spot Cooling Accessories, a Special Case, Rules for Industrial Evaporative Cooling, Cooling Load Control, Cooling System Design, Space-Cooling Comfort, Spot-Cooling Comfort, Combined Systems, The Future, Review Questions.

XIV. TEXTILE MILL EVAPORATIVE

COOLING ............... . 226

History, Materials and Processes, Primary Mill Humidification Systems, Direct Humidification, Wet Ducts, Indirect Humidification, Atomizing Power Consumption, Conversion to Evaporative Cooling, Wet Duct Cooling, Dry Duct Cooling, New Looms, The New Textiles, Central Station Evaporative Cooling, Cooling Performance, Typical Mill Cooling Problems, Heating, Finishing Mills, Localized Exhausting, Makeup Air Supply, Finishing Mill Evaporative Cooling, Heating Finishing Mills, The Future in Textile Mills, Indirect Cooling, Review Questions.

XV. ANIMAL

AND POULTRY COOLING .................... . 247

Cooling Animals, Swine Cooling, Swine Cooling Systems, Controls, Outdoor Swine Cooling, Cattle Cooling, Economic Results, Cow Barns, etc., Poultry Cooling, Cooling Needs, General Results, a DripCooler Experiment, Exhaust Fans, a Slot Experiment, Economic Results, Current Drip-Cooler Use, Alternative Systems, Special Animal Houses, Systematic Ventilating and Heating, Pure Ventilating Systems, Eivaporative Cooling Special Animal Houses, Other Animals, Review Questiolls.

XVI. GREENHOUSE AND PRODUCE COOLING ............. . 268 Tomatoes,OtherFood Plants, Specific Benefits, Flower Raising, Greenhouse Cooling Systems, Wall Panel and Fan Systems, Wall Pads, Temperature Effects, Heating and Ventilation, Controls, Food Storage and Processing, Potatoes, Citrus Fruits, Other Products, Review Questions.

XVII. DIRECT COOLER RATING AND SiZiNG ............ , .. . 283 Performance Measurement, Proposed Evaporative Cooler Rating Units, Cooling Performance by Weighing, Sensible Heat Regain,

xii / Table of Contents Conventional Calculations, Rating Units Adjusted for Weather, Economy and Power Consumption, EERs and SEERs and Direct Evaporative EERs, Air-Cooling or Machine EERs and Evaporative Cooling Units, Direct Cooler Ratings, Comparison of Coolers, Useful Cooling and Comfort, Useful Cooling Chart, Comfort Conditions, Washed Air Entry to Rooms, Special Uses, A Sample Calculation, Rough Cooler Sizing, Better Cooler Sizing, Proposed Best Cooler Sizing Method, Washed-Air Temperature Gains Indoors, Related Cooler Sizing, Duct Use and Sizing, Power Consumption Estimates, Illustrative Sizing Problem, Review Questions.

XVIII. DIRECT EVAPORATIVE

COOLER INSTALLATION

....... 302

Cooler Location, House Coolers, Commercial Buildings, Duct Design, Connection to Heating Systems, Washed Air Distribution Aims, Ceiling Outlets, Wall Outlets, Hall Plenum Systems, Basement Plenum Systems, Low Outside Wall Diffusers, Direct Evaporative Radiant Cooling Systems, Window Mountings, Effect of Washed Air Distribution on Cooler Sizing, Washed Air Indoor Travel, Washed Air Discharge Outdoors, The Up-Duct Opportunity, Building Insulation, Insolation, Controls, Review Questions.

XIX. PRECOOLERS FOR REFRIGERATION CONDENSERS .. 319 Compressor Efficiency Gains, Condenser Air Precoolers, Commercial Refrigeration Precoolers, Precoolers for Air-Conditioning Condensers, Available Precoolers and Energy Savings, Very Small Condensers, Solar-Powered Precoolers, Review Questions.

XX. INDIRECT EVAPORATIVE

COOLING SySTEMS ......... 331

History, Simple Dry-Surface Tower-and-Coil Systems, Related Problems, "Closed-System" Cooling Towers, Regenerative DrySurface Systerp.s, The Gafford System, Plate-Type Heat-Exchanger Systems, The Pennington Heat-Storage-Wheel System, Tubular Indirect Cooling Systems, Two-Stage Indirect Cooling, Advantages of Staging, Direct Evaporative Second Stages, The Kennedy Two-Stage Cooler, Indirect Radiant Cooling, Review Questions.

XXI. MODERN PLATE-TYPE INDIRECT COOLING ........... 348 Terminology, Staging and Climatic Adaption, The Author's Research, Plate-Type Background, A Modern Plate-Type Cooler, Another PlateType Cooler, Australian Plate-Type Coolers, The Dimpled Surfaces, Performance, The Pescod Coolers, Their Design and Performance, A New Plate-Type Cooler, Its Plates, Analysis and Performance, Solar Powering, Scale Prevention, Review Questions.

XXII. OTHER MODERN INDIRECT COOLING ................. 367 Simple Tower-and-Coil Systems, Open Loop Indirect Systems,

Cooling Tower Stored Cooling Systems, Tubular Indirect Coolers,

Multi-Stage Performance, Another Tubular Indirect Cooler, a Vertical-Tube Cooler, Applications and Performance, Precooling Performance, Savings Staged with Refrigeration, Thermal Storage Wheel Coolers, Heat Exchange Wheels, Leakage Problems, WheelType Indirect Cooling, Winter Heat-Recovery Service, Review Questions.

Table of Contents /

xiii

XXIII. EXPERIMENTAL INDIRECT COOLING .................. 394 Rock-Bed Indirect Cooling, Bed Sizing, Cooling the Rock Beds, Charging Times, Cooling the Rooms, A Two-Stage System, Evaluation, A Semicontinuous System, An Australian Precedent, Passive Indirect Cooling, The Cool-Pool System, The Water Columns, Water Circulation, Performance, Evaluation, Desiccant Indirect Cooling, Desiccants, Open and Closed Cycles, Desiccant Wheels, Use in Evaporative Cooling, The Drying Process, Regeneration, Cooling the Hot, Dry Air, The Principal Cooling Cycles, The Solar Connection, Performance, The Future, On the Market, Review Questions.

XXIV. THE ECONOMICS OF EVAPORATIVE

COOLING ........ 413

Power Cost Trends, EER Efficiency Ratings, The Gordian Report, Reported Power Savings over Refrigeration, Owning and Life-Cycle Costs, The Economy of Other Direct Coolers, The Cost Comparison Problem, A Route for Comparisons, Demonstration, Sample Calculation for Direct Cooling, Sample Calculation for Indirect-Direct Cooling, The Economy of Indirect Evaporative Cooling Systems, The General Case, Summer Peak Load Savings, Summary, Review Questions.

APPENDiX ............................................. 427

ASHRAE SI (Metric) Psychrometric Chart, ASH RAE SI (Metric) Conversion Table, Report that Evaporative Cooling Does Not Carry Legionnaires' Disease, Dedications and Credits, Product Directory, Vitas.

CHAPTER I

INTRODUCTION Air conditioning is the simultaneous control of air temperature, humidity, cleanliness, and distribution within enclosed spaces. This study principally concerns cooling but necessarily includes processes that affect the other factors. . Specifically, evaporative air conditioning is the cooling of air by the evaporation of water. When water evaporates into the air to be cooled, simultaneously humidifying it, it is called direct evaporative cooling, the oldest and most common form. When the air to be cooled is kept separate from the evaporation process, and therefore is not humidified as it is cooled, that is called indirect evaporative cooling. It was discovered about 60 years ago and is still relatively unknown. Neither process is widely understood today. Most other methods for cooling arose during man's literate and scientific recent past, and they have been analyzed, recorded, and taught somewhat adequately. Evaporative cooling, however, had its birth in prescientific eras, when natural processes were seldom studied. It flourished chiefly in hot, lightly populated desert areas, where isolation prevented analysis and exposition; it was almost inoperable in the more populated and temperate seacoast areas that led in scientific investigation and publication. So, the antiquity of its beginnings, its seeming simplicity, and the nature of the locations where it has traditionally been used seem to have discouraged scientific inquiry into evaporative cooling. Consequently, this industry has far outstripped its related technical literature. In 1958, when at least 1,250,000 coolers were sold, the 1272-page Guide of the then American Society of Heating and Air Conditioning Engineers (now the American Society of Heating, Refrigerating, and Air Conditioning Engineers, or ASHRAE) devoted half a page to them, without tabl~s or data. Only in 1961, following three years of a millionplus cooler sales, did the GUide add a full chapter. . And, except for pamphlets and loose-leaf sales manuals, the 1963 edition of this book was the first in the field. After that edition, cheap and effective mechanical air conditioning overwhelmed evaporative cooling, and little further was published, though there was some technical progress in the field. In the 1970s, when power a~d interest rates rose and inflation first began to handicap refrigerative systems, ~vaporative cooling resumed its climb. Sales have mounted yearly ever since, and this book reflects the growing worldwide interest. Henceforth, evaporative cooling will probably continue to compete well with refrigerated air conditioning. First, tremendous markets for cooling and ventilating industrial buildings have resulted from rising wage levels and from the noted adverse relationship between hot temperatures and human productivity. An old and apt rule of thumb is that human productivity falls 2 percent for each degree of temperature over 70F (3.6%/degree over 21.1C), and 3 percent for each degree over 90F (4.8 %/degree over 32.2C). 1

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EVAPORATIVE AIR CONDITIONING HANDBOOK

In 1956 the United States had an estimated 600 million sq ft (55.7 million m 2) of space in uncooled offices, and 12 billion sq ft (1.11 billion m2) in factories, mills, and workshops, etc. Much of that has since been cooled, but industrial growth may have trebled the total uncooled area. There are many plants that cannot afford mechanical cooling but need massive cheap ventilation. Furthermore, rising costs and the fact that staged indirect cooling can now deliver nearly the same comfort as refrigeration almost everywhere away from seacoasts suggest that much of the industrial market will eventually fall to the more economical system. And much office and white-collar cooling tonnage may well convert to evaporative if rising costs persist, as most indices suggest they will. Unfortunately, there has been a great lack of available data in the area of evaporative cooling, and many errors and inefficiencies persist in manufacture, sale, and installation. Because only facts replace rule of thumb, hearsay, half-truth, and misinformation, the purpose of this book is to supply as much objective knowledge as possible about evaporative cooling.

Omissions This study omits two subjects because standard texts everywhere cover them adequately: cooling load calculation and duct design. Conventional computations for those subjects serve all evaporative cooling except as follows:

1. No cooling loads occur from infiltering outside warm air where fans create positive indoor air pressure, as is the case with almost all coolers containing, or immediately followed by, fans or blowers. 2. Infiltration cooling loads occur principally where large exhaust fans create negative indoor air pressure, as in many textile mills, industrial plants, animal barns, poultry houses, greenhouses, etc. 3. No cooling load is caused by ordinary evaporation of moisture into indoor air from exposed water, plant foliage, human or animal skin or breath, etc. Virtually always the resulting vapors are swept outdoors by moving washed air from the coolers without creating a heat balance. 4. Ducts for evaporative cooling are usually much simpler, shorter, straighter, and larger than those for refrigerative cooling or heating. Their design is conventional' and without complications.

Abbreviations In the following chapters the following standard abbreviations will be used: Absolute Acidity units Ampere Average British thermal unit British thermal units per hour British thermal units per minute Cubic Cubic feet per minute Cubic feet per second Degree, Fahrenheit Degree, temperature difference Dew point temperature Energy Efficiency Ratio

abs pH amp avg Btu Btuh Btum cu cfm cfs F deg C deg dpt EER

Introduction / 3 Feet per minute Feet per second Foot Gallon Gallons per minute Heat content or enthalpy Horsepower Horsepower-hour Hour Humidity, absolute or specific Humidity, relative Inch Inches, water gauge Kilowatt Kilowatt-hour Mean Radiant Temperature Miles per hour Minute Ounce Pound Pounds per square foot Pounds per square inch Relative humidity Revolutions per minute Revolutions per second Second Specific gravity Specific heat Specific volume Square inch Square foot Temperature, dry-bulb Temperature, Effective Temperature, wet-bulb Volt Watt Watthour

fpm fps ft gal gpm H hp hp-hr hr sh rh in. in. w.g. kw kwh

MRT mph mm

oz

lb psf psi rh rpm rps sec sp gr sp ht sp vol sq in. sq ft For dbt ET wbt V w

wh

SI (Metric) Abbreviations Centimeter Cubic centimeter Cubic meter Cubic meters per minute Cubic meters per second Degree, Centigrade (Celsius) Degree, temperature difference Gram Hour Joule Kilogram Kilojoule Kilometer

cm cc

m3

m 3 jmin m3js deg C deg gr h

J

kg kJ km

4 / EVAPORATIVE AIR CONDITIONING HANDBOOK Kilograms per minute Kilograms per second KiloJoules per minute KiloJoules per second Kilometers per hour Kilometers per minute Kilometers per second Kilowatt Kilowatts per hour Liter Liters per minute Liters per second Meter Meters per minute Meters per second Millimeter Power, mechanical or electrical Pressure, water gauge or Pascals Refrigerating capacity or tons Square centimeter Square meter Temperature, dry bulb Temperature, Effective Temperature, wet bulb Watt Watt-hour

English-Metric Equivalents See table in Appendix.

kg/min kg/s kJ/min kJ/s kmh km/min km/s kW kW/h I l/min 1/ s

m

m/min m/s

mm

kW Pa kW cm 2

m2

Cor dbt ET wbt W

Wh

CHAPTER II HISTORY OF EVAPORATIVE

COOLING

Evaporative air cooling occurs in nature near waterfalls and streams, over lakes and oceans, under dense foliage, and on wet surfaces, in particular, human skin. Most primitive humans probably observed it, and useful exploitation occurred in many areas and ages. Early development took place in the Near East, where a hot, arid climate provided both incentive and favorable conditions.

Primitive Evaporative Cooling Evaporative cooling was known to the ancient Egyptians. Frescoes from about 2500 B.C. show slaves fanning jars of water to cool them. The vessels were porous enough to maintain wet surfaces to facilitate the process. A Herculaneum wall painting from about 70 A.D. depicts a leather water bottle used for cooling drinking water. Ladies of the court of Francis the First sent to Portugal for "earthen vessels which would render the water cooler and more healthful." Similar primitive evaporative cooling occurs today in canvas-covered canteens for soldiers' drinking water, canvas "desert water bags" used in the U.S. Southwest, and the "ollas," or porous water jars, of American Indians and Mexicans. In India evaporation even helped make ice. Shallow beds in the earth, filled with a foot (30.5 cm) of straw insulation, supported shallow earthen pans on top. On still, frosty nights, even when the air fell no lower than 43F (6.1 C), ice formed, sometimes 1.5 in. (3.8 cm) thick. Evaporation plus radiation into the night sky provided refrigeration. Travelers in Persia reported ice production behind tall masonry "ice walls" running east to west, which kept daytime sun off shallow pools to allow such freezing at night. Old homes and buildings in Iran are frequently cooled evaporatively; rooms are partially underground to escape solar heat and contain pools of running water with ventilating towers opening above them to catch wind and divert it across the water surfaces below. Reservoirs for drinking water are similarly cooled. Both ancient Persians and some American Indians topped tents with felt, which was then kept wet to provide cooling. People in India still replace windward doors in summer with tatties, which are like screen doors covered with dried khus-khus grass. Originally kept wet by hand, some are now wetted using recirculating pumps and catch basins. Many are periodically soaked by balanced troughs above. Water from supply pipes trickles into the troughs until they overturn, saturating the pads. Gravity then rights them for refilling. Another Indian evaporative air cooler is the thermantldote. It uses a wheellike, revolving framework covered with khus-khl,ls grass kept wet like fatties, and revolving in a doorway. Our western pioneers often preserved food in cloth-covered boxes or food coolers. Pans on top or troughs below kept the cloth damp by capillary action. Many such

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boxes were mounted outside kitchen windows so that wind could increase evaporation. Simple comfort cooling followed; windows facing the wind were covered with moistened burlap, or drapes in doorways were dampened,or bed sheets sprinkled with water for cooler sleeping. The author has seen a Texas porch partially surrounded by falling water; perforated pipes above allowed curtains of droplets to fall past the areas open to breezes and into shrubbery below. A similar device has been reported in Peter the Great's gardens in old St. Petersburg. A tree was piped so that falling water surrounded but did not wet benches near the trunk. Leonardo da Vinci probably made the first mechanical air cooler, to cool the boudoir of his patron's wife. It was a hollow water wheel through which air was drawn by rising and falling water in its chambers as they revolved successively into and out of a stream. Water entering the wheel splashed through the air, cooling and cleansing it and forcing it through wooden valves out the hollow axle and into the boudoir.

Modern Evaporative Cooling Modern American evaporative cooling has two origins, eastern and western. Air washers and textile mill evaporative cooling were invented in the East between 1900 and 1930, largely for industries in New England and the seaboard South. The inventions seem to have had no antecedents in ancient times. The term "air conditioning" was first used by engineer Stuart W. Cramer of Charlotte, N.C., in a 1906 talk given at a cotton mill operators' convention. Then, before 1930, two different types of indirect evaporative coolers appeared in Arizona and California, closely followed by the drip and slinger styles of direct cooler. The indirect coolers were undoubtedly inspired by the regional success of cooling towers; the direct type, by local practices inherited from Indians and Mexicans. Separately initiated, the regional systems stayed apart. The East developed better textile mill cooling and cell-type air washers; the West devised slinger and rotary-pad coolers and mass-produced drip coolers. Eastern types became universal air treating and cleaning tools for industry, used little for cooling; western ones remained purely cooling devices for homes and buildings.

Eastern Evaporative Cooling In 1899 John Zellweger of St. Louis devised air-washing fans whose blades and casings were kept wet to,remove airborne dust and lint. Appearing in Chicago the next year was Robert Thomas's "Acme Washer," which conducted air through falling sheets of water. Those developments were superseded by the first modern air washers, designed by Dr. Willis H. Carrier, then chief engineer of Buffalo Forge Company and later founder of Carrier Corporation. These were spray chambers featuring multiple pressure-type spray nozzles and eliminator plates, which allowed air to pass through them but confined the cleansing mist and spray. While designed to purify air, those air washers also cooled and humidified it. Their cooling powers were little unde.rstood or exploited, but their ability to humidify fostered much pioneering use. Because textile manufacture required high humidity, cotton mills, beginning in 1906 with Chronicle Mills in Belmont, N.C., provided widespread markets. See Chap. XIV. The air washers replaced historic textile mill humidification systems. The latter were multiple overhead water atomizing sprayers, used to humidify dry indoor air in hot weather. But control of the process was poor and resultant humidity unpredictable. Furthermore, in summer, with the drying effect of both internal and solar heat loads underestimated, few early washers sufficiently humidified enough outside air to

History of Evaporative Cooling / 7

maintain adequate indoor humidity levels. By trial and error, adequate capacities were achieved with larger flows and enough nozzles and spray pressure to give saturating efficiencies approaching 100 percent. To foster understanding, 67 pages of Department of Agriculture psychrometric tables were adapted into the first psychrometric charts. Carrier questioned the charts and in 1911 presented his famous "Rational Psychrometric Formulas," which created accurate bases for evaporative cooling and for all air conditioning thereafter. Thus, evaporative cooling is the father of all systematic air conditioning today. The success of air washers in cooling textile mills stimulated the development of another cooling system, which is best called textile mill evaporative cooling, to utilize the traditional atomizing sprays in older mills. The sprays had never contributed significant cooling because, to conserve indoor humidity and water, mills were traditionally semisealed against outside air. Without fresh outside air, the sprays humidified without cooling. That was good for textile processing but very bad for human working conditions. In the late 1920s it was discovered that indoor fan circulation allowed mist from the humidifiers to reach all corners of the mill, so evaporative cooling could occur wherever open windows let outside air evaporate it. The textile industry pioneered in providing comfort cooling for employees and long led industry in gross area of airconditioned manufacturing facilities. Eventually, the air washer, supplied with water of different temperatures, became the universal device for humidifying, dehumidifying, heating, cooling, and cleaning air and became standard in most large heating and air-conditioning systems. Few are used purely for evaporative cooling today. In 1935 the cost and bulk of conventional air washers led Walter L. Fleisher to invent simple, compact air washers, in which air passed through thick cells of loosely packed glass fibers, kept wet by low-pressure sprays. With their greatly reduced space and weight, those cell-type units replaced many standard air washers for general air cleaning in chemical, smelting, refining, rubber, textile, and similar plants, though some were used for comfort cooling.

Western Evaporative Cooling The other two classes of American evaporative cooling developed chiefly in the relatively arid climates of Arizona and Southern California, where cooling towers were familiar sights and householders had long cooled air by vertical cloth strips hung in open windward windows and kept wet by absorption from troughs on the sills. Cooling towers are industrial devices for cheaply cooling recirculating water by evaporating some of it II-S it is sprayed in contact with a maximum of moving outside air, which is immediately discarded. The cooled water is then used to cool some hot process, power generatiqn, or the condensers of large refrigerated air conditioning. Reportedly, before 1925, experimenters in Arizona pumped cooling tower water through automobile raqiators to cool indoor air. Success was instantaneous. Oscar Palmer, a Phoenix aut? radiator dealer, began manufacture. Thousands of indirect evaporative coolers were installed in Arizona homes, shops, cafes, offices, hotels, institutions, stores, and schools. Residential systems then cost about $200 per room. (See Fig. II-I.) Two different styles of indirect coolers were developed in Los Angeles. They used plate-type heat exchangers instead of coils or radiators. In the more successful type, water sprays and air blasts directed at the outside of hollow metal plates cooled dry air passing through within. Those cooling systems were installed on the roofs of many chain and department stores from California to Arizona. An early description and diagram were published in a 1935 University of California bulletin. (See Fig. 11-2.)

8 / EVAPORATIVE AIR CONDITIONING HANDBOOK Spray nozzles

Spray nozzles

SIMPLE SPRAY TOWER

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Fig. II-I. Schematic view of cooling towers used in early southwest indirect evaporative coolers. Four-room houses often needed natural draft cooling towers 20 ft. high by 8 ft. wide by 4 ft. thick (6.1 by 2.4 by 1.2 m), broadside to summer winds and powered by 3- and 4-hp pumps. Deck-type towers cooled the water best. All collected dust and dissolved minerals in their pan water and circulated them through their often eight-row indoor air-cooling coils, where they formed internal scale, cut performance, required yearly acid removal, and eventually destroyed the systems.

The first mechanical direct evaporative cooler appeared about 1932 when householders began to assist their window-hung wet cloths with electric fans. By 1933, there were thousands of those homemade coolers in Arizona. The earliest were burlapcovered wooden frames wet by dripping water and mounted outside windows; electric motors, frequently equipped with automobile fan blades, stood on the sills and blew cooled air indoors. Cafes and barber shops were early users. Soon excelsior pads replaced burlap. Experimenters placed fans in open-fronted boxes, nailed 2-in. (5.1 cm)-thick pads of excelsior sandwiched in chicken wire across the backs, wet the pads by perforated copper tubing, and mounted the units in windows. First called "wet-boxes," they became known as "desert coolers" and then as "drip coolers." Two University of Arizona professors, brothers Martin L. and Paul M. Thornburg, conducted tests to improve designs and then circulated mimeographed instructions throughout the state. They were published by the University of Arizona in 1939, as "Cooling for the Arizona Home." Soon, in California, similar booklets encouraged both home-built and tin-shop made coolers.

Mass Production Begins Al Goettl, chief engineer of Phoenix Manufacturing Company, recalled 45 years later how formal drip cooler manufacture began. Homemade drip coolers had become so popular by 1935 that many people began to ask Southwest Sheet Metal Company, employer of Al and his brothers Adam and Gust, to make them better, metal ones.

History of Evaporative Cooling

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