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Second Edition

Dr. John R. Watt

with the assistance of Richard L. Koral Loren W. Crow

Alfred Greenberg


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. TH7687.W3 1986 697.9 86-17172 ISBN-13 :978-1-4612-9387-3 e-ISBN-13:978-1-4613-2259-7 DOLlO.IO07/978-1-4613-2259-7



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.


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



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



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.



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 Rigid-Media 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 Drip-Cooler 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 Dry-Surface 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 Plate-Type 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, Wheel-Type 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.