Air coolers are enviornment- friendly (no CFC emission) and use very low electricity compare to air conditioners.

1. WORLD BANK TECHNICAL PAPER NO. 421
(I Eneegy
Series
Work in progress
for public discussion
WTP421
March 1999
Evaporative
Air-Conditioning
Applications Environmentally
for
FriendlyCooling
GelitJan Bom
Robert Foster
Ebel Dijkstra
AMIaijaTummer-s

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(List continues on the inside back cover)

3. WORLD BANK TECHNICAL PAPER NO. 421
Energy
Series
Evaporative
Air-Conditioning
ApplicationsforEnvironmentally
FriendlyCooling
GertJanBom
RobertFoster
EbelD#jkstra
Marja Tummers
The WorldBank
Washington,
D.C.

4. Copyright © 1999
The International Bank for Reconstruction
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ISSN: 0253-7494
Gert Jan Bom, Ebel Dijkstra, and Marja Tummers are development consultants at Ecozone, Haarlem,
the Netherlands. Robert Foster is a project engineer at New Mexico State University, Las Cruces.
Libraryof Congress Cataloging-in-Publication Data
Evaporative air-conditioning: applications for environmentally
friendly cooling / Gert Jan Bom . . .[et al.].
p. cm. - (World Bank technical paper; 421. Energy series)
Includes bibliographical references (p. ).
ISBN 0-8213-4334-3
1. Air conditioning. 2. Evaporative cooling. I. Bom, Gert Jan.
II. Series.
TH7687.E94 1998
697.9'3-dc2l 98-31273
CIP

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and A are
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Fuelwood Marketsand VillageManagement Natural Woodlands.
of

7. Contents
Foreword............................................................. ix
Abstract............................................................. xi
Acknowledgments ............................................................. xiii
Abbreviations, Symbols, and Glossary ............................................................. xv
1. Introduction............................................................. l1
Benefits of Evaporative Cooling .............................................................. 2
Opportunities and Limitations .............................................................. 2
Environmental Benefits.............................................................. 2
Direct Evaporative Air-Conditioning .............................................................. 3
Residential Coolers .............................................................. 3
Indirect Evaporative Air-Conditioning .............................................................. 4
Desiccant-Assisted Evaporative Air-Conditioning .............................................................. 4
Commercial Evaporative Air-Conditioners .............................................................. 5
Comparing Vapor-Compression and Evaporative Air-Conditioning ................................................. 5
Outlook .............................................................. 5
2. Opportunities and Constraints.............................................................. 9
Climatological Factors ............................................................. 9
Comfort Issues ............................................................. 10
Expected Performance of Evaporative Air-Conditioning ............................................................. 12
Power Supply ............................................................. 13
Water Supply ............................................................. 13
Advantages of Evaporative Versus Vapor-Compression Air-Conditioning .................................... 13
3. Economics............................................................. 15
Economics of Residential Coolers ............................................................. 15
Investment Costs ............................................................. 16
Market Situation ............................................................. 18
4. Technology ............................................................. 21
Direct Evaporative Air-Conditioning ............................................................. 21
Indirect-Direct Evaporative Air-Conditioning ............................................................. 26
Desiccant Cooling ............................................................. 29
5. Choosing and Maintaining Equipment ............................................................. 31
Available Equipment ............................................................. 31
v

8. vi Evaporative Air-Conditioning, Applications for Environmentally Friendly Cooling
Direct Evaporative Air-Conditioning Recommended Air Change Rate
for Design Wet-Bulb (WB) Conditions .......................................................... 33
Maintenance .......................................................... 33
6. Solar EvaporativeAir-Conditioning.......................................................... 37
The Market.......................................................... 37
Optimizing Evaporative Air-Conditioning Design for Solar Operation ..........................................
38
7. Introductionand Local Manufacturein Developing Countries.........................................................
41
Maintenance ........................................................... 41
Installation and Sizing.......................................................... 41
Manufacturing Requirements ........................................................... 41
Know-How .......................................................... 43
8. CommercialEvaporativeAir-Conditioning .......................................................... 45
Commercial versus Residential Cooling .......................................................... 45
Commercial Kitchen Evaporative Air-Conditioning .......................................................... 46
Laundry and Dry Cleaning .......................................................... 46
Extreme Heat Conditions .......................................................... 46
Industrial Applications .......................................................... 47
Factory Air-Conditioning Design Considerations ........................................................... 47
Agricultural Applications-Poultry .......................................................... 48
Greenhouses .......................................................... 49
Bibliography.......................................................... . 69
Annexes
1. Introduction to Evaporative Cooling .......................................................... 53
2. Suitability of Evaporative Air-Conditioning in Different Climate Zones ........................................
57
3. List of Manufacturers and Suppliers .......................................................... 63
Boxes
2.1 Relative Humidity and Wet-BulbTemperature .......................................................... 10
5.1 A Simple Sizing Example .......................................................... 32
Figures
1.1 Typical Direct Evaporative Air-Conditioner .3
1.2 Roof-Mounted Downdraft Evaporative Air-Conditioning Unit, El Paso, Texas .4
1.3 Direct Evaporative Air-Conditioner for Transport Use .7
2.1 Modified Evaporative Air-Conditioning Comfort Zone Taking into Account
Increased Airflow Compared with ASHRAE Comfort Zone Based on Vapor
Compression Air-Conditioning .11
2.2 Annual Energy Use Summary: Vapor Compression Air-Conditioning
(SEER= 9.5 for Phoenix, Arizona, USA).14
2.3 Annual Energy Use Summary: Indirect/Direct Evaporative Air-Conditioning
(2,000scfm, for Phoenix, Arizona, USA).14
3.1 Typical Investment Costs for Evaporative Air-Conditioning in the United States .16
3.2 Typical Investment Costs for Evaporative Air-Conditioning in India .17
3.3 Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioning
for the United States .17
3.4 Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioning for India .18
4.1 Simplified Evaporative Air-Conditioning Process .22
4.2 Psychrometric Process for Direct Evaporative Cooling, Mexico.22
4.3 Comnonly Available Rigid Cellulose Pads Provide Superior Saturation and Cooling
Compared with Ordinary Aspen Pads .24
4.4 Close-up of Rigid Cellulose Pad Made of Corrugated Paper .24
4.5 Common Cabinets for Residential Coolers in India .26

9. Contents v2i
4.6 Cutaway of a Direct Evaporative Air-Conditioning ................................................................... 27
4.7 Plate-Type Indirect-Direct Evaporative Air-Conditioning .................................................................
27
4.8 Indirect-Direct Evaporative Air-Conditioners on a Public School Rooftop,
Colorado Springs, USA.................................................................. 28
4.9 Indirect-Direct Evaporative Air-Conditioning Process ..................................................................
29
4.10 Ventilation Cycle Desiccant Cooling System .................................................................. 30
6.1 A Solar-Powered Evaporative Air-Conditioner .................................................................. 37
6.2 Evaporative Cooler Coupled with Solar Power (System installed by a homeowner
in Chaparral, New Mexico, USA).................................................................. 39
7.1 Evaporative Air-Conditioners in Kamla Market, New Delhi, India ................................................. 42
8.1 Typical Evaporative Air-Conditioning Application for Poultry Houses .......................................... 49
8.2 Evaporative Cooling Pad Section of Rigid Cellulose Pads .................................................................
50
8.3 External Evaporative Air-Conditioners on a Research Greenhouse, New Mexico
State University, Las Cruces, New Mexico.................................................................. 50
A1.1 Psychrometric Chart and Saturation Line .53
Al.2 Complete Psychrometric Chart .53
A1.3 Wet-BulbDepression of Ambient Air .54
A1.4 Saturation Effectiveness for an 80 Percent Effective Evaporative Cooling Pad .54
A1.5 Saturation Effectiveness of 80 Percent for Evaporative Cooling Pads at Different
Ambient Conditions .54
A1.6 Effectof Indirect Evaporative Cooling on Ambient Airstream .54
Al.7 Effect of Combined Indirect Evaporative Cooling Coupled with Direct Section.55
A1.8 Energy-Saving Effect of Using a Smaller Coil Coupled with Indirect and Direct
Evaporative Cooling Sections.55
A2.1 Suitability of Evaporative Air-Conditioning: Africa .57
A2.2 Suitability of Evaporative Air-Conditioning: Asia .58
A2.3 Suitability of Evaporative Air-Conditioning: Australia .59
A2.4 Suitability of Evaporative Air-Conditioning: Europe .60
A2.5 Suitability of Evaporative Air-Conditioning: North America.61
A2.6 Suitability of Evaporative Air-Conditioning: South Arnerica .62
Tables
1.1 Vapor-Compression versus Evaporative Air-Conditioning .................................................................6
2.1 Effectiveness of Evaporative Cooling by Climate Type ....................................................................
9
2.2 Relation between Wet-Bulb Temperatures and Effectiveness of Evaporative
Air-Conditioning .................................................................. 10
2.3 Evaporative Air-Conditioning Performance in Selected Locations at 1 Percent
Cooling Design Conditions .................................................................. 12
2.4 Benefits of Evaporative Air-Conditioning Versus Vapor Compression Air-Conditioning ............13
5.1 Available Residential Evaporative Air-Conditioning Equipment ..................................................... 31
5.2 Useful Cooling Chart: Percentage of Useful Cooling for Direct Evaporative
Air-Conditioning Output ................................................................... 34
6.1 Available Packaged Solar Evaporative Air-Conditioning Equipment .............................................. 38
6.2 Design Measures to Optimize Evaporative Air-Conditioning for Solar Power .............................. 38
7.1 Work Involved in Manufacturing Evaporative Air-Conditioning .................................................... 42

11. Foreword
Although evaporative coolers cannot be used in all countries and at all times, they are generally very
much underutilized in places where they can be used successfully. This is unfortunate, both for the
potential user, the country, and the global environment. Benefits include lower cooling equipment costs
and a much reduced electricity bill for the user, reduced electrical energy and power demand at peak-
times for the country, and lower greenhouse gas and CFC/HFC emissions for us all.
This handbook is designed for those who do not know evaporative coolers, but might be convinced
to try using or promoting them. It provides the advantages and disadvantages of using evaporative
coolers while comparing them to the commonly used, energy guzzling, and expensive vapor compres-
sion air conditioners. Existing markets where evaporative coolers are currently used, local manufactur-
ing possibilities, operational aspects are discussed along economic and global aspects. A world-wide list
of manufacturers and suppliers is included in the Annex.
James Bond
Director
Energy, Mining and
Telecommunications Department
ix

13. Abstract
As the harmful environmental effects of chloro-fluorocarbons (CFCs) and greenhouse gases have be-
come better known, interest has grown in environmentally friendly cooling technologies. Evaporative
air-conditioning (EAC) is such a technology. Whereas conventional vapor compression air-conditioning
(VAC)uses CFCs as cooling liquids, EAC uses water. EAC technology is simple, functional, and has both
residential and commercial applications in industrialized and developing countries. EAC can provide
superior cooling and ventilation while consuming less energy (and hence contributing less to green-
house gas emissions) than VAC. EAC works best in hot, dry climates, but it can be used in more humid
climates as well.
This paper elucidates some of the technical characteristics and fields of application for EAC and out-
lines the climatic conditions under which EAC can be most effectivelyemployed. The document begins
with a general outline of the applications and limitations of EAC and explains the differences between
"direct" and "indirect" EAC. Chapter 2 discusses the applicability of EAC in different climates and ex-
plains the use of wet-bulb temperature as a useful tool for predicting the applicability of EAC. Chapters 3
and 4 discuss the economics of EAC versus VAC in terms of energy consumption, required investments,
and life-cyclecosts. Production costs, the paper points out, are low enough so that EACs can be manufac-
tured relatively easily in the developing world, as is now being done in South Asia and the Middle East.
Chapters 5 and 6 review the market for EACs and try to show how EAC can increase individuals'
"feeling of comfort."
Chapter 7 explains the basic technology of EAC.The difference between direct and indirect coolers is
elaborated on through the use of a psychrometric chart. The hardware components of the EAC are ex-
plained: pads, motor, pump, and fan. Chapter 8 lists the equipment available on the market. It also points
out that the capacity of the cooler and the size of the room to be cooled are key elements in selection of an
EAC.A simple example is given to aid in sizing. Like any sort of mechanical equipment, EACs need to be
maintained regularly to perform well and last longer. Maintenance requirements for each component are
discussed in chapter 9. EACs require little energy, and because the presence of strong sunshine coincides
with the need for cooling, a link with solar energy appears to be attractive.
In chapter 10 the usefulness of solar EAC and the present market situation are outlined. EAC is an
attractive cooling solution, for industrial as well as for less developed countries too. The requirements for
the introduction of a relatively new technology like EAC are discussed in Chapter 11.In Chapter 12 the
usefulness of EAC for commercial applications is outlined. Commercial kitchens, laundry and dry clean-
ing and industrial applications are three areas where EAC could be useful.
xi

15. Abbreviations, Symbols,and Glossary
Design temperatures: outdoor temperatures at a fixed percentage more temperate than worst-case fig-
ures, which are a standard air-conditioning system design parameter.
Enthalpy: total heat content of air-water vapor atmospheric gas. Not altered by adiabatic cooling.
Evaporative air-conditioning: lowering of dry-bulb temperature as air passes over water. Two methods
using evaporating water to cool air: (1) direct, which is adiabatic and humidifies the air; and (2) indirect,
which is nonadiabatic and cools the air being treated.
Indirect evaporative air-conditioner. a heat and mass transfer device used to sensibly cool a primary
airstream, without addition of moisture, by means of an evaporatively cooled secondary airstream. Since
the secondary air provides wet-bulb depression, it represents a heat sink to the primary air.
Latent heat load: heat carried by water vapor in air; varies with humidity. Wet-bulb temperature is an
index to latent heat.
Saturation (cooling) effectiveness: the primary air dry-bulb temperature reduction divided by the pri-
mary air entering dry-bulb temperature less the entering secondary wet-bulb temperature.
Temperature, dry-bulb: the air temperature measured by a dry temperature sensor.
Temperature, wet-bulb: the temperature measured by a temperature sensor covered by a water-moist-
ened wick and exposed to air in motion. When properly measured, it is a close approximation of the
temperature of adiabatic saturation.
xv

16. Introduction
Evaporative air-conditioning (EAC) technologies are being used increasingly in residential and com-
mercial applications worldwide. EAC technologies-which rely on water as a coolant rather than on
chemical refrigerants-are economical to produce and use and have important environmental ben-
efits. This paper introduces the technical aspects of EAC, reviews EAC's scope of application, and
surveys the specific climatic conditions under which EAC can be used most effectively in industrial-
ized and developing countries.
Under the right conditions and applicafions, EAC can provide excellent cooling and ventilation with
minimal energy consumption using water as the working fluid and avoiding the use of ozone-destroying
chlorofluorocarbons (CFCs). Policymakers in particular should become better informed about EAC be-
cause of the opportunities it affords to reduce the use and emission of CFCs and hydrofluorocarbons
(HFCs), the reduction in CO emissions that come from the energy efficiency of the technology, and the
2
potential for mitigating problems of peak electricity demand during the hot season in many countries.
The viability of using EAC will depend on the particular application and on the local climatic conditions.
For example, for comfort cooling, EAC is most suited to dry regions, although technical improvements
such as indirect/direct and desiccant-assisted systems widen the zone of applicability. On the other hand,
some commercial applications of EAC are suitable even in humid climates.
In general, several sectors have significant reasons for considering employing EAC technologies:
* Utilities.Dissemination of EAC appliances can serve as a significant demand-side management
(DSM) tool for utilities. Power savings of EAC technology versus VAC are on the order of 70
percent for direct EAC and 50 percent for indirect EAC. This differential presents substantial
peak-saving opportunities for utilities that can promote the use of EAC within their service areas.
* Governments. goverrnent agencies and planners, cost savings from reduced electrical con-
For
sumption can be realized directly by incorporating EAC technology into buildings and other in-
stallations. In addition, government planners should encourage use of EAC technologies as a rel-
evant technology alternative to VAC that will save consumers money, reduce overall electrical
demand, reduce pollution emissions, and help meet international treaty obligations related to re-
ducing pollutant emissions.
1

17. 2 Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling
* Consumers. Consumers who use EAC at home can save money on cooling costs. The typical capi-
tal, installation, and operation costs are significantly lower for EAC technologies than for VAC
technologies. Moreover, EAC technology is simple enough so that most homeowners can main-
tain their own units.
* Privateenterprise. The manufacture and sale of EAC appliances presents significant opportunities
for both small and large enterprises. It is particularly suited to manufacture even in relatively
poor developing countries because-unlike the comparatively complex technical requirements
for production of chemical air-conditioners-EAC production requires only the basic infrastruc-
ture and skills mix related to sheet metal, motor, pump, and fan fabrication. Hence, marketers of
EACs can underbid VAC prices while maintaining comparatively high profit margins. In the
right climates, EACs can gain far more than a "niche" market: in some of the larger cities in the
southwestern United States and northern Mexico, for example, 95 percent of the residential air-
conditioning market is taken by EAC units, most of them manufactured locally.
Benefits of Evaporative Cooling
The following benefits of EAC can be cited:
* Significant local fabrication and employment
* Substantial energy and cost savings
* No chlorofluorocarbon (CFC)usage
* Reduced peak demand
* Reduced CO and power plant emissions
2
* Improved indoor air quality
* Life-cyclecost effectiveness
* Easily integrated into built-up systems
* Wide variety of packages available
* Provide humidification when needed
* Easy to use with direct digital control (DDC)
* Greater regional energy independence
Opportunities and Limitations
EAC works best for comfort cooling where it is hot and dry. EACs are widely used in the Middle East,
Australia, the Indian subcontinent, Eastern African, northern Mexico, and the southwestern United States.
Residential EACs are known in India as desertcoolers,and in such desert or dry-steppe climates EACs do
give "significant relief" during the hot months. "Significant relief" is considered to be provided when the
final supply-air temperature leaving the EAC is about 20' to 250C (680to 77°F). Even in a tropical savanna
climates such as in the northeast of Brazil, the Sahel region of Africa, the southwest Dominican Republic,
EAC can be useful in some comfort cooling applications and also for many commercial applications such
as greenhouses and poultry houses.
A limiting factor for the application of EAC is the definition of comfort. A residential cooler bringing
0
down the temperature from 450to 30°C(1130to 86T) may still be appreciated even if it does not provide
"significant" relief.
Environmental Benefits
EAC technologies represent significant enviromnental benefits related to reducing CFC/HCFC use and
for obviating C02 and other emissions, as well as for reducing peak electrical demand. For example, the

18. Introduction 3
4 million EAC units in operation in the United States provide an estimated annual energy savings equiva-
lent to 12 million barrels of oil and an annual reduction of 5.4 billion pounds of CO2 emissions. They also
avoid the need for 24 million pounds of refrigerant traditionally used in residential VAC systems. Similar
energy savings and environmental benefits are also made by commercial applications of evaporative
cooling technologies in the United States and elsewhere. Through increasing use of EAC technologies,
countries can save energy, reduce power plant emissions, obviate CFC usage, and improve indoor air
quality. Basic air conditioning with water is a relatively simple process.
Direct Evaporative Air-Conditioning
Direct EAC is the simplest, the oldest, and the most widespread form of air-conditioning. This system
typically uses a fan to draw hot outside air into a dwelling through a porous wetting medium. Heat is
absorbed by the water as it evaporates from the porous wetting medium, and the air thus leaves the EAC
at a lower temperature. The amount of cooling provided is determined by efficiency of the wetting me-
dium, the fan, and the overall design and construction of the unit.
A critical component in EAC is the use of water. This may vary from a few liters per day in small
residential coolers to perhaps a hundred liters or more in pad-and-fan EAC systems in greenhouses and
complicated duct-systems in laundries and hotel kitchens.
Residential Coolers
A residential EAC typically consists of a cubical box of sheet metal or plastic containing large vertical
filter "pads," an electric-motor-driven fan, a water pump, a water distribution system, and a water sump
at the bottom. As Figure 1.1 and Figure 1.2 show, the fan draws in warm outside air through the wetted
media, cooling the air. The water pump lifts the water from the sump through the distribution system to
the top of the pads from where it trickles down by gravity back to the water sump. The cooled air is then
delivered either directly through a grille into a single room or into a duct distribution system.
This is a "direct" EAC in which the cooled and saturated outside air flows into the room, displacing
the hot air. It is simple and cheap but is not sufficient for indoor comfort cooling once ambient wet-bulb
temperatures reach 21°C (69.8°F).
Figure1.1. TypicalDirect Evaporative
Air-Conditioner
Distribution
Manifold
d. Conditioned
Inlet Wetted Air
Air Media
Recirculation
Pump
Source:
Authors.

19. 4 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling
Figure1.2. Roof-MountedDowndraftEvaporative
Air-ConditioningUnit, El Paso,Texas
7."~ ~ ~ ~ ~~~~.
Source: R. Foster.
Indirect EvaporativeAir-Conditioning
Indirect-direct EAC is a method established only over the past 15 years. It is not as widely used as direct
EAC, but it is gaining in popularity because it cools air more than direct EAC, and cools the air down
from higher wet-bulb temperatures. hindirect EAC accomplishes these effects by building an additional
step into the cooling process. That is , the incoming air is cooled first with a normal air-to--airheat ex-
changer. This is the "indirect" stage because it does not add moisture to the supply air. Instead, only one
side of the heat exchanger is cooled with evaporating water as the supply air passes through the other
side, dropping in temperature as it does. Only then, as it passes through the direct EAC stage, is the
0
supply air moisturized. The final air leaving an indirect-direct EAC unit is generally 3.5C (6.3 F) cooler
than what could be achieved with a direct EAC unit alone.
Because it cools the air first without moisturizing it, the indirect-direct process also allows the EAC
unit to provide more comfort in slightly more humid areas. Commonly these units achieve 65 percent
indirect stage efficiency (performnance factor), which allows an ambient wet-bulb temperature of up to
250 C to provide acceptable room temperatures for real comfort.
Two-stage air-conditioners combinLing indirect and direct EAC are becoming popular in the United
States and Australia, particularly in locations where slightly higher wet-bulb temperatures (i.e.,conditions
of higher ambient humidity) do not permit sufficientlycomfortablesupply-air temperatures via direct EAC.
On the downside, however, the two-stage units have higher construction and maintenance costs.
Desiccant-Assisted EvaporativeAir-Conditioning
The use of dehumidifying chemicals (e.g., desiccants such as silica gel) further widens the scope for EAC.
Desiccant technologies can widen the scope for comfort cooling to even the most humid regions. In such
systems, the desiccant is used first to dehumidify the ventilation air to a desired state; then, EAC (either
direct or indirect or a combination thereof) is used to cool the air to the desired supply-air temperature.

20. Introduction 5
CommercialEvaporativeAir-Conditioners
Commercial EAC applications are of several types. Commercial comfort cooling applications are used
for offices,retail establishments, and so on, as determined by local climates and comfort preferences.
In other commercial applications, EAC may be used to moderate the effects of an additional internal
heat source that does not depend (only) on the climate or the time of the year. For example, temperatures
may rise inside warehouses or buildings because of the operation of ovens, machines, or the presence of
livestock. These heat sources sometimes exacerbate already high ambient temperatures. Although the
cooling requirements differ as a matter of degree, so to say, cooling of buildings affected by both internal
and external sources of heat does require a somewhat different approach from residential cooling to
moderate high outside ambient temperatures. For one thing, such commercial EAC systems may well
need to be designed for operation the year round rather than just in a "hot season." A commercialkitchen
or bakery, for example, might need cooling year-round. Moreover, the internal cooling requirements may
be quite localized within the building (e.g., spot-cooling in a manufacturing plant).
Another difference between commercial and comfort cooling with EAC is that EAC in some com-
mercial applications is the only practical alternative; that is, where VAC technologies cannot function or
compete effectivelybecause of high operating costs. The most salient example here is the cooling towers
in a power plant, but on a smaller scale, EAC is the only real alternative in agricultural applications such
as greenhouses, where VAC is both inappropriate and far too costly
Common commercial applications for EAC include the following:
* Commercial kitchens
• Hotels and restaurants
- Hospitals
• Other institutions
* Laundry and dry cleaning
* Industrial applications
- Agricultural applications
- Poultry sheds
- Greenhouses
* Schools and offices
* Transit buses (Figure 1.3)
* Industrial applications
- Warehouses
- Spot cooling
- Factories
ComparingVapor-Compressionand EvaporativeAir-Conditioning
Table 1.1 compares the basic characteristics of VAC with those of EAC.
Outlook
Worldwide, the potential for EAC is much greater than is currently realized. Investment, operation, and
replacement costs can be lowered significantly by foregoing or replacing VAC technologies and using
EAC.The potential applications are manifold: from buildings and homes to buses and kitchens. In some
developing regions of the world where air-conditioning has scarcely arrived, EAC could bring comfort,
as VAC may not be affordable by many because of its high investment and operating costs. Even where
the conventional electric grid service is available, EAC may be a viable and economically attractive op-
tion, particularly in conjunction with the use of solar photovoltaic (PV) modules.

21. 6 Evaporative
Air-Conditioning:
Applications Environmentally
for FriendlyCooling
Table 1.1. Vapor-Compression versus Evaporative Air-Conditioning
Basic characteristics Vapor compression AC Evaporative AC
Coolant CFCs/HFCs Water
Production residential coolers Small and large scale Small and large scale
Sensitivity to humidity for Applicable in all climate types Applicable in dry hot climates
comfort cooling applications for comfort cooling
Ventilation (indoor air quality) 20% outside air 100%outside air
Energy use in a typical residential 1,000kWh/yr 350 kWh/yr
air conditioner for a 100m3 room.
Investment for a residential cooler Developed country Developed country
US$1,000-1,600 US$200-700
Less developed country Less developed country
US$600-1,400 US$60-300
Maintenance Change filters every 2 years Annual pad change for aspen
sump coat every 2 years
Annual accumulated costs In USA: US$500 In USA: US$170
including power, maintenance, In India: US$500 In India: US$37
depreciation
Source:
Authors.
Some options expanding and realizing the benefits of EAC are noted below:
Low energy use/solar. Small EAC units using solar photovoltaics (PV) are available in several com-
mercial and prototype models. Manufacture and dissemination could be done through commer-
cial channels providing cost-efficient cooling in grid-and non-grid settings.
Transfer technology. EAC technologies are a fertile field for South-South transfer of technology,
I of
in particular with regard to small residential coolers and some agricultural applications.
S
. upport possibilities. EAC has substantial applicability as a demand-side management tool, in gov-
ernment offices and schools. Technical assistance to developing countries, pilot programs, and
demonstrations all may provide further opportunities for EAC.

22. Introduction 7
Figure 1.3. DirectEvaporative
Air-ConditionerforTransportUse
Note he EAC unit(onthe forklift at right) wasbut by imatran andisbeinginstalledontoatytransitbusinDenverColorado.
More than 400 buses in the United States and more than 1,200in Australia use evaporative air-conditioning.
Source: Foster.
R.

24. Opportunities and Constraints
Climatological Factors
Unlike vapor-compression air-conditioning, which can work under virtually any climatic conditions,
evaporative air-conditioning varies in applicability and efficiencywith the relative humidity of the out-
side air: that is, the drier the air, the more suitable EAC is and the better it cools. The general climatic
parameters for applying EAC for comfort cooling can be superimposed on the world map in terms of
three types of climatic zones that are, respectively, highly, moderately, and marginally suitable for EAC
(Annex 2 contains maps showing these zones of applicability of EAC for each continent). The climate
types are listed in Table 2.1, and for each type the effectiveness of EAC is indicated. This effectiveness is
rather constant for desert climates, but for both the steppe and savanna climates, a generalization about
applicability masks what may be significant month-to-month variations in the actual comfort derived
from EAC. It should be emphasized, moreover, that this sort of zoning provides only a rough indication
of suitability; each zone may contain areas that are better or worse suited for EAC than their assignment
to the zone would suggest. Moreover, some specialized EAC applications (e.g., in greenhouses or poultry
houses) are effective and commonly used in even the most humid of climates outside of these zones.
EAC is already popular in the desert climate zones such as the arid southwestern United States,
Mexico, Australia, Iran, Iraq, Jordan, Libya, Spain, Sudan, Egypt, India, Pakistan, and South Africa.These
Table 2.1. Effectiveness Evaporative
of Coolingby ClimateType
Climatetype Generaleffectiveness EAC
of
Desert Realcomfortduring the wholecoolingseason(e.g.,offices, homes,libraries,restaurants)
Steppe Realcomfortduring the dry period of the hot seasonand moderatereliefcoolingduring
more humid periods
Savanna Onlycan provide reliefcoolingduringthe hot season(e.g.,warehouses,greenhouses,
poultryhouses).
Source:Authors.
9

25. 10 Evaporative
Air-Conditioning:
Applications Environmentally
for FriendlyCooling
Box 2.1. Relative Humidity and Wet-Bulb Temperature
Apart from using the rough measure of climate zones or the level of humidity, one can predict the effectivenessof EAC for a
particular location fairly accurately using the locally prevailing wet-bulb temperatures (WB).Table 2.2 shows how these are
measured. In brief, by adding about 5-C (9°F)to the WB,one knows the effectiveroom temperature that can be reached with
EAC. Becausethe WBvaries over seasons and during the course of the day,it does not suffice to use average WB. Rather, one
should consider the WB at the time when cooling is most important-for example,around noon.
areas have in common high summer temperatures coinciding with low humidity-that is, high ambient
temperatures combined with low wet-bulb temperatures. This combination means that EACs can be
very efficient and can provide real indoor comfort (see Table 2.2 and Box 2.1 for a range of benefits). A
total of about 20 million EAC units are presently in use worldwide.
EAC is largely unknown, however, in many areas with steppe or savanna climates, even though it
could constitute a real alternative to VAC.
Comfort Issues
"Human comfort" depends on a range of factors ranging from temperature, humidity, and air movement
to clothing and culture. What is comfortable for one person in one society may be entirely uncomfortable
for another. Someone who has long lived without VAC may find an artificially air-conditioned environ-
ment uncomfortable, whereas people who take VAC for granted in their homes and workplaces may
avoid being outside during hot weather all together.
Standards
Comfort zones are often shown on standard psychrometric charts and have been developed to indicate
regions where a person is "comfortable." In the United States, the American Society of Heating, Refriger-
ating and Air-conditioning Engineers (ASHRAE)has developed comfort zones based on psychrometric
charts. However, these standard types of comfort charts have more limited relevance related to evapora-
tive air-conditioning. First, standard comfort zones are based on air velocities typical of vapor-compres-
sion air-conditioning systems, not the higher air velocities used with evaporative air-conditioners. Sec-
ond, the traditional comfort zones used today (unlike those of the past) have horizontal, constant humid-
ity-ratio (constant dew point) lines supposedly aimed to minimize respiratory diseases, mold growth,
and similar problems. Relative humidity boundary lines are just as effective (and were previously used)
and would distort comfort analysis less. Tests have shown that human comfort is a continuum, not con-
fined between dewpoint lines. Consequently, the standard comfort zones commonly used face shortcom-
ings relative to EAC.
Table 2.2. Relation between Wet-Bulb Temperatures and Effectiveness of Evaporative Air-Conditioning
Wet-bulb Typical supply air temps
temperature Type of EAC Unit (Dry-bulb) Cooling effectiveness
15-210 C Direct 17-230 C Real comfort
21-230 C Direct 23-250 C Moderate relief
Indirect / direct 22-230 C Real comfort
23-270 C Direct 25-300 C Some relief
Indirect / direct 23-260 C Moderate relief
Source:
ECI.

26. Opportunities Constraints
and 11
TheModified Comfort Standard for Evaporative Air-Conditioning
The effect of a given air stream on a person can be determined by an effective temperature chart, as is
commonly used when calculating wind chill. By increasing the velocity of movement, air feels cooler.For
evaporative air-conditioning, it is more reliable to consider a comfort zone bounded by relative humidity
and extended to take into account the cooling effect of increased airflow, as shown in Figure 2.1.
Figure2.1. ModifiedEvaporative
Air-ConditioningComfortZone Takinginto Account Increased
Airflow
Compared with ASHRAE ComfortZone Basedon VaporCompression Air-Conditioning
23.9
Wet-Bulb
Temperature (°C) 18.3 90_L_g
Modified
Comlbrt
Zone
2i < AtArddt ioning 70
7.2 12.7 18.3 23.9 29.4 35.0 40.6
Dry-BulbTemperature(0C)
Source:
ECI.
Actual Comfort
The actual comfort derived from EAC for a given dry and wet-bulb temperature depends on the follow-
ing factors:
* Saturationeffectiveness the evaporative
of Only if the saturation effectiveness is 100
air-conditioner.
percent can the temperature of the air leaving the air-conditioner be equivalent to the wet-bulb
temperature. This depends on the condition and quality of the medium, heat losses from the mo-
tor, fan, and pump, and heat absorption through exposure of the air-conditioner cabinet to direct
solar gain. Typicalsaturation efficienciesare between 60 and 90 percent for commercially available
media.
* Heat absorption the spaceto be cooled.This depends on exposure of walls and roof to solar gain,
of
shading, number, size, and location of windows and construction materials.
* Heatgenerationin the space.Number of people present in the room, their activity and the presence
of heat generating equipment such as copy machines, stoves, television, and computers.
* Sizing of the EAC unit.
* Properinstallationand airflows.Cooled air should be properly divided and directed so as to most
effectively "wash" the space and occupants to be cooled.
* Activity of the occupants.Sedentary people require less cooling than physically active persons.
EACmay only be the only realistic way to provide a high level of comfort for every day of the year in
many desert climates. In some locations, EAC maybe acceptable for users willing to experience less than
full comfort from the EAC for a few hours on the hottest days of the year because the slight discomfort
does not outweigh the extra costs associated with VAC.

27. 12 Evaporative
Air-Conditioning:
Applicationsfor
Environmentally
FriendlyCooling
Expected Performance of Evaporative Air-Conditioning
The expected performance for both direct and indirect/direct EAC units commonly found in the market
for selected locations worldwide is given in Table 2.3.
Table 2.3. Evaporative
Air-ConditioningPerfornancein SelectedLocations 1 PercentCoolingDesign
at
Conditions
1% designconditions Directsupply Indirect/Direct
Location DB/WBa Air DBb Supply Air DBC
Asia/Pacific
Alice Springs, Australia 39.4/20.0 22.9 17.6
Beijing,China 35.0/23.31 25.1 22.1
Bangalore, India 35.5/23.3 25.2 22.2
Christchurch, New Zealand 27.8/17.8 19.3 16.4
Melbourne, Australia 34.4/20.6 22.6 18.9
Kabul, Afghanistan 36.7/17.8' 20.6 15.6
Singapore, Singapore 32.2/26.1 27.0 25.6
Middle East
Riyadh, Saudi Arabia 43.9/20.0 23.6 17.1
Ankara, Turkey 36.1/18.3 21.0 16.1
Jerusalem, Israel 33.3/17.2 19.6 15.0
Tehran, Iran 38.3/16.7 19.9 13.7
Africa
Cairo, Egypt 38.9/23.3la 25.6 22.1
Casablanca, Morocco 34.4/21.1la 23.1 19.0
Europe
Madrid, Spain 35.6/20.0 22.3 18.2
South/Central
America
Cali, Colombia 28.9/20.0 21.3 19.0
Santiago, Chile 32.2/19.4 21.4 17.9
Caracas, Venezuela 28.9/20.6 21.8 19.7
San Jose, Costa Rica 29.4/20.6 21.9 19.7
NorthAmerica
Los Angeles, California, USA 35.6/20.0 22.3 18.2
Denver, Colorado, USA 33.9/15.0 17.8 12.2
Albuquerque, New Mexico,USA 35.6/16.1 18.1 13.3
Las Vegas,Nevada, USA 42.2/18.9 22.4 16.1
Dallas, Texas, USA 38.9/23.9 26.1 22.2
Guadalajara, Mexico 33.9/18.9 21.1 17.2
Mexico City, Mexico 28.9/15.6 17.6 13.9
Ciudad Juarez, Mexico 37.8/17.8' 20.8 15.2
a. Temperatures in °C, 1%Dry-bulb/Mean Coincident Wet-bulbdesign conditions (ASHRAE).
1. 1%design dry bulb condition and 5%design wet-bulb condition (U.S.Army).
la. (ASHRAE).
b. Direct saturation effectivenessof 85% is assumed; dry-bulb supply temperature °C.
c. All casesassume an overaUperformance factor of 65% for the indirect process and asaturation effectivenessof 85%for the
direct process; dry-bulb supply temperature 'C.
Source:ECI.

28. Opportunities Constraints
and 13
Power Supply
The power requirements for EAC units can range from 100Wfor the smallest units to more than 1,000W
for the larger packaged sizes. Because a packaged EAC unit has a low-mass fan and a centrifugal water
pump, it creates little demand for extra current during start-up. This means that if the unit requires a
current of 1 amp for operation, a power supply of 1 amp is also sufficient for starting. In contrast, a VAC
of, say, 1,200Wand 5 amps would require a starting current of at least 10 amps.
In developing countries where power demand often exceeds the supply, voltage drops are not un-
common. This is detrimental to VAC units because the compressor motor has to supply a constant torque
and may draw too much current and burn its windings. EAC units on the other hand are much more
tolerant of voltage fluctuations because both the fan and the centrifugal pump draw less current at lower
voltage and thus simply run at a lower speed without overheating.
Water Supply
The water consumption of most packaged EACunits varies from 5 to more than 100liters per day depending
on cooler size, ambient temperature, relative humidity, and operating hours. The units can be directly con-
nected to the main water line, controlling the water feed through a float valve, or they can be manually filled
for smaller indoor units. Accessto a water supply is a prerequisite for EAC.The units with automatic water
feed can make do with a relatively smallreservoir,but the manually filled units use a larger reservoircapacity
commensurate with the water consumption so as not to require refilling more than once or twice a day.
Advantages of Evaporative Versus Vapor-Compression Air-Conditioning
EAC has several significant benefits over VAC (Table2.4 summarizes the comparative benefits). For one
thing, EAC consumes significantly less energy than VAC. The only power-consuming components of a
direct evaporative cooler are fans and small water pumps; in contrast, VACs and heat pumps are more
complex, having more fans and a compressor (see Figure 2.2 for a summary of use by VACs).People
living in dry regions that require cooling thus can realize large energy (and cost) savings by using EAC
instead of VAC systems. As noted, the energy savings of EACs vary with humidity levels and tempera-
tures. Direct systems in low humidity regions typically yield energy savings of 60 to 80 percent over VAC
systems. Indirect/direct systems yield 40 to 50 percent energy savings in moderate humidity zones (Fig-
ure 2.3). Indirect systems with vapor-compression second stages can provide adequate comfort cooling
in high-humidity zones with savings of up to 25 percent.
Air-Conditioning
Air-ConditioningVersusVaporCompression
Table 2.4. Benefitsof Evaporative
Item EAC VAC
Power consumption 50to 70%Lowerthan AC High
Indoorair quality Muchbetter using100% outsideair Poorwith 20%outsideair
Refrigerants Water CFCs,HFCs,HCFCs
Maintenance Annualpad changefor aspen, filter change
Bi-annual
fiveyear pad changefor cellulose
Fabrication Simple Moderatelycomplicated
Pollutionemissions No CFCemissions CFC,HFC,HCFCemissions
lowerpower plant emissions high power plant emissions
Waterconsumption High (evaporation and Moderate(waterneededat the
bleed-off) power plant)
Localemployment High for fabrication,distribution, Moderatefor fabrication,
installation,and maintenance high for distribution,installation,
and maintenance
Authors.
Source:

29. 14 Evaporative
Air-Conditioning:
ApplicationsforEnvironmentally
FriendlyCooling
Figure 2.2. Annual Energy Use Summary: Vapor CompressionAir-Conditioning (SEER = 9.5for Phoenix,
Arizona, USA)
12,000 -
s 10,000
E 8,000
2 6,000
>, 4,000
NbO
2,000
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Natural gas * Electricity
Source:
ECI.
Figure 2.3. Annual Energy Use Summary: Indirect/Direct Evaporative Air-Conditioning (2,000 scfn,for
Phoenix, Arizona, USA)
12,000
,_ 10,000
8,000
> 6,000
b 4,000
2,000
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Natural gas * Electricity
Source:
ECI.

30. 3
Economics
In general, evaporative air-conditioners are much less expensive to purchase and operate than vapor-
compression air-conditioners. It must be noted, however, that these two cooling technologies must be
compared with care because VACcan always provide full comfort (provided the unit is adequately sized
for the load and the owner is willing to pay the electric bill), but EAC cooling depends on local climato-
logical conditions. Thus it is only in settings where both EAC and VAC can provide comfort cooling that
a true comparison can be made. Beforedelving into the economics of EAC and VAC, it is worth enumer-
ating several elements that play a role in the economics of both types of cooling:
* Cost of the cooler
* Cost of installation
• Length of the cooling season
* Cost of electricity
* Cost of water
* Interest rate.
Economics of Residential Coolers
Worldwide, the most widespread EAC applications are small- and medium-sized packaged residential
coolers. More than 20 million residential units are installed around the globe. They are produced in dif-
ferent ways. In India, small enterprises use a labor-intensive production process (1 million units a year
are manufactured by some 300 to 400 enterprises in New Delhi alone). These "desert coolers," made of
sheet metal, wood fiber pads, and a simple pump, find their way onto the market either as finished
products or as kits and are transported and installed all over India. The other fabrication techniques are
more sophisticated. For example indirect-direct EAC production in Australia and the United States use
coated sheet metal, plastics or fiberglass, efficient cellulose paper pads, computerized thermostats, and
bleed-offs. These units are marketed with glossy brochures and exported to a number of countries. Prices
vary as much as production. In India, the smallest coolers are about US$35 and the largest US$150or
more. In Australia and the United States, direct EAC outdoor units sell for US$300to US$700,and simple
15

31. 16 Evaporative
Air-Conditioning:
ApplicationsforEnvironmentally
FriendlyCooling
indoor units are available for US$40 and up; however, the largest and most expensive units sell for more
than US$1,200.
The investment cost for a direct-indirect system is roughly double that for a direct EAC unit (and in
fact approaches the level as VAC). However, the direct-indirect EAC's power consumption is only about
25 percent higher than direct EAC on an annual basis, and the total cost of electricity and maintenance for
indirect-direct EAC systems amounts to only about 50 percent of that of conventional VACs of compa-
rable performance.
Investment Costs
Figure 3.1 compares typical total investment costs of EAC and VAC systems for different room sizes (20,
2
60 and lOOm ) for the United States. In all cases EAC is the cheaper option.
Figure 3.1. TypicalInvestment Costsfor Evaporative
Air-Conditioningin the United States
2,500 -
, 2,000-
- 1,500 _
E 1,000
,
500-
20 EAC 20 AC 60 EAC 60 AC 100EAC 100 AC
Room size in sq m for EAC and AC
ES Installationcost Costcooler
Source: Foster.
R.
It is striking that although the cost of EAC coolers in the United States is low, the cost of installation
is relatively high, because of the labor involved in placing the cooler, connecting it to water and electric
power sources, and providing a drain for the flush water.
The same has been done for India in Figure 3.2. Here the difference between EAC and VAC is much
more pronounced because EAC units are made by small wayside industries at very low cost, whereas
VAC units are either imported or made by large, inefficient industries at much higher cost.
The cost of installation in India is low because labor is cheap. These typical investment costs for India
and the United States illustrate that the relative economic merits of EAC are more pronounced in devel-
oping countries than in the industrialized world.
Life-Cycle Costs
The life-cycle operationalcosts have alsobeen analyzedfor these two countries,as depictedin Fig-
and
ures 3.3and Figure3.4.

32. Economics 17
Figure 3.2. Typical Investment Costs for Evaporative Air-Conditioning in India
1,000-
Cei- 800
600 -
i 400 -
200-
0
20 EAC 20AC 60 EAC 60 AC 100EAC 100AC
Room size in sq m for EAC and AC
Installation cost Cost cooler
Source: Foster.
R.
Figure 3.3. Typical Life-Cycle Costs: Evaporative Air-Conditioning versus Air-Conditioningfor the United
States
6,000 -
,5,000
m) 4,000
8 3,000
2,000
1,000
0
20 EAC 20 AC 60 EAC 60 AC 100EAC 100AC
Room size in sq m for EAC and AC
* Depreciation 2 Energy n Water
D Interest Maintenance
Source: Foster.
R.

33. 18 Evaporative
Air-Conditioning:
Applicationsfor
Environmentally
FriendlyCooling
Figure3.4. TypicalLife-CycleCosts:Evaporative
Air-Conditioning
versus Air-ConditioningforIndia
6,000 - -_
rA 5,000-
4,000
8 3,000
2,000 -
1,000
0- , ,
20 EAC 20 AC 60 EAC 60 AC 100EAC 100 AC
Room size in sq m for EAC and AC
* Depreciation E Energy n Water
D:Interest Maintenance
Source: Foster.
R.
For the calculation of the operational costs it was assumed in all cases that the maintenance is done by
a hired professional, which explains the rather high annual maintenance cost for EAC in the United States.
In reality, however, many EAC owners do their own maintenance because it is easy and saves money. In
developing countries where labor is cheap, maintenance is generally done by professionals. In India, for
example, it is common for owners of EAC units to have a maintenance contract with an EAC dealer.
Market Situation
At least 20 million residential EAC units are in operation worldwide. Of these, some 8 to 10 million are in
India, and more than 4 million are in the United States. Other significant markets also exist in Australia,
South Africa, Pakistan, and Saudi Arabia. EAC also has significant market potential in many other areas
of the world (e.g., in the Sahel); yet in most of these areas, EAC technology is unknown.
A significant reason why EAC units are not in operation in more areas around the world is that half
or more of the world's population lives in coastal regions, or within 100 kilometers of coasts, and these
areas are typically humid and hence generally not the most favorable sites for EAC units. In contrast, the
most favorable climatic conditions for using EAC are in dry and hot desert regions, and these are com-
paratively sparsely populated.
Population differences notwithstanding, sufficient populations live in dry and hot regions to consti-
tute meaningful markets for EACs. In the United States, for example the current sales of direct EACs are
more than US$150million per year. Moreover, the recent growth of the U.S. EAC market has been signifi-
cant, with annual increases of 10 percent reported by manufacturers.
California, which traditionally has used VAC, represents one of the world's fastest-growing EAC
markets. The California Energy Commission (CEC), noting the 50 to 80 percent energy savings pos-
sible with EAC (as opposed to VAC)technologies statewide, adopted energy credits for EAC as part of
the Title 24 code compliance program in January 1993.Inclusion of EAC in the Title 24 program facili-
tates significant prospective growth of the industry in California. The CEC is also promoting an EAC

34. Economics 19
commercialization program that seeks to accelerate adoption of EAC to maximize its energy saving,
environmental, and economic development potentials.
Several California utilities are promoting EAC for commercial and residential applications as well.
Pacific Gas and Electric (PG&E) offers rebates for commercial use of evaporative cooling equipment.
Under the utility's customized program, hybrid and two-stage EACs can receive a US$200/kW reduc-
tion as replacements for VAC technologies. PG&E also offers a line-item rebate for the installation of
commercial evaporative cooling equipment at US$80per ton displaced of VAC for new construction as
part of a "Retrofit Express" program.
Locally in California, the Sacramento Municipal UtilityDistrict (SMUD)has a new construction rebate
program that provides rebates to EAC in the commercial sector based on calculated energy savings com-
pared with conventional cooling. In late 1992Southern California Edison began offering US$100rebates
for installation of residential EAC (direct and indirect-direct) in their service territory. The company has
promoted these rebates actively in desert locations, offering an incentive of US$125for replacement of
residential VACunits with EACequipment. Southern California Edison also provides and maintains EACs
at no cost to qualifying low-income residents in their service area. On the commercial front, the company
is interested in energy conservation in the retrofit market and offers rebates at US$75 per ton for direct
EAC and US$100per ton for indirect-direct EAC for displaced tonnage of VAC(they use 1,250cfm = 1 ton
cooling).About 30 to 50 commercial installations are taking advantage of this program each year.
The State of New Mexico is requiring the use of EAC (mainly indirect-direct systems) instead of
VAC systems in new public schools and additions. New Mexico places about 100 new EAC applica-
tions per year in schools.
The Stratospheric Ozone Protection Division of the U.S. Environmental Protection Agency (EPA)has
included EAC as an acceptable technology in the EPA's Significant New Alternatives Policy (SNAP)
rulings on alternative refrigerants and technologies. This should further encourage the adoption of EAC
technologies in the United States.
Greenpeace and other environmental organizations are advocating EAC as an environmentally re-
sponsible technology worldwide. This type of interest from environmental organizations should also
further global market development.
The greatest market development problem facing the EAC industry currently is the lack of a normal-
ized test standard for performance ratings. Saudi Arabia and Australia have some limited general test
standards. However, the American Society of Heating, Refrigerating and Air-Conditioning Engineers
(ASHRAE)standards committees on EAC have submitted a proposed test standard for testing indirect
evaporative air conditioning equipment adopted by ASHRAE in 1996. Similarly, a proposed ASHRAE
test standard for direct EAC units should be adopted in 1998.When these standards are adopted, the
industry worldwide will benefit from a proposed certification program for rating EACs based on the
ASHRAE test standards by the Evaporative Cooling Institute. This certification program will provide
design engineers worldwide with an independent performance-based test standard for rating EACunits.
The EAC market should continue to grow worldwide as interest from utilities and countries in-
creases in applying the technology as an energy conservation tool. Given advances with indirect and
hybrid systems that widen the climatic range of application, the potential market penetration of this
technology is large. Indeed, when coupled with desiccant technologies, EAC could displace VAC tech-
nologies in many applications in the coming century.

36. 4
Technology
Direct EvaporativeAir-Conditioning
A residential evaporative air-conditioner consists of a cubical box with large, vertical filter-like "pads," a
sump at the bottom, an electric-motor-driven fan, a water pump, and a water distribution system (see
Figure 4.1). The fan draws in warm outside air through the wet pads, cooling the air. The water pump
lifts the water from the sump through the distribution system on top of the pads from where it trickles
down by gravity back to the sump. The cooled air is then delivered either directly through a grill into a
single room or into a duct system to cool more than one room.
This is a "direct" evaporative air-conditioner in which the cooled and humidified outside air flows to
the room and removes the heat. An efficient wetted pad can reduce the air temperature by as much as 95
percent of the wet-bulb depression (ambient dry-bulb temperature less wet-bulb temperature), while an
inefficient and poorly designed pad may only reduce this by 50 percent, or worse. A simplified process
diagram for direct evaporative air-conditioning is shown below. There is actually very little change in
energy state of the air (i.e. there is no sensible cooling) other than energy inputs from the fan and make-
up water. Direct EAC is simple and cheap but it has the disadvantage that if the ambient wet-bulb tem-
perature is higher than 21°C(69.8°F),the cooling effect is not sufficient for indoor comfort cooling.
The saturation effectiveness of a direct evaporative air-conditioner best describes the performance of
the unit. Saturation effectiveness is defined as the difference between the entering and exit dry-bulb (DB)
temperatures over the wet-bulb (WB)depression and can be defined as follows:
Saturation effectiveness = DBI - DB2
DB, -WB1
where
DB = Entering (typically ambient) dry-bulb temperature
1
DB2 = Exiting dry-bulb temperature
WB1 = Entering (typically ambient) wet-bulb temperature
21

37. 22 Air-Conditioning:
Evaporative for Friendly
Applications Environmentally Cooling
Figure 4.1. Simplified Evaporative Air-Conditioning Process
Dry air Water Moist air
Latent
energy
35 0 C e.. Latent.
DB energy
:::. Heat needed
to evaporate
water
Direct
Sensibl evaporative
heat ~~~cooler 210 C
energy D
Water ha
You feel 35°C Sensible and You feel 21°C
latent heat energy
Sensible heat in the air is used to evaporate water
(transfered to latent energy in the moist air)
Source:
Authors.
A psychrometric chart, which shows moist air properties, more clearly demonstrates the evaporative
cooling process. The initial dry-bulb and wet-bulb temperatures are shown at the start of the process, and
the endpoint of the evaporative cooling process is found to the left at the end of the arrow along the line
of constant wet-bulb temperature. For example, taking 1 percent design conditions for Ciudad Juarez,
Mexico, of 37.7°C (99.9°F) dry-bulb temperature at a mean coincident wet-bulb temperature of 17.7°C
(63.9°F), and using evaporative media that has a saturation effectiveness of 85 percent, we find that the
evaporative media will change the state of the airstream to a dry-bulb temperature (supply air) of 20.7TC
(69.3°F). This process is shown in Figure 4.2 for Ciudad Juarez.
Figure 4.2. Psychrometric Processfor Direct Evaporative Cooling, Mexico
20.70 CDB for
S.E.=85%
a // ~~~Direct
Evaporative oa
/4/
/ ti~~Coling Process +;o
0
Cd. Jukrez, Mexico i
37.7 DBJ17.7°C WB 2
Dry-Bulb Tempearture °C
Source:
ECI.

38. Technology 23
Direct evaporative coolers do not recirculate air in applications. Instead, air is passed only once through
the system and then exhausted. This leads to superior indoor air quality. Evaporative cooling media also
act as a wetted filter that scrubs out many contaminants (see also Figure 1.1).
Pads
The pad-or medium, as it is often called-serves to bring the water and air into contact so that the air
can absorb moisture and lower the dry-bulb temperature (cooling effect). An ideal pad should have the
following characteristics:
* Minimum resistance to airflow
* Maximum air-water contact for vaporization
* Equal distribution of airflow resistance, air-water contact, and water flow
* Resistance to chemical or biological degradation
* Ability to self-clean airborne matter
* Durability and consistent performance over life-cycle
* Low cost.
In reality, all pads fall short of this ideal and thus require some trade-offs among advantages. There
are at present three major types of pads: aspen (or other similar type) wood, rigid pads, and synthetic
pads. Each has its own advantages and disadvantages.
Aspen Wood Pads. These pads are composed of thin shredded wood slivers, packed loosely to a
thickness of 3 to 5 cm. This material is spread equally over the pad-holder surface and held in place by a
flexible steel or plastic grid. The thin wood strands absorb water and ensure good diffusion of the water
over the surface of the pad, which gives it sufficient cooling characteristics. This good cooling, combined
with the very low cost (US075per replacement pad) has made aspen wood the most popularly used pad
material worldwide. Aspen pads have some serious deficiencies in performance and durability, however.
First, because wood is an organic material, it degrades fairly quickly in humid conditions. In application,
this means that the strands decrease in strength and sag under the weight of the water they have absorbed.
T'he sagging means that some areas of the pad become more compact, blocking the airflow, while other
areas become more open, increasing airflow at the cost of reduced saturation efficiency.This combination
leads to reduced cooling.Moreover,dust, pollen, and other airborne organic or inorganic matter are trapped
between the strands of the pad, increasing resistance to airflow and imparting unpleasant odors to the
cooling air if the pad is not properly dried during daily use. Similarly,when the EAC is turned off and the
remaining water in the pad evaporates, it leaves behind a deposit of minerals, called scale. This scale is not
completely dissolved when the unit is restarted and it impairs the airflow and blocks the pad.
Depending on the intensity of usage, the level at which mineral concentrations are controlled (ad-
equate bleed-off), and the outside air quality (quantity of dust in the air) aspen pads may be replaced
once a cooling season or sometimes after two cooling seasons. Even so, optimum performance of the
EAC may only be achieved in the first weeks after installation of pads. A properly packed pad may start
with 70 percent saturation efficiency but may decline to 50 percent efficiency after only a few weeks,
operating at that level or less until it is replaced.
Another problem with aspen wood pads is their sensitivity to installation technique. That is, the pads
must be installed so as to ensure that the woody material is spread in equal density across the pad's total
area. If this is not done, the saturation efficiency will be reduced from the start. Because replacement of
pads is needed regularly and appears to be a relatively simple task, many EAC owners will do it-with
varying results in terms of efficiency-themselves.
Rigid Pads. Rigid pads became available in the early 1980's. They are made of a specially impreg-
nated type of paper or glass fiber and typically use a honeycomb type structure. They are made of strips
of corrugated paper alternative with upward and downward slopes, cemented together where the corru-
gations touch (Figures 4.3 and 4.4). This arrangement eliminates most of the problems associated with
aspen wood because rigid pads have the following advantages:

39. 24 Evaporative
Air-Conditioning:
Applications Environmentally
for FriendlyCooling
Figure 4.3. Commonly Available Rigid CellulosePads Provide Superior Saturation and Cooling Compared
with Ordinary Aspen Pads
Source: Munters Corporation.
Figure 4.4. Close-up of Rigid Cellulose Pad Made of Corrugated Paper
Source:Munters Corporation.
* Long and fairly constant service life between three and seven years, depending on maintenance
* Largely self-cleaning (i.e., dust washes off)
* No biological deterioration of the pad material
* More consistent saturation efficiency of about 75 to 90 percent
* Low pressure drop across the pad.
The disadvantage is that rigid media are more costly (about US$100more on an EAC that would cost
US$300if using aspen wood pads). They are also bulkier, which makes them difficult to use in smaller
units. At present, about 25 percent of the EACs sold in the United States are fitted with rigid pads, a share

40. Technology 25
that is growing. In fact, some U.S. manufacturers expect that eventually most EACs will be fitted with
rigid pads because of their performance advantages over aspen pads.
OtherPad Materials. In a bid to improve on aspen wood, some manufacturers are supplying pads
made of woven plastic. The plastic pads avoid many of the disadvantages of aspen wood but have the
disadvantage of poor cooling efficiency because of the poor wetting characteristics (low saturation effec-
tiveness) of the plastic material. Other substances have been tried as pad materials such as woven ex-
panded paper, fabrics, wood wool made of pine, fir, cottonwood, cedar, redwood, spruce, plain and
etched glass fibers, copper, bronze and galvanized screening, but none of these are extensively used.
Country-SpecificPad Materials.In each country where evaporative air-conditioners are used or are
intended to be used it may be advisable to look for an inexpensive and easily available indigenous pad
material-such as Khus-khus grass in India-or a long-lasting alternative such as a rigid pad. The objec-
tive, of course, is to avoid the need for continuous large-scale shipment of pad materials such as aspen
wood from the United States or Australia or if corrugated paper from Europe.
Cabinet
The cabinet of the air-conditioner is usually made of hot dip galvanized steel, coated with baked on high
quality paints (see Figure 4.5). Corrosion can be a problem with drip air-conditioners because most parts
come into contact with highly oxygenated water and concentrated solutions of waterbome or airborne
chemicals. To eliminate corrosion problems some manufacturers supply stainless steel air-conditioners
and some others air-conditioners made entirely of polypropylene, polyurethane, or glass fiber. In Austra-
lia at least one manufacturer brings an aluminum air-conditioner on the market. Stainless steel air-condi-
tioners are expensive and very sensitive to electrolytic corrosion (one screw of the wrong material may
cause corrosion of the whole air-conditioner) and glass fiber or plastic models are subject to deterioration
due to ultraviolet radiation. If galvanized steel cabinets are cleaned and repainted inside after every sea-
son, they should last 10 years or more.
Fan and Motor
Small air-conditioners (up to 55m 3 /min of washed air), serving only one or two rooms are often fitted
with an axial propeller type fan. These fans, with 2 to 4 blades, operating at 900 to 1,400rpm are noisier
than centrifugal types but are about twice as efficient. For higher airflow resistance, as is usually the case
for larger air-conditioners delivering air to a duct system, centrifugal fans are more suitable. They are
very quiet in operation but the efficiencyis only half of that of an axial fan.
Axial fans are usually fitted directly on the motor shaft but centrifugal fans are belt driven and geared
down to roughly 1/3 of the motor speed. In general it can be said that the larger the fan and the lower the
speed the more quiet it is.
The motors for most residential air-conditioners are two-speed, single-phase, shaded-pole and four-
pole types in the range of 200 to 1000W.They should have a drip proof construction and a 50°Callowable
temperate rise, certified by some recognized authority. More advanced designs are beginning to incorpo-
rate variable speed motors.
Recirculation Pump
The most popular pump is a small submerged centrifugal pump driven through a vertical shaft from an
air-cooled motor mounted dry above the waterlevel in the sump. These pumps are inexpensively made
(US$15retail price) and may last no more than three to five seasons. They require no maintenance but can
be vulnerable to dry running. The capacity is generally not more than 20 1/min against a head of about
lm. In many cases there is a small outlet besides the pump discharge for the purpose of continuously

41. 26 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling
Figure4.5. CommonCabinetsforResidentialCoolers India
in
Photo: R. Foster.
bleeding off some of the water circulated to prevent an excess concentration of minerals in the water. To
combine this bleeding off with operation of the pump limits the loss of water during operation only.
Controls
Direct-drip air-conditioners can generally be run on two speeds, with or without the pump. Operating
the air-conditioner without the pump can be desirable when the outside humidity is too high for effective
cooling but ventilation still provides some comfort. In the United States and Australia many EACs are
now also supplied with an indoor thermostatic control to stop the unit when it gets too cold and start it
when it gets too hot.
The air outlet of either the air-conditioner or the duct is usually fitted with a bidirectional set of
louvers to control the direction of the airflow.
Indirect-Direct EvaporativeAir-Conditioning
A two stage air-conditioner combining indirect and direct processes is gaining popularity in the United
States in places where the higher wet-bulb temperatures (i.e.,higher ambient humidity) does not permit
sufficiently low indoor temperatures from a simple direct air-conditioner. In this system the outside air is
precooled in an indirect stage and then further cooled in a subsequent direct stage. The first stage cools
the air without adding moisture and in the second stage moisture is added. The result is that the final air
temperature leaving the air-conditioner is generally 3.5 °C lower than what could be achieved with a
direct air-conditioner only. This expands the application of evaporative air-conditioning considerably to
areas with slightly higher wet-bulb temperatures. Commonly 65 percent indirect stage efficiency (perfor-
mance factor) is reached which allows an ambient wet-bulb temperature of up to 25°C to provide low
enough room temperature for real comfort (see Figures 4.6 and 4.7 for pictures of direct and indirect-
direct evapoative air-conditioning).
The investment cost is however roughly double that of a direct air-conditioner (nearly the same level
as for refrigerative air-conditioning) but the power consumption is only about 25% higher on an annual
basis than for direct air-conditioners. The total cost of electricity and maintenance for indirect/direct
systems amounts to roughly 50 percent of that of vapor-compression for the same performance.

42. Technology 27
Figure4.6. Cutawayof a DirectEvaporative
Air-Conditioning
Key 1:galvanized and painted steel (or sometimew plastic) housing, 2: louvered pad frame for air-inlet,3: blower wheel and shaft
4: water distribution system (header), 4: motor with belt driven centrifugal fan, 5: thermally protected water pump with bleed-off,
6: extra finish is good against rust, and 7: float valve, also overflow and bottom drain are located in the water sump.
Source:ECI.
Figure 4.7. Plate-Type Indirect-Direct Evaporative Air-Conditioning
Conditioned SecondaryOutside Air
SupplyAir Pad
uts Air
Secondary Outside
Air Exhaust
Source: ECI.