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USES , ADVANTAGES AND LIMITATIONS OF EVAPORATIVE COOLERS
Dr. Osama Mohammed Elmardi Suleiman Khayal
Department of Mechanical Engineering, Faculty of Engineering and Technology, Nile Valley
University, Atbara Sudan
email@example.com address: E
Abstract The benefits and advantages of an evaporative cooler, also known as swamp cooler, air cooler, or
desert cooler include inexpensive price and lower energy consumption, as well as easier and
inexpensive installation and maintenance, when compared to traditional air conditioners; and
suitability for use in dry and arid climates, especially during hot and dry weather conditions.
On the other hand, the disadvantages of an evaporative cooler center primarily on the negative
impacts of too much humidification. These disadvantages translate further to more specific
limitations and drawbacks. For example, using an evaporative cooler for prolonged period of time
or under a hot and humid weather increase health-related risks such as respiratory distress, as well
as the susceptibility of wood-based, paper-based, and electronic products.
Evaporative cooling has both advantages and disadvantages, and the choice rests with the individual
homeowner. Therefore, the consumers should investigate all the alternatives and then make the
right decision based on technical specifications, cost preference, lifestyle and individual priorities.
Keywords: Components, advantages, limitations, evaporative cooler, maintenance
Most world population residing in hot regions have traditionally regarded evaporative cooling as a
good way to keep cool in the summer. Before the advent of residential air-conditioning it was the
only mechanical means available to make home interiors livable in the hot, dry, desert summers.
its accompanying elevated humidity and thus decreased cooler efficiency. These cooling systems
are economical in terms of energy usage. During the energy crunches of the last four decades,
evaporative cooler use was promoted as one means to control household utility bills. However, little
thought was given to cooler water consumption. With rapidly increasing population, warm
temperatures, and limited water supply, evaporative cooler water usage can no longer be ignored.
With conservation as the cornerstone of the Groundwater Management Act, researchers at The
University of Arizona Office of Arid Lands Studies developed in the mid-1980s a W-Index or index
of residential water efficiency. The index was proposed as a device to evaluate residential water
savings and as a management tool to motivate water-saving practices . The researchers noted that
for home cooling, the highest index rating is received for having no evaporative cooler, the
alternative being air-conditioning which although using more energy, uses practically no on-site
water. This advice flies in the face of all the energy-conservation practices supported by utility
companies, industry and educational institutions and leads to confusion with mixed messages to
In arid and semi-arid regions consumers have learned that air conditioning uses three to five times
as much electricity to cool their homes as evaporative cooling. They know how much their utility
bills rise in the summer months. Some have added evaporative cooling for use during the hot, dry
Others have changed over completely to evaporative cooling, reducing their cooling utility bills.
Yet evaporative cooling consumes significant amounts of water, and water is a precious and
increasingly costly commodity in most of the universe.
How much water does an evaporative cooler use. Data for evaporative cooler water use are scarce
since little research on this topic has been undertaken, and many factors, from household
composition to location of the cooler, influence cooler water use. In Cool Houses For Desert
Suburbs, Jeffrey Cook, a Phoenix architect, estimates that a 4500 CFM (cubic foot per minute)
cooler, under certain weather conditions, uses 200 gallons of water per day.
On the other hand, in a television interview in Tucson in September 1990, a Tucson Water
Company employee stated that an evaporative cooler adequafindte to cool a 1,500 square foot home
uses approximately four gallons of water per hour or 96 gallons per day, an estimate 50 percent
Tucson household cooler uses a year-round average of 16 gallons per day  . These projections of
water use convert to annual water costs in Tucson ranging from about $16 to $97 for a 26-week
A research study was initiated by the Office of Arid Lands Studies at the University of Arizona and
the Water Services Department at The City of Phoenix with funding from the Arizona Department
of Water Resources. This study monitored evaporative coolers at 46 homes in Phoenix. The
preliminary data from this study indicates that water usage of an evaporative cooler in Phoenix was
about 7.6 gallons for each hour that the cooler was operated (4.4 gallons per hour for systems
without bleed-off and 10.4 gallons per hour for systems with bleed-off)
Major Components and Functions of Evaporative Coolers
A. Major Parts of An Evaporative Cooler
The typical evaporative cooler consists of eight major parts: housing (metal or fiberglass), a blower,
recirculating water pump, water reservoir, float valve, pads, water distribution lines, and electric
B. Work Principle of An Evaporative Cooler
The cooling process works on the principle of evaporation of moisture. The fan of the cooler draws
outside air through pads soaked with water. The evaporation of the water lowers the temperature of
the air passing through the wet pads of the cooler. This cooled air is blown through an opening into
The movement of the cooled air is directed by the homeowner by means of ducts to appropriate
areas around the home and exhausted from partially opened windows, doors or ceiling ducts.
C. Ways to Use Evaporative Coolers
There are three ways to use evaporative cooling: (1) as the sole cooling system, (2) as a second
alternative cooling system to refrigeration (air conditio
One advantage to having both systems is that you get the best of two worlds - evaporative cooling
during the dry months in spring and fall, and refrigeration in the hot summer months when the
temperature and humidity are higher.
Despite the convenience of the combined system, there are drawbacks. For example, considerable
air movement is required for comfort with evaporative cooling. Refrigeration ducts are often too
small for this and result in insufficient air flow and more noise. Also from the utility standpoint, the
use of both systems results in an enhancement of the peaking problem for both water and power
suppliers and, therefore, contribute to the need for additional capacity of these systems which are
poorly utilized in off-peak demand periods.
For systems using shared ductwork, dampers must be installed to separate the two units. Without
dampers, refrigerated air will escape to the outside through the evaporative cooler and, conversely,
moist air from the evaporative cooler will enter and corrode the refrigeration unit. Many systems
have dampers that are automatic. They should be checked annually for correct operation.
Care must be used when operating the evaporative cooler and refrigeration unit alternately. The
refrigeration system will work much harder than normal since it has to remove the moisture brought
into the house by the evaporative cooler. Moisture from the cooler will condense on the refrigerant
coil and increase electrical costs appreciably; therefore, one should not directly precool air to be
refrigerated . Figs. 1 and 2 below show two types of cooling pad elements.
Fig. 1 Aspen wood fiber pad
Fig. 2 Paper cellulose pad
D. Placement of Coolers on Buildings
Evaporative coolers can be classified according to the position of the cooler in relation to the
building. Generally, there are three types: (a) down-draft (roof mounted), (b) side-draft (typically
eave or window mounted), and (c) up-draft (ground mounted).
Roof mounted, down-draft coolers (a) are sometimes preferred since they can usually be more
readily connected to duct systems and are out of the way on the roof. However, eave mounted (b) or
ground mounted (c) units can be more easily and safely serviced since the person doing the
maintenance does not have to use a ladder to inspect or repair the system. Figs. 3 and 4.
Fig. 3 Typical side draft evaporative cooler
Fig. 4 Single pad evaporative cooler
E. Use of Water by Coolers
The use of water by coolers is generally dependent on their size, air movement and relative
humidity of the air. Therefore, all things being equal, a 4500 CFM cooler uses less water than a
6000 CFM cooler. Research is showing that some units appear to more efficiently evaporate water
and, thus, produce more cooling per unit of water use
F. Selection of the Right Size of Coolers
Multiply the square footage (length by width) of the floor area by the ceiling height and divide by
two. For example, a 1600 square foot home multiplied by a ceiling height of eight feet is 12,800
cubic feet, divided by two is 6400. An evaporative cooler with a CFM number closest to 6400
should be adequate for your home. CFM are usually clearly marked on the front of the cooler.
Consult with your cooler supplier about cooler size. Too large or too small coolers are wasteful of
both water and energy and will not provide the comfort or efficient use of resources you are seeking
for your home.
G. The Advantage of a Two-Speed Cooler System
The advantage of a two-speed system is that low speed can be used at night when exterior
temperatures drop or on days when temperatures are not excessive. Low speed could also be used
during the day when family members are working. When family members return home, high speed
would quickly lower the temperature. Coolers usually run more quietly at low speed and provide
about 66 percent of the airflow of high speed. They also use about 30 percent of the energy needed
to run the cooler at high speed, thus reducing operating costs. Many individuals believe it is more
economical overall to leave the coolers off when the building is not occupied.
H. Use of Water When Operating the Cooler System At Low Speed
The amount of cooling generated by an evaporative cooler is a function of the amount of
evaporation that occurs in the unit. Increased dry air movement over the wet cooler pads will
increase the amount of evaporation and produce more cool air. At the same time, decreased air
movement will decrease the amount of water used for cooling, while the bleed-off rate will remain
I. Maintenance of Evaporative Coolers
A cooler should be inspected monthly and serviced
manual should be read to determine if more frequent servicing is required. Before starting any
maintenance operations, read all operating and maintenance instructions and observe all cautions
and warnings. During these maintenance inspections all parts should be inspected for wear or
damage. Belt tension and water level in the reservoir should be checked. Since cooling efficiency
is determined by how much water is evaporated, it is important to see that the pads receive a
uniform wetting and be thoroughly wet at all times to provide the most cooling. Dry spots will
greatly decrease cooling efficiency. The Arizona Department of Commerce Energy Office publishes
a pamphlet that describes in detail cooler maintenance procedures .
J. Advantage of Using Thermostat
A thermostat can be set to start the cooler when a certain temperature, for example 80 degrees, is
reached in the home. When the cooler is not operating, it is using neither water nor energy.
Thermostats cost from $30.00 - $45.00. Timers can also be used to start the cooler and begin the
cooling of the home prior to the arrival of the family. The use of 2 function thermostats starts the
wetting of the cooler pads prior to air movement and thus prevents the blowing of dry air into the
K. Recommended Types of Pads
Cooler pads (sometimes called media) come in several alternatives. University of Arizona
agriculture engineers have long recommended aspen wood fiber pads. They are encased in
chemically treated cheesecloth to absorb more water, and they offer the least amount of resistance
to air flow through the cooler. Aspen wood pads can be used for an entire cooling season. Although
aspen wood pads are efficient in distributing cooled air, they may also produce debris in the water
reservoir, increasing cooler maintenance. Some cooler manufacturers recommend a cellulose fiber
media or pad for use with their equipment. The media is said to be uniform throughout, to provide
consistent cooling performance and to last for several seasons. They are superior to spun aluminum
and plastic pads available at hardware or do-it-yourself stores or supermarkets. These are less
expensive initially than aspen wood but may need to be changed several times in one cooling
The newer single pad coolers require a much thicker pad. This type of pad is more expensive than
the traditional aspen wood fiber pad but is designed to last for several years if the cooler is operated
in compliance manual.
L. Effect of minerals in Hard Water in the Operation of Evaporative Coolers
Mineral deposits and scale build-up caused by hard water can cause rust and corrosion in metal
coolers. Some estimates are that this rust and corrosion can shorten a coole
Further, scale build-up on cooler pads can cause uneven distribution
on the pads and reduced cooling because of reduced air flow. Some manufacturers recommend
- valve to the recirculating water line. A bleed-off valve is installed in the
recirculating line and is typically connected to a drain line or directed to irrigate turf areas or other
landscaping. This results in draining part of the recirculating water, reducing buildup of hard water
minerals. Bleed-off valves are controversial because it is estimated that they increase cooler water
usage from 10 to 50 percent. Data from the Phoenix cooler study indicates that bleed-off systems
use an average of about 8,650 gallons during the cooling season . Horticulture specialists
discourage collecting bleed-off water for irrigating plants. The high concentration of minerals in the
water may kill or damage plants . The high salt content also can result in the sealing of soils,
especially soils with a high clay content, thus preventing moisture penetration. Some plant species
such as Bermuda and salt grass can tolerate the high salt content water . Bill Witschi, the Water
Systems Manager at the University of Arizona, suggests that bleed-off should be about 1/3 makeup
water. The rate could be lowered if no scale is observed forming on the cooler pads .
M. Increasing Cooler Life
Thorough cleaning of the cooler is suggested to remove mineral deposits and scale build-up at least
once during the cooling season. Additives to the water supply also are available to help reduce scale
build-up. Chemicals will not reduce scale build-up but they can increase the solubility of calcium
and other minerals, thus allowing a lower bleed-off rate, or they can combine with the calcium and
produce a softer scale that is easier to remove. Some cooler manufacturers do not recommend their
use because they may damage the protective coating on the cooler. Caution should also be exercised
about what chemicals are used because these can be blown into the home during the normal
operation of the cooler. Ask your cooler supplier. However, you may have to replace the cooler
sooner than you would if you used a bleed-off valve.
N. Circulating Air Without Water
With cool air in the evening and nighttime hours, the cooler fan can be run with dry pads. This
brings cool air into the home and circulates it without using water. Ceiling and/or oscillating fans
used in occupied rooms can help circulate the air for increased comfort. If cooler pads have been
allowed to dry out, either through non-use or by circulating air only, it is advisable to run the pump
and saturate the pads thoroughly before running the cooler fan. This ensures that cooler air begins to
circulate sooner and reduces the introduction of dust and pollen into the home.
season and then switch back to the
evaporative cooler as the relative humidity decreases at the end of the rainy season, remember that
standing water in the cooler pan is a stagnant pool. This water can become a good place for the
growth of bacteria, even the bacteria to drain
the cooler if it will not be used for several days. Alternatively, the water in the cooler pan can be
treated with chlorine for at least 30 minutes before turning the cooler back on.
O. Using Softened Water to Operate Evaporative Coolers
The sodium added to water by water softening will accumulate on the cooler pads and will become
concentrated in the water reservoir. Softened water also may increase the need for pad maintenance
and the rate of rusting of metal cooler parts.
P. Function of Ceiling Vents
Ceiling vents or open windows are required to permit the exhaustion of the air blown into the home
by the blower. Unlike refrigeration systems which recycle air within the home, coolers blow large
volumes of cooled outside air into the living areas, and this air needs to be vented from the home.
Ceiling vents make it possible to keep windows and doors closed while the cooler is running. This
is helpful for security. These prefabricated exhaust ducts are installed in the ceiling in several rooms
of the home. These exhaust air into the attic which must have an adequate amount of vents. UL
tested ducts that automatically close in case of fire are available from cooler equipment suppliers.
The venting of house air into the attic will also reduce the air temperature in the attic and thus the
amount of heat gain in the living area of the home.
Homeowners could also benefit from window stops, available from most hardware stores for almost
all types of windows. With stops in place, windows cannot be opened beyond a certain point chosen
by the homeowner, usually 6 to 8 inches. they are easy to install, very inexpensive, and discourage
entry. Plants with many spines and thorns, such as cactus and other desert species, can also be
planted near windows to enhance security.
Q. Cost of Operating An Evaporative Cooler
Studies have indicated that the average annual cooling energy usage for a 1,600 square foot home is
approximately 6,000 kilowatt hours for refrigeration and 1,500 kilowatt hours for evaporative
If electricity costs were 0.15 Sudanese pounds per kilowatt hour (a sample cost), the average annual
cost would be Sudanese pounds for a refrigeration system versus Sudanese pounds
for evaporative cooling. However, the cost of water must be added to the electricity cost for
evaporative cooling, but it is too small to be added, therefore it can be neglected.
R. Reasons for Covering Coolers During Winter Season
A cooler cover can provide protection for the cooler from rain, dust, and wind, and this helps to
extend the life of the unit.
Advantages and Limitations of Evaporative Coolers
Like any other space heating or cooling system, evaporative coolers have advantages and
disadvantages. Listed below are points consumers should weigh carefully in deciding how to cool
their homes for summer comfort while trying to conserve water and energy, not only for the present
but for future generations.
A. Advantages of Evaporative Coolers
1. Coolers are economical to operate, using one-third the energy of refrigerated air-conditioning.
2. Installing a new evaporative cooling system adequate for a 1,500-square-foot home costs about
For the same home, installing a new air-conditioning system, using existing duct work, costs
3. Most cooler maintenance and repairs can be accomplished by the homeowner.
4. Most cooler replacement parts (pads, belts, etc.) are nominal in cost when compared to air-
conditioning system replacement parts.
5. Coolers bring fresh, cooled, outside air into the home.
6. Coolers provide a healthy environment for plants.
A. Limitations of Evaporative Coolers
1. Coolers use on-site water, a non-renewable resource in some parts of the world, for cooling.
2. Coolers are aesthetically unattractive if not maintained and overflow of concentrated salts from
the cooler can damage roofs.
3. Air velocity when operating on high speed may cause annoying noise.
4. Open windows to exhaust air may be a security hazard. This can be overcome by installing
ceiling vents. Adequate attic ventilation is necessary for ceiling vents to function properly.
5. Cooled air may bring dust and pollen into the home causing discomfort for allergy sufferers.
Growth of microorganisms such as molds on the cooler pads may cause allergy problems in
6. Coolers require regular maintenance, difficult if the cooler is roof-mounted.
Things to Consider Before Deciding to Buy An Evaporative Cooler
The first is cost. Get at least three estimates from reliable cooling suppliers or contractors in your
community, ude the hidden costs, like installation, maintenance, and
operational costs of utilities (electricity and water).
Perhaps the greatest advantage of evaporative cooling is the low cost: about one-third as much as
refrigeration. The costs for operating a system will depend on the size and number of units, and how
homeowners choose to run the evaporative cooler or refrigeration unit and the overall thermal
properties of the home (insulation, thermal mass, amount of window area, orientation of the
The next consideration is comfort. Evaporative cooling cannot keep every home comfortable all the
time. A typical desert home will not be able to achieve temperatures in what is usually considered
the comfort range on days when the humidity is high. Performance can be maximized, however, if
all the windows are shaded from direct sunlight, the walls are properly insulated, and protected
from direct sunlight, especially on the east and west sides or passive solar concepts were used in the
construction of the home. Keep in mind that air movement, not just air temperature, contributes to
comfort: 82 feels like 75 in a moderate breeze. The basic principle of evaporative cooling is simple
and in the past the typical coolers were very simple devices. More recently, however, many
variations and innovative concepts are being applied to cooler design and construction to achieve
cooling efficiency. Therefore, before deciding what type of cooling, air conditioner or heat pump
you wish to purchase, shop by comparing their differences, comfort, capital and operating cost. For
evaporative coolers compare purchasing and operating costs, pads, construction materials (metal
versus fiberglass or stainless steel).
Some of the notable advantages of an evaporative cooler over a traditional air conditioning unit
include a more affordable price and lower energy consumption.
The simplicity of an evaporative cooler or swamp cooler when compared to an air conditioner also
translates to cheaper installation and maintenance costs. It does not have a compressor and
operation revolves chiefly around a fan and a water pump. There are also no special working fluids,
Remember that an evaporative reduces air temperature through humidification or more particularly,
by increasing the moisture level in the air. Hence, an evaporative cooler works best in areas with
dry and arid or desert climates such as the Middle East, North Africa, West Australia, and the
American Southwest. This is the reason why an evaporative cooler is also known as a desert cooler.
The aforementioned advantages translate to several specific benefits including improving comfort
and decreasing static electricity problems. There are also some health benefits as well. Dry weather
dries out the lining of the nose and throat, thus resulting in respiratory distress. It is also important
to note that low humidity can damage wooden furniture and can shrink paper-based products such
as books and artworks.
The limitations of an evaporative cooler could be summarized in: It cannot lower the ambient
temperature as much as a vapor-compression or refrigerant-based air conditioning units. In other
words, it is not as effective and as efficient as air conditioners in terms of cooling capacity; an
evaporative cooler cannot provide similar thermal comfort. In fact, because it increases humidity in
the air, it can actually increase discomfort. There is also a need to use this electric appliance
alongside exhaust ducts or open windows, or in the open air to maximize its efficiency; in areas
with high relative humidity or during hot and humid weather, using this electronic appliance can
increase thermal discomfort  .
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Osama Mohammed Elmardi Suleiman Khayal was born in Atbara,
Sudan in 1966. He received his diploma degree in mechanical engineering
from Mechanical Engineering College, Atbara, Sudan in 1990. He also
received a bachelor degree in mechanical engineering from Sudan University
of science and technology Faculty of engineering in 1998, and a master
degree in solid mechanics from Nile valley university (Atbara, Sudan) in
2003, and a PhD in structural engineering in 2017. He contributed in teaching
some subjects in other universities such as Red Sea University (Port Sudan,
Sudan), Kordofan University (Obayed, Sudan), Sudan University of Science
and Technology (Khartoum, Sudan), Blue Nile University (Damazin, Sudan) and Kassala
University (Kassala, Sudan). In addition, he supervised more than hundred and fifty under graduate
studies in diploma and B.Sc. levels and about fifteen master theses. The author wrote about forty
engineering books written in Arabic language, and fifteen books written in English language and
more than hundred research papers in fluid mechanics, thermodynamics, internal combustion
engines and analysis of composite structures. He authored more than thousands of lectures notes in
the fields of mechanical, production and civil engineering He is currently an associated professor in
Department of Mechanical Engineering, Faculty of Engineering and Technology, Nile Valley
University Atbara, Sudan. His research interest and favorite subjects include structural mechanics,
applied mechanics, control engineering and instrumentation, computer aided design, design of
mechanical elements, fluid mechanics and dynamics, heat and mass transfer and hydraulic
machinery. The author also works as a technical manager and superintendent of Al Kamali
mechanical and production workshops group which specializes in small, medium and large
automotive overhaul maintenance and which situated in Atbara town in the north part of Sudan,
River Nile State.