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Air-conditioning plays an essential role in ensuring occupants thermal comfort. However, building’s electricity bills have become unaffordable. Yet the commercially dominant cooling systems are intensively power-consuming ones, i.e. vapor compression systems. This paper aims to review the recent developments concerning evaporative cooling technologies that could potentially provide sufficient cooling comfort, reduce environmental impact and lower energy consumption in buildings. An extensive literature review has been conducted and mapped out the state-of-the-art evaporative cooling systems. The review covers direct evaporative cooling, indirect evaporative cooling and combined direct-indirect cooling systems. The indirect evaporative coolers include both wet-bulb temperature evaporative coolers and dew point evaporative coolers have been of particular interest because of high thermal performance. The dew point evaporative coolers have shown great potential of development and research opportunity for their improved efficiency and low energy use.
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AbstractAir-conditioning plays an essential role in ensuring
occupants thermal comfort. However, building’s electricity bills
have become unaffordable. Yet the commercially dominant
cooling systems are intensively power-consuming ones, i.e. vapor
compression systems. This paper aims to review the recent
developments concerning evaporative cooling technologies that
could potentially provide sufficient cooling comfort, reduce
environmental impact and lower energy consumption in
buildings. An extensive literature review has been conducted
and mapped out the state-of-the-art evaporative cooling systems.
The review covers direct evaporative cooling, indirect
evaporative cooling and combined direct-indirect cooling
systems. The indirect evaporative coolers include both wet-bulb
temperature evaporative coolers and dew point evaporative
coolers have been of particular interest because of high thermal
performance. The dew point evaporative coolers have shown
great potential of development and research opportunity for
their improved efficiency and low energy use.
Index TermsEvaporative cooling, Effectiveness, Dew point,
Dry bulb temperature.
Energy demand worldwide for buildings cooling has
increased sharply in the last few decades, which has raised
concerns over depletion of energy resources and contributing
to global warming. Current energy demand estimates stands at
between 40 and 50% of total primary power consumption. In
hot climate countries, the highest share of building energy use
is mainly due to space air conditioning using traditional
HVAC systems. For example, in the Middle East, it accounts
for 70% of building energy consumption and approximately
30% of total consumption. Nowadays, buildings air
conditioning has become a necessity for people life and plays
a vital role in ensuring indoor comfort levels. Hence,
improving the efficiency of cooling technologies are essential,
particularly ones that have the potential, i.e. high performance,
low power consumption [1].
Currently, mechanical vapor compression coolers (MVC)
are commercially dominant despite their intensive energy use
and low performance in hot climate. In contrast, evaporative
cooling systems are more environmentally friendly as they
consume less energy and their performance improves as air
temperature increases and humidity decreases. Table I shows
a comparison of coefficient of performance (COP) values of
Manuscript received May 4, 2014; revised June 10, 2014. This
publication was made possible by NPRP grant No. 4-407-2-153 from the
Qatar National Research Fund (a member of Qatar Foundation). The
statements made herein are solely the responsibility of the authors.
O. Amer and R. Boukhanouf are with The University of Nottingham,
Department of Built Environment, Nottingham, UK (e-mail:,
H. Ibrahim is with Qatar University, Department of Architecture and
Urban Planning, Doha, Qatar (e-mail:
several cooling cycles. However, the main drawback of the
evaporative cooling is their high dependency on the ambient
air conditions. Since the temperature difference between the
dry- and wet-bulb temperatures of the ambient air is the
driving force of evaporative cooling. For mild and/or humid
climate this difference is small, therefore, leads to limited
cooling capacity [2].
Evaporative cooling is a heat and mass transfer process that
uses water evaporation for air cooling, in which large amount
of heat is transferred from air to water, and consequently the
air temperature decreases. Evaporative coolers could be
classified into: (1) Direct evaporative coolers, in which the
working fluids (water and air) are in direct contact; (2)
Indirect evaporative coolers, where a surface/plate separates
between the working fluids; (3) Combined system of direct
and indirect evaporative coolers and/or with other cooling
cycles [2]. Fig. 1 illustrates a general classification of main
types of evaporative cooling systems for building cooling.
Fig. 1. A classification of evaporative cooling systems in building cooling
A Review of Evaporative Cooling Technologies
O. Amer, R. Boukhanouf, and H. Ibrahim
2014 APCBEES Nottingham Conferences Proceeding
This system is the oldest and the simplest type of
evaporative cooling in which the outdoor air is brought into
direct contact with water, i.e. cooling the air by converting
sensible heat to latent heat. Ingenious techniques were used
thousands of years ago by ancient civilizations in variety of
configurations, some of it by using earthenware jar water
contained, wetted pads/canvas located in the passages of the
Direct evaporative coolers in buildings vary in terms of
operational power consumption from zero power to high
power consumption systems. DEC systems could be divided
into: Active DECs which are electrically powered to operate
and Passive DECs that are naturally operated systems with
zero power consumption. DEC is only suitable for dry and hot
climates. In moist conditions, the relative humidity can reach
as high as 80%, such a high humidity is not suitable for direct
supply into buildings, because it may cause warping, rusting,
and mildew of susceptible materials [3].
A. Active DEC Systems
The active direct evaporative coolers are electricity-driven
systems, however, it use a fraction of power for air and water
circulation. So, it is considered much less energy intensive
than other traditional cooling technologies, with energy
saving up to 90% [3]. A typical direct evaporative cooler
comprises of evaporative media (wettable and porous Pads),
fan blows air through the wetted medium, water tank,
recirculation pump and water distribution system, as
illustrated schematically in Fig. 2-a. The direct evaporative
cooling is an adiabatic cooling process, i.e. the total enthalpy
of the air is constant throughout the process, as shown in Fig.
2-b. The water absorbs the sensible heat from the supply air
and evaporates causing the air temperature decreases and its
humidity to increase. [4].
Theoretically, the supply air could be cooled to 100%
effectiveness, but in such process a wet-bulb effectiveness of
70%-80% only is achievable because of short contact time
between the two fluids, insufficient wettability of the pads and
due to the fact that the circulated water and the supply air will
reach an equilibrium point that is equal to the wet-bulb
temperature of the supply air. Eventually the system would
not be able to cool down the incoming air lower than its
wet-bulb temperature. The wet-bulb effectiveness could reach
range between 70-95% in most current commercial DEC
coolers and mainly as a function of the type and thickness of
evaporative media, working climate, and supply air flow-rate
According to ASHRAE Handbook-HVAC Systems and
Equipment (2008) active DEC could be divided according to
types of wet media into: Random media DEC, Rigid media
DEC and Remote media DEC, as shown in Fig. 3[6].
However, active DEC coolers can be classified in terms of
water distribution system type: spray (also called air washer),
slinger (a rotating wheel), and drip (Misting) system [7].
Table II show the main types of active DEC systems:
Fig. 2. Structure, working principle and psychometric chart of a direct
evaporative cooler [4]
Evaporative media
Excelsior or plastic
fiber/foam supported by
plastic frame.
Low effectiveness
Short life-time.
Hard to clean.
Blocks of corrugated
materials: Cellulose,
plastic, fiberglass.
High initial cost.
Longer life-time.
Cleaner air.
Random or rigid Pads
mounted on wall or roof
of building
Higher power
Bacteria growth
Fig. 3. Types of DEC system Pads [6]
B. Passive DEC Systems
Passive cooling techniques use natural phenomena,
energies, and heat sinks for cooling buildings without the use
of mechanical apparatus consume electrical energy. However,
small fans and pumps could be required. Passive DEC is
relied on the climate which means the techniques applied for
hot and humid regions are different from those for hot and
arid areas. This technology is able to reduce indoor air
temperature by about 9 [7]. The main types of passive
direct evaporative cooling building integrated systems are:
1. The Mashrabiya
The mashrabiya is a traditional Islamic architecture
element used for natural ventilation and cooling of buildings
without requiring any energy. It is wooden screens/windows
provides shad, protection from the sun and allows breezes to
flow through into the building for cooling purpose. Fig. 4-a
shows a mashrabiya system coupled with porous water-jugs to
provide evaporative cooling effect for a dwelling and cooling
water inside jugs for water drinking. [8].
2. Wind Towers
The wind tower, also called wind catcher is a traditional
passive cooling technique of buildings, existed hundreds of
           
2014 APCBEES Nottingham Conferences Proceeding
e. the air tower. Basic structure of a wind tower is
illustrated Fig. 4-b. A capped tower with one face opening or
multi-face openings at the top of tower, the tower is placed on
the roof of a dwelling. Wind towers/catchers could be divided
according airflow patterns inside the tower into: downward
airflow towers and upward airflow towers.
Downward airflow wind tower   
between windward side and leeward sides of the tower. The
tower catches the ambient air which enters at top of the tower
and flow through it to the building providing fresh air. Water
could be introduced into the tower geometry by several means
i.e. water pool at bottom of tower, porous jars filled with
water located in the tower airstream or wetted pads hanged at
the top of the tower (Fig. 4-b).
Upward airflow wind tower is driven by temperature
difference between building interior and the outside
environment. In this system, the air is drawn upwards via wind
tower. Because of positive pressure on one sides of the
building the hot air could be drown down via underground
channels or water fountains before entering to the building as
cooled air, while the hot interior air rises upward via the
openings of the wind tower [8], [3].
3. Roof-pound
Roof pond is a building-integrated evaporative cooling
technique. It can contribute highly to mitigate heat by cooling
the roof passively; therefore, the indoor air is cooled without
increasing its moisture and reducing the energy consumption
and heat gain during daytime. A typical roof pound consists of
water pool in plastic or fiber-glass container stored on top of
the roof of the building. The pond could be covered by a
removable cover, a fixed cover or a fixed floating installation.
A basic configuration of a shaded roof-pond system is shown
in Fig. 4-c. During summer, the ambient air flow over the
pond causes the water to evaporate, thus, cools the pond and
the roof structure which act as a heat sink of the building
interior. During winter, the pond is emptied and the shaded
openings are closed. Roof-pond cooling systems may
incorporate water spraying system to enhance evaporative
cooling [3].
The primary idea of the indirect evaporative coolers is
cooling by decreasing air sensible heat without changing its
humidity, which is a distinctive advantage over DEC systems.
A common IEC unit comprises of: a heat exchanger (HX),
small fan, pump, water tank, and water distribution lines, as
illustrated in Fig. 5-a. Indirect evaporative coolers are
classified into: Wet-bulb temperature IEC systems and Sub
wet-bulb temperature ICE systems. [2].
A. Wet-bulb Temperature IEC System
Wet-bulb temperature IEC system are packaged unit of
flat-plate-stack, cross-flow heat exchanger, the most common
configuration and flow pattern, which can lower air
temperature close to, but not below, the wet-bulb temperature
of the inlet air. Fig. 5-b shows a schematic drawing of the
working principles of a typical HX configuration of a
wet-bulb temperature IEC system which comprises of several
Fig. 4. Types of passive cooling systems [3]
Fig. 5. IEC structure,working principle and its psychometric chart [4], [2]
pairs of adjacent channels: wet passages of the working
(secondary) air and dry passages of the supply (primary) air.
Heat transfer occurs between the two working fluids through a
heat conductive plate, therefore, the supply air is cooled
sensibly with no additional moisture introduced into the
cooled supply air stream. While, heat transfer mechanism
between the working air and water in wet channels is by latent
heat of water vaporization. The wet-bulb effectiveness of this
system is in the range of 4080%, which is lower than that of
the DEC systems [9]. Different types of IEC systems are
existed which can be classified, according to the type of heat
exchanger (HX), into: plate-type IEC, tubular-type IEC and
heat pipe IEC as summarized below:
Plate-type HX based IEC: This type of heat exchanger is
the most commonly used configuration, that is,
flat-plate-stack HX with cross- or counter-flow arrangement
of the primary and secondary airstreams. Fig. 6-a illustrates
schematically a basic plate-type IEC system. Several
researches conducted evaluation of energy saving [10], [11],
mathematically modeling of the heat transfer process and
performance evaluation [12]-[14], studying the effects of
channels dimensions, humidity ratio, primary and working air
velocities, and plate wettability percentage on the efficiency
of the system [15], [16]. However, the cooling effectiveness
of plate type IEC system s is only in the range of 5080%.
Tubular-type HX based IEC: This configuration is usually
built of circular tubes, as shown in Fig. 6-b. However, other
tubular shapes have been used such as elliptical and
rectangular tubes [17]. A common configuration consists of a
bundle of round tubes mounted in a cylindrical or rectangular
shall, where the primary air flows inside the tubes and the
secondary air flow across and/or along the tubes in the normal
direction to the primary air, while the water is sprayed over
the external surface of the tubes. So that it could offer more
uniform water film over the tubes and less pressure losses
2014 APCBEES Nottingham Conferences Proceeding
comparing with plate-type IEC. Usually, the tubes are made
of either polymer, metal, porous ceramic, PVC, or aluminum
[5]. Another common configuration is a tube-fin HX based
IEC in which round or rectangular tubes are fitted with
outside fins by soldering, brazing, or welding. For example,
Velasco Gomez et al. [18] introduced tube-fin HX based
indirect evaporative cooler, that is, a bundle of porous
ceramic tubes fitted with flat metallic fins. The results showed
air dry-bulb temperature reduction of 9-14 was achieved.
The system can be used for heat recovery in air conditioning
systems [19].
Heat pipe HX based IEC: Heat pipe is a light, simple and
thermally conductive device available in shapes and sizes, can
be applied to transport heat from the primary to secondary air
passages for cooling applications. The configuration of heat
pipe can be any type from thermo-syphon, cryogenic, rotating
and revolving, flat plate and capillary pumped loop heat pipe
[3]. In this structure, the heat pipe based IEC, the condenser
section of heat pipe is used in the secondary air (wet) channel,
and the evaporator section is used in primary air (dry) channel,
as shown in Fig. 7.
Limited studies [5], [20] carried out evaluating the
performance of the heat pipe based IEC systems for building
cooling. A finned heat pipe was used to increase convective
heat transfer between the primary air and the heat pipe, with
different methods of heat eliminations from the condenser
sections such as water sprayer on condensation section
surface, the outdoor air is precooled by air washer before
passed through the condensation section, the use of porous
ceramic water container fitted around condensation section to
assure even distribution of water. Also, In the literature many
research studies conducted on heat pipes applications in
building cooling includes HVAC systems [21], [22], [23], and
[24], and heat recovery systems [25], [26], [27], and [28].
Fig. 6. Schematics of plate-type and Tubular-type based IEC [3]
Fig. 7. Schematic of heat pipe based IEC [5]
B. Sub Wet-bulb temperature IEC Systems
To overcome some of the disadvantages of DEC systems
and to enhance the effectiveness of wet-bulb temperature IEC,
introduced a new design of the heat exchanger of IEC system
[29]. The Maisotsenko-cycle (M-cycle) based IEC system is a
combination of a cross-flow, multi-perforated flat-plate HX
and evaporative cooling, in which, the secondary air is
precooled in the dry channel before it is diverted to pass
through the wet channel to achieve further heat transfer with
the dry channel. Thus, the primary air temperature is lower
than wet-bulb temperature and approach dew-point
temperature of the incoming air. So, it is called Dew point
IEC. The wet-bulb effectiveness is in the range of 110%
-122% and a dew-point effectiveness of 55%-85%. Although
the M-cycle heat exchanger has 1030% higher effectiveness
than that of the conventional heat exchangers, its operation is
still facing some limitations; the secondary air is not fully
cooled as high proportion of it is gradually diverted early into
the wet channels, and cross-flow is unfavorable pattern for
heat exchangers. An experimental tests of the M-cycle based
IEC system showed that its dew-point/wet-bulb effectiveness
was only around 5060% and 8090% respectively [30].
Several research studies conducted to develop and modify
the thermal process of the M-cycle IEC to overcome the
above mentioned drawbacks and to enhance the efficiency
and increase the thermal performance. Zhao et al. [31]
introduced a new counter-flow heat and mass exchanger
based on M-cycle of a dew-point evaporative cooling system.
In this structure, unlike the cross-flow Maisotsenko-cycle heat
exchanger, holes are located at end of flow channels as
presented in Fig. 8. The product air flows through and along
the dry channels losing sensible heat to wet channels and at
the end of dry channels part of cooled product air is delivered
to the conditioned space and the remaining air is diverted to
the adjacent wet channels as cold working air transferring heat
latently with the water and sensibly with the product air in the
dry channel. It was found that the wet bulb effectiveness
achieve up to 130% and dew-point effectiveness of up to 90%.
Furthermore, a comparative study between cross-flow and
counter-flow M-cycle base IEC system showed that the
counter-flow arrangement achieved around 20% higher
cooling capacity and 1523% higher dew-point and wet-bulb
effectiveness respectively under the same geometrical sizes
and operational conditions. Contradictory, the cross-flow
exchanger has 10% higher performance which is due to an
increase in power consumption of counter-flow heat
exchanger [32].
Additionally, Zhao et al. [33] and [34] conducted a
feasibility study in China and the UK respectively, using the
proposed dew-point IEC system in [31].
Fig. 8. Working principle and psychometric chart of a sub wet-bulb IEC [32]
2014 APCBEES Nottingham Conferences Proceeding
It was found that the dew-point IEC system is applicable for
most of the UK and china regions, particularly where the
climate is dry. Tap water is suitable as feed water with an
adequate temperature for cooling and its consumption rate
ranged from 2.1 to 3 l/kWh cooling output. The system
cooling output is in the range of 3.1-4.3 W/m3/h air flow rate.
Also, Rogdakis et al. [35] theoretically and experimentally
evaluated the performance of an M-cycle based IEC system at
Greek climate condition. It was found that the Maisotsenko
cycle can be applied for most Greek cities without intensive
consuming of electricity and water, the effectiveness ranged
between 97% and 115%, while water consumption was in the
range of 2.5 3.0 l kW/h.
It is noteworthy that research done on the dew-point IEC
systems is still at its early stage. To date, most theoretical and
experimental works are based on the principles of the M-cycle.
Most highly ranked papers and innovative research work of
dew-point evaporative cooling systems are summarized in the
following Table III.
Since DEC have higher effectiveness but humidity
increases indoors while IEC have lower effectiveness and the
humidity is constant, a combination of both systems or in
conjunction with other cooling technologies can be a potential
and achieve the best characteristics of both systems, such as
cooler supply air at a lower relative humidity, higher
efficiency and controlled humidity. The main components of
IDEC system are heat exchanger of IEC unit, evaporative pad
of DEC unit, water recirculation system, water reservoir, and
blowers, as shown in Fig. 9.
Wet bulb
Dew point
Elberling [30]
Cross-flow M-cycle based IEC. A
multi-perforated flat-plate-stacked heat
and mass exchanger made of Aluminum.
Polyethylene as water-proof material.
cellulose-blended fiber as wettable material
Assessment of the performance of a
Coolerado Cooler in terms of air flow,
cooling effectiveness and power
Zhao et al.
Counter-flow M-cycle based IEC. A
polygonal plate-fin HX made from flat
sheets and corrugated triangular
cross-section fins as flow guides.
Introduce of a novel counter-flow HX of
M-cycle based IEC. And optimization
of the geometrical sizes and operating
conditions of the cooler
Zhan et al.
Cross-flow M-cycle based IEC.
Comparative study between cross- and
counter-flow IEC to identify the in
performance, effectiveness and cooling
capacity of both systems under the same
operational conditions
Counter-flow M-cycle based IEC.
et al. [9], [36]
Counter-flow M-cycle based IEC. HX
consists of flat-sheets-stacked structure.
Polyethylene as water-proof material, and
thin-film cotton sheet as wettable material
Evaluation of the performance at
different inlet air conditions of various
climate conditions. Developed a
numerical model to simulate the heat
and mass transfer processes and
optimize system parameters
Bruno [37]
Counter-flow plate-type exchanger based
on M-cycle indirect evaporative cooler
Experimental test of the thermal
performance of a module product IEC
for residential and commercial cooling
applications for a wide range of
operation conditions.
Cui et al. [38]
Counter-flow flat-plate-stacked HX of IEC.
The HX comprises of a dry channel and
two adjacent wet channels with a
closed-loop configuration.
Investigation of the thermal
performance under varying inlet
conditions. Also, studied the effect of
the channels surface roughness and
effect of using the return air as working
air on the overall performance
Hasan [39]
Plate-type indirect evaporative cooler
Study of heat and mass transfer process
using a numerical analysis for four
flow-configuration of HX of IEC
system to evaluate the performances
et al. [40]
The exchanger of the IEC is a counter-flow,
plate-type HX consists of two adjacent
channels with hollow, rectangular porous
ceramic panels as heat transfer wall (wet
medium) filled with water
Evaluation of the performance, cooling
capacities and other characteristics of
the cooling system
Lee et al. [41]
Counter-flow M-cycle based IEC. The HX
is a plate-fin type HX, comprises of
multiple pairs of Aluminum finned
channels brazed with a thin flat plate
Evaluation of the performance of the
system at various operation conditions.
2014 APCBEES Nottingham Conferences Proceeding
Fig. 9. Two-stage IDEC system [4]
The effectiveness ranges from 90% to 115%. However, the
high initial cost and system complexity are the obvious
drawbacks [42]. The common types of the IDEC systems are:
Two-stage IDEC: in this configuration, the IDEC
comprises of IEC stage followed by a DEC stage. The first
indirect stage (state 1) cools the outdoor air, which is then
flows through a direct stage (state 2) for further cooling to
below its wet-bulb temperature, but with additional moisture
added (state 3), as illustrated on the psychometric chart Fig.
9-b. The effectiveness is in the range of 90120%, but water
consumption increases by 55% [42], [43]. Other two-stage
IEC-DEC configurations reported by [44], [45] achieved
effectiveness of 109%-116%.
Three-stage IDEC: this system consists of two-stage IDEC
system in conjunction with a cooling cycle. For example, a
solid desiccant dehumidification with an IEC and/or DEC unit
[46], [47], [48] gives COP of around 20. Several
configurations have been reported: An IEC, cooling coil and
DEC stage [49], [50]. An IEC and a DEC system to provide
sensible and adiabatic cooling coupled with a desiccant
system for dehumidification (Fig. 10) can offer energy saving
of 54%-82% over the conventional cooling systems [47].
Multi-stage IDEC: a hybrid system of two-stage IDEC
coupled with more than one cooling cycle. For instance,
combined system of two-stage DEC-IEC coupled nocturnal
radiative cooling and cooling coil (Fig. 11) has higher
effectiveness than two-stage evaporative cooling system, with
energy saving is between 75-79% compared to MVC systems
Fig. 10. Schematics of solid desiccant and evaporative cooling systems [3]
Fig. 11. Hybrid system of radiative cooling, cooling coil, and two-stage
IEC-DEC system [51]
Using water for evaporation as a mean of decreasing air
temperature is considerably the most environmentally
friendly and effective cooling system. In this paper a review
of evaporative cooling technology that could be efficiently
applicable in building air-conditioning was carried out.
Indirect evaporative coolers showed higher values of
effectiveness and are more economical in terms of energy
consumption saving, particularly the breakthrough brought
about by the M-cycle based dew-point IEC system. However,
combined IDEC systems have similar performance or even
higher but their system complexity and high initial cost are
the major limitation. Recent works concerning indirect
evaporative cooling based on Maisotsenko-cycle have shown
considerable potential towards enhancing the performance
and cooling capacity of IEC system for building cooling.
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2014 APCBEES Nottingham Conferences Proceeding
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Mr O. Amer is a PhD degree candidate in the
department of the Built Environment, University of
Nottingham. His main research topic is sustainable
cooling technologies. Mr. Amer has an MSc in New
and Renewable Energies, University of Durham, UK.
2011. BEng degree in mechanical Engineering,
Misurata University, Libya, 2005.
He also held a position of a lecturer in Mechanical
engineering department, Misurata University, Libya between 2011-2012.
Dr R Boukhanouf is a lecturer in sustainable energy
technologies at the Department of Built Environment,
University of Nottingham. His experience in research
and teaching in the area of energy efficient and low
carbon technologies extends for over 15 years. He
obtained his PhD in 1996 from the University of
Manchester, UK.
Dr. Boukhanouf worked on numerous research
projects funded by industry and government agencies
in the area of small scale combined heat and power, active and passive
heating and cooling systems for buildings, and advanced heat transfer
enabling devices. He published a number of journal and conference papers
and is named as the inventor in six international patents.
Dr. H. Ibrahim is associate Professor at Qatar
University. Dr. Ibrahim has a long and established
research experience including managing green
construction, carbon abatement in construction
industry using knowledge based programming, and
preservation of traditional architectural and urban
heritage of Qatar. The latter being particular an ass-on
advantage for reconciling the integration of new low
carbon technologies with the traditional architectural
2014 APCBEES Nottingham Conferences Proceeding
... During the day the mechanically operated roof is opened. Exposing the roof pond to the sun so it can absorb heat to radiate to living area later [8,27]. ...
... Amer et al [27], have reviewed the technologies developed in evaporative cooling, which is one of the successful thermal cooling methods due to its high COP and low energy consumption. The study has covered direct, indirect and combined direct-indirect evaporative cooling systems. ...
Full-text available
This review paper focuses on documenting and studying published papers and works in the field of solar heating and cooling air space in residential buildings. The goal of this survey and documentation is to find out the most important flushing results and conclusions specifically in the fields of using solar energy for space heating, cooling, and ventilation of local residential buildings in Libya. This covers using active and passive solar systems in, achieving thermal human comfort in such buildings leading to reduce electrical energy consumption. This paper also concentrates on applying energy efficiency measures in buildings; planning, design, and construction stages with the use of the principles of energy conservation in buildings. There are several studies comparing traditional with modern house designs in several local cities including both famous old cities of “Ghadames” and “Gharyan”. Several conclusions and recommendations are summarized within the text of this paper.
... Evaporative cooling technologies are generally more environmentally friendly and efficient than traditional HVAC systems [18] [19] [20]. A problem that hinders this solution in climates where humidity peaks as high as 80% is that the cooling gains may not be sufficient. ...
... However, they also noted that there was still good potential in applying evaporative cooling by 'precooling outdoor air' , thus achieving significant savings in air conditioning (ibid). They failed to mention that this system, usually called indirect evaporative cooling, is expensive, is difficult to manufacture and, while more efficient than direct evaporative cooling, is still not as effective as DX air conditioning in cooling the interior [18]. ...
Full-text available
Reducing cooling loads in hot countries requires thermal insulation, and cooling methods be improved. Evaporative cooling, although problematic, is one solution that can be explored since it is significantly more efficient than regular compressor air conditioners, and the net result of using one is cooling. Furthermore, while compressor air conditioner efficiency decreases with rising temperatures in summer, evaporative ones, up to a point, are the exact opposite. A novel hybrid cooling system capable of combining both showed an 80% decrease in cooling load. The system’s efficacy was assessed in this paper by thermally simulating designs that are suitable for the hot Middle East region. Two locations with different environments and building guidelines that are representative of the variations in the area were selected. The first was the hot, dry Baghdad environment; the other was Dubai’s coastal, more humid city. Two different houses were designed to suit the municipal rules of each and accommodate the hybrid cooling system. As expected, the simulation results showed that savings in the dry Baghdad climate were high at 78% compared to a non-insulated alternative. In Dubai, unsurprisingly, they were less at 52% on the more humid coast. Further simulations revealed that this latter figure in the humid coast could also be achieved using good thermal insulation.
... The evaporative cooler was first studied in a conventional mode by using circulating water. An effectiveness of E = 0.75 was assumed for the evaporative cooler [58]. Fig. 7 shows a psychrometric chart of the ambient air conditions and the conditions of the air leaving the evaporator cooler. ...
This paper intends to numerically analyse the performance of liquid desiccant systems on the supply air conditions for closed poultry barns. A commercially available evaporative cooler for poultry barns was modified into a desiccant dehumidifier by circulating desiccant solutions of LiCl-H2O and CaCl2-H2O instead of water. Ambient air conditions for one of humid and subtropical climates were simulated based on an ∊-NTU effectiveness model for an externally cooled liquid desiccant dehumidifier. Also, a distinctive temperature-humidity index (THI) was implemented to study the environmental thermal conditions that the poultry were subjected to. Concerning the thermal comfort for broilers, the results show that conventional direct evaporative cooling systems are not feasible when the ambient air is near saturation. The THI values for ambient and direct evaporative cooler were positioned mainly in the severe heat stress region, with THI value in the range of 80 to 82, and most air outlet conditions were near saturation. The numerical results for the liquid desiccant systems show a consistent reduction in humidity ratio and air dry-bulb temperature. The assessment of air outlet temperature and humidity in terms of THI values was shifted out of the emergency and danger zone with a preference for LiCl solution.
Evaporative cooling systems have attracted increasing attention for energy-efficient air conditioning applications. A hollow fiber membrane-based direct evaporative cooler (HFM-DEC) is proposed in this study. The selected membrane material can selectively allow only water vapor to penetrate, while preventing the passage of bacteria and fungi, thereby avoiding deterioration of indoor air quality. Compared with the conventional evaporative coolers with counter-flow and cross-flow arrangements, the proposed novel configuration performed better cooling ability by installing baffles in the air flow channel to enhance the air disturbance. The parameter sensitivity analysis was conducted on the HFM-DEC with built-in baffles by employing an experimentally validated numerical model. The orthogonal test method was used to study the influence of nine key parameters of the HFM-DEC on its wet-bulb effectiveness, coefficient of performance, and the cooling capacity. According to the optimized scheme, the HFM-DEC with a relatively optimal configuration was proposed. The cooling performance of this module was investigated under various inlet air conditions. The results showed that if the inlet air velocity was maintained within the range of 0.5-2 m/s, it was capable of achieving an optimal performance with the wet-bulb effectiveness of 70%-95%, the COP of 17-78, and the cooling capacity of 60-106 W, respectively, under diverse weather conditions. Correlations of Nusselt number and Sherwood number were developed by fitting the simulation results. The influence of Reynolds number on air stream characteristics was obtained based on the analysis of the velocity field, temperature field and concentration field of this module under varying operating conditions.
Indirect evaporative cooling (IEC) is an eco-friendly technology that has the potential to reduce energy consumption by 4 times compared with conventional air conditioners (AC). However, IEC has not been widely used due to operational limitations in humid environments and water availability in arid environments. Many patents related to IEC have been granted in the past decades, aiming to make breakthrough innovations. This article reviews and discusses published patents in a chronological order and presents the different configurations of IEC devices. It presents the standards and evaluation parameters utilized to characterize the performance of IEC devices. Additionally, the current research gaps are identified, and the outlook of this technology is highlighted. This review shows that the convective air heat transfer on the dry side of the IEC heat exchangers is generally the limiting factor in how small IEC devices can be constructed. One of the main factors that negatively affect the cooling capacity of IEC technology is the non-uniform wettability of the wet channel surface. With the recent research and development, the share of IEC technology in the AC market will increase noticeably in the next decades, aiming to reduce the energy consumption and the carbon footprint in the building sector.
The poultry industry is a major contributor to worldwide food production. Poultry birds are fatally sensitive to humidity and temperature. Therefore, a temperature/humidity control system is principally required for optimum growth of the birds. Conventionally, to regulate temperature/humidity in control sheds, vapor compression air-conditioning systems are used which are not only costly but also consume an enormous amount of primary energy. Alternatively, evaporative cooling pads are also used which increase humidity level inside control sheds results in various fungal diseases. In this regard, this study explores desiccant air-conditioning (DAC) options for climatic conditions of Multan (Pakistan). These systems are operated with thermal energy that could be available via low-grade waste heat and renewable energy options. Such systems would allow the development of poultry houses in off-grid remote areas which eventually support the green smart grid’s philosophy. Two DAC options are studied which are involved in standalone DAC and evaporative cooling (EC) assisted DAC concepts. Psychrometric and thermodynamic analysis with two types of desiccant materials is used in the study (i.e., silica-gel and hydrophilic polymeric-sorbent). The study determined body-weight-gain, feed-conversion-ratio, sensible/latent heat, and temperature-humidity-index of birds. As such, the performance of the proposed systems is investigated for cooling capacity and COP. According to results, the EC-assisted polymeric-sorbent system has resulted feasible in terms of maximum cooling capacity and COP. This system could achieve thermal comfort of birds at THI of less than 30 °C.
As the global energy mix transit towards renewables, it inherently leads to fluctuations in smooth energy supply. Natural constraints with unpredictable climatic fluctuations further exacerbate the issue. The challenge to a constant energy supply can be coped using energy storage methods. There are number of ways energy can be stored, i.e., electrical mechanical, chemical and thermal. Mechanical energy storage method has geographical constraints such as in the case of Compressed Air Energy Storage systems, whereas electrical and chemical are prone to high losses in large scale systems. Thermal energy storage, although has higher thermodynamic costs, however, it out performs other technologies in terms of cost benefits, further, not only it is a zero-emission technology but has excellent grid integrity, and dispatchability characteristics, as per demand, making it widely known as the “future of renewable energy”. Thermal energy storage systems usually utilize latent heat storage material i.e., phase-change materials or sensible heat storage material i.e., solid medium or molten salts. This chapter will only focus on thermal energy storage using the molten salts. The molten salt is stored either in the form of Two-tank storage system or the direct single tank (thermocline) methods as “sensible heat”. The two-tank system involves a simple mechanism whereas the single tank system reduces the cost by about 35%. The amount of energy stored is dependent upon the temperature gradient and the heat flow from higher temperature (hot) to lower temperature (cold) using the mathematical expressions Q = m C ΔT, where Q denotes the sensible heat, m represents the mass of the salt, C denotes the specific heat of the salt, whereas ΔT represents the difference in temperature. Later, the stored molten salt is utilized to heat the water/steam and run the turbines and the thermal to electricity conversion usually proceeds through different power cycles such as the Brayton and Rankine cycles. Whereas, the cold salt is sent for storage to heat it up and continue the cycle.
Exergoeconomic analysis, a simultaneous investigation of exergetic and monetary performance has attained significant attention to analyze and improve the performance of energy conversion systems. This combined analysis allows an individual audit of all the components in the system. The research is particularly useful for multi-component systems to get a better understanding of how effectively each component consumes energy and economic capital. This chapter aims to present a comprehensive theoretical framework for exergoeconomic study of thermal systems. For this purpose, the framework is initially developed for standalone heat exchangers and then extended to commercial-scale thermal desalination systems consisting of preheaters, pumps, evaporators, and compressors, etc. The exergetic and economic values of each stream in the system were evaluated using the developed framework. The sensitivity and parametric analysis of different thermodynamic and economic parameters on the system performance was conducted to study the performance variations. The presented model can be generalized for performance analysis of other systems.
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Decreasing petroleum sources and growing requests for emission attributes of fossil fuel combustion and energy lead to researches on clean, accessible, and inexpensive energy resources. On the other hand, environmental burden that is imposed on nature through biodiesel production and its combustion has also been considered in recent years. Previous studies also focused on the production process and sometimes the exhaust emissions. However, in order to adopt the right policies, a comprehensive analysis requires a review of the entire process from farm-to-combustion. Besides, environmental studies without considering the energy consumption cannot indicate the efficiency of the produced biodiesel. Therefore, the cumulative exergy demand (CExD) method, as a new approach in determining the amount of useful energy consumed in systems, has been used for several years and the lack of this approach can be seen in the study of biofuel production. Accordingly, in this chapter, all stages of biodiesel production from cradle-to-grave including agricultural phase, oil extraction, biodiesel production, combustion and finally power generation are studied from life cycle assessment (LCA) and CExD point of view. Moreover, all these steps along with how to interpret the results are explained with examples.
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The available studies indicate the significantly enhanced pool boiling heat transfer by the modulated porous wick sintered on the heater wall. This paper sinters the modulated porous wick as the primary wick on the evaporator wall for loop heat pipes (LHPs). Three types of evaporators were fabricated to integrate with other LHP components: MWE (microchannel/wick evaporator), MME (modulated monoporous wick evaporator) and MBE (modulated biporous wick evaporator). Experiments were performed with water as the working fluid at various tilt angles. The major findings are (1) MBE LHP significantly shortens start-up time and stabilizes all temperatures during the steady operation; (2) MBE LHP decreased the evaporator wall temperatures by 20∼50 °C at moderate or high heat loads compared with MWE LHP at similar conditions; (3) MBE LHP achieved the evaporator wall temperature of 63 °C at the heat load of 200 W for the anti-gravity operation, under which the heat flux attained 40 W/cm2, which is 1.7∼6.7 times of those reported in references; (4) MBE behaves the nucleate boiling heat transfer at small head loads, and film evaporation heat transfer at moderate or large heat loads; (5) A properly designed MBE LHP achieved better performance when the evaporator is above the condenser; (6) Effect of liquid charge ratios was studied with the best liquid charge ratio of 51.3%. The best geometric parameters for porous stacks and vapor channels, as well as the best particle size were obtained. The MBE multiscale behavior majorly accounts for the performance improvement: small pores (∼μm scale) creating great capillary force for liquid suction, large pores (∼10 μm scale) between clusters increasing surface area for liquid film evaporation, and vapor channels (∼mm scale) for vapor venting. Besides, small contact thermal resistance and reduced heat flow path in the evaporator also improve the LHP performance.
The work presented in this thesis investigates design, computer modelling and testing a sub-wet bulb temperature evaporative cooling system for space air conditioning in buildings. The context of this evaporative cooling technology design is specifically targeted at locations with a hot and dry climate such as that prevailing in most regions of Middle East countries. The focus of this technology is to address the ever-escalating energy consumption in buildings for space cooling using mechanical vapour compression air conditioning systems. In this work, two evaporative cooling configurations both based on sub-wet bulb temperature principle have been studied. Furthermore, in these designs, it was sought to adopt porous ceramic materials as wet media for the evaporative cooler and as building element and use of heat pipes as heat transfer devices. In the first test rig, the prototype system uses porous ceramic materials as part of a functioning building wall element. Experimental and modelling results were obtained for ambient inlet air dry bulb temperature of 30 and 35oC, relative humidity ranging from 35% to 55% and intake air velocity less than 2 (m/s). It was found that the design achieved sub-wet bulb air temperature conditions and a maximum cooling capacity approaching 242 W/m2 of exposed ceramic material wet surface area. The wet bulb effectiveness of the system was higher than unity. The second design exploits the high thermal conductivity of heat pipes to be integrated as an effective heat transfer device with wet porous ceramic flat panels for evaporative cooling. The thermal performance of the prototype was presented and the computer model was validated using laboratory tests at temperatures of 30 and 35oC and relative humidity ranging from 35% to 55%. It was found that at airflow rates of 0.0031kg/s, inlet dry-bulb temperature of 35oC and relative humidity of 35%, the supply air could be cooled to below the inlet air wet bulb temperature and achieve a maximum cooling capacity of about 206 W/m2 of wet ceramic surface area. It was shown that the computer model and experimental tests are largely in good agreement. Finally, a brief case study on direct evaporative cooling thermal performance and environmental impact was conducted as part of a field trip study conducted on an existing large scale installation in Mina Valley, Saudi Arabia. It was found that the evaporative cooling systems used for space cooling in pilgrims’ accommodations and in train stations could reduce energy consumption by as much as 75% and cut carbon dioxide emission by 78% compared to traditional vapour compression systems. This demonstrates strongly that in a region with a hot and dry climate such as Mina Valley, evaporative cooling systems can be an environmentally friendly and energy-efficient cooling system compared to conventional vapour compression systems.
A building's energy consumption is a major source of greenhouse gas emission and one of the main causes of climatic change. Passive solar architecture relies on the use of techniques for solar and heat control, heat amortization, and heat dissipation. Solar and heat protection or exploitation techniques may involve thermal improvement by the use of outdoor and semi-outdoor spaces, layout and external finishing, solar control and shading of building surfaces, thermal insulation, control of internal gains, and so on. The aim of this chapter is to present an overview of solar architecture starting from its history and provide a short description of the solar architecture basics, followed by an account of the state-of-the-art developments regarding the building fabric, cool materials, and intelligent control techniques. The future research trends are revealed and discussed here.
The author describes how savings in energy requirements of an air-conditioning plant may be obtained with heat exchangers. A plate heat exchanger can provide heat recovery in a ventilation system with complete separation of the air streams, or it can cool the incoming air without changing the moisture content by evaporative cooling of the plates from the exhaust side. A novel design of a plate heat exchanger suitable for both uses is described, performance data are given and design studies are presented.
A regenerative evaporative cooler has been fabricated and tested for the performance evaluation. The regenerative evaporative cooler is a kind of the indirect evaporative cooler comprised of multiple pairs of dry and wet channels. The air flowing through the dry channels is cooled without any change in the humidity and at the outlet of the dry channel a part of air is redirected to the wet channel where the evaporative cooling takes place. The regenerative evaporative cooler fabricated in this study consists of the multiple pairs of finned channels in counter flow arrangement. The fins and heat transfer plates were made of aluminum and brazed for good thermal connection. Thin porous layer coating was applied to the internal surface of the wet channel to improve surface wettability. The regenerative evaporative cooler was placed in a climate chamber and tested at various operation condition. The cooling performance is found greatly influenced by the evaporative water flow rate. To improve the cooling performance, the evaporative water flow rate needs to be minimized as far as the even distribution of the evaporative water is secured. At the inlet condition of 32 degrees C and 50% RI-I, the outlet temperature was measured at 22 degrees C which is well below the inlet wet-bulb temperature of 23.7 degrees C.
The performance of a novel dew-point evaporative air cooler is theoretically investigated in this paper. The novel dew-point evaporative air cooler, based on a counter-flow closed-loop configuration, is able to cool air to temperature below ambient wet bulb temperature and approaching dew-point temperature. A computational model for the cooler has been developed. We validated the model by comparing the temperature distribution and outlet air conditions against experimental data from literature. The model demonstrated close agreement with the experimental findings to within ±7.5%. Employing the validated model, we studied the cooler performance due to the effects of (i) varying channel dimensions; (ii) employing room return air as the working fluid; and (iii) installing of physical ribs along the channel length. Using these means, we have demonstrated improved performance of the dew-point cooler – enabling it to achieve higher efficiencies. Operating under variant inlet air temperature and humidity conditions, simulated results showed that the wet bulb effectiveness ranged from 122% to 132% while dew-point effectiveness spanned 81%–93%.
In order to determine the efficiency and consumption of an evaporative cooler, which follows the Maisotsenko cycle, an experimental installation was constructed, able to provide multiple options of inlet conditions and supported by measurement systems. The degree to which it is possible to achieve the nominal efficiency levels as well as the effect of the ambient conditions on water consumption were examined, and it was discovered that under different conditions and in the optimization mode, the efficiency levels vary between 97% and 115%, while water consumption varies between 2.5 kgw kWhc−1 and 3.0 kgw kWhc−1. The experimental procedure and the measurement processing are analyzed in detail and finally, it is ascertained that Maisotsenko cycle based coolers can satisfy the cooling demand with high efficiency in the hot and arid Mediterranean climate.