The potential of evaporative cooling window system using labu sayong in tropical Malaysia: A review

Abstract

In reducing indoor temperature, evaporative cooling window system using labu sayong can be one of the alternative strategies. This system will help to tackle the issue of increasing costs in keeping the home cool by managing the energy consumption and also offers a better indoor environment. In preventing the issue of increasing energy cost, this system not only cools the indoor environment as cool as using air conditioning, but, it also relief from the indoor heat build-up. This review aims to investigate the potential of the evaporative cooling window system using labu sayong as an alternative reduction of indoor temperature environment in tropical Malaysia. As commonly known Tropical Malaysia is categorized as a warm and humid climate. Therefore, non-passive direct evaporative cooling system suitable for Malaysia. This system is integrated with mechanical ventilation energy operated by solar electricity as an environmental friendly concoction. The uniqueness of this system is using the labu sayong as a medium of porous material to provide a surface to saturate water. Through this combination, it will reduce the temperature in providing a better indoor environment.

Full text

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The potential of evaporative cooling window system using labu sayong in tropical
Malaysia: A review
Nur Hidayah Ahmad*1, Abdul Malek Abdul Rahman 2
1 Civil Engineering Department, Politeknik Sultan Abdul Halim Mu’adzam Shah, 06000 Jitra, Kedah, Malaysia
2 School of Housing, Building & Planning, Universiti Sains Malaysia, 11800 USM Penang, Malaysia
A RT I C LE I NF O
A B ST R AC T
Article history:
Received : June 2015
Accepted : August 2015
Available online : January 2017
Keywords:
evaporative cooling,
labu sayong,
indoor environment
In reducing indoor temperature, evaporative cooling
window system using labu sayong can be one of the alternative
strategies. This system will help to tackle the issue of increasing
costs in keeping the home cool by managing the energy
consumption and also offers a better indoor environment. In
preventing the issue of increasing energy cost, this system not
only cools the indoor environment as cool as using air
conditioning, but, it also relief from the indoor heat build- up. This
review aims to investigate the potential of the evaporative cooling
window system using labu sayong as an alternative reduction of
indoor temperature environment in tropical Malaysia. As
commonly known Tropical Malaysia is categorized as a warm and
humid climate. Therefore, non-passive direct evaporative cooling
system suitable for Malaysia. This system is integrated with
mechanical ventilation energy operated by solar electricity as an
environmental friendly concoction. The uniqueness of this system
is using the labu sayong as a medium of porous material to
provide a surface to saturate water. Through this combination, it
will reduce the temperature in providing a better indoor
environment.
INTRODUCTION
Natural cooling is part of passive cooling methods for energy efficient buildings by considering
heat dissipation technique. Based on the interpretation from architectural view, natural cooling can be
classified as utilize of natural heat sinks for surplus heat dissipation from internal area, including
Ventilation, ground cooling, evaporative cooling and radiative cooling [1]. Refers to [2], cooling is
to move energy from one area or from the air to another area to get a temperature decrease compared to
the normal environment [2]. The natural cooling strategies can divided into three methods and it briefly
clarified in Table 1. Within these three methods, it is potential to reduce the temperature and improve the
indoor environment quality.
Advanced Journal of Technical and Vocational Education 1 (1): 262-272, 2017
eISSN: 2550-2174
© RMP Publications, 2017

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Table 1: Three methods in natural cooling strategies
Natural Cooling
Strategies
Sectional Diagram
Quotes
Evaporative Cooling
“Evaporative cooling is the exchange of sensible heat in
air for the latent heat of vaporisation of water droplets
on wetted surfaces. It can be used to cool building air
directly by evaporation or indirectly by contact with a
surface previously cooled by direct evaporation.” [3]
Ground Cooling
“The concept of ground cooling is based on heat
dissipation from a building to the ground, which during
the cooling season has a temperature lower than the
outdoor air.” [2]
Radiative Cooling
“In the case of building radiative cooling, the building
envelope (or another appropriate device such as a
metallic flat-plate radiative air cooler) is cooled by
dissipating infrared radiation to the sky, which acts as a
low-temperature environmental heat sink.” [1]
In order to reduce temperature, the most important part is keeping the home cool by managing
the indoor heat build-up. Heat build-up gains by absorbing day lighting. Three main starting place of heat
build-up are through the roof, walls and windows. Refer to Figure 1, the heat increased from four causes,
namely solar heat gain, internal heat gain, air leakage and temperature difference[4].
Currently, in preventing this issue, there are several opportunities to keep the buildings cooling.
Bhatia believes that passive cooling works on two principles, namely minimizing or preventing heat gain
and avoid unwanted heat [5]. On the other hand, [2] categorize the passive cooling under three divisions.
Figure 2 summarized passive cooling was categorized as heat prevention or heat reduction, modifying
heat gains and removes internal heat.
Figure 1: Heat factors affect [4]

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Figure 2: Classification of passive cooling methods in energy efficient buildings [2]
Heat can be reduced with two ways, which is microclimate and solar control. Through
microclimate, a building should be designed by considering the building orientation, wind flow,
vegetation and water surface. This consideration is the key to reduce the internal heat gain besides to
enhance the passive cooling efficiency [2]. Furthermore, the building design also will influence the solar
heat gains. In ensuring the building will protected by the solar control, there are some alternatives way
must be added in the design such as shading, building finishes, glazing, insulation and aperture [4].
[6] Revealed that modify heat gains can be reached by two techniques, namely, thermal mass and
night ventilation. For the first technique, in daytime, heat will be absorbed by thermal mass which
available in building's floors and walls. The thermal mass functioned as indoor temperature controller.
Then, a part of heat which had been absorbed before this will be transferred back into the building to
reduce the maximum cooling during the night. In reaching this technique, there are some methods that
can be applied such as phase change materials (PCM) enhanced wallboard, PCM enhanced roof and PCM
enhanced glass windows. After that, for the second technique is night ventilation. The night ventilation
will be keep night coolness for the next following daytime usage. These two techniques will help to
modify the heat gains and simultaneously decrease energy consumption for cooling of buildings.

265
Besides reduce heat gains and modify heat gains, remove internal heat also can be one of the
alternatives in getting cooling of buildings. By using this alternatives, there are two techniques can be
applied. First is without thermal energy and the second one is with thermal energy storage. Refers to [2]
method under thermal energy storage is free cooling. But this research will only focus on natural cooling
which using without thermal energy technique. For natural cooling, there are several methods that can be
implemented in the building such as ground cooling, radiative cooling and evaporative cooling. All options
have advantages and disadvantages depending on the building place itself. Whatever the way in ensuring
the buildings cooling, the most important thing is to fulfil the aim to get the temperature reduction.
THERMAL COMFORT RANGE
Usually, there are five environmental factors in considering Malaysia climate; dry bulb
temperature (°C), relative humidity (%), amount of rainfall (mm), wind speed (m/s) and direction (°), and
solar radiation (MJ/m²) [7]. These factors normally affect architects to design buildings that react to the
local climate. Therefore, a variety of cooling methods had been implemented into the building to provide
thermal comfort to the occupants after the building the does not give enough comfort [8].
Thermal comfort can be explained as the situation of mind to convey pleasure from any thermal
environment [9]. Thermal comfort affected by two main factors which are environmental factors and
subjective factors [10]. Environmental factors can effect to the cooling device through air temperature,
relative humidity and average air velocity [11]. Meanwhile, the subjective factors are the activity level,
metabolic rate, clothing, dieting habits, sex, age, health condition, skin colour, human size and
acclimatization [12]. This paper will touch in deeply the environmental factors relate to the evaporative
cooling in reducing the indoor environmental temperature.
To determine the thermal comfort range, there are several field studies from the hot-humid
tropical country. Start with field study held in Singapore was examined the thermal comfort level of 583
subjects from naturally ventilated apartment and 235 subjects from air-conditioned office buildings. The
result shows that the neutral temperature in a naturally ventilated building was 28.5°C To, while the air-
conditioned building was 24.2°C Ta [13].
In Thailand there had a field study of office buildings. The study also the comparison of the
thermal comfort between naturally ventilated and air-conditioned. This study contained more than 1100
subjects show that the neutral temperature for naturally ventilated buildings was 27.4°C ET*. Then, for
the air-conditioning building was 24.7°C ET* [14]. Next study is the field study of institutional buildings in
Shah Alam, Malaysia. This study also involved a thermal comfort study in both, naturally ventilated and
air-conditioning. The study revealed the thermal comfort range was 24. 5°C to 28°C with 73%RH. While,
the best comfort temperature was 26.3°C [15].
Another field study in Kuala Lumpur, Malaysia was carried out to get the comfort condition in
naturally ventilated classroom. The study found that the thermal comfort range was 23.4°C to 31.5°C and
the neutral temperature was 27.4°C. Besides, this study also imply that when the average humidity was
65%RH, the mean air movement was 0.27m/s and mean temperature was 29.8°C [16].
In Jakarta, there also had a field study was conducted on 600 office workers from 7 office
buildings. The study includes three types of buildings namely, one naturally ventilated, one hybrid and
five air-conditioned buildings. The study was found out that the comfort temperature was 26.4°C Ta and
26.7°C To [17].
An added field study on the thermal comfort for air-conditioned office workers, situated in
Penang, Malaysia. The results showed that the comfort temperature was 24.7°C and the thermal Comfort
Range between 20.8°C to 28.6°C [18].
There was also a field study which was relate to the thermal comfort for naturally ventilated but
this time was in apartment buildings in Singapore. The study illustrate that comfort temperature was
28.9°C [19].

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As conclusion for the thermal comfort studies had been shown in table 2. The outcome of thermal
comfort range had done in this zone suggested by [9] and [20] was 23.0 – 26.0 To with the upper
acceptable comfort value was 24.5 To. While, MS 1525:2007 [21] suggested that the thermal comfort
range was 23°C - 26°C.
Table 2: Review of indoor thermal comfort studies in South-East Asian region [22]
Study
Year
Country
Comfort Range (°C)
Comfort Value (°C)
Type of Study
De Dear et. al
1991
Singapore
-
28.5 To (NV)
24.2 To (AC)
Field Study
(NV & AC)
Busch
1992
Thailand
22.0 – 30.5
27.4 ET* (NV)
26.3 ET* (AC)
Field Study
(NV & AC)
Zain-Ahmed et al.
1997
Malaysia
24.5 – 28.0
26.3
Field Study
(NV & AC)
Abdul Rahman & Kannan
1997
Malaysia
23.4 – 31.5
27.4
Field Study
(NV)
Karyono
2000
Indonesia (Jakarta)
-
26.4 Ta
26.4 To
Field Study
(NV & AC)
Ismail & Barber
2001
Malaysia
20.3 – 28.9
24.6
Field Study
(AC)
Wong et al.
2002
Singapore
-
28.9 To (NV)
Field Study
(NV)
ASHARE Std 55
1992
23.0 – 26.0 To
24.5 To
Climate Chamber
ISO 7730
1994
23.0 – 26.0 To
24.5 To
Climate Chamber
DSM
2007
Malaysia
23.0 – 26.0 with
55 – 70%RH
na
For AC non
residential building
To=Operative Temperature, ET* temperature=Effective Temperature, NV=Naturally Ventilated, AC=Air
Conditioned
EVAPORATIVE COOLING SYSTEM AND TEMPERATURE REDUCTION
Basically, [23] is saying evaporative cooling can becomes a method of converting hot air into a
cool breeze using the process of evaporating water. Evaporative cooling is a technology that can
substantially reduce the cooling energy requirement in the building [24]. Referring to the [3], he agrees
with [23] but he explained it in detail that in making cooling of buildings, evaporation can be produced
either indirectly or directly.
Evaporative cooling techniques can be divided by two basic types namely direct evaporative
cooling and indirect evaporative cooling. [5] Acknowledges that in direct evaporative cooling, it will be
directly into the airstream and reduce the temperature with humidifying the air. While [25] with [26]
believes that there are strong relationship between temperature and humidity in direct evaporative
cooling. Through this evaporation, temperature will decrease when humidity increases.
Next, for the second basic type of evaporative cooling techniques is indirect evaporative cooling.
[25] with [26] has the same opinion that this basic type will not affect increasing of humidity. Moreover,
Mattheos [26] and [5] agree that this system used sensibly cooling where there is no moisture adding up
through heat exchanger.
Besides the basic types of evaporative cooling techniques, [27] with [24] believes that
evaporative cooling can be divided into three groups (table 3), namely direct evaporative cooling, where
moisture is added to the air stream, indirect evaporative cooling, where the moisture content of the air
stays constant and another one is a combination of these two methods which is indirect and direct
evaporative cooling.

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Table 3: Types of evaporative cooling techniques
Evaporative Cooling
Strategies
Typical Sectional Diagram [27]
Description [5]
Direct Evaporative
Cooling
Direct evaporative cooling introduces
water directly into the supply airstream
(usually with a spray or some sort of
wetted media). As the water absorbs heat
from the air, it evaporates and cools the
air.
Indirect Evaporative
Cooling
Indirect evaporative cooling lowers the
temperature of air via some type of heat
exchanger arrangement, in which a
secondary airstream is cooled by water
and which in turn cools the primary
airstream. The cooled air never comes in
direct contact with water or environment.
Indirect/Direct
Evaporative Cooling
Indirect/direct evaporative cooling is
accomplished by passing air inside a heat
exchanger that is cooled by evaporation
on the outside. Then, the pre-cooled air
passes through a water-soaked pad and
picks up humidity as it cools. Because the
air supply to the second stage evaporator
is pre-cooled, less humidity is added to
the air, whose affinity for moisture is
directly related to temperature.
The effectiveness of evaporation is depends on relative humidity, temperatures, air movement
and surface area [5]. In warmer climates, natural ventilation cannot circulate enough air through a
building to provide sufficient cooling at night to remove the day’s heat.
Table 4: Summary of the latest studies conducted on evaporative cooling in South-East Asian region
Studies
Methods
Results
Figures
1. [24]
Use direct evaporative cooling
method.
*Location: Malaysia
The findings indicate that the function of relative
humidity as exergy efficiency of the evaporative
cooling process with T0 = 29.25°C.
Then, the function of relative humidity as exergy
efficiency of the evaporative cooling process with
RH = 70%.
2. [28]
In theory and practically, the
cooling pond system is designed
and built for 0.16 ton coreless
induction furnace. As option for
smelted in foundry shop, it utilize
in two induction furnaces.
Location: Myanmar
The advantages of this system are simplicity, low
capital cost and cooling water with the ambient
wet-bulb temperature. This system also had
disadvantages like, water is lost by evaporation, if
the water level hard to rise, it will cause reduction
of heat transfer. Another disadvantage are effect
of corrosion and fouling trouble from flying dust
and impurities which are drawn into the tower.
The cooling towers also had disadvantage, because
it dependent to temperature and humidity, when
temperature and humidity high, the efficiency will
be decline.
Open-Circuit System with
Evaporative Cooling
Tower

268
3. [29]
The Torrent Research Centre
consists of six laboratory and
office blocks. Four of it integrates
with passive downdraft
evaporative cooling system.
*Location: India
Plan and section of a
PDEC Building
Torrent Research Centre
(drawings and photo
courtesy: Abhikram)
4. [30]
This research use of various
cooling pad materials.
The systems use the Maisotsenko
Cycle is to discover a multiclimate
application such dry and humid.
*Location: India
Maisotsenko Cycle (M-cycle) has a high possibility
to save energy in variety approach. The greatest
example is Coolerado Cooler.
This method gets the benefit of the
thermodynamic properties of air. Both, direct and
indirect cooling technologies applied in this
cooling system. It was cooler than indirect
evaporative cooling and drier than direct cooling.
Cross section of direct
evaporative cooling
Cross section of indirect
evaporative cooling
Working of M-cycle
Cellulose porous stack
heat exchanger
configuration of a DPEC
5. [31]
When air is not too humid passed
through a wet surface,
evaporative cooling happened.
The quicker evaporation rate will
give the better cooling. The
efficiency of an evaporative
cooling structure relies on the
humidity of the environment air.
Location: Nigeria
Evaporative cooling principle can be utilized in
two methods which are passive-direct evaporative
cooling and non-passive direct evaporative
cooling.
Passive-direct evaporative cooling system
depends on the natural wind velocity. While, non-
passive direct evaporative cooling system used fan
to give air movement.

269
The review of table 4 shows the latest studies conducted on evaporative cooling in South-East
Asian region. From the table 4, non- passive direct evaporative cooling system to be possible for
increasing cooling when wind speed is limited. As commonly known Tropical Malaysia is categorized as a
hot and humid climate. This system need to be integrated with mechanical ventilation energy operated by
solar electricity as an environmental friendly concoction.
Consequently, mechanical ventilation can provide continuous moving air that will keep the
indoor environment cooled in the day and night through circulating fans with evaporative coolers.
Window fans are best used in windows facing the prevailing wind or away from it to provide cross-
ventilation. Window fans will augment any breeze or create a breeze when the air is still. The purpose is
for the windows fan support the evaporative cooling which is installed in windows. As a result, the indoor
environment or section of building will be cooled [32].
EVAPORATIVE COOLING WINDOW SYSTEM USING LABU SAYONG
[8] Showed that in making rational building design which are pleasurable, relaxing and secure
environment must have cooperation between engineers and architects. Indoor spaces can achieve an
accurate cooling with this ideal combination. In order to achieve it, this strong relationship was presented
as an evaporative cooling using porous material. It was controlled and promoted by means of some
mechanical device. This integration created one of innovation for cooling.
Technology has been changed together with the times. Since centuries ago, evaporative cooling
has been existed in several different forms by using different materials. The usage of porous water pot for
evaporative cooling has been well known and it is still relevant till now. Porous water pot, porous water
jar, porous ceramic and porous clay pots are made from the same material which is clay [3]. Labu sayong
also made from clay and it has been chosen for this reason.
The porosity of labu sayong absorbs the moisture by capillary action. Even though, the minor
water drops on labu sayong surface which caused by capillary action could not be noticed. The capillary
action had happened when pours the water in the labu sayong. When the water saturated at the surface of
labu sayong, evaporation occurred. Therefore, theoretically, the cooling of water in labu sayong occurs
because of two processes. First, the increased of water on the surface of labu sayong and the second one
was evaporation.
After the water cooled, the outside heat transfer to the labu sayong until the system reached
thermal equivalence. Then, the porosity of the labu sayong surface was completely saturated with water
and later, only evaporation process happened in the cooling process. Consequently, the cooling effect
depends on the water evaporation on the labu sayong surface.
Figure 3: Estimation of porous clay radius was same with a radius of clay soil pore [33]
Water
Pore
Pore

270
Referring to [33] if water evaporation happens, surely water temperature is lower than air
temperature. The result will show that the water in labu sayong is cooler than room temperature. From
this theory, it can be concluded that labu sayong can make the water inside it always cool. This
characteristic was support why labu sayong had been chosen in this review.
By using the labu sayong in the evaporative cooling window system, this system is expected can
promote tourist to come visit Malaysia.
CONCLUSION
In conclusion, for reduce air temperature, evaporative cooling window system using labu sayong
have potential to implement in tropical Malaysia. This review investigates the various types of
evaporative cooling strategies. Based on the result, non-passive direct evaporative cooling window
system is anticipated giving promising in reaching the target. Nevertheless, more researches are
necessary in order to verify the design of evaporative cooling window system using labu sayong.
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