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The Amount of Fresh Water Wasted as by Product of Air Conditioning Systems: Case Study in the Kingdom of Bahrain

  • University of Technology Bahrain


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The Amount of Fresh Water Wasted as
by Product of Air Conditioning Systems:
Case Study in the Kingdom of Bahrain
Husham M. Ahmed, PhD
College of Engineering
AMA International University Bahrain
Kingdom of Bahrain
Abstract—Millions of air conditioning units consume about
60-64 % of total produced electrical energy in GCC Countries
in the summer season. Conditioning the air involves taking the
heat out and also extracts moisture (humidity) out of the air.
This dehumidification process utilizing the evaporator of air
conditioning units could be an alternative and sufficient means
to obtain fresh distilled water. There is a strong potential for
condensate collection technology to impact water shortages in
the regions of the world where suitable conditions exist.
This paper presents case study analysis of experimental
investigation and practical application of the amount of
condensed fresh water can be collected and utilized from the
discharge pipe of a two tones of refrigeration indoor air
conditioning unit installed in a house during the summer
season in the Kingdom of Bahrain.
Up to 7 liters/hour of freshwater was obtained with an
overall average rate of 2.07 Liters/hour. The study gives a
good prediction of the amount of condensed fresh water output
for particular indoor relative humidity.
Keywords—humidification–dehumidification, condensate
water from Air-conditioning systems, water desalination and air-
condition systems.
Water is abundant in nature. However, there is a severe
shortage of drinking water in most of the humid and hot
environment areas around the world. Most of these countries
depend on water desalination systems to supply their water
demands [1]. The Arabian Gulf countries suffer from severe
freshwater scarcity and rely mainly on thermal or membrane
desalination techniques to produce fresh water from seawater
to meet their ever-increasing needs. These conventional
methods of producing freshwater are energy-intensive
technologies [2]. Almost all countries round the world and
in particular Arabian Gulf Countries rely mainly on air
conditioning systems for thermal comfort. The demand on
air condition systems are continuously increasing. The
byproduct of air conditioning systems are absolute fresh
distilled water [3].
Cooling load imposes significant effects on the demand
for electricity in all GCC countries. Domestic sector
consumption in these countries accounts for more than half
the total energy sold in the system. The pattern of local
consumption is very sensitive to climatic conditions and
therefore consumption increases during the summer period.
The greatest impact on electric load comes from the use of
air conditioning systems. Air conditioning load alone is
responsible for about 65% of electricity consumption. Due to
high temperatures and humidity during the summer seasons,
people use air conditioning on a large scale [4]. The domestic
sector in the United State of America consumes more than
40% of total energy produced. In Singapore, the warmer
country, this up to 57% because of the continuing
need for space cooling. These figures are expected to
increase as a result of the rapid growth of world's population
and wormer global climates [5]. Fig. 1 show a comparative
size of residential electricity consumption in 2010 per capita
for different countries round the world [6].
Fig. 1. Comparative size of residential electricity consumption in 2010 per
capita [6].
Reference [7] reported that the use of the air-conditioning
system has increased rapidly worldwide, and is now almost
necessary in parallel with the widespread demand for thermal
comfort, which is a luxury not long ago. They added that air
condition load considered as the largest energy use in both
the residential and non-residential sectors in Europe and the
United States of America. Their statistical data for energy
consumptions in Europe and United state is shown in table 1.
TABLE 1. Energy consumption by end use in residential sector [10]
End use in the residential sector (%)
Space conditioning
Domestic hot water
Lighting and appliances
Dehumidification technique depends on the use of
moisture in the air. When water vapor in the air comes in
contact with a colder surface, the water changes from a gas
to a liquid and collects onto the cold surface. Humidity is the
general term used to indicate the amount of water vapor in
the air [8]. Each cubic meter of air, up to 600 meters above
sea level and throughout earth, contains 4-5 grams of water
vapor (depending on the atmospheric temperature),
potentially allowing water supplies to be available in
virtually any place inhabited by people. The amount of water
vapor held in the air depends on the temperature. More water
vapor can be held at higher temperature. As temperatures
start falling, the amount of water vapor that can be held by
the air falls. At a low temperature called dew point, the water
vapor will start forming water droplets on surfaces lower
than that temperature[9].
The cooling system is called an air conditioner and not an
air cooler because conditioning the air involves more than
just taking the heat out. Moisture extraction is as important a
function as an air cooler. Humid internal air absorbs thermal
energy more efficiently and is more difficult to cool. The
condensed air moisture on the evaporator cold surface is
usually carried outside the house through the drainage and
most likely to the house sewerage system. Dry air feels
cooler to occupants [10].
Reference [11] considered the collection of condensate
water from large air conditioning is one of the important
ways that can contribute to alleviating water scarcity
problems. Analyzing the data collected from 2000 to 2010,
they were able to identify regions with the greatest possible
collections. They also reported that that the quality of
condensate water collected from various locations and
different air conditioning unit types was very high with
conductivity less than 18 μS/cm and turbidities of 0.041
NTU. Reference [12] conducted an investigation on a
laboratory building as a case study. He found that condensate
collection, from the air conditioning units installed in the
building, could provide for the building’s total water closet
and urinal needs as well as a large part of the building’s
cooling tower demand with water of high quality. Reference
[13] Reported that the collection of clean, high-quality, low-
cost water from a large number of installed air conditioning
units in areas with a shortage of potable water can be a very
good solution to increase the total water supply. The results
of reference [14] indicated that the condensation water
collected from different locations in Saudi Arabia, in humid
and dry zones, and with different climatic conditions was of
very high quality. They found that the total dissolved solids
(TDS) were about 15 mg/L. In comparison to the
conventional desalination methods, the potable water
produced by reverse osmosis contains TDS of about 300
mg/L. They concluded that condensate water of this quality
can be used in a number of valuable applications including
irrigation, municipality, cooling towers, boilers, and various
industrial functions. Reference [15] identified the condensed
water produced by air conditioning systems, which are
usually disposed of in sewage, as a potential source of clean
water. The condensate can be used for water sustainability
and building energy recovery. Reference [16] used the
concept of dehumidification to conduct an experimental
investigation on the performance of an air conditioning
system. The reported that condensed water collected was of
good quality and can be used for verity of purposes. The
average water collection rate was 0.3 ml / s. Based on their
results, the researchers reported that the amount of water
collected depended on cooling coil capacity, Humidity, flow
rate, heat transfer coefficient and time of residence of air
inside the air conditioning unit.
This case study is an experimental investigation to
predict the amount of condensed fresh water can be collected
and utilized from the air condition systems in the Kingdom
of Bahrain and other countries.
This research is an experimental investigation and
practical application of the amount of distilled water that can
be obtained from a cooling air condition system with
capacity of two tons of refrigeration installed in a living
room area of 24 square meter (volume of about 72 m³) in a
house containing five bedrooms, reception room, and
corridor, in addition to the living room subject to the test. All
rooms equipped with 2-tonne cooling devices . The house is
inhabited by five adults. The corridor has four access
passages. One with the house entrances (the main door), the
second with the living room (slide door), the third with the
reception room (slide door) and the fourth is leading to the
kitchen, bed room and to upstairs’ rooms (no doors in this
opening). There is a slide door connecting the living room
with the corridor, the opening and closing of this slide door
for the purpose of entry and exit of the family members have
left free to normal natural situation in most test period.
Opening and closing of the living room door led to the
movement of moisture from inside the house and from
outside to the living room subjected to test. In some cases,
the amount of moisture was controlled by controlling the
opening or closing period of the door between the living
room hall and the corridor and consequently with the rest of
the house area.
Ambient temperature and outside humidity, living room
humidity and temperature were recorded during the test
period. The dew point temperatures were extracted from the
psychometric chart.
The basic idea of the test stemmed from measuring the
amount of natural distilled water under realistic practical
conditions and not in the laboratory situation.
Split unit air conditioning systems contain a design that
collect the water accumulated on the cooling coils to the
outlet drain. This drain has been connected to plastic tube led
to a 20 letter capacity container. Fig. 1, shows the split unit
inside and outside installation, the connecting plastic pipe,
the collecting container and the graduated measuring flask.
The accumulated amount of water was measured by a
graduated flask every hour for six months in 2018 April to
October 2018.
Fig. 1a The outside part of the AC split unit
Fig.1b The inside part of the AC split unit
The condensed water has been collected for seven months
(from April to October 2018) for different days on hourly
basis from two tons of refrigeration split unit system.
Ambient temperature, Room temperature, outside and inside
relative humidity has been recorded. Dew point has been
calculated. It has been found that at high relative humidity,
up to 7 liters/h of fresh water can been collected. At low
relative humidity, a minimum of 0.01 liters/h has been
It has also been found that the production rate depend
directly on the inside relative humidity and indirectly on the
outside relative humidity. This can be seen in Fig. 2 where
all measured inside and outside relative humidity were
plotted against the production rate. Best fit line can represent
the relation between production rates and both inside and
outside relative humidity.
It also can be seen from Fig. 2, that at high range of outside
relative humidity (higher than RH40%), the inside relative
humidity is in general lower than the outside relative
humidity due to the action of the AC of reducing the relative
humidity. For low range of relative humidity (below RH30
%), the inside relative humidity in general is higher than the
outside relative humidity. The RH% range between 30% -
40% mixed trend can be found and can be regarded as a
transition rang.
The higher inside relative humidity than the outside relative
humidly at lower range (despite the action of AC of reducing
the temperature and humidity) is due to the fact that the
inside temperature is lower than the outside temperature.
Therefore the water content inside the room is still lower
than the outside and the difference is the amount condensed.
Table 1 illustrates the case: for example if the inside
temperature is 20C and the relative humidity is 20%, the
water content is 2.92 gm/kg of air, while at 40C and RH10%
at the outside, the water content in the air is much higher at
5.09 gm/kg of air.
Fig. 2 shows the measured inside and outside relative humidity for the
seven month period.
TABLE 1. Water content at different temperature and %RH
Water Content gm/kg of air
The month of September showed the highest average
output of 2.49 L/h while the month of May yield the lowest
average production rate of 1.74 L/h. This is because the
average relative humidity of the month of September was
62.01% while in the month of May; the Average relative
humidity was 46.86%.
The total average output was found to be 207 L/h. Table
2 and Fig. 3 show the average monthly output per hour for
each of the seven month period.
Fig. 3 Average monthly production rate L/hour
TABLE 2. Average monthly production rate L /hour
The results obtained represent a case study in which a
two ton of refrigeration air condition unit installed in a room
of a house has been subjected t to investigation and analysis
for seven month period. It can be concluded that:
The fresh water output from the AC depend directly on
the inside room humidity and indirectly on the outside
An average of 2.07 L /h of fresh condensed water may be
Up to 7 L/h can be obtained
The relative humidity inside the room is lower than the
outside relative humidity for the range of outside relative
humidity higher than RH40%
The relative humidity inside the room is lower than then
the outside relative humidity for the range of outside relative
humidity less than RH30%.
The study gives a good prediction of the amount of
condensed fresh water output for particular inside relative
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253 – 260..
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