ENGINEERING CLEAN WATER SYSTEM
FOR OFF-GRID COMMUNITIES
P.M. Cabacungan2, J.C. Cheng2, D.L.C. Landoy 2, A.C. Silang2,
R.A. Buenafe, G. L. Tangonan1, N. J. C. Libatique1, T.H. Calasanz1
1: ERDT Faculty, ECCE Department, Ateneo de Manila University, Quezon City 1108, Philippines
2: Electronics, Computer and Communication Engineering Department, Ateneo de Manila University, Quezon City 1108,
Philippines
Email: pcabacungan@ateneo.edu
Abstract
The Solar-powered Atmospheric Water Generation and Purification (SAWGAP) system is a hybrid system, coupling
rainwater collection with water-from-air condensation. It has built-in ceramic filter and ultraviolet irradiation for water
purification. It can be powered by solar energy stored in battery banks coupled with a variable frequency DC-AC inverter,
which can operate at higher voltages. Its engineering design emphasized the use of readily available automotive and
refrigeration components and non-specialty solid state circuits for adoption and adaptation by remote communities far from
grid power facilities.
In the initial unoptimized tests, it generated 18.3 liters of water in 24 hours in ambient air conditions with an average relative
humidity of 70% RH. Within this period, it consumed 2 kilowatt-hours of energy per liter of water generated. All water
samples collected were tested and found to conform to the Philippine National Standards for Drinking Water (PNSDW).
1
INTRODUCTION
Severe water shortages are currently experienced by 470 million people and it is projected that by 2025, the number of people
living in water-stressed countries will increase to 3 billion [1]. It is also estimated that 2.4 billion people in the world lack
access to safe drinking water and that there are about 1.7 million deaths per year worldwide because of diseases found in poor
water quality [1]. In the Philippines, Department of Health statistics show that approximately 18 people die each day from
diarrhea and water-borne diseases [2].
Clean water remains in demand, with various sectors competing for the same scarce resource. Basic water requirement
(BWR) of 50 liters per person per day has been recommended to serve as the standard to meet basic domestic needs [3]. For
agriculture, 70% of the total global fresh water is consumed [4] while industry utilizes 20-22% of the world’s freshwater. It
is expected that water consumption in industry will increase to 1170 km3/yr by 2025 [5]. Business also needs water for
power and steam generation, for sanitation or as a component of products [6].
Different water treatment technologies are made available in an attempt to address concerns on both water scarcity and
contamination. Technology to extract potable water from domestic wastewater is being looked into [7]. However, passing
off sludge as fertilizer can have disastrous effects on the agricultural soils [8]. Chemical disinfection is also being widely
used. Oxidizing chemicals, such as chlorine and ozone, kill a variety of pathogenic microorganisms during treatment [9].
The downside of using these chemicals is the generation of disinfection by-products (DBPs) which may have effects on
human health [10].
In a recent paper, it was mentioned that UV irradiation is quickly gaining popularity in the consumer market as a safe,
effective, and economical approach to disinfection [11]. There are many pathogenic organisms that are more susceptible to
UV than they are to chlorine [12]. On the other hand, ceramic water purifiers (CWPs) have been found to reduce E. coli up
to 99.99%. It also reduced MS2, a viral surrogate, by a mean 90-99% in laboratory testing [13].
Atmospheric water generator technologies can address the need for clean water without any health or environment
concerns. They are already available in locations that have grid power and public waterworks. This paper reports the design
and fabrication of a water-from-air system, coupled with rainwater collection, that can run from battery banks powered by the
sun. A custom DC-AC inverter was also developed and built into the system to allow off grid operation. The DC-AC
inverter circuits for UV lamps do not need high purity low harmonic content specifications. To drive down costs, high
harmonic content of about 50% is still suitable in this context. The engineering design also emphasized the use of readily
available parts for low-cost community production
This work presents one of the first designs for a solar-power compatible clean water system that can be easily deployed
in remote and disaster-stricken areas where potable drinking water and public electric grid system are not available.
2
SYSTEM CONFIGURATION
The whole Solar-powered Atmospheric Water Generation and Purification (SAWGAP) system is divided into three
major parts: Water Generation, Water Treatment and the DC-AC Solar Power Generation. Water collected, both from the
rain water catchment set-up and water generator, will pass through the water treatment system. A solar powering device will
run the whole system. Figure 2.1 illustrates these parts and their relationships to each other.
Figure 2.1 Block diagram of the SAWGAP system
The solar panels will charge the car batteries through a charger circuit. Energy from the batteries will pass through the
DC-AC inverter to power the water generator and the water treatment system.
Two prototypes of water generation were assembled. Prototype A in Figure 2.2 was made of a refrigerator compressor, a
car evaporator and condenser coils, copper tubes, capillary tubes, and a filter dryer. This set-up was found to be feasible but
had to be optimized.
Prototype B in Figure 2.3 was a modified dehumidifier which used a commercial household dehumidifier with its
compressor replaced by a 1.1 kilowatt car compressor and assembled with an electric motor, a valve and a filter dryer. The
humidifier can be replaced by a car condenser and evaporator coils and exhaust fan to drive the costs down. Figure 2.4 shows
the process of air vapor condensation and water generation in Prototype B. Prototype B is the one being referred to in all the
experiments done in this paper.
Figure 2.2 Water generator prototype A
Figure 2.3 Water generator prototype B
Figure 2.4 Block diagram of prototype B
Figure 2.5 shows the process of water treatment. The collected water will pass through a ceramic filter and ultraviolet
(UV) irradiation for disinfection. Figure 2.6 shows the actual water treatment system used for this study.
2
Figure 2.5 Block diagram of the water treatment system
Figure 2.6 Water treatment system
The circuit diagram in Figure 2.7 presents the control circuit of the inverter. It switches the primary terminals of the
transformer to give the desired AC voltage output. Figure 2.8 shows the actual DC-AC inverter assembled.
Figure 2.7 DC-AC inverter circuit diagram.
Design courtesy of Engr. Tristan Calasanz,
Associate Lecturer, Ateneo de Manila University.
3
Figure 2.8 DC-AC inverter circuit
SYSTEM FABRICATION AND PERFORMANCE MEASUREMENTS
3.1
Water Generation System
3.1.1 Operation of SAWGAP System. Powered by grid electricity, the car compressor liquefies the tetra-fluoroethane
refrigerant (R134a) at a pressure of 200-250 per square inch (psi) and raises the coil temperature to about 80-89 degrees
celsius (oC). This hot liquid passes through the filter dryer that removes unwanted sediments and absorbs moisture. It, then,
passes through an expansion valve that automatically regulates the flow of refrigerant with respect to the temperature of the
cold suction coil of the compressor. This compressor is run by an AC motor and a car battery to enable its magnetic coil. The
refrigerant expands at a low pressure of 30-40 psi and at a coil temperature of 10-21 oC. At this temperature range, the water
vapor from air condenses into liquid to an average of 763 milliliters per hour at an average of 70 % RH. Figure 3.1 shows the
graphical form of the data gathered on the volume of water generated vis-à-vis other significant readings on the system.
3.1.2 Data Interpretation.
The effect of changes in capacity of a given system increases as the capacity of the
component increases. In the table shown by B. Kaufman in the graphical analysis for air conditioning system performance,
an increase of 10% capacity in performance results to an increase of system capacity of the compressor, evaporator coil, and
condenser by 6.2 %, 1.8 % and 0.8%, respectively [14].
3
Figure 3.1 Correlation of volume of water with
temperature and pressure components. (Note that
the graphs are not in-scale with each other. They
were purposely scaled up or down to see
variation of values.)
Similar trend was observed in Figure 3.1.
The volume of water was affected primarily by
the (1) compressor’s performance, (2) evaporator
or cold coil’s increase in temperature due to the
increase of mass air flow entering the system,
and the (3) condenser’s temperature that is
proportional with the compressor’s high-side
pressure which drives the expansion valve’s
operation. Upon further examination of these curves, we noted that the depreciating graph of the high pressure readings was
caused by the loosening of the compressor-motor belt. Several moisture characteristics can be drawn from this chart
including the dew points. Since we are concerned with water generation, the efficiency of the system could be defined as the
amount of benefits generated per unit of energy consumed. In this case,
Efficiency = 1 liter of water / 2 kWh
3.2
DC-AC Inverter
The five volt DC source was not supplying enough current for the power transistors to work. Part of the inverter circuit
that had to be replaced for stronger current is shown in Figure 3.2. The design of the additional circuit is shown in Figure
3.3. This design provided an ampere current from the battery strong enough for the input signals to reach and drive the
power transistors.
The designed circuit that could give the
amount of current necessary to enable the
power transistors was arrived at by
computing for base current, maximum
allowable current and resistances. Result
led to the usage of ceramic resistor R5 rated
at eleven ohms and ten watts. This designed
circuit in Figure 3.3 was inserted at the four
branch circuits of the main schematic
diagram in Figure 2.7 in between the nodes
C and P, replacing the four 100-ohm
resistors.
3.3
Water Treatment System
The system set-up used an off-the-shelf water purification system. The initial set-up was a built-in water catchment
system which relied on gravity for collection. Water dripped slowly making potable water collection time-inefficient. A
motor-driven water collection system was used where water was pumped into the ceramic filter and to the UV radiation,
which made the water collection and treatment process faster. The collected water is pumped from the storage tank by a
submersible pump at a flow rate of up to 83.3 liters per minute. This water pump is needed to provide the minimum pressure
of 50 psi to run ceramic filter with a production flow rate of 750ml per minute. This is where water sediments are removed.
It then proceeds to the final treatment level -- the UV irradiation where remaining pathogens, bacteria, and viruses are
eliminated in the water by exposing it to a UV light with 253.7 nm wavelength [15].
4
WATER QUALITY RESULTS
Water samples collected from SAWGAP system were submitted for bacteriological analysis at three stages: pretreatment, post ceramic filtering, and post-UV irradiation. It was found that, prior to treatment, water generated from air was
comparable to tap water quality and conformed to the Philippine National Standards for Drinking Water (PNSDW) with
regard to the absence of coli form bacteria. All samples, after passing through ceramic filtration and UV irradiation, had less
than two most probable number (MPN) of coliform per 100 mL.
The Ateneo Chemistry Department also conducted ion chromatography tests on different samples of tap, rainwater and
dehumidifier water. All peak areas were below limits of detection (LOD – 0.5 ppm) which means that no traces of sulfates
and nitrates were found.
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5
SCALING UP THE SAWGAP SYSTEM FOR SMALL COMMUNITIES
Table 5.1 shows that the Water Generator, its DC-AC Inverter, and DC-AC Inverter for Purification system were
recommended to have two units each for reliability of performance.
Main Components
Water Generator
Purification System
DC-AC Inverter for Water
Generator (1280 watts)
DC-AC Inverter for
Purification System (320 watts)
Solar Panels, 200 watts, 48
volts, 5 amperes
Batteries, deep cycle, 200
ampere-hours
Solar Charger
Grand Total, Php
Qty
2
1
Unit Cost
16,000.00
10,000.00
Total Amount
32,000.00
10,000.00
Table 5.1 Estimated cost of SAWGAP
system’s main component for deployment
This estimate is enough to deploy the
Solar-powered
Atmospheric Water Generation
2
20,000.00
40,000.00
and Purification System for a continuous
2
10,000.00
20,000.00 twenty-four hour daily operation. However,
this estimate does not include maintenance,
12 100,000.00
1,200,000.00 shipment, housing of the system and
technician costs.
A ferro cement design could be adopted
96
5,000.00
480,000.00
for
the
construction of a Rainwater Catchment
1
8,000.00
8,000.00
(RWC) system [16]. We could design a
1,790,000.00
rainwater-catchment system for a barangay or
local municipality with a hundred, a thousand, and a ten thousand size population by calculating the needed area of the RWC
system from the volume of water needed per family, average rainfall, and efficiency of collection. Using the formula: liters
caught = (area of catchment)x(average rain fall/ year) x (efficiency of collection) x 1000 [17], one can determine the roof
area and the volume of water storage tank needed by a given population.
Collected rainwater can be made potable by the purification part of the SAWGAP system. In areas where there is no
grid electricity, the DC-AC inverter at 320 watts (or any over-the-counter DC-AC inverter, at least 200 watts) will be more
than enough to power a UV germicidal lamp and a small pump that pushes water into a ceramic filter.
The system can be adapted in any parts of the Philippines. Its usage efficiency will be determined by the amount of
rainfall in a given area at a particular period of time. In areas with heavy amount of rainfall, it can be used only for
purification of rainwater. Since the whole country has an average relative humidity of 82%, the system can condense a
considerable amount of water from the atmosphere. Table 5.2 gives the projected volume of water, in liters, that can be
collected from air, depending on the relative humidity (%RH) and ambient temperature ( oC).
*Temperature
(oC)
15
20
25
30
35
50%
5.5
7.4
9.7
12.2
15.0
60%
5.7
8.4
12.4
18.0
24.4
65%
7.2
9.6
15.6
20.8
28.0
Humidity
70% 80%
8.7
9.5
11.0 12.4
18.3 22.0
25.7 29.2
32.9 37.2
90%
12.4
17.4
27.3
37.2
47.0
100%
14.3
23.7
33.3
47.3
57.0
Table 5.2 Projected volume of water in
varied
humidity
conditions
and
temperatures
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CONCLUSION AND RECOMMENDATIONS
The system set-up done in this research has yet to be optimized. The different system parts comprising the whole Solar
Powered Atmospheric Water Generation and Purification (SAWGAP) system are found to be workable.
The water generator, made from car air-conditioning and dehumidifier parts, generated an amount of water enough to
supply a regular household’s drinking needs. It addresses the need for safe drinking water in remote areas and responds to
the impending scarcity of potable water in certain areas due to the effects of global warming and natural disasters. It can also
replace or supplement the currently available water devices in the market to reach the more remote areas in the Philippines.
Car air conditioning parts were used to assemble the system. On the surface, capital expenditure may still look high
initially due to the cost of solar panels. In reality, we have calculated that from the viewpoint of the consumer and under
certain assumptions such as 10-15 years amortization, solar power has already attained parity with electrical grid costs. Solar
panels have a life span of 25 years and rechargeable batteries can last for 62.5 years, making the whole system durable.
In order to bring down the manufacturing cost of this system, it is recommended that a further study be done on the
fabrication of ceramic filter. There is available literature explaining the procedures in making red ceramic pots as water
filter [18]. In addition to this, the process of making activated carbon can also be studied. Literature states that activated
carbon removes coloration and unwanted odor from water. There is a way to make activated carbon using materials readily
available and abundant in the Philippines, like coconut shell [18]. Knowing this can further supplement the water filtration
method in a less costly way.
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In making the system easier to deploy in remote areas, it is recommended that other powering alternatives that can be
operated off-grid can be explored, for instance, wind powering. It does not only make the system easily accessible in remote
areas but it can also lower electric consumption, and keep the system environment-friendly.
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