THERMAL ANALYSIS OF A DISCARDED PLASTIC BOTTLE SOLAR
WATER WALL
Ramal Janith Samarasinghe, Richard John Schuhmann
B.S., Mechanical Engineering, Department of Mechanical and Nuclear Engineering; Assistant
Professor of Engineering Design and Science Technology and Society
ABSTRACT
2. SCIENTIFIC BACKGROUND
Solar Trombe walls have the ability to passively store and
subsequently radiate solar energy into a dwelling. The
objective of this project was to investigate the feasibility
of using a solar water wall constructed of discarded
plastic water bottles to heat and insulate a house in an
urban Moroccan slum community. Initial testing was
aimed at determining the heat absorption and radiation
properties of different liquids and developing a thermal
model of the system. Subsequently, a scale model of a
house with a solar water wall was built and temperature
variations in the bottles and the inside of the house were
measured at various times of the day. This test was
repeated using bottles with various types of liquids. The
data were used to determine the effectiveness of the wall
in the absorption, retention and radiation of heat. A wall
of bottles filled with water and black dye proved to be the
most effective at absorbing heat during the daytime and
radiating it back into the house during the nighttime.
A solar Trombe water wall is a closed system with a fixed
mass; therefore the principles of conservation of mass,
energy and momentum can be applied to this system in
accordance with the First Law of Thermodynamics.
1. INTRODUCTION
Morocco is a country in Northern Africa with a population
of around 32 million and a land area of 446,550 km² [1].
Out of the 5 million tons of solid waste generated annually
in Morocco only 2% is recycled.[2] Much of the waste
generated in Morocco is plastic and much of the plastic
waste is empty water bottles.
Morocco has an equatorial climate with extreme
temperatures (i.e. upward of 80°F during the daytime and
close to 40°F in the nighttime).[3] An appropriate thermal
wall must absorb heat during the day and radiate heat into
the house during the night.
Enabling poor urban Moroccan residents to make use of
discarded plastic bottles to create a heating system for
households meets with the triple bottom line[4] of
sustainable engineering design; plastic is kept out of
landfills (and streets) and homes provide greater comfort
to occupants at little or no cost.
Water has a much higher volumetric heat capacity
(4186KJ/m3-K) than wood, adobe, or concrete whose heat
capacity values range from 1300KJ/m3-K to 2600KJ/m3-K
and thus can store thermal energy better than traditional
building materials. The stored thermal energy is then
released as heat into a building space through convection;
the thermal conductivity of water (0.6W/m-K) is also
higher than wood and dry adobe and aids in this heat
transfer process.[5] A wall constructed with water has
better absorption and heat releasing properties than a wall
constructed with more traditional building materials.
The following equation which is a simplification of the
conservation of energy equation describes the
thermodynamics of the solar water wall system.
Qin – Qout = ΔU
Where: Qin = Heat energy into the system
Qout = Heat energy out of the system
ΔU = Change in system internal energy
This experimental system consisted of the water filled
bottles in the wall and a data acquisition unit. The energy
input to the system consisted of solar radiation from
sunlight. The output of energy corresponded to the heat
that was radiated from the wall into the home. In order to
quantify this, temperature was measured as voltage
change across the data acquisition unit.
3. EXPERIMENTAL PROCEDURE
3.1. Test to determine properties of liquids
Experiments were conducted in Spring 2010 to analyze
the heat absorption and retention capacities of various test
liquids. Bottles filled with a test liquid were monitored
with thermocouples and temperature variation recorded by
an Agilent 34970A data acquisition unit. A total of 15
bottles were tested, consisting of 3 bottles each of 5
different modifications. All 15 bottles were one liter
(approximately 33.81oz) AquafinaTM bottles.
The water used was plain tap water from the State College
area. Because the color black absorbs all the wavelengths
of incident solar radiation, and reflects none, the first
modifications to a clear bottle and pure tap water were to
paint one bottle black and add black food dye to the water
in another.[6]
The effect of having photosynthetic organic matter in the
bottle was tested by using aquatic plants in three of the
bottles. To compare the efficiency of heat absorption by
water with the efficiency of heat absorption of another
liquid with a different heat capacity, commercial
vegetable oil was used in 3 of the bottles.
In summary, the final experimental setup comprised:
i.
3 bottles with tap water
ii.
3 bottles with tap water dyed black using five
drops of food dye per Liter of water
iii.
3 bottles containing tap water with their outside
surfaces painted black
iv.
3 bottles with tap water containing aquatic plants
v.
3 bottles with commercial vegetable oil
The bottles fitted with thermocouples were placed next to
a large south facing window. The Agilent 34970A data
acquisition unit collected readings once every 10 minutes
for 8 days (3/25/2010 – 4/2/2010) from the thermocouples
inside the bottles. A total of 1129 readings were collected
from 17 channels: 15 channels for collecting temperature
data from inside the bottles, 1 channel for collecting room
temperature data and 1 channel for collecting sunlight
intensity data from the pyranometer. The data were
transferred to a computer and graphs were plotted in Excel
to view the results.
3.2 Constructing a pyranometer
Insolation is a measure of the sunlight reaching the
horizontal surface of the Earth and is measured in W/m2.
Insolation is affected by various factors including time of
the day, time of the year, geographical location, and
humidity and can be measured using a pyranometer. An
inexpensive pyranometer can be constructed using a
miniature silicon solar cell detector. The photo detector is
enclosed in a plastic casing (covered by Teflon) and
measures the voltage of wavelengths emitted by the sun
It is important to keep the photo detector face clean and
unobstructed in order to ensure accurate results.
Fig 1: Pyranometer Circuit Diagram
3.3. Construction of model
In Fall 2010 a model of an urban house in Morocco was
constructed using wood and cardboard into which a scaled
wall was built. The wall frame was designed to withstand
the weight of 30 0.5L bottles filled with water. A 21”x21”
frame was constructed to house the water bottles at a 60°
angle so as to obtain the maximum effect of the incoming
sunlight and to allow easy access to the bottles to modify
experimental conditions. The solar water wall contained
three rows of ten bottles each for a total of thirty bottles.
Thermocouples were placed inside of each plastic water
bottle as well as at locations behind the wall and inside of
the model home to measure temperatures. (Fig 2) The wall
was placed at the end of a 21”x21”x40” cardboard box
which was used to model the house.
3.4. Selection of liquid
In order to achieve a set of comparative results, two tests
were conducted using two different liquids inside the
plastic water bottles. The initial test was performed
between 11/5/2010 and 11/12/2010 with State College tap
water. A subsequent test was performed between
11/15/2010 and 11/20/2010 with water (0.5 L) mixed with
black food dye (5 drops) inside of the bottles. Black dye
was selected based on the results of the experiment
conducted in spring 2010 which studied and compared the
properties of various liquids.
3.5. Experimental setup
The experimental apparatus was located in a temperature
controlled room used to house computer servers on the
south side of the third floor of the Hammond Building at
the Pennsylvania State University in University Park,
Pennsylvania. This allowed for a comparative analysis
between the temperature of the room and the temperature
inside the model to observe the insulating effects of the
solar water wall. The experiments were conducted
between 11/5/2010 and 11/20/2010 and the southern
exposure allowed the bottles to capture and absorb the
maximum amount of sunlight throughout the day. An
Agilent 34970A data acquisition system collected and
stored temperature readings from the thermocouples every
ten minutes over a span of 5 days for the first test and over
a span of 7 days for the second test.
not included in the results as the thermocouple failed after
the first several readings. Hence, only two groups of
readings were used to determine the average for the
bottles containing the aquatic plants. Once the averages
were determined, a graph of temperature against time was
plotted.
Fig 2 shows the distribution of the thermocouples in the
wall and the house. The blue rectangles represent the
water bottles in the wall and numbers represent the
channels of the data acquisition unit. Channels 6 to 11
monitored thermocouples that measured the bottle
temperatures. Channels 12 to 16 monitored thermocouples
that measured the temperatures inside the house. Channel
1 monitored a thermocouple which measured the
temperature at the exterior of the house and Channel 17
was connected to the pyranometer[7] that was used to
measure solar intensity.
Fig 3: Graph of temperatures vs. time comparing the
properties of liquids (spring 2010)
Analysis of this graph indicated that the bottle painted
black had the maximum heat absorption followed closely
by the bottle that contained the aquatic plants. The
temperature fluctuations in the bottles changed
consistently relative to pyranometer readings.
4.2 Analysis of heat absorption and heat retention in
the model house
Fig 2: Distribution of thermocouples in the wall and
the house
4. RESULTS
4.1 Comparison of properties of liquids
The readings from the data acquisition unit acquired in
Spring 2010 were first transferred to a spreadsheet on the
computer. The data for each bottle type included three
readings every ten minutes for duration of 8 days. The 3
data points for each ten minute interval (corresponding to
one data point each 10 minutes for each bottle within a
bottle type) were averaged to yield a single 10-minute
average temperature for each bottle type. The readings
obtained from one of the bottles with aquatic plants were
The data acquired in Fall 2010 was downloaded into a
computer and plots of temperature vs. time were created.
Each data point increment represented 10 minutes of real
time.
The first data set was acquired with the bottles filled with
just tap water. Figures 4 and 5 show the temperature
variation with respect to time for the wall and the inside of
the house respectively.
Fig 4: Graph of temperatures in wall of bottles filled
with water (fall 2010)
Fig 5: Temperatures in house with wall of bottles filled
with water (fall 2010)
It was observed that when the exterior temperature was
high, the bottles heated up to around 20°F above the
outside temperature and the temperature of the inside of
the house rose proportionally. This result is undesirable
since in Morocco the daytime temperatures can reach
upward of 80°F which exceeds a comfortable indoor
temperature. During the nighttime, however, when the
temperature drops, the house remains warmer than the
outside as the bottles radiate heat that was absorbed earlier
in the day.
Next, a data set was obtained with the bottles filled with
water with black food dye added. Data was acquired for a
period of 5 days and graphs of temperature vs. time were
plotted. Figures 6 and 7 show the graphs for the wall and
the house respectively.
Fig 6: Temperatures in wall of bottles filled with water
and black dye (fall 2010)
Fig 7: Temperatures in house with wall of bottles filled
with water and black dye (fall 2010)
In this case, the temperatures of the bottles fluctuated
similar to the earlier data. Since black color absorbs all
wavelengths of light, it was expected to increase the
ability of the liquid to store more energy.
The fact that the sunlight was now blocked from entering
the house by the dye was also a cause for seeing lower
interior daytime temperatures. When clear water was used,
the direct exposure of the air inside the house to sunlight
caused the high temperatures during daytime as shown in
figure 5. Adding the black dye to the water blocked the
sunlight from going inside and heating the air and thus the
daytime indoor temperatures were lower as shown in
figure 7.
In summary, temperature within the house followed a
similar trend to the outside temperature during the
daytime and remained comfortable (i.e. around 70°F). The
temperature within the house stayed warmer than the
outside during the night. These combined results are a
more ideal outcome for practical use in Morocco.
5. CONCLUSIONS
8. REFERENCES
The goal of this project was to observe how a solar water
wall would heat up and insulate a house through
determining the heat absorption and radiation properties of
different liquids, developing a thermal model of the
system and conducting experiments on a scale model.
Data was collected for walls constructed with plastic
bottles filled with water and water with black dye. From
the results of the experiments, a conclusion was reached
that the wall made of bottles filled with water and black
dye was more suitable for the purpose of insulating and
heating the house. The bottles with black dye absorbed
solar energy and heat from the outside air during the day
without increasing the temperature of the inside of the
house and more effectively radiated the heat back to the
house during the night when the solar energy ceased and
outside temperatures dropped.
[1] Statistics by country – Morocco, Central Intelligence
Agency – World Fact Book, 2010.
[2] Solid Waste Management Summary, Mediterranean
Environmental Technical Assistance Program,
Morocco, 2003.
[3] Casablanca, Morocco: Climate, Global Warming,
and Daylight Charts and Data, http://www.climatecharts.com/Locations/f/FM60155.php
[4] Elkington, J., Cannibals with forks: The triple
bottom line of 21st century business. New Society
Publishers, British Columbia, Canada, 1998.
[5] Incopera F.P., DeWitt D.P., Bergman T.L., Lavine
A.S., Fundamentals of Heat and Mass Transfer, 6th
Edition, Wiley, Hoboken, NJ, 2006.
[6] Tipler, P.A., Loewellyn, R.A., Blackbody Radiation,
Modern Physics, 5th edition, W. H. Freeman, New
York, NY, 2008.
[7] Brooks, D., Measuring sunlight at earth’s surface:
Build your own pyranometer, 2009.
6. RECOMMENDATIONS
These results showed the effects that different liquids had
on the absorption and radiation rates of a solar wall.
Future studies should continue experimenting with various
other liquids with better thermal properties. (e.g. seawater)
It would also be useful to build two identical models
which enable comparison of two different liquids, bottles,
bottle angles etc. under the same operating conditions.
Also, conducting these experiments in an outdoor
environment would produce results that would better
simulate a real world situation.
Another possible solution to increase the efficiency of the
wall would be to drape a tarp on the inside of the wall
during the day and on the outside of the wall during the
night so as to improve absorption and radiation rates.
To improve the validity of the model, scaled bottle sizes
would also be an improvement
7. ACKNOWLEDGEMENTS
The authors extend their sincere thanks to researchers
Shruthi Baskaran, Abhinav Chowdhri, Bill Finney, Tyler
Pritz, Justin Markel, Majd Daher, Andy Gula and
Christian Glaug for all their hard work, Dr. Lau and Dr.
Poese of The Pennsylvania State University for offering
their knowledge and expertise, and Adam Hackenberg and
Scott Pusey for allowing access to Room 303 Hammond
to conduct the experiments. The project would not have
been possible without all of their guidance and assistance.