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1. Heat Transfer by Solar Radiation through
Permeable Pavement
Ashton Guest, Ryan Calvert, and Dr. Caye Drapcho
BE 4120, Biosystem Engineering, Clemson University,
Clemson, SC, 29674
Abstract
An Important part of all construction is the type of materials that are used. In this
experiment, we will test and observe the effects that color and material play on
absorbance and emissivity. In order to gain a better understanding of the effect a
material can have on the heat transfer from solar radiation a simple test was
conducted. While using HOBO temperature instrumentation and infrared
thermometers, we introduced four different permeable pavement samples to heavy
sunlight on a hot day and analyzed the temperature change at the surface and beneath
the material. By comparing the temperature changes of each surface, we can analyze
and determine the qualities of a material that will serve the greatest purpose
economically and environmentally.
Introduction
Thermal radiation is the form of heat transfer that occurs by electromagnetic waves
between surfaces. Solar radiation is the energy that is released from the sun and can
be measured in Watts/meters2. This radiation flux, also called irradiance, is annotated
with G. About 1370 W/m2 of solar radiation reaches the top of earth’s atmosphere and
can be measured at the surface with a pyranometer.. Solar radiation can be absorbed,
reflected and transmitted through a material. Most of the solar radiation that strikes the
surface of a material is absorbed at the surface and converted to heat that is then
transferred through the material through conduction. By using the equation in figure 1,
the net heat flux due to radiation between an object exposed to the sun and sky can be
calculated and used to understand the properties of a material. A material that absorbs
large amounts of heat from the sun can be used to save energy costs in a colder
environment while a material that does not absorb very much heat from the sun would
be better in a hot environment.
By observing the surface temperature of a material after exposure to sunlight, the
absorbance of the material can be analyzed to gain a better understanding of it. By
also taking the temperature beneath the material, the ability of the material to convert
the electromagnetic waves to heat can be observed.
Methods
The permeable pavement tested in the experiment is made by SureSet. SureSet is
company located in the uk that specializes in design of permeable pavement that is
high in quality with goals in sustainability. The pavement samples used were all made
of medium texture materials that were designed for footpaths and driveways. The four
samples chosen varied in color being, Meadow Green, Bronze, Golden Pearl, and
Atlantic (blue).
For Data collection a 4-Channel Analog HOBO Logger was used with 6’ stainless steel
temperature probes. The probes were placed directly under the pavement samples
with insulation material underneath. The data was logged with the HOBO Micro Station
software, and the surface temperatures were recorded every 5 minutes. The
experiment was conducted over a 30 minute time interval. To obtain an irradiance
value, a HOBO pyranometer sensor was placed beside the experimental setup.
To model the experiment, total energy transfer was simulated with Stella Architect
software and displayed in the figures. .
Results and Discussion Analysis
Figure 2 shows the surface temperature of each pavement as they increase from the
solar radiation. When the electromagnetic waves from the sun hit the surface of the
pavement the radiation is slowly converted to heat that is then transferred through the
material by convection. At about 20 minutes the Golden Pearl and Bronze samples that
were made of aggregate appear to reach steady state. About 5 minutes later at 25
minutes the Meadow green and Atlantic samples, which were made of recycled
material, appear to reach steady state. At these times the surface temperature drops
and in figure 3, which shows the temperature below the pavement, the temperature
begins to plane off. This shows that it took longer for the polymer like recycled material
to conduct the radiation through compared to the mixture of pebble aggregate which
took about 5 minutes less. Interestingly the meadow green pavement reached the
highest surface temperature but maintained the second lowest temperature beneath
very steadily. The green material quality allows a higher absorbance but also results in
a high emissivity value and keeps the material from getting as hot. As most plants are
green, this is most likely what allows them to use the sun's energy so efficiently.
Figure 4 shows the data from the pyranometer throughout the course of the
experiment. About 20 minutes in, the irradiance jumped up almost 200 W/m2 and stays
there the rest of the time. This most likely was from a cloud being in front of the sun
when the experiment started.
In figure 5 we estimated the values of absorptivity and emissivity based on similar
materials and colors and calculated the heat flux due to the radiation for each of the
samples that we used. The estimates accurately represent the results that we obtained.
Conclusion
The goal was of the experiment was to determine how the different types of SureSet
permeable pavement absorb solar radiation when in the sun. When designing an area
where permeable pavement is needed it is important to think about how the radiation
from the sun will affect the area. During the experiment SureSet’s “ Golden Pearl”
pavement kept the lowest heat flux throughout testing. The pavement colored “Atlantic”
had the highest heat flux throughout. Looking at these results we have a better idea of
which direction to go in when designing a paved area such as a city parking lot. From
the results golden pearl pavement should be used in hot areas that would benefit from
retaining less energy from the sun. In cooler areas, Atlantic pavement would be a
better choice in order to benefit from the higher amount of absorbed solar radiation.
Correctly recognizing this energy difference when designing can save several degrees
in average temperature in either direction, saving money used to control temperature in
other ways.
References
Drapcho, Caye. Unpublished notes: Lecture 16: Radiation; Clemson University,2018.
Absorbed Solar Radiation, www.engineeringtoolbox.com/solar-radiation-absorbed-
materials-d_1568.html.
Acknowledgements
Dr. Caye Drapcho
q”=𝝰SG+𝛆𝛔(Tsky
4-TS
4)
Figure 1: Heat Flux equation due to radiation between an object exposed to the sun and sky
Figure 2: Surface temperature of each material over time once exposed to direct sunlight
Figure 3: Temperature underneath pavement over the same time period
Figure 4: Irradiance (G) value during experiment
Figure 5: Estimated net heat flux (q”)
from solar radiation