Presentation and discussion of the simply laws of Thermodynamics; Why heated air rises over cooler air?
The teacher can talk about the Density of Substances and why air acts and weighs differently as the
temperature changes. Further discussions concerning air density in weather changes, hot air ballooning,
the makeup of our atmospheric gases and anything else pertaining to the air we breathe. Suggested
additional ideas could be in those areas where air plays a role in movement like in a pneumatic cylinder.
Simple experiments in the pressurization of air in a balloon or tire can be done and compared to
a universal solvent or liquid they all know, water. Here I try to bring out a thermodynamic principal used
widely around the world called Thermo-siphoning.
This course is mainly targeted for middle school grades of perhaps 7th & 8th grade levels but could be
suitable for 1st or 2nd years of High School depending on how intense the teacher would like to get into the
laws of Thermodynamics for the class level of understanding and how we utilize that knowledge.
Explanation of Thermo-Siphoning technique:
In any closed loop system when gases or liquids are present there can be a natural flow or convection that
occurs without any prime motive force needed like a fan or pump. This principal is demonstrated in a Solar
heated duplex birdhouse. Warm air rises up through the air baffles in a forced direction picking up some
speed and heat on its way into the nesting area. After filling the rooms with warm air it travels up through an
air slotted hole in the rear ceiling area of the nesting area. It then enters the attic and after cooling some gets
heavy again (more dense) and falls down the rear slot (two slots are made but the one closest to the rear
leads to the empty plenum chamber in-between walls of the back of the birdhouse. Air is pulled back toward
the front of the birdhouse in the empty chambered area under the bird nesting floor. Following on further to
the slotted hole in the upper back side of the solar heater section. This then leads downward to the resupply
slot for the heated air makeup completing the basically closed loop system. The bird entry points allow some
fresh air to come in and replace Carbon Dioxide buildup. It is suggested if the teacher plans to go with this
project you should do a left or right section view or cut away or even to hide various parts from the view in
order to understand the convection air flow concept. I first saw this same concept being studied at the
Brookhaven National Laboratory on Long Island, New York, around 1980. It was being studied for home
heating through an adaptive configuration for the homes windows. One word of advice. Although only a
general direction orientated toward the path of the sun across the sky is needed; this can work to a degree
temperature in excess of the comfort levels of our feathered friends in warmer climates. A suggestion here
would be to cut wood or cardboard to cover all or perhaps three quarters or half of the solar absorption area
facing towards the sun. The solar heater is meant for winter or very early springtime use, then it should be
covered all the way or turned away from the sunlight especially if nesting and egg laying have begun. The
adult birds will leave the nest but the little ones might not be able to fly away as of yet. Birds are warm blood-
ed animals and not cold blooded like so many think.
Submittal Design Assembly and parts:
Here I submit my design plans for the building of a Solar Heated Duplex Birdhouse, using materials that can
easily be purchased at many places locally. If 1/2” plywood is not acceptable then clean layers of cardboard,
layered and glued together to make up a nominal size equivalent of 3/8” or 1/2” in thickness but the edges
should be sealed off using Elmer’s Wood Glue or any type of equivalent can be used. I strongly advise all
teachers contemplating this as a school, class or individual project to use the sectional viewing tool within
SolidWorks to see through the side to help them grasp the idea of this worthwhile project.
Project Building Tips:
The Solar Absorption Heater Section (Painted in a flat Black) is that color to help with the solar heating.
However, many solar enthusiast will tell you that it is not necessary because only sunlight of a certain infra-
red spectrum can travel through the Plexiglas front cover. As it travels through the Plexiglas it changes it’s
frequency and gives up heat in the process which is how the air gets hot. Reminder here, a car with all the
windows rolled up and left in the summer sun can reach 140-160 degrees Fahrenheit easily. The reason I
have kept it flat black in color is to promote the idea that dark rough surfaces tend to absorb while light
colored smooth surfaces tend to reflect solar radiation.
Wood Glue like Elmer’s Carpenter Glue when applied to clean and smooth wood surfaces is an excellent
joining method for wood working. Clamping or using weights can insure proper mating of objects or parts.
Many solar projects can be done using cardboard materials but there is a further level of tool usage needed
To make sure students using very sharp cutting instruments don’t get hurt. My suggestion here is to let a
professional do the cutting of the parts or someone well versed in the use of cutting tools. The treatment of
medical emergencies is not what this project hopes to teach.
When joining or mating surfaces together, please pay special attention to the joints being made. It is sugg-
ested that they are very tightly made as much as possible. Air gaps between pieces can cut down on the
efficiency needed to make this work properly.
Elmer’s Wood Glue in the 16 oz., package should be more than enough. Paper towels and water for clean
up is also strongly suggested. It can get messy.
Non-toxic wood paints colors to your taste and water based is best for student clean-up. Only black paint
Is suggested for the solar absorption section inside and just as well paint it that color on the outside.
A tube of silicon sealant to glue the Plexiglas down to the wood or cardboard surfaces. Buy a squeeze tube
rather than the one that fits inside of a caulking gun, unless you have one of course.
A full sheet of half inch plywood would work the best but cardboard can be substituted for it. Appropriate
wood cutting saws needed or if using cardboard very sharp box cutters of razor blade knives work fine. A
strong straight edge for part layout as well as for cutting of the cardboard pieces is strongly advised.
Two pieces of 1/8” thick Plexiglas for the solar heater front cover and for the birdhouse apartment front
Enjoy and if you need help: Richard.