HOT BOX EXPERIMENT

The hot box is a solar thermal energy project designed to test the greenhouse principle. Simple cut down shoe boxes are all that's needed for this experiment.

The scientific method requires that we only have one variable. What variable do you think I'm talking about? 
If you answered color you are right. One is darker than the other. Why? What are we testing?

You'll need a few shoe boxes or enough cardboard to make two boxes of about the same size,
glue to laminate layers of cardboard,  aluminum foil to line the inside of both boxes,  a glazing like clear plastic like saran wrap,  duct tape to hold the saran wrap on top of the hot box and a thermometer to take some temperature readings.

FIRST: Glue several layers of cardboard to the sides and bottoms of your boxes.  The extra layers of cardboard provide insulation and slow down heat loss. Use the same amount of insulation on both boxes. 

SECOND: Glue aluminum foil to the bottoms of both boxes and paint the inside of one box black. If you don't have black paint you could use a tar solution.

THIRD: After the paint dries attach clear plastic to the tops of both boxes with duct tape. 

Congratulations! You just built the same kind of hot box that Horace de Saussure built in 1760. Now we're ready to do some experimenting. First we'll want  to find out which box gets hotter when exposed to sunlight for the same period of time. We'll need to test both hot boxes at the same time since sunlight intensity varies. Pick a clear sunny day to run your experiment. Cut a hole just large enough to slide in the thermometers. One per box should be sufficient.

1. If possible support the hot boxes so that they point directly at the sun . Make sure you can take temperature readings without interfering  with the light striking these hot boxes. Record the ambient or outside, in the shade temperature.

2. Take readings every minute for 20 minutes for both hot boxes.

3. With the data you collect plot graphs of temperature rise with time.

4. Which box gets hotter faster? Why? What is the greenhouse effect?

5. Try different glazings such as glass or thick plastics and repeat this experiment.

 

To give you some idea of what your graph might look like I've included a plot of some temperature vs. time data that I recorded on January 14, 2004.  I used a special kind of glazing in my hot box called Kalwall. It has the insulating ability of plastic and the heat trapping ability of glass.

The ambient temperature for January 14, 2004 on Long Island was 20 degrees F. Notice how rapidly the temperature inside the hot box rises after 10 am. By 11 AM the hot box temperature is about 170 F. Eventually the hot box temperature peaks at 200 F. After that some clouds roll in and the temperature drops off. Your hot box might not perform as well as this one, but who knows it might perform better. The important factors concerning solar heat gain that you should now understand include:

1. The Greenhouse Effect 
2. The importance of color
3. The importance of insulation
4. The importance of glazing

Good luck with your project ...

 

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