Not too hot. Not too cold

This exercise is a part of Educator Guide: Health Effects of Climate Extremes and Thermal Technology / View Guide

Directions for teachers:
To engage students before reading the article, have them answer the “Before Reading” questions as a warmup in class or for homework. Then, ask students to read the online Science News article “This ‘thermal cloak’ keeps spaces from getting either too hot or cold” and have them answer the “During Reading” questions. As an optional extension for deeper analysis, have students discuss the “After Reading” questions. A version of the article, “This ‘thermal cloak’ keeps spaces from getting either too hot or cold,” appears in the August 12 issue of Science News.

Before Reading

1. Consider the types of things in a typical home that run on electricity. List three major categories of such products. (For example, one of your categories could be household appliances, such as coffee pots, dishwashers, etc.) Which of these categories do you think consumes the most energy in a typical home? To what extent does this consumption change with the season or over the course of a year? Explain your answer.

Answers will vary. Categories could include household appliances, heating, cooling, computers, or lighting. Students may pick any of their categories as the top consumer. The student must state and explain whether they think their chosen category would or would not change by season. Note that “seasonal changes” may not be weather-related. For example, students may say the school season leads to greater computer usage.

2. Imagine two dark blue cars on a hot summer day. One car sits in the shade. The second sits in the sun. You place your hand on each car’s hood. Do you predict the sunny car’s hood will feel hotter, cooler, or equal to the temperature of the shaded car’s hood? Identify one environmental variable that differs between the two cars.  Identify one factor that is the same. To what extent did the differing factor affect your prediction? To what extent did this variable factor into your prediction? Explain your answer.

Answers will vary. The student may predict the sunny car’s hood to be higher, lower or the same. A variable that differs between the cars is the presence or absence of direct sunlight. Regardless of prediction accuracy, the student should explain the extent to which sunlight did, or did not, factor into their reasoning.

During Reading

1. What characteristics of the new device might help reduce a home’s energy use? Globally, what percent of total energy consumption goes to heating and cooling?

The new device doesn’t require external power. Therefore, it may reduce energy consumption associated with heating or cooling. Globally, 12 percent of total energy consumption goes to heating and cooling.

2. According to Aaswath Raman, would using this new device be likely to increase, decrease or have no effect on levels of carbon dioxide emissions? Why or why not?

Aaswath Raman predicts the new device could reduce carbon dioxide emissions because less electricity would be used by devices needed to control a car’s internal temperature.

3. The cloak is made of two layers. How does the “outer layer” interact with light to keep the space underneath it cool?

The “outer layer” reflects light, which dissipates heat. At the same time, it also absorbs some heat, re-emitting it as infrared light. Both would tend to keep the temperature under the cloak cooler.

4. What two materials make up the “outer layer?” Identify the type of light that each material interacts with.

The “outer layer” is composed of silica fibers and boron nitride. The silica fibers contribute to the cloak’s function by reflecting visible light. The boron nitride reflects ultraviolet light.    

5. What material makes up the “inner layer”? Explain how that material contributes to the cloak’s function.

The inner layer is composed of aluminum foil. The aluminum traps heat under the cloak, keeping the space warm at night.

6. Under what “extreme conditions” did the researchers test their new material? Provide a measurement of one test condition.

Researchers tested their material at extreme temperatures. They tested the fabric at 800 degrees Celsius.

7. Describe one way that researchers tested the performance of the full-size prototype. Identify one city in which such investigations took place. How did temperatures inside the cloaked car compare to those outside of it? How did the temperatures inside the cloaked car compare to those inside the non-cloaked car? Give your answers in degrees Celsius.

Researchers created a car-sized cloak of their new material and tested it on an electric car in Shanghai. They compared the inside temperature of the uncloaked car with the cloaked car. The cloak kept the inside of the cloaked car 8 degrees Celsius cooler than the outside temperature. The cloak kept the temperatures inside the cloaked car 28 degrees Celsius cooler than inside the uncloaked car.

After Reading

1. What color is the “outer layer” of this fabric? To what extent do you think the fabric’s color contributes to its function? If the fabric was navy-blue, would it work better, worse or the same? Explain your reasoning. 

The outer layer of the fabric is white. The color should contribute to its function because the white would be expected to reflect more sunlight. If the outer layer were black, it would likely absorb more sunlight and re-emit that energy as heat. That should lower the cloak’s ability to keep the car’s interior cool.

2. Based on the information in this story, identify one variable the researchers controlled (did not allow to change between the cars) in their Shanghai study. Now consider other variables that if not controlled might affect study results. Write down one variable the researchers may or may not have controlled (but that you can’t tell from the information given). In one sentence, explain how this variable could affect the outcome of this study.

Researchers controlled for outside temperature, season and location. Answers could vary based on the variables that were not taken into account. Here are some examples of possible responses. The story did not explicitly state that researchers controlled for sunlight exposure (intensity or duration based on whether, for instance, it might have been in a building’s shadow for part of the day). It is unclear whether the covered and uncovered cars were tested at the same time of day. The story makes no mention of the uncovered car’s color, which could also be a factor if it’s different from the color of the covered car’s cloak.