Lesson 6 — Activity 1: Heating and Cooling Systems



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We use heating and cooling systems to improve our daily lives and to make us comfortable. Examples include fans that cool us on hot days and furnaces that heat our homes in the winter. Other examples include air conditioners, solar panels, and electric heaters. In this activity, you will examine two other examples of heating and cooling systems.



 
By Pbroks13 - Own work by uploader; The New Book of Knowledge 1997. p. 102., CC BY 3.0
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Many household technologies either transfer or prevent the transfer of heat through conduction, convection, or radiation.


Heating system: How Does an Oven Work?

When an oven is turned on, convection air currents move heat inside it. Air at the bottom of the oven is heated by an electric element or by burning gas. Heated air becomes less dense and rises to the top of the oven. Cooler air sinks to the bottom. The hot air heats the oven walls. The walls then radiate heat in all directions. So food in the oven is cooked by both convection and radiation. There is also conduction from baking pans.


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Cooling System: How Does a Radiator in a Car Work?


Combustion of fuel inside an engine produces a large quantity of thermal energy. If this energy were not removed, the engine would overheat and be damaged. Here is how an engine is protected:

1. The engine’s cooling system contains a liquid coolant. Heat is conducted from the engine to the coolant.

2. The coolant is pumped through the engine block to the radiator. A radiator is a honeycomb made of a metal alloy. The metal alloy is a good conductor. Heat from the coolant is conducted through this alloy to air.

3. Either a fan or the motion of the vehicle forces this air through the radiator.

Heat is transferred to the air that rushes through the radiator.
These three techniques use conduction to protect vehicle engines from heat damage.


Encyclopaedia Britannica, Inc.



Self-Check

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Try the questions below on your own first and then click on the tab to check your answers!

Fill in the blanks for the following statements.


How does an oven work?

1. When an oven is turned on, ________ ________ ________ move heat inside it.

2. Heated air becomes ________ ________ and rises to the top of the oven.

3. The ________ ________ heats the oven walls. The walls then ________ heat in all directions.

4. So food in the oven is cooked by both ________ and ________.



1. convection air currents
2. less dense
3. hot air; radiate
4. convection; radiation






Digging Deeper


Click on the Play button to watch a video that explains another heating and cooling system.


Digging Deeper

Here's an example of a heating and cooling system used in a traditional Aboriginal structure.

Teepees were designed using natural convection flows for heating and cooking.



A conical skin-and-frame dwelling, the teepee was an easily moved yet substantial structure used by Indigenous peoples living on the plains. The teepee was 4 to 6 metres in diameter at the bottom and tapered upward to form a smoke hole at the top. The frame was draped with a sewn cover of 8 to 12 buffalo skins arranged over as many as 20 poles. The teepee averaged 7 to 8 metres in height, with the entrance commonly facing east.

Despite the absence of a real chimney, the interior lining created a chimney effect. The warm air rising inside the teepee created an air current and drew cold air from the outside. This cold air came in under the cover and went up behind the lining, creating a perfect draft for the fire and guiding the smoke out the smoke holes.
 
When the weather was extremely hot, the cooking fire was moved outside, and both the cover and lining were raised 3 to 4 feet and propped open on forked sticks. Here the chimney effect again came into play as air flowed continually through the teepee — in at the bottom and out the smoke hole at the top.

In extremely cold weather, another layer of insulation was added, building a structure of wood and poles around the outside of the teepee. Together with the inside lining, this outside wall prevented most of the heat from escaping.

In extremely hot weather, when strong winds made it impractical to raise the cover and lining, an outside wall of wood and poles was used, made from whatever trees were available. The purpose was to block the wind and the sun's rays to increase insulation, thereby helping to keep out the heat.