1. Notes 7: Using Heat
Chapter 6 Section 3 Page 172

2. Heating Systems
During the winter and fall months, it gets cold outside. To make ourselves comfortable, we use a heating system to keep the insides of our homes warm.
There are three common types of heating systems:
Forced-Air Systems
Radiator Systems
Electric Heating Systems

3. Forced Air Systems
This is the most common type of heating system. It uses convection to heat a room.
In this system:
A fuel is burned in a furnace and heats a volume of air.
A fan blows the warm air through ducts (large pipes).
The ducts lead to vents (opening in the floor) and blows the warm air into rooms.
Cold air then returns through additional vents to the furnace where it starts again.

4. Forced Air Systems

5. Radiator Systems
Still used, but is considered an older form of heating your home. It uses conduction to heat a room.
In this system:
A fuel is burned in a furnace and heats a tank of water.
A system of pipes carries the hot water to radiators in different rooms.
The now hot radiators heat the air in the room by conduction.
After the water cools, it flows through the pipes back to the tank to be reheated.

6. Radiator Systems

7. Electric Heating Systems

8. Electric Heating Systems
Electric heating does not use a furnace like forced-air and radiator systems. Instead it heats the room using electrical energy. It again uses conduction to heat a room.
In this system:
An electric heater is connected to an outlet.
When it is switched on, electrical energy is converted into thermal energy (typically by heating oil inside of it).
The electrical energy is turned off once the room gets warm and turns on if the room gets cold again.

9. Solar Heating
The Sun emits an enormous amount of radiant energy that strike the Earth every second of every day. This can be used to heat homes and buildings.
There are two types of systems that use the Sun’s energy for heating:
Passive solar heating
Active solar heating

10. Passive solar heating
In passive solar heating, materials inside your home absorb the radiant energy from the Sun during the day and heat up.
At night when the building begins to cool, thermal energy absorbed by these materials keep the room warm.
This is why in the winter months you
should keep your window shades open
during the day and closed at night.

11. Active Solar Heating
Solar Collector - Device used in an active solar heating system that absorbs radiant energy from the Sun.
The collectors are installed on the roof of your home and uses the radiant energy of the Sun to heats air or water. The hot air or water is then moved through pipes into radiator systems to heat your home.

12. Thermodynamics
Thermodynamics - study of the relationship between thermal energy, heat, and work.
There is another way to increase the thermal energy of an object besides adding heat.
For example, what do you do with your hands to warm them up during the winter? Are you adding heat?

13. The First Law
First Law of Thermodynamics - states that the increase in thermal energy of a system equals the work done on the system plus the heat added to the system.
Basically the temperature of a system can be increased by adding heat OR by doing work.
A fire will warm your hands with radiation AND you can warm your hands more by doing work and rubbing them together.

14. The Second Law
Second Law of Thermodynamics - states that it is impossible for heat to flow from a cool object to a warmer object unless work is done.
Basically, heat always flows from hot objects to cold objects UNLESS work is done.

15. Converting Heat to Work
Heat Engine - device that converts thermal energy into work.
An example of a heat engine is a car’s engine. It turns the heat of burning gasoline into the work of turning the wheels.

16. Internal Combustion Engine
Internal Combustion Engine - heat engine that burns fuel inside the engine in chambers or cylinders.
Remember from Notes 6 that when temperature increases, volume is expanded!

17. Heat Movers
How does the inside of a refrigerator stay cold? According to the 2nd Law of Thermodynamics, a fridge should get warmer.
A Heat Mover does the opposite of a Heat Engine! It does work to move heat rather than using heat to do work.

18. Refrigerators
A refrigerator contains a coolant that is pumped through pipes on the inside and outside of the refrigerator.
The coolant is a special substance that can absorb thermal energy inside of the refrigerator and transport that thermal energy to the outside of the refrigerator. The coolant requires a compressor which does work to move the thermal energy.
Because of this the inside of the fridge gets colder and the outside of the fridge gets warmer.

19. Refrigerator

20. Air Conditioners
An air conditioner works identically to a refrigerator. It does work to move heat from inside your home to outside your home.

21. Sweating
Your body uses the evaporation of sweat to keep the internal temperature of your body constant.
When a liquid changes to a gas, energy must be absorbed from the liquids surroundings (your body).
Therefore as the tiny beads of sweat evaporate, it carries away heat to cool your body.