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Energy Efficiency. Key Questions:. How do we heat/cool our homes? How do we get our heat? How does heat transfer? How do we increase energy efficiency? Why increase efficiency?. How do we heat/cool our homes?. Forced Air Heating and Cooling What? Air heated/cooled
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Key Questions: How do we heat/cool our homes? How do we get our heat? How does heat transfer? How do we increase energy efficiency? Why increase efficiency?
How do we heat/cool our homes? • Forced Air Heating and Cooling • What? • Air heated/cooled • Distributed through ductwork • How? • Natural Gas/Electricity • Why? • Can be used for heating and cooling • Relatively inexpensive • High Annual Fuel Utilization Efficiency (AFUE) • Efficiency of converting fuel to energy.
How Does Heat Transfer? • Second Law of Thermodynamics • Heat goes from a warm place to a cold place. • In homes: • When heating, heat is lost to the outside. • Hot objects will cool to room temperature. • When cooling, heat is gained from the outside). • Cool objects will warm to room temperature.
Conduction • Heat is transferred through materials by direct contact (transferred to adjacent molecules). • Ex. Putting a spoon in hot water
Thermal Conductivity Conductors vs. Insulators
Convection • Heat is transferred by mass motion fluids such as air or water. • Ex. Forced air by fan • What happens to particles when you heat them? • They spread out less dense. • Hot air rises, cool sinks down and takes it place
Radiation ? • Heat is transferred by electromagnetic waves. • The source heats an object but not the median in between. • Ex. The Sun heating a house.
Radiation Absorption vs. Emission