Transcript SNC1D1 Efficiency of Appliances

12.4 Efficiency
Efficiency
• Efficiency refers to how well a load (electric device)
changes electrical energy to useful energy
• Consumers can determine which appliances are most
energy efficient by reading the appliance’s EnerGuide
Label
Efficiency
• By comparing the efficiency of different
devices, we can judge both their energy cost
and their environmental impact.
• A mini refrigerator from the 1970s uses the
same energy as a modern full-size refrigerator
as a result of improvements in insulation and
efficiency of the compressor motor.
Energy Star
• The Energy Star symbol is used to indicate that a
product meets specific criteria of energy consumption
set by the EPA (Environmental Protection Agency).
• The Energy Star label was established to reduce
greenhouse gas emissions from inefficient use of energy
and to help consumers purchase energy efficient
products, which help lower energy bills.
Percent
Efficiency
• The efficiency of a device is the ratio of the useful
energy that comes out of the device to the total
energy that went in.
• The more input energy that a device converts into
usable output energy, the more efficient the device
is.
• Efficiency is usually calculated as a percentage:
Percent Efficiency
• An incandescent light produces a lot of
heat. In fact, only about 5% of the energy
that goes into the bulb is used as light,
useful energy.
• A compact fluorescent bulb in comparison
is about 20% efficient.
Sample Problem
Determine the percent efficiency of a 60-W fluorescent
light bulb that uses 2000 J of electrical energy to produce
400 J of light energy.
Given: Total electrical energy input = 2000 J
Useful energy output = 400 J
Required: Percent efficiency
Analysis:
Useful energy output
Percent efficiency =
Total electrical energy input
x 100 %
Sample Problem, continued
Solution:
Percent
efficiency =
Percent
efficiency =
400 J
2000 J
x 100 %
20 %
Paraphrase: The percent efficiency of a 60-W fluorescent light bulb
is 20%.
Homework
• “Power and Efficiency” Worksheet