Energy Fundamentals: Forms, Transformations, and Efficiency
Chapter 1: Energy Basics
What is Energy?
Energy is the capacity to do work. It can be converted from one form to another, but it cannot be created or destroyed. Energy is a property of matter that can be converted into work, heat, or radiation.
Forms of Energy
Several forms of energy exist, including:
- Kinetic Energy: Energy possessed by a body due to its motion (e.g., a flying airplane).
- Potential Energy: Energy that a body possesses by virtue of its physical position (e.g., water stored behind a dam).
- Chemical Energy: Energy stored in the bonds that hold molecules together (e.g., pizza, batteries).
- Electrical Energy: Energy of electrons in motion.
- Radiant Energy: Energy that travels in waves (e.g., visible light).
- Nuclear Energy: Energy locked in the nucleus of an atom and released by the destruction of mass (E=mc^2).
- Mechanical Energy: The sum of kinetic and potential energy.
- Thermal Energy/Heat: The energy of moving atoms and molecules within a substance.
Units of Energy
Common units of energy include:
- Joules (J): The SI unit of energy.
- Calories (cal): The energy required to raise the temperature of 1g of water by 1 degree Celsius.
- Kilowatt-hour (kWh): The unit of electrical energy.
- Food Calories: Equivalent to 1000 calories.
Note: Meters are a unit of distance, not energy.
Energy Transformations
Energy can be converted from one form to another. For example, chemical energy in food is converted to mechanical energy when we move. However, not all transformations are possible. For instance, chemical energy cannot be directly converted to nuclear energy.
Work and Power
Work is done when a force causes displacement. It is calculated as Force x Displacement. The unit of work is Joules (J).
Power is the rate at which work is done. The unit of power is Watts (W).
Energy Efficiency
Energy efficiency is the ratio of useful energy output to the total energy input. It is usually expressed as a percentage. For example, if a light bulb produces 100 J of light from 200 J of electrical energy, its efficiency is 50%.
Human Needs and Energy
Basic human needs include air, food, water, and shelter. Energy is essential for meeting these needs, such as heating homes, cooking food, and powering transportation.
Heat Transfer
Heat is the transfer of thermal energy from a region of higher temperature to a region of lower temperature. There are three modes of heat transfer:
- Conduction: Heat transfer through a solid medium.
- Convection: Heat transfer through the movement of fluids (liquids or gases).
- Radiation: Heat transfer through electromagnetic waves, which does not require a medium.
Chapter 2: Energy in Homes and Buildings
Home Heating and Cooling
Space heating is the largest energy consumer in homes. The amount of heating required depends on factors like weather and insulation. Heating Degree Days (HDD) are an indicator of heating requirements, with higher values in colder regions like the North Pole.
Cooling Degree Days (CDD) measure the amount of cooling needed in summer, with higher values in warmer regions.
Insulation plays a crucial role in reducing heating and cooling costs. The R-value indicates the resistance to heat transfer, with higher values indicating better insulation.
Passive home heating utilizes natural heat sources like sunlight to reduce the need for external fuel or electricity.
Energy Sources for Home Heating
Natural gas is the most common energy source used for home heating in the US.
Water Heating
Energy usage for water heating can be minimized by:
- Lowering the water heater thermostat temperature.
- Taking showers instead of baths.
- Not using running water while brushing teeth.
Lighting
Incandescent light bulbs are inefficient, as much of their energy is converted to heat. Fluorescent lights use mercury vapor and are more efficient. Halogen lights produce the maximum heat and are often used for security lighting and car headlights. Compact fluorescent bulbs (CFLs) consume the lowest amount of energy.
Refrigerators
Refrigerators, also known as heat movers, use a refrigerant to transfer heat from the inside to the outside. The compressor raises the temperature and pressure of the refrigerant, while the expansion valve lowers the temperature.
Commercial Buildings
Space heating is also the largest energy consumer in the commercial sector. Electricity is the most common energy source used in commercial buildings.
Chapter 3: Energy in Industry and Transportation
Industrial Energy Use
The industrial sector is the largest consumer of energy overall. The chemical industry uses the most energy. Boilers are used to generate steam and hot water for various industrial processes.
Transportation
Gasoline is the most common energy source used in transportation in the US.
Chapter 4: Energy Efficiency and Sustainability
Energy Conversion Efficiency
Energy conversion efficiency is the ratio of useful energy output to the total energy input. Different energy conversion devices have varying efficiencies. For example, automobile engines typically have low efficiency, while electric motors are more efficient.
Energy Demand and Resources
Energy demand is growing exponentially. Doubling time is the time it takes for energy demand to double. Reserves are the quantity of an energy source that is known to exist and can be economically recovered.
Energy Sources and Sustainability
Coal is the primary energy source for electricity generation in the US, but its use is expected to decrease in the future. Natural gas is used for electricity generation and home heating. Nuclear energy use is also expected to decrease. Renewable energy sources, such as solar and wind, are expected to play a larger role in the future.
Calculating Energy Efficiency
Several examples are provided to illustrate how to calculate energy efficiency in different scenarios, such as a power plant boiler, a heat engine, and an automobile.
Units of Power and Work
Watts (W) are a unit of power, while Joules (J) are a unit of energy or work. Work is measured as the force against an object times the distance it moved.
Energy Forms in Different Processes
Examples are provided to illustrate the different forms of energy involved in various processes, such as mining coal, powering a light bulb, and running an automobile engine.
Worldwide Energy Trends
Worldwide, the use of coal and nuclear energy is expected to decrease over the next 20 years. The use of hydroelectric power is expected to remain relatively stable.
Energy Use in the US
In the US, we rely less on energy from wood than in earlier decades. Much of the electricity in the US is generated by burning natural gas. The transportation sector uses energy the least efficiently.