Energy Management Strategies - Lecture

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Energy Management Strategies (Sci355)
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Week 1-2: Energy Systems: An Overview

Practice Problems

Definition of Energy
Energy can be defined as the "capacity to do work"
(Also see handout on class definitions of "energy")
Work = force x displacement
W = F x d
Measurement Systems
Length-Mass-Time Systems
British System: force in pounds and distance in feet; energy (work) in ft-lbs
Metric System (MKS): force in Newtons (N); distance in meters; energy in joules (J)
Metric (cgs): force in dynes; distance in centimeters; energy in ergs
Principles of Energy Management
Concepts & Terminology
Importance of Energy to Systems
All systems need energy to exist
Laws of Thermodynamics
1^st law: Law of Conservation of Energy/Mass

total amount of energy in a closed system remains constant
energy is neither created nor destroyed
energy can be converted from one form to another

2^nd law: Law of Entropy

energy conversions are not 100% efficient
using energy changes the energy into a degraded form (useless to system)

Conversions of Energy
Law of Entropy - Results in an energy loss to the system in which transformations occur
The more steps in a conversion process, the lower the efficiency of the entire process
Electricity generation (~30%)
Involves conversion of fuel for heating water to produce steam to turn a turbine in a magnetic field, thus producing a flow of electrons
[See Spreng, Net Energy Analysis readings - Chap. 5, 12]
Forms of Energy
Kinetic Energy (energy of motion)
Ek = ½ mv2
M(mass) = measure of an object’s resistance or inertia to being set in motion (slug, kg, gm)
V (velocity) = distance traveled/time (ft/s, m/s, mile/hr, km/hr)
Work Energy
Ft-lb = weight of mass x distance moved
m (mass) = measure of an object's resistance or inertia to being set in motion;
(not dependent on location)
British System: slug, Metric System: kg or gm
Equivalency: 1 slug = mass accelerated at 1 ft/sec² by a force of 1 lb = 14.6 kg
v (velocity) = distance traveled/time; (ft/s, m/s, mile/hr, km/hr)
Ft-lb = weight of mass x distance moved (1 pound x 1 foot)
Joule = Force of 1 newton displaced 1 meter in the direction of the force (kg*m)
Erg = Force of 1 dyne displaced 1 cm (g*cm)
Newton = Force required to displace 1 kg the distance of 1 m/s²
Dyne = Force required to displace 1 gm the distance of 1 cm/s²
Mass versus Weight:
Mass is the measure of a body's resistance to acceleration
Mass is proportional to weight
Mass is independent of position but dependent on its motion in respect to other bodies
Weight on earth is the force with which the earth pulls on a mass
Units of force: Pound or Newton
Weight (force) = (Mass) x g
g = acceleration of a freely falling object due to the gravitational field of the earth
32.174 ft/s², or 9.8 m/s²
1 Pound = Weight of a standard 1 pound mass subject to the earth's gravitational force
Potential Energy
Energy of position (e.g., mass at some height above the ground; because of its position, it is capable of doing work)
Ep = mgh [mass x gravitational force x height]
Will gain kinetic energy if it falls back to earth
Other examples (spring, pendulum)
Mass Energy (Nuclear Energy)
Based on Theory of Relativity (Einstein)
E = MC² [E = energy; M = mass; C = velocity of light (3x10⁸ m/s)
When the mass of some system is reduced by an amount, delta M, then an amount of energy is released
Chemical Energy
When certain chemicals combine (or break apart), energy can be released, usually as heat, expressed as Calories
Comparative Examples:
Coal Burning [C + O₂ = CO₂ + 95 kcal/mole (mole is gram molecular mass = sum of atomic masses in grams, same as the number of protons and neutrons in nucleus)]
Sugar Combustion in Living Cells [C₆H₁₂O₆ + 6O₂ = 6CO₂ + 6H₂O + 690 kcal/mole]
Heat Energy
Heat energy is not thought of in absolute terms but in terms of an amount of heat (delta Q) transferred into or out of a substance
When heat is added into some substance, two changes can occur:
(1) Increase in the internal energy (delta U), i.e., increased kinetic energy of the molecules, or increase in the temperature of the material
(2) Material expands and performs work on some external system (e.g., push a piston), and delta W (work) is performed
[delta Q = delta U + delta W]
Heat is traditionally measured as BTUs (British thermal units), or in calories (cgs system) or Kilocalories (MKS system)
British thermal unit = Amount of heat energy to raise 1 lb of water 1^oF
Fahrenheit versus Celsius Temperature Scales [Tf = 9/5 Tc + 32] or [Tc = 5/9(Tf – 32)]
Calorie (cal) = Amount of heat energy needed to raise the temperature of 1g of water 1 degree Celsius
Kilocalorie (kcal) = Amount of heat energy needed to raise 1 kg of water 1oC
Mechanical equivalent of heat can be calculated
1 cal = 4.184 Joules
1 Btu = 778.2 ft-lb = 0.252 kcal = 1055 J
e.g., How many BTU of heat energy was added to the water if the temperature of 15 lbs. of water in a tank was heated by 10 degrees? What is the energy in joules?
Electrical Energy and Power
Power = Energy (or Work)/ Time
1 Watt (W) = 1 J/s
1 Horsepower (HP) = 550 ft-lb/s
1 HP = 746 W = 0.746 kW
Applications of these terms
Vehicles (horsepower) – work performed
Appliances (kilowatts) – energy consumed
Electricity (kilowatt-hours, kwh)
Comparison of Power Units
1 kWh = 103 Watts x 3600 s = 103 J/sec x 3.6x103 s = 3.6 x 106 J
Ohm’s Law (accounts for resistance of a material to the flow of electrical current through a material)
I (amperes) = V (volts)/ R (ohms)
Important concept in electrical transmission (longer transmission distances results in resistance losses)
W (watts) = V x R
V (volts) = W (watts)/I (amperes) and W = VI
Electromagnetic Radiation (emf)
Represents the field of force associated with electrical charge in motion
Electronmagnetic Spectrum includes radio waves, microwaves, infrared radiation, light, UV radiation, electromagnetic fields, x-rays, and gamma rays
Most important source of energy (electromagnetic radiation from the sun)
Characteristics of waves
Wavelength (Greek symbol lamda)
Frequency (f) – measured in hertz (cycles/sec)
Amplitude (height of the wave)
Electron volts (eV) used for shorter wave radiation
Energy and power units of J and W are generally used
The eV (electron volts) is used for shorter wavelength radiation such as x-rays and gamma rays

Measurement Systems
British System (Pound, Foot, Second, British Thermal Unit or BTU, Horsepower, Watt)
Metric System (MKS or cgs)
MKS = Newton, Meter, Kilograms, Second, Liter, Kilocalorie, Joule)
CGS = Dyne, Centimeter, Gram, Second, Milliliter, Calorie, Erg)
Units are “convertible”
Conversions occur regularly due to the global nature of the energy supply
Common Use of Measuring Units
Petroleum (Barrels-bbl; Million gallons/Day-mgd)
Coal (British tons-Ton; Metric ton-Tonne)
Natural gas (Therms, CCF)
Gasoline (Liters, Gallons)
Uranium (Tons, Tonnes, Grams, Kilograms)

Primary Energy Sources
Naturally occurring energy resources
Fossil fuel sources (coal, crude oil, natural gas, tar sands, oil shale)
Hydropower (waterfalls, tidal currents, wave action-primarily for electrical generation)
Source for fissionable materials (uranium)
Solar (sunlight for heat capture or electricity production-photovoltaics)
Geothermal (capture of earth’s heat or use of steam to produce electricity)
Wind (capture of kinetic energy)
Plants (production of biodiesel and alcohols)
Secondary Fuel Supply
Petroleum products (gasoline, fuel oil, jet fuel, kerosene, diesel, asphalt)
Shale oil (kerogen derived from oil shale)
Refined natural gas
Biomass conversions (anaerobic processes that produce methane; direct burning to produce heat or steam)
Coal conversion technologies (coal gasification and coal liquefaction)
Nuclear Fission (capturing the radionuclides from fissionable uranium to produce heat and then steam – electricity generation)
Electricity (generated from coal, oils, nuclear fission, photovoltaics, wind, hydropower, etc.)
Space and water heating (heat captured from burining chemical fuels, solar gain, biomass conversion, geothermal sources, electricity)
Biodiesel (oils generated from flax, corn, microbial transformation)
Fuel Cells (using hydrogen sources to generate electricity)
End Users
Industrial (factories, waste processing)
Commercial (service sector, business sales)
Residential (homes)
Transportation (auto, train, bus, shipping companies)
Tracking Energy Flows
Energy Flow Analysis
Tracking the conversions of energy in a process and accounting for entropy losses
Can use symbols to depict the utilization, storage, or losses of energy from a system
Fuel Cycles & Energy Accounting Systems
Accounting for all the steps in capturing primary energy sources, conversion to secondary fuels, and applications by end users
(more steps in process, more energy lost from the system)

Transformation of Energy in Energy Flow Diagrams
In energy flow diagrams, R (respiratory loss) represents the heat loss from a system (see textbook for examples of energy flow charts)
Aside from nuclear energy, major part of energy we use comes either from the sun directly or is energy that came from the sun
tens to hundreds of millions of years ago which is stored as chemical energy in fossil fuels.

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Copyright
Gaytha A. Langlois, Ph.D., 1999
Bryant University, Smithfield, RI 02917
e-mail: langlois@bryant.edu
Last Updated: August 2006