ENVS115 Energy Power and Operational Costs Paper Complete the worksheet it is the doc.Relationship between Energy and Power: Energy and power are different

ENVS115 Energy Power and Operational Costs Paper Complete the worksheet it is the doc.Relationship between Energy and Power:
Energy and power are different, but related concepts. Energy is the capacity to do work. Power is the rate of
energy use or doing work. The relationship between energy and power is shown in the following equations.
Power = Energy or the same equation rearranged as Energy = Power * time
time
Units for Energy and Power:
There are several different units commonly used for energy. For this assignment we will use watt hours for
energy and hours for time. Thus, in the equation below, hours cancel out and watts are the units for power.
Power (watts) = Energy (watt hours)
time (hours)
By definition, a watt = joule/second. ENVS 115: Energy, Power, and Operational Costs
Relationship between Energy and Power:
Energy and power are different, but related concepts. Energy is the capacity to do work. Power is the rate of
energy use or doing work. The relationship between energy and power is shown in the following equations.
Power = Energy
time
or the same equation rearranged as
Energy = Power * time
Units for Energy and Power:
There are several different units commonly used for energy. For this assignment we will use watt hours for
energy and hours for time. Thus, in the equation below, hours cancel out and watts are the units for power.
Power (watts) = Energy (watt hours)
time (hours)
By definition, a watt = joule/second. Joules are a unit for measuring energy, so again we see that watts
expresses a rate of energy use. Consider a 60 watt light bulb, the wattage is the rate (60 joules per second) that the
bulb uses energy. Wattage does not indicate the brightness of the light bulb! Different types of light bulbs can
all have the same wattage (i.e. use energy at the same rate), but some will produce more light than others.
Calculating energy use and the operational cost:
To calculate the energy use for a light bulb (or any appliance), you need to know the rate the object uses energy
(power in watts) and the time the object is on (in hours). Energy is then calculated using the 2nd from above.
Energy (watt hours) = Power (watts) * time (hours)
We pay for electricity based on how many kilowatt hours (kwh) we use. There are 1000 watt hours in 1.0 kwh.
So to convert watt hours to kwh, simply divide watt hours by 1000. In Redwood City, the price per kwh is
approximately $0.14/kwh. To calculate operational costs (in dollars) multiply kwh used by $0.14.
Exercise #1: Calculating the electricity costs for one simple room in your home.
The “room” here has very few electrical loads, but the same process can be used for entire house with many
electrical loads. Record answers to questions 1-3 in the table.
1. Calculate the amount of energy used each day in one room of your home. The room contains four 50 watt
bulbs, a 180 watt television (old school from grandma, no home entertainment center for you), and a 1200
watt space heater. On an average day, you use the lights for 5 hours, watch television for 3 hours, and use
the space heater for 2 hours. Fill in the first 4 columns of the table.
Power
(watts)
light bulb
Energy
Cost
($/kwh)
$0.14/kwh
television
$0.14/kwh
N/A
N/A
heater
$0.14/kwh
N/A
N/A
Total
N/A
Hours
Used
(h)
N/A
Daily
Energy Used
(wh)
N/A
Daily
Energy Used
(kwh)
Daily
Operation
Cost ($)
Monthly
Operation
Cost ($)
N/A
Yearly
Operation
Cost ($)
N/A
$0.14/kwh
2. Calculate your total daily energy costs for that simple room. (Fill in the Daily Operation Cost column.)
3. Extrapolate your total costs to one month (assume 30 days) and one year (assume 365 days).
ENVS 115: Life Cycle Costs
Consumers often don’t see the whole picture. Too often we are motivated simply by the initial price tag. If we
are truly interested in saving money (and energy), we consumers need to accurately determine the total cost of
owning and using an appliance. At a minimum, when we purchase an appliance, we need to consider purchase
price (including a consideration of the lifespan of the appliance), cost of operation, and disposal costs.
Exercise #2: Light up your life: Comparing Light Bulbs
Standard incandescent bulbs are no longer sold in California, but they are still used for comparison. Bulbs are
often marketed as 60W equivalents, indicating they produce about the same amount of light as old 60W bulbs.
In this exercise you will calculate the costs of buying and operating 3 types of light bulbs (i.e. Halogen
Incandescent, Compact Fluorescent, and LED) that all produce a similar amount of light (in lumens). We will
assume that we want to use the bulb for 24,000 hours. Record your answers to questions 1-3 in the table below.
1. Purchase Price:
A. I have given you the cost per bulb in dollars, based on recent prices at a local Home Depot.
B. How many of each type of bulb will you need to purchase to have light for 24,000 hours?
C. What is the total purchase price for each type of bulb?
2. Cost of Operation:
A. I have given you the power (in watts) for each bulb. Notably, this info is on every light bulb package.
B. How much total energy would each bulb used during 24,000 hours of operation?
• Remember: power x time = energy
• Calculate the energy use in watt hours (wh) and convert to kilowatt hours (kwh)
C. How much are you paying to operate each bulb? Assume your electricity rate is ($0.14 per kwh)
3.
Total Costs: Add your total purchase cost and the total cost of operation for each bulb.
Bulb Type
Halogen
Incandescent
(750 lumens)
Compact
Fluorescent
(900 lumens)
LED
(830 lumens)
Bulb
Life
(hours)
# Bulbs
Needed
(bulbs)
Purchase
Price
(per bulb)
($)
Total
Purchase
Price
($)
Power
(watts)
Hours
Used
(h)
Energy
Used
(wh)
Energy
Used
(kwh)
Energy
Cost
($/kwh)
986
$1.12
43
24,000
0.14
12,053
$ 6.97
14
24,000
0.14
24,983
$ 14.97
11
24,000
0.14
Total
Operation
Cost
($)
TOTAL
COST
($)
4. Which bulb is the economical choice? Do most consumers buy these bulbs? Why or why not?
5.
Which component of lifecycle costs was not considered in our example? Does it differ for the 3 bulbs?
(Notably one type of bulb is considered hazardous waste and must be disposed of properly.)
Life cycle costs should be considered when any appliance (e.g. refrigerator, clothes washer/dryer) is purchased. Not just light bulbs!

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