Hallway lights energy use summary

1
Hallway lights energy use summary

• First what assumptions did we make?
• All lights had the same wattage bulbs
• Number of hours lights were on during the day
• All bulbs were on all the time
• All fixtures had the same number of bulbs in them
• Electricity costs 0.11 per kilowatt hour

2
Hallway lights energy usage

• Room KW /day yearly cost
• TCCW 1 49.9 1,976
• TCCW 2 78.6 3,156
• TCCW 3 74.1 2,975
• TCCW 4 66.6 2,672
• Total for TCCW 10,779

3
Hallway lights energy usage

• Room KW /day yearly cost
• Snell B 14.0 562
• Snell 1 64.7 2597
• Snell 2 13.6 547
• Snell 3 58.96 2367
• Snell 4 19.5 781
• Total for Snell 6,854
• (3686.77)

4
Horse power

• Arose as a result of the invention of the steam
  engine. People needed a way to compare the power
  of a steam engine to that of the horses it was
  replacing.
• Confusing unit there are too many different
  definitions!

5
BTU

• BTU British Thermal Units - an energy unit
• the amount of heat required to raise the
  temperature of one pound of liquid water by one
  degree from 60 to 61Fahrenheit at a constant
  pressure of one atmosphere
• Used in the power, steam generation, heating and
  air conditioning industries and the energy
  content of fuels.
• However, BTU is often used as a unit of power,
  where BTU/hour is often abbreviated BTU.
• So you need to watch the context!

6
Back to Watts..

• A human climbing a flight of stairs is doing work
  at a rate of about 200 watts.
• A typical household incandescent light bulb uses
  electrical energy at a rate of 25 to 100 watts,
  while compact fluorescent lights typically
  consume 5 to 30 watts.
• A 100 Watt light bulb consumes energy at the rate
  of 100 joules/second.
• After 1 hour, this light bulb uses 100 watt-hours
• 1 kilowatt (kw) is 1000 Watts

7
Examples

• In a certain room in your house, you use a 100 W
  light bulb. This light is on for 5 hours every
  day. How much energy does it use?
• 1 W 1 J/s and there are 5hours x 60min/hour x
  60 sec/min 18,000s in 5 hours so the total
  energy used is 100 j/s 18000s 1.8 x 10 6 J.
• Lets assume the same lighting level can be
  achieved using a 30 W compact florescent bulb.
  How much energy is used by the compact florescent
  bulb?

8
Examples

• Total energy 30 j/s x 18000 s 5.4 x 105 j.
• So how much energy is saved every day using the
  compact florescent bulb? Take the difference
  between the energy used by the two different
  light bulbs 1.8 x 10 6 j - 5.4 x 105 j 1.3
  x106 j.
• Lets look at this in something you might be able
  to relate to better than joules---dollars!

9
Example continued

• After 5 hours, our 100 W light bulb uses 500
  Watt-hours, or 0.5 Kwh. The 30 W bulb will use
  150 Watt hours or 0.15 Kwh.
• Assume electricity costs 11 cents/Kwh (roughly
  the average cost in the US in October 2010). So
  it costs .5 KwH x 11 cents/Kwh 5.5 cents every
  day to run the 100 W light bulb and 0.15Kwh x 11
  cents 1.65 cents every day to run the compact
  florescent.

10
Example continued

• So in a year, the 100 W light bulb costs you 5.5
  cents/day X 365 days/year 20.00 and the 30 W
  bulb costs costs you 1.65 cents/day x 365
  days/year 5.50.
• Savings of 14.50/year per 100 W light bulb!
• There are now 13 Watt LEDs that can replace 100 W
  light bulbs.
• These would cost 2.61 per year. Thats a 17.39
  per year per bulb savings.

11
How do CF bulbs work?

• made of glass tubes filled with gas and a small
  amount of mercury.
• produce light when the mercury molecules are
  excited by electricity running between two
  electrodes in the base of the bulb.
• mercury emits ultraviolet light, which in turn
  excites the tubes phosphor coating, emitting
  visible light.

12
Limitations of CF bulbs

• Take longer to turn on
• Do not work with dimmer switches
• Contain mercury, a known toxic substance

13
Mercury in CFLB

• 4-5 milligrams per bulb, about the size of a
  period.
• Old mercury based thermometers contain about 500
  milligrams.
• Should be disposed of carefully at recycling
  centers, not in the trash.
• If broken, specific steps need to be followed to
  be safe, but you do not need to call a hazmat
  crew.

14
Is the government taking away your incandescent
light bulbs?

• Provision in the Energy Independence and Security
  Act of 2007 signed in to law by president
  George Bush
• Set energy efficiency standards for light bulbs
  that many incandescent light bulbs to not meet
  it does not ban current generation of light
  bulbs, simply sets energy efficiency standards
  for light bulbs sold and used in the US which
  will phase out use of the current generation of
  incandescent light bulbs.
• Incandescent light bulbs currently exist that are
  affordable (2.99 for a two pack) and meet the
  new energy standards-so you dont have to buy the
  CFLB.