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
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
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)
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!
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 61°Fahrenheit 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!
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
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?
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!
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.
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. That’s a 17.39 per year per bulb savings.
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 tube’s phosphor coating, emitting visible light.
Limitations of CF bulbs • Take longer to turn on • Do not work with dimmer switches • Contain mercury, a known toxic substance
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.
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 don’t have to buy the CFLB.