Comparing LED with Metal Halide Light Fixtures

Comparing LED with Metal Halide Light Fixtures

The city of Raleigh, NC, was building a new downtown convention center as part of a downtown revitalization plan. The city had an objective to implement many elements of sustainability in the design and construction of this new complex. The project included a new three-level underground parking deck, which required round-the-clock lighting. The construction of the deck was well underway by the time an evaluation of LED lighting began, and the lighting locations were already set. The initial specifications called for 544 fixtures using 175W metal halide lamps. You will compare the LED alternative with the traditional lighting system by examining the economic impact of each. You will need to use the following data:

·  Capital costs: The LED light fixtures are more expensive than the metal halide fixtures, and the additional initial cost for each of the 544 LED light fixtures is $482. This means that the Halide require no additional initial capital.

·  Energy costs: Each metal halide fixture consumes 218W (175W for the lamp and 43W for the ballast), while each LED fixture consumes 110W (74W for the LED and 36W for the power supply). The city pays a rate of about $.06 per kWh (kilowatt-hour) for electricity. Assume a 3% per year increase in electricity costs in the future.

·  Maintenance costs: The metal halide lamps require replacement on average every 15 months at a cost of $76 per fixture ($60 for labor and $16 for materials), for an annual average maintenance cost of $33,075 for 544 fixtures. Assume a 3% annual increase in maintenance costs in the future. The LED fixtures require no maintenance costs.

·  Replacement costs: After 50,000 hours, or about 6 years, the LED modules are rated to be operating at about 70% of the original light output, and they will need to be replaced. Given that the cost of LED technology has been declining, the replacement costs in year 6 and year 12 are estimated at $160,200 and $131, 750, respectively, including labor.

1. Using the data given above, obtain a 15-year table of values for the annual accumulated cost of the metal halide lighting. Fit a linear model to your data.

2. Using the data given above, obtain a 15-year table of values for the annual accumulated cost of the LED lighting. Fit a linear model to your data. (Note: Your model will need to be piecewise defined. This means that you will derive three different linear equations with specific domains)

3. Graph both sets of data on the same axes, together with sketches of the linear models.

4. Comment on the two cost analysis models. Which alternative is better in the short run? Which one is better in the long run? How long does each solution need to be in place for the relative cost effectiveness to switch from one to the other? What is the total savings after 15 years of using the most economical solution? Explain. (You may want to come up with a third model, which is the difference in costs of the two models.)

5. Suppose you change the cost of electricity to about $.11 per kWh, which is what it is in New Hampshire. How will that change when in time the break-even point occurs?

Reference:

www.raleighnc.gov/content/AdminServSustain/Documents/LEDs/MunicipalGarageLEDReport.pdf

Video link: http://www.youtube.com/watch?v=NHujtcoeHlI