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Sometimes Wrong but rarely in doubt!

12 March 2012

LED Lighting Analysed - No Green Washing

In the jurisdiction that I work in the current version of the building code has requirements for energy efficiency built-in.  The code bascially allows you to follow a prescriptive path, comply with ASHRAE 90.1-2007 or do an energy model analysis of the building and demonstrate that it beats the MNECB by 25%.  All greek?  Translated it means do it this way, use this alternate method to demonstrate compliance or simulate the building.

The first two methods mean that essentially there is an energy budget for the building and you have to stay within it.  These are the two methods I primarily apply.  The problem is that this budget is pretty austere for small rooms.  Big office buildings can be done with conventional fluorescent fixtures but in a building chopped up into small rooms you get pushed towards LED fixtures. 

On a recent project I had to demonstrate the payoff for LED fixtures.  The results are interesting.  A conventional fluorescent Troffer and a comparable LED fixture are used in the following analysis:

Troffer = $70
LED 'Troffer' = 295$

Additional cost of LED Troffer $225

At it's most expensive electricity costs 11cents per kWH locally.  The difference in consumption between the LED and fluorescent fixture is about 25W.  Assuming the building is operated 12 hours per day over a year the LED fixture saves 109.5 kWH, or about $12.  The LED fixture will pay itself off after 22 years.  But there's more, LED's last 50,000 hours, you'll have to replace the LED board in 11.5 years and as things stand now that really means replacing the fixture.

Despite the numbers I do like LED's for illumination, I just think that the technology is not quite there yet and it will be more advantageous to use them for street-lighting and other areas where the duty cycle is low.  By cycling the lighting to conform to the duty cycle ie turn the lights off or to a low level when no car or pedestrian is present LED's can realize a cost savings that may offset their high capital cost.  Keep in mind thought that in outdoor fixtures the cost difference is even higher (~$100 vs $900).    When I have some info on the difference in energy consumption I will update this analysis.

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