Tuesday, August 22, 2006

Avoided cost of cooling with CFLs

I decided to investigate how much the extra heat of incandescent light bulbs over CFLs might cost a customer in a/c cooling costs.

I ran across a slightly dated (1993) EIA report on home heating and cooling costs. In particular Table C2 in Appendix C of the report (okay, I have too much time on my hands) provided a key data point...1 million BTU of cooling costs $10. Assuming a SEER of 8.3 and 8.3 cents/kWh electricity costs. Also 1 watt = 3.414 Btus/hr. I further assume that air conditioning is needed 6 months a year (4380 hours).

A 100W incandescent bulb will produce 250 btus/hr more heat than a 100W equivalent CFL (~25W). If the incandescent bulb is run 24/7 for the 6 months that a/c is used, this adds up to over 1 million Btu of extra heat (compared to the CFL) or an extra $10/yr in cooling costs.

If you only run the light 6 hours a day, this still adds up to $2.50/yr difference in cooling costs, which is about the price of a 25W CFL at Home Depot. And that is just one bulb!

This avoided cost of cooling for a CFL is significant. I'm surprised that this figure is not more widely reported.


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