QUESTION about eco-friendlier A/C options-- pls help if you've researched

[snot]

We need to replace a commercial, 3 ton, 3 phase, package a/c unit. We've gotten quotes from several companies, and if we go with an energy-saving unit, it'll cost $1,500 more even with the tax credit. My partner says that per online research, the electric bill savings wouldn't be that great -- that we'd have to keep the same unit for 20 years in order to get back the extra $1,500 for the eco-friendly unit -- when the life expectancy of the unit is probably only about 10 years. He says the only way we'd be better off with the eco-friendly unit is if the cost for electricity increases dramatically during the next ten years. I'm guessing that could happen, but who knows.

I'd be interested in advice from anyone who knows more about this stuff than we do.