cost effective, are they nuts? did they look at their own numbers quoted in the article. they say themselves that it costs about 2 cents per gallon. they also said that 10 billion gallons of water fall on NYC roofs in 1 year. okay, let's do the math here. 10 billion times 0.02 dollars = 200 million dollars PER YEAR! we could do a lot better than that to stop runoff. even if we only use their 30% number that Con Ed's building captured, then 30% of 10 billion gallons at a rate of $0.02 per gallon for maintenance, is still 66 Million Dollars!
Um no!
Now, mind you, white roofs, which would also cool the city in the summer, would make sense. still, then, i ask this, is it better to be cooler in the summer saving power then, and cooler in the winter meaning extra heating costs. My though is yes. There are many more hours of sun in the summer than in the winter, so the amount of solar heating you'd get, by heating your roof and the surrounding area thereby making your A/C work that much harder, should be much less than what you'd spend on any potential heating obtained in the winter with the fewer hours of sun anyway. Especially since the lower angle of the sun in the winter should allow more light/heat to come in through the windows.
so, i say, white roofs, yes, green roof, only if you happen to like it.
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