When leaving the restroom, we are often faced with an interesting question. Should we use paper to dry our hands or should we use the electric dryer?
The electric dryer claims to be healthier while at the same time being better on the environment. I made a mental note of some information listed on the typical machine.
The dryer operates at 20 Amps and 115 volts. It runs for about 20 seconds and I use it twice to get my hands entirely dry.
In order to dry my hands with paper I usually use about 3 feet of paper that is about 6 inches wide.
While the electric dryer does not require the cutting down of trees to use, it does produce CO2, a greenhouse gas that is largely responsible for global warming. On the flip side, though, trees absorb CO2 during their life.
Figuring out which truly is better for the environment would take a simple simulator. This is beyond the scope of this paper, however, and we'll just be focusing on the time it takes for the fraction of the tree that you would have used to dry your hands to absorb the CO2 produced by using the electric dryer instead.
To do this, we'll first find the amount of energy required to run the electric dryer.
E = Power * time average power = I(rms) * V(rms) P = 20 * 115 P = 2.3 kW
We run the dryer for 40 seconds total, so energy is .0256 kW hours.
The average coal power plant produces 2lbs of CO2 for every kilowatt hour, and there are 2.2 kilograms in a pound. Therefore, we produce .112 kg of CO2 when we dry our hands with the dryer.
Next we figure out what percent of a tree we are using when we dry our hands with paper. Then we will figure out the amount of oxygen that that part of the tree would have produced in a given time.
Area of paper: 6" * (3' * 12") = 216 squared inches
But how much paper does a tree have? An average lumber tree has around 27,000 8 1/2" by 11" sheets of paper. That's 2524500 squared inches of paper.
Using that, we learn that we use up .00856% of a tree when we dry our hands with paper. A mature tree absorbs one metric ton of CO2 every year, so our fraction of a tree could have absorbed 8.55 kg of CO2 by the end of the year had we not used it for drying our hands.
Therefore, we can figure out that it takes 4.8 days for the fraction of the tree you spared to absorb the CO2 produced by the electric heater.
I'd like to thank the UTA Women's Studies Program for forcing into my hands the scrap paper on which these calculations were performed. I apologize if I never showed up to MAIDENS, MAVENS & MOMS IN THE MEDIA.
(c)2005 Nic Reveles