Saturday, December 19, 2015

No More Stumpscapes

My typical dog-walking route passes by the site of a rotting tree stump.  It had been one of a long row of street trees--perhaps a red maple--cut years ago.  The stump was not very large or in any other way special.  But a year ago, after passing it many times, I was suddenly struck by the way the patches of moss that grew on it made a kind of miniature landscape.  I knelt and took a few photos.  

That was a year ago.  Since then I have photographed the same square foot of moss, grass, bark, and the odd mushroom at different times of year and in different weather and light.  I came to call these photos "stumpscapes."  I probably worried the occasional neighbor who saw me.  But probably not many, since most already knew I was a little odd.

I am not a photographer, and my camera is a fairly idiot-proof, small point-and-shoot that I carry in my pocket.  I am a little proud of my efforts, though.  I never altered the landscape, other than removing an inconvenient leaf a few times.  I tried to shoot at angles that would not show the surrounding neighborhood and spoil the effect, though the power lines across the street were hard to avoid.  I did not alter the digital files (as near as I can recall) beyond cropping out tell-tale background once or twice.  

The results seem to me to be mostly to be mountain landscapes and lush alpine meadows.  Some are chilly and severe.  A few scenes with mushrooms look like something from a 50s science fiction movie.  

On today's walk I felt a little disoriented: a patch of fresh earth marked the place the stump had been.  Of course, it was a city tree, and it would have been unreasonable to assume it would simply be allowed to quietly rot away indefinitely.  Probably a nearby property owner complained of the appearance.   I'm a bit sad, but also glad I took the photos when I had the chance.

Saturday, December 12, 2015

I saved 3 kilowatt-hours of electricity and kept 6 pounds of CO2 out of the air today! (And much more by staying off the road!)

How much energy did I save today by line-drying, I wondered, 

as I hauled a full basket of boy-clothes (including three heavy sweat jackets and a pair of jeans) indoors after dark.  This particular basket weighed* 27lb out of the washer, 23lb after it came off the line, and (because it was still damp with no prospect of improvement in the near future) 20lb coming warm from the dryer. 

Because the dryer is electric, this is easier to figure out than you might imagine.  Key fact: evaporating water takes about 2265 kJ/kg.  (A kiloJoule is about a quarter of a Calorie--a more familiar measure of energy--while a kilogram of water weighs 2.2lb and works out to one liter.)  In other words, the two kilograms of water that evaporated from the clothes while on the line absorbed about 4500 kiloJoules or roughly a thousand Calories of energy in the form of (free!) sunlight. 

I also benefited from my time outside on a sunny, breezy day.

Now for the easiest part: we can directly convert the energy needed to evaporate that water into energy units familiar on our electric bill.  (Stay with me here.)  The familiar Watt of energy is actually a metric unit of power equal to 1J/s (one Joule per second).  And the nearly-as-familiar kilowatt-hour we see on our electric bills is 1000 Watts (1kJ/s) of power expended for one hour's time; in other words, 1 kW-hr equals 3600kJ.  The 4500kJ needed to evaporate the 5lb of water in my son's clothes needed 1.25kW-Hours of electricity just for the evaporation.  If done in the dryer, more electricity would have gone to the motor that keeps the clothes tumbling, and a bit more to see to it that the moist air coming out of the vent was warmer than the dry air that went in. 

That was just the one load.  Before that, I had line-dried a big load of towels and other heavy, absorbent cotton things, and also a smallish load of whites.  I'm guessing the sun evaporated about 5kg of water in all, saving 11,000kJ of energy, equal to at least 3 kilowatt-hours. 

That might not seem like much in monetary terms, but consider that the electric clothes dryer is typically the biggest energy hog in the home, and alone accounts for over one-quarter of the electric bill.  Consider also that--in most areas of the US--generating that energy produces planet-warming carbon dioxide.  Just how much?  Well, that turns out to depend on what fossil fuel is being burned.  Coal runs a little over 2lb of CO2 per kW-hr, while natural gas produces only 1.2lb.  That compares to about 18lb of CO2 produced for every gallon of gasoline your car uses. 

An eye-opening comparison.

My Ford Focus goes about 30 miles on a gallon of gas, which produces about 18lb of carbon dioxide.  So the amount of carbon dioxide I save by a month's worth of line-drying is cancelled out by one day's 30-mile-round-trip commute to work.  (That result surprised me: cars are an even bigger problem than I thought!)**

If you have a gas dryer, by the way, the numbers are much better.  Only a half-pound or so of CO2 is given off by enough natural gas to produce 1 kilowatt of heat--making it four times more efficient.  This is partly because natural gas is a better fossil fuel than coal, but more because a lot of energy is saved by burning the gas directly, and not generating electricity as an intermediate step.  

*And no, if I had any friends I suppose I wouldn't be doing geeky things like weighing my wash and calculating energy use!

**If you own a big car, the best and easiest gift you can give the environment is to switch to a smaller one!  (That makes an even bigger difference than going from a small car to a Prius!)

Monday, December 7, 2015

The Science and Art of Line-drying

For most people, energy is a lot like art--they aren't sure what it is, but they know it when they see it.  People see it in sunlight, in a rock balanced on the edge of a cliff, in a runaway dump truck, in electrons coursing through wires.  But what is it?  Big Picture, that is.

One formal definition is that energy is the ability to do work.  That works okay until you wonder what "work" is.  Answer: work is done when energy is expended.  Kinda circular!  Just to show how mysterious the whole business really is, I quote a physics prof I knew a few years ago: "When you remove all matter from the universe, energy is what's left over."

My own favorite definition, gleaned from a beginning physics text (high school level): Energy is anything that can cause change.

Energy is my all-time favorite Unifying Theme, and a very useful one, too.

For example, as a new but rabid fan of line-drying the wash, I am keenly aware of how much energy is needed to dry a load of clothing (a LOT), how much I depend on the sun to get 'er done, and how much energy=money=greenhouse gas I am saving by doing it.  

Here's a quick look into the physics of drying clothing. 

We will count our energy in calories, since it is a familiar unit to many people, and particularly well-suited to this topic.  A calorie is defined as the amount of energy needed to raise the temperature of one gram of water (almost a thimble-full) by one Celsius degree.  (The "big C" Calories familiar on food labels are actually ten times this large, and technically called kilocalories.  One kilocalorie could raise the temperature of a kilogram (liter bottle) of water by one Celsius degree.) 

Here's the rub in drying clothes, and the reason it's so expensive to run our electric clothes dryer: although it only takes one kilocalorie to warm a liter of water a degree, it takes 540 kilocalories to evaporate that same amount of water!  In households that have them, the electric dryer alone typically accounts for more than a quarter of the electric bill!

A last few damp garments huddle in the little sun still available.

Needing to dry our clothes, what can we do to conserve our electricity?

First, avoid heavy materials that hold a lot of water.  Jeans, heavy cotton sweatshirts and the like.  The lighter the material, the less water you'll need to evaporate.

Second, use a washer that has a very high spin speed: the faster the spin, the less water will be left behind in clothing, needing to be dealt with.

Third, dry your wash on a clothesline in the sun.  Solar energy is free, and very effective at this job.  Darker clothing is best, since it absorbs more light.  Your clothes line must be in full sun for as long as possible at this season, and of course it will be time-consuming and require forethought to get your wash out at the right time and in the right weather. 

Dry air alone will do the job in absence of sunlight, but the process will be veeerry slow--especially at this time of year.  It is well worth it to take special care to get your clothes out at the right time and in the best place. 

Dark pair of PJs in direct sun on a December day: the PJs are warmed by the sun,
increasing evaporation.  The water vapor coming off the top makes its presence known
as fog condensing in the cooler air.

What does the sun actually do, here?  Wherever there is liquid water, it is always evaporating and condensing at the same time.  It evaporates much faster in the higher temperatures your clothes reach in full sun (especially if they're dark colored).  So with warmer clothes in fairly dry air, evaporation will rapidly win the race over condensation, and you will be able to haul in even your thick (and dark) towels bone-dry in only an hour or two. 

What to do when the weather is uncooperative?  Line drying is difficult in damp or overcast weather,and impossible in the rain.  But you can still hang your clothes indoors over a drying rack.  This is slower that line drying in the sun (leave the rack up overnight).  It is also not free: the water evaporating out of your clothes is still absorbing heat (that same 540 Calories per liter), but it is absorbing it from your warm house, which will fire up the heating system to compensate.  This is still better than using the dryer, though--at least at my house.  We have an oil furnace, which is a cheaper way to generate heat than electricity.