Science to Live By: Watt’s Cooking?


Energy Part Two: Watt’s Cooking?

© J. Dirk Nies, Ph.D.

The Washington Post editorial board wrote a column titled A Presidential Race Low on Energy following the Republican and Democratic National Conventions. The Board began their September 9 editorial as follows:

“In the past two weeks, both President Obama and Republican challenger Mitt Romney claimed to possess farsighted plans for powering America’s economy. At their parties’ nominating conventions, the candidates and their surrogates described a future in which the country is more energy-independent, nearly everyone in the energy business succeeds and the energy-dependent economy hums along.

In fact, the visions articulated of late are far from farsighted. Neither adequately described the real and massive energy and environmental challenge America faces, let alone offered a credible strategy to face it.”

These Science To Live By monthly essays address “real and massive challenges.” As we proceed together, I wish to encourage each of us to formulate strategies for powering our local economy. We may not be in a position to influence or implement energy policy at the national level, but we do have the opportunity and responsibility to put into practice innovation solutions right here at home.

This month we will learn about an eighteenth-century Scotsman who played a foundational role in the shaping how we describe and use power today.

James Watt was born in 1736 near Glasgow, Scotland, in a seaport town on the Firth of Clyde. As a young boy, he demonstrated a natural mechanical aptitude tinkering in his father’s shipwright workshop. Around 1760, he obtained work as an instrument-maker at the University of Glasgow, preparing apparatus for lecture demonstrations. In that capacity he was charged with bringing into working order a model of the Newcomen ‘fire-engine,’ the state-of-the-art commercial steam engine of its day. While trying to get the model engine to run properly, he discovered fundamental flaws in its design. The engine’s cylinder needed to be kept hot to conserve the amount of coal burned in the boiler, while at the same time, to maximize power, the cylinder had to be cooled down after each and every power stroke. In 1765, while walking across Glasgow Green on a Sunday afternoon, Watt had an inspiration. He realized by diverting the steam from the working cylinder into a separate condenser that was kept permanently cold, he could solve this dilemma.

Watt put his inspiration into practice and in 1769 patented the world’s first steam engine with a condenser. After many trials and innovations, his condensing steam engine achieved enormous savings in fuel while operating much faster because the time and energy wasted heating up and cooling down the cylinder after each stroke were eliminated. In 1775, he formed a partnership with Matthew Boulton, a toy maker, silversmith, industrialist and venture capitalist. It was Boulton who understood that this source of steady, reliable power was of huge economic significance. “I am selling what the whole world wants: POWER,” he wrote to Catherine the Great, Empress of Russia.

To help market their product, Watt developed a way of rating the capabilities of his steam engine against a common source of industrial power of the day, the draft horse. For example, by walking round and round in a circle, a horse in a harness could be used to turn a mill that ground corn. Watt observed that a mill horse completed 144 trips around the circle in an hour. The radius of the circle trod by the horse was 12 feet, and from this, he calculated that the horse travelled at a speed of 181 feet per minute. Watt also determined that the horse could pull with a force of 180 pounds at this steady pace. By multiplying the speed of the horse by the force with which it pulled, he arrived at 32,580 foot-pounds per minute (181 feet per minute x 180 pounds of force). This value he defined as the rate (per minute) at which a horse could do work (foot-pounds), the power of one horse. In 1783, Watt and Boulton standardized one horsepower (hp) at 33,000 foot-pounds per minute, the figure we use today.

With the development of this new power rating system, Watt was confident that his steam engine offered a competitive advantage in many applications. This confidence was reflected in the Boulton & Watt sales agreement. Installation and servicing of the steam engines was done for free! In return, the agreement stipulated that owners pay royalties (for the next 25 years) equal to one-third of realized fuel savings. For example, if the steam engine was used in place of horses, then Boulton & Watt received an annual royalty based upon the difference between the higher cost of the hay formerly used and the lower cost of coal now used. This is how the company made its profit.

Watt retired at the age of 80. During his career, the partnership installed hundreds of Boulton & Watt steam engines. The first engines were sold to mining companies to pump water (more water than coal was removed from a typical English mine). By the mid-1780s, Watt had designed a double-acting piston that provided direct rotating power. With these innovations, the market greatly expanded and their engines were sold to power factories, mills and the first prototypes of the steam locomotive.

Watt has been described as one of the 100 most influential figures in human history. In honor of his contributions to science, engineering and the economy, the world’s scientific societies have defined the ‘watt’ as a fundamental unit of power (745.7 watts = 1 hp; 1,055 watts = 1 Btu per second).

To help grasp the meaning of these units in human terms and everyday life, I will apply these power concepts to the running of our own homes.

In the United States, annual household energy consumption (electric, natural gas, heating fuel, etc.) was 10.2 quadrillion Btu in 2009 according to the Energy Information Administration (EIA). Recalling from last month that total annual energy consumption is 98 quadrillion Btu in 2010, American households consume about 10 percent of our economy’s energy.

Given that there are about 114 million housing units in the US, household energy usage works out to be 89.6 million Btu per residence according to the EIA’s Residential Energy Consumption Survey. Dividing this value by the number of seconds in a year, we find that each apartment, townhouse, and home, when averaged all together, consumes energy at a rate of 2.84 Btu per second. This energy consumption rate is equivalent to 3,000 watts per residence (2.84 Btu per second x 1,055 watts per Btu per second = 2,996.2 watts).

A laborer can work at about 10 percent the rate of a draft horse. One-tenth horsepower is the same as 75 watts, and with this in mind, we can now proceed to put our household energy consumption rate into a human context.

In each American household, on average, we use the labor equivalent of 40 workers to heat, cool, clean and illuminate our homes, to heat and pump water, to cook food, and to run electronic devices and equipment (3,000 watts per household divided by 75 watts per worker).

This may seem hard to believe. Do we actually require 40 workers to keep our residences running? An explanation becomes apparent when we realize that appliances are more powerful, in human terms, than we might at first think.

Based upon nameplate wattages (the maximum power drawn by appliances) listed on the Estimating Appliance and Home Electronic Use webpage, here a few examples of the strength of electronic appliances, when run at full power, compared with a 75-watt worker: personal computer and monitor (3-4 workers); microwave oven (10-15 workers); coffee maker (12-16 workers); toaster oven (16 workers); hair dryer (16-25 workers); clothes dryer (24-67 workers); water heater (60-73 workers).

Next month, I will elaborate upon our energy expenditures in the food and household sectors of our economy.  General principles and rules of thumb will emerge regarding how we can achieve substantial energy savings in both.