Ways to Save Energy
It should by now be common knowledge that finding ways to use less energy are key to a sustainable energy future. Though many became more frugal in their use of energy when its price escalated in the 1970s, the more recent era of cheap energy has led to a resurgence of energy extravagance in many individual lifestyles. At the same time, energy conservation measures that were institutionalized in the 1970s remain with us, and the search for new such conservation measures continues -- especially when they lead to quick financial payback.
Such a measure was presented by Lynn Stiles of the Richard Stockton College of New Jersey to the joint meeting of the New Jersey and Southeastern Pennsylvania Sections of the American Association of Physics Teachers at Princeton University on 13 March 1999. Titled "Geothermal Energy: How You Can Save Money and Protect the Environment," Stiles' presentation told how Stockton was extracting energy from the earth with heat pumps in the winter and replenishing it with heat from air conditioning systems in summer. The heat pump system at Stockton cost $5,194,970 as opposed to a conventional heating system for $3,567,493; but the annual cost to run the heat pump of $627,089 is less than the $753,136 annual cost for the conventional system. (You can give your students these data to ask them to calculate the payback time.) Translated to heating and cooling a single home, Stiles' figures showed that the cost of heat pump heating and cooling was less than that of gas heating alone. The energy used by the heat pump eventually produces a net output of heat (though much less than a conventional system, which vents heat to the environment during all seasons). If the net heat output from the heat pump system were sent into the ground, the annual temperature increase of their "well field" would be 1.2oC, which cannot be ignored over the long run, because of temperature sensitivity of soil microbiota. The surplus heat is vented to the atmosphere via cooling towers, though the smaller amount generated by an individual house would not require this.
The heat released to the environment by heating and cooling systems causes central cities to be warmer than surrounding areas, and "urban heat islands" are made even hotter by their absorption of sunlight by black roofs and streets, which comprise from 20 to 25% of urban surface area. Melvin Pomeranz of the Lawrence Berkeley National Laboratory addressed this problem at the American Physical Society centennial meeting in Atlanta on 25 March. He noted that black shingles reflect 5% of incident sunlight and that conventional white shingles reflect 29% of incident sunlight but that a special white shingle could be made to reflect 80% of incident sunlight. Many don't like white roofs, Pomeranz acknowledged, but he pointed out that the nearby Georgia Dome has an attractive white roof made of teflon and fiberglass, which is also translucent to admit sunlight (the 30% it doesn't reflect). Net energy savings could be achieved from white roofs as far north as New York City and Chicago, he claimed.
Addressing the reflectivity of pavement, Pomeranz stated that fresh asphalt reflects 5% of incident sunlight (thus attaining a daytime temperature of 123oF), while this increases to 10% as the asphalt ages (leading to a daytime temperature of only 115oF). He has developed a prototype asphalt coating to reflect 50% of incident sunlight (corresponding to a daytime temperature of 88oF). Pavement is actually only 15% asphalt and 85% rock, he said, so the color can be further lightened by using white rock. Still to be determined is whether materials dark in the visible could be made to reflect infrared solar radiation (which comprises half the solar spectrum).
Home Spring 99 Full Screen
The TEACHERS CLEARINGHOUSE FOR SCIENCE AND SOCIETY EDUCATION