Friday, August 26, 2011

Big-City Green

by Richard Crews
Greenifying ones domain is commonly thought of as the purlieu of well-healed suburbanites, but there are plenty of things that big cities and big-building owners can do too. The list at the bottom of this essay comes (modified) from Scientific American, August 25, 2011.

However, there are two remarkable possibilities that are not mentioned in the SciAm article: wind-generated electricity and rain catchment.

Imagine, if you will, a large city with a forest of windmills soaring above the parks and gardens of its high rooftops. The windmills would be silent, turning slowly; they would not interfere with bird migrations or helicopter surveillance or transportation. The electricity they generated would be used by the building that hosted them with the excess fed into the municipal power grid.

Windmills have significant advantages over solar panels: they are far less ecologically costly to produce and--in stark contrast to the few-years life expectancy of solar panels--they laugh at the passage of decades. A newly installed windmill can confidently be expected--with little or no maintenance--to be functioning efficiently 25 to 50 years later.

In addition, the rain that falls on the vast roof-top acreage of a big city is now channeled through run-off gutters and conduits into sewers for waste-water processing. It has two valuable attributes that are thus lost. First, rainwater (in contrast to ground water or well water) has no mineral contamination--no arsenic, lead, copper, manganese, sulfur, etc. Purifying it, even to the level of drinking and cooking purity, is cheap and simple--it involves course filtration (to remove leaves and debris) and minimal anti-bacterial and anti-viral oxidation (for example with ozone or ultra-violet light). Such purification can readily be done in small, roof-top appliances.

Second, when water lands on a roof, it has positional energy; in other words, it is high up. Most simply stated, it does not need to be pumped around for processing or delivery--properly channeled, it runs downhill to wherever it is wanted or needed. This can provide a significant energy savings.


There are other ideas around for greenifying big cities and big buildings. The following list, reorganized and summarized, is from the Scientific American article.

Green and White Roofs

Rooftop vegetation insulates buildings against heat and cold and absorbs storm water that might otherwise pollute waterways. Many cities are pursuing these roofs, and friendly competitions for the most square feet of green roofing have arisen among Chicago; New York; Washington, D.C.; and others. Enclosed rooftop farms above restaurants, schools, hospitals, or other institutions that serve many meals might be a coming urban trend.

Designs exist for entire high-rise, indoor, vertical farms. Growing food indoors can reduce fertilizer and freshwater use, shorten transportation routes for delivery, and recycle gray water otherwise dumped for processing by city water-treatment plants.

Rooftops painted white reflect heat, lowering a building's cooling cost and a city's heat buildup. U.S. Secretary of Energy Steven Chu emphasized this technique in a speech he gave in 2009. He extolled white roofs as an inexpensive move that can be done quickly and provide immediate payoff.

Urban Solar Electricity and Hot Water

Extensive solar panels can generate electricity in lieu of power plants doing so, and also shade rooftops to lower a building's cooling needs. Together, the cities of Ontario and Redlands in California, working with the Southern California Edison utility, have erected seven "neighborhood power stations" on large industrial rooftops, totaling 306,500 square meters (more than 75 acres).

Photovoltaic sheets on south-facing building facades can generate significant electricity. One notable demonstration of this is in Berlin. Thin films typically are less efficient than solar panels, but they can be cheaper to make (per unit area) and are flexible, leading to novel architectural designs.

Water-filled tubes connected to tanks on roofs can be heated by the sun to provide domestic hot water instead of using gas or electric furnaces. All new buildings in the fast-growing city of Rizhao, China have rooftop systems that provide hot water for bathing. The systems cost around $200. In the U.S., hot water accounts for 17 percent of energy used by homes.

High-Rise Construction and Reconstruction

Super-insulated windows quadruple the thermal performance of double panes and can be made from the glass in existing windows. Serious Energy reused the glass in all 6,514 windows in the Empire State Building, New York City to make super-insulated windows that are four times more energy efficient. The retrofit took seven months and will be paid for in energy-cost savings in less than ten years.

Construction material made locally with carbon dioxide that is pumped out by city power plants could reduce greenhouse gas emissions. Calera Corp. is bubbling the gas from a power plant in Moss Landing, California through nearby seawater to make cement. The process also eliminates the roughly one ton of emissions that would normally be created in making a ton of cement the conventional way.

Urban Transportation

Commuter trains, subways, and even many primary roads in Portland, Oregon are located underground in massive tunnels, freeing the surface for easy, clean bike and pedestrian traffic. Many cities have miles of subterranean transportation but Portland is diverting such traffic as part of an integrated overall plan to encourage more walking and biking, and to provide for the redesign of public spaces.

Large portions of taxi fleets converted to hybrid vehicles reduce air pollution and greenhouse gas emissions in San Francisco and New York City. After New York City Mayor Michael Bloomberg had encouraged fleets to purchase hybrids (and many did), his administration tried to penalize owners who didn't switch, but courts struck down the policy. Nevertheless, about one third (4,300) of the city's yellow cabs are now hybrids.

Charging drivers higher rates to drive in congested neighborhoods (so called "congestion pricing") eases traffic. By the end of a six-month trial in Stockholm, traffic had dropped by 25 percent, emissions had decreased 14 percent, and 40,000 more people daily were taking public transit; moreover, buses were reaching their stops more quickly. The Stockholm Congestion Charging System is now permanently in place. Singapore has initiated similar efforts.

Subterranean garages near commuter destinations eliminate the need for cars to surface. Many cities have had enough foresight to build at least some underground parking but Paris stands out. Drivers are encouraged to use the lots with fees that are typically lower than for above-ground spots, and the lower levels are monitored by security cameras, so they are considered safer than city streets.

Ample bike lanes and bike racks encourage more people to ride instead of drive; they also promote health. These straightforward steps can make a huge difference. Despite its long, cold winters, Minneapolis has been ranked as the best cycling city in the country by Bicycling magazine, largely because such measures have encouraged many riders, even when the mercury dips low.

Wave and Tide Power

In Orkney, Scotland hinged cylinders anchored in the seafloor are pushed by waves, turning onshore turbines that create electricity. In New York City licensure is pending for installation of 30 turbines on the bottom of the East River along Manhattan. These could generate one megawatt of power (enough to satisfy the power needs of 200 to 250 homes).

Three-Bin Recycling

Requiring businesses and homes to separate refuse spares landfills. San Franciscans use three garbage bins: recyclables (papers, bottles, cans, and plastics), compost (food scraps, soiled paper), and trash (the rest). The city charges residents for collection based on the volume in the trash bin, not the others, which encourages compliance.

Satellite Irrigation

Satellite control of park and lawn irrigation systems cuts water consumption and pumping power. Municipalities such as Los Angeles subscribe to a service provided by companies (such as HydroPoint Data Systems) which forecast weather and soil moisture for each area and turn portions of the irrigation systems on or off accordingly, greatly reducing wasted watering and lowering water bills.

Low-Flow Appliances

In San Francisco; New York City; and Austin, Texas, water-saving toilets and showerheads installed in new and existing buildings save millions of gallons annually. Austin began a retrofit program years ago that has left most of the city with low-flow devices, reducing water usage by 19 million liters (5 million gallons) a day and wastewater flows by 680,000 liters (180,000 gallons) daily.