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Green Buildings: Conserving the Human Habitat
(Released October 2006)

 
  by Ethan Goffman  
 

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Renewable (and reusable) Energy

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In the fable, the wind only causes the old man to grip his coat more tightly, while the gentle sun seduces him into removing it. In reality, the sun and wind, if used properly, are both forms of renewable energy, although at the scale of individual buildings the sun has proven far more useful. See CSA's Renewable Energy Issues for an overview of key alternative energy sources (http://www.csa.com/discoveryguides/
ern/00jan/overview.php
). Current photovoltaic cell technology makes solar power practical for individual buildings.

Solar panels, usually placed on the roof of a building, convert sunlight to direct current (DC) energy. Only about 1/100th of an inch thick, solar cells are usually "rectangular or circular wafers made of silicon (sand), but some consist of a thin film that is mounted on glass or thin metal."28 An inverter then converts this energy to alternating current (AC). Batteries of such cells are mounted where they have good access to sunlight, generally at a southern exposure. Energy not immediately used may be sold back to the electrical grid, with potential for a negative electric bill. Battery storage is another option for excess solar energy.

diagram of PV array
Stand Alone Photovoltaic System

Although the cost of photovoltaic cells has dropped drastically,29 currently energy from photovoltaic cells still costs "about 25 cents per kilowatt hour . . . double to quadruple what most people pay for electricity from their utilities."30 This high price is largely due to the initial cost of installing the system. However many states offer a variety of incentives, and the federal government also offers financial support for commercial buildings, helping to offset the high start-up price. The wider social costs of pollution from, for instance, coal, are an environmental factor beyond the immediate cost.

house with panels
This San Diego development features water heating collectors on the roof
A more currently cost-effective use of solar power is for heating water. A passive system which stores water where the sun naturally heats it, is effective in warm climates. Active systems, needed in colder climates, "rely on electric pumps, and controllers to circulate water, or other heat-transfer fluids through the collectors" to heat water.31

contemporary wind turbine
A wind turbine on a German building
The use of wind power dates back to well before Don Quixote's epic struggle with the windmills, but today's versions are far more energy efficient. While the large wind farms currently favored often face local opposition, the use of smaller wind turbines on green buildings remains in the exploratory stage. While proponents believe that micro-wind turbines mounted on buildings can compete with solar power,32 in practice vibrations from roof mounted turbines can cause difficulties for occupants and put stress on a building's structure.33

Biomass provides yet another way to save energy through using-and often reusing- "natural replenishable organic matter to produce energy."34 Crop and forest residuals are common examples of biomass, with ethanol being a much discussed version. Regarding buildings, "a plant and process energy study revealed the opportunity to use waste materials from operations such as wood waste and saw dust."35 More such creative reuse of waste is to be expected in the future, "such as hydrolysis of cellulosic biomass to sugars and lignin and thermochemical conversion of biomass to synthesis gas."36

Another intriguing strategy is to reuse energy already present in a building, such as that generated by the human body. ARUP Services Ld. employs "the principle that a building can be designed . . . structurally to generate and recycle enough of its own energy to become self-sustaining[;] the ARUP system absorbs heat from human bodies, computer equipment, plants, and other heat-releasing sources within work-space interiors."37 Other buildings rely on geothermal energy, heat from within the earth.38 Currently, however, solar panels remain the most common renewable energy source for green buildings.

sleek white structure
Ventiform - Experimental Project, 2001 [unbuilt].
Foster and Partners. ©Nigel Young
The Ventiform research project was an attempt to integrate an electricity-generating wind turbine into a mixed-use, high-rise building

A huge factor in reducing energy use, already well integrated into buildings, is energy efficient products. Following the oil crises of the 1970s, the energy star program has spurred tremendous savings in air conditioning, heating, office equipment, refrigeration, dishwashers, lighting, and many other products. Indeed energy star products have become so commonplace that most of us are not even aware of its "green" status, providing hope that today's programs will be as successful.

Despite its increasing benefits, however, locally generated renewable energy has built-in limitations. Depending on surrounding conditions, such energy varies greatly from day to day and season to season. It is therefore most useful as a supplement to conventional energy. In many states, on days that solar or other renewable methods generate more energy than a building uses it may then be returned to the power grid for a net negative balance. Battery storage is another way of handling excess local renewable energy, although current technology is problematic: solid oxide fuel cells (see CSA's http://www.csa.com/discoveryguides/fuecel/overview.php) and hydrogen storage (see CSA's http://www.csa.com/discoveryguides/hydrogen/overview.php) are two methods being developed to store renewable energy.

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