Housewatch: The biggest bang for your energy buck
Austin architect Peter Pfeiffer had a problem. His clients were captivated by the idea of tapping Mother Nature's sun and wind to generate their own electricity. It's a romantic notion but one that is quickly dashed by practicalities. Solar photovoltaic arrays and wind turbines are still hugely expensive and rarely cost-effective.
Wanting to retain his clients' enthusiasm for energy-saving measures and help them spend their dollars wisely, Pfeiffer devised an "Energy Use Pyramid" with Dallas architect Betsy del Monte.
You'll quickly grasp its message because it's based on another pyramid that you know well -- the U.S. Department of Agriculture's "Food Guide Pyramid." In that diagram, the broad base highlights the food group you should eat most often, and its top spot is reserved for the foods you should eat sparingly. In Pfeiffer's pyramid, the base represents the energy-saving strategies that give the biggest bang for the buck, while the top spot is reserved for the pricey renewable ones that exceed most budgets.
A careful look at the icons at the base of Pfeiffer's pyramid shows that none of these energy-saving measures draws any power; all of them concern the building envelope, and some are the same strategies that your great-grandparents' generation used. Orienting the house on the building site to make it more comfortable throughout the year and using shade trees and roof overhangs to reduce summer heat gain were commonly done in 1909.
Some things have changed, however. In great-grandpa's day, a person built the largest house he could afford -- and it was invariably small. Today Pfeiffer and many others encourage small houses because they use less energy. The emphasis on a tight building envelope that is well insulated with no air leaks has gained currency as energy costs have soared and once-obscure building-science principles have become mainstream ideas.
The midsection of Pfeiffer's pyramid zeros in on the items that do draw power -- all the equipment that will be used in the finished house. He encourages his clients to get the most energy-efficient models on the market. They cost more to purchase but less to operate. They're also far more durable and, over time, will save money.
Pfeiffer's top spot goes to the power you can generate yourself by capturing the energy of the sun or wind. When clients learn how much these renewable-energy systems cost, they immediately understand why renewables occupy such a small portion of the pyramid, he said.
(To power an extremely energy-efficient two-story, 2,500-square-foot house, you would need a 5-kilowatt system. The installed cost for a 5-kilowatt solar array would be about $35,000 to $45,000. For a 5-kilowatt wind turbine, the installed cost would be about $30,000 to $60,000, depending on whether it is a horizontal type mounted on a tower (for this you need at least a one-acre lot) or a vertical-axis type mounted directly on a roof, assuming that your site has sufficient wind.
If you think about the message Pfeiffer has embedded in his pyramid diagram, you'll realize that the most cost-effective strategies come into play at the beginning of a new-home project, and this may cause you to rethink the whole process.
For example, a sensible building orientation means more than capturing the best views. As any building scientist, including Pfeiffer, will tell you, it also allows you to tap the free energy of the sun to heat your house in the winter and exclude it in the summer. It's about trying to limit your western exposure and that hot afternoon sun in July and August while maximizing your southern exposure on those frigid days in January and February.
As you begin to sort this out, you'll find that the shape of the house and the location of those huge expanses of glass that most homeowners want will begin to have some constraints. You can't just design a box and stick an air conditioner and a furnace in it.
The shade trees are not just an aesthetic plus that will help with resale; they are a practical asset that will help lower your utility bills. When shade trees are combined with generously sized roof overhangs that shade the walls below, you'll notice a difference during the hot season. When you add correctly sized windows and insect screening, you'll save even more energy, Pfeiffer said. He used these strategies to shade his own Austin house, and they save more energy in a year than the 2.5-kilowatt solar panel array on his roof can generate.