Tuesday, September 25, 2007

Wedge Strategy: Building Efficiency - Methods+Factors

Passive solar heating is the process in which the sun’s rays are absorbed (or reflected) to equalize the temperature of the target building to a greater comfortable equilibrium.
  • In Direct Solar Gain, this is done through strategic placement of windows, skylights, and other light-allowing apertures.
  • In Indirect Solar Gain, heat is captured by a thermal mass and then transmitted indirectly throughout the building via conduction and convection.
  • Isolated Solar Gain is a system in which a liquid or air is used to transfer heat in and out of the building.
  • In Active Solar Systems, panels attached to a building either gather heat (via fluids running through the panels) or generate electricity (via photo-voltaic cells).
  • Passive Solar capabilities allow buildings to improve thermal efficiency, and thus they require fewer resources to heat and cool. Active solar systems allow buildings to supplement their supply of electricity, and thus cause less strain on the grid during peak hours.
Heat Exchanger
A heat exchanger recovers heat by transferring heat from outgoing air into incoming air. Hot water heat transfer does the same thing for outgoing water (standard units recovering 60% of heat energy during a hot shower).

The insulation (of both walls and glazing) and thermal mass of a building play a crucial role in mitigating energy spent on heating and air conditioning.

Building Automation
Building automation provides a system, often times computer controlled, to regulate the use of energies based on need, and to harness available interior and exterior conditions to the maximum efficiency. Examples include louvers that regulate sunlight coming in, lights that turn off when their room is unoccupied, an air movement system that sucks in cold air during the night to keep the building cooler during the day, etc.

Building Placement
One of the most central factors to the energy efficiency of a building is the location that it is built in, specifically the density. Urban structures are far more efficient than suburban or rural structures. This is due to the economies of scale, as well as more people relying on the same amount of infrastructure, and also the vastly decreased volume to surface area ratio of larger urban structures. The per capita electricity usage in Dallas is four times as great as the same in New York City. Additionally, that does not account for the transportation efficiencies that urban living holds over suburban and rural transportation models.

The effects of these systems vary drastically project to project. In some cases, buildings with energy saving features are more efficient by factors of ten. Sometimes these “green” buildings are not able to compensate for the luxuries taken with their construction (high area per occupant, vast interior lobbies, etc.). System effectivity varies by climate, funtion, natural resources in the area, maintenance, and many other factors. Generally, most commercially designed green buildings see efficiencies cutting down 20% to 60%, with the middle ground being 40%.

Buildings use 75% of the energy created in the United States. The country places 6,049,435,000 tons of Carbon into the atmosphere every year. Attributing 4.5 billion tons to buildings would mean that in order to reduce emissions by one of our 1 billion ton wedges, a full half of the buildings in the United States, including all new construction, would have to be retrofitted with energy saving features (having more of these features be placed in suburban and rural buildings would be even more effective, since buildings in these areas already use more energy). Making this a requirement for renovated buildings would mean that this goal could feasibly be achieved in 25 -35 years, provided there are proper government incentives and codes.

No comments: