Friday, September 2, 2011

redefine performance

mpg or mph?
Monitoring performance seems to be an important aspect of sustainability. Measuring resource consumption helps promote conservation, both because we use less when we can monitor it, and because good performance data in existing buildings is essential to improving the design of future buildings.

But how do we measure performance?

We wrote last month about embodied energy, the measure of how much energy is expended making and moving the materials from which the building is assembled. Together with the energy used during the operation of the building and that used to demolish the structure, this comprises the energy component of lifecycle costs, the measure of energy used over the course of the building's life. This is important, since it helps us determine whether it is worth using more energy-intensive construction methods (eg. concrete block) in exchange for greater savings during operation or demolition.

A good measure of energy use during the operation of the building is the HERS Index. The HERS Index measures the total energy consumption and production of a building (thus accounting for conservation and generation) against the standard established by the 2004 International Energy Conservation Code. Our LEED consultant's preliminary calculations show tin box reaching a HERS score around 25, which translates into the house using just 25% of the net energy required by a house built to code.

In redefining performance, we need to be flexible - not dogmatic - in the way we measure resource usage. For example, beware of the obsession with reducing the size of a building. In general, smaller structures use less resources. But not always. In hot regions like South Florida, high ceilings help encourage air circulation, leading to lowered air conditioning loads, and thus the extra material invested in construction may be offset by the reduced energy required to make the building feel comfortable in hot weather.

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