Life-Cycle Analysis

Embedded Energy (trim)

The design of the IL Centre focused on producing a building that would not only expose students to sustainable design, but would exhibit as many construction methods as possible. To do both, the building was split in two: the small administration wing, and the large teaching wing. Each side was built using a different construction method, but the most environmentally sustainable system was to be used in the largest portion.

To determine which should go where, both construction methods were evaluated for their environmental sustainability:

  1. Cast-in-place concrete;
  2. Structural steel with a composite deck.

To determine the more environmentally friendly choice, Halsall Associates Ltd. employed a life-cycle analysis tool called Athenaâ„¢, developed by the Athena Materials Institute. The program summarizes environmental impacts by calculating six different measures: weighted resource use, global warming potential, air toxicity, water toxicity, solid waste emission, and embodied energy inputs.

Embodied energy means the amount of energy used to extract, process, transport, install, maintain, and dispose of a product. Embodied energy values can be separated into initial and recurring components. Material extraction and installation belong to the “initial” category; buildings require few changes over their lifetime, so the recurring component is generally small.

Resource use measures all the natural resources it took to get or create the building materials. This means the materials in the end product as well as everything required to install and manufacture the product, like formwork and falsework for cast-in-place concrete. Since the environmental impacts of extracting raw materials are not the same, an ecologically weighted system was used to compare construction products. The total is expressed as an ecologically weighted mass of raw material consumption. Concrete scores higher in this index, but the IL Centre has taken additional steps to reduce this figure.

Global warming is expressed as an equivalent mass of carbon dioxide released into the atmosphere as the result of the manufacture, transportation, installation, and operation of a building component. Gases other than CO2, such as nitrous oxide, methane, or chloroflorocarbons trap heat within the Earth’s atmosphere in much the same way, so their impact is listed as an equivalent mass of CO2. The life cycle analysis included the release of greenhouse gases from both the combustion of energy and from manufacturing processes. Concrete is much better than steel deck, mostly because of the environmental costs of smelting.

Solid waste emissions represent the total mass of emissions deposited into landfills as a result of using various building materials. (The analyses don’t distinguish between hazardous and non-hazardous wastes, as neither steel nor cast-in-place concrete have any appreciable amount of hazardous solid waste). Concrete scores higher on this index, so the IL Centre has taken additional steps to reduce this further.

Air and water toxicity quantifies the health effects from substances emitting toxins throughout the life cycle of building materials. Steel decking came out far higher than concrete on this measure. The indices are based on the volume required to dilute the single most contaminating by-product down to acceptable levels. Only one by-product is used in the index because it is believed that, in most cases, the same volume of air or water can simultaneously dilute several pollutants.

These results and definitions were summarized from Halsall Engineering’s life-cycle report on the IL Centre. The results of the analysis were a surprise for a building the size of the IL Centre. They clearly showed that cast-in-place concrete was a more sustainable building method. As a result, the larger teaching wing of the IL Centre was constructed using this method, while the administration wing was constructed using structural steel with a composite deck.

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The Halsall Life-Cycle Report on the IL Centre’s embedded energy impact.353.77 KB