Measures of Sustainability
Overview / Embodied Energy / Operating Energy / Exergy / Durability/
Externalities / Ecological Footprint / Eco-Labeling / Life Cycle Assessment

Operating energy
Operating energy is a significant measure of sustainability which enables straightforward comparisons between alternative building technologies. Buildings consume energy for heating, cooling, ventilation, lighting, equipment and appliances. Passive energy systems rely on the building enclosure or envelope to take advantage of natural energy sources such as sunlight, wind, water, and the surrounding soil. Active energy systems represent mechanical, electrical and/or chemical processes. Occupants of buildings can also contribute to the heating of buildings by virtue of the heat produced through metabolic processes. Building energy demands exceeding those captured and/or supplied by renewable sources must be supplemented by non-renewable sources.

Renewable Versus Non-Renewable Energy
Most buildings in Canada rely heavily on non-renewable sources such as coal, oil, natural gas, propane and nuclear power. Renewable energy is defined as energy that is renewable within the time of its use. Solar, wind and water energy sources are not normally depleted within the time of their use. Biomass fuels, such as wood, may be renewable or non-renewable depending on harvesting practices. In most mixed wood forest regions of Canada, the threshold of sustainable harvesting has been estimated as 1.78 m3/hectare/year, or approximately 1.5 cords/acre/year (1).

A woodlot will remain sustainable as long as the harvesting of mature trees does not exceed this volume of new wood growth. However, many additional factors also must be considered in order that the woodlot remains part of a sustainable forest resource.

Another aspect of the distinction between renewable and non-renewable energy sources involves the nature of the energy conversion technology. Hydroelectric power may imply extensive environmental impacts, as lands are flooded to create reservoirs, displacing indigenous peoples and animal species. Storage batteries for solar power systems may contain materials which are far from benign, and their life cycle may render them relatively unsustainable. As with all human interventions, it is important to consider entire processes and their associated impacts rather than seeking simple criteria upon which to base our decisions. An interesting perspective on benign, renewable energy sources is found in The Pembina Institute Green Power Guidelines for Canada by Marlo Raynolds and Andrew Pape, July 2000.

 

The future of renewable energy in Canada is steadily improving. The table to the right indicates the recently rapid growth in wind power generating capacity being developed in Canada. It remains to be seen if our growth in generating capacity is exceeded by our energy appetite.

Canadian Wind-Power Capacity, 1990 to 1999 (Megawatts)
[Source: Improving Energy Performance in Canada: Report to Parliament under the Energy Efficiency Act 1997-1999, Office of Energy Efficiency, Natural Resources Canada, Ottawa, 2000.]

Energy Use in Canadian Buildings
Energy use in buildings may be defined as the non-renewable energy used to heat, cool, humidify/dehumidify, ventilate, illuminate and operate buildings, and the equipment and appliances they contain.

In Canada, buildings fall under two broad classifications:
Commercial buildings - including offices, schools, hospitals, malls, shops, restaurants, hotels, and recreational facilities; and

Residential buildings - including single and multi-family, low and high-rise developments.

Approximately one-third of Canada's secondary energy use is due to the operation of buildings. To clarify terminology, the literature typically refers to two types of energy use: primary energy use and secondary energy use, which are defined as:

Primary energy use
Represents the total requirements for all uses of energy, including energy used by the final consumer (see secondary energy use), non-energy uses, intermediate uses of energy, energy in transforming one energy form to another (e.g. coal to electricity), and energy used by suppliers in providing energy to the market (e.g. pipeline fuel).

Secondary energy use
Energy used by final consumers for residential, agricultural, commercial, industrial and transportation purposes.

The following breakdown of energy use by economic sector was obtained from Energy Efficiency Trends in Canada 1990 to 1999 - An Update, published by the Office of Energy Efficiency, Natural Resources Canada, 2001. The industrial sector is the largest energy user, accounting for 39 percent of total secondary energy use in 1999. The transportation sector is the second-largest energy user at 28 percent, followed by the residential sector at 17 percent, the commercial sector at 13 percent, and the agricultural sector at 3 percent.

Secondary Energy Use by Sector
[Source: Office of Energy Efficiency, Natural Resources Canada.]

Looking at the residential sector, the largest components of energy use are space heating and water heating. It is important to recognize that these figures represent the entire housing stock, and for new housing, the space heating represents a smaller fraction. Regardless, the possibilities for passive solar space heating and active solar water heating represent significant opportunities in the retrofit of existing housing stock, and the construction of new housing.

Breakdown of Residential End Use Energy
[Source: Office of Energy Efficiency, Natural Resources Canada.]

The energy profile of commercial buildings is not unlike that for residential buildings, however, lighting, auxiliary motors/equipment, and space cooling account for a more significant fraction of total energy consumption. Again, this composite profile includes many types of buildings ranging from centuries old churches without insulation to contemporary role models of energy efficiency.

Breakdown of Commercial End Use Energy
[Source: Office of Energy Efficiency, Natural Resources Canada.]


The chart to the right provides a more meaningful picture of the current state of commercial building energy efficiency. Typically, today's commercial buildings use less energy per unit area of conditioned floor space, with two notable exceptions - cooling and equipment. In the past, many buildings were not equipped with air conditioning whereas virtually every new commercial building has some form of mechanical cooling. In addition, increased use of computers in new buildings has resulted in higher energy consumption contributing to increased cooling loads.

The potential for energy efficiency improvement is significant in new commercial buildings. Heat recovery from exhaust air could satisfy virtually all domestic water heating demands. Passive cooling and natural ventilation have the potential to reduce mechanical system demand by at least 30 to 50 percent, and to an even greater extent if appropriate fenestration and sun shading strategies are employed. These can be engineered to improve daylighting, further reducing artificial lighting energy consumption and its contribution to cooling loads.

Commercial Sector Energy Usage: Overall Versus New Stock
[Adapted from Report to Parliament on the Administration and Enforcement of the Energy Efficiency Act, 1994-1995, Natural Resources Canada, Ottawa, 1995.]

Energy Use and Greenhouse Gas Emissions
Buildings account for almost one-third of Canada's annual greenhouse gas (GHG) emissions, closely paralleling energy use. Based on the statistics from the table below, the buildings sector has had differential success in addressing Canada's commitment to the Kyoto Agreement, which requires reductions to six per cent below 1990 GHG emission levels between 2008-2012. Government investments in residential buildings research and development since the 1980s, through a variety of energy efficiency and technology transfer programs, have yielded impressive returns in terms of avoided energy use and greenhouse gas emissions. Looking at the residential sector, without the last decade of improvements in codes, standards and practices, today's GHG emissions would have been at least 9 megatonnes higher, representing a 13.2% increase over 1990 levels. By contrast, in the commercial sector, the ubiquity of air-conditioning (cooling), coupled with the increasing intensity of computer use in offices, has resulted in a 13.7% growth in GHG emissions since 1990.

Building Sector Trends: Energy Consumption and Greenhouse Gas Emissions in Canada, 1990 to 1999.
[Source: Energy Efficiency Trends in Canada 1990 to 1999 - An Update, Natural Resources Canada, Ottawa, 2001.]

Despite the differential success in improving energy efficiency in Canada, it is somewhat sobering to consider the following commentary:

Although both energy use and greenhouse gas emissions increased in Canada between 1990 and 1999, the increase would have been much greater if not for improvements in energy efficiency. As a result of this progress, Canadians are saving about $5 billion per year in energy costs, and greenhouse gas emissions are five percent below what they would otherwise have been.

The State of Energy Efficiency in Canada, Natural Resources Canada, Office of Energy Efficiency, Ottawa, October 2000.

Viewed from the perspective of our national debt, operating energy is a vital indicator of sustainability.

 

Relationship of Operating Energy to Embodied Energy
The relationship between operating and embodied energy for a typical office building, as modeled in the previously referenced study by Cole and Kernan, is depicted in the figure below. The data shown here represent average operating energy consumption between Vancouver and Toronto climatic conditions, assuming conventional levels of envelope and equipment energy efficiency.

The initial embodied energy remains constant at 4.82 GJ/m2 over the 50 year period which was examined, while the recurring embodied energy increases from zero at the time of building completion, to a cumulative value of 6.44 GJ/m2 by year 50. The operating energy eclipses both forms of embodied energy at a cumulative value of 70.28 GJ/m2 and represents just over 85% of the total energy at the end of the 50-year period.

This relationship has prompted some practitioners to conclude that embodied energy is comparatively irrelevant. However, as the level of operating energy efficiency is improved, the contribution of embodied energy to total energy becomes more significant. Further, as the life cycle is increased beyond 50 years to 100 years, the recurring embodied energy can eventually exceed operating energy in buildings with low operating energy demands. Looking further into the future, should benign sources of renewable energy come to power our buildings, it is likely that embodied energy will again become the rage in sustainable architecture.

Components of Energy Use During 50-Year Life Cycle of Typical Office Building with Underground Parking, Averaged Over Wood, Steel and Concrete Structures in Vancouver and Toronto [Cole and Kernan, 1996].

The next section deals with Exergy as a measure of sustainability.

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FOOTNOTES:
1. Criteria and Indicators of Sustainable Forest Management in Canada 1997, Canadian Forest Service, Natural Resources Canada, Ottawa, 1996.