The method of assessing lifetime building energy is known as Life Cycle Energy Analysis (LCEA). LCEA is an easily-conducted form of Life Cycle Assessment (LCA) and measures both the operational and embodied energy attributable to buildings over their lifetime (maintained, refurbished, extended and demolished). This measures the embodied energy (environment degraded in the mining of raw materials, the manufacturing of building materials and products, and finally their transportation and assembly into buildings).
The main benefit of LCEA is that the embodied energy costs of products, design modifications and strategies used to optimise operational energy can be evaluated. For example, thermal insulation has an embodied energy cost – the energy to make the insulation –but savings in operational energy accrue over time. LCEA can be used to estimate the net savings over the building’s life and, perhaps more importantly, the ‘energy payback period’ (the time taken for the initial embodied energy cost to be paid back by the ongoing operational energy savings accrued). The life cycle energy implications of an energy-saving strategy need to be considered in net terms.
Life cycle energy comprises the operational energy of the building and its initial and recurrent embodied energy over its expected lifetime. Life cycle energy is calculated using the equation:
LCE = E i + E rec + (OE x Building lifetime)
LCE = the life cycle energy;
EE = the initial embodied energy of the building; i
EErec = the recurrent embodied energy (for future maintenance and refurbishment); and
OE = the total annual operational energy (including thermal and non-thermal).
The energy embodied in a product comprises the energy to extract, transport and refine the raw materials, and then to manufacture components and assemble the product. The energy consumed directly at each phase is clearly definable and measurable. However, the energy required indirectly to support the main processes is less obvious and more difficult to measure.
Total initial embodied energy of initial construction of building = DIRECT ENERGY (energy purchased by contractors on-site and off-site to facilitate any construction + prefabrication +administration + transport activities under their control (i.e. including sub-contractors) and INDIRECT ENERGY of construction (energy embodied in building materials). The Australian National average input-output analysis suggests that the direct energy of residential construction is approximately 3% of the total embodied energy of the building (Treloar 2007). Recurrent embodied energy analysis would include the major appliances and replacement factors for many of the items in the building such as – paint, windows, plumbing and electrical systems, appliances and roofing materials.
Three embodied energy calculation methods:
- Process Analysis (most commonly used): Focuses on the energy required for particular industrial processes (e.g. brick-making) but this method may not cover any large or small inputs of goods and services in detail (i.e. only energy to make a brick and not any other costs) (Boustead and Hancock 1979).
- Input-Output Analysis: Estimate of all direct and indirect energy embodied in a product is known as input-output analysis using national statistical information compiled by governments for the purpose of analysing national economic flows between sectors. Several methodological problems so not considered reliable for embodied energy analysis of an individual product (Crawford 2008, 2011).
- Hybrid Analysis: Combines strengths for process analysis (reliable energy consumption figures for particular processes) with those of input-output analysis (theoretically complete system framework) while eliminating, as much as possible, their weaknesses (incompleteness and inherent errors, respectively) (Bullard et al. 1978). This method lacks of a comprehensive and reliable database of energy use data from industry and unreliable input-output data has to be relied upon for many significant processes.
Energy for space heating and cooling, hot water heating, lighting, refrigeration, cooking and appliance and equipment operation can be simulated using computer programs such as EnergyPlus, TRNSYS, IES-VE or DOE2.2.
The thermal energy can be modelled on different levels of insulation. Non-thermal energy requirements, i.e. the energy used for lighting, cooking, hot water, appliances and other power, must also be estimated based on estimates for household energy use.
Delivered vs. primary energy
Delivered energy: is energy used by consumer that is metered at the point of entry to the property or building. This Energy delivered energy varies according to fuel type (for example, electricity or gas) and the means of production (for example, coal-fired power station or hydropower).
Primary energy (used to measure LCEA): energy required from nature embodied in the energy consumed by the purchaser. For every unit of electricity used in Australia, on average, approximately 3.4 units of primary energy, such as coal, are required (Treloar 1997). This ratio of 3.4 to 1 for electricity production, or simply 3.4, is termed the primary energy factor for electricity. Primary energy is proportional to energy-related CO2 emissions. Therefore primary energy is a more appropriate measure of the environmental implications of energy use than delivered energy.
Overall, LCEA method provides a framework for decision-making relating to design and implement energy efficiency strategiesto reduce energy–related environmental impacts. Assumptions about the future must be made to balance the decisions that will be made today regarding the optimal level of energy efficiency required. The level of embodied energy required to build a new building also highlights the benefits of retrofitting existing buildings rather than building new ones. Other opportunities exist in substituting materials with low embodied energy for energy intensive ones, reducing construction waste, reusing products, using products with a high recycled content and designing for adaptability, durability, recyclability and deconstruction.
Source: UT Knoxville, Crawford, R. Life cycle Energy Analysis,