Estimates of embodied energy and emissions for canadian buildings in gbc ‘98
The Environmental Implications of Building New
versus Renovating an Existing Structure
ATHENA™ Sustainable Materials Institute
P.O. Box 189, Merrickville, Ontario, Canada, K0G 1N0
This case study demonstrates the value of using the ATHENA™ life cycle assessment (LCA) tool
during the conceptual design process in two ways:
1. to gauge the environmental implications of retaining the structure and envelope of an existing
building instead of replacing it with a new structure; and
2. to help weigh building performance goals against design and material mix choices for a new
THE CASE STUDY BUILDING AND METHODS
As the basis for the assessment, our analysis drew upon two versions of an office building design
prepared for Natural Resources Canada’s C2000 Building performance program. The design basics,
common to both versions, include a single basement level and 13 above grade floors with a total
gross floor area of 21,740m2. The two versions of the building, which are characterized in terms of
operating energy performance as the ASHRAE 90.1 and C2000 versions, differ in their respective
fenestration type and area, overall insulation level, and HVAC system efficiency.
Table 1 below outlines both the common and different elements incorporated in the ASHRAE andC2000 designs as well as the operating energy use estimates.
Table 1 — Design/Energy Use Summary:
ASHRAE & C2000 Office Building Versions
ASHRAE 90.1 Design
DOE2 Operating Energy Est.*
Note: * DOE 2 simulation results were provided in the original C2000 program report.
The scope of the environmental LCA undertaken using ATHENA™ was limited to the officebuilding’s initial structure, envelope components and related annual operating energy. This limitedfocus was necessary due to the objectives of the study itself, which did not require study of commonelements in the comparative scenarios. The results therefore underestimate the total life cycleenvironmental impacts of constructing a new building.
1 The objective of the C2000 Program is to promote the adoption of leading-edge technologies and buildingmanagement techniques to attain a very high performance – a 50% improvement in operating energy over the ASHRAE90.1 standard
ATHENA™, the Institute’s environmental life cycle assessment decision support tool, has been under
development since the early 90s. The ultimate objective is to assist the building community in
making more informed decisions regarding the selection of design and material options that will
minimize a building’s life cycle environmental impact. The model summarizes results across six
key environmental measures covering initial (embodied) energy use; weighted raw resource use;
greenhouse gas emissions (both fuel and process generated); measures of air and water pollution;
and, solid waste emissions.RESULTS
Initial New Building Impact (ASHRAE & C2000 Performance Designs)
Tables 2 below summarize the office building environmental life cycle assessment results for the
two performance designs by component grouping on both an absolute and per unit of floor area
basis. The first year operating (HVAC) energy effects per m2 are also reported.
Table 2 – Summary: Initial Environmental Impact Profile by Performance Design
Note: Global warming and other effects of HVAC operating energy reflect the upstream production andtransportation of energy as well as its combustion. Air and water pollution effects, while calculated, are notreported here to save space
Both the ASHRAE and C2000 performance designs share the same structure, which accounts forroughly 75% of the building’s initial embodied energy burden. But the C2000 version incorporatesabout 15% more embodied energy in its envelope materials compared to the ASHRAE design.
Overall, then, there is only a 4% difference between the two designs in terms of embodied energyfor their respective structure plus envelope materials. For the C2000 design, the modest increase inmaterial use contributes, in combination with increased HVAC efficiencies, to a 2.5 foldimprovement in annual operating energy use.
It’s notable that as operating energy efficiency improves, the importance of the initial structure andenvelope embodied energy increases. In the less efficient ASHRAE design, initial embodied energyis equivalent to about 4 years of HVAC operating energy use, but in the C2000 design, initialembodied energy is equivalent to approximately 10 years of operating energy. The relativeimportance of embodied energy would be even greater if the estimates covered all of the recurringas well as excluded building elements.
While contrasting the embodied energy of the structural and envelope materials with operatingenergy is useful, the shear enormity of the total energy involved can easily go unnoticed. To helphumanize the results we made a quick calculation which revealed that the energy embodied in thestructure and envelope of the ASHRAE design is equal to driving a small car (consuming8L/100km) a total of 12 million km or 300 times around the earth.
In summary, just building a new square meter of ASHRAE performance level office floor space –a) requires 1.53 Gj of energy and 1.23 ecologically weighted tonnes of raw resources;b) produces greenhouse gases equivalent to 370 kg of CO2;
c) requires 19.7 cubic metres of air and 2 cubic metres of water to dilute these pollutants to
d) results in 60 kg of solid waste going to landfill.
This conservative assessment clearly demonstrates the significant environmental impacts related tomaterials comprising a new building, impacts that become relatively more significant as steps aretaken to improve a building’s operating energy.
Environmental Impact Avoidance Associated with Renovating
When choosing to renovate, a building’s structure is typically retained but the original envelope
may or may not be left intact. So environmental impact avoidance scenarios for a major
retrofit/renovation involve contrasting a complete demolition and new construction activity with:
a) retention of the structural system only and estimation of the environmental impacts avoided by
not demolishing the structure (minimum avoided impact case); and
b) estimation of the impacts avoided by not demolishing either the structural system or the
envelope (maximum avoided impact case).
Minimum Avoided Impact Case
The minimum avoided environmental impact case involves saving only the structural system of anexisting building, with reconstruction of the rest of the building. The avoided impacts equal theeffects of:
demolishing a structural system + rebuilding a comparable structural system.
Here the effects of demolishing the envelope are not avoided and we assume that the environmentalcost of rebuilding the envelope on an old building would be the same as constructing the envelopeon a new building.
Maximum Avoided Impact Case
This case involves saving the envelope as well as the structure and avoided impacts equal theeffects of:
demolishing a structural/envelope system + rebuilding a comparable structural/envelope system.
Table 3 summarizes the energy savings and other avoided environmental impacts for the maximum
avoided impact case. The results for the minimum avoided impact case, in which only the structuralsystem is retained, can be readily derived from the estimates in Table 3 by simply subtracting thevalues for constructing the envelope in each impact category.
Table 3 – Results Summary: Environmental Impact Avoidance Scenario
New Construction Totals
Total Avoided Impacts
Note 1: Demolition of cast-in-place structure only; no demolition effects available for envelope materials.
The above table does not consider the eventual operating efficiencies of the new versus renovatedbuildings, another factor that may have a bearing on the decision to build or renovate.
Unfortunately, however, the data is not available to adequately include this aspect.
To put the Table 3 results in perspective, we can compare them to the results for construction andoperation of a new C2000 building presented in Table 2. By reusing the structure and envelope of abuilding and thereby avoiding demolition of these component systems, the total energy savedapproaches the energy used to construct the C2000 office building and operate it for a year.
Alternatively, the total environmental avoidance is equivalent to 10 years of HVAC operatingenergy for the C2000 office building design. Either perspective indicates that the avoidedenvironmental impact is indeed, significant.
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