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Environmental auditing for building construction: Energy and air pollution indices for building materials
Buildingand Emtr,mment.VoL2-. No. I. pp. 2-'~30.1992.
0360-132392$5.00-0.00 0 1902PergamonPresspie.
Pnntedin GreatBntain.
Environmental Auditing for Building Construction: Energy and Air Pollution Indices for Building Materials R A Y M O N D J. COLE* DAVID ROUSSEAU* The design community has a reasonable understanding of the factors which affect operational energy in buildings and has a rariety of computational tools for assessing it. By contrast, the broader encironmental consequences of producing and operating buildings are poorly defined. Since operating energy represents the current extent of em'ironmental attditing, a significant advance is to inchtde the energy and emissions associated with the production of construction materials. This paper outlines the key issues associated with environmental assessment of the production and use of materials and presents examples of energy and ah" pollution audits for four comparable commercial building assemblies with similar thermal resistances.
1. INTRODUCTION
2. ENVIRONMENTAL AUDITING
F R O M THE early 1970s until the mid-1980s there was a steady transformation from viewing energy and resource use as an ecological issue to an economic one [1]. However, with the broad-based resurgence of ecological preservation concerns in the late 1980s this trend is reversing. Resource use is now discussed within a broader environmental agenda, particularly in the context of global warming, ozone depletion and local and regional pollution. Changing the economic equation to include current hidden environmental costs and to restrain the rapid depletion of certain resources will radically affect the way building construction is viewed [2]. The significance for the construction industry will be the expansion of environmental auditing from a simple assessment of operating energy to include a broader assessment of resources used in building [3]. This will necessitate both an improved general understanding of the environmental consequences of buildings by design professional as well as access to comparative evaluations of the environmental impact of various building components and assemblies. In this regard, a significant step is to compile the energy use and environmental emissions associated with the production of construction materials. This paper outlines the key issues associated with environmental assessment of the production and use of materials, defining which are currently quantifiable, and presents a practical framework for energy and air pollution audits. The paper concludes with example energy and air pollution audits of four comparable commercial building assemblies with similar thermal resistances.
An environmental audit for building construction is an accounting of the quantifiable environmental factors that will be incurred in building production and use. reducing them to equivalent terms and presenting them in meaningful categories. The purpose of the audit is to add an environmental dimension to design decisions. An environmental audit includes both energy and nonenergy related factors, each of which has direct and indirect components : Direct environmental effects include : • Emissions of carbon oxides, oxides of sulphur, oxides of nitrogen, particulates and unburned hydrocarbons from combustion. • Air, water and solid waste impacts of material processing and handling. • Depletion of limited reserves of non-renewables. Indirect environmental effects include : • Damage to terrestrial and aquatic habitats due to energy production and industrial development. • Production of hazardous wastes with long-term consequences. The direct environmental effects of energy production and industry are typically more readily quantifiable than the indirect effects. 2.1 Quantifiable encironmental effects Environmental studies have produced considerable data on the environmental effects of the processes and materials associated with building construction, however very little is available in a form which is useful to the design professions. Some of the significant environmental factors associated with the production and maintenance
* Environmental Research Group, School of Architecture. University of British Columbia, Vancouver, BC. Canada. V6T IW5. BAE 27:1-C
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R. J. Cole and D. Rousseau
24
of buildings for which there is environmental data available, but which cannot set be used comparatively in building design and operational decision making are : • The consumption of non-rene~vable energy and mineral resources incurred in the production of construction materials, components, and buildings • The pollution of air, water and soil incurred in the transformations of energy and mineral resources in all stages of materials and building production • The resources consumed and pollution incurred in the maintenance and replacement of building materials and assemblies over the life-span of the building • The recoverability of resources contained in buildings at the time of their demolition. The indirect consequences are extremely difficult to quantit) and probably are best characterized as "loss of ecological capital" [4]. The work presented in this paper pertains only to the direct environmental effects of building production and operation. Within this framework the scope is further limited to the energy consumption and air pollution factors. 3. ENERGY-RELATED FACTORS Energy related factors include all transformations of energy in the production and use of buildings. Though research in the mid-1970s clearly demonstrated that significant amounts of energy are required to produce a building [5, 6], energy accounting over the past fifteen years has focused almost exclusively on operational energy use in buildings and the development of strategies to reduce it. In the 1990s it is becoming increasingly important to resume the work on evaluating the energy for producing buildings and to extend it to embrace a broader environmental agenda.
3.1 Embodied eplergy A complete audit of a building will include the energy used to create building materials and components and to construct a building, i.e. the embodied energy. Embodied energy is the "'direct" and "'indirect" energy used to manufacture, transport and install building products. • Direct energy is the energy actually consumed in the construction of buildings. It represents the final transportation and installation of a component or assembly. Direct energy is a relatively small portion of embodied energy. European and U.S. figures estimate the construction portion to be about 7-10% of total embodied energy [7, 8]. • Indirect energy represents the energy consumed in the production of building materials and their associated transportation during processing. Indirect energy is the largest portion of embodied energy. It represents the production of a component exclusive of its transportation to and installation on site. Embodied energy thus represents the component or assembly in place. However. when full life-cycle analysis is undertaken, embodied energy should rightfully be extended to also include the energy associated with maintaining, repairing and replacing materials and components over the lifetime of the building.
3.2 Energy intensio' vahws Energy Intensity is the energy used only in the production of a building material or component. It represents the indirect energy in unit terms either expressed as energy/mass or volume such as M J kg or M J m 3 or energy/standard unit such as M J/sheet or block etc. Energy intensity is also calculated, from statistical data, in M J, $. Limited international research over the past 15 years in the field of energy intensities of building materials has produced reasonable agreement on acceptable values for some materials, but it has also produced some significant differences for others (see Table I). There are several reasons for these differences : • • • •
System boundaries Data source reliability International differences Thermal energy content of feedstock materials.
3.2.1 System boundaries. There is no absolute or correct energy intensity of a material [9]. A stated value is a direct function of what was included and what was excluded from its derivation. An example of the importance of system boundaries is readily found in comparisons of aluminum. Figures for the Canadian aluminum industry in 1976 indicate a value of 236.3 MJ/kg [10]. Although substantial efficiency improvements have been made since 1976 the figure is still reasonable today if one includes the energy costs of mining, concentrating and shipping ore, most of which is produced in the Caribbean. The Canadian figure compares well with those of Switzerland [11], Finland [12], and the U.S. [13]. New Zealand studies [14] however place aluminum at only 145 MJ/kg based on some limited reporting by industry and some analysis of the processes. New Zealand's ore, like Canada's, is also imported, but national statistics on the flow of energy and materials in the aluminum industry cannot be disaggregated from other non-ferrous metals. Assessment of energy intensity figures must, therefore, be accompanied by definitions and clear boundaries. The commonly accepted limit includes analysis of all of the industrial processes of extraction, transportation and processing of a material. This limit typically captures about 90% of the gross energy requirements of a manufactured item [15], but there may be important exceptions to this. For example in a case where highway transport of raw materials is a key (or dedicated) component of a manufacturing system, a portion of the energy capital and maintenance energy for the highways and vehicles should be included, and may significantly affect the analysis. The choice of level of analysis depends on the objective of the analysis, the available data and the type of evaluation methods. Ideally the system boundaries must include the following in order to reasonably reflect the embodied energy of materials and assemblies : . The energy requirements for extraction, beneficiation and transportation of raw materials. • The energy requirements for primary processing such as smelting, milling, drying, machining, chemical synthesis etc. as well as the transportation energy to the secondary stages.
Environmental Auditing for Building Construction
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Table 1. Energy intensities of selected materials (MJ/kg) Material
Canada
U.S.
N.Z.
S~itz.
Finland
Metals Aluminum Nickel Steel (general) Zinc
236.3* 168.3" 25.7* 64.1"
192.0" 58.0* 39.0*
145.0" 261.7¢
189.0, 468.0t
Non-metallic minerals Glass (sheet) Gypsum Brick Glass wool Cement products Cement Concrete Mortar Plastics Polyethylene Polystyrene Paint (water base) : dry
32.0* 68.4*
27.7t 68.4* 21.6* 1.4+ 3. l't 18.0t
10.2, 7.4"1" 4.9:~ 22.3:[;
19.8" 7.2* 5.8* 14.0"
16.7"
5.9:~ 1.2++ 2.2:1:
9.4* 1.3"
7.4* 2.0*
87.0~ 105.0++ 76.0:[:
4.9"]" 0.9t 1.4"t 49.3t 122.8"t
77.7*
43.2t 16.5+ 2.8t 23.4t 4.9"t
118.8+ 76.7t
* Mid 1970s data, f Early 1980s data. ++Mid 1980s data.
• The energy requirements for secondary fabrication, assembly etc., where applicable. • The thermal energy potential of the raw material feedstock if it was to be used as a fuel (this applies specifically to petroleum based products). A more detailed analysis will also include the energy cost of producing energy. For example the energy cost of petroleum refining in Canada is 11.5% of production [16]. As the use of building materials with recycled content expands there must also be credits applied to the audit to reflect the energy and resource capital savings as well as pollution reductions from the use of recovered materials. There are practical limitations however, particularly in rapidly emerging areas such as recycling where reliable data is difficult to find. 3.2.2 Data sources and reliability. The data sources for energy intensity analysis are also problematic. There are three main sources of energy and production data for most industries, though all are not necessarily available. These are : • National statistics: Records compiled by national agencies from industry reporting. • Process analyses: Engineering analyses of processes accounting for energy use step-by-step. • Industry statistics : Records kept internally by plants or compiled by industry associations. Each data source has its shortcomings in application to energy intensity analysis and may not alone produce reliable results. By using several types of analysis however, one can judge the reliability of results through comparing the consistency of figures derived from different data sources. 3.2.3 International differences. There
are several
important factors which also affect international figures and, to some extent, even national figures. These are : • Fuel type: The most regionally available and inexpensive fuel source is likely to be used, within regulatory boundaries. For example, virtually all of Canada's aluminum is produced with hydroelectricity, while production in the U.K. uses some thermal electricity. This leads to very significant increases in gross energy input through the thermal conversion losses encountered in the U.K. • Raw materials imports: Some industries rely on imported raw materials for which the overseas extraction costs may be difficult to assess. The transportation factor also becomes more significant. Again, in the aluminum industry, Canada's production relies on ore imports from Jamaica where some of the primary processing also takes place. Energy costs and pollution figures are difficult to get. • Different accounting methods : For example, as noted before in New Zealand, many non-ferrous metal statistics are lumped together making it difficult to distinguish copper from aluminum, etc. A similar practice is used in Canada. 3.2.4 Energy content of feedstocks. Another problematic decision is the inclusion of the thermal energy content of the feedstock in the gross energy requirement. For those materials which are petroleum based it seems clear that the thermal value of their feedstocks, had they been burned as fuels, must reasonably be included. However should one use their theoretical thermal value, or their actual value when burned in a process of average efficiency? Many researchers have opted for the theoretical value and this explains the relatively high energy intensity for most synthetic resins [17]. 3.3 Direct environmental consequences of ener#y ,tse Energy use entails emissions of carbon dioxide, particulates, oxides of sulphur, oxides of nitrogen, carbon
26
R. J. Cole and D. Rousseau
monoxide and unburned hydrocarbons from combustion. The characteristics and air pollution consequences of these emissions are : • C O : - - o f primary concern as a greenhouse gas. • Particulates--primarily, carbon, with a range of associated mineral and metal compounds, primarily a local air pollutant. • SO_,--urban and regional effects both as an air pollutant and precursor to acidic precipitation. • NO~--urban and regional effects both as an air pollutant, photochemical oxidant and precursor to acidic precipitation. • C O - - o f primary concern as a local air pollutant. • H C - - a broad range of fugitive volatile organic compounds from uncombusted fuel, primarily of concern as photochemical oxidants. The proportions of these vary significantly with the type of fuel and the combustion efficiency. Table 2 shows typical emissions expressed as g,"MJ for common stationary (non-transportation) uses of conventional fuels [18-21]: 3.4 Air emission index Operating energy audits have the relative simplicity of being reducible to a common energy units. It is clearly more difficult to compare the relative effects of different pollutants within a particular medium (e.g. air) as well as between media (e.g. air, water and soil). Several European researchers employ an accounting system based on volume equivalents in which accepted limiting values are used to determine the volume of air which is polluted with a certain contaminant up to a limiting value [22]. The resulting polluted or consumed volumes of air are therefore equivalent units and can then be combined and used as simple indices to evaluate the degree of environmental air pollution associated with the material or component. For example, where the output of SO, is y mg and the admissible level of SO,. is x mg/m 3 of air, it can be transformed into m 3 of air contaminated to the allowable limit by : Used volume of air = y / x (m 3) A critical decision within this approach to aggregating air contaminants is the choice of acceptable limits [23]. Legislated limits, which are inevitably derived through compromise rather than direct health criteria, can relate to either emission rates from the plant or, more stringently, to ambient air quality. In the work reported in this paper. Canadian ambient air quality standards have
been chosen provisionally until international criteria t\~r environmental auditing have been agreed upon. The volume equivalents approach is suitable for tour of the major air contaminants which are usually regulated in national ambient air quality programs: Suspended particulates (from combustion), SO:, NO, and CO, The ambient air quality objectives set by' the Canadian Environmental Protection Act are presented in Table 3. Although the concentrations specified in the National Ambient Air Standards are very low and thus yield very high volumes of contaminated air, they do provide a useful relative basis for weighting the importance of different air pollutants. The important criteria is clearly the relative acceptable concentrations of the various contaminants. 4. NON-ENERGY RELATED FACTORS Energy related emissions account for only a portion of overall environmental effects from an industrial process. Process emissions refers to those emissions which are the direct result of smelting, kilning, distilling, drying. grinding, casting and all other industrial processes exclusive of fuel combustion. These include both the same categories of emissions associated with fuel combustion as well as a very wide range of other particulate and gaseous compounds. These additional compounds each have their own characteristics and environmental consequences, ranging from relatively benign dusts from overburden removed from mines, to highly toxic halogen compounds and heavy metals. In some cases, such as the cement industry, the energy emissions are the most significant factor in the overall assessment, because the process emissions include only some dusts (which are relatively low risk) and some water contamination (mostly with low risk solids). Metals smelting, on the other hand, produces a wide range of air emissions such as sulphur oxides from ore reduction, and fluorides, which are high environmental stressors. 4.1 Quantifvin 9 non-eneryy related emissions Non-energy related air emissions are relatively easy to characterize with some accuracy, but are difficult to quantify. For example dusts of predictable types are inevitably produced by dry milling processes, but varying degrees of dust controls are in place and varying amounts of trapped dusts are returned to the process. Data is available on "uncontrolled emissions" [24] which are derived from process studies, but data on the effectiveness and application of control measures is more difficult to
Table 2. Air emission by fuel and use Fuel use Distillate oil (conventional). 0.5% S Natural gas Coal (bituminous), 3% S Coal fired electricity Canadian electricity*
CO, (g/MJ)
Part. (g/M J)
SO: (g/M J)
NO, (g/M J)
CO (g/M J)
HC (g MJ)
72.1 50.5 87.5 248.9 52.3
0.0065 0.006 0.11 0.31 0.07
0.23 0.0002 0.85 2.36 0.50
0.2 0.09 0.27 0.75 0.16
0.015 0.007 0.060 0.170 0.040
0.0020 0.0080 0.0030 0.0080 0.0017
* Electricity production: Canadian split (62% hydro, 20.1% coal, 16% thermonuclear; 0.5% gas and 1.4% oil). Based on 35% overall efficiency for thermal production.
Environmental Auditing for Buildin9 Construction
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Table 3. National Ambient Air Quality Objectives
Concentration Limit (g'm ~)
Particulates
SO:
NOx
CO
0.00012
0.00003
0.00006
0.006
find [25, 26]. There are also rapid developments in plant emissions controls which are driven by regulation. For example Statistics Canada reports that copper and zinc smelting are, by far. the largest industrial sources of SO~ emissions in Canada [27], however plant improvements are expected to alter that picture in a very short time. Other differences, such as the composition of raw materials, also introduce variables which are difficult to quantify. One brick kiln, for example, will produce markedly different emissions from another due to the composition of the clay. The characteristics and air pollution consequences of these non-energy related emissions are :
• NO~ from energy related processes • CO from both energy and non-energy related processes. The Air Emissions Index presented in this work is the aggregate of the volume equivalents generated from the four emission categories above. Given that the significance of an air pollution index is not in the actual units (m 3 for example) used, but in comparisons between the magnitude of the index derived for various materials or assemblies, they have been reduced by an arbitrary factor of 10-'. This gives the Air Emissions Index a more manageable scale.
• Particulates--a very broad range of carbon, mineral and metal compounds each with specific urban and regional air and soil effects. • SOz--urban and regional effects both as an air pollutant and precursor to acidic precipitation. • C O - - o f primary concern as a local air pollutant. • H C - - a broad range of volatile organic compounds, many of which are environmental toxins as well as photochemical oxidants. The nature, extent and proportions of these emissions are specific to each of several thousand processes within the materials industries.
5.3 Other air pollution indices Other air pollutant quantities are more difficult to convert into a common index because they comprise a collection of a number of different chemical compounds with widely varying environmental risks, each of which has to be evaluated separately. At this stage in the development of the air pollution indices these are grouped together in two categories and presented in association with the final Air Emissions Index. The categories are :
5. COMPONENTS OF AIR EMISSIONS INDICES
Further development of the air pollution indices will lead to a more detailed evaluation of the environmental impact of the various particulate emissions and fugitive hydrocarbons through assessing their various chemical categories and utilizing applicable concentrations for each. Once this is accomplished they will be in comparable terms to the Air Emissions Index and can be added to it.
An underlying premise of the work presented in this paper is that the large body of complex data on the energy and environmental implications of producing building materials must be reduced to manageable terms in order to be useful in environmental auditing of buildings. Some data can be readily reduced to a common unit while others cannot, and are more appropriately left discrete. Given the commonalities and differences of energyrelated and non-energy related emissions, the following approach has been adopted for summarizing them on a common basis.
5.1 Carbon dioxide CO., release from fuel combustion can be simply summarized as the mass of CO: created by the production of a unit of building material. Concentration limits are not applicable in the case of CO:, so it is simply presented as the "greenhouse gas contribution" of the material or assembly. 5.2 Air emission index The following can be reduced to a common index by the application of the volume equivalents method described in 3.4 using Ambient Air Quality Standards in Table 3 : • Particulates from fuel combustion • SO, from both energy and non-energy related processes
• Particulates from non-energy related processes • Fugitive hydrocarbons from both energy use and non-energy processes.
6. ENERGY AND AIR P O L L U T I O N AUDITS O F WALL ASSEMBLIES Material selection in the building industry is rarely made in isolation. Materials used in buildings can only reasonably be compared in the context of their performance in building assemblies. For purposes of environmental auditing, one must invariably compare alternative building assemblies offering similar performance characteristics [28]. Figure 1 shows sections of four non-load bearing wall assemblies used in commercial construction which all attain an approximate RSI = 3.6 m 2 Deg C/W : • Wall #1 is a precast concrete panel clad wall with rigid polystyrene board insulation and gypsum board interior finish. • Wall # 2 is brick clad construction with lightweight steel framing containing fibreglass insulation and gypsum board finishes. • Wall # 3 is an exterior insulation and finish system
R. J. Cole and D. Rousseau
28
.I ~ i
Material 75mm precast concrete panel Steel reinforcement Steel anchors (galvanized) Weather barrier (polyolefin) Steel flashings (galvanized) Steel furrings (galvanized) 75ram polystyrene insul, board 15mm interior gwb. (finished) 3 coats latex paint (0.3 litres) TOTAL
__
Wall
Mass/m 2 180.0 kg/m2 7.2 3.0 0.07 0.5 2.5 3.8 11.8 0.4 209.3 kg/m2
•
i
•
.
°
,"
i
Material Mass/m 2 lOOmmface brick (clay) 165.0 kg/m2 Mortar 28.0 Steel shelf angle (strut. steel) 4.0 Steel ties and screws (galvanized) 1.0 Weather barrier (polyolefin) 0.07 Sheathing (wp. gwb.) 9.8 150ram steel studs (galvanized) 10.0 150ram fiberglass batt insulation 5.4 Vapour barrier (polyethylene) 0.05 12.5ram interior gwb. (finished) 10.0 3 coats latex paint (0.3 litres) 0.4 TOTAL 233.8 kg/m2
U
~
m
Wall #2
[,
>-<...j
i/!i:: i:?. •
°
.
Wall #3
Material Mass/m 2 2 coats acrylic rood. stucco 6.0 kg/m2 Glass fiber mesh 0.8 19ram polystyrene insul, board 0.6 Steel fasteners and flashings (galv.) 1.0 Weather barrier (oolyolefin) 0.07 Sheathing (wp.gwb.) 9.8 100ram steel studs (galvanized) 6.9 100ram fiberglass batt insulation 3.6 Vapour barrier (polyethylene) 0.05 12.5ram interior gwb. (finished) 10.0 3 coats latex paint (0.3 litres) 0.4 TOTAL 39.3 kg/m2
Material Porcelain steel, or Anodized aluminum, or 6ram glass sheet Aluminum mullion/rail/spandrel Weather barrier (polyolefin) 150ram steel studs (galvanized) 150ram fiberglass batt insulation Vapour barrier (,polyethylene) 12.5ram interior gwb. (finished) 3 coats latex paint (0.3 litres) TOTAL
#1
Wall #4
Mass/m 2 9.6 kg/m 2 5.3 16.0 22.0 0.07 10.0 5.4 0.05 10.0 0.4 57.6 kg/m2 (Steel) 53.3 kg/m2 (Alum.) 64.0 kg/m2 (Glass)
. ° .
Fig. 1. Sections of non-load bearing wall assemblies used in commercial construction.
using acrylic stucco, polystyrene board insulation and lightweight steel framing with gypsum board finish. Wall # 4 is an aluminum curtain wall system with three alternative cladding panels: porcelain steel, aluminum, and glass. It incorporates fibreglass insu-
lation
and
gypsum
board
interior
finish.
Table 4 presents the total mass/m 2 and summary energy use and air pollution characteristics for the four wall assemblies in Fig. 1.
E n v i r o n m e n t a l Auditing f o r Building Construction
29
Table 4. Environmental characteristics of different wall assemblies Energy
Mass kgm-' Wall # I Wall #2 Wall #3 Wall #4: steel Wall #4: alum. Wall # 4 : glass
209.3 233.8 39.3 57.6 53.3 64.0
Emissions
Total Ref. Nat. energy Feedst. Pet. Gas Coal Elect. Other MJ/m2 MJ:mz MJ/m: MJ/m: MJ/m: MJ/m2 MJ/m2 1148 1799 929 6235 7263 5974
317 115 300 42 42 42
125 221 90 691 766 639
254 930 263 543 4ll 510
246 214 95 236 170 120
169 297 166 4715 5866 4656
37 22 16 8 8 8
CO: g 52200 90260 36700 113200 110700 94500
Part. : ,Air NonEmiss. Energy HC Index g g 2810 2850 1610 7710 7640 7240
1230 2230 420 630 560 580
310 560 220 370 260 260
Notes: • Total Energy; energy of wall assembly including feedstock energies. • Feedstock : gross thermal content of petroleum used in feedstocks for synthetic resins. • Fuels ; fuel use, by type, used in production of the component materials. • C02; total mass of CO., created by fuel combustion in the production of the assembly. • Air Emissions Factor: mass of particulates SO,, NO~, and CO, divided by their respective Canadian national ambient air quality maximum concentration limits. • Non-energy related particulates ; summary,of all particulates from processes. • HC; all fugitive hydrocarbons from both energy and non-energy related processes.
The energy summary includes : Total The total embodied energy of 1 m 2of wall Energy : assembly including feedstock energies. Feedstock : The feedstock energy represents the gross thermal content of petroleum used in synthetic resins. Feedstock energy is not included in the calculations of emissions from energy use. Fuels: These represent fuel use by type consumed in production of the component materials. Other fuels represents mainly the wood waste used in paper production for gypsum wall board and the waste rubber, wood etc. burned in cement kilns. The emissions are presented according to the four categories : C02 :
Air Emissions Index :
Non-energy related particulates : HC:
A summary of the mass of CO2 created by fuel combustion in the production of the assembly. Generated by summing all particulates and NO~ from energy use, SO2, and CO from both energy and non-energy processes, and dividing them by their respective Canadian national ambient air quality maximum concentration limits (Table 3). A summary of all particulates from processes based on the emission factors and typical control efficiencies from the data. All fugitive hydrocarbons from both energy and non-energy related processes, also incorporating typical control efficiencies, These reflect emissions from boilers, coal coking, polymer production, degreasing etc. Both particulates and HCs represent far too wide a range of chemical compounds to readily convert to air emissions factors at this time, and are therefore presented separately.
Emissions from fuel use are calculated from the fuel
factors given in Table 2 except the electricity used in primary aluminum production which is assumed to be all hydro in Canada. 6.1 Key observations The following observations can be made : • It is often assumed that low mass construction implicitly has low environmental consequences. This comparison shows that, although the lowest mass assembly (Wall #3) does indeed demonstrate this point, others with similar mass (Wall # 4) have energy and air emissions that are greater by an order of magnitude. • Even within the family of non-metallic mineral materials with similar mass, there are distinct differences in energy intensity and CO_, emission. Wall # 1, for example, entails the emission of 52.3 kg of CO.,. Wall # 2, despite having similar mass, entails 90.25 kg. However the Air Emissions Index of these two wall assemblies is almost identical. • The very high embodied energy figures for the walls which are largely composed of steel and aluminum are also reflected in proportionally higher COz production and Air Emissions Index. However, what is not reflected in these figures is the inherent capacity to eventually reduce a significant portion of future environmental costs through recycling. • Although the selection of a glass cladding panel in Wall # 4 has little effect on mass, there are distinct reductions in embodied energy, CO: emission and the Air Emissions Index.
7. CONCLUSION This paper has presented key characteristics of environmental auditing as well as examples of audits in use. It is clear that embodied energy is only one part of environmental auditing: environmental emission from both energy use by fuel type and non-energy related
30
R. J. Cole and D. Rousseau
process emissions are. in man5 cases, more significant indicators of the environmental cost of materials. Environmental audits, including energy use for materials production and installation as well as air pollution indices can provide criteria for design decisions when choosing materials and assemblies offering similar performance for a given application. Generalities about the environmental impact of materials choices do not stand up well due to the distinct and markedly different environmental attributes of the families of materials used
for comparable applications, e.g. non-metallic minerals are fundamentally different from metals. Acknowledgements--Funding for on-going research is provided by an operating grant from The Natural Sciences and Engineering Research Council of Canada (NSERC). The authors also wish to acknowledge the research assistance of Beate NemethWinther, Robert Boyd and Gary Helps, and extend this acknowledgement to Dr Niklaus Kohler at LESO. Swiss Federal Institute of Technology Lausanne. for offering direction in the formative stages of the project.
REFERENCES
1. I. Cooper. Environmental quality: responding to a new agenda. Proceedings: Designing.~)r Ent'ironmental Quality "89. Solihull, U.K., September (1989), 2. D. Cope, Reported in "Towards Green Buildings'. Richard Lorch, RIBA Journal, pp. 58-59 (Februar,. 1990). 3. R. Lorch, RIB.4 Journal. pp. 58-59 (February, 1990). 4. H.T. Odum. Energy .4nalysis, Energy QualiO" and Environment. Energy Analysis: A New Public Policy Tool, Westvie~ Press (1978). 5. R.G. Stein. D. Serber and B. Hannon, Energy Use for Building Construction, Center for Advanced Computation. University of Illinois. and R. G. Stein and Associates. U.S. Department of Energy. EDRA Report (1976). 6. P.F. Chapman. The energy costs of materials, Energy Policy, pp. 47-57 (March 1975). 7. R.G. Stein. et al.. (1976) op cit. 8. R. Salokangas. A. L. Perala and P. Kontuniemi, Energi-lnnehallet 1 Husbyggande (Energy Contents q/" House Buildings--Finland) Nordic conference on total energy in buildings and energy related environmental effects. Copenhagen, (Sept. 11, 1990) (in Swedish). 9. N. Kohler. Life c~cle costs of buildings. Proceedings: Buildings attd the Em'ironment, University or BC. Vancouver, Canada. (March 15th 1991) (in press). 10. Energy Mines and Resources Canada, Mineral Policy Series # 164, Present and Projected Energy Consumption in the Mineral Industry of Canada, Ottawa (1976). 11. N. Kohler. Energy consumption and pollution of building construction, Proceedings oflCBEM '8-. Lausanne Sept. 28-Oct. 2nd (1987). 12. R. Salokangas ez al. (1990) op cit. [3. R.G. Stein et al. (1976) op cir. 14. G. Baird and S. A. Chan. The Energy Cost of Houses and Light Construction Buildings, New Zealand Energy Research and Development Committee (NZERDC contract # 3175), Auckland, New Zealand (1983). 15. Ibid. 16, The Canadian Statistical and Socio-economie Information Management System (CANSIM Mainbase) data seeice of Statistics Canada is the source &national and regional data used in this research. 17, OECD, The Petrochemical Industry--Energy aspects of structural change, Organisation for Economic Cooperation and Development (1985). 18. Environment Canada. Canadian emissions inventory of common air contaminants (1985), Report EPS 5-AP-3. Otta~a (1990). 19. Statistics Canada, Human Actieity and The Emironment, Supply and Services Canada, Ottawa (1986). 20. U.S. EPA. Compilation @Air Emission FactorsJbr the 1985 NAPAP, National Technical Information Services, Wash., DC (1989). 21. G. Marland and R. M. Rotty, Carbon dioxide emissions from fossil fuels .... Carbon Dioxide Research Di~ ision, Report # DOE/NBB-0036 TR-003, US Dept. of Energy (1983). 22. N. Kohler(1991).opcit. 23. N. Kohler and Th. Lfitzkendorf. Energie- und Oekobilanzen yon Niedrigenergiegebduden. Statusseminar Energieforschung im Hochbau. EMPA-KWH, Zfirich (1990). 24. U.S. EPA (1989), op cir. 25. M. Sittig, Enz'ironmental Sources and Emissions Handbook, Noyes Data Corp., New Jersey (1975). 26. Environment Canada, Nationwide Inventory of Emissions of Air Contaminants (1976). Report # EPS 3-AP-80. Ottawa (1981). 27. Statistics Canada (19861. op cir, 28. P. Russell. S. Moffit and K. Cooper, Sustainable housing: Criteria, design tools and materials, Proceedings ~y'6th Canadian Building Congress, Toronto (Dec. 1990) (in press).
0360-132392$5.00-0.00 0 1902PergamonPresspie.
Pnntedin GreatBntain.
Environmental Auditing for Building Construction: Energy and Air Pollution Indices for Building Materials R A Y M O N D J. COLE* DAVID ROUSSEAU* The design community has a reasonable understanding of the factors which affect operational energy in buildings and has a rariety of computational tools for assessing it. By contrast, the broader encironmental consequences of producing and operating buildings are poorly defined. Since operating energy represents the current extent of em'ironmental attditing, a significant advance is to inchtde the energy and emissions associated with the production of construction materials. This paper outlines the key issues associated with environmental assessment of the production and use of materials and presents examples of energy and ah" pollution audits for four comparable commercial building assemblies with similar thermal resistances.
1. INTRODUCTION
2. ENVIRONMENTAL AUDITING
F R O M THE early 1970s until the mid-1980s there was a steady transformation from viewing energy and resource use as an ecological issue to an economic one [1]. However, with the broad-based resurgence of ecological preservation concerns in the late 1980s this trend is reversing. Resource use is now discussed within a broader environmental agenda, particularly in the context of global warming, ozone depletion and local and regional pollution. Changing the economic equation to include current hidden environmental costs and to restrain the rapid depletion of certain resources will radically affect the way building construction is viewed [2]. The significance for the construction industry will be the expansion of environmental auditing from a simple assessment of operating energy to include a broader assessment of resources used in building [3]. This will necessitate both an improved general understanding of the environmental consequences of buildings by design professional as well as access to comparative evaluations of the environmental impact of various building components and assemblies. In this regard, a significant step is to compile the energy use and environmental emissions associated with the production of construction materials. This paper outlines the key issues associated with environmental assessment of the production and use of materials, defining which are currently quantifiable, and presents a practical framework for energy and air pollution audits. The paper concludes with example energy and air pollution audits of four comparable commercial building assemblies with similar thermal resistances.
An environmental audit for building construction is an accounting of the quantifiable environmental factors that will be incurred in building production and use. reducing them to equivalent terms and presenting them in meaningful categories. The purpose of the audit is to add an environmental dimension to design decisions. An environmental audit includes both energy and nonenergy related factors, each of which has direct and indirect components : Direct environmental effects include : • Emissions of carbon oxides, oxides of sulphur, oxides of nitrogen, particulates and unburned hydrocarbons from combustion. • Air, water and solid waste impacts of material processing and handling. • Depletion of limited reserves of non-renewables. Indirect environmental effects include : • Damage to terrestrial and aquatic habitats due to energy production and industrial development. • Production of hazardous wastes with long-term consequences. The direct environmental effects of energy production and industry are typically more readily quantifiable than the indirect effects. 2.1 Quantifiable encironmental effects Environmental studies have produced considerable data on the environmental effects of the processes and materials associated with building construction, however very little is available in a form which is useful to the design professions. Some of the significant environmental factors associated with the production and maintenance
* Environmental Research Group, School of Architecture. University of British Columbia, Vancouver, BC. Canada. V6T IW5. BAE 27:1-C
23
R. J. Cole and D. Rousseau
24
of buildings for which there is environmental data available, but which cannot set be used comparatively in building design and operational decision making are : • The consumption of non-rene~vable energy and mineral resources incurred in the production of construction materials, components, and buildings • The pollution of air, water and soil incurred in the transformations of energy and mineral resources in all stages of materials and building production • The resources consumed and pollution incurred in the maintenance and replacement of building materials and assemblies over the life-span of the building • The recoverability of resources contained in buildings at the time of their demolition. The indirect consequences are extremely difficult to quantit) and probably are best characterized as "loss of ecological capital" [4]. The work presented in this paper pertains only to the direct environmental effects of building production and operation. Within this framework the scope is further limited to the energy consumption and air pollution factors. 3. ENERGY-RELATED FACTORS Energy related factors include all transformations of energy in the production and use of buildings. Though research in the mid-1970s clearly demonstrated that significant amounts of energy are required to produce a building [5, 6], energy accounting over the past fifteen years has focused almost exclusively on operational energy use in buildings and the development of strategies to reduce it. In the 1990s it is becoming increasingly important to resume the work on evaluating the energy for producing buildings and to extend it to embrace a broader environmental agenda.
3.1 Embodied eplergy A complete audit of a building will include the energy used to create building materials and components and to construct a building, i.e. the embodied energy. Embodied energy is the "'direct" and "'indirect" energy used to manufacture, transport and install building products. • Direct energy is the energy actually consumed in the construction of buildings. It represents the final transportation and installation of a component or assembly. Direct energy is a relatively small portion of embodied energy. European and U.S. figures estimate the construction portion to be about 7-10% of total embodied energy [7, 8]. • Indirect energy represents the energy consumed in the production of building materials and their associated transportation during processing. Indirect energy is the largest portion of embodied energy. It represents the production of a component exclusive of its transportation to and installation on site. Embodied energy thus represents the component or assembly in place. However. when full life-cycle analysis is undertaken, embodied energy should rightfully be extended to also include the energy associated with maintaining, repairing and replacing materials and components over the lifetime of the building.
3.2 Energy intensio' vahws Energy Intensity is the energy used only in the production of a building material or component. It represents the indirect energy in unit terms either expressed as energy/mass or volume such as M J kg or M J m 3 or energy/standard unit such as M J/sheet or block etc. Energy intensity is also calculated, from statistical data, in M J, $. Limited international research over the past 15 years in the field of energy intensities of building materials has produced reasonable agreement on acceptable values for some materials, but it has also produced some significant differences for others (see Table I). There are several reasons for these differences : • • • •
System boundaries Data source reliability International differences Thermal energy content of feedstock materials.
3.2.1 System boundaries. There is no absolute or correct energy intensity of a material [9]. A stated value is a direct function of what was included and what was excluded from its derivation. An example of the importance of system boundaries is readily found in comparisons of aluminum. Figures for the Canadian aluminum industry in 1976 indicate a value of 236.3 MJ/kg [10]. Although substantial efficiency improvements have been made since 1976 the figure is still reasonable today if one includes the energy costs of mining, concentrating and shipping ore, most of which is produced in the Caribbean. The Canadian figure compares well with those of Switzerland [11], Finland [12], and the U.S. [13]. New Zealand studies [14] however place aluminum at only 145 MJ/kg based on some limited reporting by industry and some analysis of the processes. New Zealand's ore, like Canada's, is also imported, but national statistics on the flow of energy and materials in the aluminum industry cannot be disaggregated from other non-ferrous metals. Assessment of energy intensity figures must, therefore, be accompanied by definitions and clear boundaries. The commonly accepted limit includes analysis of all of the industrial processes of extraction, transportation and processing of a material. This limit typically captures about 90% of the gross energy requirements of a manufactured item [15], but there may be important exceptions to this. For example in a case where highway transport of raw materials is a key (or dedicated) component of a manufacturing system, a portion of the energy capital and maintenance energy for the highways and vehicles should be included, and may significantly affect the analysis. The choice of level of analysis depends on the objective of the analysis, the available data and the type of evaluation methods. Ideally the system boundaries must include the following in order to reasonably reflect the embodied energy of materials and assemblies : . The energy requirements for extraction, beneficiation and transportation of raw materials. • The energy requirements for primary processing such as smelting, milling, drying, machining, chemical synthesis etc. as well as the transportation energy to the secondary stages.
Environmental Auditing for Building Construction
25
Table 1. Energy intensities of selected materials (MJ/kg) Material
Canada
U.S.
N.Z.
S~itz.
Finland
Metals Aluminum Nickel Steel (general) Zinc
236.3* 168.3" 25.7* 64.1"
192.0" 58.0* 39.0*
145.0" 261.7¢
189.0, 468.0t
Non-metallic minerals Glass (sheet) Gypsum Brick Glass wool Cement products Cement Concrete Mortar Plastics Polyethylene Polystyrene Paint (water base) : dry
32.0* 68.4*
27.7t 68.4* 21.6* 1.4+ 3. l't 18.0t
10.2, 7.4"1" 4.9:~ 22.3:[;
19.8" 7.2* 5.8* 14.0"
16.7"
5.9:~ 1.2++ 2.2:1:
9.4* 1.3"
7.4* 2.0*
87.0~ 105.0++ 76.0:[:
4.9"]" 0.9t 1.4"t 49.3t 122.8"t
77.7*
43.2t 16.5+ 2.8t 23.4t 4.9"t
118.8+ 76.7t
* Mid 1970s data, f Early 1980s data. ++Mid 1980s data.
• The energy requirements for secondary fabrication, assembly etc., where applicable. • The thermal energy potential of the raw material feedstock if it was to be used as a fuel (this applies specifically to petroleum based products). A more detailed analysis will also include the energy cost of producing energy. For example the energy cost of petroleum refining in Canada is 11.5% of production [16]. As the use of building materials with recycled content expands there must also be credits applied to the audit to reflect the energy and resource capital savings as well as pollution reductions from the use of recovered materials. There are practical limitations however, particularly in rapidly emerging areas such as recycling where reliable data is difficult to find. 3.2.2 Data sources and reliability. The data sources for energy intensity analysis are also problematic. There are three main sources of energy and production data for most industries, though all are not necessarily available. These are : • National statistics: Records compiled by national agencies from industry reporting. • Process analyses: Engineering analyses of processes accounting for energy use step-by-step. • Industry statistics : Records kept internally by plants or compiled by industry associations. Each data source has its shortcomings in application to energy intensity analysis and may not alone produce reliable results. By using several types of analysis however, one can judge the reliability of results through comparing the consistency of figures derived from different data sources. 3.2.3 International differences. There
are several
important factors which also affect international figures and, to some extent, even national figures. These are : • Fuel type: The most regionally available and inexpensive fuel source is likely to be used, within regulatory boundaries. For example, virtually all of Canada's aluminum is produced with hydroelectricity, while production in the U.K. uses some thermal electricity. This leads to very significant increases in gross energy input through the thermal conversion losses encountered in the U.K. • Raw materials imports: Some industries rely on imported raw materials for which the overseas extraction costs may be difficult to assess. The transportation factor also becomes more significant. Again, in the aluminum industry, Canada's production relies on ore imports from Jamaica where some of the primary processing also takes place. Energy costs and pollution figures are difficult to get. • Different accounting methods : For example, as noted before in New Zealand, many non-ferrous metal statistics are lumped together making it difficult to distinguish copper from aluminum, etc. A similar practice is used in Canada. 3.2.4 Energy content of feedstocks. Another problematic decision is the inclusion of the thermal energy content of the feedstock in the gross energy requirement. For those materials which are petroleum based it seems clear that the thermal value of their feedstocks, had they been burned as fuels, must reasonably be included. However should one use their theoretical thermal value, or their actual value when burned in a process of average efficiency? Many researchers have opted for the theoretical value and this explains the relatively high energy intensity for most synthetic resins [17]. 3.3 Direct environmental consequences of ener#y ,tse Energy use entails emissions of carbon dioxide, particulates, oxides of sulphur, oxides of nitrogen, carbon
26
R. J. Cole and D. Rousseau
monoxide and unburned hydrocarbons from combustion. The characteristics and air pollution consequences of these emissions are : • C O : - - o f primary concern as a greenhouse gas. • Particulates--primarily, carbon, with a range of associated mineral and metal compounds, primarily a local air pollutant. • SO_,--urban and regional effects both as an air pollutant and precursor to acidic precipitation. • NO~--urban and regional effects both as an air pollutant, photochemical oxidant and precursor to acidic precipitation. • C O - - o f primary concern as a local air pollutant. • H C - - a broad range of fugitive volatile organic compounds from uncombusted fuel, primarily of concern as photochemical oxidants. The proportions of these vary significantly with the type of fuel and the combustion efficiency. Table 2 shows typical emissions expressed as g,"MJ for common stationary (non-transportation) uses of conventional fuels [18-21]: 3.4 Air emission index Operating energy audits have the relative simplicity of being reducible to a common energy units. It is clearly more difficult to compare the relative effects of different pollutants within a particular medium (e.g. air) as well as between media (e.g. air, water and soil). Several European researchers employ an accounting system based on volume equivalents in which accepted limiting values are used to determine the volume of air which is polluted with a certain contaminant up to a limiting value [22]. The resulting polluted or consumed volumes of air are therefore equivalent units and can then be combined and used as simple indices to evaluate the degree of environmental air pollution associated with the material or component. For example, where the output of SO, is y mg and the admissible level of SO,. is x mg/m 3 of air, it can be transformed into m 3 of air contaminated to the allowable limit by : Used volume of air = y / x (m 3) A critical decision within this approach to aggregating air contaminants is the choice of acceptable limits [23]. Legislated limits, which are inevitably derived through compromise rather than direct health criteria, can relate to either emission rates from the plant or, more stringently, to ambient air quality. In the work reported in this paper. Canadian ambient air quality standards have
been chosen provisionally until international criteria t\~r environmental auditing have been agreed upon. The volume equivalents approach is suitable for tour of the major air contaminants which are usually regulated in national ambient air quality programs: Suspended particulates (from combustion), SO:, NO, and CO, The ambient air quality objectives set by' the Canadian Environmental Protection Act are presented in Table 3. Although the concentrations specified in the National Ambient Air Standards are very low and thus yield very high volumes of contaminated air, they do provide a useful relative basis for weighting the importance of different air pollutants. The important criteria is clearly the relative acceptable concentrations of the various contaminants. 4. NON-ENERGY RELATED FACTORS Energy related emissions account for only a portion of overall environmental effects from an industrial process. Process emissions refers to those emissions which are the direct result of smelting, kilning, distilling, drying. grinding, casting and all other industrial processes exclusive of fuel combustion. These include both the same categories of emissions associated with fuel combustion as well as a very wide range of other particulate and gaseous compounds. These additional compounds each have their own characteristics and environmental consequences, ranging from relatively benign dusts from overburden removed from mines, to highly toxic halogen compounds and heavy metals. In some cases, such as the cement industry, the energy emissions are the most significant factor in the overall assessment, because the process emissions include only some dusts (which are relatively low risk) and some water contamination (mostly with low risk solids). Metals smelting, on the other hand, produces a wide range of air emissions such as sulphur oxides from ore reduction, and fluorides, which are high environmental stressors. 4.1 Quantifvin 9 non-eneryy related emissions Non-energy related air emissions are relatively easy to characterize with some accuracy, but are difficult to quantify. For example dusts of predictable types are inevitably produced by dry milling processes, but varying degrees of dust controls are in place and varying amounts of trapped dusts are returned to the process. Data is available on "uncontrolled emissions" [24] which are derived from process studies, but data on the effectiveness and application of control measures is more difficult to
Table 2. Air emission by fuel and use Fuel use Distillate oil (conventional). 0.5% S Natural gas Coal (bituminous), 3% S Coal fired electricity Canadian electricity*
CO, (g/MJ)
Part. (g/M J)
SO: (g/M J)
NO, (g/M J)
CO (g/M J)
HC (g MJ)
72.1 50.5 87.5 248.9 52.3
0.0065 0.006 0.11 0.31 0.07
0.23 0.0002 0.85 2.36 0.50
0.2 0.09 0.27 0.75 0.16
0.015 0.007 0.060 0.170 0.040
0.0020 0.0080 0.0030 0.0080 0.0017
* Electricity production: Canadian split (62% hydro, 20.1% coal, 16% thermonuclear; 0.5% gas and 1.4% oil). Based on 35% overall efficiency for thermal production.
Environmental Auditing for Buildin9 Construction
27
Table 3. National Ambient Air Quality Objectives
Concentration Limit (g'm ~)
Particulates
SO:
NOx
CO
0.00012
0.00003
0.00006
0.006
find [25, 26]. There are also rapid developments in plant emissions controls which are driven by regulation. For example Statistics Canada reports that copper and zinc smelting are, by far. the largest industrial sources of SO~ emissions in Canada [27], however plant improvements are expected to alter that picture in a very short time. Other differences, such as the composition of raw materials, also introduce variables which are difficult to quantify. One brick kiln, for example, will produce markedly different emissions from another due to the composition of the clay. The characteristics and air pollution consequences of these non-energy related emissions are :
• NO~ from energy related processes • CO from both energy and non-energy related processes. The Air Emissions Index presented in this work is the aggregate of the volume equivalents generated from the four emission categories above. Given that the significance of an air pollution index is not in the actual units (m 3 for example) used, but in comparisons between the magnitude of the index derived for various materials or assemblies, they have been reduced by an arbitrary factor of 10-'. This gives the Air Emissions Index a more manageable scale.
• Particulates--a very broad range of carbon, mineral and metal compounds each with specific urban and regional air and soil effects. • SOz--urban and regional effects both as an air pollutant and precursor to acidic precipitation. • C O - - o f primary concern as a local air pollutant. • H C - - a broad range of volatile organic compounds, many of which are environmental toxins as well as photochemical oxidants. The nature, extent and proportions of these emissions are specific to each of several thousand processes within the materials industries.
5.3 Other air pollution indices Other air pollutant quantities are more difficult to convert into a common index because they comprise a collection of a number of different chemical compounds with widely varying environmental risks, each of which has to be evaluated separately. At this stage in the development of the air pollution indices these are grouped together in two categories and presented in association with the final Air Emissions Index. The categories are :
5. COMPONENTS OF AIR EMISSIONS INDICES
Further development of the air pollution indices will lead to a more detailed evaluation of the environmental impact of the various particulate emissions and fugitive hydrocarbons through assessing their various chemical categories and utilizing applicable concentrations for each. Once this is accomplished they will be in comparable terms to the Air Emissions Index and can be added to it.
An underlying premise of the work presented in this paper is that the large body of complex data on the energy and environmental implications of producing building materials must be reduced to manageable terms in order to be useful in environmental auditing of buildings. Some data can be readily reduced to a common unit while others cannot, and are more appropriately left discrete. Given the commonalities and differences of energyrelated and non-energy related emissions, the following approach has been adopted for summarizing them on a common basis.
5.1 Carbon dioxide CO., release from fuel combustion can be simply summarized as the mass of CO: created by the production of a unit of building material. Concentration limits are not applicable in the case of CO:, so it is simply presented as the "greenhouse gas contribution" of the material or assembly. 5.2 Air emission index The following can be reduced to a common index by the application of the volume equivalents method described in 3.4 using Ambient Air Quality Standards in Table 3 : • Particulates from fuel combustion • SO, from both energy and non-energy related processes
• Particulates from non-energy related processes • Fugitive hydrocarbons from both energy use and non-energy processes.
6. ENERGY AND AIR P O L L U T I O N AUDITS O F WALL ASSEMBLIES Material selection in the building industry is rarely made in isolation. Materials used in buildings can only reasonably be compared in the context of their performance in building assemblies. For purposes of environmental auditing, one must invariably compare alternative building assemblies offering similar performance characteristics [28]. Figure 1 shows sections of four non-load bearing wall assemblies used in commercial construction which all attain an approximate RSI = 3.6 m 2 Deg C/W : • Wall #1 is a precast concrete panel clad wall with rigid polystyrene board insulation and gypsum board interior finish. • Wall # 2 is brick clad construction with lightweight steel framing containing fibreglass insulation and gypsum board finishes. • Wall # 3 is an exterior insulation and finish system
R. J. Cole and D. Rousseau
28
.I ~ i
Material 75mm precast concrete panel Steel reinforcement Steel anchors (galvanized) Weather barrier (polyolefin) Steel flashings (galvanized) Steel furrings (galvanized) 75ram polystyrene insul, board 15mm interior gwb. (finished) 3 coats latex paint (0.3 litres) TOTAL
__
Wall
Mass/m 2 180.0 kg/m2 7.2 3.0 0.07 0.5 2.5 3.8 11.8 0.4 209.3 kg/m2
•
i
•
.
°
,"
i
Material Mass/m 2 lOOmmface brick (clay) 165.0 kg/m2 Mortar 28.0 Steel shelf angle (strut. steel) 4.0 Steel ties and screws (galvanized) 1.0 Weather barrier (polyolefin) 0.07 Sheathing (wp. gwb.) 9.8 150ram steel studs (galvanized) 10.0 150ram fiberglass batt insulation 5.4 Vapour barrier (polyethylene) 0.05 12.5ram interior gwb. (finished) 10.0 3 coats latex paint (0.3 litres) 0.4 TOTAL 233.8 kg/m2
U
~
m
Wall #2
[,
>-<...j
i/!i:: i:?. •
°
.
Wall #3
Material Mass/m 2 2 coats acrylic rood. stucco 6.0 kg/m2 Glass fiber mesh 0.8 19ram polystyrene insul, board 0.6 Steel fasteners and flashings (galv.) 1.0 Weather barrier (oolyolefin) 0.07 Sheathing (wp.gwb.) 9.8 100ram steel studs (galvanized) 6.9 100ram fiberglass batt insulation 3.6 Vapour barrier (polyethylene) 0.05 12.5ram interior gwb. (finished) 10.0 3 coats latex paint (0.3 litres) 0.4 TOTAL 39.3 kg/m2
Material Porcelain steel, or Anodized aluminum, or 6ram glass sheet Aluminum mullion/rail/spandrel Weather barrier (polyolefin) 150ram steel studs (galvanized) 150ram fiberglass batt insulation Vapour barrier (,polyethylene) 12.5ram interior gwb. (finished) 3 coats latex paint (0.3 litres) TOTAL
#1
Wall #4
Mass/m 2 9.6 kg/m 2 5.3 16.0 22.0 0.07 10.0 5.4 0.05 10.0 0.4 57.6 kg/m2 (Steel) 53.3 kg/m2 (Alum.) 64.0 kg/m2 (Glass)
. ° .
Fig. 1. Sections of non-load bearing wall assemblies used in commercial construction.
using acrylic stucco, polystyrene board insulation and lightweight steel framing with gypsum board finish. Wall # 4 is an aluminum curtain wall system with three alternative cladding panels: porcelain steel, aluminum, and glass. It incorporates fibreglass insu-
lation
and
gypsum
board
interior
finish.
Table 4 presents the total mass/m 2 and summary energy use and air pollution characteristics for the four wall assemblies in Fig. 1.
E n v i r o n m e n t a l Auditing f o r Building Construction
29
Table 4. Environmental characteristics of different wall assemblies Energy
Mass kgm-' Wall # I Wall #2 Wall #3 Wall #4: steel Wall #4: alum. Wall # 4 : glass
209.3 233.8 39.3 57.6 53.3 64.0
Emissions
Total Ref. Nat. energy Feedst. Pet. Gas Coal Elect. Other MJ/m2 MJ:mz MJ/m: MJ/m: MJ/m: MJ/m2 MJ/m2 1148 1799 929 6235 7263 5974
317 115 300 42 42 42
125 221 90 691 766 639
254 930 263 543 4ll 510
246 214 95 236 170 120
169 297 166 4715 5866 4656
37 22 16 8 8 8
CO: g 52200 90260 36700 113200 110700 94500
Part. : ,Air NonEmiss. Energy HC Index g g 2810 2850 1610 7710 7640 7240
1230 2230 420 630 560 580
310 560 220 370 260 260
Notes: • Total Energy; energy of wall assembly including feedstock energies. • Feedstock : gross thermal content of petroleum used in feedstocks for synthetic resins. • Fuels ; fuel use, by type, used in production of the component materials. • C02; total mass of CO., created by fuel combustion in the production of the assembly. • Air Emissions Factor: mass of particulates SO,, NO~, and CO, divided by their respective Canadian national ambient air quality maximum concentration limits. • Non-energy related particulates ; summary,of all particulates from processes. • HC; all fugitive hydrocarbons from both energy and non-energy related processes.
The energy summary includes : Total The total embodied energy of 1 m 2of wall Energy : assembly including feedstock energies. Feedstock : The feedstock energy represents the gross thermal content of petroleum used in synthetic resins. Feedstock energy is not included in the calculations of emissions from energy use. Fuels: These represent fuel use by type consumed in production of the component materials. Other fuels represents mainly the wood waste used in paper production for gypsum wall board and the waste rubber, wood etc. burned in cement kilns. The emissions are presented according to the four categories : C02 :
Air Emissions Index :
Non-energy related particulates : HC:
A summary of the mass of CO2 created by fuel combustion in the production of the assembly. Generated by summing all particulates and NO~ from energy use, SO2, and CO from both energy and non-energy processes, and dividing them by their respective Canadian national ambient air quality maximum concentration limits (Table 3). A summary of all particulates from processes based on the emission factors and typical control efficiencies from the data. All fugitive hydrocarbons from both energy and non-energy related processes, also incorporating typical control efficiencies, These reflect emissions from boilers, coal coking, polymer production, degreasing etc. Both particulates and HCs represent far too wide a range of chemical compounds to readily convert to air emissions factors at this time, and are therefore presented separately.
Emissions from fuel use are calculated from the fuel
factors given in Table 2 except the electricity used in primary aluminum production which is assumed to be all hydro in Canada. 6.1 Key observations The following observations can be made : • It is often assumed that low mass construction implicitly has low environmental consequences. This comparison shows that, although the lowest mass assembly (Wall #3) does indeed demonstrate this point, others with similar mass (Wall # 4) have energy and air emissions that are greater by an order of magnitude. • Even within the family of non-metallic mineral materials with similar mass, there are distinct differences in energy intensity and CO_, emission. Wall # 1, for example, entails the emission of 52.3 kg of CO.,. Wall # 2, despite having similar mass, entails 90.25 kg. However the Air Emissions Index of these two wall assemblies is almost identical. • The very high embodied energy figures for the walls which are largely composed of steel and aluminum are also reflected in proportionally higher COz production and Air Emissions Index. However, what is not reflected in these figures is the inherent capacity to eventually reduce a significant portion of future environmental costs through recycling. • Although the selection of a glass cladding panel in Wall # 4 has little effect on mass, there are distinct reductions in embodied energy, CO: emission and the Air Emissions Index.
7. CONCLUSION This paper has presented key characteristics of environmental auditing as well as examples of audits in use. It is clear that embodied energy is only one part of environmental auditing: environmental emission from both energy use by fuel type and non-energy related
30
R. J. Cole and D. Rousseau
process emissions are. in man5 cases, more significant indicators of the environmental cost of materials. Environmental audits, including energy use for materials production and installation as well as air pollution indices can provide criteria for design decisions when choosing materials and assemblies offering similar performance for a given application. Generalities about the environmental impact of materials choices do not stand up well due to the distinct and markedly different environmental attributes of the families of materials used
for comparable applications, e.g. non-metallic minerals are fundamentally different from metals. Acknowledgements--Funding for on-going research is provided by an operating grant from The Natural Sciences and Engineering Research Council of Canada (NSERC). The authors also wish to acknowledge the research assistance of Beate NemethWinther, Robert Boyd and Gary Helps, and extend this acknowledgement to Dr Niklaus Kohler at LESO. Swiss Federal Institute of Technology Lausanne. for offering direction in the formative stages of the project.
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