- Email: [email protected]
Benchmarks for sustainable construction
Energy and Buildings 37 (2005) 1147–1157 www.elsevier.com/locate/enbuild
Benchmarks for sustainable construction A contribution to develop a standard M. Zimmermann a,*, H.-J. Althaus b, A. Haas c a
Centre for Energy and Sustainability in Buildings (ZEN), Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, CH-8600 Du¨bendorf, Switzerland b Technology and Society Laboratory (TSL), Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, CH-8600 Du¨bendorf, Switzerland c Laboratory for Energy Systems/Building Equipment, Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, CH-8600 Du¨bendorf, Switzerland
Abstract Sustainability has been enshrined as a goal of society to ensure that the satisfaction of present needs does not compromise the ability of future generations to meet their own needs. It is thus a social objective, achievable only where all areas of society co-operate in fulfilling the associated demands. Ecological sustainability is, in turn, a basic prerequisite for sustainable economic and social development. The first step in formulating an effective response to this challenge, focused solely on the environmental issues, entails a quantification of the contribution required from the various areas of human activity for the achievement of sustainable development. Without binding sub-targets for the different sectors, it will be all but impossible to move systematically towards a sustainable society. These benchmarks for sustainable construction therefore set out to define the requirements to be met by buildings and structures in contributing to the achievement of a sustainable society. The permissible impact of buildings, in terms of energy demand and pollutant loads, during construction, maintenance and operation is determined. The analysis focuses on identifying the permissible levels of loads based on the specific energy consumption per m2 and year for heating, hot water, electricity and construction. A conscious attempt is made to combine existing methods with the general political consensus by taking account of: ¨ kobilanzen mit der Methode der - the ecological scarcity method [G. Brand, A. Scheidegger, O. Schwank, A. Braunschweig, Bewertung in O o¨kologischen Knappheit (Life cycle analysis using ecological scarcity method), Environmental Publication no. 297, Swiss Agency for the Environment, Forests and Landscape (SAEFL), 1997] used to define critical pollutant loads; - the limitation of greenhouse gas emissions specified by the intergovernmental panel on climate change (IPCC) [Intergovernmental Panel on Climate Change, Climate Change 2001, IPCC Third Assessment Report, www.grida.no/climate/ipcc_tar/]; - the demands of the 2000 W society [Leichter leben – Ein Versta¨ndnis fu¨r unsere Ressourcen als Schlu¨ssel zu einer nachhaltigen Entwicklung – die 2000-Watt-Gesellschaft (Easier living – understanding our resources as the key to sustainable development – the 2000 Watt society), novatlanis, sia, energieschweiz, January 2005] for the conservation of energy resources. The study shows that buildings designed to the Passive House standard just about comply with the requirements for sustainable construction, provided electricity generation is based largely on renewable or low-CO2 resources (Swiss power supply mix). The targets are substantially harder to meet where mainly fossil-fuel-generated electricity (European supply mix UCTE) is used. # 2005 Elsevier B.V. All rights reserved. Keywords: Sustainable housing; Environmental benchmarks; 2000-W society; Sustainable construction; Environmental impact
1. Preliminary considerations
* Corresponding author. Fax: +41 44 823 4009. E-mail address: [email protected] (M. Zimmermann). 0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2005.06.017
The principle of sustainability is based on the premise that society should use the available resources on a scale consistent with the ability of future generations to meet
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their own needs. The achievement of sustainable development thus necessitates a concerted effort in all areas of society to meet the appropriate criteria. Yet, if – as in Ref. [1] – sustainability is defined as a state in which a stable social order underpinned by a suitable economic framework can prevail in the long term without overtaxing the earth’s overall ecological capacity, provision needs to be made for quantifying the contribution required from the various areas of human activity to achieve such a sustainable society. Sustainability depends on the establishment of a consensus regarding the contribution to be made by each sector, e.g. buildings. In this case, for instance, the permissible buildingspecific environmental loads compatible with overall sustainability targets need to be specified. Without binding sub-targets for the different sectors, it will be almost impossible to move systematically towards a sustainable society. This standard for sustainable construction therefore endeavours to define the requirements that have to be met by buildings in Switzerland if these are to make an appropriate contribution to the achievement of a sustainable society. Particular priority is attached to determining the permissible pollutant loads resulting from the construction, maintenance and operation of a building. 1.1. Ecological capacity of the environment Scientists have not yet conclusively determined the absolute capacity of our ecosystem in acting as a sink for pollutants. Switzerland has nonetheless enacted various laws and ordinances to specify binding thresholds for a range of environmentally relevant materials. These thresholds represent a political compromise between potential environmental damage, risks, possible prevention and the associated costs. Critical flows derived from the thresholds are used in life cycle analysis as a basis for the ‘‘ecological scarcity’’ assessment method [2]. For the purposes of this study, ecological sustainability is defined as that state in which none of the flows exceeds the relevant critical flow derived from the thresholds. In this respect, it is not the consumption of material resources per se, but much rather the resulting pollutant emissions that are currently regarded as an obstacle to sustainable development. Energy resources represent a key exception due to our heavy economic and social dependence on a secure energy supply. The concept of the 2000 W society developed by the ETH Domain focuses on the requirements for a sustainable energy supply. The vision foresees a global per capita energy use of 2000 W (17,500 kWh/a primary energy), a figure slightly above the present worldwide average. This quota is designed to ensure that all societies are provided with adequate energy resources to develop and achieve an appropriate level of prosperity. The ultimate goal is to promote economic and social sustainability. Yet, if global warming is to be stabilized and natural resources conserved, only around 500 W can be generated
Fig. 1. Basic consumption sectors as shown in the energy statistics. The figure for buildings considers all building types, also the construction and operation of industrial and commercial buildings.
by fossil fuels, the balance of 1500 W being met by renewable energy sources. This will allow compliance with the Intergovernmental Panel for Climate Change (IPCC [3]) target of approximately 10 Gt CO2 emissions (3 Gt carbon) p.a. (long-term temperature rise of 2 K). Given an assumed global population of 10 bn, this approximates to 1 tonne CO2 emissions per capita. 1.2. Requirements for solution procedure - The procedure adopted to define the benchmarks shall allow specification of thresholds for specific consumption sectors (Fig. 1), e.g. housing. These sectors together shall cover all human activities with an environmental impact. - The thresholds presented in the study shall be calculated on the basis of data provided by regular surveys. This will facilitate future updating. - The procedure adopted in the standard shall allow consistent threshold specification so as to ensure that all sectors together do not exceed the permissible load.
2. Solution procedure Four steps are needed to determine thresholds for the maximum acceptable environmental load per building unit (m2 floor area and year) in line with Switzerland’s sustainability targets (Fig. 2): - The first step is to establish the maximum acceptable total environmental load consistent with sustainable development. The relevant pollutant data for Switzerland have ¨ kobilanzen mit der been compiled in ‘‘Bewertung in O Methode der o¨kologischen Knappheit’’ (Life cycle analysis using ecological scarcity method) [2]. - Second, the proportion of the total permissible load, as defined in Step 1, allocable to the construction sector is determined. No standard or generally recognized procedure exists here. This standard puts forward a proposal. - The third step involves definition of the functional unit to which the assessment relates. This may, in the case of housing, be 1 m3 building volume, 1 m2 heated floor area
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Fig. 2. Procedure to determine sustainability of a building. Steps 1–3 serve to define threshold. Step 4 involves determination of effective values for building.
or a dwelling unit to be more closely specified. In this study 1 m2 heated floor area was used as functional unit to allow a link to the existing energy related building regulations. - Finally the calculation, for a particular facility, of the effective environmental load per functional unit and its comparison with the predetermined thresholds must be feasible.
3. Possible loads for specific consumption sectors The following section examines several options for breaking down the total permissible load in order to determine thresholds for specific consumption sectors. While a simple extrapolation of the previous distribution, i.e. the uniform downscaling of loads across all sectors to a sustainable level, would doubtless be the simplest allocation method, this would fail to allow for future trends, e.g. the growing importance of IT and transport or fundamental new technologies. It seems essential that the selected allocation method should allow for the requirements and potential of future developments. Three methodological approaches were investigated: 3.1. Threshold specification using quotas extrapolated from prior breakdown This approach starts from the previous situation and shares out the sacrifices, i.e. required cuts in environmental loads, proportionally among the different sectors. This method fails to make allowance for any progress achieved to date or for any future shifts in particular sectors and simply infers the future situation from the past. Definition of when the ‘‘future’’ begins/began is also required, 1990 being the standard cut-off point adopted for this purpose.
3.1.1. Background data A detailed survey into the environmental impact of interesting technologies, products and services would be needed, along with the possibility of allocating the loads to the various sectors. The simplest option would be to derive the required data from the associated energy flows, as detailed in the energy statistics. 3.1.2. Sectors The breakdown by sectors depends on the level of classification detail implemented in databases. The energy statistics contain data for households (i.e. housing). Appropriate procedures are needed to provide data for other commercial/industrial-sector buildings. 3.1.3. Dynamic adjustment The dynamic adjustment of sustainability targets is impossible. Regular updating of sustainability goals would be counterproductive in that it would punish the ‘‘model’’ sectors while rewarding the ‘‘problem children’’. 3.1.4. Regulating effect In the long run – and the achievement of a sustainable society is a long-term objective – the extrapolation of the previous distribution without dynamic adjustment is undesirable as this would fail to take account of new or shifting needs in society. 3.2. Threshold specification using quotas based on projected trends by sector This approach is based on the assumption that the potential to cut energy use and environmental loads varies between different technologies. The permissible environmental loads would be apportioned according the predicted significance and needs of the various sectors.
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Fig. 3. Expenditures as shown in the household surveys conducted by the Swiss Federal Statistical Office. The figure for habitation and energy is representing the share for residential buildings (Survey 2002).
3.2.1. Background data The prerequisite here would be regular across-the-board forecasts of trends in technology and demand, together with the derived environmental impacts of the different sectors. There is currently no institution that conducts surveys of this scope. 3.2.2. Sectors The simultaneous monitoring of technologies and demand would tend to blur boundaries. The monitoring of technologies alone, under the assumption of constant demand, would unduly simplify the breakdown. 3.2.3. Dynamic adjustment Dynamic adjustment is feasible, provided forecasts are regularly updated. 3.2.4. Regulating effect The regulating effect only operates where the forecasts address technological potential. Projections must not simply specify the anticipated demand, as this would create little incentive for change. 3.3. Threshold specification based on share of consumer spending per sector This approach starts from the notion that people – with their basic and luxury needs – are both the cause of and sole justification for all environmental impacts. The breakdown of household spending among the various (consumption) sectors reflects the consumers’ implicit evaluation of their needs. This ‘‘assessment’’ is applied to the distribution of permissible loads. The quota of permissible environmental loads assigned to the individual sectors is therefore equal to their respective share of average consumer spending. That portion of the permissible environmental impact not occurring during product use or service provision is passed on, through payment, to the manufacturers or disposal agents. The business community is thus provided with a ‘‘load budget’’ to cover all environmental loads caused by its
activities, the necessary infrastructure, e.g. buildings, along with the loads from all upstream processes. 3.3.1. Background data Given the regular household surveys conducted by the Swiss Federal Statistical Office, up-to-date information is permanently available for residential buildings (Fig. 3). Hardly any data exist from which thresholds for commercial facilities can be derived. The cost structure data regularly published by associations for particular business sectors may be used to supplement the official statistics. 3.3.2. Sectors The ‘‘consumption’’ for residential buildings is well charted by statistics. The production of goods and services is the overriding perspective for commercial facilities. The available business statistics, however, are primarily geared to sectors from which no data on specific building categories can be derived. 3.3.3. Dynamic adjustment Dynamic adjustment is relatively straightforward in the case of residential buildings given the regular availability of data from surveys. Commercial facilities are subject to the above qualifications regarding data provision. 3.3.4. Regulating effect Though it clearly expresses the social significance of consumption, consumer spending is not directly linked to the imposed environmental loads. There is a danger of allocating environmental quotas to sectors where no environmental impact occurs or vice versa. No significant regulating effect can be achieved in the absence of suitable instruments for trading with load quotas. 3.4. Overall assessment None of the models represents a convincing regulating tool for the achievement of sustainable development
M. Zimmermann et al. / Energy and Buildings 37 (2005) 1147–1157 Table 1 Evaluation of allocation models for permissible environmental loads (++: very good, +: good, O: average, : poor and : very poor) Data
Sectors
Adjustment
Effect
a. Extrapolated loads
+
O
b. Projections Technology Demand
O
O
+ +
+
c. Spending-based Household Business
+
++ O
+ +
(Table 1). While a fair apportionment of permissible loads (i.e. one reflecting the given potential) should, as far as possible, be sought, this should also create incentives to meet the targets. In terms of effect, an allocation system derived from reliable forecasts is likely to produce the best results. Yet, the data and models necessary to achieve a consensus solution are lacking. Load extrapolation currently represents the fairest allocation model as it is based on the actual present situation. Its drawback lies in its inability to allow for future changes. While the spending-based system exhibits good adaptability to relative future shifts, it cannot – when used in isolation – be directly correlated to the assessment of environmental loads.
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4.2. Sectors The breakdown by sector depends on the classification detail permitted by the determined environmental load and household spending data. 4.3. Dynamic adjustment Dynamic adjustment is achieved by making allowance for actual spending. This approach may be problematic in the extreme long term should major social and technological change occur. In the short-to-medium term, however, it offers an appropriate means of factoring in growth and shifts in consumer behaviour. 4.4. Regulating effect The specification of a starting point implies the adoption of specific base data, e.g. for 1990, for use in load allocation. Any technological advances and optimisations achieved before this date effectively amount to a handicap in that they reduce the claim to future loads. However, this downside has to be accepted. As any progress made in meeting the permissible environmental loads is fully taken into consideration and not cancelled out by subsequent respecification of the thresholds, the method is very effective in regulating developments.
4. Proposed allocation method for permissible loads 5. Determination of permissible environmental loads A useful allocation model may be created by combining two of the systems described above: - apportionment of permissible loads based on situation to date (uniform downscaling); - adjustment of permissible loads based on shifts in spending. Account is taken of present-day realities through the integration of current environmental loads in the model. Regular adjustment in line with changes in spending provides for a long-term view of growth and consumption/investment behaviour. Such a model, however, fails to allow for the achievements to date and future optimisation potential. The model assumes that all sectors exhibit equal scope for improvement. Technological development is seen as an incentive and not as a reason for redistributing the permissible loads. 4.1. Background data Three distinct data sources are required: - data on previous loads for sectors and processes/ technologies; - data on household spending, to allow for shifts; - data on functional units for considered sectors.
5.1. Definition Buildings shall be classed as (ecologically) sustainable where the environmental loads resulting from their construction, operation and demolition/dismantling and their energy demand do not exceed their allotted share of the permissible environmental loads. The permissible environmental loads are defined as the critical pollutant flows determined by the ecological scarcity method [2] and the permissible greenhouse gas emissions specified by the IPCC [3]. Permissible energy use is specified as the primary energy demand target defined for the 2000 W society [4]. The total permissible environmental load is broken down into permissible quotas for each sector using the ratio of loads by sector to total loads in 1990 and an adjustment factor reflecting post-1990 changes in the sector’s social significance (Fig. 4). The permissible load of a particular sector (e.g. housing) may be determined as follows: Lhousing crit ¼
Ltot crit Lhousing 1990 Iexpenditures Ltot 1990
where Lhousing crit is the critical load for housing, Lhousing 1990 the load for housing in 1990, Ltot crit the critical overall load
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Fig. 4. Present compliance with pollutant thresholds based on ecological scarcity assessment method [2] (total loads, basis: 1997). Half of the recorded environmental loads currently exceed the critical value (100%) and have to be cut.
(current data for 1997 [2]), Ltot 1990 the overall load in 1990 and Iexpenditures is the index expressing share of sectoral spending in relation to 1990 share. 5.2. Calculation The permissible loads are determined in three steps: - determination of load breakdown in base year (1990); - uniform downscaling of loads in compliance with critical flows; - adjustment of permissible loads to reflect shifts in economic significance. 5.2.1. Load breakdown in 1990 The load breakdown is based on the Swiss Total Energy Statistics, which, particularly for the household (housing) sector, present a reasonably faithful picture. These figures cannot be directly applied for other (commercial/industrial) facility types as they fail to distinguish between buildings and processes. They must therefore be supplemented by estimates based on construction-sector data and life cycle analyses. To this end, estimates were prepared for the individual building classes including commercial/ industrial buildings. The calculation comprised the following steps: - Calculation of the operating energy for heating/hot water and domestic power for the various building categories based on their energy reference floor area (ERFA) [5] and representative energy indices. - Estimation of aggregate energy demand for construction and refurbishment for the individual building categories. This was based on a detailed model calculation for a multifamily home (i.e. apartment block) performed with the OGIP [6] programme, with appropriate adjustment for the different building categories.
- Reconciliation of final building-specific energy values with Swiss Total Energy Statistics [7]. - Conversion of final energy demand into primary energy using conversion factors from ecoinvent v1.1 [8] (oil/gas: 1.31, UCTE electricity 3.57, construction processes 1.85). - Determination of environmental loads. The ecoinvent v1.1 [8] inventories for individual energy carriers were applied for direct energy use, while an outline ecoinvent analysis of the environmental impact of a specimen building (multi-family home) was used for the construction processes. Table 2 shows the calculated energy demand values used as a basis for the uniform downscaling of loads in line with the critical flows. Fig. 5 illustrates the environmental loads imposed by residential buildings. 5.2.2. Calculation of critical flows Primary energy demand is used as the benchmark for checking compliance with the critical flows. Other values are less appropriate due to the lack of either suitable target values or present consumption details (Table 3). The permissible primary energy use is weighted in line with a sector’s growth of significance since 1990 using the change of the share of household spending by sector. As the proportion spent on housing and energy has risen slightly (by 2%) since 1990 [9], the permissible primary energy use for residential buildings may be increased by 2% (assuming that 2005 value approximates to 2002 value, no more recent figures being available). An equivalent rise may also be applied to other building categories, for which no separate statistics exist. 5.2.3. Calculation of target energy indices The target energy indices are calculated on the basis of the previous energy demand per building category and the existing energy reference floor area.
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Table 2 Energy statistics for 1990 [5], with separate posting of buildings (including industry and commercial buildings), used as basis for study (ERFA: energy related floor area)
I. Housing: multi-family homes
II. Housing: single-family homes
Million m2 ERFA 1990
Energy index MJ/(m2 a)
239.0
508 120 73
121330 28674 17443
Total MFH
167447
TJ real primary zenergy TJ
%
158913 83332 32340 21
274586
22
64383 11002 11460
Total SFH
86845
Heating, hot water Power, ventilation, air-conditioning Construction materials, production
11782 3699 3005
Total office buildings
18486
2
31754
3
Heating, hot water Power, ventilation, air-conditioning Construction materials, production
263340 58469 42839
34 8 5
382285 169923 79424
30 13 6
Total buildings
364648
47
631632
50
80760
10
149405
12
80050
10
148093
12
Transport
253470
33
332046
26
Total
778928
100
1261176
100
Total buildings
Industrial processes Commercial, service, agricultural sectors
38.5
539.4
562 96 100
Heating, hot water Power, including on-peak Construction materials, production
%
Heating, hot water Power, including on-peak Construction materials, production
III. Office/administration buildings
114.6
TJ real final energy TJ
306 96 78
488 108 79
Excluding construction sector, building operation Excluding construction sector, building operation
121698 31973 21247 11
174917
14
15432 10750 5572
Fig. 5. Relative environmental loads resulting from construction and operation of residential buildings (multi-family home, 1990). The value 1.0 is equivalent to the critical pollutant loads determined by the ecological scarcity method [2]. The electricity demand is assumed to be met by the European power supply mix (UCTE).
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Table 3 Percentage allocation of primary energy based on 1990 consumption
Total primary energy demand Primary energy demand for buildings Primary energy demand for multi-family homes
1990 (TJ)
2000 W society (TJ)
%
1299905 670361 293579
471214 247362 108330
100 52 23
The permissible primary energy demand envisaged by the 2000 W society [4] allows for a rise in population (2005 estimate: 7,471,050).
- 1990 energy reference floor area: 539.43 million m2; - 2005 energy reference floor area: 644.45 million m2 (projection [5]); - Change 1990–2005: +19.47%. As the 2005 energy reference floor area applies in determining the target energy indices, the 2% relative increase in household spending must be set alongside a nearly 20% increase in the floor area served. In calculating construction-sector energy indices (final energy), separate conversion is required for the three categories heating/ ventilation/hot water, power and construction/refurbishment. A uniform downscaling of the values for heating/ ventilation/hot water, power and construction/refurbishment in line with the targets of the 2000 W society [4] would, however, be unrealistic given the varying savings potential held by the three categories. The following assumptions were therefore adopted for the housing sector:
- construction/refurbishment: 15%; - power: Swiss Standard SIA 308/1 threshold 50%; - heating/ventilation/hot water: total minus share for power and construction/refurbishment. This allocation of saving potentials is very rough and should be investigated in more detail in a separate study. As the calculations show (Table 4), a standard of construction consistent with the 2000 W society [11] is just about feasible in Switzerland (Swiss power supply mix), at least in the housing sector, given mainly solar hot-water production in conjunction with a 50% cut in power compared to the SIA 380/1 thresholds [10]. Heating, hot water and ventilation energy indices of 80–110 MJ/(m2 a) are realistically achievable with the Passive House and Minergie-P standards. The 15% reduction in the primary energy content of construction materials should also be possible given appropriate design and product selection. The electricity demand, however, remains critical, particularly where the European power supply mix (UCTE) is used. This is true for the housing
Table 4 Energy indices for various building categories: 1990 Swiss mean, SIA 380/1 thresholds [10], 2000 W society targets given Swiss or UCTE power supply mix based on [8] Energy indices 1990 MJ/(m2 a)
SIA 380/1 MJ/(m2 a)
508 120 73
357 100 73
81 50 62
66 50 62
701
530
193
178
562 96 100
395 80 100
112 40 85
101 40 85
758
575
237
226
III. Office/administration buildings Heating, hot water 306 Power, ventilation, AC 96 Materials, production 78
215 80 78
18 40 66
7 40 66
I. Housing: MFH Heating, hot water Power, including on-peak Materials, production Total MFH II. Housing: SFH Heating, hot water Power, including on-peak Materials, production Total SFH
2000 W MJ/(m2 a) CH power
2000 W MJ/(m2 a) UCTE power
Total office buildings
480
373
124
113
Total buildings Heating, hot water Power Materials, production
488 108 79
343 90 79
80 45 68
67 45 68
676
513
193
180
Total buildings
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Fig. 6. Ecopoints relative environmental loads resulting from construction and operation of residential buildings applying the Minergie-P or Passive House standard (multi-family homes). The electricity demand is assumed to be met by the European power supply mix (UCTE).
sector, and even more so for the other building categories, where radical cuts in the energy demand for heating and ventilation are sometimes needed. In many cases, however, this reduction may be considerably offset through internal gains from power consumption. The hot water demand can also be largely ignored here. Further cuts in electricity demand, e.g. in office buildings, are nonetheless essential. 5.2.4. Calculation of environmental loads The key goal of the 2000 W society [4] is to secure a sustainable energy supply. The focus is on a fair distribution of the available energy resources and the mitigation of the greenhouse effect due to CO2 emissions. The standard for ecological construction aims to go one step further by preventing the release of harmful quantities of pollutants into the environment. The critical pollutants flows determined by the ecological scarcity method [2] serve as a benchmark here. Construction is deemed sustainable where the pollutant emissions arising from the production and operation of buildings and structures do not overburden these critical flows. The same calculation method as for primary energy demand is applied here, i.e. the available quota of critical pollutant flows for construction and operation in each case corresponds to the ratio of permissible primary energy to total primary energy demand. Analysis of the environmental impact of residential buildings that meet the targets of the 2000 W society [11] reveals that three of the 24 recorded emissions – nitrogen oxides, sulphur dioxides and chemical oxygen demand to water – significantly exceed the critical flow. The overall environmental impact only reaches around
75% of the critical value, while the release of greenhouse gases into the atmosphere marginally exceeds the critical level by a factor of 1.3 (Fig. 6). Where energy use is cut to the Minergie-P or Passive House standard, construction and refurbishment clearly emerge as a major source of environmental loads. Accordingly, progress will also depend on improvements in this field. A similar picture emerges when all building categories are considered together. This is due both to the predominance of the housing sector (which accounts for some 45% of the energy reference floor area) and to the fact that all calculations are based on the same eco-inventory dataset (ecoinvent v1.1, multi-storey building). Detailed analysis of a specific construction project may well produce different results.
6. Interpretation of results As the results show, the achievement of sustainable construction poses stiff challenges. Considerable efforts will be required to meet the primary energy targets for the 2000 W society [4], the CO2 emission targets set by the IPCC [3] and the pollutant emission targets determined by the ecological scarcity method [2]. These demands are set to increase in line with future population growth and, in particular, an expanding building stock. 6.1. Primary energy The limitation of per capita primary energy use to 2000 W represents the toughest target for sustainable development
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Table 5 Threshold values per capita Sector
Threshold values (per capita)
Percentage (%)
Total primary energy
Primary energy fossil
Primary energy renewable
CO2-Eq
All sectors (total)
2000 W 17500 kWh/a
500 W 4375 kWh/a
1500 W 13125 kWh/a
1000 kg/a 520 kg/a
100 52
Building sector
1040 W 9100 kWh/a
260 W 2275 kWh/a
780 W 6825 kWh/a
Housing sector
745 W 6475 kWh/a
186 W 1619 kWh/a
559 W 4856 kWh/a
370 kg/a
37
(Table 5). Even the reduction of present demand to a level below 40% is a major challenge. Of the available 2000 W, 1050 W may be used for the construction, maintenance and operation of the entire building stock, with 745 W for housing. The various energy demand values cannot be uniformly downscaled to a level below 40%. The low savings potential held by construction and refurbishment needs to be offset by disproportionately high cuts in operating energy consumption for heating and water consumption (Fig. 7).
6.3. Pollutant emissions Most pollutant emissions result from construction and refurbishment. Only two of the 24 recorded emissions, however, are problematic: - sulphur dioxide: mainly due to fossil-fuel power generation; - fine particulates: mainly caused by the degradation of mineral construction materials.
6.2. Greenhouse effect Compliance with the IPCC requirement of cutting greenhouse gas emissions (from the present 6) to 1 tonne CO2 equivalent [3] imposes no additional demands on the buildings sector, where the Swiss power supply mix is assumed—the reason being that the achievement of the 2000 W society already entails drastic cuts in fossil fuel consumption (housing: by a factor of 6.3). The low-CO2 power generation in Switzerland allows the IPCC targets to be met, if not surpassed in some cases. A different picture emerges where the European power mix (UCTE) is used in place of the Swiss supply. Here, the CO2 target would not be fully met. This ultimately reflects the increasing need to use renewable (wind, PV) or at least low-CO2 energy sources in generating European power.
The discharge of organic substances into water (COD) is chiefly a local problem; the critical flows are not achieved nationwide.
7. Outlook This study for sustainable construction has analysed various building categories and is described in detail in Ref. [11]. The calculations may be easily updated as soon as more accurate or recent data – ecological inventories in particular – are available for specific building classes. Likewise, the standard may be readily extended to cover other consumption sectors, e.g. transport. Only when each area of society knows its own specific targets and sets about meeting them, a sustainable society can be achieved.
References
Fig. 7. Threshold values for energy demand and greenhouse gas emissions for residential and office buildings (calculation based on average m2 energy related floor area per capita). Electricity demand figures are prominently at the primary energy level.
[1] WCED (World Commission on Environment and Development), Our Common Future, Oxford University Press, Oxford, 1987. [2] G. Brand, A. Scheidegger, O. Schwank, A. Braunschweig, Bewertung ¨ kobilanzen mit der Methode der o¨kologischen Knappheit (Life in O cycle analysis using ecological scarcity method), Environmental Publication no. 297, Swiss Agency for the Environment, Forests and Landscape (SAEFL), 1997. [3] Intergovernmental Panel on Climate Change, Climate Change 2001, IPCC Third Assessment Report, www.grida.no/climate/ipcc_tar/. [4] Leichter leben – Ein Versta¨ndnis fu¨r unsere Ressourcen als Schlu¨ssel zu einer nachhaltigen Entwicklung – die 2000-Watt-Gesellschaft (Easier living – understanding our resources as the key to sustainable development – the 2000 Watt society), novatlanis, sia, energieschweiz, January 2005.
M. Zimmermann et al. / Energy and Buildings 37 (2005) 1147–1157 [5] Wu¨est&Partner: Entwicklung des Geba¨udeparks (Building stock trends), August 1994. [6] S. Heitz, OGIP (Optimization of construction costs, energy consumption and environmental impact of buildings), http://www.the-software.de/BauenUmwelt.html. [7] Swiss Federal Office of Energy: Swiss Total Energy Statistics 1991, 3.34.92 d/f. [8] Ecoinvent – Swiss Centre for Life Cycle Inventories, ecoinvent data v1.1, June 2004, http://www.ecoinvent.ch.
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[9] Swiss Federal Statistical Office (BFS): 2002 Income and Consumption Survey, press release dated 15 July 2004. [10] Swiss Society of Engineers and Architects (SIA): Swiss Standard SIA 380/1: Thermische Energie im Hochbau (Thermal Energy in Buildings), SIA, Zurich, 2001. [11] M. Zimmermann, H.-J. Althaus, A. Haas, Benchmarks fu¨r die Beurteilung der Umweltvertra¨glichkeit von Hochbauten – Beitrag zur Entwicklung eines Standards fu¨r nachhaltiges Bauen, Empa, 2005.
Benchmarks for sustainable construction A contribution to develop a standard M. Zimmermann a,*, H.-J. Althaus b, A. Haas c a
Centre for Energy and Sustainability in Buildings (ZEN), Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, CH-8600 Du¨bendorf, Switzerland b Technology and Society Laboratory (TSL), Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, CH-8600 Du¨bendorf, Switzerland c Laboratory for Energy Systems/Building Equipment, Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, CH-8600 Du¨bendorf, Switzerland
Abstract Sustainability has been enshrined as a goal of society to ensure that the satisfaction of present needs does not compromise the ability of future generations to meet their own needs. It is thus a social objective, achievable only where all areas of society co-operate in fulfilling the associated demands. Ecological sustainability is, in turn, a basic prerequisite for sustainable economic and social development. The first step in formulating an effective response to this challenge, focused solely on the environmental issues, entails a quantification of the contribution required from the various areas of human activity for the achievement of sustainable development. Without binding sub-targets for the different sectors, it will be all but impossible to move systematically towards a sustainable society. These benchmarks for sustainable construction therefore set out to define the requirements to be met by buildings and structures in contributing to the achievement of a sustainable society. The permissible impact of buildings, in terms of energy demand and pollutant loads, during construction, maintenance and operation is determined. The analysis focuses on identifying the permissible levels of loads based on the specific energy consumption per m2 and year for heating, hot water, electricity and construction. A conscious attempt is made to combine existing methods with the general political consensus by taking account of: ¨ kobilanzen mit der Methode der - the ecological scarcity method [G. Brand, A. Scheidegger, O. Schwank, A. Braunschweig, Bewertung in O o¨kologischen Knappheit (Life cycle analysis using ecological scarcity method), Environmental Publication no. 297, Swiss Agency for the Environment, Forests and Landscape (SAEFL), 1997] used to define critical pollutant loads; - the limitation of greenhouse gas emissions specified by the intergovernmental panel on climate change (IPCC) [Intergovernmental Panel on Climate Change, Climate Change 2001, IPCC Third Assessment Report, www.grida.no/climate/ipcc_tar/]; - the demands of the 2000 W society [Leichter leben – Ein Versta¨ndnis fu¨r unsere Ressourcen als Schlu¨ssel zu einer nachhaltigen Entwicklung – die 2000-Watt-Gesellschaft (Easier living – understanding our resources as the key to sustainable development – the 2000 Watt society), novatlanis, sia, energieschweiz, January 2005] for the conservation of energy resources. The study shows that buildings designed to the Passive House standard just about comply with the requirements for sustainable construction, provided electricity generation is based largely on renewable or low-CO2 resources (Swiss power supply mix). The targets are substantially harder to meet where mainly fossil-fuel-generated electricity (European supply mix UCTE) is used. # 2005 Elsevier B.V. All rights reserved. Keywords: Sustainable housing; Environmental benchmarks; 2000-W society; Sustainable construction; Environmental impact
1. Preliminary considerations
* Corresponding author. Fax: +41 44 823 4009. E-mail address: [email protected] (M. Zimmermann). 0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2005.06.017
The principle of sustainability is based on the premise that society should use the available resources on a scale consistent with the ability of future generations to meet
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their own needs. The achievement of sustainable development thus necessitates a concerted effort in all areas of society to meet the appropriate criteria. Yet, if – as in Ref. [1] – sustainability is defined as a state in which a stable social order underpinned by a suitable economic framework can prevail in the long term without overtaxing the earth’s overall ecological capacity, provision needs to be made for quantifying the contribution required from the various areas of human activity to achieve such a sustainable society. Sustainability depends on the establishment of a consensus regarding the contribution to be made by each sector, e.g. buildings. In this case, for instance, the permissible buildingspecific environmental loads compatible with overall sustainability targets need to be specified. Without binding sub-targets for the different sectors, it will be almost impossible to move systematically towards a sustainable society. This standard for sustainable construction therefore endeavours to define the requirements that have to be met by buildings in Switzerland if these are to make an appropriate contribution to the achievement of a sustainable society. Particular priority is attached to determining the permissible pollutant loads resulting from the construction, maintenance and operation of a building. 1.1. Ecological capacity of the environment Scientists have not yet conclusively determined the absolute capacity of our ecosystem in acting as a sink for pollutants. Switzerland has nonetheless enacted various laws and ordinances to specify binding thresholds for a range of environmentally relevant materials. These thresholds represent a political compromise between potential environmental damage, risks, possible prevention and the associated costs. Critical flows derived from the thresholds are used in life cycle analysis as a basis for the ‘‘ecological scarcity’’ assessment method [2]. For the purposes of this study, ecological sustainability is defined as that state in which none of the flows exceeds the relevant critical flow derived from the thresholds. In this respect, it is not the consumption of material resources per se, but much rather the resulting pollutant emissions that are currently regarded as an obstacle to sustainable development. Energy resources represent a key exception due to our heavy economic and social dependence on a secure energy supply. The concept of the 2000 W society developed by the ETH Domain focuses on the requirements for a sustainable energy supply. The vision foresees a global per capita energy use of 2000 W (17,500 kWh/a primary energy), a figure slightly above the present worldwide average. This quota is designed to ensure that all societies are provided with adequate energy resources to develop and achieve an appropriate level of prosperity. The ultimate goal is to promote economic and social sustainability. Yet, if global warming is to be stabilized and natural resources conserved, only around 500 W can be generated
Fig. 1. Basic consumption sectors as shown in the energy statistics. The figure for buildings considers all building types, also the construction and operation of industrial and commercial buildings.
by fossil fuels, the balance of 1500 W being met by renewable energy sources. This will allow compliance with the Intergovernmental Panel for Climate Change (IPCC [3]) target of approximately 10 Gt CO2 emissions (3 Gt carbon) p.a. (long-term temperature rise of 2 K). Given an assumed global population of 10 bn, this approximates to 1 tonne CO2 emissions per capita. 1.2. Requirements for solution procedure - The procedure adopted to define the benchmarks shall allow specification of thresholds for specific consumption sectors (Fig. 1), e.g. housing. These sectors together shall cover all human activities with an environmental impact. - The thresholds presented in the study shall be calculated on the basis of data provided by regular surveys. This will facilitate future updating. - The procedure adopted in the standard shall allow consistent threshold specification so as to ensure that all sectors together do not exceed the permissible load.
2. Solution procedure Four steps are needed to determine thresholds for the maximum acceptable environmental load per building unit (m2 floor area and year) in line with Switzerland’s sustainability targets (Fig. 2): - The first step is to establish the maximum acceptable total environmental load consistent with sustainable development. The relevant pollutant data for Switzerland have ¨ kobilanzen mit der been compiled in ‘‘Bewertung in O Methode der o¨kologischen Knappheit’’ (Life cycle analysis using ecological scarcity method) [2]. - Second, the proportion of the total permissible load, as defined in Step 1, allocable to the construction sector is determined. No standard or generally recognized procedure exists here. This standard puts forward a proposal. - The third step involves definition of the functional unit to which the assessment relates. This may, in the case of housing, be 1 m3 building volume, 1 m2 heated floor area
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Fig. 2. Procedure to determine sustainability of a building. Steps 1–3 serve to define threshold. Step 4 involves determination of effective values for building.
or a dwelling unit to be more closely specified. In this study 1 m2 heated floor area was used as functional unit to allow a link to the existing energy related building regulations. - Finally the calculation, for a particular facility, of the effective environmental load per functional unit and its comparison with the predetermined thresholds must be feasible.
3. Possible loads for specific consumption sectors The following section examines several options for breaking down the total permissible load in order to determine thresholds for specific consumption sectors. While a simple extrapolation of the previous distribution, i.e. the uniform downscaling of loads across all sectors to a sustainable level, would doubtless be the simplest allocation method, this would fail to allow for future trends, e.g. the growing importance of IT and transport or fundamental new technologies. It seems essential that the selected allocation method should allow for the requirements and potential of future developments. Three methodological approaches were investigated: 3.1. Threshold specification using quotas extrapolated from prior breakdown This approach starts from the previous situation and shares out the sacrifices, i.e. required cuts in environmental loads, proportionally among the different sectors. This method fails to make allowance for any progress achieved to date or for any future shifts in particular sectors and simply infers the future situation from the past. Definition of when the ‘‘future’’ begins/began is also required, 1990 being the standard cut-off point adopted for this purpose.
3.1.1. Background data A detailed survey into the environmental impact of interesting technologies, products and services would be needed, along with the possibility of allocating the loads to the various sectors. The simplest option would be to derive the required data from the associated energy flows, as detailed in the energy statistics. 3.1.2. Sectors The breakdown by sectors depends on the level of classification detail implemented in databases. The energy statistics contain data for households (i.e. housing). Appropriate procedures are needed to provide data for other commercial/industrial-sector buildings. 3.1.3. Dynamic adjustment The dynamic adjustment of sustainability targets is impossible. Regular updating of sustainability goals would be counterproductive in that it would punish the ‘‘model’’ sectors while rewarding the ‘‘problem children’’. 3.1.4. Regulating effect In the long run – and the achievement of a sustainable society is a long-term objective – the extrapolation of the previous distribution without dynamic adjustment is undesirable as this would fail to take account of new or shifting needs in society. 3.2. Threshold specification using quotas based on projected trends by sector This approach is based on the assumption that the potential to cut energy use and environmental loads varies between different technologies. The permissible environmental loads would be apportioned according the predicted significance and needs of the various sectors.
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Fig. 3. Expenditures as shown in the household surveys conducted by the Swiss Federal Statistical Office. The figure for habitation and energy is representing the share for residential buildings (Survey 2002).
3.2.1. Background data The prerequisite here would be regular across-the-board forecasts of trends in technology and demand, together with the derived environmental impacts of the different sectors. There is currently no institution that conducts surveys of this scope. 3.2.2. Sectors The simultaneous monitoring of technologies and demand would tend to blur boundaries. The monitoring of technologies alone, under the assumption of constant demand, would unduly simplify the breakdown. 3.2.3. Dynamic adjustment Dynamic adjustment is feasible, provided forecasts are regularly updated. 3.2.4. Regulating effect The regulating effect only operates where the forecasts address technological potential. Projections must not simply specify the anticipated demand, as this would create little incentive for change. 3.3. Threshold specification based on share of consumer spending per sector This approach starts from the notion that people – with their basic and luxury needs – are both the cause of and sole justification for all environmental impacts. The breakdown of household spending among the various (consumption) sectors reflects the consumers’ implicit evaluation of their needs. This ‘‘assessment’’ is applied to the distribution of permissible loads. The quota of permissible environmental loads assigned to the individual sectors is therefore equal to their respective share of average consumer spending. That portion of the permissible environmental impact not occurring during product use or service provision is passed on, through payment, to the manufacturers or disposal agents. The business community is thus provided with a ‘‘load budget’’ to cover all environmental loads caused by its
activities, the necessary infrastructure, e.g. buildings, along with the loads from all upstream processes. 3.3.1. Background data Given the regular household surveys conducted by the Swiss Federal Statistical Office, up-to-date information is permanently available for residential buildings (Fig. 3). Hardly any data exist from which thresholds for commercial facilities can be derived. The cost structure data regularly published by associations for particular business sectors may be used to supplement the official statistics. 3.3.2. Sectors The ‘‘consumption’’ for residential buildings is well charted by statistics. The production of goods and services is the overriding perspective for commercial facilities. The available business statistics, however, are primarily geared to sectors from which no data on specific building categories can be derived. 3.3.3. Dynamic adjustment Dynamic adjustment is relatively straightforward in the case of residential buildings given the regular availability of data from surveys. Commercial facilities are subject to the above qualifications regarding data provision. 3.3.4. Regulating effect Though it clearly expresses the social significance of consumption, consumer spending is not directly linked to the imposed environmental loads. There is a danger of allocating environmental quotas to sectors where no environmental impact occurs or vice versa. No significant regulating effect can be achieved in the absence of suitable instruments for trading with load quotas. 3.4. Overall assessment None of the models represents a convincing regulating tool for the achievement of sustainable development
M. Zimmermann et al. / Energy and Buildings 37 (2005) 1147–1157 Table 1 Evaluation of allocation models for permissible environmental loads (++: very good, +: good, O: average, : poor and : very poor) Data
Sectors
Adjustment
Effect
a. Extrapolated loads
+
O
b. Projections Technology Demand
O
O
+ +
+
c. Spending-based Household Business
+
++ O
+ +
(Table 1). While a fair apportionment of permissible loads (i.e. one reflecting the given potential) should, as far as possible, be sought, this should also create incentives to meet the targets. In terms of effect, an allocation system derived from reliable forecasts is likely to produce the best results. Yet, the data and models necessary to achieve a consensus solution are lacking. Load extrapolation currently represents the fairest allocation model as it is based on the actual present situation. Its drawback lies in its inability to allow for future changes. While the spending-based system exhibits good adaptability to relative future shifts, it cannot – when used in isolation – be directly correlated to the assessment of environmental loads.
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4.2. Sectors The breakdown by sector depends on the classification detail permitted by the determined environmental load and household spending data. 4.3. Dynamic adjustment Dynamic adjustment is achieved by making allowance for actual spending. This approach may be problematic in the extreme long term should major social and technological change occur. In the short-to-medium term, however, it offers an appropriate means of factoring in growth and shifts in consumer behaviour. 4.4. Regulating effect The specification of a starting point implies the adoption of specific base data, e.g. for 1990, for use in load allocation. Any technological advances and optimisations achieved before this date effectively amount to a handicap in that they reduce the claim to future loads. However, this downside has to be accepted. As any progress made in meeting the permissible environmental loads is fully taken into consideration and not cancelled out by subsequent respecification of the thresholds, the method is very effective in regulating developments.
4. Proposed allocation method for permissible loads 5. Determination of permissible environmental loads A useful allocation model may be created by combining two of the systems described above: - apportionment of permissible loads based on situation to date (uniform downscaling); - adjustment of permissible loads based on shifts in spending. Account is taken of present-day realities through the integration of current environmental loads in the model. Regular adjustment in line with changes in spending provides for a long-term view of growth and consumption/investment behaviour. Such a model, however, fails to allow for the achievements to date and future optimisation potential. The model assumes that all sectors exhibit equal scope for improvement. Technological development is seen as an incentive and not as a reason for redistributing the permissible loads. 4.1. Background data Three distinct data sources are required: - data on previous loads for sectors and processes/ technologies; - data on household spending, to allow for shifts; - data on functional units for considered sectors.
5.1. Definition Buildings shall be classed as (ecologically) sustainable where the environmental loads resulting from their construction, operation and demolition/dismantling and their energy demand do not exceed their allotted share of the permissible environmental loads. The permissible environmental loads are defined as the critical pollutant flows determined by the ecological scarcity method [2] and the permissible greenhouse gas emissions specified by the IPCC [3]. Permissible energy use is specified as the primary energy demand target defined for the 2000 W society [4]. The total permissible environmental load is broken down into permissible quotas for each sector using the ratio of loads by sector to total loads in 1990 and an adjustment factor reflecting post-1990 changes in the sector’s social significance (Fig. 4). The permissible load of a particular sector (e.g. housing) may be determined as follows: Lhousing crit ¼
Ltot crit Lhousing 1990 Iexpenditures Ltot 1990
where Lhousing crit is the critical load for housing, Lhousing 1990 the load for housing in 1990, Ltot crit the critical overall load
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Fig. 4. Present compliance with pollutant thresholds based on ecological scarcity assessment method [2] (total loads, basis: 1997). Half of the recorded environmental loads currently exceed the critical value (100%) and have to be cut.
(current data for 1997 [2]), Ltot 1990 the overall load in 1990 and Iexpenditures is the index expressing share of sectoral spending in relation to 1990 share. 5.2. Calculation The permissible loads are determined in three steps: - determination of load breakdown in base year (1990); - uniform downscaling of loads in compliance with critical flows; - adjustment of permissible loads to reflect shifts in economic significance. 5.2.1. Load breakdown in 1990 The load breakdown is based on the Swiss Total Energy Statistics, which, particularly for the household (housing) sector, present a reasonably faithful picture. These figures cannot be directly applied for other (commercial/industrial) facility types as they fail to distinguish between buildings and processes. They must therefore be supplemented by estimates based on construction-sector data and life cycle analyses. To this end, estimates were prepared for the individual building classes including commercial/ industrial buildings. The calculation comprised the following steps: - Calculation of the operating energy for heating/hot water and domestic power for the various building categories based on their energy reference floor area (ERFA) [5] and representative energy indices. - Estimation of aggregate energy demand for construction and refurbishment for the individual building categories. This was based on a detailed model calculation for a multifamily home (i.e. apartment block) performed with the OGIP [6] programme, with appropriate adjustment for the different building categories.
- Reconciliation of final building-specific energy values with Swiss Total Energy Statistics [7]. - Conversion of final energy demand into primary energy using conversion factors from ecoinvent v1.1 [8] (oil/gas: 1.31, UCTE electricity 3.57, construction processes 1.85). - Determination of environmental loads. The ecoinvent v1.1 [8] inventories for individual energy carriers were applied for direct energy use, while an outline ecoinvent analysis of the environmental impact of a specimen building (multi-family home) was used for the construction processes. Table 2 shows the calculated energy demand values used as a basis for the uniform downscaling of loads in line with the critical flows. Fig. 5 illustrates the environmental loads imposed by residential buildings. 5.2.2. Calculation of critical flows Primary energy demand is used as the benchmark for checking compliance with the critical flows. Other values are less appropriate due to the lack of either suitable target values or present consumption details (Table 3). The permissible primary energy use is weighted in line with a sector’s growth of significance since 1990 using the change of the share of household spending by sector. As the proportion spent on housing and energy has risen slightly (by 2%) since 1990 [9], the permissible primary energy use for residential buildings may be increased by 2% (assuming that 2005 value approximates to 2002 value, no more recent figures being available). An equivalent rise may also be applied to other building categories, for which no separate statistics exist. 5.2.3. Calculation of target energy indices The target energy indices are calculated on the basis of the previous energy demand per building category and the existing energy reference floor area.
M. Zimmermann et al. / Energy and Buildings 37 (2005) 1147–1157
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Table 2 Energy statistics for 1990 [5], with separate posting of buildings (including industry and commercial buildings), used as basis for study (ERFA: energy related floor area)
I. Housing: multi-family homes
II. Housing: single-family homes
Million m2 ERFA 1990
Energy index MJ/(m2 a)
239.0
508 120 73
121330 28674 17443
Total MFH
167447
TJ real primary zenergy TJ
%
158913 83332 32340 21
274586
22
64383 11002 11460
Total SFH
86845
Heating, hot water Power, ventilation, air-conditioning Construction materials, production
11782 3699 3005
Total office buildings
18486
2
31754
3
Heating, hot water Power, ventilation, air-conditioning Construction materials, production
263340 58469 42839
34 8 5
382285 169923 79424
30 13 6
Total buildings
364648
47
631632
50
80760
10
149405
12
80050
10
148093
12
Transport
253470
33
332046
26
Total
778928
100
1261176
100
Total buildings
Industrial processes Commercial, service, agricultural sectors
38.5
539.4
562 96 100
Heating, hot water Power, including on-peak Construction materials, production
%
Heating, hot water Power, including on-peak Construction materials, production
III. Office/administration buildings
114.6
TJ real final energy TJ
306 96 78
488 108 79
Excluding construction sector, building operation Excluding construction sector, building operation
121698 31973 21247 11
174917
14
15432 10750 5572
Fig. 5. Relative environmental loads resulting from construction and operation of residential buildings (multi-family home, 1990). The value 1.0 is equivalent to the critical pollutant loads determined by the ecological scarcity method [2]. The electricity demand is assumed to be met by the European power supply mix (UCTE).
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Table 3 Percentage allocation of primary energy based on 1990 consumption
Total primary energy demand Primary energy demand for buildings Primary energy demand for multi-family homes
1990 (TJ)
2000 W society (TJ)
%
1299905 670361 293579
471214 247362 108330
100 52 23
The permissible primary energy demand envisaged by the 2000 W society [4] allows for a rise in population (2005 estimate: 7,471,050).
- 1990 energy reference floor area: 539.43 million m2; - 2005 energy reference floor area: 644.45 million m2 (projection [5]); - Change 1990–2005: +19.47%. As the 2005 energy reference floor area applies in determining the target energy indices, the 2% relative increase in household spending must be set alongside a nearly 20% increase in the floor area served. In calculating construction-sector energy indices (final energy), separate conversion is required for the three categories heating/ ventilation/hot water, power and construction/refurbishment. A uniform downscaling of the values for heating/ ventilation/hot water, power and construction/refurbishment in line with the targets of the 2000 W society [4] would, however, be unrealistic given the varying savings potential held by the three categories. The following assumptions were therefore adopted for the housing sector:
- construction/refurbishment: 15%; - power: Swiss Standard SIA 308/1 threshold 50%; - heating/ventilation/hot water: total minus share for power and construction/refurbishment. This allocation of saving potentials is very rough and should be investigated in more detail in a separate study. As the calculations show (Table 4), a standard of construction consistent with the 2000 W society [11] is just about feasible in Switzerland (Swiss power supply mix), at least in the housing sector, given mainly solar hot-water production in conjunction with a 50% cut in power compared to the SIA 380/1 thresholds [10]. Heating, hot water and ventilation energy indices of 80–110 MJ/(m2 a) are realistically achievable with the Passive House and Minergie-P standards. The 15% reduction in the primary energy content of construction materials should also be possible given appropriate design and product selection. The electricity demand, however, remains critical, particularly where the European power supply mix (UCTE) is used. This is true for the housing
Table 4 Energy indices for various building categories: 1990 Swiss mean, SIA 380/1 thresholds [10], 2000 W society targets given Swiss or UCTE power supply mix based on [8] Energy indices 1990 MJ/(m2 a)
SIA 380/1 MJ/(m2 a)
508 120 73
357 100 73
81 50 62
66 50 62
701
530
193
178
562 96 100
395 80 100
112 40 85
101 40 85
758
575
237
226
III. Office/administration buildings Heating, hot water 306 Power, ventilation, AC 96 Materials, production 78
215 80 78
18 40 66
7 40 66
I. Housing: MFH Heating, hot water Power, including on-peak Materials, production Total MFH II. Housing: SFH Heating, hot water Power, including on-peak Materials, production Total SFH
2000 W MJ/(m2 a) CH power
2000 W MJ/(m2 a) UCTE power
Total office buildings
480
373
124
113
Total buildings Heating, hot water Power Materials, production
488 108 79
343 90 79
80 45 68
67 45 68
676
513
193
180
Total buildings
M. Zimmermann et al. / Energy and Buildings 37 (2005) 1147–1157
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Fig. 6. Ecopoints relative environmental loads resulting from construction and operation of residential buildings applying the Minergie-P or Passive House standard (multi-family homes). The electricity demand is assumed to be met by the European power supply mix (UCTE).
sector, and even more so for the other building categories, where radical cuts in the energy demand for heating and ventilation are sometimes needed. In many cases, however, this reduction may be considerably offset through internal gains from power consumption. The hot water demand can also be largely ignored here. Further cuts in electricity demand, e.g. in office buildings, are nonetheless essential. 5.2.4. Calculation of environmental loads The key goal of the 2000 W society [4] is to secure a sustainable energy supply. The focus is on a fair distribution of the available energy resources and the mitigation of the greenhouse effect due to CO2 emissions. The standard for ecological construction aims to go one step further by preventing the release of harmful quantities of pollutants into the environment. The critical pollutants flows determined by the ecological scarcity method [2] serve as a benchmark here. Construction is deemed sustainable where the pollutant emissions arising from the production and operation of buildings and structures do not overburden these critical flows. The same calculation method as for primary energy demand is applied here, i.e. the available quota of critical pollutant flows for construction and operation in each case corresponds to the ratio of permissible primary energy to total primary energy demand. Analysis of the environmental impact of residential buildings that meet the targets of the 2000 W society [11] reveals that three of the 24 recorded emissions – nitrogen oxides, sulphur dioxides and chemical oxygen demand to water – significantly exceed the critical flow. The overall environmental impact only reaches around
75% of the critical value, while the release of greenhouse gases into the atmosphere marginally exceeds the critical level by a factor of 1.3 (Fig. 6). Where energy use is cut to the Minergie-P or Passive House standard, construction and refurbishment clearly emerge as a major source of environmental loads. Accordingly, progress will also depend on improvements in this field. A similar picture emerges when all building categories are considered together. This is due both to the predominance of the housing sector (which accounts for some 45% of the energy reference floor area) and to the fact that all calculations are based on the same eco-inventory dataset (ecoinvent v1.1, multi-storey building). Detailed analysis of a specific construction project may well produce different results.
6. Interpretation of results As the results show, the achievement of sustainable construction poses stiff challenges. Considerable efforts will be required to meet the primary energy targets for the 2000 W society [4], the CO2 emission targets set by the IPCC [3] and the pollutant emission targets determined by the ecological scarcity method [2]. These demands are set to increase in line with future population growth and, in particular, an expanding building stock. 6.1. Primary energy The limitation of per capita primary energy use to 2000 W represents the toughest target for sustainable development
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Table 5 Threshold values per capita Sector
Threshold values (per capita)
Percentage (%)
Total primary energy
Primary energy fossil
Primary energy renewable
CO2-Eq
All sectors (total)
2000 W 17500 kWh/a
500 W 4375 kWh/a
1500 W 13125 kWh/a
1000 kg/a 520 kg/a
100 52
Building sector
1040 W 9100 kWh/a
260 W 2275 kWh/a
780 W 6825 kWh/a
Housing sector
745 W 6475 kWh/a
186 W 1619 kWh/a
559 W 4856 kWh/a
370 kg/a
37
(Table 5). Even the reduction of present demand to a level below 40% is a major challenge. Of the available 2000 W, 1050 W may be used for the construction, maintenance and operation of the entire building stock, with 745 W for housing. The various energy demand values cannot be uniformly downscaled to a level below 40%. The low savings potential held by construction and refurbishment needs to be offset by disproportionately high cuts in operating energy consumption for heating and water consumption (Fig. 7).
6.3. Pollutant emissions Most pollutant emissions result from construction and refurbishment. Only two of the 24 recorded emissions, however, are problematic: - sulphur dioxide: mainly due to fossil-fuel power generation; - fine particulates: mainly caused by the degradation of mineral construction materials.
6.2. Greenhouse effect Compliance with the IPCC requirement of cutting greenhouse gas emissions (from the present 6) to 1 tonne CO2 equivalent [3] imposes no additional demands on the buildings sector, where the Swiss power supply mix is assumed—the reason being that the achievement of the 2000 W society already entails drastic cuts in fossil fuel consumption (housing: by a factor of 6.3). The low-CO2 power generation in Switzerland allows the IPCC targets to be met, if not surpassed in some cases. A different picture emerges where the European power mix (UCTE) is used in place of the Swiss supply. Here, the CO2 target would not be fully met. This ultimately reflects the increasing need to use renewable (wind, PV) or at least low-CO2 energy sources in generating European power.
The discharge of organic substances into water (COD) is chiefly a local problem; the critical flows are not achieved nationwide.
7. Outlook This study for sustainable construction has analysed various building categories and is described in detail in Ref. [11]. The calculations may be easily updated as soon as more accurate or recent data – ecological inventories in particular – are available for specific building classes. Likewise, the standard may be readily extended to cover other consumption sectors, e.g. transport. Only when each area of society knows its own specific targets and sets about meeting them, a sustainable society can be achieved.
References
Fig. 7. Threshold values for energy demand and greenhouse gas emissions for residential and office buildings (calculation based on average m2 energy related floor area per capita). Electricity demand figures are prominently at the primary energy level.
[1] WCED (World Commission on Environment and Development), Our Common Future, Oxford University Press, Oxford, 1987. [2] G. Brand, A. Scheidegger, O. Schwank, A. Braunschweig, Bewertung ¨ kobilanzen mit der Methode der o¨kologischen Knappheit (Life in O cycle analysis using ecological scarcity method), Environmental Publication no. 297, Swiss Agency for the Environment, Forests and Landscape (SAEFL), 1997. [3] Intergovernmental Panel on Climate Change, Climate Change 2001, IPCC Third Assessment Report, www.grida.no/climate/ipcc_tar/. [4] Leichter leben – Ein Versta¨ndnis fu¨r unsere Ressourcen als Schlu¨ssel zu einer nachhaltigen Entwicklung – die 2000-Watt-Gesellschaft (Easier living – understanding our resources as the key to sustainable development – the 2000 Watt society), novatlanis, sia, energieschweiz, January 2005.
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