Energy and building technology for the 2000 W society—Potential of residential buildings in Switzerland

Energy and Buildings 37 (2005) 1158–1174 www.elsevier.com/locate/enbuild

Energy and building technology for the 2000 W society—Potential of residential buildings in Switzerland A. Pfeiffer a,*, M. Koschenz a, A. Wokaun b a

Laboratory for Energy Systems/Building Equipment, Swiss Federal Laboratories for Materials Testing and Research (Empa), Ueberlandstrasse 129, 8600 Duebendorf, Switzerland b PSI, Paul Scherrer Institut, General Energy Research Department, 5232 Villigen, Switzerland

Abstract The 2000 W society, achievable through cuts in resource consumption and per capita CO2 emissions, is closely related to the goals of sustainable development. This study identifies the specific targets that need to be met both globally and by Switzerland to realize the vision. As a major energy consumer, the buildings sector will have to make a substantial contribution to meeting these targets. The report starts by examining the energy-saving potential of individual residential buildings through different combinations of building standard and building services system. Various building concepts already available today offer considerable potential and, as individual solutions, often achieve the targets of the 2000 W society. Yet, as the impact of such individual solutions on the building stock is dampened by a range of factors (e.g. long refurbishment cycles, low energy prices, scepticism of investors towards new technology), the effective gains fall far short of the theoretical potential. As the considered implementation scenarios and building stock projections show, the average buildings-sector targets required for the 2000 W society are nonetheless attainable. However, in order to tap the potential in the residential buildings sector, there is an urgent need for immediate action at various levels (e.g. through financial incentive systems, consumer information campaigns). # 2005 Elsevier B.V. All rights reserved. Keywords: 2000 W society; Energy-saving potential; Residential buildings; Primary energy use; Energy perspectives; Energy scenarios

1. Introduction The 2000 W society embodies the goals of sustainable social development. In environmental terms, the halting of climate change constitutes one of the most pressing challenges on the path to such a society. Hence, the necessity, especially in the industrialized nations, of cutting total energy consumption and per capita anthropogenic CO2 emissions in all spheres of life. Given the significance of these two factors as indicators for sustainable development, both total and fossil energy use are considered in the 2000 W society. In assessing the potential contribution of the buildings sector to the achievement of a 2000 W society, the study uses the Swiss residential building stock as an example. The impact of new technologies and their implementation, of structural changes in grid power generation and of building stock trends is * Corresponding author. Present address: Robert Aerni Engineering Ltd., Industriestrasse 24, CH-8305 Dietlikon, Switzerland. Tel.: +41 44 805 47 47; fax: +41 44 805 46 67. E-mail address: [email protected] (A. Pfeiffer). 0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2005.06.018

discussed. The energy-saving potential of residential buildings may be examined at two different levels. First, various permutations of building type, classed by energy standard (SIA, Minergie, Minergie-P), with specific building services systems are investigated. Here, the potential offered by the individual solutions currently available and by future technology is discussed. Yet, being subject to the refurbishment cycle of the building stock, these individual solutions are not amenable to immediate, broad implementation. The second part of the examination therefore focuses on the refurbishment of the building stock and accompanying implementation of the individual solutions. This approach ultimately promises to achieve the needed reductions. 2. Background 2.1. Vision of the 2000 W society The envisaged 2000 W society is targeted to achieving a sustainable development. Brundtland [1] defines sustainable

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1159

component of overall consumption by this time must therefore not exceed 500 W per person, the balance of 1500 W being met by a non-fossil, i.e. ‘‘CO2-free’’, source.

Fig. 1. Three aspects of sustainable development.

development as ‘‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’’. Sustainability may be assessed in terms of ecology, economy and society (Fig. 1). The first attempts to quantify an energy reduction scenario were undertaken by Kesselring and Winter [2]. Having coined the idea of a 2 kW society, they postulated its technical feasibility through energy-efficient conversion, coupled with a minimization of non-renewable and maximization of renewable energy use. In 1998, the concept of a 2000 W society was further developed in the ‘‘Strategy of Sustainability in the ETH Domain’’ [3]. The following sections set out to quantify the targets for fossil energy use in terms of CO2 emissions (Section 2.1.1) and for total energy use with reference to social and economic factors (Section 2.2.2). 2.1.1. CO2 emissions The halting of climate change and stabilization of atmospheric CO2 concentrations are two issues that loom large in the sustainability debate. Experts assume that atmospheric warming at a rate of 0.2 K per decade should pose no threat to biodiversity and the ecosystem. Using a study prepared by the Intergovernmental Panel on Climate Change (IPCC), Watson et al. [4] shows the need for a longterm stabilization of atmospheric CO2 concentrations at 550 ppmv to keep temperature rises at this level. Both the scenarios drawn up by Wigley et al. scenarios [5] and those of Enting et al. [6] describe possible CO2 emission trends that would stabilize CO2 concentrations. Both reports conclude that global per capita CO2 emissions must not exceed 1 tonne p.a. in the period 2150–2200. With fossil-fuel consumption accounting for the lion’s share of anthropogenic CO2 emissions, drastic cuts in fossil energy use are crucial. On the assumption that coal will be the only remaining fossil energy carrier available in 2150, 1 tonne of CO2 will roughly correspond to a continuous fossil-fuel-generated output of 500 W. The fossil energy

2.1.2. Social and economic aspects The study produced by Spreng et al. [7] shows the threshold of 63 GJ per capita primary energy p.a., equivalent to 2000 W per person, to be appropriate in ecological, economic and social terms. Per capita energy use is also proposed as the most suitable indicator for assessing sustainability. Goldemberg and Johansson [8] (Fig. 2) consider gross energy consumption in relation to the Human Development Index (HDI). The Human Development Index is a composite indicator developed by UNDP to show countries’ relative well being in social as well as economic terms. Gross energy consumption is defined as the primary energy needed within a country’s national borders, as determined by Auditing Method B (see Appendix A.1.2). Fig. 2 shows that a HDI of 0.8 or higher currently requires a minimum per capita energy use of 2000 W. It is important to note that a higher than five-fold rise in energy consumption does not significantly increase the HDI. It may thus be argued that 2000 W per capita primary energy is the basic amount required to ensure continuing economic prosperity. Without restructuring of the current energy supply, the long-term depletion of crude oil and, later, natural gas resources will eventually breed social and economic tensions that are present in embryonic form even today. The world’s energy supply is still primarily satisfied by fossil resources, some 80% of global demand being met by either crude oil, natural gas or coal. According to Jochem [9], a variety of factors necessitate the more efficient use of resources. This goal can, for instance, help mitigate the negative economic consequences of a surge in prices due to long-term crude oil depletion. A failure to embrace sustainable policies also seems likely to fuel the potential for international conflicts, as shortages grow. According to Campbell [10], the depletion mid-point for crude oil and natural gas will probably be reached in 2015. The depletion mid-point is defined as that point in time at which half the total estimated crude oil resources will be exhausted. From that time onwards, production constraints will gradually force down annual crude oil output. A wide range of forecasts have been assembled and compared by Rempel [11]. The comparison reveals widely diverging estimates, depending on source, regarding peak production—its occurrence being predicted some time between 2015 and 2065 for both conventional and non-conventional crude oil production. Given the likely availability of adequate coal reserves to meet the energy demand over the next 100–200 years, climate rather than resource issues will likely dominate the long-term agenda. 2.2. Energy reduction paths 2.2.1. Worldwide targets The vision of the 2000 W society assumes a reduction of annual per capita primary energy use in the OECD countries

1160

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

Fig. 2. Relationship between HDI and per capita energy use in kg oil equivalent (kgoe), 1999/2000, source: Goldemberg and Johansson [8], 2000 W corresponds to 1500 kg oil equivalent.

to 63 GJ, equivalent to an average 2000 W power. This is roughly equal to the present global average. By comparison, per capita energy use is currently around 5000 W in Europe and even tops 10,000 W in the USA. Fig. 3 shows past trends in per capita total and fossil primary energy use worldwide according to various energy statistics [12–14]. The CO2 emissions scenario set out in the IPCC studies [15–17] leading to a stabilization of CO2 concentrations at 550 ppmv may be used to calculate the maximum permissible worldwide fossil energy use. This, in conjunction with

various global demographic projections (United Nations [18], World Bank [19]), allows calculation of the permissible per capita fossil energy use (grey zone). The World Energy Council’s (WEC) [20] energy perspectives provide details of regional trends in primary energy use. Of particular note is Scenario C1, comparable to the 2000 W society in its ecological targets, which foresees a cut in CO2 emissions to 7.3 Gt by 2100. This scenario allows a breakdown of the maximum permissible fossil energy use by region.

Fig. 3. Maximum permissible total and fossil primary energy use worldwide for achieving a 2000 W society, source: Ref. [21].

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1161

Fig. 4. Maximum permissible total and fossil gross energy use in Switzerland for achieving a 2000 W society, source: Ref. [21].

2.2.2. Targets for Switzerland The cuts in current energy use rates in Switzerland required to achieve the 2000 W society will now be quantified. Auditing Method B (see Appendix A) is applied to determine primary energy demand within the national borders. This component of primary energy is, in the following, termed ‘‘gross energy use’’. Details of nationwide gross energy use in 1990 and 2000 are presented in the Swiss Total Energy Statistics [22]. Crude oil and natural gas products deliver for some 60% of energy use in Switzerland (3000 W). Nuclear power and renewable sources (at present,

almost exclusively hydropower) each contribute a further 1000 W. A national target for Switzerland is derived from the global fossil energy use targets dictated by the ecological constraints. Energy scenarios that reflect a sustainable climate policy foresee a halving of fossil energy use within 60 and 40 years for western Europe [20] and Switzerland [23], respectively (Fig. 4). Given the mandate of the Kyoto Protocol, implementation of the CO2 law [24] – which prescribes a 10% cut in CO2 emissions by 2010 compared to the 1990 figure – represents the key national objective. Moreover, to achieve a 2000 W society, Switzerland must

Fig. 5. Per capita gross energy use, broken down by building class and services installation.

1162

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

address the long-term goal of pushing down per capita CO2 emissions to 1 tonne [3], equivalent to an average fossilfuel-generated output of around 500 W. According to the IPCC, this goal needs to be met at the latest by the 22nd century. These figures may be used to develop a target path for fossil energy cuts. This envisages the achievement of a ‘‘fossil 2000 W society’’ by around 2030 (Fig. 4).

energy sources to meet the residual energy demand is a further key factor. Achieving these objectives requires consistent application of the following four principles:

3. Present situation

3.4. Reinvestment cycles for buildings

3.1. Relevance of buildings sector

Given the longevity of buildings, major opportunities to introduce new technology arise only every 40–50 years. In other words, a building erected today is very likely to exist in 2050. Achieving a ‘‘fossil 2000 W society’’ by 2030 will necessitate improvements during the next refurbishment cycle, to the energy efficiency of components.

The gross energy use in Switzerland may be broken down into several key consumers. The operation of residential buildings accounts for some 28% of overall consumption. A further 18% is needed by service-sector, industrial, agricultural and other commercial buildings. Added to that is the component of energy use in the industrial and transport sectors needed for the construction and refurbishment of buildings (10%). The total proportion required for the construction, operation and refurbishment of the built environment therefore exceeds 50% of nationwide gross energy use. The remaining energy is needed for general transport, industrial processes, etc. 3.2. Energy use of Swiss building stock A knowledge of the current gross energy use of buildings – including a detailed breakdown of final energy consumption by energy carrier, building class and energy-consuming equipment (space heating, hot water, electricity, etc.) – is essential for a clear definition of the starting point. As these data are beyond the scope of the energy statistics, they have been compiled using various existing surveys [25,26]. The embodied energy data for construction materials, site operations and transportation to site shown in Fig. 5 are based on the final energy use for the particular trades and the proportions allocable to the construction sector [26]. Building operation accounts for some 45% of overall consumption. If embodied energy is added, the building stock’s energy share exceeds 50%. As Fig. 5 shows, housing is responsible for some 60% of the gross energy use of the overall building stock, while 50% of energy is needed for space heating.

1. 2. 3. 4.

improved building envelope; changes in occupant behaviour; more efficient energy systems; use of renewables.

4. Boundaries 4.1. Energy demand of residential buildings The single-family house (SFH) used in Ref. [27] and shown in Fig. 6 is used in following calculations. Assuming a four-person occupancy, the associated heated floor area of 232 m2 (58 m2 per person), a figure roughly on par with the current Swiss average. The ratio of envelope area to heated floor area of 1.9 represents a typical value. The ratio of heated floor area to dwelling area is equal to 0.82. 4.1.1. Energy demand of present-day buildings Table 1 compares the energy demand for various building standards to the mean energy demand of Swiss households in 2000. Compared to the averages for 2000, the energy demand of a Minergie-standard building is reduced by a factor of 1.7–2.2 depending on the selected energy system, while the Minergie-P building exhibits a three-fold reduction, irrespective of building services system. A particularly sharp fall in space heating demand is observed in all cases. A Minergie building requires 2.1–3.4 times less heating energy, depending on the choice of energy system, while the equivalent figure for a Minergie-P building is a full seven times less. The electricity demand falls only slightly due to the enhanced requirements placed on equipment by

3.3. Savings potential of buildings The fact that the buildings sector currently accounts for some 50% of overall gross energy consumption makes it necessary focus on energy-saving and efficiency-boosting strategies. In view of the long lifespan of buildings, top priority must be given to cutting heating energy demand by means of an efficient building envelope. The energy demand may be further reduced through efficient conversion and the use of on site renewable energies (e.g. active and passive solar energy, ambient heat, etc.). The increasing use of non-fossil

Fig. 6. Geometry of investigated SFH with envelope ratio of 1.9.

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1163

Table 1 Energy demand (useful energy) per square metre energy reference floor area of present-day residential buildings Energy demand per square metre reference floor area

Swiss households, 2000 (MJ/m2a)

SIA target level [28] (MJ/m2a)

Minergie (MJ/m2a)

Space heating Domestic hot water Ventilation electricity Domestic electricity

347a 59a –e 87a

155 50 –e 80

100b–168c 50 8 66

Total

493

285

224–292

a b c d e

Minergie-P (MJ/m2a) 52 d 50 8 53 163

Based on Scenario IIa of Swiss Energy Perspectives [25]. Based on Minergie requirements [29] using SFH in Fig. 6 and technical data for NGSo system. Based on Minergie requirements [29] using SFH in Fig. 6 and technical data for HPSo system. Based on Minergie-P requirements [30] using SFH in Fig. 6. No mechanical ventilation normally provided.

the higher building standards, while the hot water heating demand remains constant. 4.1.2. Energy demand of future buildings Table 2 compares the future energy demand for three different building standards, featuring enhanced building services systems, to the mean energy demand of Swiss households in 2000. Because primary goal of the Minergie standard is to limit the energy consumption of the overall system, any gains achieved by a more efficient building services system may be cancelled out by a less efficient building envelope. Hence, the energy demand of buildings constructed (space heating) to the current Minergie standard is likely to rise slightly in future (compare Table 1 and Table 2). As Table 2 shows, hot water heating demand which is similar in magnitude to space heating demand in Minergie-P houses. As standards continue to improve (future Minergie-P+), hot water production will become the determining factor alongside electricity consumption. With the Minergie-P+ standard, it is assumed that technical innovation and economic incentives will result in still further reductions. Such buildings will feature a high-efficiency envelope with improved thermal insulation and vacuum windows. 4.2. Building technology As Tables 1 and 2 suggest, the energy demand for domestic hot water provision looks set to gain in significance

as building standards improve. Unlike space heating, domestic hot water is needed throughout the year. No conclusions may be drawn about final energy or even gross energy use on the basis of the energy demand for heating and electricity. In determining final energy use, the efficiency of the energy and building services systems is crucial. 4.2.1. Available technologies Six energy-efficient and cost-effective system combinations were selected from the range of technologies currently available. Table 3 specifies the building services systems used in conjunction with a SFH built to a particular standard (SIA target level, Minergie and Minergie-P), as shown in Section 5.1.1. The system efficiency values stem from manufacturers’ data or simulation calculations. The solar fraction of solar thermal systems combined with different sizes of energy store was investigated using the simulation program [31]. The efficiency of the solid oxide fuel cell (SOFC) fuel cell is based on the detailed surveys described in Ref. [27]. Allowance was also made, irrespective of heating plant, for the efficiencies governing heat storage, distribution and emission (Table 4). 4.2.2. Future technologies Future systems will achieve superior energy performance by means of technical innovation and the increased use of renewable energies. The relevant features are outlined in Tables 5 and 6. Although combined solar and seasonal

Table 2 Energy demand (useful energy) per square metre energy reference floor area of future residential buildings Energy demand per square metre reference floor area

Swiss households, 2000 (MJ/m2a)

Minergie (MJ/m2a)

Space heating Domestic hot water Ventilation electricity Domestic electricity

347a 59a –e 87a

163b–206c 42 6 44

Total

493

255–298

a b c d e

Based on Scenario IIa of Swiss Energy Perspectives [25]. Based on Minergie requirements [29] using SFH in Fig. 6 and technical data for NGSo+ system. Based on Minergie requirements [29] using SFH in Fig. 6 and technical data for HPSo+ system. Based on Minergie-P requirements [30] using SFH in Fig. 6. No mechanical ventilation normally provided.

Minergie-P (MJ/m2a) 52 d 42 6 44 144

Minergie-P+ (MJ/m2a) 17 42 6 44 109

1164

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

Table 3 Currently available building energy systems and their properties System

Space heating

Domestic hot water

Heat pump with a seasonal performance factor (SPF) of 3.5

Heat pump with a seasonal performance factor (SPF) of 3.5

Electricity Electrical energy from the Swiss public electricity grid

Solar thermal hot water system with an annual fraction ( f) of 70%, remaining 30% with heat pump

Wood (biomass) fired boiler with an annual efficiency (hp) of 80%

Electrical energy from the Swiss public electricity grid

Electrical energy from the Swiss public electricity grid

Wood (biomass) fired boiler with an annual efficiency of 80%

Solar thermal hot water system with an annual fraction ( f) of 70%, remaining 30% with boiler

Electrical energy from the Swiss public electricity grid

Natural gas fired condensing boiler with an annual efficiency (hp) of 95%

Solar thermal hot water system with an annual fraction ( f) of 70%, remaining 30% with boiler

Electrical energy from the Swiss public electricity grid

SOFC fuel cell (operating with natural gas) with auxiliary heater

Electrical energy from the fuel cell, with surplus fed into the Swiss public electricity grid.

The annual efficiency from [27] to meet energy demand of an SIA target level building: 89% Total annual efficiency (hp) Annual efficiency for electricity (hel) 27% For Minergie and Minergie-P buildings: Total annual efficiency (hp) Annual efficiency for electricity (hel)

82% 29%

energy storage systems (SoSa+) are already technically feasible, further innovation is needed to make them affordable. Details of the future conversion processes for the various energy carriers are required to determine gross energy from final energy demand. Particularly crucial are the future electric power supply mix and gross energy content of the individual energy carriers (see Appendix B). As the following systems represent future technologies, they are correlated to the relevant building standards, as shown in Section 5.1.2. 4.3. Embodied energy of buildings Energy is needed not only for the operation of buildings, but also for their construction, refurbishment and demolition. This so-called ‘‘embodied energy’’ is generally defined as the aggregate energy consumed in the manufacture and transportation of all products needed in the construction and refurbishment process. Embodied energy analyses normally

take account of all key processes and ancillaries, from raw materials extraction to provision on site in the specified form. Embodied energy is always considered at the primary energy level. Using the ETH Domain energy consumption figures [26] and the construction output for 1990 determined by Wu¨est et al. [32], the average embodied energy for residential buildings may be estimated at 4200 MJ/m2 heated floor area (HFA). Written off over a mean lifespan of 40 years, the embodied energy is thus equivalent to 105 MJ/ m2 HFA p.a. Investigations have been conducted by Binz et al. [33], Kasser and Po¨ll [34], Lalive d’Epinay [35] and Seyler et al. [36] into the embodied energy of specific buildings. The embodied energy of individual buildings varies widely due to differences in design, compactness and material composition. The values for housing (single-family homes and apartment blocks) determined in these studies range between 45 and 120 MJ/m2 p.a. Buildings designed to a high standard (such as Minergie) may incorporate slightly more embodied energy than conventional buildings. This is

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1165

Table 4 Energy efficiency of various currently available subsystems

Table 6 Energy efficiency of various future subsystems

Subsystem

Efficiency (%)

Subsystem

Efficiency (%)

Domestic hot water storage system Domestic hot water distribution system Energy distribution for space heating system Heat emission and control system (non-optimal control)

80 97 95 93

Domestic hot water storage system Domestic hot water distribution system Energy distribution for space heating system

90 100 98

due to a somewhat higher material content (e.g. thermal insulation, ventilation system, etc.). However, the impact of compactness and selected materials on embodied energy is currently thought to be far greater than the building energy standard. For this reason, the calculation of present primary energy use assumes a value of 80 MJ/m2 p.a. for embodied energy, irrespective of building standard and building services system. Though ambitious, this value is realistically achievable. Reducing embodied energy offers substantially less potential than heating energy, for instance. For achieving cuts in embodied energy, with possible reductions, as estimated in Ref. [33], being no more than 35% compared to the present average. For the future combinations of building standard and services systems, a value of 50 MJ/m2 p.a. is assumed to be feasible through the use of less energyintensive materials and a more efficient deployment of materials in the building design. Given that embodied

energy analyses are always based on Auditing Method A (see Appendix A), an estimated embodied energy component of around 25%, for consumption outside Switzerland is ignored in applying the nationally oriented Method B. The fossil component of embodied energy is put at 60% for contemporary new-build schemes and at 40% for future buildings in Switzerland.

5. Results 5.1. Energy-saving potential of individual residential buildings The energy demand discussed in Section 4.1, building services systems outlined in Section 4.2, space requirement per person and gross energy content of energy carriers (see Appendix B.2) are used to calculate per capita energy use, which is presented for each permutation of building standard

Table 5 Future building energy systems and their properties System

Space heating

Domestic hot water

Electricity

Heat pump with a seasonal performance factor (SPF) of 6.0

Solar thermal hot water system with an annual fraction ( f) of 85%, remaining 15% with heat pump

Electrical energy from the future Swiss public electricity grid

Wood (biomass) fired boiler with an annual efficiency (hp) of 90%

Solar thermal hot water system with an annual fraction ( f) of 85%, remaining 15% with wood-fired boiler

Electrical energy from the future Swiss public electricity grid

Natural gas fired condensing boiler with an annual efficiency (hp) of 100%

Solar thermal hot water system with an annual fraction ( f) of 85%, remaining 15% with boiler

Electrical energy from photovoltaic system with an annual efficiency of 20% and an area of 2.5 m2 per person, the difference being supplied by the future Swiss public electricity grid

Fully modulating biogas-operated fuel cell Total annual efficiency (hp) Annual efficiency for electricity (hel)

90% 50%

Thermal solar energy system with seasonal energy storage and a fraction ( f) of 100% for heating and domestic hot water

Electrical energy from the fuel cell, with surplus fed into the Swiss public electricity grid

Electrical energy from the future Swiss public electricity grid

1166

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

and building services system. A distinction is drawn between fossil and non-fossil energies, as described in Appendix A.2. The results presented below are based on the methods and framework described in the Appendix. No allowance is made for the energy consumed in manufacturing the building services components. Experience shows this figures to be very low, ranging between 5 and 10% of the total embodied energy. A rise in the heated floor area per person for residential buildings, from 60 to 72 m2 between 2000 and 2050, is factored into the future scenario. In assessing the future system combinations, the power generation variants described in Appendix B.1 is considered. Efficiency gains in grid power generation resulting from technology substitutions can thus be factored in. Potential efficiency gains in specific power station technologies are, however, ignored. 5.1.1. Present-day situation Fig. 7 shows the gross energy use for various buildings combining three present building standards with currently available building services systems. Fossil gross energy is plotted on the x-axis and total gross energy on the y-axis. Total gross energy use is largely a function of energy demand and therefore, indirectly, of the selected building standard. When used in conjunction with a Minergie-P building, all the investigated systems achieve a three-fold reduction in total gross energy use, compared to the present Swiss average. Fossil gross energy use for the wood-fired boiler and heat pump systems is down by a factor of 12. Being largely independent of building standard and building services system, domestic power consumption and the building’s embodied energy represent a largely constant component of gross energy use. The higher the building standard and the more efficient the system, the closer energy

consumption will approach this basic level. The impact of building standard on total gross energy use gradually diminishes as the efficiency of building services systems increases (e.g. HPSo system). 5.1.2. Future situation Fig. 8 presents the investigated combinations of building standards (Minergie-P and Minergie-P+) with building services systems (HPSo+ to SoSa+). The impact of the three different electric power supply mixes described in Appendix B.1 is also indicated. The diagram shows gross energy use to be dictated by building standard, building services system and power generation structure. Used in conjunction with a Minergie-P or Minergie-P+ building, the FC+ system achieves a more than 25-fold cut in fossil energy use, compared to the present average. For the HPSo+ and SoSa+ systems too, fossil gross energy use is down by a factor of between 7 and 20, depending on the electric power supply mix. These systems are likely to bring about a fivefold or higher reduction in total gross energy use. While the wood-fired boiler system (BmSo+) performs similarly well in terms fossil energy, the level of on site energy production here is somewhat lower than for the HPSo+ and SoSa+ systems and the total gross energy-saving potential is thus limited to a factor of 3.5 (Minergie-P) and 4.5 (MinergieP+). Despite considerable efforts towards technical innovation, the NGSo+ system remains too heavily geared to fossil energy carriers and hence achieves only a four-fold (Minergie-P) or seven-fold (Minergie-P+) cut in fossil gross energy use. Fig. 8 also shows gross energy use for the SoSa+ system to be independent of building standard (matching curves for Minergie-P and Minergie-P+) as the full heating demand is met by solar energy. Here, domestic power constitutes the only remaining energy requirement. The

Fig. 7. Total and fossil gross energy use for present building standards and building services systems (including embodied energy).

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1167

Fig. 8. Total and fossil gross energy use for future building standards and building services systems (including embodied energy).

NGSo+ and FC+ systems display the lowest dependence on electric power supply mix as, here, electrical power is partly or wholly supplied by off-grid generation equipment. This contrasts with the conspicuously high dependence on electric power supply mix exhibited by the HPSo+ system, due to the additional electrical demand for the heat pump. Electric Power Supply Mix C, with its low fossil and total gross energy content, provides the ideal basis for attaining the goals of the 2000 W society.

potential for 2050—with the aim of demonstrating the possible contribution of the residential buildings sector to the achievement of a 2000 W society. The calculations take account of the results from Section 5.1 along with various projections for the development of the residential building stock. For increased transparency, the calculation of potential assumes a constant electric power supply mix. The implications of a change in the power generation structure are shown in Fig. 8.

5.2. Energy-saving potential of residential building stock

5.2.1. Development of residential building stock (DBS) An analysis of trends in the heated floor area of the residential building stock over the next 50 years is key to assessing the possible achievement of the 2000 W society in the housing sector. Here, it is crucial to know precisely when which parts of the stock will be newly built, refurbished or demolished. Wu¨est et al. [32] have created a detailed model for the development of the building stock. This was used by Aebischer et al. [38] to produce an updated projection, which, in this study, serves as an initial reference trend for the development of the building stock. To supplement the existing data, two further building stock projections were produced by EMPA using the established Wu¨est & Partner Model [32] to investigate the impact of new-build and refurbishment cycles on energy use.

Cuts in energy consumption are required across all sectors to meet the targets of the 2000 W society. Yet, what contribution may reasonably be expected in the various areas (transport, industry, consumer sector, etc.)? The different processes entailed by the services in different sectors prevent comparable improvements in energy performance from being achieved across the board. Moreover, greater advances have already been made in some sectors than in others. The book ‘‘Factor Four’’ [37] gives examples of potential energy cuts in various consumer domains. Sustainable building standards and efficient building services systems can only contribute to the achievement of a 2000 W society if they are applied as rapidly as possible to both new-build and refurbishment schemes. Even today, as shown in Section 5.1.1, combinations of building standard and building services system are feasible which, as individual solutions, hold considerable energy-saving potential. Possible efficiency paths for the Swiss residential building stock are identified for a predetermined range of implementation scenarios as a basis for calculating the energy-saving

 The DBS-I building stock projection, based on the Wu¨est & Partner Calculation Model [32], is borrowed from the study by Aebischer et al. [38]. As these data only extend as far as 2030, technology cycles and the preceding building stock trends were used to extrapolate the development up to 2050.

1168

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

Table 7 Various building technology implementation scenarios Technology implementation scenario

New buildings between 2000 and 2050

Full refurbishments between 2000 and 2050

Partial refurbishments between 2000 and 2050

TIS-I

SIA 380/1 target level for new buildings

No changes

HP, Bm, NGSo and FC systems

SIA 380/1 threshold value for new buildings HP, Bm, NGSo and FC systems

TIS-II

Minergie HP, Bm, NGSo and FC systems

SIA 380/1 target level for new buildings HP, Bm, NGSo and FC systems

No changes

TIS-IIIa

Minergie-P and after 2030 Minergie-P+ HP, Bm, NGSo and FC systems, after 2030 HPSo+, BmSo+, NGSo+, FC+ and SoSa+

Minergie HP, Bm, NGSo and FC systems

No changes to building structure, but in 20% of cases replacement of energy system with heat pump

TIS-IIIb

Minergie-P and after 2030 Minergie-P+ HPSo, BmSo, NGSo and FC systems, after 2030 HPSo+, BmSo+, NGSo+, FC+ and SoSa+

Minergie HP, Bm, NGSo and FC systems

No changes to building structure, but in 20% of cases replacement of energy system with heat pump

TIS-IIIc

Minergie-P and after 2030 Minergie-P+ HPSo, BmSo, NGSo and FC systems, after 2030 HPSo+, FC+ and SoSa+

Minergie and after 2030 Minergie-P HPSo and BmSo systems

No changes to building structure, but in 50% of cases replacement of energy system with heat pump

 The DBS-II building stock projection was developed on the basis of our own calculations and the Wu¨est & Partner Model [32] to investigate the impact of a slightly higher refurbishment activity and demolition rate on energy use in the building stock. The development of the building stock is determined by implementation and demolition probabilities in function of the elapsed time since the previous building works. An implementation probability of 70% was assumed for this projection, while the selected demolition probability was such as to result in an average annual demolition rate of 0.21% over the next 25 years. The level of new-build development was adjusted to reconcile the residential building stock with the DBS-I projection.  A third building stock projection (DBS-III) was computed to assess how a sharp rise in construction would affect energy use by the building stock. A higher level of development activity implies a more regular refurbishment of residential buildings in future, coupled with an increase in the proportion of new replacement buildings. The implementation probability was accordingly raised to 85% and the demolition probability adjusted so as to achieve an average annual demolition rate of 0.38% over the next 25 years. The level of new-build development was again modified to bring the overall stock in line with the DBS-I projection. 5.2.2. Technology implementation scenarios (TIS) The implementation of building standards and building services systems was considered in five different scenarios. As shown in Table 7, these foresee different measures for new-build, full refurbishment and partial refurbishment schemes. Allowance is made for the use of more advanced

technology with higher efficiency and a lower energy demand for post-2030 development activity. 5.2.3. Estimated energy-saving potential Fig. 9 shows the energy-saving potential for 2050, compared to 2000, for various building stock projections and technology implementation scenarios. The far-right column shows the maximum theoretically possible energy-saving potential at some indefinite time in the future, calculated on the basis of the Minergie-P+ standard combined with a balanced mix of the HPSo+, BmSo+, NGSo+, FC+ and SoSa+ systems. This maximum value is equivalent to an approximately 5-fold cut in total gross energy and a 14fold reduction in fossil energy use. Due to the longevity of buildings, these values cannot be achieved by 2050. The TIS-IIIa and TIS-IIIb implementation scenarios demonstrate the feasibility of cutting total gross energy use in the residential buildings sector by a factor of between 1.6 and 2.1 through immediate application of the Minergie-P standard in conjunction with a balanced selection of efficient technologies. Fossil primary energy use can, at the same time, be more than halved. This would allow the average targets for the 2000 W society to be met. The TISIIIc implementation scenario surpasses the average targets for 2050, irrespective of the building stock projection. This analysis reveals that, depending on implementation scenario, energy savings in the residential buildings sector may suffice to balance out a small amount of excess energy consumption in other sectors (e.g. transport, industry, etc.). As Fig. 9 shows, the development of the building stock significantly affects the energy-saving potential. Hence, given a building stock development in line with the DBS-II or DBS-III projections, even the TIS-II implementation

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1169

Fig. 9. Energy-saving potential in residential buildings sector by 2050, for various building stock projections and technology implementation scenarios.

scenario would allow achievement of the average targets of the 2000 W society as set out in Fig. 4. The TIS-I implementation scenario is inadequate in all cases. Its adoption would necessitate surplus gains in other sectors (e.g. transport, industry, etc.) to offset the below-average cuts achieved in the residential buildings sector.

6. Conclusions The most efficient individual solutions at present include the Minergie-P building in conjunction with a heat pump or wood-fired boiler, in either case supplemented by a solar domestic hot water system. These solutions achieve a 3-fold reduction in total gross energy use, along with a 12-fold cut in fossil gross energy use, compared to the present Swiss average. A wide range of currently available technologies, as individual solutions, meet the average targets of the 2000 W society for 2050 (see Figs. 4 and 7). Substantial energy savings are feasible through a 25% cut in total energy demand beyond the present Minergie-P standard (i.e. Minergie-P+) results from further advances in building services technology. If account is taken of structural changes in grid power generation, this would bring about a 5-fold reduction in gross energy use coupled with an up to 25-fold cut in fossil energy use, compared to present levels. Yet, the individual solutions described are subject to the new-build and refurbishment cycle and do not allow immediate, across-the-board implementation throughout the residential buildings sector. The achievable reductions are seen to vary according to the future development of the residential building stock and available technologies. The various estimates show how the longevity of buildings and

services systems prevents full exploitation of the technological potential by 2050. The ambitious TIS-IIIa implementation scenario involves adoption of the Minergie-P standard for buildings erected between 2000 and 2030 and the Minergie-P+ standard for post-2030 schemes. It foresees a reduction in total gross energy use by a factor of 1.6–2 by 2050, depending on building stock projection. Fossil primary energy use would be reduced by a factor of 1.9– 2.7. These values are, if anything, slightly better than the average target factors required for 2050. Therefore, the residential buildings sector, in its current structure and given favourable building stock trends, can balance out some excess energy consumption in other sectors. To fully capitalize on the potential identified in the residential buildings sector, it is urgent to take immediate action. One essential task is to create incentives to encourage the use of the available technical solutions and hasten refurbishment or replacement of the building stock.

Acknowledgements This work has been partially funded by novatlantis and EMPA. Contributions by Prof. A. Binz and our many dear colleagues at EMPA are gratefully acknowledged.

Appendix A. Methodology A.1. Definition of primary and gross energy The concept of the 2000 W society requires the conversion of final energy use into primary energy, which

1170

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

is defined in Ref. [20] as that energy directly obtained from nature, e.g.:      

mined coal; extracted crude oil or natural gas; harvested biomass; exploited hydropower; solar energy absorbed by collectors; heat generated by nuclear reactor.

Primary energy normally has to be converted into a suitable secondary energy carrier, such as gaseous fuel or electricity (at a refinery, power station, etc.), prior to use. Two different methods may be used to calculate primary energy consumption. A.1.1. Method A The systems-theoretical approach, hereinafter termed Method A, factors in both the direct and indirect energy use for consumed products and services (Fig. 10). All energy use throughout the value-added chain (e.g. from exploration to centralized conversion, distribution and disposal) is allocated to the consumer, regardless of national borders. Allowance is therefore made for the embodied energy in net goods imports [39] and due consideration given, in the assessment of final energy consumption, to the varying environmental impact of production and distribution for different energy forms up to the national border. Inventories detailing the aggregate primary energy use for various production processes (e.g. from primary to secondary energy carrier) are provided by Ecoinvent [40]. Together with the chemically or physically bound energy of the carrier, this primary energy use may be regarded as the primary energy content. Primary energy

is divided up according to the five categories: fossil, nuclear, biomass, wind/solar/geothermal and hydropower. In this study, however, primary energy content is simply classed as either fossil or non-fossil (nuclear, biomass, wind/solar/geothermal and hydropower). A.1.2. Method B Unlike Method A, the nationally oriented Method B limits the assessment to primary energy use within the relevant national borders (Fig. 11). For this, the Swiss Total Energy Statistics [22] uses the term ‘‘gross energy’’. Based on the premise that any country has only an indirect influence on production processes in other countries, no allowance is made for the embodied energy in imported goods and services. With imported secondary energy carriers (e.g. petrol, electrical energy, etc.) too, the associated production (conversion) energy is allocated to the exporter. The energy content of the carrier is, however, assigned to the importer as gross energy use. This method is consistent with the International Energy Agency (IEA) convention. Auditing Method B is also applied in the White Book [41]. Yet, the calculated gross energy use does not necessarily stand in direct relation to the effective primary energy use of the population in any particular country, as national energy consumption may be indirectly exported in the form of goods or services. The determined absolute energy use thus depends on the auditing method and tends to be some 25% higher for Method A than for Method B, due to the allowance made, in the first case, for the embodied energy in net goods imports. At the same, as a further study [21] shows, the potential identified by the two methods is roughly the same, as the bulk of technological improvements are achieved within the national borders.

Fig. 10. Auditing Method A for primary energy, applied to Switzerland.

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

1171

Fig. 11. Auditing Method B for gross energy, applied to Switzerland.

A.2. Classification by energy source

A.3. System boundaries in buildings

As climate issues make fossil energy a key factor for the 2000 W society, this study distinguishes between fossil (CO2-producing) and non-fossil (CO2-free) energy. This method is clear-cut and easy to apply, while allowing direct comparison with the targets for the 2000 W society. Nonfossil energies embrace both renewable carriers and nonrenewable sources, such as nuclear energy. Total energy use, as a further indicator in the 2000 W society, serves as a measure of natural resource consumption and the efficiency of the relevant conversion chain.

To permit assessment of the different energy systems, a clear definition of system boundaries for energy auditing is required. The following two principles apply in this connection: 1. Energy supplied to a particular building across the system boundary (tradable energy) is added to the gross energy use. This may be checked against the Swiss energy statistics. 2. Allowance is made, as a demand reduction, for renewable energies used on site by the relevant

Fig. 12. Energy conversion processes, as exemplified by residential building supply.

1172

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

building. This is designed to reward those consumers investing in renewable technologies for their own buildings. Typical examples include the use of active and passive solar energy and heat pumps tapping ambient heat.

B.1. Structural changes in electrical grid power generation in Switzerland This study uses three electric power supply mix variants from the Swiss Energy Perspectives [25,23] for 2030. The associated gross energy contents are given in Appendix B.2.

A.4. Energy conversion Energy is needed both for building operation, in the form of heat and power, and for the erection, refurbishment and demolition/dismantling of construction facilities. The example in Fig. 12 shows the conversion chain needed to provide the operating energy for a building. In simplified terms, four energy levels may be distinguished: 1. 2. 3. 4.

Appendix B. Further calculation boundaries

primary energy; gross energy; final energy; useful energy (=net energy demand).

The conversion of primary energy into useful energy involves a varying number of process stages, depending on energy carrier or source. Each conversion entails a loss of usable energy along with an equivalent rise in primary energy use per consumed final energy unit. As a rule, the fewer process stages undergone by an energy carrier, the lower its primary energy content. In Switzerland, the average conversion efficiency from primary to useful energy stands at around 33% [3].

Electric Power Supply Mix A: This mix is based on Variant 1 in Scenario I of the Swiss Energy Perspectives [25]. Along with hydropower (47%) and nuclear power (29%), imports (20%) account for a substantial share of the electricity supply. The power generation structure is more or less equivalent to the present situation. Electric Power Supply Mix B: This mix is based on Variant 2 in Scenario IIa of the Swiss Energy Perspectives [25]. Electricity demand is met by hydropower (54%), gas thermal power stations (19%) and cogeneration (12%). The present nuclear power component is replaced by the use of fossil-fuel technologies. Import/ export activity is lower than for Power Supply Mix A. Scenario IIa also foresees a lower nationwide electricity demand than that assumed for Power Supply Mix A. Electric Power Supply Mix C: Power Supply Mix C is based on the projected electricity demand in Scenario IV of the Swiss Energy Perspectives

Table 8 Fossil, non-fossil and total gross energy content for different energy generation processes, calculated using relevant process efficiencies for domestic production Process

Electric power Current power supply mix CH Power Supply Mix A (future) CH Power Supply Mix B (future) CH Power Supply Mix C (future) CH Hydropower station CH Gas and steam power station Cogeneration (heat 70/90 8C) Nuclear power station CH Wind power station Photovoltaic CH Biogas engine Geothermal power station

From

Efficiency

Electric grid Electric grid Electric grid Electric grid Power station Power station Power unit Power Power Power Power Power

station station station station station

Gross energy content

Source

Fossil (MJ/MJ)

Non-fossil (MJ/MJ)

Total (MJ/MJ)

45% 48% 61% 56% 80% 58% 35% electric, 55% thermal 33% 25% 15% 30% 10%

0.09 0.08 0.70 0.17 0.00 1.72 2.26

2.14 2.01 0.93 1.62 1.25 0.00 0.00

2.23 2.09 1.63 1.79 1.25 1.72 2.26

0.00 0.00 0.00 0.00 0.00

3.03 4.00 6.67 3.33 10.0

3.03 4.00 6.67 3.33 10.0

[43] See Section B.1. See Section B.1. See Section B.1. [43] [44] Electricity exergy allocation factor of 0.79, [45] [43,42] [40] [46] Estimation (EMPA) [42]

Fuels Oil products Natural gas Wood

Stock Pipeline Forest

98% 99% 100%

1.02 1.01 0.00

0.00 0.00 1.00

1.02 1.01 1.00

[43] [43] [43]

Heat use Cogeneration (heat 70/90 8C)

Power unit

35% electric, 55% thermal 72%

0.38

0.00

0.38

0.69

0.69

1.38

Heat exergy allocation factor of 0.21, [45] [43] and estimation (EMPA)

District heating

Heat exchanger

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

[23]. As Scenario IVassumes an electricity demand for 2030 12% below the present figure, most of the national requirement can be met by hydropower (67%). The few supplementary technologies required include renewable energy sources, such as geothermal power, wood/biomass, solar energy (9%) plus a small proportion of fossil-fuel power stations (8%), e.g. thermal power and CHP (cogeneration) stations. B.2. Primary energy content of different energy carriers and conversion processes Gross energy content is calculated using the process efficiencies specified in Refs. [42,40,43]. The electric power supply mix calculations are based on the energy consumption for 2001 given in the Swiss Total Energy Statistics [43]. Only the domestic process chain is considered. Table 8 lists the applied gross energy contents. References [1] G. Brundtland, Our Common Future: The World Commission on Environment and Development, Oxford University Press, Oxford, 1987. [2] P. Kesselring, C.-J. Winter, World Energy Scenarios: A Two-Kilowatt Society Plausible Future or Illusion? Energietage 1994, PSI Villigen, 1994. [3] ETH Domain, 2000 Watt Society—Model Switzerland, Strategy of Sustainability in the ETH Domain, Economy Platform, 1998, see www.novatlantis.ch (in German). [4] R.T. Watson, et al. Climate Change 2001: Synthesis Report, standalone ed., IPCC, Geneva, Switzerland, 2001. [5] T.M.L. Wigley, R. Richels, J.A. Edmonds, Economic and environmental choices in the stabilization of atmospheric CO2 concentrations, Nature 379 (1996) 242–245. [6] I.G. Enting, T.M.L. Wigley, M. Heimann, Future Emissions and Concentrations of Carbon Dioxide: Key Ocean/Atmosphere/Land Analyses, CSIRO Division of Atmospheric Research Technical Paper 31, Mordialloc, Australia, 1994. [7] D. Spreng, A. Scheller, B. Schmieder, N. Taormina, The Energy Consumption Window Which is no Window, CEPE, Zurich, 2002 (in German). [8] J. Goldemberg, Th.B. Johansson, World Energy Assessment: Overview 2004 Update, UNDP, New York, 2004, ISBN: 92-1126167-8. [9] E. Jochem, Farsightedness—Learn to Think Sustainable, A.P.E.S. Conference from 24th July 2004, Bilanz04 SwissEnergy, Farsightedness – Outlook – Moment, Zurich, 2004 (in German). [10] C.J. Campbell, The Essence of Oil and Gas Depletion, Multi-Science Publishing Group, Brentwood, 2003, ISBN: 0-906522-19-6. [11] H. Rempel, Will the hydrocarbon era finish soon? DGMK/BGR Conference ‘‘Geosciences in Exploration and Production: Information Exchange for Research and Industry’’, Hanover, 23 May 2000, see http://www.bgr.de (in German). [12] IEA, International Energy Agency, Energy Balances of OECD Countries (2001 ed.) and Energy Balances of Non-OECD Countries (2001 ed.), 2001. [13] BP, BP Statistical Review of World Energy 2003, see www.bp.com. [14] WEO, World Energy Outlook 2002, OECD/International Energy Agency, 2002, ISBN: 92-64-19835-0. [15] IPCC, Climate Change 1995, Second Assessment, 1995, see www.ipcc.ch.

1173

[16] IPCC, Climate Change 2001: Mitigation—Contribution of Working Group III to the Third Assessment Report of IPCC, Cambridge, United Kingdom and New York, NY, USA, Cambridge University Press, 2001, see www.ipcc.ch. [17] N. Nakicenovic, et al., IPCC Special Report, Emissions Scenarios, Summary for Policymakers, 2000. [18] UN, Long-Range Population Projections, United Nations, Department of Economic and Social Affairs, Population Division, 2003. [19] E. Bos, M.T. Vu, World Population Projections: Estimates and Projections with Related Demographic Statistics, 1994–1995 ed., The World Bank, Washington, DC, USA, 1994. [20] N. Nakicenovic, A. Gru¨bler, A. McDonald, Global Energy Perspectives, IIASA/WEC, Cambridge University Press, 1998, ISBN: 0-52164569-7. [21] M. Koschenz, A. Pfeiffer, Potential of Residential Buildings, Energy and Building Technology for the 2000 Watt Society, novatlantis and EMPA, Faktor-Verlag, Zurich, 2005, ISBN: 3-905711-00-1 (in German). [22] Swiss Total Energy Statistics 2000, Swiss Federal Office of Energy (SFOE), Berne, 2001 (in German). [23] K. Eckerle, Completion of the Swiss Energy Perspectives 1990–2030 Scenario IV and Sensitivity Study of Scenario I, Prognos, 1997 (in German). [24] Emissions Based on CO2 Law and Kyoto Protocol, Swiss Agency for the Environment, Forests and Landscape (SAEFL), Department of Economy and Research, Berne, 2004 (in German). [25] K. Eckerle, K.P. Masuhr, Swiss Energy Perspectives and Scenarios I to III 1990–2030, Synthesis Report, Prognos, 1996 (in German). [26] ETH-Domain, Buildings and Energy, Final Report of the Working Group, Strategy of Sustainability at the ETH-Domain, Economic Board, 2000 Watt Society, Working Group 1, 1999 (in German). [27] V. Dorer, R. Weber, Sustainable Domestic Energy Supply with Fuel Cells and Renewable Energies, novatlantis, Duebendorf, 2004 (in German). [28] Building Energy Standard SIA 380/1: Thermal Energy in Buildings, Swiss Society of Engineers and Architects (sia), Zurich, 2001. [29] Minergie Association, Minergie Evidence Form, Version 8, 24-page guideline, Author: Huber Energytechnology, Zurich, 2003 (in German). [30] Minergie Association, Minergie-P for a Plus in Building Quality, 8page brochure, Berne, 2003 (in German). [31] Polysun Version 3.3.4a, A Simulation Program for Thermal Solar Energy System, Institut fu¨r Solartechnik SPF, Rapperswil, 1992– 2001. [32] H. Wu¨est, et al., Background Data and Forecasts for Building Stock Development in Switzerland 1990–2030, Wu¨est & Partner, 1994 (in German). [33] A. Binz, M. Erb, G. Lehmann, Ecological Sustainablity in Residential Buildings, An Assessment of Refurbishment Strategies, Basel Institute of Technology and Management (FHBB), Swiss Federal Office of Energy (SFOE), 2000 (in German). [34] U. Kasser, M. Po¨ll, Embodied Energy of Building Materials, second completely revised ed., Office for Environmental Chemistry, Zurich, 1998 (in German). [35] A. Lalive d’Epinay, Environmental Compatibility as a Determining Factor in Architectural Design, Thesis, ETH, no. 13610, Zurich, 2000 (in German). [36] Ch. Seyler, Ch. Stoy, I. Lu¨tzelschwab, S. Kytzia, Primary energy characteristic values for ecology-oriented building design, in: Conference Proceedings of 13th Swiss Status Seminar 2004—Energy and Environmental Research in Civil Engineering, EMPA ZEN, Zurich, 2004 (in German). [37] E.U. von Weizsa¨cker, et al. Factor Four, Doubling Wealth, Halving Resource Use, London, 1997, ISBN: 1-85383-407-6. [38] B. Aebischer, et al., CO2 Reduction Potential with Natural Gas, Project Phase 1: Reference Scenario, Final Report, Centre for Energy Policy and Economics (CEPE), Zurich, 2002 (in German).

1174

A. Pfeiffer et al. / Energy and Buildings 37 (2005) 1158–1174

[39] G. Du¨rrenberger, N. Patzel, Ch. Hartmann, Household energy consumption in Switzerland, International Journal of Environment and Pollution 15 (2) (2001) 159–170. [40] Ecoinvent Centre, ecoinvent v1.1, Swiss Centre for Life Cycle Inventories, Du¨bendorf, Switzerland, 2004, online version: http://www. ecoinvent.ch. [41] E. Jochem, et al. Steps towards a sustainable development, A White Book for R&D of Energy-Efficient Technologies, Novatlantis, 2004. [42] Key World Energy Statistics issued by IEA, International Energy Agency (IEA), 2002. [43] Swiss Total Energy Statistics 2001, Swiss Federal Office of Energy (SFOE), Berne, 2002 (in German).

[44] R. Bachmann, Thermal Fossil Power Stations, Workshop held on 2 July 2004, Energy Perspectives 2035/2050 (in Switzerland): Future of the Electric Power Supply, Swiss Federal Office of Energy (SFOE), 2004 (in German). [45] M. Me´nard, R. Dones, U. Gantner, Electric Power Supply Mix in Life Cycle Analysis, Consequence of Electricity Model Choice for Product and Life Cycle Analysis, Project: GaBE, Paul Scherrer Institute (PSI), 1998 (in German). [46] F. Staiß, Yearbook of Renewable Energies 02/03, Stiftung Energieforschung Baden-Wu¨rttemberg, Bieberstein-Fachbuchverlag, Radebeul, 2003, ISBN 3-927656-17-8 (in German).