1 Introduction
1.1 Macro-scale analysis of housing stocks—state of the art
1.2 Linking energy simulations and LCA at micro-scale (building level)—state of the art
2 Methods
2.1 Selection of the scenarios
2.2 Modelling approach
Life cycle stage | Baseline scenario | Eco-innovation scenario |
---|---|---|
Production of materials (baseline scenario) | x | x |
Production of additional materials needed for the eco-innovation measure | x | |
Construction stage (baseline scenario) | x | x |
Construction stage: additional processes/products required for the eco-innovation measure | x | |
Use phase: energy and water consumption (baseline scenario) | x | |
Use phase: energy and water consumption when eco-innovation measure is taken | x | |
Use phase–maintenance of the building and its components (baseline scenario) | x | x |
Use phase–maintenance of the additional components | x | |
End of life (baseline scenario) | x | x |
End of life of additional materials | x |
2.3 Scenario modelling
2.3.1 Scenario I: insulation of outer walls
Single family house | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
SFH_warm_ < 1945 | SFH_warm_ < 1945–1969 | SFH_warm_1970–1989 | SFH_warm_ < 1990–2010 | SFH_mod_ < 1945 | SFH_mod_ < 1945–1969 | SFH_mod_1970–1989 | SFH_mod_1990–2010 | SFH_cold_ < 1945 | SFH_cold_1945–1969 | SFH_cold_1970–1989 | SFH_cold_1990–2010 | ||
Baseline scenario | Uvalue_walls (W/m2K) | 1.71 | 1.71 | 1.47 | 0.82 | 1.54 | 1.54 | 0.98 | 0.50 | 0.64 | 0.64 | 0.52 | 0.39 |
Insulation thickness_walls (m) | 0.00 | 0.00 | 0.00 | 0.02 | 0.00 | 0.00 | 0.00 | 0.05 | 0.04 | 0.04 | 0.05 | 0.06 | |
Heating energy consumption (kWh/m2 year) | 108 | 102 | 76 | 62 | 220 | 184 | 151 | 100 | 190 | 175 | 150 | 115 | |
Scenario increased wall insulation | Uvalue_walls (W/m2K) | 0.86 | 0.86 | 0.74 | 0.41 | 0.77 | 0.77 | 0.49 | 0.25 | 0.32 | 0.32 | 0.26 | 0.195 |
Insulation thickness_walls (m) | 0.02 | 0.02 | 0.02 | 0.06 | 0.02 | 0.02 | 0.04 | 0.12 | 0.10 | 0.10 | 0.12 | 0.15 | |
Heating energy consumption (kWh/m2 year) | 86 | 81 | 55 | 49 | 163 | 136 | 123 | 85 | 170 | 157 | 129 | 101 | |
Scenario increased wall insulation | Additional insulation (m) | 0.02 | 0.02 | 0.02 | 0.04 | 0.02 | 0.02 | 0.04 | 0.07 | 0.06 | 0.06 | 0.07 | 0.09 |
Additional insulation (kg/m2wall) | 1.05 | 1.05 | 1.22 | 2.20 | 1.17 | 1.17 | 1.84 | 3.60 | 2.81 | 2.81 | 3.46 | 4.62 | |
m2 wall insulation/dwelling (see baseline scenario) | 146 | 146 | 146 | 146 | 119 | 119 | 119 | 119 | 123 | 123 | 123 | 124 | |
Additional insulation (kg/dwelling) | 154 | 154 | 179 | 320 | 139 | 139 | 218 | 428 | 345 | 345 | 425 | 573 | |
Additional insulation (kg/dwelling, year) | 1.54 | 1.54 | 1.79 | 3.20 | 1.39 | 1.39 | 2.18 | 4.28 | 3.45 | 3.45 | 4.25 | 5.73 |
2.3.2 Scenario II: thermal solar system for production of domestic hot water
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Tin (warm climate) = 15 °C
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Tin (moderate climate) = 10 °C
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Tin (cold climate) = 5 °C
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Tuser = 45 °C
Solar collector (m2)/dwelling | ||||||||
---|---|---|---|---|---|---|---|---|
Single family house | Multi-family house | |||||||
< 1945 | 1945–1969 | 1970–1989 | 1990–2008 | < 1945 | 1945–1969 | 1970–1989 | 1990–2008 | |
Warm zone | 4.12 | 4.12 | 4.12 | 4.12 | 2.44 | 2.44 | 2.44 | 2.44 |
Moderate zone | 3.25 | 3.25 | 3.25 | 3.25 | 2.46 | 2.46 | 2.46 | 2.46 |
Cold zone | 3.39 | 3.39 | 3.39 | 3.39 | 2.01 | 2.01 | 2.01 | 2.01 |
Water storage tank (litres)/dwelling | ||||||||
---|---|---|---|---|---|---|---|---|
Single family house | Multi-family house (16 apartment units) | |||||||
< 1945 | 1945–1969 | 1970–1989 | 1990–2008 | < 1945 | 1945–1969 | 1970–1989 | 1990–2008 | |
Warm zone | 250 | = 2500/16 | ||||||
Moderate zone | 200 | = 1400/16 | ||||||
Cold zone | 200 | = 1000/16 |
Annual energy production solar collector ((kWh)/dwelling) | ||||||||
---|---|---|---|---|---|---|---|---|
Single family house | Multi-family house | |||||||
< 1945 | 1945–1969 | 1970–1989 | 1990–2008 | < 1945 | 1945–1969 | 1970–1989 | 1990–2008 | |
Warm zone | 1554 | 1554 | 1554 | 1554 | 560 | 860 | 860 | 860 |
Moderate zone | 439 | 439 | 439 | 439 | 397 | 397 | 397 | 397 |
Cold zone | 453 | 453 | 453 | 453 | 314 | 314 | 314 | 314 |
Annual remaining energy demand to be covered by the conventional system ((kWh)/dwelling) | ||||||||
---|---|---|---|---|---|---|---|---|
Single family house | Multi-family house | |||||||
< 1945 | 1945–1969 | 1970–1989 | 1990–2008 | < 1945 | 1945–1969 | 1970–1989 | 1990–2008 | |
Warm zone | 516 | 516 | 516 | 516 | 365 | 365 | 365 | 365 |
Moderate zone | 2403 | 2403 | 2403 | 2403 | 1747 | 1747 | 1747 | 1747 |
Cold zone | 2850 | 2850 | 2850 | 2850 | 1642 | 1642 | 1642 | 1642 |
2.3.3 Scenario III: night setback of setpoint temperature in HVAC systems
Heating energy consumption (kWh/m2 year) | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Single family house zone Warm zone | Single-family house Moderate zone | Single-family house Cold zone | ||||||||||
< 1945 | 1945–1969 | 1970–1989 | 1990–2010 | < 1945 | 1945–1969 | 1970–1989 | 1990–2010 | < 1945 | 1945–1969 | 1970–1989 | 1990–2010 | |
Baseline scenario | 108 | 102 | 76 | 62 | 220 | 184 | 151 | 100 | 190 | 175 | 150 | 115 |
Scenario night setback temperature | 69 | 65 | 46 | 40 | 176 | 148 | 120 | 79 | 162 | 150 | 128 | 99 |
2.3.4 Scenario IV: combined scenario
2.4 Life cycle impact assessment
3 Results and discussion
Impact category | Unit | Baseline scenario | Scenario wall insulation (I) | Scenario thermal solar system (II) | Scenario night setback temperature (III) | Combined scenario (IV) |
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Climate change | kg CO2 eq | 2.62E+03 | 2.33E+03 | 2.56E+03 | 2.36E+03 | 2.08E+03 |
Ozone depletion | kg CFC-11 eq | 3.33E−04 | 2.93E−04 | 3.24E−04 | 2.98E−04 | 2.60E−04 |
Human toxicity, non-cancer effects | CTUh | 2.70E−04 | 2.39E−04 | 2.68E−04 | 2.43E−04 | 2.17E−04 |
Human toxicity, cancer effects | CTUh | 3.48E−05 | 3.29E−05 | 3.51E−05 | 3.31E−05 | 3.20E−05 |
Particulate matter | kg PM2.5 eq | 2.90E+00 | 2.48E+00 | 2.85E+00 | 2.52E+00 | 2.13E+00 |
Ionizing radiation - human health | kBq U235 eq | 2.05E+02 | 1.92E+02 | 2.01E+02 | 1.93E+02 | 1.78E+02 |
Photochemical ozone formation | kg NMVOC eq | 6.11E+00 | 5.46E+00 | 6.00E+00 | 5.53E+00 | 4.93E+00 |
Acidification | molc H+ eq | 1.34E+01 | 1.21E+01 | 1.32E+01 | 1.23E+01 | 1.10E+01 |
Terrestrial eutrophication | molc N eq | 1.84E+01 | 1.68E+01 | 1.81E+01 | 1.69E+01 | 1.53E+01 |
Freshwater eutrophication | kg P eq | 1.48E−01 | 1.39E−01 | 1.48E−01 | 1.41E−01 | 1.34E−01 |
Marine eutrophication | kg N eq | 1.68E+00 | 1.52E+00 | 1.65E+00 | 1.54E+00 | 1.39E+00 |
Freshwater ecotoxicity | CTUe | 1.14E+03 | 1.04E+03 | 1.13E+03 | 1.05E+03 | 9.61E+02 |
Land use | kg C deficit | 4.84E+03 | 4.21E+03 | 4.74E+03 | 4.27E+03 | 3.66E+03 |
Water resource depletion | m3 water eq | 1.51E+02 | 1.43E+02 | 1.47E+02 | 1.44E+02 | 1.35E+02 |
Mineral and fossil resource depletion | kg Sb eq | 1.18E−01 | 1.13E−01 | 1.18E−01 | 1.16E−01 | 1.13E−01 |
Impact category | Unit | Baseline scenario | Scenario wall insulation | Scenario thermal solar system | Scenario night setback temperature | Combined scenario |
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Abiotic depletion potential—fossil | MJ | 4.84E+04 | 4.35E+04 | 4.71E+04 | 4.40E+04 | 3.88E+04 |
Abiotic depletion potential—minerals/metals (ultimate reserve) | kg Sb eq | 5.13E−03 | 4.95E−03 | 5.29E−03 | 5.01E−03 | 4.98E−03 |
4 Conclusions and outlook
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The use of archetypes is useful for analysing the effects of scenarios acting at the European level but implies also a certain degree of approximation at the building level, compared to the building-by-building approach. In fact, there is a trade-off between the data granularity of the model, which is higher at the small scale and lower at the large scale, and the relevance of the results obtained in support to policy decisions, which is of course higher when the model is built at a larger scale.
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With reference to the previous point, the uncertainty due to the use of average values instead of specific ones referred to real buildings may arise from the variability of service life of buildings, construction materials used, morphological features of the buildings, etc.
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Another limitation of the BoP baseline model used for this study is that the building stock is modelled in a static way and does not take into account stock dynamics over time. For instance, the effect of the European Energy Efficiency Directive is not captured in the basket of products housing, because its baseline year (2010) is the first year of implementation of the Directive. This aspect is reflected also in the results of the scenarios, which are modelled on the same reference buildings used in the baseline scenarios. It should also be pointed out that the construction of new buildings (that are adapted to the new regulation) suffered a setback due to the economic crisis of 2009, and existing buildings continue to be upgraded at a very low rate. It is estimated that the existing European building stock is currently being retrofitted at a rate of only approximately 1–3% of the total needed per year (Ascione et al. 2011).
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When using dynamic energy simulations applied to a stock of buildings modelled through archetypes, some simplifications are needed, in comparison of studies with dynamic simulations for specific buildings. In the present study, the dynamic simulations regarding the increase of envelope thermal resistance focused only on the U value, while it is well known that also other parameters could influence the buildings energy performance (for instance, materials density and heat capacity). These properties would have been raised exponentially the cases to analyse, without leading to significant differences, as the study is limited to the winter conditions, when the envelope inertia plays a marginal role on the energy consumptions.
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The dynamic energy simulations in this study were limited to predict the heating demand. In further research, this could be broadened to include also cooling demand. This is especially important for warm climates, but even so for air-tight nearly zero energy buildings in moderate climates. As overheating risks in buildings are expected to become even more important due to climate change, it is recommended that this is further investigated in future research.
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Extending the analysis to the warm season, the effect of each action above described will be reduced in terms of energy saving respect to the total (whole year) energy consumption.
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Finally, as for all the LCA studies, the use of background databases (in this specific case, the Ecoinvent database 3.2) is a source of uncertainty because background data are not directly referred to the system under study. In the BoP housing, this aspect was partially addressed by adjusting the background datasets to the European average conditions as far as possible.