Research questions

Based on the updated results of the different paper presented in Section 4, the research questions are addressed in this section. This concerns (A) the origins of the high demand and impacts, (B) the energy and GHG reductions, (C) the cost-effectiveness and (D) the large-scale implementation of energy retrofit.

5.1.1 Question A: Origins of high demand and impacts

What are the origins of the high demand and impacts in the building stock?

Research Question A is addressed by the investigation of the thermal performance of the building stock in Paper I, as well as the simulation of the energy demand by the steady-state bottom-up model of Paper II. The results in Section 4.2 indicate that up to 70% of all the building elements in the Swiss residential building stock are not reaching the thermal performance of the last two decades. The results of the statistical analysis show that despite partial energy retrofit of older building elements, the respective U-Values of building elements constructed prior to 1990 would have to be further reduced by a factor of three to reach low energy building standards, with windows requiring a six fold decrease in U-Values. This concerns in particular elements of buildings constructed before 1945 and in the 1970s, which seem to be an obvious target area for improvement due to their high surface share in the building stock. This low performance in the building envelopes across the older building stock leads to very high thermal losses, as indicated by the results of the energy model in Section 4.3. Due to their low performance, large surface share in the stock and very low retrofit rates, exterior walls are accounting for almost a third of the thermal losses and specific losses from walls are particular high (50 kWh/(m²a)) for buildings constructed between 1920 and 1945. This is

Discussion

followed by thermal losses through ventilation and windows, which each can reach up to 20% of the total thermal losses.

These high losses are furthermore amplified by the high share of inefficient and/or GHG-intensive fossil fuel based or direct electric heating systems of buildings constructed before 1980, which account for very high energy demand and/or GHG emissions in the stock. The results in Section 4.3 show that differences in the specific delivered energy demand (per square meter ERA) among the different archetypes can be traced back to three major correlations: 1) Buildings located in rural areas are showing on average a higher demand than suburban and in particular urban buildings (up to 19% higher on average). 2) SFHs are featuring on average a higher demand than MFHs (18% higher). 3) Older buildings are consuming significantly more than recent buildings (up to 220% higher). The combination of all these factors can then lead to a threefold increase in energy demand between the least energy efficient building archetype and the most energy efficient. The latter concerns in particular SFHs constructed between 1920 and 1960. Another major factor leading to a high demand is the colder climate in the more rural and mountainous regions in the northeast and southern parts of Switzerland. The low performance, high losses and large shares of ERA for older buildings in the stock lead subsequently to very high shares in relation to the total final space heating and DHW energy demand. The results in Section 4.3 show that buildings constructed before 1970 alone contribute 60% of the total delivered energy demand. Buildings with high share of delivered energy demand also have high primary energy requirements. In general, it seems that the energy demand from useful, final, delivered all the way to primary are closely linked to each other, with similar share for most archetypes in the total stock. In contrast, the results show that the impacts of GHG emissions are not featuring the same hot spots among the building archetypes as for the various types of energy demand, shifting the origins of high impact to building archetypes with high share of fossil-based heating systems.

Section 4.3 presents the weighted demand by archetype category. In contrast, Fig.

5.1.1 presents the distribution of relative differences in average energy demand for the exact same group of (archetype) buildings, following a “ceteris paribus”

approach. This allows to get a better understanding of the isolated influence of the different archetype categories on the demand and the impacts in the stock. In general, the comparison shows that the location (canton), construction period

Discussion

(age) and in particular the heating system influence most strongly the energy demand for a comparable building. The differences between building types and the typology are found to be very marginal and the differences in the weighted demand (see Section 4.3) for these archetype categories must originate from the composition and shares among the most influential categories as described above.

Fig. 5.1.1 Distributions of relative differences in demand or impact for the same archetype building as a function of variations in one archetype category (ceteris paribus, e.g. the same building archetype in different cantons). Results are presented for specific delivered energy demand, specific primary energy demand and specific GHG emissions.

In more detail, the same building situated in a canton with a colder climate (such as NW, OW or JU), might increase the energy demand or GHG emissions of these buildings by up to 25% (compared to the weighted demand of the overall archetype group), while on the other end of the spectrum lower demand in the same range can be expected (TI with -25%). However, a similar increase or reduction can occur from the different construction periods for a comparable building, with buildings constructed between 1920 and 1970 showing a higher demand of around 25%. In contrast, similar buildings constructed in the last 10 years might require only half of the energy demand. The most influential archetype category for

Delivered energy GHG emissions Primary energy

Construction period

Building type

Typology

Heating system

Canton

-1 0 1 2 -1 0 1 2 -1 0 1 2

<1920 1921-'45 1946-'60 1961-'70 1971-'80 1981-'90 1991-'00 2001-'10 2011-'20

MFHSFH

Rural SuburbanUrban

ElectroWoodGasDHHPOil

AGAI ARBEBSFRBL GEGL GRNELUJU OWNWSGSHSOTGURVDZGSZVSZHTI

Relative difference

Category & Class

Discussion

changes in demand or impacts is the installed heating system. For delivered energy, a HP heating system would reduce the energy demand of all buildings by over -50%. Also similar buildings equipped with direct electric heating and or DH show a high probability of lower relative demand (-10%), while a wood or oil based heating system would primarily lead to a higher demand (10-20%). For the GHG emissions, the influence of the heating system is even more pronounced. Similar buildings equipped with a DH, direct electric and in particular HP or wood-based heating system, might reduce the GHG-emissions by up to -90%, while oil based system always lead to higher GHG emissions. In the case of primary energy demand, a direct electric heating system leads in most cases to a more than 100%

increase in demand for a comparable archetype building.

The comparison with the official statistics in Section 4.1 has shown a good coverage of the CECB data for the Swiss building stock, which indicates a good representativeness of the CECB data for the building stock composition.

Furthermore, the comparison with related studies based mainly on external survey data has shown a good match for the U-Values (original and partially retrofitted) as well as in terms of the shares of retrofitted surface by element. Given this comparison, it can be stated that the statistical analysis of the energy performance certificate data in this thesis allows to determine the overall state of a building stock on a national level, with a high degree of detail concerning building archetypes and building elements.

5.1.2 Question B: Energy and GHG reductions

To which extent can energy retrofit reduce the specific or total energy demand or impacts across the building stock?

The hot spots of high energy demand identified in the previous research question are also representing distinctive hot spots for energy demand and impact reductions. Hence, deep-energy retrofit of the building envelope, in particular for elements of buildings constructed before 1945 and in the 1970s, seem to be an obvious target area for improvement. Furthermore, the replacement of fossil fuel based and direct electric heating system should be targeted to address the high GHG emissions and high energy use in the stock. In order to assess how much of the demand and impact could be reduced across the building stock, Paper III introduces different retrofit packages, allowing to reach low energy or even passive house standard after retrofit. The simulation of all building archetypes for each of

Discussion

the retrofit packages in the SwissRes model allows to determine their saving potential. In relative terms, the results in Section 4.4 indicate that the different retrofit packages if applied to the entire stock could reach relative savings of 46%

up to 86% for the delivered energy demand and 61% to 92% for the GHG emission.

In terms of specific energy demand, the results in Section 4.3 indicate that an insulation of older walls in order to reach the current thermal performance standard could reduce the specific thermal losses of these buildings by around 20% for SFHs and 25% for MFHs. This is also reflected in the possible reduction of energy intensity in the building stock as illustrated in Fig. 5.1.2, whereas the retrofit of walls and other building envelope components could drastically reduce the specific energy consumption of the current stock. The additional installation of a mechanical ventilation system allows a more pronounced reduction of the final energy demand. If this is paired with a replacement of inefficient heating systems by HPs, this is accompanied by significant additional GHG emission savings.

In the best case, a passive house (SysP) retrofit could then reduce the final energy intensity from roughly 130 down to 40 kWh/(m² a), while at the same time resulting in a reduction of GHG intensity from approximately 25 down to 2.5 kg CO2eq/(m² a) for the entire stock. Slightly less energy reduction could be achieved with a deep energy retrofit of the envelope without replacement of the heating system by a HP (Sys1), which however would lead to a still relatively high GHG intensity of around 10 kg/(m²a). In contrast, a more partial improvement of the envelope (Sys2-Sys5) combined with a HP reaches almost passive house level for the GHG emission intensity, but leads to a lower reduction of the final energy demand. Finally, the replacement of the heating system with a HP alone, could reduce the GHG intensity substantially to around 5 kg/(m²a), but it only slightly reduces the specific final energy demand. It should be noted, that if the ambient heat is excluded and only the delivered energy is used as indicator for the energy demand, the HP alone allows to get close to the low energy building level (Sys2-Sys5).

Discussion

Fig. 5.1.2 Snap-shot reduction potential of final energy and GHG intensity through energy retrofit for the different retrofit packages and their related retrofit steps.

To get a better understanding of the effectiveness of the different retrofit packages across the archetypes, Fig. 5.1.3 shows the final energy and GHG intensity for the most influential archetype categories for demand and impact as identified when studying the previous research question. The passive house package leads to the lowest final energy intensity and with the exception of wood-based heating systems, also to the lowest GHG intensity in the stock. The results also show that despite different starting points buildings with a fossil fuel based heating system (gas and oil) are reaching basically the same end point for the different retrofit packages. Since buildings with HP or DH based heating system do not require the replacement with a HP, their reduction in GHG intensity is linear to the reduction of the final energy intensity. Wood based systems are considered as basically carbon free energy sources, and a switch to only a HP is therefore leading to an increase in GHG emission intensity. In these buildings, only a complete envelope retrofit with a renewal of the existing heating system (Sys1) can reduce GHG intensity significantly. A renewal of direct electric heating system is forbidden by law, which means that the assumed switch to a gas based heating system in Sys1 would again lead to higher GHG intensity and in terms of final energy (not delivered) the installation of a HP does not have a big influence on the demand.

0 10 20 30 40

0 50 100 150

Final energy intensity [kWh / (m2 a)]

GHG intensity [kg CO2eq / (m2 a)]

Retrofit step: ^wall

window roof ground

ventilation

heating Retrofit package: ^HP

RENEWAL Sys1 Sys2

Sys3 Sys4

Sys5 SysP

Discussion

Fig. 5.1.3 Snap-shot reduction potential of final energy and GHG intensity through energy retrofit for the different retrofit packages and most influential archetype categories.

In comparison with other studies, the achievable savings of the retrofit packages considered in our model are on the lower side, meaning that very low energy and GHG intensity after retrofit are targeted in this study. In terms of relative savings, the differences are less significant and the results are well in line with other scholars.

5.1.3 Question C: Cost-effectiveness of energy retrofit

In which cases is energy retrofit economically viable and/or effective?

In order to address research Question C, Paper III provides a comprehensive analysis of the cost-effectiveness of retrofit packages under different economic assessment approaches for the current building stock. This is extended by a scenario analysis of the influence of potential future changes on the economic viability of retrofit measures in Paper IV. The results in Section 4.4 indicate that

<1920 1921-'45 1946-'60 1961-'70 1971-'80 1981-'90 1991-'00 2001-'10 2011-'20

DHElectroGasHPOilWood

0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200

0 3 6 9

0 5 10

0 10 20

0 1 2 3 4

0 10 20 30 40

0 1 2 3 4 5

Final energy intensity [kWh / (m2 a)]

GHG intensity [kg CO2eq / (m2 a)]

Retrofit package: ^HP_Sys1 ^Sys2_Sys3 ^Sys4_Sys5 ^SysP

Discussion

the stakeholder perspective represented by three different economic assessment approaches has the largest influence on the economic viability and subsequently on the economic saving potential in the Swiss residential building stock.

It is shown that exclusive profit orientation as represented by the FULL approach leads to a very low economic viability, with average levelized cost of 120 CHF/MWh for delivered energy reduction and 350 CHF/t CO2eq for GHG emissions. This leads to a very marginal economic potential of energy retrofit covering a little more than 2% (1.1 TWh/a) of the total delivered energy demand.

In terms of GHG emissions, this value is even smaller and only a 1% (0.1 Mt CO2eq/a) reduction can be achieved economically viable according to the results.

Such an approach is therefore not compatible with today’s energy and climate policy objectives. In contrast, systematic energy retrofitting following the natural refurbishment cycles (retrofit at end of the economic lifetime), as implemented by the IMP approach, offers an economic potential for delivered energy and GHG savings of roughly 62% (44 TWh/a) and 80% (10 Mt CO2eq/a) for the Swiss residential sector, with levelized costs in the range of -60 CHF/MWh and -150 CHF/t CO2eq. However, it might not be possible to overcome all related barriers of implementing measures always in line with the refurbishment cycles for each building element, which may make it necessary to consider the DEP approach, allowing to capture early energy retrofit strategies and the intrinsic asset value of buildings. This approach would lead to an reduced but still moderate economic reduction potential for delivered energy and GHG emissions of 30% (16.6 TWh/a) and 42% (5.3 Mt CO2eq/a), with related levelized costs in the range of 40 CHF/MWh and 20 CHF/t CO2eq respectively. It is worth noting that the reduction of final energy (not delivered) is significantly less attractive in economic terms in all approaches.

In order to get a better understanding of the isolated influence of the different archetype categories on the economic viability, Fig. 5.1.4 presents the relative changes in NPV for the variation in one archetype category for a similar building (ceteris paribus for all archetype categories). It should be noted that a positive number does not mean that the NPV is above zero (i.e., economically viable), but that the NPV is higher in this archetype class compared to a similar building. In general, there seems to be a higher economic viability for a HP retrofit compared to the other packages. This confirms the finding that single HP retrofit allows to enlarge the economic potential. In the case of the FULL approach, the economic

Discussion

viability depends mainly on the heating system and to some extent on the building type. For the DEP approach, Fig. 5.1.4 indicates a stronger relation with construction period and heating system, while the IMP approach is very sensitive to all categories but in again particular to the heating system.

Fig. 5.1.4 Distributions of relative differences in economic viability (NPV) for the same archetype building as a function of variations in one archetype category (ceteris paribus, e.g.

the same building archetype in different cantons). Negative values represent a reduced economic viability and positive values an increased economic viability.

According to the sensitivity analysis in Section 4.4, the economic viability and with this the economic saving potential of both final energy and GHG emissions for all economic assessment approaches could be significantly improved with a reduction in investment cost and/or an increase in achievable energy savings.

According to the literature review in Paper III, there is no related study that present

Discussion

the economic potential of energy retrofit in the Swiss residential building stock that could be compared to the results. However, the comparison of the specific cost of energy and GHG emission reductions are in the range reported by other Swiss and European studies.

As will be discussed in more detail in Section 5.1.5, the economic potential can be extended significantly if a dynamic and cost-optimal perspective is adopted.

Furthermore, the consideration of the timing of retrofits has a strong influence of the economic viability in the DEP approach, with decreased investment cost in the DEP approach, the closer the element gets to its economic end of life.

5.1.4 Question D: Large-scale implementation of energy retrofit

Which pathways could lead to large-scale implementation of energy retrofit in the building stock and what are the expected trade-offs?

In relation to research Question D, Paper IV provides a comprehensive scenario analysis of different retrofit pathways according to economic or environmental objectives based on a dynamic building stock model and geospatial climate change scenarios in combination with an optimization model. The results from this analysis in Section 4.5 indicate that the building stock will continue to increase, with a pronounced transition from old to new buildings, in particular for MFHs.

Despite this natural replacement of older and less energy efficient buildings by new and efficient ones and the warmer climate in the future, the annual energy demand and greenhouse gas emissions can be expected to decrease only by a quarter until 2060, with high investment cost for refurbishment of the aging building stock in the range of 2-3 billion CHF per year. This reduction will not be sufficient to even get close to the Swiss targets of 60% energy demand reduction and net zero greenhouse gas emission target for 2050. The same is true for a somewhat more ambitious strategy that focuses on retrofitting only those buildings in the stock that are supposed to continue to exist at least until 2090, since this leads to very high cumulated impacts of non-retrofitted buildings, in particular in the first decades.

The results of the retrofit pathways based on the optimization shows that a strategy that aims for lowest investment cost would result in too low retrofit activity and

The results of the retrofit pathways based on the optimization shows that a strategy that aims for lowest investment cost would result in too low retrofit activity and