4 Results
4.3 One-stop-shop for renovation
4.3.3 Case studies
First, energy savings by individual measures were documented for a so-called ‘master builder’ house constructed in 1927 and a standard detached house constructed in 1972, see Figure 28 and Figure 29. These categories of single-family houses have been identified as having the greatest potential for energy savings (see Section 2.3.1).
Then, the impact of combining the individual energy-saving measures into packages as described in Table 6 on energy use, thermal indoor environment and cost-efficiency was documented using primary energy factors for the houses renovated in accordance with Class 2010 and low-energy Class 2015; see Figure 30, Figure 31 and Table 7.
Figure 28: Primary energy use and savings (kWh/m2 per year) for typical individual technical renovation measures for the master builder house.
Figure 29: Primary energy use and savings (kWh/m2 per year) for typical individual technical renovation measures for the house constructed in 1972.
As can be seen from Figure 28 and Figure 29, individual renovation measures are different for the two types of house. For example, many people regard the façades of
‘master builder’ houses as being worth preserving. Façades can be thermally improved by filling the cavity, e.g. with granulated mineral wool, whereas the façades of detached houses constructed during the 1960s and 1970s, which are characterized by having large roof overhangs, may be more likely to be renovated by adding external insulation.
0 35 70 105 140 175 210 245 280 315 350 385
R A B C D E F G H I J K
Primary energy use [kWh/m2]
Primary energy use Energy savings
R Existing building
A 80mm insulation in cavity wall B Internal wall insulation, 95mm C External wall insulation, 95 mm D 75-200mm insulation in roof E 70mm extra insulation in floor F Storm windows, 4mm energy glass G New low-energy windows
H VHR, efficiency: 85%, SFP: 0.6 kJ/m3 I Replacement of existing circulation pump J Replacement of existing oil fired boiler
with new condensation oil boiler K Replacement of existing oil fired boiler
with heat pump
0 35 70 105 140 175 210 245
R A B C D E F G H I J K
Primary energy use [kWh/m2]
Primary energy use Energy savings
R Existing building
A External wall insulation, 100-150mm B 345 mm insulation in roof
C External wall insulation, 200-250 mm D 150 mm extra insulation in floor E New energy efficient windows F New low-energy windows
G VHR, efficiency: 80%, SFP: 1 kJ/m3 H VHR, efficiency: 85%, SFP: 0.6 kJ/m3 I Replacement of existing circulation pump J Replacement of existing boiler
with new condensing boiler K Solar panels for domestic hot water
From a technical point of view, adding external insulation is the best option for a
‘master builder’ house too, but should be seen as an extensive renovation measure because it influences the appearance of the house and might cause architectural problems with additional changes to the roof. A more detailed description of the houses and the renovation measures can be found in earlier work by the authors (Vanhoutteghem et al., 2010 and 2011).
Figure 30: Primary energy use (kWh/m2 per year) and thermal indoor environment for packages of technical renovation solutions applied to the master builder house.
Figure 31: Primary energy use (kWh/m2 per year) and thermal indoor environment for packages of technical renovation solutions applied to the house constructed in 1972.
From the analyses of combined renovation packages in Figure 30 and Figure 31, it can be generally concluded that typical Danish houses can be renovated to a level of energy performance which is comparable with the requirement for new houses today.
However, the target for primary energy for new buildings today, calculated to approximately 63 kWh/m2 per year for both houses (DEA, 2013), can only be reached with a complete energy-efficient renovation with extensive post-insulation and sealing of the building envelope, installation of a mechanical ventilation system with high efficiency heat recovery and low electricity use and an energy-efficient heating system (renovation package 5). Primary energy savings of 81% and 70% are then obtained for the ‘master builder’ house and the standard detached house, respectively.
0 5 10 15 20 25 30
0 35 70 105 140 175 210 245 280 315 350 385
R S1 S2a S2b S3 S4
Hours with Tint >26oC
Primary energy use [kWh/m2] Energy framework 2010
Low-energy class 2015 Venting 1.5 h-1 (Ref)
R Existing building S1 A+D+F
S2a A+D+F+H+J S2b A+D+F+H+K S3 B+D+E+G+H+J S4 C+D+E+G+H+J
0 100 200 300 400 500
0 35 70 105 140 175 210 245
R S1 S2 S3 S4
Hours with Tint >26oC
Primary energy use [kWh/m2] Energy framework 2010
Low-energy class 2015 Venting 1.5 h-1 (Ref) Venting 3.0 h-1 External shading
R Existing building S1 A+B+E
S2 A+B+E+H+I+J S3 A+B+E+H+I+J+K S4 B+C+D+F+H+I+J+K
To reach the target for buildings constructed in accordance with low-energy Class 2015 (approximately 36 kWh/m2 per year for both houses), more ambitious measures or an additional supply by renewable energy would be needed.
Thermal comfort will generally be improved by insulation and air-tightness measures that will increase surface temperatures and reduce draught, e.g. from badly insulated windows. A ventilation system with heat recovery will also contribute to good thermal comfort with a draught-free supply of fresh air. However, one side effect of insulation measures that reduce heat losses may be some overheating, especially in detached houses constructed during the 1960s and 1970s, which can effectively be avoided by using external movable solar shadings and/or to some extent by a higher venting rate e.g. using automatically controlled windows. However, external shading is usually costly to install and may be sensitive to hard winds.
Results from cost analyses, see Table 7, show that all the renovation packages are very cost-effective when applied in the ‘master builder’ house since the house is originally heated by an oil-fired boiler and the price for oil was estimated at 0.90 DKK/kWh2 (Vanhoutteghem et al., 2010). This is so even when the total investment cost for all renovation measures was used for CCE-calculations because none of the renovation measures applied in the different packages was needed for an improvement of the physical condition of the existing building. In the standard detached house, the windows needed replacement and work done to the bathroom and kitchen. Two different calculations were made: one where the total investment was used and a second where only the cost of energy-efficient measures was taken into account.
Results are compared to a price for gas roughly estimated to 0.80 DKK/kWh3 because the house is originally heated by a gas boiler. Looking at the results from the calculation of the total CCE, it is better not to renovate the house. However, when calculating the CCE based on the investment cost in energy-efficient measures, all scenarios are cost-effective and the effect of the two-fold benefit of renovation when only taking into account these investment costs in energy-efficient measures is clearly reflected in the results. From the results in Table 7, it can also be concluded that for both houses, it is more cost-effective to improve the building envelope, install a new boiler and VHR (package 2) than just to improve the building envelope (package 1).
Table 7: Calculation of cost-effectiveness of the different renovation packages.
Existing building S1 S2a S2b S3 S4
‘Master builder’
house Total CCE
(DKK/kWh) Ref 0.29 0.26 0.24 0.28 0.26 Standard
detached house Total CCE
(DKK/kWh) Ref 2.43 1.75 ‐ 1.78 1.65 CCE energy-efficient
measures (DKK/kWh) Ref 0.72 0.65 ‐ 0.7 0.72
2 1 DKK = 0.13 €
3 1 DKK = 0.13 €