Energy-efficient residences put to the test: at least 60 per cent less energy consumption

dena study demonstrates savings potential of residential buildings refurbished to improve energy efficiency / energy transition targets technically achievable today

Residential buildings that have undergone energy-efficient refurbishment and new buildings consume at least 60 per cent less final energy than an average house. These are the findings of a new study by the Deutsche Energie-Agentur (dena) – the German Energy Agency – which has established what energy savings are achievable in practice. For this purpose, they analysed the energy bills of 121 energy-efficient residential buildings, along with information from the owners regarding usage and the condition of their houses.

‘Anyone who has been in any doubt up to now about the effectiveness of energy efficiency measures can now confidently go ahead with their building plans. Our study shows how much energy-efficient residences actually contribute to the reduction in greenhouse gases and energy costs,’ says Andreas Kuhlmann, Chief Executive of dena. ‘It also shows that we already possess the technical capability to achieve the Federal Government’s targets for the building sector.’

Details of the study

Of the new or refurbished residential buildings tested by dena, those that were heated by oil, gas, district heating or wood consumed around 60 per cent less final energy than the average. In the case of electric heating, the figure was as much as 90 per cent. The extent of the reduction in energy consumption in a new or refurbished house depends on a variety of factors: the insulation, the type of heating, the energy source and consumer behaviour. Energy-efficient buildings not only reduce the burden on the climate and increase living comfort; they also reduce energy costs for residents accordingly.

As a reference value, the study used the energy consumption of the average residential building in 2008 – the reference year for the Federal Government’s energy transition targets. Annual final energy consumption in 2008 was around 150 kilowatt hours per square metre of usable floor space. By contrast, refurbished and newly constructed buildings only consume around 50 to 60 kilowatt hours per square metre of usable floor space per year if heated by gas, oil or pellets, or around 20 kilowatt hours per square metre of usable floor space per year if they have electric heat pumps. In terms of energy performance certificate ratings, that would equate to an improvement from E (or F to G for unrenovated houses) to between A+ and B.

Most of the data collected for the study come from structures newly built or refurbished since 2006 using standard building practice, and therefore offer a feasible representation. Some come from dena pilot projects. The 121 energy-efficient houses tested included 50 new detached and semi-detached houses, 7 new apartment buildings, 46 detached and semi-detached houses refurbished to improve energy efficiency, and 18 apartment buildings refurbished to improve energy efficiency. All of the houses have an insulated building envelope and efficient construction technology. The study is an extension of dena’s 2013 consumption study, which investigated the consumption figures of 63 refurbished residential buildings from dena’s Efficient House Pilot Project.

One of the Federal Government’s energy transition targets is a reduction in the primary energy needs of buildings by 80 per cent by 2050. Primary energy is defined as energy including the pre-production processes in the generation of electricity, gas, district heating, etc., and provides a better indication of the environmental impact of energy consumption than the final energy that consumers can see on their meter readings. In order to reduce primary energy by 80 per cent, depending on the energy source, around 60 per cent at least must be saved on final energy through building efficiency measures.

The latest study, ‘Evaluation of the Consumption Figures of Energy-Efficient Residential Buildings’, was commissioned by the Federal Ministry for Economic Affairs and Energy.