Robert Bosch: A Refurbished Building Becomes an Energy Plus Home
Millions of existing buildings in Europe have yet to be refurbished with respect to energy efficiency. These houses offer an enormous potential for reducing energy costs. The consistent upgrading of an existing building to the Energy Plus Home standard shows how the energy balance can be improved considerably. A house that used to have a negative energy balance is turned into an energy supplier: it generates more energy than it consumes. The following example shows that state-of-the-art technology can turn an existing single-family home into an Energy Plus Home.
General Data
A family of four live in a single-family house in Würzburg (Bavaria, Germany), which was built in 1965 and has a floor area of 178 square metres. In the mid-1990s, heat insulating windows were installed and 5 cm wall insulation was added to the 24 cm brickwork. The primary energy consumption is about 200 kilowatt hours per square metre and year, the heating requirement is 90 kilowatt hours per square metre and year, which has thus far been covered by a condensing gas boiler. The energy required for domestic water heating is 3,800 kilowatt hours per year; in addition, the family consumes about 4,700 kilowatt hours of electricity in the same period. The roof has a surface area of 50 square metres available for photovoltaics and solar thermal systems and has a pitch of 45°.
The Energy Plus Technology
The washing machine Logixx 8 VarioPerfect from Bosch takes care of the family’s laundry. Compared to energy efficiency class A, the power consumption of the appliance is even 30 percent lower: in the standard programme with eight kilograms of laundry, the washing machine consumes 1.03 kilowatt hours of electricity and 56 litres of water.
The south side of the roof as well as the southward façade of the house are used for the installation of the photovoltaic system. The S_19 modules from Bosch efficiently turn the solar energy into electrical energy. They achieve an efficiency of 13.7 percent. The nominal output is 225 watts.
When it comes to ventilation, the family benefits from the advantages of the Aerastar controlled ventilation from Junkers, a brand of Bosch thermotechnology. It provides for reliable and efficient ventilation and achieves an efficiency rating of 91 percent. In contrast, 50 to 70 percent of the heat is usually lost when you open the windows to ventilate. In addition, Aerastar has a very high electrical efficiency: with one kilowatt hour of electricity, Aerastar recovers up to thirty times the equivalent amount of energy. Aerastar features silent operation thanks to low-noise direct current ventilators and optimum case insulation. High-quality filters provide for very good air quality even for allergy sufferers.
A condensing gas solar combination is installed in the cellar of the house. The Cerapur Solar unit was also supplied by Junkers, the Bosch thermotechnology brand. It consumes up to 30 percent less energy than a conventional condensing gas boiler. The appliance is exceedingly simple to combine with almost all energy and heat sources. As the complete heating hydraulics including mixing valve are integrated, a solar heating support can be realised quite simply – as in the exemplary building in Würzburg. Only two additional hydraulic connections and the system cylinder with integrated solar station and electronics are required for this purpose. With four solar collectors connected, Cerapur Solar works as efficiently as a conventional system with five collectors. The efficiency of this condensing gas solar combination has also been confirmed by the Fraunhofer ISE (Institut für Solare Energiesysteme).
The Result
The house started off with an annual primary energy consumption of about 200 kilowatt hours per square metre. It now has a surplus of 2 kilowatt hours per square metre. The consistent upgrading of the energy efficiency of the existing building using state-of-the-art technology pays off in the medium and long term. While the investment was about € 53,000 for state-of-the-art household appliances, a photovoltaic system, controlled ventilation and condensing gas heating and solar collectors, the energy cost saved per year is € 4,300. Even with constant energy prices, the investment breaks even after about twelve years – turning the refurbished building into an Energy Plus Home.
More details on the project are available here.