Robert Bosch: State-of-the-Art Technology Turns a 4-Litre House into an Energy Plus Home
Many single-family homes built today are categorised as “4-litre houses” in Germany. This means that these buildings consume only four litres of oil per square metre of floor space and year. But if the focus is already on energy efficiency, why not take things a step further and turn the energy consumer into an energy provider? The following example shows that it is quite easy to achieve this goal.
General Data
The 4-litre house in question is located in Würzburg in northern Bavaria. The contemporary prefabricated house has 178 square metres of floor space for the family of four. The building was erected with a light frame construction plus a 25 cm thick insulation. The reference heating system is a condensing gas boiler. The energy consumption for domestic water heating is about 3,800 kilowatt hours per year. In addition, the family consumes about 4,700 kilowatt hours of electricity for the household in the same period. The roof has a pitch of 30° and a surface area of 78 square metres available for photovoltaic collectors.
The Energy Plus technology
A++ rated household appliances help reduce power consumption. The refrigerator-deep freezer combination KGN39A97 NoFrost from Bosch complies with this standard. With a power consumption of only 220 kilowatt hours per year, this appliance is among the most efficient ones in its class.
On the roof, the photovoltaics modules S_19 from Bosch collect the power of the sun and efficiently convert it into electricity. With a nominal output of 225 watts, the system has an efficiency of 13.7 percent.
A system for controlled ventilation provides fresh air and a pleasant climate. The vent from Bosch controls the ventilation reliably, achieving an efficiency of 91 percent. This means that a heat exchanger transfers almost the entire heat of the ambient air to the incoming fresh air, thus considerably reducing the power required for heating the building. The efficiency of the ventilation is underlined by its electrical efficiency: with one kilowatt hour of electricity, it recovers up to thirty times the equivalent amount of energy. Allergy sufferers can take a deep breath, too, because high-quality filters maintain good air quality in the long run – with optimum case insulation and low-noise direct current ventilators.
The heart of the heating system is the brine/water heat pump Compress 3000 LWM from Bosch with an output of 6 kilowatts. It uses the soil as a heat source. Brine circulates in long plastic pipes down under the ground. The brine takes the heat that is collected in the ground to the surface and re-leases it into the heat pump. The heat pump further increases the temperature level through pressure and passes the generated heat on to the heating circuit and the DHW cylinder. The electricity required for this purpose is used very efficiently: from one kilowatt hour of electricity, the heat pump generates up to 4.5 times as much heating energy. But the ready-to-install module not only provides for great heating comfort – a 163 litre stainless steel DHW cylinder easily covers the entire hot water consumption of the family of four.
The Result
The primary energy consumption of the house described above is about 150 kilowatt hours per square metre and year. Efficient appliances, power generated on the roof, controlled ventilation and environmentally friendly geothermal heat turn the 4-litre house into an Energy Plus Home. This way, the primary energy consumption of the building is not only reduced to zero but the house even boasts a positive energy balance, as it generates clearly more energy than it consumes. The surplus is 79 kilowatt hours per square metre and year. The acquisition and installation of the four components described cost about € 61,000. Every year, the inhabitants save about € 5,300 in comparison to conventional condensing gas heating. Even with constant energy prices, the investment breaks even after about eleven years.
More details on the project are available here.