Robert Bosch: Home Owners and Residents Alike Benefit from the Positive Energy Balance of a Multi-Family House
More than one third of the European population live in rented flats in multi-family houses. These tenants are interested in low ancillary costs for electricity and heating. This is why there is now also a focus on increasing the efficiency of multi-family houses. With the technology that is available today, a multi-family house can be turned into an Energy Plus Home at a reasonable price. The following example shows how it works.
General Data
This example assumes a four-story multi-family house comprising 28 flats located in Würzburg (Germany). The calculation is based on an average heating requirement of 53 kilowatt hours per square metre and year – with three inhabitants per unit. The fact that the heating requirement is lower than in a single-family home is due to the compact construction (ratio of building shell and volume), which reduces the transmission heat loss. The reference heating system for the flats with a floor space of about 90 square metres is a condensing gas boiler. Each unit has an average energy consumption for domestic water heating of 1,900 kilowatt hours per year and an electricity consumption of 2,600 kilowatt hours per year. On top of the building, with a floor space of about 625 square metres, there is room for a 700 square metre photovoltaic system.
The Energy Plus Technology
Efficient household appliances are required in multi-family houses as well. The dishwasher SMS69T25EU from Bosch is a genuine energy saver featuring innovative Zeolith technology. With its standard programme, this appliance consumes only ten litres of water and 0.86 kilowatt hours of electricity. This means that it complies with the requirements of energy efficiency class A++.
The roof has enough space for a photovoltaic system. A total of 700 square metres are available here. The S_19 modules from Bosch efficiently turn the solar energy into electricity. With a nominal output of 225 watts, the system achieves an efficiency rating of 13.7 percent.
Regular ventilation is very important in rented flats. Without a regular exchange of air, mould may start to form and damage the rooms. This is not only a risk to the health of the residents: removing mould can be expensive for landlords and tenants alike. A system for controlled ventilation including heat recovery brings fresh air and a pleasant climate into all flats at all times. The Logavent HRV ventilation system from Buderus, a brand of Bosch thermotechnology, achieves an efficiency rating of up to 91 percent. With one kilowatt hour of electricity, Logavent HRV recovers up to thirty times the equivalent amount of energy. Another advantage: allergy sufferers can take a deep breath thanks to the built-in dust and pollen filters.
In the boiler room of our exemplary multi-family house, everything is about efficient gas heating. Natural gas-powered combined heat and power plants (CHP) are genuine marvels of efficiency – they use the heat released during power generation for heating and domestic water heating on the basis of heat and power cogeneration. The new CHP complete module Loganova EN20 from Buderus is a particularly efficient example. The system achieves a gross efficiency of 94.6 percent (33.9 percent electrical efficiency, 60.7 percent heating efficiency in an 80/60 centigrade set-up). Rated for an electrical output of 19 kilowatts and a thermal output of 34 kilowatts, the CHP plant is tailored to the requirements of the building. A Logamax Plus GB 162-100 condensing gas boiler from Buderus reliably covers the peak consumption.
The Result
Five technological components – efficient household appliances, photovoltaics, controlled ventilation with heat recovery, CHP plant and condensing gas boiler – turn a primary energy requirement of 406 megawatt hours per year into a primary energy surplus of 21 megawatt hours per year.
With a total floor space of 2,520 square metres, this corresponds to a surplus of about eight kilowatt hours per square metre and year. This shows that a surplus can also be achieved in a multi-family house. Moreover, an Energy Plus multi-family house is not only beneficial with regard to energy consumption, but also in terms of the financial investment. This is proven by a comparison of the initial investment and the costs saved over time. The acquisition and installation costs for the five components are about € 584,000. The measures described can save about € 50,000 per year – compared to a building heated by a condensing gas boiler. Even at constant energy prices, the investment would break even after only twelve years.
More details on the project are available here.