Three multi-family houses built between 1949 and 1957 have been modernised and given an energy efficient retrofit with the aim of achieving a CO2-neutral heat supply. The urban densification of the existing space by construction of a fourth (new) building and the addition of another floor on each of the three existing buildings made this project, located in an attractive area in Munich's city center, financially attractive for the building owner, the housing company GWG Munich.
- Vacuum insulation panels on the external wall facing the street
- Solar supported local district heating network with a gas-driven geothermal heat pump
- Large photovoltaic system on the roof
The following description focuses on one of the 3 renovated buildings (if not clearly mentioned otherwise). However the applied renovation measures and the resulting energy figures are similar to the other two renovated buildings. The heat supply system is central for all 4 buildings (local district heating system, only for the 4 buildings).
The project received funding from the Federal Ministry for Economic Affairs and Energy within the research initiative EnEff:Stadt (Energy Efficient City)
The additional costs for innovative measures (insulation of wall/ground floor, gas motor heat pump, ground-water coupling and automation) were 5,563,000 € or 489 €/m².
Living area: 4,584 m² (before renovation) / 5,863 m² (after renovation); total of 4 buildings after renovation: 9,338 m²
Note: The German living area is a floor area similar to the net floor area used as size of an apartment in case of rent or sale.
Residential units: 110 (before renovation) / 77 (after renovation)
The building is comprised of 6 storeys. The apartment structure after the renovation (remodeling) is presented in the graphic enclosed as Floor Plan.
The massive walls are insulated with vacuum insulation wrapped in polystyrene (in total 10 cm) on the street side to reduce the overlap of the wall to the pathway. The other sides have been insulated with 14 cm of external thermal insulation composite system with resol rigid foam). The new wooden roof is insulated by 30 cm of mineral wool. The cellar ceiling is insulated from above by using 2 cm of vacuum insulation as part of the new floor system and 2 cm of expanded polystyrene. The windows are triple glazed with low e-coated glazing in highly efficient PVC frames.
|Cellar ceiling||0.20 W/m²K|
Building service systems
Heating: Central heat generation unit for 4 buildings (local district heating unit): Ground-water coupled gas motor heat pump (125 kW), gas condensing boiler for peak load (240 kW), 234 m² solar thermal collectors, 12 m³ buffer storage, 4 pipe local district heating network (separate pipes for heating and DHW), floor heating and radiators.
Domestic hot water (DHW): Combined with heating (central heat generation unit), 1,500 l DHW storage, legionella prevention using anodic oxidation, central distribution system from local DHU to buildings.
Cooling: No cooling system.
Ventilation: In one part of the building a mechanical exhaust ventilation system with ventilation slots in the window frames that open, depending on the indoor air humidity, has been installed. The other part of the building is ventilated by opening windows (cross ventilation possible). Window contacts stop the hot water flow through the radiators.
Lighting: user dependent lamps, on-off control
Household appliances: user dependent
Renewable energy systems
- 234 m² vacuum pipe solar thermal collectors (for all 4 buildings, heating + DHW)
- Geothermal energy use via ground-water coupled gas motor heat pump (125 kW, for all 4 buildings, heating + DHW)
- 1,469 m² polychristalline photovoltaic collectors (for all 4 buildings, feed-in)
Building Energy Performance
Final energy use
|Final energy [kWh/m²yr]||Calculated: DIN 4108-6/ DIN4701-10||Measured: 2014|
|Ventilation||3.1 (auxiliary)||to be analysed|
|Household appliances||unknown||not measured|
|Common area electricity||unknown||not measured|
Primary energy (non-renewable)
-10.3 kWh/m²a including heating, DHW, ventilation, auxiliary and self-generated electricity
RES contribution rate: 56% of final energy (+ solar thermal, geothermal)
Improvement rate: 94% compared to 254 kWh/m²a calculated final energy before renovation.
As written in the title of the case study the aim of the project was to achieve a CO2 neutrality for the heating energy use. For this the energy used for heating and domestic hot water together with the auxiliary energy (including the ventilation electricity (fan motors)) are multiplied with the CO2 equivalent factors of each energy source (here gas and electricity) and balanced by the CO2 equivalent emissions saved by PV electricity generated on the building and fed into the electricity grid. Here, the total PV electricity produced on the site for all 4 buildings was multiplied with the factor of the living area of the specific building divided by the living area of all 4 buildings). The CO2 equivalent factors were taken from the national information source GEMIS.
The calculation is performed as an annual balance and presented in the table below:
CO2 eq. factor
CO2 eq. emissions
Total CO2 eq. emissions
Auxiliary (incl. ventilation)
Electricity production (PV)
The calculation was performed as an annual balance and resulted a total of -13.9 t CO2 equivalent emissions per year. The building thus has a positive balance of the CO2 equivalent emissions. It generates fewer emissions than it saves by producing electricity by renewable energy.
Based on the measured values of year 1 the building would not achieve the CO2 neutrality. As written in the lessons learned chapter the running time of the heat pump was much lower in the first year than expected. With a smooth running heat pump the building should meet the calculated values in the second monitoring year.