Practices

CO2-neutral heat supply of a renovated multi-family house in Munich

Highlighted Case April 2015
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Project summary

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.

 

Project highlights

  • 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).

 

Construction costs
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.

 

Building size

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.

 

Building envelope

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. 

ComponentU-value

Wall:

Street side

Other sides

 

0.15 W/m²K

0.14 W/m²K

Roof0.10 W/m²K
Cellar ceiling0.20 W/m²K
Windows/doors0.90 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/ DIN4701-10Measured: 2014
Heating 18.3 33.6
DHW 10.1 17.1
Cooling   0.0   0.0
Ventilation   3.1 (auxiliary)to be analysed
Lightingunknownnot measured
Household appliancesunknownnot measured
Common area electricityunknownnot measured
Total 31.5 51.0
Self-generated electricity-17.5-11.4
Total balance14.039.6

 

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.

 

 

CO2 neutrality

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:

 

Energy source

Energy use

CO2 eq. factor

CO2 eq. emissions

Total CO2 eq. emissions

Heating

Gas

18.3 kWh/m²a

0.253 kg/kWh

4.63 kg/m²a

27.1 t/a

DHW

Gas

10.1 kWh/m²a

0.253 kg/kWh

2.56 kg/m²a

15.0 t/a

Auxiliary (incl. ventilation)

Electricity

3.1 kWh/m²a

0.664 kg/kWh

2.06 kg/m²a

12.1 t/a

Electricity production (PV)

Electricity

-17.5 kWh/m²a

0.664 kg/kWh

-11.62 kg/m²a

-68.1 t/a

Total

 

14.0 kWh/m²a

 

-2.37 kg/m²a

-13.9 t/a


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.

 

 

Acronym of the case

Lilienstraße Munich

Lessons learnt

The installation of the vacuum insulation was no problem despite the contractor´s first time experience with the system. The central automation system proved to be too complicated for the small company selected in the tendering process. Several rounds of analysis and corrections were necessary. There were problems with the coupling of the heat pump. Therefore, the running time was lower than planned and the boiler was used more often. This is also visible in the measured final energy consumption which has a higher final energy use. We hope that the results will be better during the second year of monitoring. The installed solar thermal system runs without glycol for improving the efficiency. In the case of frost, tap water is pumped through the system. The pump failed once and major frost damage was the result (covered and paid for by insurance). The project was financially attractive because of the addition of another floor on each of the three existing buildings and a greater utilization of built up areas by urban densification with the construction of an additional building in the existing space.

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Start date - End date

Sunday, 1 January, 2012 to Thursday, 31 December, 2015

Operational date

Tuesday, 1 January, 2013

Relevant tools

Calculation of the German energy performance of buildings standard DIN V18599 with ibp18599

Source of funding

Funding description

The project received funding from the Federal Ministry for Economic Affairs and Energy within the research initiative EnEff:Stadt (Energy Efficient City)

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