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Efficiency House Plus - Renovation of 2 Row Houses from 1938, Neu-Ulm Germany

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Building data:

Location: Pfuhler Str. 4+6 / Pfuhler Str. 12+14 Neu-Ulm, Bavaria, Germany

Building Owner: NUWOG Neu-Ulm Housing Company

Architects: Werner Sobek, Stuttgart / o5 Architects bda, raab hafke lang, Frankfurt Main

HVAC planer: Werner Sobek Green Technology, Stuttgart / EGS-Plan, Engenierung company for energy- building- and solar technology mbH, Stuttgart

Monitoring: RWTH Aachen University E3D, Institute of Energy Efficiency and Sustainable Building

Type of building: Multi storey dwelling

Number of residential units: 10 / 8

Heated net floor area: 600 m² / 678 m²


Project summary

In Neu-Ulm, in the southern part of Germany, the first Efficiency House Plus projects from an existing building stock were finished in 2015 with the renovation of two multi-storey dwellings owned by the housing company NUWOG. The two row house complexes, Pfuhler Str. 4+6 and Pfuhler Str. 12+14, built in 1938 were part of a planning competition for universities in cooperation with consultants that was held by the Federal Government in cooperation with the NUWOG. The conditions were an energy efficient retrofit with the aim of achieving the Efficiency House Plus standard by generating more energy than the building needs for its own use. Both wining concepts implemented the extra energy by building-integrated photovoltaics, solving at the same time the high standard of architecture and comfort. 


Pfuhler Street 4+6, Neu-Ulm


The Stuttgart architect Werner Sobek utilized as a planning element partially prefabricated wall and roof elements that surround the building. The stock roof was completely removed and replaced with new elements. The highly insulated façade system in timber was then mounted on the existing exterior wall including ventilation and other supply ducts.


Building envelope

The partially prefabricated outer shell of the façade elements containing internal supply pipes and a thermal insulation layer of 30 cm mineral wool has a U-value of 0.10 W / m²K. The roof elements consist of web beams with intermediate mineral insulation layer, air-tightness level on the underside and plasterboard cladding with installation level. They are provided with the substructure for a PV system on a foil seal. The U-value of the roof is 0.10 W / m²K.


The windows were designed as passive house windows with triple glazing. The U-value is 0.71 W / m²K. The ceiling to the basement was preserved and underneath provided by an insulating layer. The U-value of the ceiling to the unheated basement is U = 0.16 W /m²K.


Building service system

The minimized building technology with heat pump, hot water storage and ventilation system is arranged in the basement. Here, there is enough space available and the plant is easily accessible for maintenance purposes. All pipes can be installed horizontally in the basement and only short vertical risers are needed in the façade to reach the individual apartments.


The heat supply for heating and domestic hot water is provided by a brine-water heat pump. The distribution of heating energy is conventionally via tube radiators. Due to the low heating demand only one geothermal probe is necessary in the garden. The heat pump supplies a 1000 l combination tank, which ensures the supply of heating and hot water demand. In each apartment, a fresh water station is installed to raise the temperature of the drinking water level and to prevent Legionella formation.


A highly efficient ventilation system with 80 % heat recovery supplies five apartments in each section of the building. The outside air is taken in centrally in the area of the balconies on the ground floor, on the north facade of the garden side, and is directly led into the cellar. Supply air and exhaust air are laid horizontally in the basement, to lead via vertical channels in the curtain wall directly to the respective rooms. This avoids channeling in the low-rise apartments. Each apartment is provided with its own sewer system to avoid telephony or fire problems. Living and sleeping rooms are supplied with supply air, exhaust air is extracted in the kitchen, bathroom and toilet. By means of a cascade ventilation, the necessary air exchange can be reduced to a hygienic minimum of 30 m³ per person by directing the supply air from the bedroom to the living room, down the hall to the kitchen or into the bathroom. The energy-saving ventilation system can be supplemented at any time via individual window ventilation.


All apartments are equipped with highly efficient lamps. The household appliances have the highest possible energy efficiency rating (A++ or better).


The south roof and the flat roof are covered with monocrystalline PV modules on an area of 214 m² and have a capacity of 33.5 kWpeak. The modules are ventilated and bolted to a metal substructure above the foil roof.


Building Energy Performance

The delivered energy use was calculated due to the German Energy Saving Ordinance (EnEV) by the German Standard DIN V 18599. For the Efficiency House Plus standard the assessment method is extended to include the energy need for lighting and domestic appliances. An overall final energy demand of 20 kWh/m² is assumed.


During a monitoring period of two years all energy flows of the building were recorded. The overall energy consumption and the energy generated from the PV installations have been measured constantly. The comparison of the calculated delivered energy demand of 41.3  kWh/m²yr and the measured energy consumption of 33.6 kWh/m²yr in the first measuring period and 35.7 kWh/m²yr in the second measuring period showed a lower consumption of about 20 %. Accompanying by a 16 % higher production of renewable energy by the PV-system the energy surplus generated by building was more than 200 % higher than calculated.


The technical installation with the heat pump and the central ventilation system with heat recovery were implemented successfully and present a convenient system to ensure the Efficiency House Plus standard. Additionally the subsequent enlargement of the PV area generated more renewable energy and led to a higher plus than calculated. After the first measuring period the plus was 19.753 kWh/yr and after the second measuring period 18.781 kWh/yr, calculated were a plus of 6.905 kWh/yr. The ratio of self-use PV-generated electricity was about 10 %.


Construction costs

The construction costs due to the German DIN 276 for the cost category 300 (building construction) were 893.500 € (1.490 €/m²NFA). The costs for the category 400 (technical devices.) had an amount of 543.400 € (906 €/m²NFA). For both groups the costs were in total 1.436.900 € (2.400 €/m²NFA).


Pfuhler Street 12+14, Neu-Ulm


The team around o5 Architects from Frankfurt carried out both floor-plan based changes and improvements of the thermal insulation of the building envelop. Four dwellings were extended with one room on the back of the building. Spacious maisonettes were created upstairs under the roof. Living and cooking areas were combined.


Building envelope

The transmission heat losses of the building are reduced due to the low U- values of the building envelope and a thermal bridge reduced construction. The existing massive outside wall was insulated with a thermal insulation system with 20 cm mineral wool. The construction achieves a U-value of 0.20 W/m²K. The roof construction was reinforced by carpenters and provided with a 24 cm mineral wool. This gives the roof construction a U-value of 0.16 W/m²K. The ceiling above the unheated cellar was retained in the existing building and provided with a 15 cm thick insulation layer underneath. The U-value of the construction is 0.18 W/m²K. The now floor-deep windows are fitted with triple insulating glazing and achieve a UW value of 0.75 to 0.78 W/m²K. On the south side of the building there is an external sun protection made of wooden sliding elements, which can be controlled manually.  


Building service system

The heat supply for the heating is provided by a brine-water heat pump, which uses the ground as an environmental heat source by means of helical probes. The distribution is carried out via vertical pipe lines on the facade, the transfer via low-temperature radiators (max. 45°C), which are also arranged on the outer walls. Four 700 l storage tanks are installed for the central storage of heating heat. The decentralised domestic hot water heating is provided by exhaust air heat pumps in the bathrooms. They are equipped with an enlarged storage tank (200 l to 300 l) and use the warm ambient air as a heat source, which is extracted centrally by the appliances and flows through defined supply air openings in the facades. In order to precondition the supply air openings are arranged behind the low-temperature radiators. By integrating the exhaust air system into the water heating system, supply and exhaust air pipes in the building can be largely dispensed with and generated domestic hot water is virtually free of charge. All apartments are equipped with highly efficient lamps. The household appliances have the highest possible energy efficiency rating (A++ or better). Energy is generated via a roof-integrated photovoltaic system with monocrystalline modules with a size of 161.60 m² and an output of 24.93 kWpeak.


A monitor-supported system for displaying energy consumption was adapted to the special requirements of a rented apartment. By using the data already recorded in the monitoring and adding some fewer other sensors, as well as a simple presentation of the results, a robust and inexpensive solution for use in rented housing has been found (e.g. use of a web interface instead of a monitor in the apartment).


Building Energy Performance

The calculated delivered energy demand was calculated by 41 kWh/m²yr. In both measuring periods the consumption was 50 % higher than calculated, so that after two years the Efficiency House Plus Standard could not be reached. High thermal energy losses led to an increased consumption of heating energy which was twice as high as previously predicted. Both the high thermal losses caused by the decentral exhaust air heat pumps and the inadequate heat capacity of the ground for the central brain water heat pump required an additional electrical heating. This energy consumption was higher than the energy generated by the PV-system. During the first year of measuring the dwellings need 8.730 kWh/yr and during the second year 9.198 kWh/yr more than they generated by the PV installation. The ratio of self-use PV-generated electricity was about 24 %.


Construction costs

The costs due to the German DIN 276 for the cost category 300 (building construction) were 796.800 € (1.337 €/m²NFA). The costs for the category 400 (technical devices.) had an amount of 519.200 € (871 €/m²NFA). For both groups the costs were in total 1.316.000 € (2.208 €/m²NFA).

Lessons learnt

Due to increased consumption of heating energy, with increased ventilation heat consumption the building Pfuhler Str. 12+14 did not attain the Efficiency House Plus standard. Obviously all individual components for dimensioning the building service systems have to match to each other optimally. This also requires high quality in planning, execution and adjustment with a good communication between all parties involved in the process. The level of self-use PV-generated electricity with an average of 10 % (Pfuhler Str. 4+6) and 24 % (Pfuhler Str., 12+14) is due to a non-existent tenant flow concept and a lack of electricity storage rather low.

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