Wednesday, March 2, 2011

Passive House Case Study Hannover-Kronsberg, Germany

Passive House Case Study Hannover-Kronsberg, Germany

This case study looks at the 32 terraced passive housing project in Hanover Kronsberg built in 1998 by the developer Rasch & Partner in cooperation with the Stadtwerke Hannover. For the first time a heating system using exclusively post heating of the fresh air necessary was used. This very simple and cost efficient house technology concept is possible thanks to extremely high building envelope efficiency with very good insulation, thermal-bridge free construction, airtight building element junctions and windows of a quality not previously available. Together with the heat recovery system, this leads to a space heating requirement in the houses of less than 15 kWh/(m²a), a figure which is roughly a seventh of that used in typical new German housing.

The houses are arranged in four rows with eight houses in each row. This arrangement offers the advantage of reduced envelope surface area to volume ratio. This project was unique at the time and the main intention of this project was to show, that heat supply in passive houses can be realized by warming up the supply air of the balanced ventilation system. These houses have no conventional heating system with radiators, except one in the bathroom.

Passive solar
The main windows are directed to south, so daylighting is provided by direct solar radiation for the duration of the day. In winter, solar gains through windows cover about one third of space heating energy demand. In summer, a manual-driven shading system protects the rooms from too high temperatures. Besides this, the high quality thermal insulation in combination with the large internal masses (concrete) help to keep the temperatures in summer on a moderate level, if cross ventilation during the night is applied.

The walls and roofs are made of light-weight wooden construction with Uvalues of Uwall= 0.13 W/(m²K) and Uroof = 0.10 W/(m²K). The core of the building, the cross-walls and end-walls are made of prefabricated concrete elements. In addition, triple-glazed windows with specially insulated window frames as well as a home ventilation system with a high efficiency heat exchanger were installed.

Thermal Image of Passive House
The roof is built from prefabricated lightweight wood elements with 400 mm high I-beams, which span from one partition wall to the next. An internal polyethylene foil forms the essential airtight layer. The outer wall elements for the north and south facades are also built using prefabricated lightweight wood elements. So-called half box beams are used as shafts. An internal polyethylene foil forms the airtight layer. The outer wall of the gable sides is, like the house partition walls, built from loadcarrying reinforced-concrete slabs. This is protected on the outside against heating losses by a 400 mm polystyrene external thermal insulation compound system. The
Thermal Bridge Free Eaves Junction
concrete itself forms the airtight layer for the gable wall. The floor slab consists of 240 mm prefabricated steel-reinforced slabs, which is insulated underneath by factory-made 300 mm polystyrene external thermal insulation. The concrete floor itself also forms the airtight layer. Only the exhaust and intake ducts in the gable area and the drainage pipe through the base plate penetrate the thermal envelope. The ventilation system and the supply pipes run to the building services container in the gable area of the houses.



  1. Dec, good blog well done. I was just wondering did you come across if any of the houses suffer from any over-shading as they appear to be close enough together from the photo above??

  2. Hey Dec.
    This is a very interesting development because it demonstrates the use of the Passive House standard on a large scale. Developments such as give us an insight to what public housing in the future may look like. Also this development shows up how far ahead Germany is in terms of Passive House development, due to the fact that this project was completed in 1998.
    Just some questions...
    1. How is heating for hot water provided ?
    2. Seen as this development has been in use since 1998, it should be a strong testament to the quality of the Passive House standard. Are the houses performing as they should and have any design flaws been realised ?

  3. Hello Dec, Were there any considerations to be made for the fact that the thermal envelope extends to the row of houses and not each house unit from the point of view of airtightness and insulation. For example if a neighbouring house is unoccupied for any reason the windows could be left open, or the lack of heating when unoccupied could cause an increased heat load on the adjacent units if there isnt sufficient insulation in the party walls. I imagine that the thermal difference would still be minimal enough not to cause issues but I wonder if this was looked into at all.

  4. In reply to the first comment by EGG

    Well Egg the reason that the houses appear so close together is that they are actualy terraced houses as stated at the start of the blog. As you can see from the aerial photograph the shawdows cast are not interferring with the solar gain of the buildings. The terraced block of passive houses are facing south west to maximise solar gain and the two blocks of housing are too far apart to cause any over shading.

  5. In reply to the second comment by David

    The heating for the hot water is supplied by the solar thermal system. The solar thermal system consists of a ca. 4 m² flat collector field on the southern roof, a control unit, the expansion vessel as well as the heat exchanger in the lower part of the hot water tank. It functions as an independent system with an anti-freeze liquid filled closed circuit. Under sufficient solar radiation, the control unit activates the pump. Due to the placement of the heat exchanger in the lower part of the water tank, it can be completely heated from below (300-litres). The storage tank temperature sensor is mounted in the area of the solar heat exchanger. The second temperature sensor is located in the collector on the roof. The temperature in the storage tank can be heated up to roughly 85 °C by solar energy. The above mentioned water mixer makes sure, through the mixing of cold water, that no scalding occurs at the taps.

    In reply to your second question.

    The houses were monitored over a period of time. In regards to thermal comfort the houses only saw a slight deviation in room temperature with an average of 21,1°C in the middle of the winter and very slight deviation (20,9°C) on the coldest day which shows that comfort is guaranteed, independent of the climate conditions in these passive houses. In summer time the room temperatures deviated between 25°C and 25,7°C on the hottest day of the year.
    In regards heating load the passive house measured between 8,8 W/m² the first year and 7,0 W/m² in the second year which is well below the required value of 10 W/m² therefore the passive house proved successful in this regard.
    In relation to heating consumption the houses measured at 16,0 kWh/(m²a) in the first year which is slightly above the required 15 kWh/(m²a) but in the second year the energy consumption was reduced to 13,3 kWh/(m²a) which is below the required value. Overall the houses have lived up to the expectations of passive house construction

  6. In reply to the third comment by Sean,

    Yes Sean that actually caused variations in temperatures of neighbouring houses which lead to increased energy consumption of the house with the higher set temperature as the difference in temperature results in heat flow through the partition wall from one house to its neighbour. This lead to a reduction in one of the houses energy consumption but an increase in energy consumption in the other house. To explain this better consider that neighbour A has set his room temperature at 23°, whereas neighbour B has set his at 19°C. The resulting heat flow through the partition wall from A to B in a Passive House standard terraced house is almost 900 kWh/a. House B’s heating consumption is thus reduced by about 7,6 kWh/(m²a), whilst house A’s consumption is increased by the same amount. The heat has not been lost, it is just in the neighbour’s house. The absolute level of this effect is not dramatic; the effect is economically compensated due to the only partially consumption-dependent billing.