Monitoring results 2006-2010 in Hannover

As part of the act2 project, a total of 50 buildings in Hannover (encompassing 382 dwelling units and around 24,000 m² of living space) have undergone energy efficiency refurbishment. The majority - 39 multiple-occupancy dwellings with 340 dwelling units and 21,000 m² of living space - are owned by two housing-development companies, Gundlach GmbH & Co. KG and Spar- und Bauverein eG. In all of the buildings, full refurbishment has been (or will be) carried out to a standard considerably higher than that required by law: with an insulation thickness of 14-16 cm for the outer walls and 20 cm for the top-floor ceilings, and with windows renovated and cellar ceilings insulated, even the requirements stipulated for new buildings under German energy-saving regulations have been exceeded.
The refurbishment work on multiple-occupancy dwellings has seen single-storey gas heating replaced by a central heating and hot-water supply system. Most buildings have been connected to district heating systems, which are far more environmentally sound than gas heating owing to the high proportion of cogeneration involved. Under the Concerto project, even wood pellets have been used to fuel a combined heat and power station, so that - on paper at least - these buildings are virtually carbon-neutral in their operation. A shared central-heating plant with a wood pellet-fired boiler system went into service, supplying eight buildings, and one building has, since 2009, been heated using a ground source heat pump with a peak load gas boiler.
For 25 multiple-occupancy dwellings with district heating, consumption data covering two or three heating seasons has already been analysed. Although, to date, measured levels of consumption are somewhat higher than predicted, 50-70 per cent heating energy savings indicate that these buildings are considerably outperforming conventionally refurbished ones. Owing to rather more ambitious measures (complete window replacement with a heat transfer coefficient of 1.3; optimisation of thermal bridges), Gundlach's properties achieve a superior standard (45-58 kWh/m²a heating-energy consumption) to the buildings of the Spar- und Bauverein (56-69 kWh/m²a) in which, for example, only the glass in the old window frames has been replaced, and critical thermal bridges have been taken into account only as dictated by building-physics requirements. Prior to refurbishment, average consumption across all 25 buildings was above 140 kWh/m²a.
Both of these housing-development companies have thus gained valuable experience in carrying out full energy efficiency refurbishment to an appreciably higher standard than that required by the statutory regulations. Inconvenience to tenants was kept to a minimum owing to their provision with intensive support while the work was being done. The intention is that future refurbishment measures should also be undertaken to a comparable standard.
Monitoring of consumption data has revealed, as would be expected in buildings that have undergone energy efficiency refurbishment, that hot-water consumption is of increasing importance: the proportion of energy use it accounts for rose from 10-15 per cent to 30-40 per cent. At around 30 kWh/m²a it is, post-refurbishment, around 50 per cent higher than before in absolute terms owing to the poorer efficiency of hot-water storage tanks and higher distribution losses.
There is as yet no indication that dispensing with controlled ventilation has resulted in any difficulties. Average humidity, as revealed by sampling, was not at a level that should pose any problems.
Private house-builders are also taking part in the project: a total of four detached and seven multiple-occupancy dwellings (with 38 dwelling units) were refurbished. Part of the heating requirement here is met by district heating or wood pellet-fired boilers. In four buildings, a solar installation was also put in place for water heating. It is not yet possible to draw any conclusions about energy savings, as consumption data have yet to be analysed. It is, however, expected that the saving will be similar to that achieved by the housing-development companies; initial results are expected in the autumn.
Finally, the Concerto-act2 demonstration buildings include nine properties owned by the Stadtwerke Hannover AG energy utility and the City Council. Results are already available for four projects:
In the Lister Bad outdoor swimming pool, a solar absorber has enabled the energy used for pool heating to be halved.
In the Burgweg depot, a pellet-fired boiler has been installed which has for two years been meeting around 50 per cent of the heating requirements.
Revenue generated by the Stadtwerke Hannover AG's Wood Energy Centre has been almost doubled since 2008. In 2009, over 1,500 tonnes of firewood, wood pellets and woodchips were sold, with an information centre advising interested customers on heating with wood.
A photovoltaic plant with an output of 75 kW has been installed by the Stadtwerke. Power generation from this facility has, at 75,000 kWh in its first year of operation, exceeded expectations by 15 per cent.