Home Hannover Monitoring and Evaluation Monitoring results 2006-2012 in Hannover

Monitoring results 2006-2012 in Hannover


Monitoring from 2006 to 2012

As part of the act2 project, a total of 52 residential buildings in Hannover encompassing 398 dwelling units and around 26.000 m² of living space have undergone energy efficiency refurbishment. The majority (39 multiple-occupancy dwellings) are owned by two housing-development companies, Gundlach GmbH & Co. KG and Spar- und Bauverein eG. After a full refurbishment all of the buildings now have an energetic standard considerably higher than that required by law. It was a main target of the project to reach at least the standard of the German energy-saving regulations (EnEV) stipulated for new buildings. With an insulation thickness of 14-16 cm for the outer walls and 20 cm for the top-floor ceilings the requirements have even been exceeded. This exemplary retrofitting convinced the housing company Wohnungsgenossenschaft Herrenhausen (WGH) to participate in the Concerto project with three multi-occupancy buildings (1.704 m²).The refurbishment work on 42 multiple-occupancy dwellings has seen single-storey gas heating replaced by a central heating and hot-water supply system. 33 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 the 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 in the district of Ahlem, which now also are heated in a carbon-neutral way. One building in the district of Vahrenwald has, since 2009, been heated using a ground source heat pump with a peak load gas boiler.

For 29 multiple-occupancy dwellings with district heating, consumption data covering five or six heating seasons could be analysed. Although measured levels of consumption are somewhat higher than predicted, 55-65 per cent heating energy savings indicate that these buildings are considerably outperforming conventionally refurbished ones. The rather more ambitious measures (complete window replacement with a heat trans-fer coefficient of 1.3; optimisation of thermal bridges) of Gundlach's properties have no significant effect on the energetic standard: the average heating-energy consumption of about 60 kWh/m²a is very similar to the buildings of the Spar- und Bauverein 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 re-quirements. Prior to refurbishment, average consumption across all buildings was above 140 kWh/m²a. The investment costs for energetic refurbishment of the building shell covered a range of 130-210 € per m² living space. Die additional costs for the connection to district heating lay between 77 and 115 €/m².

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 25-45 per cent. At around 33 kWh/m²a it is, post-refurbishment, around 75 per cent higher than before in absolute terms owing to the poorer efficiency of hot-water storage tanks and higher distribution losses - in extreme cases including the energy losses of a small heating net even up to 2,5 times as high before the measures with hot water preparation in the dwellings. So, the total energy consumption for heating and domestic hot water in these objects of about 80-90 kWh/m²a is substantially higher than the energy consumption only for heating, thus the savings of 35-55 per cent are lower. 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 were also taking part in the project: six multiple-occupancy buildings were refurbished and the three owners gained valuable experience in carrying out full energy efficiency refurbishment of 30 rented flats on a high level. Inconvenience to tenants was kept to a minimum owing to careful coordination of construction sched-ule 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.

At least four private house builders of detached buildings took part in the project and refurbished their houses according to Concerto standard. With only one exception all of them an additional thermal solar system was installed. The energy savings results of these four buildings are very different. The energy consumption for heating and domestic hot water could be reduced from partly over 250 kWh/m²a to 50 - 95 kWh/m²a. This corresponds to savings of about 50 -80 per cent. One building owner decided for very ambitious measures including the installation of a ventilation system with heat recovery.

Finally, the Concerto/act2 demonstration buildings include ten properties owned by the Stadtwerke Hannover AG energy utility and the City Council. The following results could be achieved: Three school buildings, after a full refurbishment, realised energy savings of 44-65 per cent to remaining consumption values of 58-113 kWh/m²a. The future energy cost savings for the municipality amount to over 50.000 € per year. Additionally two photovoltaic energy plants (83 kWp and 16 kWp) financed by citizens have been installed on the roofs of the school buildings and gained an average total solar energy production of 144 MWh per year.In the Lister Bad outdoor swimming pool, a solar absorber has enabled the energy used for pool heating to be more than halved.The municipality of Hannover, due to four new wood pellet systems, now is saving a total of 1.770 MWh fossil energy or 432 t of CO2 emissions and about 80.000 € energy costs in its own buildings every year. In the Burgweg depot, a pellet-fired boiler since 2007 covers 75-85 per cent of the heating requirements.The Stadtwerke Hannover AG's decided for the construction of a Wood Energy Centre to guarantee a long-term reliable supply of energy wood for the owners of biomass heating systems. Since November 2007 wood fuels are produced and distributed here. Revenue generated has been almost doubled since 2008. In 2009, over 3.100 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 on the roof of a storage depot by the Stadtwerke. Power generation from this facility has, at 74.000 kWh ex-ceeded expectations by 15 per cent.