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“Old Zöllner District” model project within Weimar’s inner city

EnEff:Stadt - Forschung für die energieeffiziente Stadt
Sanierungsobjekt im innenstadtnahen alten Zöllnerviertel

Building awaiting refurbishment in the “Old Zöllner District”, located close to the inner city


Settlement summary

Block, ensemble
Project status Projektstatus: Phase 2Planning
Location of local community 99423 Weimar, Thüringen
Settlement in figures Area: 84.26 km²; population: 65,230
Developer, organizer Max-Zöllner-Stiftung, Weimar
Settlement Wilhelminian-era buildings, inner city residential and commercial developments
Utilisation type mixed area
Gross floor area, before (according to DIN 277) 20.460 m²
Gross floor area, after (according to DIN 277) 25.468 m²
Residential area, before 8.241 m²
Residential area, after 10.200 m²
Schools, kindergartens area, before 10.746 m²
Schools, kindergartens area, after 10.746 m²
Total public facilities area, before 1.473 m²
Total public facilities area, after 4.522 m²
Age structure 1 listed villa built c. 1900; 7 residential buildings and a school built c. 1925, partly listed; 3 buildings (school, child day care centre) from the 1960s
State of construction and refurbishment poor– requires considerable refurbishment (residential buildings), partly refurbished (school, child day care centre)
Heating system Before: individual stoves (coal), individual heating systems (natural gas), central heating systems (heating oil, natural gas); after: decentralised energy supply using renewable energy, CHP and local heating
Ownership structure Rented by foundation, partly owned by the City of Weimar
Project themes

Project description

Because of existing characteristics such as the building and supply structure and the still low use of renewable energies, inner city residential districts offer considerable potential for increasing the efficient and ecological use of energy. They can therefore make a considerable contribution to protecting the climate and conserving resources.

The community

With funds from the German Federal Ministry for the Environment, the City of Weimar is currently working on an integrated, community climate protection concept called “Electricity, Heating, Cooling”. The “integrated climate protection concept” is concerned with analysing the energy requirement coverage in Weimar, revealing potential for lowering the energy consumption, increasing energy efficiency and the proportion of renewable energies, examining possibilities for action in the community and, finally, with specifying measures for lowering greenhouse gas emissions as part of a priority list. The intention is to create a “total potential atlas” for Weimar showing the potential for saving energy, for using local heating with cogeneration and for using renewable energies. This atlas shall provide the basics for defining specific climate protection goals for Weimar. Based on this, a catalogue of measures will be drawn up with district-related and target group-oriented action plans.

The district

The site is situated to the southwest of Weimar’s city centre in the middle of an area whose structure has evolved with the town’s expansion at the beginning of the 20th century. The high-quality residential district with its Wilhelminian villas, the very well developed school and nursery location with the Pestalozzi School and the Kindergarten schools in Shakespearestrasse and Böhlaustrasse, as well as the new-build schemes that are to be integrated, offer an ideal location for developing and implementing an innovative energy supply concept for inner city areas.

The project

With is diverse range of new-build measures, refurbishment schemes and different use concepts, the “Old Zöllner District” project in Weimar offers an excellent opportunity to implement innovative technologies and, by means of integrated planning, to link various trades and project participants, to investigate and implement the objectives as part of a model project in an inner city area with a mixed structure, and to monitor them during the long-term operation.

The project partners are endeavouring to achieve a standard for the model project that accords with German Energy Savings Ordinance EnEV 2009 minus 30 per cent for the modernisation, with a passive house standard for the new buildings. It is intended to achieve such an energy standard by simultaneously implementing solar thermal energy, geothermal energy and cogeneration in combination with a local heating network and long-term storage for supplying an urban district with a mixed structure. Because of the given and planned levels of use in the redevelopment area, it is intended to incorporate and implement the knowledge gained from the “Energy efficient schools”, “Energy-optimised new buildings” (EnBau), “Energy-oriented improvement of the building fabric” (EnSan) and “Heating and cooling with low exergy” (LowEx) projects.

The following technologies, methods and processes shall be incorporated in the conception and implementation:

• Thermal cooling technology for the summer-time air conditioning, all-year use of solar energy, geothermal energy, combined heat, power and cooling generation with communal energy management based on cutting edge information technologies
• Planning and optimising a local heating network with innovative storage technologies
• Reducing consumption in the buildings with lowered costs through using innovative thermal insulation measures on historical facades
• Recovering heat from waste water systems.


After recording the current state, different alternatives for a decentralised energy supply concept for the inner city refurbishment area will be developed, simulation calculations will be conducted and the proposed overall systems will be assessed in terms of use, expenditure, economic feasibility, viability and environmental friendliness. The most economic and energy-efficient version will be selected and the preliminary planning conducted to implement the concept.
In the second project phase, the energy concept will be implemented and supported with long-term monitoring that will check the efficiency of the measures. Based on the experience gained, generally applicable assessment criteria and guidelines for action will be derived for inner city mixed structures.

Concept and heat supply options

By integrating a diverse range of innovative technologies available on the market, it is intended to construct an innovative, optimum supply system for inner city areas that utilises wasteland. This is because the Zöllner District in Weimar generally offers diverse possibilities for utilising renewable energies and for producing electricity using gas-fired combined heat and power generation. The roofs of the buildings also enable, for example, the use of solar collectors or photovoltaic systems on a total surface area of 750 m².
Two refurbishment versions result in the following heating requirement forecasts:

• Current condition and new buildings according to EnEV 2009:
Balanced heating requirement for the existing, non-refurbished buildings in their current condition and construction of new buildings in accordance with the EnEV standard 2009 This combination results in energy consumption values for the building heating amounting to 2.635 GWh p.a.
• Refurbishment (KfW Efficiency Building 70) and new construction (passive house): Refurbishment of existing buildings in accordance with the KfW Efficiency House 70 standard (EnEV 2009) and construction of new buildings to the passive house standard. This results in a heating requirement of 1,375 GWh p.a. This leads to 48% energy savings.

For supplying the “Old Zöllner District” with heating energy, three alternatives were initially considered that differ in terms of the heat generation and local heating network and in terms of the solar feed, heat storage and control systems.

Version I:
• Heat generation: central
• Local heating network: separate networks for space/water heating, solar and geothermal energy
• Solar feed system: central
• CHP operation: electricity driven
• Heat storage system: seasonal storage tanks for solar and CHP waste heat, central storage tank for geothermal energy
• Control system: Separate controls for the CHP, solar power system and peak load boiler on the one hand and for the geothermal system on the other, with communication between them and with the loads.

Version II:
• Heat generation: decentralised CHP and gas condensing boiler for building groups
• Local heating network: ring main between the loads, all generators feed into the network
• Solar feed system: decentralised
• CHP operation: heat-driven
• Heat storage system: storage of CHP waste heat in the geothermal field (summer) and in the ring main (winter); buffer storage tanks for heating water
• Control system: peak loads and the daily heating requirements are produced and balanced out by the heat distribution systems themselves through retaining heat.

Version III:
• Heat generation: independent supply of individual building groups
• Local heating network: network for building groups
• Solar feed system: decentralised
• CHP operation: heat-driven
• Heat storage system: decentralised storage tanks for solar thermal and geothermal energy
• Control system: intelligent control system to enable surplus energy and peak loads to be balanced out between the individual generators.


Project phase 1 (recording the current condition, decentralised energy supply concepts, simulation calculations, assessment of the conceived overall systems) is being supported with funds from the German Federal Ministry of Economics and Technology (EnEff:Stadt research initiative).

Energy characteristics

before potential after unit
Total area with energy requirement 25.468,00   25.468,00
Final energy requirements (electricity) 21,00 12,00   kWh/m²
Final energy requirements (heat) 53,00 28,00   kWh/m²
Primary energy requirement (heat) 131,00 66,00   kWh/m²