Free trial

Reliable planning and execution – despite special requirements

eZeit Ingenieure

The Berlin-based planning office is simulating the complex energy-efficient refurbishment of a large-scale building complex in Polysun: Sustainable concept implemented and funding secured

eZeit Ingenieure is a planning office for architecture, building and energy technology. The Berlin-based company focuses on energy-optimized, sustainable construction. This means holistic thinking, planning, financing and implementation – from large-scale urban development projects to thermal bridge details. The planners’ range of services covers all areas of residential and commercial construction, from single-family homes and large residential complexes to entire neighborhoods. The specialists attach great importance to tailor-made concepts for economically energy-optimized construction projects in both new builds and refurbishments.


In a Berlin apartment building, the task was to carry out an energy-efficient refurbishment of the existing building. The building, with around 2,400 square meters of living space, originally had 17 residential units. An extension (3 units) and a new attic (4 units) with a total of seven new residential units were added as part of the refurbishment of the apartment building.

The requirement was by no means trivial. The renewal of the pipe network had to be “minimally invasive”. The reason: existing chimney flues in the building had to remain usable. And the existing radiators also had to be retained.

The details of the refurbishment were as follows: The old gas floor heating systems were replaced by a modern energy center. The energy concept included an exhaust air heat pump, a brine heat pump with nine deep boreholes and a gas peak load boiler in conjunction with solar thermal energy and photovoltaics on the roof surfaces. The old chimney flues could actually be used for the installation of the technical building equipment (TGA), including electrical installations, and no additional shafts were required in the existing building. The radiators were not replaced either.

The eZeit engineers wanted the energy renovation of the apartment building, which was built in 1900, to be holistic. This was the only way to make the conversion fit for the future. “The principle was therefore that everything in the planning and subsequent refurbishment was not just focused on the building envelope. Only the precise interplay between the building envelope and building technology reliably reduced CO2e emissions,” says Bernd Paarmann, an engineer at the Berlin-based company who specializes in building energy and information technology.

The consequence of this mixed situation: a large number of decisions had to be made before the conversion. The simulation-based planning, design and optimization of the integrated energy systems with Polysun from Vela Solaris paid off here.

Image@eZeit Ingenieure


In Polysun, Bernd Paarmann and his colleagues were able to record the input parameters – such as the building geometry, envelope, use and building services in the existing building. Only then was a precise planning of the building and energy technology tailored to the building carried out. Site-specific factors such as local weather data were also taken into account.

In order to plan cost-efficiently, the generator output should of course not be too high, but should be selected to suit the project in question. At the same time, the comfort requirements for hot water and heating/cooling had to be reliably met. Polysun was also used here.

“We also used Polysun to calculate how the future energy costs of operating the system would compare to the unrenovated state and the old gas heating systems,” says Paarmann. This was particularly about the topic of “green, affordable energy”.

The aspect of “minimally invasive refurbishment” could also be reliably simulated in Polysun. As some chimney flues in the existing building could not be used and additional new shafts were not required, the original separation of the heating network into high-temperature (existing radiators and hot water) and low-temperature (surface heating in the new building area) had to be removed. This left only one high-temperature network heating circuit, which is mixed down if necessary. New variants were added to the simulation in Polysun and calculated, as the question arose as to whether the planned energy concept would still work under these unfavorable conditions. It was important to ensure that the desired and required annual coefficient of performance could still be achieved and what the effects would be on the proportion of renewable energy and the proportion of electricity in relation to fossil fuels.

The latter aspect was therefore crucial: as possible subsidies could also be included in the profitability analysis of the energy and refurbishment concept, the specific seasonal performance factors of the heat pump were simulated precisely. The resulting efficiency can actually make it possible to obtain subsidies, which makes the refurbishment more attractive for both the building owners and the tenants.


“As we were able to use the simulation to determine the proportions of different energy sources such as electricity, gas and environmental heat, we were able to draw up a forecast of the development of energy costs in a comparison of new and old system technology,” says expert Paarmann. “This clearly showed the building owner and the tenants that, as the electricity transition progresses – the proportion of renewable energy in the German electricity mix continues to rise – and CO2 prices increase, our energy concept is much more sustainable in terms of energy costs than continuing to use gas.”

By substituting fossil gas with electricity and environmental heat, the eZeit engineers were able to realize a system concept that is prepared for the energy transition and the associated price developments in Germany, enables economical operation and has a small ecological footprint that will certainly meet the target requirements for the year 2045.

The funding programs of the Federal Ministry of Economics require a certain annual coefficient of performance. Proof of this must be provided by means of a simulation for more complex systems. “For this construction project, we used the simulation to secure funding for the energy-efficient refurbishment. These lower investment costs result in a lower rent increase for the tenants.

The simulation also enabled the Berlin engineers to check the necessary planning changes to the strings and the associated increase in the temperature level with regard to the criteria of the proportion of renewable energy, economic efficiency and future energy costs. “With the Polysun simulation, we were able to reliably ensure that the desired plant system can be implemented, qualifies for subsidy programs and guarantees economical operation of the plant,” says Bernd Paarmann, drawing a satisfied conclusion from the Polysun application.

Key features

At a glance

  • Customer: eZeit Ingenieure GmbH
  • Industry: Planning office for architecture, building and energy technology
  • Location: Berlin


  • Simulation of the energy-efficient refurbishment of an existing building
  • Complex specifications such as mapping the minimally invasive refurbishment of the building
  • Provide proof of economic efficiency in the simulation
  • Ensure proof of eligibility for subsidies in the simulation


  • Polysun Designer


  • Precise forecast of the development of energy costs in a comparison of new and old system technology, i.e.: proof of funding provided
  • Cost-saving planning realized: Win-win situation for tenants and building owners
  • Minimally invasive refurbishment reliably simulated
  • Long-term and sustainable system concept realized

Get in touch with us!

Contact us