Eighteen Soviet-era khrushchyovka apartment blocks built in the 1960s and 70s have been renovated as part of the Project SmartEnCity which aimed to move the notoriously energy-inefficient buildings into Class A, the most efficient possible.

In addition to a thicker-than-usual insulation layer, all buildings received a demand-based heat recovery ventilation system and a roof-mounted solar power plant. During the renovation, all windows were replaced with triple-pane windows and the cold bridges around the windows were reduced.

Last year, researchers studied the effect of the renovations of more than half of the renovated buildings.

Preliminary data on energy use shows that the energy demand has decreased by an average of 43 percent compared to the past. In total, grid electricity and natural gas have fallen by 27 percent and 58 percent, respectively. District heating has seen a reduction of 43 percent.

Tartu City Council said even less is spent directly on heating, as part of the district heating is now also used to heat domestic water, which was previously done with gas or electricity.

Looking at thermal images taken before the renovation, the most significant heat losses were found around the windows, in the location of the radiators under the windows, and in the panel joints. However, the thermal images taken from the renovated houses in February of this year showed evenly coloured facades, which means that there were mostly no heat leaks. In some isolated cases, minor temperature differences were observed. 

Engineer Kalle Virkus from the Tartu Regional Energy Agency, said the final figures will be known one to two years after construction, and these apartments were only finished in 2020.

"This is related to the optimization of technical systems and the drying out of moisture during construction, as well as the residents growing accustomed to the new systems," he said.

The SmartEnCity project started in Tartu in 2016 and 18 apartment building associations in the center of Tartu signed up. So far, seventeen have been completed and turned into "smartovkas". A smart and energy-efficient solutions district has been created in the city center.

"With the support of the project, 17 apartment buildings built in the 1960s and 1970s in Tartu's City Centre District were reconstructed, having now become the most energy-efficient reconstructed apartment buildings in Estonia", said Tartu Deputy Mayor Raimond Tamm.

"The indoor climate of buildings has also improved significantly, to which the innovative CO 2 -based ventilation management in all these buildings makes an important contribution."

The SmartEnCity project is funded by Horizon 2020 – The EU Framework Programme for Research and Innovation, and will run until July 2021.

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