Tallinn University of Technology

Increasing stormwater volumes caused by climate changes is becoming more and more a global problem. A couple years ago the Mechanics of Fluids and Structures Research Group of Tallinn University of Technology set a goal to find new applications of the increasing amounts of stormwater. As a result of the research a scholarly article titled "An optimal solution of thermal energy usage in the integrated system of stormwater collection and domestic-water heating" was published in the reputable professional journal Urban Water Journal.

According to one of the leaders of the research, Associate Professor Janek Laanearu, growing urbanisation causes inevitably increase in stormwater volume: "Simple calculations show that during the last decade the annual average of stormwater volume in the impervious catchment area in Tallinn was approximately 45 million cubic metres, which significantly exceeds the volume of water in Lake Ülemiste“.

Thus, new solutions are needed for mitigation of floods accompanying severe weather rainfalls. In European cities the storage tanks are increasingly being used for reducing loads in stormwater systems and for rainwater harvesting. More than fifty per cent of the volume of water used in commercial and public buildings does not have to meet the requirements for clean drinking water quality; e.g. on the plot of the office building at Sõpruse pst 157 (which is a so-called green office building) in Tallinn an underground storage tank has been installed that allows the collected rainwater to be used in the toilets of the building.

In Janek Laanearu's opinion, seeking a solution for using stormwater heat for domestic hot water production in different type buildings (e.g. commercial, public or residential) constitutes a multifunctional optimisation task. Within many possible solutions the stormwater volume in storage tank and rainwater catchment area need to be determined that correspond to the precipitation statistics of the rainy seasons and the hot water consumptions of the buildings.

The availability of stormwater thermal energy depends in turn significantly on water flow in the stormwater system and on the heat extraction technology. For effective heat extraction from a storage tank it is necessary to simulate temperature stratified flow. However, it is not possible to solve the task only by using the flow hydraulic formulae which is why CFD (Computational Fluid Dynamics) simulation needs to be used in future study.

"Stormwater thermal energy is also one of the renewable energy sources that could be, in addition to wind, solar and hydraulic energy, a viable alternative to fossil fuel energy. An interesting solution for extracting heat from a natural water body, for example, is used for seawater heating-cooling system of the hangars at the Seaplane Harbour of the Estonian Maritime Museum in Tallinn, “Associate Professor Laanearu adds.

Kersti Vähi, TTÜ Research Administration Office