Project name: town Šal’a
Country: Slovakia
Settlement: 44.96 km²
No. population: 25,000 inhabitants
Building construction: 2018
Heating power: 10-12 MW
Heat source: water/water
Application: waste water heat recovery
Project name: town Šal’a
Country: Slovakia
Settlement: 44.96 km²
No. population: 25,000 inhabitants
Building construction: 2018
Heating power: 10-12 MW
Heat source: water/water
Application: waste water heat recovery
Šal’a is a town with almost 25,000 inhabitants located in the Nitra region of Slovakia, just over 60 km from the capital city of Bratislava. The town is surrounded by beautiful nature, with a river running through it. Šal’a is also known for its historic architecture dating back to 1002, when it was first formally mentioned and recorded.
Update of the district heating system
Like many other towns, Šal’a has decided to upgrade its district heating system with a nominal power of 22.5 MW, which serves 15,000 people. As the river divides the town into two banks, the district heating system consists of two separate circuits: CK 31 and CK 34. CK 31 has a total thermal power of 13.7 MW from gas boilers using natural gas, while CK 34 has 9.75 MW. In the future, the town plans to connect both circuits and establish a unified system.
The central heating system involves heat production in a central heat source and its supply to multiple heat consumers through heat distribution. The communal central heating system in Šal’a mainly supplies the residential and communal sector as well as local industry.
However, despite transitioning to a more environmentally friendly energy source, the city did not completely solve its energy problem. What was the problem? Not all geothermal heat utilization is necessarily energy-optimized, and this was the biggest problem with the system in Šal’a. While they did exploit geothermal water using heat exchangers, which had a temperature of 65 °C at the surface, up to 1.5 MW of heat at 47 °C was being wasted as they discharged the excess hot water into the river. Water with a temperature of 47 °C at the heat exchanger outlet represented a significant unused potential for renewable energy, while causing ecological damage to the river and significant financial losses. Šal’a was in conflict with itself: in its well-meaning efforts to become carbon-free, it had created a new, unforeseen environmental damage that incurred unnecessary costs. If only there were a way to better utilize the obtained geothermal energy… But there is!
Where does wastewater go when heating with a heat pump? The most environmentally friendly way is to inject wastewater back into the ground. However, in the city of Šal’a, this is not possible due to impermeable gravelly soil that makes it difficult for water to seep through, so wastewater is discharged into the river. Legal regulations apply to the temperature at which the wastewater must be cooled before being discharged into the river, to avoid endangering the aquatic ecosystem (in Slovenia, between 25 °C and 30 °C). The more the water is utilized (cooled), the smaller the concession the company has to pay!
How did we at Kronoterm solve the problem of underutilized geothermal energy in the city of Šal’a? The project involved upgrading the CK 31 circuit with four gas boilers, which was later enhanced in 2010 with a system for utilizing geothermal water heat extracted from a 1800-meter-deep borehole. We designed an update or upgrade of the system with appropriate heat pump technology, enabling better utilization of geothermal energy, being more environmentally friendly, significantly reducing costs, and requiring less gas consumption for heat production.
The implementation of the system upgrade took place in two phases. The first phase involved studying and integrating heat pumps into the system with maximum efficiency. The second phase involved producing special heat pumps to efficiently utilize wastewater in geothermal heat pump heating, with the possibility of heating water on the secondary side to over 80 °C. This technology was developed in 2017 by Kronoterm in collaboration with a compressor manufacturer.
We integrated the heat pump into the system to utilize waste geothermal heat on the primary side. The entire system can be controlled through a central monitoring system.
Let the results speak for themselves
The result was simply fantastic. The geothermal heating system upgrade designed by our company, Kronoterm, significantly improved the utilization of geothermal energy. Now, the water temperature before discharge into the river is less than 25 °C, or nearly 50% less than before the upgrade. This means a 50% increase in efficiency at the same inlet temperature to the system. As a result, the city’s heating system achieved an exceptional heat pump efficiency, and all other problems associated with the initial problem of suboptimal system utilization were subsequently resolved. Costs have been reduced, and Šal’a has set an excellent example for other advanced cities by meeting environmental requirements.
For the most skeptical, the exceptional results can be illustrated with figures: experimental operation showed that the cost of heat production with heat pumps was more than half lower than that of production with gas, and greenhouse gas emissions were four times lower! Thus, the Kronoterm study conducted before the system upgrade was also confirmed in practice.
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