Achieving Maximum Utilization of Geothermal Energy with High-Efficiency Heat Pumps

The project of district heating in Slovakia, which we carried out at Kronoterm, proves that there are no limits to the use of heat pump technology. Representatives of a public district heating company in the town of Šal’a, Slovakia, contacted us and asked for help in designing a solution and optimizing their existing district heating system.





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

A Town in the Middle of Nature


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.


The city is located in the beautiful natural landscape of Nitra, with a river running through it. Thanks to the modernization of the district heating system with Kronoterm heat pumps, the city will be able to preserve its natural beauty.


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.


Kronoterm has designed an innovative solution for the town of Šala to utilize the heat of waste water with heat pumps. This contributed to the reduction of emissions and heating costs.


Update of the district heating system


The previous heating system in the city was based on coal and was becoming increasingly outdated, so it was logically replaced by natural gas. However, this brought new problems, such as energy dependence, and greenhouse gas emissions were still too high according to modern guidelines. The ideal and most logical solution presented itself. The Nitra region, where Šal’a is located, is rich in geothermal energy, which can be used for district heating. Therefore, the city upgraded its gas system to a geothermal energy system.


How can the utilization of geothermal heat be optimized even more?


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!


City machinery. The waste water generated by the city machine shop is fully utilized for its heat, and then it is returned to the river after being cooled. This helps to maintain the integrity of the river ecosystem.


When Kronoterm comes to the rescue


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.


Thanks to the implementation of a new system, heating costs for residents have significantly decreased!


Utilization of waste water heat


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.


The increase in efficiency with Kronoterm heat pumps at the same supply temperature is 50%!

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.


Do you want to save on heating costs for your industrial building? Do you need an innovative solution for remote heating of a village or town that provides significant savings? Check out our offer here or call us at 080 23 22.