Heating and cooling with saline solution

Today, about half of the energy consumed in Europe goes into heating and cooling. Among the efforts towards making heating and cooling more efficient in the future is the innovative approach pursued by the EU research project H-DisNet (Intelligent Hybrid thermo-chemical District Network). Its international research consortium includes the ZHAW School of Engineering, which is implementing the first demonstration systems in Switzerland in collaboration with two partners.

Thermo-chemical network without heat loss

The idea is as follows: In contrast to conventional thermal heating networks, such as district heating or low-temperature networks, thermo-chemical networks do not transport heat energy as such. Instead, a chemical potential, for instance in the form of concentrated saline solutions, is transported to the place where the heat is needed in order to produce the useful heating or cooling in situ. The crucial advantage of this method lies in the fact that no heat is lost during transport and storage. «In this way, many waste heat sources can be used commercially no matter where they are or when the heat is needed», says Thomas Bergmann from the Institute of Energy Systems and Fluid Engineering (IEFE). «In addition, pipelines and storage tanks do not require expensive insulation, which leads to considerable savings in comparison with conventional heating networks.»

Transforming thermal potential into chemical potential

On Martin Wipf’s farm in Marthalen there is a biogas plant. The biogas fuels an internal combustion engine, which, in turn, is connected to an electric generator. What is produced is not only electricity, but also a great deal of engine waste heat. «The qualitative value of the energy depends on the temperature level; the further we get from the ambient temperature, the more valuable the energy is», Thomas Bergmann explains. The engine exhaust is about 500 degrees Celsius and therefore high-quality. «We want to transform the temperature difference, the thermal potential, into what we call chemical potential.» Thomas Bergmann and his team do this by storing the potential in a saline solution. The solution is separated from the environment and can be stored or transported for an indefinite amount of time. The potential stored in the saline solution can be released in a different place at a different time in order to generate heating or cooling simply by using the ambient energy. In this particular case, the place in question is the orchid nursery of Meyer Pflanzenkulturen AG in Wangen, near Dübendorf. «There, we use the chemical potential to generate heating or cooling, depending on what is needed», says Thomas Bergmann. The principle can be compared to an absorption heat pump. «What is special in our case is that the generation of useful heat takes place separately in time and space from the regeneration, that is, the extraction of chemical potential.»

Stable operation and cost efficiency as a foundation

Thomas Bergmann and his team are still at the very beginning of their project and doing pioneering work. Only a longer period of operation of the demonstration systems will show whether this technology works reliably and whether it can be cost effective. «If we are able to ensure a provably stable operation, we could put the system into place permanently and expand to further possible locations», says Thomas Bergmann. «It would, of course, be ideal if we detected waste heat sources nearby and could then, perhaps, install a combined network of pipelines.»

For more information, see the official project website: www.h-disnet.eu