Using lakes and rivers for extraction and disposal of heat: Estimate of regional potentials

Significance 

Fossil fuels and electricity-driven devices are used for heating and cooling of buildings and infrastructure. However, the increasing willingness to reduce the use on the use of fossil fuels due to their high carbon emission rates as well as the need of more effective energy utilization strategies have motivated researchers and engineers to seek alternative cooling and heating methods. Recently, ambient heat in water bodies, air, and ground has attracted significant research attention for various thermal uses. Their use relies mainly on their closeness to the sources of heat considering the high costs for heat transportation.

In a recent paper published in the journal, Renewable Energy, a group of researchers at the Swiss Federal Institute of Aquatic Science and Technology (Eawag): Adrien Gaudard, Professor Alfred Wüest and Martin Schmid explored the potential role of water bodies as a renewable energy source for heating and cooling applications. Specifically, they evaluated the thermal use of lakes and rivers taking Switzerland as a regional case study. Besides the bulk parameters water volume and discharge, meteorological conditions drive the thermal regimes of lakes and rivers, which also defines the potential heat extraction and disposal associated with different water bodies. In mid-latitude lakes, for example, vertical mixing results in a uniform temperature and density during winters. However, thermal energy from these water bodies should be appropriately used to avoid any impact on the ecosystem.

Briefly, the research team commenced their research work by estimating the heat extraction and disposal potential for the main lakes, rivers and lake outlets in Switzerland. To minimize the impact on the aquatic life, realistic thermal use conditions with limits to maximum allowed temperature changes and specific waterbody properties were taken into consideration. Next, the population living close to the water bodies was estimated to determine the potential regional demand for cooling and heating.

Lakes and rivers in Switzerland exhibited high thermal potential that exceeded the local demand in most cases. This did not, however, rule out the potential changes that may occur through thermal use. Therefore, appropriate thermal management strategies are highly desirable. Furthermore, given that temperatures of most waterbodies are currently increasing due to climate change, introducing additional heat by using them for cooling is considered to be more critical than removing heat for heating purposes.

Lastly, a hydrodynamic model was used to analyze the influence of different operating parameters which helped in evaluating the practical application and limitation of the thermal use. The authors modeled temperature effects in two lakes: Large Upper Lake Constance with low demand and small Lake Zurich with high demand to assess the impacts on realistic thermal use. Mean temperature variations of -0.05 to +0.02°C and -0.60 to +0.22°C respectively were projected.

Although the results obtained in this study obtained specifically for Switzerland cannot be simply directly transferred to other regions of the world, they indicate a promising potential for heating and cooling applications in various parts of the world.

Reference

Gaudard, A., Wüest, A., & Schmid, M. (2019). Using lakes and rivers for extraction and disposal of heat: Estimate of regional potentials. Renewable Energy, 134, 330-342.

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