Comparison of different carbon-free near surface heating and cooling sources usability in low energy network

Ground source heat has been utilized for a heating and cooling several decades in Finland. The bottom of a water body is also another heat source used but no so commonly in Finland. The asphalt and seabed sediment heat sources are quite new approaches. In this paper these four different heat energy sources are reviewed, analyzed and compared. All these heat sources are originating from solar radiation which makes them annually renewable. The evaluation data for the four heat sources have been collected during a one year period, 2014-2015. One year period is enough to see a short term behavior during the four seasons. The actual temperatures of topsoil ground, seabed sediment and subterranean layers beneath the asphalt are measured by distributed temperature sensing method. These three sources are located on the Vaasa Region, Finland in the radius of 5 km. Only the temperature data for the bottom of water body are obtained from the literature. All four sources provide promising temperatures. Sediment, ground and bottom of water body temperatures were quite stable but the seasonal variation can be noticed. Instead soil temperatures beneath the asphalt layer response the summer season rather strongly. That is why asphalt heat can be collected for storing in addition to direct usage for heating and cooling buildings.