Aquathermy is the extraction of heat from water. Here we distinguish three types, depending on which type of water the heat is extracted from.
Heat or thermal energy (TEO) from surface water
Together with Deltares, CE Delft has investigated the possibilities for aquathermy in the Netherlands. Benno Schepers, team leader, says about extracting heat from surface water: Water contains heat and the average temperature of surface water in winter is 7 degrees, but in summer it can be as high as 25 degrees. Usually this heat is generated by the sun but in rivers it is also possible that warmer water from industry heats the surface water. The heat can be transferred to the building via a heat network or heat exchanger or stored in an underground storage facility for use in cold weather.
The cooled water can be returned to the source once it has given up its heat. In theory, this method of heat extraction from surface water can meet 40% of the heat demand of urban areas in the Netherlands. The advantage of TEO is that when heat is extracted from surface water, the temperature of the water drops and therefore the chance of blue green algae occurring is greatly reduced. The knife cuts both ways.
A good example of TEO is the energy supply in Wageningen at the Torckdael residential and care center. In the winter the building is heated with the warm water that was taken from the town canal in the summer and stored in the ground. This also has the advantage that the water in the city canal is cooler in the summer (an average of 3 degrees) and therefore of better quality. This cooler water can absorb more oxygen and reduces the risk of fish mortality and botulism. The system in Wageningen has an efficiency that is more than 25% more favorable than if an electric heat pump had been used.
Heat or thermal energy (TEA) from wastewater
Wastewater discharge to surface water also provides opportunities for Aquathermy. Usually the water is warmer than the surface water and the advantage is that the heat in a continuous and even flow. This also applies to sewage pumping stations. This makes it very suitable for extracting heat from that water. It looks a bit like riothermy, but riothermy is the extraction of heat from shower and dishwater and is done on a smaller scale. This also makes it slightly more expensive. Aquothermal energy from wastewater can theoretically meet 15% of the heat demand in urban areas in the Netherlands.
Heat or thermal energy (TED) from drinking water
When we cool drinking water, heat is released that can be used to heat buildings. The cooled drinking water then goes back into the water supply. Theoretically, Aquathermy from drinking water can meet 1.4% of the heat demand in urban areas in the Netherlands.
If this is to be possible, the source must be no further than 5 kilometers from the buildings that need the heat. Otherwise the heat loss during transport is too high. Successful implementation also requires low temperature heat networks (ZLT) and therefore well insulated houses. The principle is based on a base heat which is additionally heated by a heat pump to the desired temperature suitable for heating buildings.
Those who want to know more or study CE Delft’s report can find it here.