Aquathermal energy: heating and cooling with water

Large-scale application of aquathermal energy is possible

To really exploit the potential of aquathermal energy, it is important to apply the technology on a large scale, for example in cities or large parts of cities. The technology has proven itself on a small scale, from a few houses to a small residential area. Over the past fifty years, more than one hundred aquathermal systems have been installed successfully in the Netherlands. During the past two years, Deltares has been acquiring knowledge and experience in collaboration with other parties to make the step to large-scale applications possible.

That knowledge relates to areas such as the potential, feasibility and impact of the systems. How promising is aquathermal energy for a specific area? How can we organise heat distribution? Or what are the effects on ecology and can we determine the relevant boundary conditions? Most of this knowledge has been developed in the WarmingUP collective, which brought together more than forty parties from the entire heating sector to work jointly on the development of practical knowledge so that collective heating systems will be reliable, sustainable and affordable for the purposes of the heating transition. In the National Growth Fund programme NieuweWarmteNu! we are moving ahead, focusing on learning from practice, balancing different factors and validating the models, including the decision-making models.

The technology and experience for developing large-scale aquathermal systems and heat grids are available. The challenge relates mainly to the financing, and the operational strength and capacity of the parties involved. Building heat grids is quite simply expensive and complicated.

Bonne van der Veen, governance consultant at Deltares

Aquathermal energy in practice

We are seeing how provincial authorities are increasingly embracing the potential of aquathermal energy. We reviewed the possibilities in the municipalities of Almere, Nijmegen and Breda, in each case from a different perspective. For example, for the municipality of Almere, we conducted research, and discovered that more than 35,000 new homes in a planned extension to the municipality could be heated and cooled with water. Ronald Roosjen, expert in energy from water and soil at Deltares: “Working with the municipality of Almere, we looked at the design for the area, structuring it and adapting it where necessary so that the aquathermal source will be used properly.”

Large-scale aquathermal energy using the river Waal as a sustainable source is also a realistic option for Nijmegen for supplying heat to existing buildings in a large part of the city in the future. That included looking at whether aquathermal energy can meet the demand for heat, whether this heat can be stored in the subsurface, and whether there is enough space.

The municipality of Breda also wants to add aquathermal energy to its energy mix. Our study shows that about 8,000 homes could be supplied with heat from the river De Mark, which runs right through the centre of Breda. On the basis of a combined water and energy plan, we estimated how much heat could be extracted without affecting underwater life. With the municipality of Breda and the Brabantse Delta water authority, we laid the foundations by identifying the steps you need to take together to include aquathermal energy in the overall mix of sources and how this can be achieved with a spatial energy plan.

What are effects on the water system and ecosystem?

More and more water authorities are thinking about the use of aquathermal energy, on the one hand because of the questions and applications they are receiving and on the other because water managers see aquathermal energy as an opportunity to contribute to the energy transition. The change in water temperature, the use of water filters and the flow caused by technology can affect flora and fauna in surface water. Water managers want to know what the consequences are for aquatic life before they approve aquathermal systems and issue permits.

To meet this need, Deltares, working with water authorities and STOWA, has developed special tools that water authorities can use to estimate the effects. Those tools include the ‘guideline for modelling cold discharges’ and the ‘monitoring plan for the ecological effects of thermal energy from surface water’. They allow water managers to get to grips better with the ecological effects, whether positive or negative. These tools also show that you can use design choices to influence the impact of heat extraction and that you can design it to optimise the effects on the water system and ecosystem. Colder water improves oxygenation and clarity, and reduces the likelihood of blue-green algae during hot summers. Water circulation and temperature gradients resulting from aquathermal systems can also be good for water quality.

What is thermal energy from surface water?

Thermal energy from surface water (TES) is a form of aquathermal energy, a collective term for sustainable heating and cooling with water, and therefore one of the alternatives for sustainable heating from the Climate Agreement. In the Netherlands, TES is the technology with most energetic potential by comparison with the other two forms, waste water (TEW) and drinking water (TED).

TES systems exploit the temperature differences in surface water between the seasons. They bring together a number of existing technologies to extract energy from surface water. Heat is extracted from the surface water using a heat exchanger in summer. This heat is transported in a network and then either delivered directly or stored in an aquifer thermal energy system (where heat and cold are stored) in the subsurface. This heat can be used at colder times for heating using a heat pump, which operates a lot more economically in this situation because the temperature of a hot ATES well is about 18°C. That is much higher than the temperature of the surface water or the air outdoors in the winter.

The questions we can help you answer

With our expertise in the fields of, for example, flow processes, both in surface water and around inlet and outlet systems, in mains systems and the effects on ecology, we can advise you from the detail to the system level. We help municipalities, provinces, heat suppliers and water authorities with:

• integration issues, the performance of the system and the monitoring of the effects on the water system and soil system
• understanding the effects and risks of using aquathermal energy as a renewable source
• the selection and preliminary design of TEO locations
• the technical and spatial description of the large-scale application of TES in combination with heat networks and underground storage, including the reduction of carbon emissions
• visualising the potential of aquathermal energy in relation to existing buildings or the design of new buildings at the district or city level and the use of aquathermal sources
• clarifying the impact of TES systems on the ecology with numerical modelling or monitoring, or a combination of both, including advice about how to structure these systems.
• the balancing of different factors when including aquathermal energy in a source mix
• the balancing of different factors that benefit the heating transition without overburdening the water and soil systems
• the water energy plan approach.