Aquathermal energy is a unique source of heat and cold. In the Netherlands, it has a great potential to partly provide the heat demand of the built environment. The concept is technically not complex, but there are some complicating factors. In this article the concept is explained, and the question is being asked how this is managed by other countries.
By Arianne de Vries, Energy transition consultant, Rijkswaterstaat Water, Department of Knowledge and Innovation Management and Reinier Romijn MSc., Policy Advisor Energy, Water en spatial planning, Dutch Water Authorities
Earthquake victory for the environment
The Netherlands has for a long time been able to sustain heat to houses and utility buildings with its own natural gas extracted in the province of Groningen, the northernmost part of the country. The comfortable and ‘unlimited’ supply of natural gas meant the insulation of houses was not the first priority – until now. In recent years, due to natural gas extraction, multiple earthquakes have occurred in the province.
The earthquake issue in Groningen has a positive effect on the awareness of natural gas enhances climate change. This awareness plays an important role as the Netherlands is committed to the Paris Agreement.
In regard to the alternatives for sustainable heat ing, the focus is on Denmark as one of the most energy efficient countries in the world because of a well-developed district heating (DH) infrastructure. By making rigorous choices decades ago, Denmark has a pole position in DH >70˚C.
The Dutch are inspired by this Danish District Heating Model, but the development of the DH grids is a challenge. Not only financially but also as forming new governance and ensuring enough sustainable heat to meet the demands. The Dutch Water Authorities are convinced that Aquathermal energy, heat (and cold) from surface, waste, and drinking water, is a new energy source that can provide sustainable warmth.
Aquathermal energy as an alternative heat (and cold) source
The Netherlands is a country rich in water, and no matter where you are, water is almost always near. The high density of waterways results in the fact that supply and demand of heat and cold from water can be achieved nearby.
Research from 2018 shows that aquathermal energy (in Dutch: TEO, TEA, and TED) can provide a significant part (<50%) of the heat demand of Dutch households, utility buildings, and greenhouses. TEO has by far the greatest potential due to the large availability of surface water. TED has the least potential because the source is only available in small quantities and in specific locations.
The Netherlands is continuously researching the possibility of using aquathermal energy as an alternative heat source for natural gas-free districts. In May 2019, many parties signed the so-called Green Deal Aquathermie with the Dutch Water Authorities, Rijkswaterstaat (the agency of the Ministry of Infrastructure and Water Management), and the Ministry of Economic Affairs and Climate.
The Green Deal is used to bring aquathermal energy to the attention of stakeholders and to develop and share knowledge about aquathermal energy to further develop this technique.
Ever since the Green Deal Aquathermie was signed, the participants have been working to make aquathermal energy an indispensable part of the energy transition. While working on raising awareness for aquathermal energy in The Netherlands, a search for aquathermal energy projects abroad started. Several TEA projects were found, for example, in Turku, Finland , but TEO and TED projects are hardly developed.
How does it work?
Technically, it is a simple concept to get the heat from the source to the building. The heat (or cold) is extracted from the surface, waste, or drinking water using a heat pump. The technique uses low-temperature heat (20-25˚ C), which is enhanced to the desired temperature (40-70˚C) with the aid of (collective) heat pumps and distributed to houses and utility buildings with a DH grid. The most energy-efficient method for TEO and TED systems is to store the heat in the summer for use in the colder winter months.
Dutch examples of TEO projects are Blaricum, Heeg, and Amsterdam. In Blaricum, over 700 newly built houses are connected to a DH grid using aquathermal energy. The grid will be extended to other houses. The latter two TEO projects are in the advanced stages of preparation.
The TEO project in Heeg is an initiative by the local people who want to make the heating of their houses sustainable by using the lake water nearby; in Amsterdam, the municipality is constructing a new residential area, Strandeiland, with a DH grid using aquathermal energy from the lake IJ.
In the summer, the surface water is warmed up by the sun. In Dutch cities, the warming up leads to excessively warm surface water. In extreme situations, the temperature of the surface water rises to >25˚C. This has negative effects on the water quality and contributes to the urban heat island effect. TEO could be part of the solution to counter these effects. By extracting part of the heat from the surface water, the water cools down.
This is, in principle, beneficial to the water system and the urban environment. The heat is stored, for example, in an Aquifer Thermal Energy Storage (ATES), and is distributed with a DH grid to the buildings in the area for heating when needed. Enhancing the temperature can be performed at different moments in the system, for example collectively before distributing in the grid or individually as the water enters each building.
As there are no extensive DH grids in The Netherlands, DH is still limited. The options for implementation are still under consideration but currently are:
- a low temperature (20-30˚C) DH grid and individual heat pumps (or per block of houses);
- a medium temperature (40-50˚C) DH grid (boosted with a collective heat pump) and individual booster pumps are only needed for tap water ;
- a medium temperature (40-50˚C) DH grid with a collective heat pump to 70˚C; no individual heat pumps are needed.
Research has also been completed on storing the heat in an ATES at a higher temperature (40-70˚C). The heating temperature is boosted during the time of a sustainable electricity surplus and is stored at a higher temperature in the ATES. However, legislation in The Netherlands does not allow this method yet.
The TEO principle can also be applied outside the urban environment or even with seawater. The latter has already been applied in Scheveningen in the past and is currently being investigated for implementation at the Wadden Islands.
District heating grids
The most cost valuable item in the aquathermal heat chain is the installation of the DH grid. The Danish District Heating Model with publicly owned companies could be the most appropriate for implementation in The Netherlands. However, the Dutch heating market is not regulated, and there is currently an ongoing discussion on this matter, both public and commercial.
Commercial companies want their investment payback time to be shorter than publicly owned companies. The return on investment period for creating DH grids highly affects a technique such as aquathermal energy compared to all-electric solutions without DH grids. Additionally, the costs of a DH grid are largely determined by the chosen configuration. The Ministry of Economic Affairs and Climate has not made this decision yet.
The ATES is another expense. Not installing an ATES leads to lower energy efficiency, but the development costs will decrease.
Although the concept is technically rather simple, in governance terms, it is quite complex. This complexity arises from the fact that a large number of parties are involved in the heat chain from source to building and because there are many degrees of freedom in the Dutch energy transition; for example, an individual household cannot be obliged to participate in a collective solution such as a DH grid.
The fact that the use of aquathermal energy is a new technology that has not often been applied on a large scale makes project developers, government, investors, and housing corporations uncertain about the financial aspects and the reliability of the system. The system cannot fail when the demand for heat is high. The concept will have to prove itself on a large scale if it’s to become mainstream.
Unique selling points
Aquathermal energy has unique selling points, such as local, sustainable heat, it is available almost everywhere in The Netherlands, it can be developed quickly, has a relatively low electricity consumption, no uncertain drilling is required, it is scalable heat (1 – 10.000+ homes, the sources are quite reliable, and the water authorities are fairly reliable as (semi) public administrations. In addition, it is a bonus for the Dutch that heat from water is used as a sustainable source for the heat demand in the energy transition.
Aquathermal energy is a unique source of heat. In The Netherlands, due to the high density of waterways, the source has a great potential to partly provide the existing and future heat demand. To this end, a large number of parties, together with the water authorities, are committed to further developing this technique into usable concepts for large-scale projects as an opportunity in the transition from natural gas to sustainable heating.
The concept is technically not complex, but there are complicating factors, such as the barely developed DH system. The Netherlands wants to use water as an energy source for sustainable energy for heating and cooling and is curious about how other countries manage this source.