Successful PWN aquathermal pilot project to be followed up at De Watergroep

Thermal Energy from Drinking Water (TED) is one of the options to meet the aim stated in the Dutch climate agreement of reducing carbon emissions in the built environment. Since eighty percent of the energy requirement for homes and buildings is for heating purposes, the primary focus is on developing sustainable heat sources. Water is suitable for this purpose because it is a good heat carrier. But obviously, drinking water quality must not be compromised. That is why drinking water utilities want to know if, and in which conditions, supplying TED, or heat or cold from the drinking water mains, is safe.

PWN and De Watergroep

In response, a pilot project was conducted at PWN as part of the research collective WarmingUP to investigate the microbiological effects on water quality of extracting cold from drinking water during the winter. After the completion of this successful pilot project, the baton was passed on to the Accelerating the Energy Transition with Aquathermal Energy (EVA) 2.0, project with a pilot plant at De Watergroep in Flanders. The project is part of the research programme Water in the Circular Economy (WiCE). Moreover, the energy transition is one of the social challenges on which KWR is working.

Unique pilot plant

“We built a unique pilot plant in a container,” says Moerman. “We can direct water from a water pipe through the plant without the water flowing back into the mains. So it is 100% safe. By adding micro-organisms to this water in an advanced way, we can see what happens to microbiological safety. We can also vary the temperature, the materials used and volume flows. We have to introduce these micro-organisms in order to establish a picture of growth in conditioned circumstances. Without that step, the trial would take far too long.”

Exploring the limits

The trial at PWN explored the limits to see how the microbiology develops. For example, the drained water from the mains was warmed up from about 10-12 to 18, and even 24, degrees Celsius. Moerman: “You won’t come across temperatures this high in practice but we wanted to explore deliberately what is – and isn’t – possible. One of the ways TED is used involves balancing Aquifer Thermal Energy Storage systems that require more cold than heat, such as systems in shopping centres. This means that you have to warm the water up slightly in the winter. But how far can you go? Conducting the tests in those winter conditions to see how far we could allow the temperature to rise without undesirable microbiological growth means that we know that this risk is well under control below 18 degrees Celsius. That is much warmer than we have assumed until now.”

Pilot project in Flanders

The Water & Energy Network Group of the drinking water utilities and KWR is very enthusiastic about the subject of aquathermal energy, knows Moerman. “The group consists of experts from almost all Dutch drinking water utilities, as well as De Watergroep in Flanders. Our Belgian colleagues were also keen to use the container with the pilot plant, and that step has now been completed. The nice thing about the mobile facility is that it can be taken straightforwardly from A to B. We have just added the micro-organisms to the water in the pilot plant and so the measurements can begin.”

Comparisons with other types of water

Does Moerman expect the results at De Watergroep to be different from those at PWN? Our southern neighbours use low doses of chlorine in drinking water preparation to prevent the growth of micro-organisms. The situation in the Netherlands is different. “I think the outcomes will be comparable,” says the researcher. “Because we don’t want to take any chances with aquathermal energy, we are applying the technology to slightly different types of water so we can compare the outcomes. For example, it would also be interesting to install the pilot plant in Germany or France. But it would, of course, be absolutely wonderful if all the Dutch drinking water utilities want to use it for research in the future. Using the pilot plant teaches us a great deal about the possible later growth in a particular type of water at locally higher temperatures and flow conditions. For example, you could also use the plant to study the effects of pipelines warming up, for example because of heating networks. The construction of the pilot plant was cost-intensive, and it would be a shame not to use it more. No new investments are needed and it can be used anywhere.”

Sustainable mix of heat sources

When Moerman is asked about how he sees TED technology in the future, he switches to the bigger picture. “There are three sources for aquathermal energy: surface water, wastewater and drinking water. Obviously, surface water has much greater potential in terms of heat and cold extraction than drinking water. The volume involved is many times larger. But drinking water does have specific advantages. For example, it’s clean and you don’t have to treat it. And the pipelines are already in place. Of course, the application of TED is relatively limited. You can’t start heating every house on every street in this way. So I see this technology and our research more as a contribution to the search for a sustainable mix of heat sources.”

Contributing to social challenges

Moerman explains further how this works in practice. “Because of the energy transition, we are looking at water infrastructure differently than in the past. When a drinking water utility is planning to build a major mains pipeline somewhere, the focus should no longer be exclusively on transporting water. We have to realise that, when you move a lot of water from one place to another, it also means moving a lot of heat and cold. So the pipeline immediately acquires a dual function, which also reduces the costs for society. That means the knowledge we obtain from pilot studies like this one is important for accelerating the energy transition. Because we want to make sure that aquathermal energy from drinking water won’t cause any problems with water quality. Drinking water utilities have to be able to explain how this works to their customers. And they should also be able to be proud of it so that they can say: this is how we are doing our part to meet the social challenges we face.”

Image 1: Interior of the pilot plant. Five “flow cells” allow two different materials and two different temperatures to be simulated and analysed. The fifth flow cell is for reference.

Image 2: Example of sampling material for biofilm analysis. The material in the picture is EPDM, a synthetic rubber of which gaskets in heat exchangers are made.