In this section, we speak with key figures who have made a significant contribution to the development and realisation of Geothermie Delft: partners, suppliers, experts, and government bodies. Read about their experiences, motivations, and lessons learned.
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Today's guest: Rass Butt, CEO of Geothermie Delft.
The geothermal source of Geothermie Delft (GTD) is currently supplying sustainable heat to university buildings and DUWO student accommodation on the TU Delft Campus. Later this year, in 2026, GTD will also begin supplying heat to the residential districts of Voorhof and Buitenhof, combining this with TU Delft's existing Combined Heat and Power (CHP) plant for back-up and peak moments in heat demand. The new Heat Pump Central (HPC) is expected to go live after August 2027, adding extra capacity and flexibility to the system so that the heat supply can be scaled up further.
What role will the new HPC play in this expanded heat system for Delft? And how will this plant contribute to a reliable, sustainable, and highly scalable heat supply for both the campus and the residential neighbourhoods?
RB: "GTD expects to deliver geothermal heat to the Voorhof and Buitenhof residential districts as early as 2026, using the current geothermal source as a sustainable baseline and TU Delft’s existing CHP plant for back-up and peak demands in heat consumption. To achieve this, we are utilising the infrastructure that is already in place to take the first step towards further expansion into the city.
The upcoming Heat Pump Central (HPC) will add extra capacity and flexibility to the system from the moment it is commissioned. This will make it possible to scale up the heat supply further, connect more homes and buildings in the neighbourhoods, and utilise the available geothermal heat even more efficiently. You should therefore view the heat pump central as an additional system building block alongside the geothermal source, the CHP plant, the thermal buffer, and eventually the High-Temperature Thermal Energy Storage (HTES). Together, these assets form the source mix for Delft."
With the commissioning of this local geothermal heat source, Delft is leading the way in the energy transition. Once this new heat pump central is operational in 2027 and supports the geothermal plant in heating the neighbourhoods, what is the most important lesson you can offer the rest of the Netherlands regarding scaling up geothermal energy for existing residential areas?
RB: "I would say the most important lesson is that the energy transition is not about a single technology, but about cleverly combining different technologies within a single integrated heat and energy system.
In Delft, we are demonstrating that geothermal energy forms the sustainable foundation. Around this, we are building a system step-by-step where every asset has its own distinct role:
The CHP plant provides back-up and peak capacity.
The buffer offers flexibility throughout the day.
The heat pump central will soon increase efficiency and available capacity.
And in the future, the High-Temperature Thermal Energy Storage will allow us to store heat in the summer and deploy it in the winter. The HTES is a 180-metre-deep permeable layer in which warm water is stored for periods of higher heat demand, such as winter.
It is precisely this system-thinking approach that makes it possible to decarbonise existing residential areas reliably and on a large scale."
When delivering such a substantial heat pump station, GTD works closely with technical partners like Equans, who supply the materials and handle the construction. As the client and operator, how do you safeguard strategic control and the long-term vision?
RB: "Overall control of the total heat system rests with Geothermie Delft. Together with our partners (Gaia Energy, EBN, and TU Delft), we determine how the system develops, what investments need to be made, how the various installations interact, and how the heat network will expand over the coming decades.
GTD does not look at a single installation; we look at the entire heat system. This requires a long-term vision where we balance factors such as sustainability, affordability, technology, operations, and security of supply. Within this framework, Equans delivers a crucial component: the heat pump central. Equans brings an immense amount of technical expertise and execution power to the table. This is a vital link in the complete heat system that GTD is realising here in Delft."
How will GTD manage the entire system in the future, with the geothermal plant, the CHP, the HPC, and eventually the HTES?
RB: "GTD will indeed manage a mix of heat sources. The geothermal source will provide as much sustainable baseload heat as possible. The CHP plant will be deployed for back-up and peak loads when required—for instance, in the morning when many people hop into the shower.
Following its commissioning in 2027, the heat pump central and the buffer will also become part of that integrated management system. This will allow us to utilize the available geothermal heat even more efficiently, adjust temperatures when necessary, and release extra capacity for the further expansion of NetVerder's heat network.
In due course, we will also add the High-Temperature Thermal Energy Storage to the mix. Ultimately, this creates a single smart heat system where all sources are continuously optimised against one another to achieve the highest standards of sustainability, security of supply, and efficiency."
When you transport hot water from the GTD location all the way to Voorhof and Buitenhof, that water travels through kilometres of piping arranged in a loop through the city. Do residents at the far end of this loop receive just as much heat as the campus, which sits right next to the source? How does this closed circulation system work?
RB: "Fortunately, a modern heat network doesn't work by connecting houses sequentially to a single pipe, which would cause the 'last' house to receive lukewarm water.
The network consists of a flow pipe and a return pipe. All buildings are connected in parallel to this main infrastructure. Each building draws hot water from the exact same flow pipe, transfers heat to the property via a heat exchanger, and then sends the cooled water back through the return pipe.
As a result, a home at the very end of the network receives virtually the same flow temperature as a building situated right next to the source. Naturally, there is a minor loss of heat along the way, but modern heat networks are exceptionally well-insulated, meaning this loss is minimal and fully accounted for in the engineering design.
The real challenge is therefore not the distance, but the total heat demand. As more homes and buildings are connected, the required capacity of the system grows. That is why we are investing step-by-step in supplementary assets like the heat pump central and, later on, High-Temperature Thermal Energy Storage. This ensures that our heat system can continue to grow reliably well into the future."
