Brunssum's 5GDHC network digs deep for sustainable heating and cooling!

As part of the D2Grids project, which has been promoting 5th generation for heating and cooling grids since 2018, we spoke to data analysis expert Jibbe Bertholet about the deployment of this concept at the Brunssum pilot site in the Netherlands.

Can you tell us more about why Brunssum applied for the D2Grids project?

The Brunssum pilot site is built and operated by Mijnwater Energy B.V. Mijnwater started in 2005 by distributing a heating and cooling grid in a town next to Brunssum, Heerlen. These grids use abandoned coalmines - because we are in a former mining area - to produce energy. Many consider the Mijnwater District Heating and Cooling to be the world's first public 5th generation heating and cooling grid (5GDHC). The Mijnwater network has been expanded 5 times over the past decade, but all these new connections are linked to each other by a central backbone and the minewater reservoirs. Due to exchange of heating and cooling energy, local storage and use of low temperature waste heat these expansions were done without the need to upscale the geothermal wells.

This is where the Brunssum pilot site has become innovative: the idea was that if a smart thermal grid is able to utilize enough local green sources and storage, then the availability of a minewater reservoir is no longer a precondition to develop this kind of 5GDHC grids. As such the 5GDHC concept can be deployed in a vast potential of urban areas. The Brunssum pilot is designed as an autonomous grid, not linked to the other grid or a minewater source. From this project idea, Mijnwater applied for the D2Grids project, and became the project’s lead partner. Working in such an international project is -in my opinion- very interesting because of the knowledge and experience sharing between the different partners.

What has been achieved and what remains to be done on this 5GDHC grid?

At the moment, the Brunssum pilot is a mini 5GDHC grid: 200 dwellings have been connected and are using an aquifer thermal energy storage (ATES) combined with heat pumps to provide heating, cooling and domestic hot water.

However, The ATES system is currently unbalanced, which means that more heat is extracted from the source than reinjected, which means that it is slowly depleting. This is not within the concept of 5GDHC, as the first principle of 5GDHC is closing the energy loop. The main reason for this outcome is that the original plan was to connect up to 1.000 dwellings and also commercial buildings. This would create a spread in demand profiles and bigger flow of heat exchange between end users. Due to political and business economics reasons, this expansion was delayed and as such crating the imbalance in the system.

So, we need a way to balance the ATES on short term. This was supported by the project's 'capitalisation call', which we also call the 'cap call'. The initial plan was to add photovoltaic, thermal and hybrid solar panels on the roofs, but due to a lack of roof space, this was not feasible. Plan B will therefore be to install an air source heat pump (ASHP) to generate additional heat for the system during summertime.

As already mentioned, the Brunssum site is a pilot site and thus in a pilot stage. In order to become a fully 5th generation grid, it should expand significantly. Today, only 200 homes are connected, but there is a need to connect more utility buildings and more dwellings in order to enable heating and cooling exchange between those connections, and fully operate as a 5GDHC.

D2Grids project has been extended to strengthen synergies between renewable energies and innovative DHC.
Why and how did Brunssum decide to be part of it?

It's difficult to answer that question right now.

To exploit the characteristics of a 5th generation heating and cooling grid, it must comply as closely as possible with the five principles that define this concept. For example, the grid will be able to use more diversified sources of heat, such as waste heat, because of its closed circuit and the exchange between users (first principle), or other sources of low-temperature renewable energy on a regional scale, such as shallow and low-temperature geothermal energy.

The Brunssum pilot site is currently only focusing on setting up an autonomous grid to supply new built dwellings, so it does not have all features yet of a true 5th generation grid.

To meet this target, the network would need to be connected to different types of buildings, with various energy requirements. For example, a supermarket needs cooling all year round for its fridges, while dwellings have relatively uniform demand profiles (when it's hot, all homes need cooling; when it's cold, all homes need heating).

To avoid a large demand of external energy supply, it is required to have a diversification of consumers such as supermarkets, shops, offices and data centers. This diversity means that energy can be exchanged between those consumers through the grid, turning them into ‘prosumers’. Moreover, the low grid temperatures (LT) allow for low graded renewable energy sources and/or industrial waste heat and cold to be injected into the grid. On the other hand, low-temperature grids using energy from mines, sewage, aquathermy, etc. cannot be directly used to deliver 70- or 80-degree hot water to consumers. For this reason, decentral heat pumps are used (on building or neighborhood level) to increase the supply temperatures. Nevertheless, energy sources such as mines or wastewater treatment plants can bring large amounts of (low graded) energy, to feed those local heat pumps and operate them on a high level of performance (high CoPs).

There were 2 main reasons to apply for the extension (Interreg NWE Cap call). The first was to add local heat to the system since it was imbalanced from utilizing the aquifer as single source. The second reason was an upcoming trend of net congestion on the power grid. From the interaction of different sectors, we wanted to research the impact of 5GDHC on avoiding peaks in electricity consumption.

The Brunssum pilot so far, mainly focused on how to operate a remote network with an ATES system. So, it is not yet a full-fledged 5GDHC.

For the network, in order to increase this synergy, substantial green sources should be added, like PV-panels, PVT-panels or solar thermal panels. Moreover, thermal and battery storage should be added to the system. In the application for the Cap call these features were foreseen, but due to new company strategies delayed in time. An alternative solution was found in the air source heat pump.

What are the key messages you want to get across?

I think one of the most important messages we want to get across is that we need to take a bottom-up, funnel-shaped approach: what is the energy demand of a building, a group of buildings and the whole district, what local energy source are available, for example, supermarkets, datacenters, geothermal energy, etc.  Find out if this is enough or do you need something extra, for example, an ATES, solar thermal, etc.

Only then, it’s possible to decide whether a site is suitable for a 5th generation heating and cooling grid or not. It’s also required to look at the investment required, the sizing that would be needed, and whether there is any budget left for the rest of the project. The 5th generation heating and cooling grid might therefore not the best option for all areas!

More generally, 5th generation district heating and cooling grids are based on several principles that define the concept, which can be found in this article.

The D2Grids project has also developed indicators (KPIs) that can be used to assess the effectiveness of the concept.

Do you want to assess a DHC grid? Please, contact us:
Gert Moermans: [email protected]
Jibbe Bertholet: [email protected]