Experiences with low-temperature district heating and cooling in the Netherlands
In this article, we describe the ambitions, considerations, and choices of five Dutch project teams working within the national Natural Gas-Free District pilot Programme (PAW) to realise low temperature district heating. In doing so, we link to the principles of 5th generation district heating as developed in the D2Grids project.
Since 2018, the Dutch central government's "Programma Aardgasvrije Wijken (PAW)" programme has been subsidising dozens of pilot projects where natural gas-free districts are being realised. A first tranche of 27 pilot projects started in 2018. In 2020, 23 new pilot projects were added. The third tranche, from 2021, consists of 16 pilot projects.
Whereas in the first tranche the emphasis was on medium temperature (MT) and high temperature (HT) grids, we see that in the latest tranche the emphasis is on low temperature (LT) district heating grids and very low temperature (VLT) district heating, some of which can also be used for cooling.
LT district heating is characterised by supply temperatures ranging between 30 and 55°C. Unlike "medium-temperature" or "high-temperature" district heating, residential LT district heating requires a facility to achieve the right temperature for domestic hot water. On the other hand, heat losses in LT grids are significantly lower. Heat generation can take place at substantially higher efficiencies due to the lower supply temperatures. Looking at the number of districts where LT district heating is deployed, a positive trend can be observed in the period 2018-2021, see the figure above (source in Dutch).
5th generation district heating (5GDHC)
The increased focus on LT grids fits the trend of district heating being less and less "top-down" (from a large central heat source to many customers) but instead developing more and more "bottom-up". Ideally, optimisation takes place with savings measures at the customer, the lowest possible temperature levels and the highest possible use of local renewable sources through, among other things, thermal storage. If possible and useful, there is a combination with sustainable cold supply, which is in fact also a source of heat. If smart control of the heat pumps also prevents additional peaks in the electricity grid, we have all the ingredients for a 5th generation district heating and cooling system (5GDHC). For more information, see the article "Perspectives on fourth and fifth generation district heating" by Hendrik Lund et al (March '21).
5 pilot projects
Based on the pilot's grant applications, the conclusion seems justified that there are currently 9 pilot projects with ambitions for LT district heating. As an LT grid can be challenging, it is interesting to check how project development is going, and to verify whether an LT grid will actually be realised. Heat specialist Jeroen Roos (Stroomversnelling) looked at the characteristics of the 9 pilot projects and selected 5 cases, all from the third tranche, for further investigation.
We then interviewed representatives of these 5 projects. Based on a short, standardised questionnaire, we tried to find out which principles are followed in project development. In addition, we examined to what extent the project in question meets the characteristics of a 5th generation district heating (and cooling) system as named in the D2Grids project that is running in 5 European countries with EU support.
Link to D2Grids project
Looking 'through the eyelashes' at the 5 principles defined in the D2Grids project, we see that many of the pilot projects considered pay above-average attention to them, or even comply with them to a large extent. We conclude that interesting developments can be seen in these pilots. If the experiences with VLT backbones and LT district heating are positive, this could potentially have a major effect on the construction of new district heating systems due to the potential knock-on effect of the PAW program. In addition, but probably to a more limited extent, this could potentially influence the sustainability of existing district heating. The use of lower temperatures enables the use of sustainable, local sources that can meet heat demand with relatively little (fossil) auxiliary energy.
The 5 cases we zoomed in on are:
Municipality of Eindhoven - pilot project Generalenbuurt
Number of dwellings: 559
Number of utility buildings: 21
Technical solution: VLT backbone (< 30⁰C) with collective upgrade to LT grid (50⁰C).
Expected completion: 2040
Municipality of Het Hogeland - pilot project Zuidwolde
Number of dwellings: 382
Number of non-residential buildings: 15
Technical solution: LT district heating (10-45⁰C)
Expected completion: 2028
Municipality of Peel and Maas - pilot project Panningen-centre
Number of dwellings total development: ~5,500
Number of residential units: 357
Number of non-residential buildings: 80
Technical solution: LT district heating (approx. 30-55⁰C) with various sources including waste heat and solar thermal.
Expected completion of phase 1: 2024
Municipality of Vlissingen - pilot project Panorama district
Number of dwellings: 641
Number of non-residential buildings: 1
Technical solution: VLT source grid linked to LT district heating (new buildings approx. 30-55 ⁰C) and MT district heating (existing buildings approx. 70⁰C supply temperature)
Expected completion: 2025 - 2030
Municipality of Zuid-West Friesland - pilot project Heeg
Number of dwellings: 1170
Number of non-residential buildings: 104
Technical solution: LT and MT district heating based on thermal energy from a canal. Different district heating temperatures due to different dwelling types/years of construction.
Expected completion: 2030
Preliminary conclusions based on the sample of pilot projects:
- In most of the pilot projects (Generalenbuurt, Panorama district, Heeg and probably also Zuidwolde), there is a VLT grid feeding LT or MT district heating, depending on the efforts needed to make the customers suitable for an LT grid.
- In a few cases (Eindhoven, Vlissingen), there will appear a large backbone fed by a VLT source such as thermal energy from surface water, thermal energy from sewage water, thermal energy from a drinking water pipe, outdoor air or ground heat that can supply several districts with VLT source energy.
- The pilot sites deal with connecting existing buildings in different ways. This ranges from relatively heavy dwelling insulation improvement to ‘energylabel B’ before connection to a LT grid (Panningen, Eindhoven, Vlissingen) to limited interventions and connection to a MT grid (part of Heeg project).
- Everywhere, deployment of electric heat pumps is foreseen, although in different ways. Where there are local VLT and LT sources, heat pumps provide upgrading to usable temperature; at LT or, if necessary, MT level.
- Supply of cold is an option at several locations, where it is still uncertain whether this will actually be realised. Source of the cold is the (Z)LT source, whether or not in combination with heat pumps and sometimes integration with the return of heat supply ('closing the loop').
- Use of fossil energy still takes place but in many cases this will be temporarily: sometimes for peak supply by means of gas boilers and to produce electricity (outside the pilot project) for the heat pumps.
- Booster heat pumps for domestic hot water are largely provided in LT grids, deployment of (less efficient) resistance heating for the temperature lift needed for domestic hot water has been applied in Eindhoven.
- Mitigation of peaks in the electricity grid through smart control of deployed heat pumps (and short-term heat/cold buffering) has not received attention in some pilot projects and is not seen as a major problem there.
- Seasonal storage (in aquifers) of ambient heat plays a role in most projects to have sufficient source heat of the highest possible temperature available in winter for the deployed heat pumps.
- In terms of new buildings (Vlissingen), we see that there is still a consideration as to whether these will be connected to VLT (with individual heat pumps) or LT (with heat pumps on district level).