Today the district heating networks feed 10 % of the European housing. This figure hides important disparities; the percentage is higher in Northern and Eastern Europe than in Western and Southern European countries and in some big countries: Iceland (92 %), Denmark (61 %), Poland (50 %) against France (7 %), Italy (4 %), Switzerland (4 %), the USA (3 %), UK (1 %).
They have nevertheless since a few years a renewed interest. What are the reasons? And is this interest well justified?
The various reports published these last years about the district heating (and cooling) networks converge on a list of advantages and drawbacks, which I suggest reviewing with the energy challenges of Smart Cities in mind.
- The district heating networks are local systems: they feed between 500 and some ten thousand housing. By their size, they go into the field covered by a city government.
- The district heating networks can be fed by several sources of energy, distributed along the network. The network is thus evolutionary: sources of heat can be added or modified over time. Besides, they allow benefiting from renewable sources of heat, more with difficulty usable otherwise (incineration of waste, biomass, geothermal energy, recycling of industrial heat). By this characteristic, the district heating networks have a very strong potential influence on the local energy mix.
- Managed by professionals, of more important size than the individual systems or building’s boilers, often submitted to stricter requirements and regulation, they allow a more successful control and processing of the rejections of combustion.
- The energy efficiency of a district network is better than that of the smaller installations. The earnings are on average of the order of 20 %.
- These networks allow implementing solutions of storage, in particular cold storage, which is mature and environment-friendly.
- The price of the heat is lower, generally, for the consumer.
- The comfort of the user is always considered upper: no maintenance, no noise, no smell.
Compared to these advantages, district networks have inconveniences:
- They require, for the implementation of the distribution networks of heat and cold, heavy works in streets, disturbing for the traffic.
- They cause important investments and need a long-term investment thinking with durations of return on investment between 10 and 15 years.
- The connecting of existing buildings with no heating circuit is complex.
- They are adapted to areas exceeding a certain density of population ranging, in 80 % of the cases, from 3 to 8 MWh / meter of pipe
- They are better adapted to areas offering a high diversity of use: the needs for heat are more regular along the day.
In the light of this global evaluation, the interest of district heating networks for the energy transition and for the energy efficiency is doubtless. There is there, material to justify the renewed interest they present today.
The determination, within every city, of the geographical perimeter of profitability of this type of installation, is compulsory to estimate, in every case, their precise interest.
During my missions with cities of Western and South Europe, I often met a fear so deeply anchored of the necessary works that it hid the energy and economic profits. We can understand this attitude but a Smart City cannot skip over a precise evaluation of areas favourable to the deployment of a district network and on an elaborate explanation to the citizens of profits brought by these networks.
From an energy point of view, it is not thinkable to go without, whenever possible, profits of a district network. It seems to me important to justify exactly reasons why we choose not to deploy a district network while cities often emphasize the precise justification of the decision to deploy a district network.