District heating is seen by a number of countries as one of the strategies necessary to decrease CO2 emissions and make the transition to a sustainable energy system. Indeed, it can: valorize energy sources that would otherwise be discarded such as industrial waste heat; be generated by combined heat and power, increasing overal system efficiency; or make use of renewable energy sources such as biomass, geothermal heat and solar energy.However, some scholars are adopting a more cautious position and suggest that the presence of a district heating system can, as it has been experienced in Germany and Sweden, slow down the implementation of low energy houses. Indeed, in such a system, the costs of the infrastructure are high and in areas where linkage to a local district heating network is compulsory, developpers may not have an incentive to invest both in the district heating and in technologies to decrease the energy demand of houses and buildings. Moreover, when industrial waste heat is used as an input, the heat produced during industrial processes changes from being considered as waste to being considered as a by-product of economic value. As such, industries may not be willing to invest in innovations that could increase their efficiency. As a result, district heating can cause a lock-in both in the input and in the output side resulting from economic, technical and institutional barriers.
Nevertheless, when analysing possible causes of lock-in, the inherent and potential multifunctional character of district heating have not fully been considered. Indeed, first district heating is usually used to provide heat both for space heating and domestic hot water, applications for which the demand in term of quality differs. Second, it is very often linked to a cogeneration unit, integrating the district heating system with the electricity system. Third, in summer, when heat demands are low, the district heating network can for instance also be used to deliver heat to absorption chillers that can in turn produce chilled water for cooling purposes. This is the case in Copenhagen for example. Fourth, cogeneration can also be considered as one of the options for demand side management if proper heat storage is developed. And finally, Hemmes et al are investigating the possibility to use internal reforming fuel cell for the tri-generation of heat, power and hydrogen. The hydrogen could be used to power fuel cell vehicles, in which case the district heating system could indirectly be linked to the transport system as well. In summary, a variety functions are and could be associated with district heating energy system.
The consequences of this (potential) multifunctionality on long term sustainable innovation potential, be them positive or negative, have not yet been investigated schematically. On the one hand multifunctionality implies technical and economic interdependencies, as well as legal possibly political commitment. All these aspects are known to increase the risk of undesirable locked-in. On the other hand, multifunctionality also allows the combination of different level of expertise which could lead to the discovery of new possible connections. This could increase the system’s capacity to innovate, facilitating transition to a sustainable mode of development.Using district heating as an example, we have tried to show that long term consequences of a given technology or technological system on sustainable innovation potential are difficult to evaluate. It is even more so when the system is or can perform multiple functions, creating connections between various actors, each with their own needs and requirements. Moreover, we must acknowledge the fact that by continuously questioning the long term consequences of technologies, we face the risk of not taking any constructive decisions. Besides given that the future can not be predicted with accuracy, we can question how much of these consequences can actually be foreseen. However, despite this uncertainty, it worthwhile to investigate necessary conditions and to develop strategies under which potential threats can be turned into opportunities.