# The Role of Low Temperature Waste Heat Recovery in Achieving 2050 Goals: A Policy Positioning Paper
## 1 Introduction  
The European Commission has proposed that the 2050 target of climate neutrality should become law [1]. One important contribution towards meeting this target is to expand the use of renewable district energy solutions. Heating and cooling are the largest energy-consuming sectors in the EU, representing half of total energy use. Industrial waste heat has huge potential for helping meet this demand in Europe with an estimated 2.7 EJ/year available [2]. This could meet approximately 25% of the heat and hot water demand in European buildings. Recently, another abundant heat source has been identified in the form of low temperature heat. Around 1.2 EJ/year of low temperature heat is available from urban heat sources in Europe (e.g., heat from infrastructure like sewage water and metrosystems, service sector buildings and data centres) [3]. The combination of industrial and urban waste heat sources provides great potential to contribute to the replacement of fossil fuel based heating in Europe and globally. The global extent of waste heat recovery potential from industrial sources is not known. However, it is estimated that, in 2014, around 331 PJ of industrial heat was recovered. Around 16 PJ of this was recovered in Sweden. The potential for industrial heat recovery in district heating systems has been estimated for the UK [4], Spain [5], Germany [5,6], China [7,8] and the EU as a whole [9]. Despite the great potential for urban waste heat recovery, uptake has, so far, been low. Research has shown that urban waste heat recovery investment is hindered by untested technical solutions, the absence of standardised contracts and the current cost of carbon, making the business model more appropriate for circumstances beyond 2050 [3]. Conventional district heating (DH) systems are a combination of heat from recycled sources (combined heat and power generation, waste to energy plants and industrial processes) and, increasingly, from renewable sources such as biomass fuels and solar collectors [10]. The conventional wisdom is that heat is collected or produced locally and distributed to customers in a citywide distribution network [11]. The most recent technological development is the use of local, low temperature, heat sources in city infrastructure such as metro systems and sewage and commercial activity from sources such as data centres [3]. Urban waste heat is carbon neutral and tends to create high political interest but has low utilisation. These characteristics imply that there are barriers preventing its greater utilisation. In a recent paper [3], the main barriers to urban waste heat recovery investments were identified: (i) low technical maturity of the existing system solutions, (ii) long investment payback periods, (iii) diverging views regarding the value of heat, (iv) competition from existing incentives for renewables and combined heat and power generation, (v) the absence of standardised contracts and (vi) the absence of a legal framework for urban waste heat recovery. Low temperature heat recovery is referred to as fourth or fifth generation district heating technology, where the fifth generation represents lower distribution temperatures than the fifth. The technology shift is, at present, new and far from established [12]. However, utilisation of urban heat sources will become increasingly important in a future with no fossil fuels, lower available volumes of waste to incinate and demand for alternative uses of biofuels. This presents an opportunity since waste heat sources are numerous and tend to be situated close to urban areas of high heat demand; aspects that reinforce the resilience of the energy system overall. In order to meet the objectives of the 2016 Paris Agreement, it is estimated that approximately 27 trillion USD needs to be invested in renewable energy between 2016 and 2050 [13]. Urban waste heat recovery investments are typically smaller than those institutional investors look for and therefore will not automatically be appealing.