Nearly 80% of energy consumption in EU households comes from heating. Thus, alternative, low-carbon sources of heat will play a major role in the energy transition. Waste heat is one such source, which deserves to be looked at.  

To better understand its potential, Kristina Lygnerud from the Swedish Environmental Institute (IVL) and Matthias Kolb, from ANEX, a Swiss consulting company, shared their insights with the members of the Decarb City Pipes 2050 consortium.  

What is waste heat? 

In general, waste heat is excess heat that is generated during industrial processes or the normal functioning of infrastructure.  

The current amount of industrial heat recovery in the EU can be estimated at 3 exajoules per year, which is about 1% of the full technical potential¹.

The potential of urban waste heat recovery has been identified at 1.2 exajoules (equivalent to about 30 million tons of oil per year) for the EU, which corresponds to approximately 10% of its total heat demand². Urban waste heat can be generated from the activities undertaken by the cities’ inhabitants, such as taking the metro (radiated bodily heat), using the bathroom (heat arising from processing of sewage) or using a computer (heat from an activated data centre). 

The potential is large but merely a fraction of the waste heat is recovered. Why? 

The technical aspects of harvesting waste heat 

To better understand the technical capacities of the use of waste heat, we invited Matthias Kolb (Anex Ingenieure AG, Zürich) to share a couple of successful implementations of waste heat recuperation schemes. 

There is first the case of a family house energy cooperative in the Friesenberg area of Zürich – Familienheim-Genossenschaft Zurich (FGZ). The cooperative unites 5,500 residents in 2,300 houses. Two big companies, Swisscom and the Crédit Suisse, are installed in the area and use data centres. After one and a half years of negotiations between the cooperative and the companies, an agreement was reached: the cooperative and the data centres will be connected, to form a closed loop, recover the waste heat, and inject it into the district heating (DH) system for free.

The data centres have been equipped with heat exchangers and a seasonal heat storage tank was installed. The extracted heat can either go straight to the housing units or be stored in the tank for later use, in the winter for instance. The evolution of the heating & cooling systems of the data centres and of the DH can be seen in Figures 1 and 2 below.

Thanks to this, CO2 emissions have observed a 35% yearly decrease in the cooperative. In addition, the water savings sum up to the equivalent of four times a 50-metre swimming pool!

Another example from the industrial area of Gaiswerwald, in St. Gallen, saw a strong participation of local actors to have waste heat included in the DH system. The local energy association noticed that, from a technical perspective, this area was excellent due to the high, yet unused, waste heat density, with the 17 private companies in the surroundings. After negotiations and reflection from the municipalities and energy suppliers, a company was founded to make a public-private partnership with the concerned industries who agreed to participate in a common heat distribution network, providing sustainable heating to the nearby area.

The barriers of harvesting waste heat

Various projects and literature reviews on the topic of waste heat have spotted several barriers: 

1. The price of waste heat is much discussed: often the owner of the waste heat and the district energy provider have different views on the value of a certain amount of heat. Putting all of one’s eggs in one basket is also seen as a risk: what if the waste heat provider shuts down its activity³ and what happens if customers eventually decide to leave the grid? One solution to mitigate barriers is to write precise contracts containing relevant clauses such as mitigation (what happens if either party fails to meet its obligations), regular updates of contracts (to remind why the waste heat recovery was undertaken in the first place) and clear boundary conditions (where does responsibility begin and end). The ReUseHeat project offers good examples of contractual forms. 

2. One large barrier that cannot be contracted away is that of regulation falling short of supporting waste heat recovery. There is no clear definition of “green” waste heat which would allow to better understand how and when it is comparable to a renewable energy source. 

3. Directly linked to this lack of definition is the absence of legal framework for waste heat in Europe which accounts for risk. Yet, when there is risk, there is lower appetite for investment and so waste heat investments are not taking off but rather competing with incentivised investments in other forms of renewable energy. An alternative to mitigate the risk would be for insurance companies to invest in DH at early stages: that way they could be close to the investment and mitigate if industrial activity was closed.

The main barriers to waste heat recovery are typically not technical in nature. They are related to regulation and to stakeholders identifying the possibility of undertaking activities outside of their core business and with new partners.

Key takeaways

During this session, consortium members received a general introduction to waste heat and the opportunities and challenges it faces. The two examples of decarbonisation of DH systems thanks to waste heat recovery clearly illustrated this, especially in terms of negotiations. Indeed, negotiating with companies is key to reaching an agreement on the use of waste heat. This means reflecting on the best way for a city to contract with the companies, reflecting on the payback time, the possibility of an insurance scheme and also to foresee a backup plan if the waste heat source moves away.

References:

[1] Miro L, Brückner S, Cabeza LF. Mapping and discussing Industrial Waste Heat (IWH) potentials for different countries. Renew Sustain Energy Rev 51 (2015) 847-55 

[2] Persson, U.; Averfalk, H. Accessible Urban Waste Heat. Available online: https://www.reuseheat.eu/wpcontent /uploads/2019/02/D1.4-Accessible-urban-waste-heat.pdf 

[3] Lygnerud K, Werner S. Risk assessment of industrial excess heat recovery in district heating systems. Risk assessment of industrial excess heat recovery in district heating Systems, Energy 151 (2018) 430-441