Waste heat as a driver for greenfield heat networks? Planning trade-offs illustrated using a case study for Zelzate, Belgium

Many studies see district heating (DH) as an important lever to reduce greenhouse gas emissions in the building sector. Here, excess heat can drive the development of new heating networks in greenfield developments. However, determining the optimal size of a new network presents a question: should it be constructed to fully utilize waste heat, maximize project NPV, or connect as many buildings as possible? Consequently, tradeoffs may arise during planning. For instance, the size of a network has implications on investments and heat losses due to increased piping. In short, smaller networks result in lower heat losses and investments, while larger networks benefit more households. We investigate this trade-off in a Belgian municipality that considers options for building a new DH network utilizing excess heat from a nearby steel mill. We investigate the mentioned trade-off using THERMOS, a tool to design and simulate DH networks. To achieve this goal, we create three network designs that connect a different number of buildings to the DH network to be built in Zelzate (Belgium), each with unrefurbished or refurbished demand - resulting in six technical scenarios. Using indicators such as heat distribution costs and excess heat share in the DH network, we compare and evaluate the results of these simulations. 110 Our results indicate that the designs analyzed have their specific advantages and disadvantages. For example, heat distribution costs are significantly lower for designs where fewer buildings are connected than for designs where more buildings are connected. For example, the heat distribution costs for the unrefurbished scenario, where 30% of the demand is connected, are about 4.3 ct/kWh; for the design where 100% is connected, they are about 6.9 ct/kWh. In summary, our case study indicates that the aforementioned trade-off in greenfield planning is indeed relevant. For example, in the case study analysed, project developers tend to choose planning approaches where fewer buildings are connected, although larger networks could also be beneficial in the future. Therefore, further research is needed to find out which planning heuristics, technologies and/or strategies could help to deal with such trade-offs.