Potential for district heating networks from waste heat: an assessment tool and its application to sewage treatment plants in the Canton of Zurich

Abstract

Industrial waste heat is a valuable heat source to provide a decarbonized supply to district heating networks. In particular, sewage water treatment plants are a widely-available source of waste water, which can be used as part of low-temperature district heating networks. In this paper, we present an assessment framework to estimate the potential from existing heat sources to supply a new district network, in terms of heat supplied consumers (number, location and heat coverage) and plausible network layout. The case-study application is an evaluation of the waste-water potential in the canton of Zurich. Considering 61 waste-water treatment plants for a total unexploited potential of 607 GWh, we show that 13,077 buildings could be connected to a district heating network originating from such plants. This value represents about 6% of the building stock in the canton of Zurich and 6% of the current estimated heating demand. By considering decentralized water-water heat pumps for each building connected to the network, we find that a 14% electricity saving could be obtained compared to standalone air-water heat pumps. By clustering substations according to the potential net revenue for the network operator and automating the tracing of the shortest-path network layout, we estimate the pipework length and the related investment costs.