Assessing waste heat recovery potential in Ottawa

City of Ottawa’s wastewater collection system is a vast network of sewer pipes and associated infrastructure. Much of the water that enters the sewer system is warm, which means it could provide a widely distributed source of low-carbon thermal energy. To this end, the city will conduct a feasibility study to determine the wastewater collection system’s waste heat recovery potential. This study aligns with the Ottawa’s Energy Evolution Strategy under its Climate Change Master Plan. Phase 1 of the strategy identifies a survey of available waste heat as a catalyst project that could support the city’s goal of achieving net-zero carbon emissions by 2050 through significantly reducing its fossil fuel heating. Fossil fuel heating currently accounts for around 40% of the city’s total community greenhouse gas emissions. The City of Ottawa's Energy Evolution model projects that 700 terajoules (TJs) of heat from the sewer could be recovered by 2030, and this could rise to 1,600 TJs by 2040. Recovered waste heat is expected to mostly replace natural gas heating, resulting in an annual greenhouse gas reduction of 21,000 tonnes of carbon dioxide equivalent (tCO2e) by 2030 and 84,000 tCO2e by 2050. This rate of potential energy capture was quantified based on sewer heat capture in municipalities around the world, prorated to Ottawa's population. The benefits that will be considered in the study include the following: 1. Protection from rising heating costs: Because it is a renewable heat source, sewer waste heat will protect end users from fuel cost increases. 2. Reduction in the combustion of fossil fuels: Burning fewer fossil fuels will improve air quality in Ottawa; it will also reduce the risk of gas leaks and the property damage and contamination that could result. 3. Creation of a new source of revenue for the municipality: The revenue generated from recovered waste heat would enable further spending on climate change solutions and social services. This study will collect and quantify flow and temperature data from strategic sewer locations. To the maximum extent possible, the thermal properties of the sewer system will be examined, detailed and managed through a city-wide geographic information system (GIS). The study will also identify potential users of the recovered heat, and review and assess different technologies for capturing the thermal energy. The city has also included a task within the scope of this project to assess where geo-exchange could be an economically viable source of heat for buildings and district energy systems based on data from wells drilled across Ottawa. While a complete study of both underground aquifers and sewer lines goes beyond the scope of this study, this task was added to the project given the overlap in the knowledge expertise of the consultants retained for the study. The sample business cases developed in this study will identify opportunities for implementation, both at the specific sites modeled and for similar use-cases. Business cases will be developed for a district energy system, a major building, snow-melting, and domestic water preheating. Innovative aspects: Capturing waste heat from sewers is a relatively new concept for municipalities in Canada and Ottawa had never considered the idea before this project. The analysis tool developed through this study will be used to share the opportunity for waste heat capture for both the municipality and all other large heat consumers in Ottawa. Replicability: The findings of the study will be shared through networks such as the Building Owners and Managers Association, the Canada Green Building Council, the Ottawa Board of Trade, and the Climate Ambassador's Network. The results are expected to be applicable to other municipalities transitioning to more sustainable heating options. The results of this study and any resulting policies and contractual arrangements will be shared through municipal networks such as Clean Air Partnership, Canadian Urban Sustainability Practitioners, and Partners for Climate Protection. (Project description from original funding application)