- Net reduction of greenhouse gas emissions when natural gas is replaced by heat recover from treated wastewater or sewer lines. Heat pumps consume electricity, so the "upstream" emissions of electricity production need to be factored in.
- Reduced overall cost of wastewater treatment plant due to revenue source.
- Heat pumps have a lower cost than other heat sources over the lifecycle of the systems.
- Less fluctuation and energy price increases than fossil fuels.
- Revenue from energy subscribers paying for heat.
- Potential for heat storage and demand charge savings.
- Industrial processes
- Refrigeration and cooling
- Vented indoor air
When is it Waste?
When produced as a by-product of other processes.
Allow heat to dissipate into surrounding environment.
Recover heat energy and apply to other processes and uses.
How It Works
Waste heat recovery is possible in most systems that have an exhaust stream or another waste stream in either gas or liquid form. The captured thermal energy can be used within the same system it came from or transferred to a new system. In either case, the waste heat is used to pre-heat air or water for space or water heating, or industrial processes.
Waste heat recovery has many applications and is common in industry and buildings. Examples include heat recovery ventilation and drain water heat recovery in buildings, extracting heat from flue gases in industrial processes, and capturing heat from water used in cooling processes.
Waste heat is recovered with heat exchangers (such as in heat recovery ventilation) or with heat pumps. Heat exchangers capture a portion of the waste heat and transfer it, whereas heat pumps use electricity to recover low temperature heat and make this heat available at suitable temperatures for heating and for hot water systems. For every unit of electricity consumed by heat pumps, they typically produce three to four units of higher temperature heat.
An innovative example in local government operations is capturing heat produced as an output from ice rink cooling and using it to preheat water for a swimming pool or space heating in the recreation centre. This application of waste heat recovery reduces the need for new energy sources to heat the pool and building.
Wastewater Heat Recovery
How It Works
Heat pumps are used to extract heat from treated wastewater, which is transferred to nearby buildings for space and/or water heating. The cooled treated water can then be used for air conditioning or refrigeration. Treated wastewater is significantly warmer than other sources of energy for heat pumps (e.g. air during the winter, ground-sources, lakes or the ocean), so energy can be recovered from wastewater more efficiently. Treated wastewater from local plants can be delivered through ordinary pipes to heat pumps located in buildings near treatment plants.
What are the costs?
Heating systems in buildings would need to be adapted to use this form of energy. Conversion costs would include the capital and operating costs of the heat pumps, heat exchangers, and any necessary modifications to the building's heating system. Heat pumps normally require replacement every twenty years. New developments close to a source of wastewater heat recovery could be constructed with heat transfer technology.
Either the community or a local energy company could pay for the cost of infrastructure such as the water piping required to deliver the treated water to heat pumps.
The economics of heat pumps are strongly affected by the temperature of the heat source. The higher the temperature, the lower the capital and operating costs, as the heat pumps can be
Where is it Happening?
Saanich Peninsula Wastewater Treatment Plant Heat Recovery System
Sewer Heat Recovery
How It Works
Rather than extract heat from treated wastewater at the wastewater treatment plant, sewer heat recovery involves transferring heat directly from untreated sewage in the sewer line using heat pumps. While more common in Europe, this technology is relatively new in Canada.
Where is it Happening?
Southeast False Creek Neighbourbood Energy Utility
Considerations for Implementation
If the needs of buildings for energy and reclaimed water are taken into account when communities plan for wastewater treatment infrastructure, then treatment plants can be sized and located to deliver the greatest amount of energy (and even reclaimed water) to the greatest number of buildings. The reverse is also true: new developments or community buildings close to wastewater infrastructure can be designed to take advantage of waste heat. This approach tends to favour a network of distributed small treatment plants over the more traditional option of large centralized plants. Locating decentralized wastewater treatment plants near clients for heat energy will require a different approach to planning on the part of local governments than the current system of fewer, centralized plants.