Building Designers & Owners
Buildings Create Environments for People to Live & Work. They Also Need Heating/Cooling.
Building designers and owners decide how buildings will keep their occupants comfortable. How heating & cooling will be done and what energy sources will be used to achieve this.
Because buildings last for a long time, these choices are important because they lock in these choices.
Decarbonisation of cities requires decarbonisation of the buildings within the cities. This means increasing the energy efficiency of buildings via fabric upgrades, and transitioning away from fossil fuel usage as a heat source. Transitioning away from fossil fuels will require require a large shift to electrification, but public and private transportation is also shifting to electrification, so there will competing demands for electricity. City electrical supplies and distribution networks are coming under increasing pressure to cope with these shifts and changes in demand. And meanwhile time keeps ticking away....
But as infrastructure designers and owners, you know cities have wastewater networks. Do you think about the huge amounts of free low grade heat they are carrying. This heat energy is reliable, predictable, stable and already in the city where it is needed by buildings, and the infrastructure collecting and transporting this heat is already there (the sewer network). Tragically the heat energy is just ignored and flushed away every day. The favorable temperatures of wastewater allow wastewater source heatpumps to operate more efficiently than air source heatpumps in both heating and cooling modes. So capturing and recycling wastewater heat allows electrification of buildings to be achieved using less electricity (so helping manage the growing demands on the electrical infrastructure).
Global Final Energy Consumption By Sector (Source Energy Technology Perspectives, IEA, 2017)
Did you know?
The amount of thermal energy available within wastewater is enormous.
Typically 20%-35% of total housing energy + up to 40% of low temperature heat used in commercial & industrial sectors gets turned into hot water, which then goes into a city's sewers. Of course this hot water also gets mixed with cold water and so the sewer networks carry a large flow of warm to neutral temperature water.
This water is stable in temperature and typically is warmer than air in the winter and cooler than air in the summer. Plus water is a much better conductor of thermal energy than air. These favourable characteristics allow wastewater source heatpumps to operate very efficiently compared to air source heatpumps.
But this thermal energy is invisible and so building designers do not typically think about this as a potential thermal source for buildings, and tragically the thermal opportunity is normally simply flushed away everyday.