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)
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.
We can help with mapping the heat in wastewater networks. You can already see cities which have had their wastewater networks heatmapped on our global map. These cities are: Christchurch - NZ, Dunedin - NZ, Nelson - NZ and we want more! Click here to have a look. If your city has a wastewater network heatmap, you will know with a click of your mouse how much wastewater heat energy is available in relation to your site. And this heat energy and the collection infrastructure is available today, time is not a constraint to utilize it. If your city does not yet have a heatmap, we encourage you to contact your city officials and ask them when they will.
The Water Research Foundation Report 'State of the Science and Issues Related to Heat Recovery from Wastewater' says this about wastewater network heat mapping: "The mapping process is an essential tool for policy makers. It allows the governing community and the
developer community to conceptualize the resources available and how to connect them to needs."
We can help with education and training. We have a network of experts in North America, Asia, Europe, Scandinavia and Australasia who can provide presentations, training courses etc. to
We can help by providing technical support. Our experts can provide engineering and mapping support with things such as:
The first wastewater heat recycling buildings were constructed in Switzerland in the 1980's. We estimate that there are now more than 1,000 installations world wide.
You will not be the first building to do this.
Have a browse of our selection of case studies to see where and what others have done. If you know of sewage heating/cooling installations that 'fly under the radar' then please let us know. We love hearing about these.