Every single day, every city on the planet is flushing vast and valuable quantities of thermal energy literally down the drain, wasting the opportunity to recycle wastewater heat. In response, a new information and global mapping portal for wastewater heat recycling has been launched by a leading group of experienced engineers and expert map-makers. wastewaterheat.online
The amount of thermal energy available within wastewater is enormous — typically 20%-35% of total housing energy and up to 40% of low-temperature heat used in commercial and industrial sectors gets turned into hot water, which then goes down the city sewers, simply flushed away, every single day.
The current energy crisis in the EU, being driven by an urgent move away from Russian gas & oil, will require a change in thinking about where energy comes from and how it is used. Heating for homes, buildings and industries is a large part of the energy usage in the EU, and the REPowerEU strategy aims to electrify heating via a massive transition to heatpumps over the next few years. This will place new demands on city electrical networks, coming at the same time as electrification of transportation (cars, bikes, light commercial etc.) also placing new demands on city electrical networks. Planning and management of these competing energy demands will be difficult.
But all European cities have wastewater networks right under your feet, carrying huge amounts of free low-grade heat. This heat energy is already in the city, where it is needed by buildings, and the infrastructure collecting and transporting this heat (the sewer network) is already built and available. Sadly, this energy is typically just ignored and flushed away every day.
The amount of thermal energy available within wastewater is enormous — typically 20%-35% of total housing energy (figures from UK, China and New Zealand) and up to 40% of low-temperature heat used in commercial and industrial sectors gets turned into hot water, which then goes down the city sewers, and it’s simply flushed away, every single day.
Here is a quote from a former wastewater utility manager in the USA; “Anyone who has ever performed confined space entry into a sewer during the winter months, understands the value of this heat. Team members would often argue about who would get to go into the warm sewer and who would have to stay topside and freeze.”
Pros & Cons
Compared to air source heatpumps, a wastewater heat recycling system will normally be more expensive to install. This is due to the cost of civil works often needed to the sewer network. However, the favorable temperatures of wastewater allow wastewater source heatpumps to operate more efficiently than air source heatpumps (roughly twice as efficiently is quite common), so capturing and recycling wastewater heat allows electrification of more buildings to be achieved using less electricity (so helping manage the growing demands on the electrical infrastructure). There are also other benefits of wastewater heat recycling heatpumps which are particularly relevant within cities locations. These include:
- Smaller equipment size – sometimes inner-city buildings simply do not have enough space to accommodate the air source heat exchangers (these are typically mounted on the roof of a building). The size of wastewater heat recycling equipment is normally smaller and installed within the basement or just outside the building.
- Noise generation – air source heatpumps require fans to move air through the outdoors heat exchanger. Naturally these fans create some noise which can be problematic in urban locations where there might be people sleeping or working/learning. Wastewater heat recycling systems do not have fans outside. The equipment is all mounted within the basement or room and so noise is contained.
Why is this not being used more?
Our experience is that the barriers to recycling of this energy are:
- Lack of awareness – many people just don’t know about wastewater heat recycling. So, it does not get included in policy development and energy planning processes.
- Disconnects between different sectors. There are different sectors (we like to call them ‘worlds’) that need to come together to help each other and stop this tragic energy wastage. These worlds can be described as:
- The water sector and the buildings sector
- The below ground infrastructure sector and the above ground infrastructure sector
- The public sector and the private sector
Put simply, the water world has this free heat energy supply available, but they do not really have uses for it. The buildings world has uses for the energy but doesn’t know where it is located or how much there is available. Energy policy planners typically ignore it in their planning processes.
How do we start using this free heat?
So how do cities integrate wastewater heat energy into their policies and planning? The first step is mapping the heat within the wastewater networks. With this information, policy makers have another energy resource available for them to integrate into planning policies. If this information is made available on a web-map, policy makers and building designers will all be able to see how much heat energy is available and how it is distributed throughout the city. And this heat energy and the collection infrastructure is available today, time is not a constraint to utilize it.
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.” Heat maps provide a bridge between the different sector described above, no matter what language you speak.
Recently an information portal has been launched to provide easy to understand information about wastewater heat recycling, and to provide a global webmap to display wastewater network heat maps. The portal is at wastewaterheat.online. Currently there are three cities with wastewater network heat maps displayed and these cities are all located in New Zealand. This information can and should be generated for every city in Europe. The costs involved in heat mapping a city wastewater network are normally not expensive and the value the information offers is very large. The network of companies behind this portal can provide wastewater network heat mapping services for cities in Europe, as well as providing training/capacity building and technical support.
Below are shown snips from Christchurch city (which does have a wastewater network heatmap) showing an example of the available heat within a wastewater pipe, 23MW in this example. Also shown is a snip from Brussels, the only thing missing is a wastewater network heatmap for Brussels.
The portal has dedicated information pages for energy policy makers, building designers and wastewater utilities, to help each of these sectors with their specific needs. There are also a selection of 27 case studies from around the world, to show a range of actual operating buildings already using wastewater heat recycling.
What are the good opportunities for wastewater heat recycling?
Generally, wastewater heat recycling is suited to projects with some scale such as larger commercial buildings, industrial processes and district heating systems for precincts, campuses or multiple houses.
As guidance, the following generalizations can be made for what are likely to be good opportunities for using wastewater heat recycling:
- Installations into new buildings are more cost effective than retrofitting into existing buildings.
- A large installation is more cost effective than a small installation. E.g. a large building such as a hospital, swimming pool centre or large retail mall is normally more financially feasible than a small office building. Equally a single wastewater thermal energy centre which provides heating/cooling via a small-scale district energy system to a number of buildings (in a city block or a campus) is normally more financially feasible than each building providing their own small wastewater heat recycling installation.
- Installations with long utilization periods are more feasible than projects with short utilization. For example, buildings such as hospitals, swimming pool centres or some industrial facilities have a demand for heating and/or cooling all year around and so the thermal system is fully utilized for 12 months per year. This makes a much better business case than a building which requires heating and/or cooling only for only a few months of the year.
- If a city is planning to renew existing wastewater pipes or install new wastewater networks, that is the time to plan ahead and install access points into the wastewater network to allow the heat energy within the wastewater to be recycled. Perhaps the energy might not be used for some years, but if the access is already easy it is more likely to happen and it is significantly more cost effective to install access points while the wastewater network is anyway being constructed than coming back later and retrofitting access points.
What about maintenance costs? The routine maintenance needed for the specialised wastewater energy equipment varies from one equipment supplier to the next, but in general terms the amount of maintenance needed is similar to other normal commercial building HVAC plant or wastewater equipment. Typically, commercial HVAC equipment should all have a minor service every 3 or 6 months (depending on equipment supplier) and a 12 monthly annual service. It is the same for wastewater energy equipment.
So when buildings capture and recycle wastewater heat using heatpumps, it allows them to stop burning fossil fuels and electrification of heating for more buildings to be achieved using less electricity (so helping manage the growing demands on the electrical infrastructure). Win/Win/Win for the environment, the buildings and electrical authorities.
There is an old saying in English
“Don’t throw the baby out with the bathwater” which means ‘Don’t discard something valuable along with something undesirable’
This saying fits perfectly with wastewater heat recycling. The water may be dirty, but the heat energy within it is clean!
Don’t throw out the clean energy with the dirty water!