The largest sewer heat-recovery project in the US is now under construction in Denver. The AU$1.3 billion project is designed to use the consistent temperature of wastewater beneath the National Western Complex by way of an epic heat pump that works like a reversible air conditioning unit.
Home to a stock show and rodeo, the complex is being adapted into a massive hub for art, education and agriculture. It includes about 93,000m2 of interior space, all heated and cooled with heat from sewer pipes that run below the 101-hectare campus.
“With the advent of large-sale heat pumps, we can cost-effectively use, say, 70-degree (21°C) wastewater to heat our buildings and our hot water systems,” says researcher Shanti Pless.
The technology opens up possibilities of “renewable heat mining”.
Although sewer infrastructure has turned off developers in the past, that may not be the case in the future. In fact, builders might seek them out to save energy costs and avoid greenhouse gas emissions.
The technology to harvest sewer heat is far from complicated.
The wastewater that will be reused for the Denver project inside stays between 13°C and 24°C regardless of the weather outside. The consistent temperature can then be “mined” to heat and cool above-ground buildings.
It’s estimated the campus will be able to avoid about 2,600 metric tonnes of carbon per year.
At the heart of the process is an enormous heat pump to be housed in a central plant on the campus. In the winter, the heat pump will transfer energy from the sewage into a clean water loop connecting the buildings, warming interior spaces. The process can be switched to cool buildings in the summer.
Because the wastewater is never exposed, occupants aren’t impacted by malodourous conditions.
One of the biggest barriers to the approach is that sewer heat recovery often works best as part of a district-sized energy system.
These types of systems have fallen out of favour in recent times as costs to maintain them have fallen to customers.