Buildings lose potential energy every day as wastewater flows down the drains. But new technology means that building owners can create wastewater heating and cooling strategies to save money.

Lynn Mueller of International Wastewater Systems explains how heat can be recovered from a building’s sewage, and why property owners and managers should consider putting such as system in place.

What is a wastewater heat system and how does it work?

Sewage heat recovery captures the heat in water leaving a building and uses it to re-heat hot water tanks and the building itself. Using sewage heat recovery, the heat energy flowing down drains never has to leave the building. Water enters buildings at between seven and nine degrees Celsius and leaves at between 20 to 25 degrees Celsius.

The technology is not complicated. First, a filter is used to separate out solids, which make up about two to three per cent of our sewage. Then, with the help of a heat exchanger, the heat from the sewer water is transferred into clean water and this warm, clean water is sent back into the building. At the end of the cycle, the clear sewer water picks up the solids that were extracted at the start and flushes them back into the municipal sewer system.

Why should property owners consider using this system? 

There are a number of benefits to property owners including energy savings, rapid return on investment, reduction of greenhouse gas emissions, long life cycle of reliable operation, and qualifying for additional LEED points.

The system is easy to install and operate, with low-cost maintenance. It is designed to be clog-proof with an automatic back flush to effectively clean the equipment. Moreover, an industry-leading computer monitoring system will flag any potential problems long before they become an issue. Maintenance for the system involves quarterly service intervals with three service levels.

How is contamination prevented in the system?

Wastewater never comes into contact to the clean water supply, or even near it. This is achieved by first transferring the heat to a clean process loop, which supplies water-to-water heat pumps that are used to heat a building’s domestic hot water tanks, or the building loop. The system is also hermetically sealed, meaning there is no associated smell.

What barriers stand in the way of properties that may want to use a wastewater heat system? 

Access to sewage supply is important when implementing a wastewater heat recovery system. There must be an adequate flow of wastewater to provide the heat source. Although sewage heat recovery systems are applicable to any building, they work best in residential buildings with more than 200 units, or in institutional buildings, such as hospitals and prisons, that have exceptional hot water usage.

In cooler climates, sewage temperatures are slightly reduced. In the summer, buildings with sewage heat recovery systems can reverse their heat pumps and use the waste water to reduce a building’s air conditioning costs. In this scenario, the pumps extract heat from the building and transfer it through the exchanger into the sewer water.

Lynn Mueller, is the president of the Vancouver-based International Wastewater Systems. He has been a leading advocate of sustainable space conditioning energy systems for the last 25 years.