What Is Drain and Wastewater Heat Recovery?
Everyday activities like showering, using sinks, and washing laundry demand a significant amount of hot water use. After these tasks are complete, the used water—now wastewater—still contains valuable heat energy. Instead of letting this energy go down the drain, wastewater heat recovery (WWHR) and drain water heat recovery (DWHR) technologies capture and reuse this thermal energy before it is wasted. This recovered heat can be utilized to preheat domestic hot water, space heating, or even industrial processes. In addition, integrating HVAC systems with wastewater heat recovery improves energy efficiency by using wastewater as a stable thermal source or sink, enabling low-carbon heating, cooling, and domestic hot water production. By capturing and reusing this thermal energy, the primary heating and cooling systems can significantly reduce the energy typically required to heat or cool water, offering both environmental and cost-saving benefits.
- DWHR typically refers to capturing heat from greywater, which comes from showers, sinks, and dishwashers. Greywater doesn’t contain significant organic waste or solids, making it easier to process.
- WWHR involves capturing heat from both greywater and blackwater (wastewater from toilets containing organic waste). This process requires more robust systems to handle the added complexity of blackwater.
DWHR systems normally take the form of a long vertical copper drainpipe with a spiral copper tube wrapped around the drainpipe that acts as the heat exchanger. This is where the warm greywater runs alongside the colder incoming water to exchange the heat. WWHR systems typically integrate wastewater heat pumps to release or capture thermal energy from wastewater. A heat exchanger extracts heat from the wastewater and transfers it to a refrigerant. Where it is then used to cool or heat water or air for the building. By reclaiming heat that would otherwise be lost, these systems can significantly reduce energy use and utility costs.
Incorporating heat pumps with wastewater significantly boosts energy efficiency by capturing and reusing the thermal energy naturally present in wastewater streams. Instead of relying solely on electricity or gas to generate heat, a heat pump can extract low-grade heat from wastewater, which typically stays between50–77°F1, and upgrades it to useful temperatures for space heating, domestic hot water, or even industrial processes. This approach reduces energy consumption, lowers utility bills, and enhances system performance, especially in colder climates where air-source heat pumps are less efficient. Stable wastewater temperatures also enable systems to operate more consistently year-round compared to systems that rely on outdoor air.
As the demand for sustainable, energy-efficient building solutions grows, wastewater heat recovery is becoming an increasingly important technology. It aligns with the push for greener buildings and operational cost savings, making it an effective strategy for meeting energy efficiency goals. Many municipalities and organizations are prioritizing energy recovery methods like this as part of long-term sustainability initiatives, further increasing interest in its adoption.
What Are the Benefits?
- Using otherwise wasted heat to preheat water reduces the energy required for water heating, leading to potentially significant energy savings.
- Wastewater heat recovery systems decrease the demand for traditional water heating methods. This reduction can help lower energy bills, especially in commercial, high-rise, multifamily, and industrial settings with high hot water usage.
- Preheating water reduces the time and energy needed to reach the desired temperature, enhancing the efficiency of water heating systems and extending equipment lifespan.
- Designers can pair wastewater heat recovery systems with HVAC systems, using wastewater as a stable thermal source or sink. This approach improves efficiency and enables low-carbon heating, cooling, and hot water production.
- Lower energy consumption results in less carbon being released into the environment. This reduction supports California’s sustainability goals of reaching carbon neutrality by 2045 through decreased greenhouse gas emissions and improved energy efficiency in buildings.
- Wastewater heat recovery can improve hot water delivery times and overall system efficiency. These improvements help reduce water waste, particularly in multifamily and commercial buildings where users often let water run while waiting for it to heat up.
What Are the Challenges/Constraints?
- The high upfront investment for specialized equipment, design, and installation can deter adoption despite long-term energy savings.
- These systems are most beneficial when integrated early in the design phase, as they may require additional space. Retrofitting them into existing buildings can be more challenging.
- Installation can be complex and may require professional expertise, potentially leading to longer installation times.
- Lack of awareness, standards, and data limits widespread implementation and confidence in this technology.
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Resources:
- HUBER SE. (n.d.). Heating and cooling buildings with wastewater. Heating and Cooling Buildings with Wastewater-Huber Technology Waste Water Solutions – huber-se.com
- Monchamp Meldrum LLP. (2018, September 20). SB 100 and EO B-55-18: California’s new 100% clean energy policy. SB 100 and EO B-55-18: California’s New 100% Clean Energy Policy – Monchamp Meldrum LLP – mlandlaw.com
