Thermal Performance of Conventional-Metal and Novel-Plastic Drain Water Heat Recovery Device

Abstract

Drain water heat recovery (DWHR) systems are effective for reducing energy consumption by capturing waste heat from drain water and using it to preheat the primary water supply in buildings. However, traditional DWHR devices, with copper helical tubes wrapped around a central pipe, can be expensive for residential use, deterring homeowners. This study introduces an innovative 3D-printed DWHR design using Nylon PA material. This design eliminates contact and conduction resistances of helical tubes, resulting in reduced thermal resistance, weight, manufacturing cost, and improved performance. Experimental testing compares the new plastic DWHR device with the conventional metal one under steady and transient conditions. In addition, detailed heat transfer models and thermal networks are given for both devices. The plastic device consistently outperforms the metal one, achieving higher effectiveness within the first few minutes of operation across various water flow rates. This advantage is particularly beneficial for short-term drain water usage like sinks and showers. Additionally, the novel DWHR device maintains a 16–20% higher steady-state effectiveness at high flow rates. This innovative approach promises cost-effective and efficient heat recovery, making DWHR technology more accessible for residential and commercial applications.