How hot is piping hot?: lower energy consumption with smarter hot water delivery

Abstract

In typical US homes, water heating is the largest energy consumer besides space heating and cooling, and it accounts for approximately 17% of residential energy consumption on average. In this paper, we propose and evaluate a new technique to reduce energy waste due to pipe loss: delivering lower temperature water whenever possible. We created a Smarter Water Heater (SWH) that uses data fusion techniques to infer 1) the fixture being used 2) the mixed water temperature at the fixture 3) the pipe volume for that fixture. After learning a model for each fixture, it solves a control optimization problem to decide when and at what temperature to deliver water to minimize energy use without sacrificing comfort of the user. We evaluated the SWH in three stages. First, we built a physical prototype and measured energy efficiency. We then deployed 18 sensors into a home's piping system for a 50-day in-situ study to stress test the SWH's sensing sub-system. Finally, we collected traces of hot water use from 5 different homes over 10 days each to determine how different water usage habits and piping structures affect energy savings. The results indicate that the SWH reduces total water heating energy by 8--14% with little to no effect on user comfort.