Code Changes and Implications of Residential Low-Flow Hot Water Fixtures

This study investigated strategies to improve hot water delivery quality in single-family homes to reduce energy and water waste. The investigation examined a range of improvement strategies that include pipe layout optimization, using two water heaters, moving the water heater closer to the fixtures, pipe size reduction, compact architectural design, and lower-flow fixtures. Using the results of single-pipe testing from a 2005 Public Interest Energy Research project, the research team developed a distribution performance model to analyze the multi-pipe distribution networks found in homes. Since most hot water events are of very short duration, the water temperature rarely reaches steady-state. The model can account for the transient nature of the hot water delivery process found in realistic hot water use schedules. Based on performance assessment results, the study provided design solutions to reduce distribution loss by more than 50 percent and system energy and water consumption by more than 25 percent. Research results were shared with key stakeholders.

Improving architectural compactness and hot water distribution system designs can reduce the first costs and save energy and water, improve hot-water delivery quality, and reduce emissions over the operational life of the building. The researchers found that compact wet-room architectural designs can reduce the first cost of hot-water distribution system installation by $1,000–$2,000 per home. If low-flow fixtures are used in addition to compact wet-room architectural designs, an average home will save 19 therms and 3,180 gallons of water per year, which represent about 26 percent reduction from baseline. Correspondingly, California ratepayers will save about 1.9 million therms of natural gas and 318 million gallons of water in the first year.