This paper describes results of recent laboratory tests on common hot water distribution system piping sizes and types under a variety of flow rate, temperature, and environmental conditions. Importantly, buried pipe performance data are presented for the first time. The tests measured the time spent waiting for hot water to arrive at fixtures and the amount of water wasted to drain while waiting. From these, the energy waste associated with the water waste can be computed. Results are presented as plots of the ratio of actual flow volume divided by pipe volume (AF/PV) vs flow rate, temperatures, and other parameters of importance. Several unanticipated flow regimes were observed that dramatically alter behavior from what might be expected based on either plug flow or fully developed flow theory.

Units: Dual