This paper describes results of recent laboratory tests on PEX-aluminum-PEX hot water distribution system piping and compares them to previous test results on rigid copper pipe. These tests allowed calculation of measured piping heat loss (UA) factors under a variety of different temperature and flow conditions, with various insulation levels. Several unanticipated flow regimes were observed, causing results not to behave as would be expected using fully developed flow theory. This piping UA information can be used to estimate piping heat loss and steady-state temperature drop under any desired temperature and flow conditions. The UA data can additionally be used to determine piping cool-down rates after flow has ceased. Piping heat loss data are one critical part of the information necessary to accurately estimate total energy losses associated with piping systems. This paper includes examples of how to use heat loss information to estimate energy loss effects due to heat loss from piping. These energy loss effects extend beyond just energy loss from the pipe itself and include, for example, increases in tank heat loss caused by the need to set temperatures higher to overcome temperature drop of water flowing through the pipe.

Units: Dual