Hot-Water Distribution System Piping Heat Loss Factors—Phase III: Test Results

摘要

This paper describes results of recent laboratory tests on additional piping types and sizes in a variety of environments including in-air, in-attic, and in-floor, both insulated and uninsulated, and compares them to previous test results by the author on other pipe configurations and environments. New pipes tested included chlorinatedpolyvinyl chloride (CPVC) and high-density cross-linked polyethylene (PEX), in both in-air and in-attic environments, and rigid copper, in both in-attic and in-floor environments. These tests allowed calculation of measured piping heat loss (UA) factors under a variety of different temperature and flow conditions, with various insulation levels. 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 associatedwith piping systems. 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. A separate related paper discusses time, water, and energy waste while waiting for hot water to arrive at fixtures.