HI-02-08-2 -- Field Test Comparison of Hot Water Recirculation Loop vs. Point-of-Use Water Heaters in a High School PDF

Conventional piping heat loss calculations show that potable hot water recirculation loops having significant length loose significant amounts of energy; however, little, if any, field test data existed to verify and quantify this energy loss. The effort reported here sought to experimentally document energy consumption and heat loss from a gas-fired hot water recirculation- loop system in a high school and to experimentally compare said energy consumption to that of an electric resistance point-of-use water heating system serving the same end uses. To achieve these objectives, a suitable test site was located and the existing gas-fired hot water recirculation loop was instrumented and monitored for a period of time. Next, the hot water recirculation-loop system was modified by the addition of a recirculation-loop pump timer control and the system was then monitored for an additional period. Finally, the hot water recirculation-loop system was replaced with a set of electric resistance point-of-use water heaters serving the same end uses, and the system was further monitored for an additional period. Total monitoring period was one calendar year.

Performance of the three system configurations was then analyzed as if each had been operating for the entire 12 calendar months, in each case using the actual temperatures and amounts of hot water consumed as observed each day. Energy consumption, overall delivered efficiency, and energy savings for each configuration were thus computed on a 12 calendar month basis and the results presented here.

Units: Dual