Impact of Horizontal Run-Out Length on the Thermal Response of Full-Scale Energy Foundations

Abstract

This paper includes the results of a combined thermal response test performed simultaneously on four full-scale energy foundations beneath a new building at the U.S. Air Force Academy. The temperatures of the fluid circulating in and out of each of the closed loop heat exchangers in the drilled shaft foundations were monitored over the course of 21 days during application of a constant input energy. The temperatures of the foundations at different depths were also monitored. The horizontal length of pipe connecting each energy foundation to the manifold through the grade beam of the building was different. The results of the tests indicate that a longer horizontal run-out length leads to a lower apparent thermal conductivity, potentially due to the greater mass of concrete being heated, or lower heat transfer in the grade beam due to the higher temperatures of the ground surface during testing.