Energy Exchanges And Related Temperatures Of An Earth-Tube Heat Exchanger In The Heating Mode

Abstract

An instrumented earth-tube heat exchanger was designed, installed, and operated as a single-pass heat exchanger to investigate its potential as an alternate energy source. Energy exchange magnitudes were determined and related to concurrent temperatures of operation. The system consisted of 64 m (210 ft) of 15-cm (6-in.) diameter metal pipe buried 1.8 m (6 ft) deep in red clay soil with risers provided at the inlet and outlet and at 15-m (50-ft) intervals. The system was equipped with a high pressure, direct-drive industrial type blower with radial blade wheels. Air temperatures and the peripheral soil temperatures were obtained at both the inlet and outlet ends of the tube, and the outlet air was exhausted to the atmosphere. The system was operated on a 24-hour daily schedule, and this article reports results selected from winter periods of two separate years. Energy exchanges are presented including the effects of ambient air temperature and daily weather types. Also, data related to both lateral and longitudinal gradients of soil, tube wall, and airflow temperatures are presented. The results provided a descriptive and encouraging overview of earth-tube energy exchange performance and related temperatures of operation.