Energy Performance of Concrete Earth Tubes for the Pre-Heating and Pre-Cooling of Supply Air in Cold Climate (ST-16-C060)

In Canada, outside air temperatures can vary significantly during the year. A temperature gradient of 70 ⁰C between the cooling and heating season is common in many regions. Because of the high thermal inertia of the soil, airflow circulating in earth tubes will benefit of  a significant temperature increase or decrease with respect to heating or cooling season . The advantages of an earth-to-air heat exchange system are its simplicity, high pre-cooling and pre-heating potential leading to fossil fuel savings and related emisssions and low operation maintenance costs. Very few experimental studies of ground temperature impact on heating with earth-to-air heat exchanger were found in the literature for cold climate. This paper deals with the performance of an earth-to-air heat exchange system for an operational Canadian building, with the aim of characterizing its efficiency. The building, called Earth Rangers, is a visitors’ centre built to educate children about biodiversity, conservation and the adoption of more sustainable behaviors. The earth tube system is an earth-to-air heat exchanger system which consists of nine 900 mm diameter, 20 m long pre-cast concrete pipes buried beneath the frost line (approximately 1500 mm below grade). Outside air is drawn through the buried concrete pipes allowing surrounding earth to moderate the temperature of the incoming air so that it is either pre-heated or pre-cooled depending on the time of year. The performance assessment of the earth tube system consisted of continuous monitoring between January and November 2014.Results from winter and summer field monitoring are presented in terms of overall heat exchanger effectiveness and comparing the pre-heating effectiveness of the  monitored earth tubes and exploring what could be done to improve the design. This long-term field study on earth tubes has confirmed the overall effectiveness of this passive means during the winter and summer conditions.