Optimizing economic performances of foundation earth-to-air heat exchangers for low-technology residential air-conditioning

Despite its classification as a low-technology and nearly passive sustainable system, the use of earth-to-air heat exchangers in residential settings remains relatively uncommon, primarily due to the expenses associated with excavation. Nevertheless, positioning the heat exchanger around the building's foundations during construction offers a potential solution to mitigate these costs. This study conducts an economic viability analysis for such a configuration, focusing on a typical single-family dwelling in Montréal, Canada. A sizing investigation revealed that ducts with relatively small diameters (approximately 20 cm), constructed from cost-effective materials, are optimal. These ducts should be placed as deep and as distant from the foundation as feasible. The optimal heat exchanger configuration reduces the building's heating/cooling load by 701 kWh per year (4.3 %). However, despite minimal excavation expenses, the economic analysis suggests an unviable Levelized cost of Energy for the province of Quebec (0.182 US$.kWh⁻¹) compared to the low electricity rates in the area (a domestic fare of 0.059 US$.kWh⁻¹). The findings underscore notable losses attributable to thermal short-circuiting influenced by the basement walls and coupling affected by the mandatory Heat Recovery Ventilation system. Overall, it was determined that only 60 % of the sensible heat exchanged with the soil effectively contributes to load reduction.