Field experiment and analytical study of commercial earth-air heat exchanger performance in a solar greenhouse

Earth-Air Heat Exchangers (EAHEs) are low-energy thermal management technologies with simple design and low operating and maintenance requirements. However, commercial-scale experimental research on their performance and soil thermal response remains limited, particularly for horizontal parallel designs in cold climates, where existing assessments are predominantly simulation-based. This study investigates a horizontal parallel EAHE in a commercial solar greenhouse in Ontario, Canada, evaluating an as-built multi-pipe array at the inlet/outlet manifolds as a complete system, measuring air and soil sides simultaneously, and converting depth-resolved soil temperatures into layer-wise stored energy. During an 11-day July experiment, greenhouse conditions, EAHE inlet and outlet temperatures, control signals, and soil temperatures at multiple depths and positions near a buried pipe were recorded every 6 min while the EAHE ran on a fixed twice-daily schedule. Soil temperature profiles were reconstructed by least-squares quadratic fitting to quantify heat storage, and performance assessed using inlet-outlet temperature differences, coefficient of performance (COP), and matched 4.5-day periods with and without EAHE operation. Afternoon cooling produced inlet-outlet differences near 7 °C and a maximum COP of 9.73, averaging 7.11, consistent with other measured greenhouse installations. Early-morning heating reached a maximum COP of only 1.25 because of small air-soil temperature differences. Soil adjacent to the pipes charged during afternoon operation and retained heat between cycles, indicating short-term load shifting, while near-surface soil followed greenhouse air temperature and solar gains. Fixed-schedule operation reduced ventilation heat loss by only 5.7% while increasing total electrical use; real-time temperature-based control is therefore recommended. The dataset is published openly for model validation.