Flow velocity impact on energy and carbon metrics of earth-based cooling systems

Abstract

This article investigates the thermal performance and sustainability of U-shaped and serpentine earth-to-air heat exchanger (EAHE) systems with varying flow velocities. The life cycle analysis, embodied energy, carbon credit, and energy payback period for earth air heat exchanger systems are also investigated. This study reveals that increasing flow velocity leads to higher convective heat transfer coefficients but reduced air-ground contact time, resulting in a smaller temperature difference at higher velocities. Interestingly, pipe configuration shows minimal impact on outlet temperatures. The energy analysis, employing computational fluid dynamics simulations, reveals a decreasing trend in percentage heating and cooling potential increases with higher airflow velocities, notably showing a rise of approximately 35% from 2 to 3 m/s and diminishing to about 8% from 4 to 5 m/s for both EAHE systems. Additionally, annual thermal energy evaluation indicates a 34.7% increase from 2 to 3 m/s, followed by a reduced rise of 13.4% from 4 to 5 m/s. Embodied energy is estimated at 2991.403 kWh, with total annual energy outputs of 1193.2 and 1206.7 kWh for U-shaped and serpentine EAHEs, respectively. With a 50-year system lifespan, energy payback time stands at 2.51 years for U-shaped and 2.47 years for serpentine EAHEs. Assessing long-term environmental impact, the study quantifies CO₂ emission mitigation and carbon credits, indicating 93.67 tonnes reduction and Rs. 1,59,801.02 credits for U-shaped EAHE and 94.73 tonnes reduction and Rs. 1,61,609.38 credits for serpentine EAHE.