Optimization of Earth-Tube Heat Exchangers for Winter Ventilation of Swine Housing

ABSTRACT THE thermal and economic performance of both conventional and earth-tube ventilating systems for 10, 20, 30 and 40 sow farrowing houses were evaluated theoretically to optimize design recommendations. Thermal performance was simulated using finite difference techniques to obtain tubing outlet temperatures as a function of lateral length, tube diameter and air flow rate per tube. Optimal combinations of tube length and number of tubes were determined for several tube sizes for winter conditions using an economic analysis. For a 20-sow farrowing house having a 0.15 m diameter earth-tube system, the minimum equivalent annual cost of $483 was obtained with seven - 30 m long laterals having an air flow rate of 0.0357 mVs-tube. The winter fuel cost for this system was $263. Equivalent annual cost for a conventionally ventilated building was $611 with a fuel cost of $431. Other system designs providing substantial cost and energy savings were determined. As tubing diameter increased, optimal lateral lengths increased and the optimal number of laterals decreased.