Tempering ventilation air in a swine finishing barn with a low-cost earth-to-water heat exchanger

Abstract

An earth-to-water heat exchanger (EWHE) can reduce livestock heat stress and also save electricity and water. A 4-kW EWHE system comprising 154 m of a polyvinyl chloride (PVC) pipe (35 mm ID) buried in 3.2 m of soil was evaluated for its ability to provide cooling to 60 pigs in a finishing barn in Raleigh, NC. A low-cost tube-and-fin heat exchanger was used to exchange energy between water (38 l/min) and air (0.58 to 1.22 m3/s). After 8 h of cooling, at 1.22 m3/s, the temperature change (ΔT), energy produced (qh), and coefficient of performance (COP) were as high as 3 °C, 4.3 kW, and 8.2, respectively. After 12 h of continuous operation for air tempering during winter, |ΔT|, |qh|, and COP were 2.2 °C, 3.4 kW, and 6.7, respectively. While the EWHE pens were slightly warmer than the Control pens cooled with stir fans and sprinklers on very hot days, pig performance in the EWHE pens was unaffected. The EWHE reduced the electricity use by >50% and eliminated the sprinkling water use. Burying plastic pipes in slinky coils instead of using double pass rigid PVC pipes could improve system performance as would wetting the soil around the pipes. In addition to being sustainable, the EWHE could be cost-effective for zone-cooling of high-value pigs as well as greenhouse cooling in many parts of the world.