Design and Feasibility of a Novel Sprinkler Control Algorithm for Swine Heat Stress Alleviation

Pigs have a relatively low capacity to dissipate excess body heat and depend more on reducing metabolic heat production through a reduction in voluntary feed intake in hot conditions, resulting in a growth performance decrease. Effectiveness of current cooling devices (e.g., evaporative coolers or sprinklers) in facilities is governed by the Water Vapor Pressure (WVP) concentration gradient between the air (a function of dry-bulb temperature; t_db, Relative Humidity; RH, and atmospheric pressure) and saturated WVP at a wet surface. Traditional Sprinkler Control Systems (TSCS) often operate solely on t_db feedback and at fixed ‘off’ intervals to allow dispersed water to evaporate. This control strategy does not account for the WVP concentration gradient; hence, water is wasted and only a limited amount of latent heat can be removed from the animal. Therefore, the objectives were to develop and simulate a novel Variable Interval Sprinkler Control System (VISCoS) that dynamically changes the ‘off’ interval based on t_db, RH, and airspeed feedback. A theoretical convective mass transfer model (i.e., evaporation) was developed to estimate water evaporation rate as a function of the thermal environment, surface area, skin temperature, and volume of water applied. A pig’s geometry was assumed a cylinder approximately 30% wet with a 1 mm film of water. The feasibility of implementing VISCoS was evaluated at six locations (AZ, IA, MN, MO, IN, and NC) by simulating water usage for a 1000 hd, mechanically ventilated, grow-finish building with an assumed water delivery (75.71 L/min), sprinkler ‘on’ time (30 s), and constant BW (100 kg). Typical Meteorological Year 3 weather data (365 d) was used to determine outdoor t_db and RH at each location, where indoor t_db was assumed 2°C greater than outdoor t_db with a 2 m/s air velocity across the animal’s back. The VISCoS performance was compared with two TSCSs with fixed ‘off’ intervals (15 and 30 min; ‘on’ t_db ≥ 29.44°C). Simulation results for each region showed water usage for 15 min (154, 72, 60, 50, 80, 164 m³) and 30 min (79, 37, 31, 26, 41, 83 m³) ‘off’ interval TSCS to be greater than VISCoS (49, 15, 8, 10, 17, 44 m³). Duration (±SD) for complete water evaporation estimated by VISCoS (19.6±1.4, 28.0±3.6, 27.8±2.5, 31.8±6.5, 32.2±3.3, 26.9±3.3 min) varied by region and provides insight on incorporating more thermal environment measurements to reduce water usage in swine facilities.