Computational prediction of the effective temperature in the lying area of pig pens

Abstract

Using solid floor instead of drained or slatted floor in the lying areas of pig pens has distinct advantages in relation to animal welfare, odour abatement and ammonia emission, energy consumption and reduced building costs. However, pig producers often opt out of providing a solid floor due to the risk of manure fouling in the lying area during warm periods, fouling that may increase work load, reduce animal welfare and degrade the indoor environment. The risk of fouling the lying area increases as indoor temperature increases, and it is therefore recommended that the indoor temperature should be maintained at around 13°C during the last part of the growing period if diffuse air intake is used. Undesired higher indoor temperatures still occur during about 40% of the time each year, even in the relatively cold Danish climate (where outdoor temperatures average about 8°C).This study aims to investigate the potential benefits of using a hinged ceiling flap inlet to control the air velocity and experienced thermal environment for pigs in the lying area of finisher units. A new equation for the effective temperature (ET) has been developed and used to express how temperature, humidity and velocity, individually contribute to the combined effect of the thermal condition raising pigs are exposed to. Computational Fluid Dynamics (CFD) simulations were conducted to estimate the relevant parameters and, finally, the ET. Furthermore, the developed ET equation was implemented in the CFD model as a Custom Field Function to calculate the distribution of ET in the animal occupied zone. It was assumed that a traditional diffuse ceiling air inlet would deliver the required airflow rate as long as the outdoor temperature was below 10°C. At higher outdoor temperature, a ceiling-jet inlet above each pen was opened gradually depending on the cooling requirements. When the inlet was only slightly open, it formed a wall jet attached to the ceiling. After reaching the end wall, the jet of air was deflected toward the lying area. When the jet inlet was more fully open, it sent the jet directly to the lying area.Our investigations showed that the ceiling-jet inlet could be used to control air speed in the animal occupied zone and generate the same ET in the preferred lying area at a 9-degree higher outdoor temperature than if the same ventilation rate were delivered though the defuse ceiling only. This indicates that the periods of undesired high indoor temperature can be reduced from 40% to 5% of the time under Danish climate conditions. In addition, the results showed that the largest cooling effect was obtained when the ceiling-jet inlet was opened less than 30% due to the generation of the jet’s being attached to the ceiling.