Simulation of natural ventilation for livestock structures
Pig production in Malawi and in most of the developing countries is shifting increasingly from pasture or dirt lot to total confinement with improved housing facilities. Keeping pig level temperatures within the comfort zone in hot weather is a common problem in naturally ventilated intensive pig buildings. Automatically controlled natural ventilation (ACNV) has proved to be effective in reducing the problem of heat build up in pig houses and is becoming very popular. However, a method for reducing summer temperatures at animal level in non-automated naturally ventilated intensive pig buildings has not been developed. An attempt was made to develop a natural ventilation system which would maximise the cooling effect of wind at animal level by manual control in buildings suitable for the Tropics. The research project was conducted in three stages: (1) air flow pattern studies, using 1:20 scale two-dimensional models, (2) wind tunnel testing, using three-dimensional, 1:20 scale models with simulated pigs, and (3) validation of results from the wind tunnel studies made with a 1:4 scale model, put out in the field. Air deflectors were used as a means of increasing the effect of wind on the ventilation pattern in the models. Monopitch, duopitch and offest gable models were tested in the water table, and monopitch models were tested in the wind tunnel. The use of air deflectors in monopitch and offset gable models showed a marked increase in airflow towards the animal zone area and a reduction in the difference between the surface temperature of the model pigs and the outside air temperatures. The deflectors improved the performance of the models by about 10% with the front orientation and about 20% with the rear orientation. In the duopitch model an increase in the roof overhang improved flow circulation on the leeward side. The use of air deflectors also improved flow circulation on the leeward side. The wind speed and air temperature at the experimental site for the 1:4 scale model were used to validate the results from the wind tunnel tests. The measured temperature values showed similar response curves to the predicted values. Temperature differentials increased with an increase in the angle of the deflector.