A dynamic computer model for optimization of the internal climate in swine housing design

Climate control is essential for animal production, but building parameters concerning the internal climate may not always be reliable if calculated using a steady-state approach. As an aid for design, a software tool has been developed to simulate the transient environmental conditions inside closed animal buildings such dairy cow or pig barns. The main program inputs were: wall, roof and floor materials (including insulating air spaces), building orientation, vent opening characteristics (size and position), wind speed and direction, overall building dimensions, type of animal housed, and latitude and longitude. The program output included the heat balance (sensible and latent) and temperature humidity index during the day. The simulation model accounted for the daily sun path, the eventual roof shadowing on the walls, and the water evaporation from the floor and the manure. Heat transmission through walls was calculated by the finite difference method. Natural ventilation was evaluated numerically calculating first the neutral plane, and then calculating the air flow at each time step due to buoyancy and wind effects (using the pressure coefficients method). The model has been validated through a comparison between the calculated internal air temperature and humidity and actual measurements in a barn for fattening pigs. The complete simulation of internal environment permits the optimization of the thermal performance of the buildings during the entire year. This allows a means to reach the best compromise (in terms of building design) between the opposite requirements of cold winters and hot summers.