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Climate control is essential in animal production, but building parameters concerning the internal climate may not always be reliable if calculated in a conventional stationary way. As an aid for design, a software tool has been developed to simulate the transitory climatic conditions inside closed buildings such dairy cow barns or pig houses.

Main program inputs were: wall, roof and floor material layers (including insulating air interspace), building orientation, opening specifications (size and position), overall geometrical dimensions, kind of breeding, latitude and longitude. Furthermore wind speed and direction were considered. The program output concerns heat balance (sensible and latent) and temperature humidity index over 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 has been evaluated numerically calculating firstly the neutral plane, and then calculating the air flow at each time step due to buoyancy and wind effects (this last using the pressure coefficients method). The model had been validated through a comparison between the calculated internal air temperature and humidity and real values measured in a house for fattening pigs.

The complete simulation of internal climate permits the optimisation of the thermal performance of the buildings during the whole year. This allows a means to reach the best compromise (in terms of building design) between the opposite requirements of the cold winter and hot summer climatic conditions.