The parameters of natural ventilation system of animal shed

Abstract

The analytical results reflect the mean values of experimental data under natural conditions of operation rather accurately. The difference between the experimental and calculated air speed values in the outlet opening was insignificant and was within 0-8% range. In designing a natural ventilation system for animal shed, it is necessary to assess the ventilation induced by thermal buoyancy and wind forces during different seasons and under different animal housing conditions. By applying analytical and experimental research, a methodology was prepared to establish the ventilation intensity caused by thermal buoyancy and wind, and the data on thermal buoyancy and wind values and their relationship. The innovation of the methodology can be described by the fact, that a simple equation was formed to calculate the air speed in inlet and outlet openings, a mathematical expression of thermal buoyancy and wind ratio achieved and the required inlet opening area to let fresh air in compared with the outlet opening area to let polluted air out was substantiated to ensure all polluted air be removed through a rooftop aperture in winter. It was calculated that the average air speed in the rooftop aperture of a typical cold-type cowshed was 1.3 m/s (when there is no wind, this speed decreases down to 0.3 m/s), thermal buoyancy and wind ratio was 0.27 and in order to have all polluted air removed through the rooftop aperture in winter the inlet opening area in the walls must not exceed 40% of the rooftop aperture area. The accuracy of the prepared methodology was tested under natural conditions of animal shed operation, when the distance between air inlet openings and outlet was 6.5 m. During the investigations, indoor and outdoor temperatures, air speed in the outlet and wind speed were measured. During the experiments, the difference of the indoor and outdoor temperatures varied from -2 to +16C and air speed in the outlet - from 1.2 to 1.9 m/s.