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Journal of Environmental Engineering and Landscape ManagementPublication details, including instructions for authors and subscription information:Abstract. In designing a natural ventilation system for animal sheds 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 investigation a methodology was prepared to establish ventilation intensity caused by thermal buoyancy and wind and data were achieved 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 was achieved and the required inlet opening area to let in fresh air compared with the outlet opening area to let out polluted air was substantiated to ensure that all polluted air is removed through a rooftop open in winter. It was calculated that the average air speed in the rooftop outlet opening of a typical cold-type cowshed is 1.3 m/s (when there is no wind, this speed decreases to 0.3 m/s), thermal buoyancy and wind ratio is 0.27 and in order to have all polluted air removed through the rooftop open in winter the inlet opening area in the walls must not exceed 40% of the rooftop opening area. The accuracy of the prepared methodology was tested under natural conditions of barn operation when the distance between air inlet openings and outlet openings was 6.5 m. During the investigation indoor and outdoor temperatures, air speed in the outlet and wind speed were measured. During the experiments the difference of indoor and outdoor temperatures varied from -2 to +16 o C and air speed in the outlet -from 1.2 to 1.9 m/s. 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.

1 Lietuvos žemės ūkio universiteto Žemės ūkio inžinerijos institutas, Instituto g. 20, Kauno r., Lietuva. El. paštas: bkavolelis@mei.lt 2 Lietuvos žemės ūkio universitetas, Šilumos ir biotechnologijų inžinerijos katedra, Studentų g. 15, Kauno r., Lietuva. El. paštas: Rolandas.Bleizgys@lzuu.lt Įteikta 2006 02 28; priimta 2006 05 17 Santrauka. Darbo tikslas -pagrįsti karvidės temperatūrinio-drėgmės režimo optimalias reikšmes, taikytinas projektuojant ir eksploatuojant vėdinimo sistemą. Sudaryta lygtis, patalpos oro santykinį drėgnį siejanti su patalpos ir lauko oro temperatūrų skirtumu. Taip pat sudaryta lygtis, rodanti, koks yra didžiausias leistinas temperatūrų skirtumas, kad vandens garai nesikondensuotų ant išorinių atitvarų vidinio paviršiaus. Analiziniais ir eksperimentiniais tyrimais pagrįsta, kad galimas minimalus karvidės oro santykinis drėgnis yra apie 5 % mažesnis už lauko oro santykinį drėgnį. Optiminalus temperatūrų tarp patalpos ir lauko oro skirtumas šaltuoju laikotarpiu yra apie 4 °C.Prasminiai žodžiai: karvidė, šiluminės savybės, temperatūrų skirtumas, santykinis oro drėgnis.

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