There are various technical solutions and modes used in the ventilation systems of animal pens depending on the consumption of energy and the economical viewpoint. During the recent ten years the agricultural enterprises have transformed into specialised and intensified systems. In most cases air exchange in piggeries takes place by natural influx through ventilation channels in the walls and by mechanical suction. In order to ensure microclimate parameters corresponding to the norms of animal well-being, the consumption of energy increases to ensure the microclimate in the pens. There are great losses of thermal energy in the ventilation systems. To diminish the losses of heat through the ventilation systems, we used the supply air processing, utilisation of the heat of the exhaust air in the emissions of the ventilation systems and optimal regulation of these systems. Operating schemes of the ventilation systems were studied using the climatological data and the necessary amount of energy which is necessary to ensure the calculated microclimate during the heating period. The energy consumed to operate the ventilation systems was calculated according to the variations in the enthalpies after the air preparation processes were finished, and to the repetition frequency of the outdoor air parameter combinations in the heating season. In Latvia the heating season lasts 205 days – from October till April, including.