he prices for energy resources, global trends for greenhouse gases emission limitation makes the application of higher efficient chillers with process air evaporative cooling more common. In order to determine the economical feasibility for choosing the particular type of cooling unit for the specific building, many factors should be taken into account, which are not always available. One of these factors is the European seasonal energy efficiency ratio (ESEER) defined by the Eurovent Certification Company. It overtakes the outdoor air temperatures from +20° to +35°C with different cooling loads, which is not completely suitable for the Baltic States. Within the research monitoring of cooling system and air parameters was performed during the cooling season. It was indicated that the distribution of the energy generated by the investigated object differs significantly from the distribution of influence factors according to ESEER test methodology. The calculation of the annual energy consumption for the particular historic building according to the recorded power distribution within the outdoor air temperature ranges was performed. Using the proposed method the results are much closer to the actual annual energy consumption of the cooling plant than the one performed using the seasonal efficiency with the base temperature of 18°C.