The main goal of the final work is to get acquainted with the parts that make up the cooling system of seawater pumping station and compressor station in Oil Rafinery Rijeka (further in the texr RNR) and to calculate the associated pipelines and pumps. The calculation of pipelines and pumps was done according to the calculation instructions contained in the manual „ Heating and Air conditioning 2004“ by Recknagel, Sprenger, Schramek, Čeperković. After getting acquainted with the cooling system and their division, based on the documentation obtained from the RNR, the circular cooling system(further in the text KRS) of fresh water and its delivery to the cooling plants were processed. Next, the KRS of seawater that is sent via a seawater pumping station to a part of the RNR plant called Energana is described. When explaining KRS we encounter the parts that make up KRS as whole such as: valve, piping. In the calculation part, the total pressure drop in the scheme of the seawater pumping station and the compressor station, which was made according to the drawings of the mentioned systems obtained from the RNR, was calculated. Finally, the operating point of the system obtained by the intersection of the pump and pipeline performance curve is shown.