The volume of an electric motor is directly related to the thermal exchange capacity of the cooling system used in the machine. Losses are inevitable in the engine and the heat generated by them must be dissipated, it must be transferred to the engine coolant, usually ambient air. The way the heat is exchanged between the heated parts of the engine and ambient air is what will set the cooling system.
The classification of the cooling methods of the electric motors was defined according to ABNT-NBR 5110 and / or IEC-60034-6. There are essentially two types of cooling circuits in electric motors, open circuits and closed circuits. https://www.mrosupply.com/motors/ac-motors/hvac-motors/2269629_b206_marathon-electric/ The open circuit is distinguished by the passage of the refrigerant medium (air or liquid) originating from the external environment or uncontaminated enclosure through the engine, returning to the external environment or uncontaminated environment. The closed circuit is characterized by the circulation of the refrigerant medium (air or liquid) within a closed circuit, through the machine or in a heat exchanger in which heat is transferred from the machine to the refrigerant environment.