Refrigeration and refrigerating machinery Air conditioning 223 Maintenance and repair 67 Heating 49 Ventilation 23 Equipment and supplies 21 Electric equipment 14 Electric engineering 13 Heating and ventilation industry 13 Heat 12 Transmission 12 Cold storage 11 Vocational guidance 11 Cooling towers 10 Energy consumption 10 Heat pumps 10 Refrigerators 9 Design and construction 8 Lubrication 8 Cooling 7 Buildings 6 Efficiency 6 Environmental engineering 5 Factories 5 Automobiles 4 Control 4 Energy conservation 4 Frozen foods 4 Solar radiation 4 Air conditioning industry 3