The document discusses different types of heating systems including natural gas, fuel-oil, electric resistance, heat pumps, and solar. It explains that high energy costs, more operating time, and less equipment life result from high heat loads, while low energy costs, less operating time, and increased equipment life result from reducing heat loads. External heat loads come from glass, walls, ventilation, and infiltration, while interior heat loads come from occupants, lighting, machines, and own installation. The document also outlines the components of an air conditioning system, including an expansion valve, compressor, condenser, evaporator, fans, and electrical system. It notes that air conditioning reduces humidity and temperature in summer and heats and humidifies in winter.