Mechanical System - Any building service using machines. They include plumbing, elevators, escalators, and heating and air-conditioning systems. The introduction of mechanization in buildings in the early 20th century brought about major adjustments; the new equipment demanded floor space, and the design team began to include electrical and HVAC (heating, ventilating, and air-conditioning) engineers. Heating and cooling changed dramatically. Modern buildings, with their large heat gains, turned central heating into little more than a supplement.