Heating  is defined as a form of energy that acts upon a substance to raise its temperature.

Ventilation is the process of supplying or removing air, by natural or mechanical means, to or from any                               space. Such air may or may not be conditioned.

Air-Conditioning  is the process or treating air so as to control simultaneously its temperature, humidity,                         cleanliness, and distribution so as to satisfy the requirements of the conditioned space.

Refrigeration is the process of removing heat from an enclosed space, or a substance, and rejecting it                             elsewhere for the primary purpose of lowering the temperature of that enclosed space or                                         substance, and then maintaining that lower temperature.