Heating, ventilating and air conditioning are the 3 main aspects of HVAC systems. In some structures, this is sometimes combined with the additional refrigeration aspect if there is a need to freeze or keep frozen things or units which are integral to the function of the building.
Many HVAC installers and contractors rely on the design of the building when it comes to the capacity and the design of the heating, cooling and ventilating itself. Some buildings may not need as much ventilation as others if it is designed to be airy with less closed windows and doors. You can see this here http://www.ryananthonysheatingservice.com/hvac-installations/ to know more about HVAC installation.
Lower types or smaller buildings may not need a large unit to provide ventilation as well as cooling and heat.
The comfort of the occupants of the structure is usually foremost in the minds of installers or manufacturers of any HVAC unit or system.
Equipment and supplies
HVAC also plays a crucial role in keeping device and elements in the good situation. some structures or establishments require a cooling or freezing system kept at a fixed temperature for the good of supplies such as food, medicines and other perishables which will need to be kept frozen to ensure freshness or at least that they will last longer.
Some hospital and computer system also require certain coolness for them to function well or the absence of dust to ensure that they do not corrupt easily. Dust can emancipate computers if there is not enough maintenance or cleaning while its presence itself can worsen the corruption.