I am having little confusion over basic concept of HVAC system? please do read my detail question below

Centralising of an (one) Air Conditioning equipment throughout the Project/ Building is called as Centralised Air Conditioning Process, This is actually a Process of Air Conditioning.

Types of Air Conditioning Equipments:

Chilled Water System:

• Water Cooled Chillers - (out door units)
• Air Cooled Chillers - (out door units)

Indoor Units are like Fan Coil Units, Air Handling units. (These all are Ductable Units)

Direct Expansion System:

• One Outdoor unit and One Indoor Unit (Split type, Celing Concealed, Floor Standing/ Floor Mounted, (all Ductable), Decorative type(Ductless) 
• Unitry Package Air Conditioning Unit  doesn't require any indoor unit, The Ducts are passed throughout the required space.

VRF System:

• It is the Advanced Technology Mixture of both of the above concepts (Excluding the Unitry Package unit), it is effective, efficient, space saving, low maintanance, easy Installation cost

The only Problem with this is High Installation Cost.

Hvac systems are two types DX Refrigerant system and Chilled water system.

Dx Type system-- Unitary type limited to multiple rooms/ offices showroom low size central Package system, Split ductable system, Decorative split system

 Chilled water System--This is central colling system used for cooling of multi storey buildings , Multiplex, Malls, District cooling for residential commercial community.                                             

Packaaged Systems belong to Unitary Systems. 

Below definitions might help also. 

A unitary or package air conditioning system uses equipment where most or all of the basic components have been assembled in the factory.

A central or built-up air conditioning system uses equipment centrally located in mechanical equipment rooms. Each piece of equipment is installed separately and connected on the job, rather than manufactured as a package.

HVAC is Heating Ventilating and Air Conditioning. It's goal is to provide thermal comfort and acceptable indoor air quality of occupants, food & dairy products, equiptment and electronics devices.

Short for heating, ventilation, and air conditioning. The system is used to provide heating and cooling services to buildings. HVAC systems have become the required industry standard for construction of new buildings.

• HVAC systems are comprised of the heating, air conditioning, and ventilation systems in a residential or commercial building. These mechanical systems provide thermal comfort and air quality in indoor spaces.  Types of HVAC systems include air conditioners, heat pumps, furnaces, boilers, rooftop units, chillers, and packaged systems. A building’s HVAC system encompasses components such as ductwork and air handlers which are essential to system performance.

  More information about the energy efficiency of specific components can be found here:

  Heating

  • Boilers
  • Furnaces
  • Heat Pumps

  Air Conditioning

  • Air Conditioners
  • Heat Pumps

  Research, policies, and programs related to general HVAC systems and specific ventilation systems can be found in the links below and to the right. The consumer guide has specific guidance and tips on heating, ventilation, and air conditioning

HAVC system can work with refrigeration and steam its depended on ambient temperature for example in Europe its working with hot water or heater. In GCC its working with refrigeration.

Packaged and ducted split system also can work with HVAC its depended on location and suitable equipment’s which comfort with the space .And chilled water also can use for central Air conditioning system..

Decretive Split system normally using for domestic purpose only.

I advise you not to be get ridden along your thoughts. If you are in the A/C field then for each model of the A/C unit the manufacturer itself defines the category of A/C to its best suitable one. Simply go through the manufacturer's manual and solve your problem and consider that as a common concept. Special request is that you do concentrate on the job/work you are doing right now.

Unitary system means a system which combines heating, cooling, and fan sections all in one(Packaged) or a few assemblies(Split). Package Unit and Split systems can be used as unitary system and centralized system. Consider for a substation, a large capacity packaged unit can be used as unitary system. The same packaged unit can be used to supply for two or three separate areas with or without terminal controls.

Package unit ,VRF/VRV unit ,Chiller,AHU's are part of centralized system