**4. Classification of HVAC systems**

The major classification of HVAC systems is central system and decentralized or local system. Types of a system depend on addressing the primary equipment location to be centralized as conditioning entire building as a whole unit or decentralized as separately conditioning a specific zone as part of a building. Therefore, the air and water distribution system should be designed based on system classification and the location of primary equipment. The criteria as mentioned above should also be applied in selecting between two systems. **Table 1** shows the comparison of central and local systems according to the selection criteria [3, 4].



condition the building, and it can be centralized or localized based on the availability,

Types of HVAC Systems

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**d.** Vertical shaft: provide space for air distribution and water and steam pipe distribution. The air distribution contains HVAC supply air, exhaust air, and return air ductwork. Pipe distribution includes hot water, chilled water, condenser water, and steam supply, and condenser return. The vertical shaft includes other mechanical and electrical distribution to serve the entire building including plumbing pipes, fire protection pipes, and electric conduits/closets.

**e.** Equipment access: the equipment room must allow the movement of large, heavy equip-

Air distribution considers ductwork that delivers the conditioned air to the desired area in a direct, quiet, and economical way as possible. Air distribution includes air terminal units such as grilles and diffusers to deliver supply air into a space at low velocity; fan-powered terminal units, which uses an integral fan to ensure the supply air to the space; variable air volume terminal units, which deliver variable amount of air into the space; all-air induction terminal units, which controls the primary air, induces return air, and distributes the mixed air into a space; and air-water induction terminal units, which contains a coil in the induction air stream. All the ductwork and piping should be insulated to prevent heat loss and save building energy. It is also recommended that buildings should have enough ceiling spaces to host ductwork in the suspended ceiling and floor slab, and can be used as a return air plenum

location, and cost. It is preferable to have easy access to outdoor air.

ment during the installation, replacement, and maintenance.

**Figure 1.** Horizontal hierarchy representation of HVAC system requirements.

to reduce the return ductwork.

**Table 1.** Comparison of central and local HVAC systems.
