**5. HVAC system requirements**

Four requirements are the bases for any HVAC systems [4]. They need primary equipment, space requirement, air distribution, and piping, as shown in **Figure 1**.

Primary equipment includes heating equipment such as steam boilers and hot water boilers to heat buildings or spaces, air delivery equipment as packaged equipment to deliver conditioned ventilation air by using centrifugal fans, axial fans, and plug or plenum fans, and refrigeration equipment that delivers cooled or conditioned air into space. It includes cooling coils based on water from water chillers or refrigerants from a refrigeration process.

Space requirement is essential in shaping an HVAC system to be central or local. It requires five facilities as the following:


condition the building, and it can be centralized or localized based on the availability, location, and cost. It is preferable to have easy access to outdoor air.


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 to reduce the return ductwork.

**5. HVAC system requirements**

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

five facilities as the following:

Four requirements are the bases for any HVAC systems [4]. They need primary equipment,

Accessible to equipment to be located in the basement or the living space. However, it is difficult for roof location due to bad weather

Reliable equipment, although the estimated equipment service life may be less

Placed in numerous locations to be more

flexible

Primary equipment includes heating equipment such as steam boilers and hot water boilers to heat buildings or spaces, air delivery equipment as packaged equipment to deliver conditioned ventilation air by using centrifugal fans, axial fans, and plug or plenum fans, and refrigeration equipment that delivers cooled or conditioned air into space. It includes cooling

Space requirement is essential in shaping an HVAC system to be central or local. It requires

**a.** Equipment rooms: since the total mechanical and electrical space requirements range between 4 and 9% of the gross building area. It is preferable to be centrally located in the building to reduce the long duct, pipe, and conduit runs and sizes, to simplify shaft

**b.** HVAC facilities: heating equipment and refrigeration equipment require many facilities to perform their primary tasks of heating and cooling the building. The heating equipment requires boiler units, pumps, heat exchangers, pressure-reducing equipment, control air compressors, and miscellaneous equipment, while the refrigeration equipment requires water chillers or cooling water towers for large buildings, condenser water pumps, heat exchangers, air-conditioning equipment, control air compressors, and miscellaneous equipment. The design of equipment rooms to host both pieces of equipment should consider the size and the weight of equipment, the installation and maintenance of equipment, and the

**c.** Fan rooms contain the HVAC fan equipment and other miscellaneous equipment. The rooms should consider the size of the installation and removal of fan shafts and coils, the replacement, and maintenance. The size of fans depends on the required air flow rate to

coils based on water from water chillers or refrigerants from a refrigeration process.

space requirement, air distribution, and piping, as shown in **Figure 1**.

**Criteria Central system Decentralized system**

attractive benefit when considering its long

alternative source of HVAC or backup

maintenance and saving equipment in excellent condition, which saves

Maintenance cost Accessible to the equipment room for

52 HVAC System

Reliability Central system equipment can be an

service life

maintenance cost

Flexibility Selecting standby equipment to provide an

layouts, and centralized maintenance and operation.

applicable regulations to combustion air and ventilation air criteria.

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

The piping system is used to deliver refrigerant, hot water, cooled water, steam, gas, and condensate to and from HVAC equipment in a direct, quiet and affordable way. Piping systems can be divided into two parts: the piping in the central plant equipment room and the delivery piping. HVAC piping may or may not be insulated based on existing code criteria.
