*2.1.1 Air handling unit (AHU)*

Air handling unit can be considered as the heart of all-air systems since cooling and heating take place in the air handling unit. It also mixes the outside air after being purified with the return air, then the necessary psychometric processes are carried out. Air conditioner is then expelled or withdrawn to the place to be airconditioned. These units are used for capacities exceeding 100,000 CFM (50 m<sup>3</sup> /s) air. The main components of the air handling unit are shown in **Figure 1** [1–6].

The main components of the air handling unit shown in **Figure 1** are described below:


any system depends on its advantages and disadvantages [1–5]. The following sections will provide descriptions of all types of central air conditioning systems.

In these systems air alone is used as working fluid to produce cooling or heating in air-conditioned zones; besides that air is responsible for controlling the zones' humidity level and provide the required ventilations to air-conditioned zones. In addition, in all-air systems, air is used for aromatizing purposes. Therefore, only air as working fluid is responsible for providing comfort, i.e., cooling, heating, controlling of humidity and ventilation odor, and thus these systems are called all-air

Air handling unit can be considered as the heart of all-air systems since cooling and heating take place in the air handling unit. It also mixes the outside air after being purified with the return air, then the necessary psychometric processes are carried out. Air conditioner is then expelled or withdrawn to the place to be airconditioned. These units are used for capacities exceeding 100,000 CFM (50 m<sup>3</sup>

air. The main components of the air handling unit are shown in **Figure 1** [1–6]. The main components of the air handling unit shown in **Figure 1** are described

• **Supply fan**. Centrifugal fan type is used to provide the conditioned air to

• **Fan motor**. Electric motor is used to provide the rotating motion to the supply

• **Cooling coil**. Coil placed in AHU where cold water from chiller is circulating in medium- and large-capacity AHU or expanded refrigerant in small-capacity

/s)

**2. Classifications of central air conditioning systems**

**2.1 All-air systems**

*Low-temperature Technologies*

systems [1–5].

below:

fan.

AHU.

**Figure 1.**

**2**

*A schematic diagram of an air handling unit with its main components.*

*2.1.1 Air handling unit (AHU)*

various zones.


### *Low-temperature Technologies*

It is may be of interest to note that the configuration of air handling unit can differ slightly in design and components according mainly to the type of application and AHU capacity (e.g., healthcare buildings or other), but also initial and running costs can affect the selection of various AHU components. In addition, air handinbased on various classificationsg units can be classified based on the structure and based on the location where it is placed [2]. The following sections will demonstrate all types of air handling units based on various classifications.
