*2.2.2.2 Multi-piping systems*

#### *A. Three-pipe systems*

**Disadvantages of fan coil unit**s

*Low-temperature Technologies*

optional air ventilation duct systems.

*2.2.2 Types of all water systems*

*2.2.2.1 Single piping systems*

the return water.

**Figure 15.**

**14**

coil units, into two types [1–5], namely:

*A. Single piping system (reversed return)*

*B. Single piping system (direct return)*

return water from each fan coil unit.

1.Do not provide good control of room air humidity.

2.Require maintenance within the air-conditioned places.

3.Provide suitable medium for bacteria grow in water pipes.

4.The ventilation of the rooms is affected by the speed of wind and rain and insect leakage through the wall openings and cracks which are associated with

The all water systems are classified based on water pipe connections to the fan

In this system, there are two pipes, one pipe to feed either the cold or hot water to the fan coil unit and another pipe for returning the water back to the chiller or boiler (see **Figure 15**). In these systems the supplied water is in counterflow with

In this system, there are two pipes, one pipe to feed either the cold or hot water to the fan coil unit and another pipe for returning the water back to the chiller or boiler (see **Figure 16**). In these systems the supplied water is flowing in a pipe which is connected directly to the chiller or boiler, where the same pipes receive the

*A schematic diagram of a fan coil unit, two-pipe system of reversed return. Redrawn from [2].*

In these systems, there are two pipes for providing hot and cold water to the fan coil unit and one pipe for return water (three-pipe system). **Figure 17** shows a three-pipe all-water-type system.

#### *B. Four-pipe systems*

In these systems, there are two pipes for providing hot and cold water to the fan coil unit and two pipes for return, one for cold water return and one for hot water return (four-pipe system). These systems are considered as the best system as the use of two return pipes can maintain efficient energy performance. **Figure 18** shows a four-pipe all-water-type system.

### **2.3 Air-water systems**

In these systems both air and water produce heating and cooling effects. Usually induction or fan coil units can be used in air-water systems. The following section will describe the induction unit systems and fan coil system [1–5].

*A schematic diagram of a fan coil unit of four-pipe system. Redrawn with modification from [2].*

generally used in multiroom buildings such as hotels, hospitals, and apartments

Advantages of these systems over induction units are the quite operation and the means to control required condition as fan speed can be usually controlled. But the initial cost of fan coil unit which is higher than induction units makes the induction units more preferred. **Figure 20** shows a schematic diagram of a fan coil unit with

This chapter reviews the types of central air conditioning systems. Specifically, the types and applications of all-air, all-water, and air-water systems are provided. In addition, this chapter gives further insight to all systems through several developed schematic diagrams as various components and working principles of these diagrams and systems can be identified and figured out, respectively. Moreover, the differences

among the given systems can be easily distinguished through this chapter.

where the operating mode can be switched to work in cold season.

*A schematic diagram of a fan coil unit system. Readapted with modification from [5].*

*Central Air Conditioning: Systems and Applications DOI: http://dx.doi.org/10.5772/intechopen.89455*

its components [1–5].

**3. Conclusion**

**17**

**Figure 20.**

#### **Figure 19.**

*A schematic diagram of an induction unit system. Readapted from [5].*

#### *2.3.1 Induction unit system*

Induction unit systems in air-water central air condition are used in building of multi-surrounding rooms such as offices, hotels, hospital patient rooms, as well as apartments. These systems are used where higher thermal loads are present. In addition, these systems are suitable where some rooms require cooling, while the next other rooms require heating. Besides that, these systems are suitable for buildings such as skyscrapers where the spaces are limited. **Figure 19** shows a schematic view of induction unit system which uses primary air and external air. Return air can be used if all primary air is greater than the minimum ventilation requirements [1–5].

#### *2.3.2 Primary air fan coil systems*

The working principle of primary air fan coil systems is very similar to the induction unit system. The main difference is the use of fan. These systems are *Central Air Conditioning: Systems and Applications DOI: http://dx.doi.org/10.5772/intechopen.89455*

generally used in multiroom buildings such as hotels, hospitals, and apartments where the operating mode can be switched to work in cold season.

Advantages of these systems over induction units are the quite operation and the means to control required condition as fan speed can be usually controlled. But the initial cost of fan coil unit which is higher than induction units makes the induction units more preferred. **Figure 20** shows a schematic diagram of a fan coil unit with its components [1–5].
