**2.2 All-water systems**

In all-water systems, water is used as a working fluid for providing heating and cooling. Water is pumped to the fan coil unit located in the zone which is to be conditioned. And then the fan coil unit will use the zone air or sometimes outdoor air for cooling or heating purposes. If outdoor air is used with the fan coil units, then separate air duct system will be introduced to the structure of the building [1–5].

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

**Figure 13.** *Pictures of some common variable air volume terminal units. Readapted from [2].*

*2.2.1 Fan coil unit*

7.Higher filter efficiencies can be attained.

placed away from zones.

**Figure 12.**

*Low-temperature Technologies*

system will be enlarged.

*2.1.2.6 Variable air volume (VAV) systems*

terminal units of variable air volume [1–5].

**2.2 All-water systems**

**12**

requirements of the building.

Disadvantages of the dual-duct systems

currently these systems are not recommended.

8.Low-cost operation can be obtained with these systems.

*A schematic diagram of dual-duct system. Redrawn with modification from [1].*

9.These systems are operating quietly as the refrigeration machines and fan are

10.These systems have flexible air duct system designs. The choice of medium and high air speeds is possible on an economic basis and according to the

1.The use of separate ducts increases the initial cost compared to other systems.

2.Precise control needs a large handling unit, and as a result the total cost of the

Variable air volume systems can vary the thermal loads according to zone thermal load variations. One advantage of these systems is that both the initial cost and the operating cost are low because the air volume requires simple control within 20% of the air outlets. These systems are used with fixed thermal loads throughout the year. Applications of these systems can be found in commercial stores, office buildings, hotels, hospitals, housing, and schools. **Figure 13** shows various common

In all-water systems, water is used as a working fluid for providing heating and cooling. Water is pumped to the fan coil unit located in the zone which is to be conditioned. And then the fan coil unit will use the zone air or sometimes outdoor air for cooling or heating purposes. If outdoor air is used with the fan coil units, then separate air duct system will be introduced to the structure of the building [1–5].

3.The dual-duct systems are considered inefficient energy systems, and

Fan coil units are used in all-water central air conditioning. Cold and/or hot water from central chillers and boilers flows through the unit coils. The air temperature is controlled by controlling the flow rate of water through the coil via control valves, e.g., solenoid valves. Fan coil units are cheap in price and widely used in hotels, office buildings, and medical centers. **Figure 14** shows a schematic diagram of a fan coil unit [1–5].
