Air Conditioning System Configurations

The air-conditioning components and equipments may be designed and assembled in hundred different ways but in practice these are broadly classified into three categories:


1- Decentralized Systems (Individual Room Systems): This can be divided to three major types as follows:

• Mini-Split Cooling Units (ductless split Units).
• Window Units.
• Mini- Heat Pump.

2- Semi- centralized systems (packaged systems): This can be divided to two major types as follows: 

• One piece systems (Unitary Packaged Systems): 

1. Packaged Air Conditioners with Water Cooled Condenser.
2. Packaged Air Conditioners with Air Cooled Condensers.

• Two pieces systems (ducted Split system).

3- Centralized systems (Central Hydronic systems): This can be divided to three major types as follows:

• Centralized Ducted “All – Air” Systems.
• Centralized Fluid Based Hydronic Systems.
• Combined (Hybrid) Water and Air Systems.

The following table will show a comparison between these configurations as follows:

1- Decentralized Systems (Individual Room Systems)

These are systems in which heating and cooling is conducted locally, these systems are relatively common in schools, small hotels, domestic applications, residential homes and small offices.

Decentralized Systems are essentially direct expansion (DX) systems, which operate using direct expansion of refrigerant in the finned tubes across the air path.

In smaller buildings, smaller room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.


The major types of decentralized systems are:

• Split Cooling Units.
• Window Units.
• Split Heat Pumps.

A- Split Cooling Units

The split systems are individual systems in which the two heat exchangers are separated (one outside, one inside). The split air conditioner can be installed in rooms and offices where you don’t want to disturb the setup of the room and avoid demolitions in your favorite space.

There are two main parts of the split air conditioner. These are:

1) Outdoor unit:

This unit is installed outside the room or office space which is to be cooled and houses important components of the air conditioner like:

The compressor:
External power has to be supplied to the compressor, which is utilized for compressing the refrigerant and increases its pressure before sending it to the condenser. The size of the compressor varies depending on the desired air conditioning load. In most of the domestic split air conditioners hermetically sealed type of compressor is used. In such compressors the motor used for driving the shaft is located inside the sealed unit and it is not visible externally.

Condenser coil:
It is the coiled copper tubing with one or more rows depending on the size of the air conditioning unit and the compressor. The condenser is also covered with the aluminum fins so that the heat from the refrigerant can be removed at more faster rate.

Condenser Cooling Fan:
The condenser cooling fan is an ordinary fan with three or four blades and is driven by a motor. The cooling fan is located in front of the compressor and the condenser coil. As the blades of the fan rotate it absorbs the surrounding air from the open space and blows it over the compressor and the condenser with the aluminum fins thus cooling them. 

Expansion Valve: 
The expansion valve is usually a copper capillary tubing with several rounds of coils.The high pressure and medium temperature refrigerant leaves the condenser and enters the expansion valve, where its temperature and pressure drops suddenly.



2) Indoor unit:

The most common type of the indoor unit is the wall mounted type though other types like ceiling mounted and floor mounted are also used. the indoor unit produces the cooling effect inside the room or the office and houses

The evaporator coil or the cooling coil:
The cooling coil is a copper coil made of number turns of the copper tubing with one or more rows depending on the capacity of the air conditioning system. The cooling coil is covered with the aluminum fins so that the maximum amount of heat can be transferred from the coil to the air inside the room.

Cooling Fan or Blower:
The blower sucks the hot and unclean air from the room and supplies cool and clean air back. The shaft of the blower rotates inside the bushes and it is connected to a small multiple speed motor, thus the speed of the blower can be changed. When the fan speed is changed with the remote it is the speed of the blower that changes.

The drain pipe:
The drain pipe helps removing dew water collected inside the indoor unit.

Louvers or Fins: 
The cool air supplied by the blower is passed into the room through louvers. The louvers help changing the angle or direction in which the air needs to be supplied into the room as per the requirements.

There are two types of louvers: horizontal and vertical. The horizontal louvers are connected to a small motor and their position can set by the remote control and the vertical louvers are operated manually and one can easily change their position as per the requirements

Air filter:
It removes all the dirt particles from the room air and helps supplying clean air to the room. The air filter in the wall mounted type of the indoor unit is placed just before the cooling coil.

Operation Method:
In the outdoor unit there is a fan that blows air over the condenser thus cooling the compressed Freon gas in it. This gas passes through the expansion coil and gets converted into low pressure, low temperature partial gas and partial liquid Freon fluid, after passing from the expansion coil, the chilled Freon fluid enters the cooling coil. The blower sucks the hot, humid and filtered air from the room and it blows it over the cooling coil. As the air passes over cooling coil its temperature reduces drastically and also loses the excess moisture. The cool and dry air enters the room and maintains comfortable conditions of around 25-27 degree Celsius as per the requirements.

Controls:

The temperature inside the space can be maintained by thermostat setting.

Note: These days, multi-split air conditioners are also being used commonly. In units for one outdoor unit there are two indoor units which can be placed in two different rooms or at two different locations inside a large room.

B- Window Units 

• Window-mounted air conditioners cool the individual conditioned spaces. 
• A window unit is an encased assembly designed primarily for mounting in a window, through a wall, or as a console. 
• A window unit produces cool air on one side and rejects hot air on the other and provides delivery of conditioned air to a room without ducts. 
• A window unit has a low initial cost and is quick and easy to install. 
• A window unit requires outside exposure for heat rejection and cannot be used for interior rooms 

A/C Window Unit Construction 

Window Unit Construction: 

• Condenser (outdoor coil).
• Condenser fan.
• Hermetic compressor.
• Capillary tube.
• Evaporator (indoor conditioning coil).
• Evaporator fan.
• Controls: The controls for window units are simple and inbuilt, with a rotating switch marked with a hot-cold scale with no temperature settings. Most units will heat as well as cool. Fresh air control, if it exists, is normally adjusted by a manual lever. 

C- Mini- Heat Pumps

• A cooling only system cools the indoor air but a heat pump provides cooling in summer season and heating in winter season. 

• DX system operating in reverse vapor compression cycle is classified as Heat pump. Through an addition of a special four-way reversing valve, heat flow in mechanical refrigeration loop can be reversed so that heat is extracted from outside air and rejected into the building. 

• Such a facility is required during winter season to heat the indoor using the same physical components. Due to added heat of compression, the efficiency of heat pump is higher compared to the cooling cycle. 

• A supplementary electric resistance heater may also be used to assist the heat pump at lower outdoor temperatures. In colder climates, heats pumps require defrost period. During defrost times the electric heater is the only means of heating the interior of the building. 

• Split heat pumps are Air-to-Air types and they are the most common type of heat pumps. It is particularly suitable for factory-built unitary heat pumps, and has been widely used for residential and commercial application. Air is used as the heat source and heat sink. Extended surface, forced convection heat transfer coils are normally employed to transfer the heat between the air and the refrigerant. When selecting or designing an air-source heat pump, two factors in particular must be taken into consideration: 

1. The variation in temperature experienced in a given locality. 
2. The formation of frost.

In the next Topic, I will explain other types of air conditioning systems configurations " Semi- centralized systems and centralized systems air condition". so, please keep following.

Note: these topics about HVAC in this course EE-1: Beginner's electrical design course is an introduction only for beginners to know general basic information about electrical HVAC Power loads. but in other levels of our electrical design courses, we will show and explain in detail the HVAC Loads Estimation and HVAC equipment Capacities with examples for different types of buildings.