Air Conditioning Systems (All-water & All-air system)

Air conditioning systems can also be classified based on the type of fluid that is either used in heating or cooling the space.


In this article, I will share their components and how these two air conditioning system works.


You have to understand that when it comes to the classification of air conditioning systems according to the type of fluid they use to either heat or cool a space, all-water and all-air systems are not the only ones in this category.


We also have a direct expansion system, combined system and heat pump systems.


But in this article, I will only discuss the all-water and all-air systems.


Without wasting time, let me share the things that you need to know about these two systems.


Main components of All-air system.

Dampers; are mainly used to regulate the amount of air in the air conditioning system to meet the demands of airflow.


There are different types of dampers used in air conditioning systems e.g automatic dampers, relief dampers and hand dampers.


Cooling coil; the cooling coils are made with extended surface tubing that is mainly used to cool the air entering the air conditioning system.


Heating coil; similar to the cooling coil, it also has extended surface tubing that is mainly used to heat the air entering the air conditioning system.


Supply Fan; the supply fan is used to supply the heated air from the heating coil to the humidifier.


Humidifier; the humidifier is used to control the moisture content in the air without changing the dry bulb temperature.


Ducts; are used to convey the air through the air conditioning system.


Return fan; this fan is used to return air to the damper and exhaust some air into the atmosphere through the exhaust of the air conditioning system.


Air filter; it’s used to clean the air entering the air conditioning system.


Working principle of all-air conditioning system.

It uses air as its main fluid to either heat or cools a space.


The air is sucked into the air conditioning system by the action of the fan. The air is filtered before it enters the cooling coil, then passed to the heating coil where its temperature is raised to increase its energy and also kills pathogens in the air.


Heating the air also increases the quality of the air thus making it safe for the occupants or the space that needs to be conditioned.


The supply fan takes the heated air from the heating coil to the humidifier.


In the humidifier the humidification process takes place, and the moisture content of in the air is increased without changing the dry bulb temperature of the air.


The air is then taken to the space to be conditioned and after being used up the air is extracted from the conditioned space by the return fan and this gives room for another volume of air to occupy the space.


The return fan also aids in the extraction of exhaust air to the atmosphere and pumps the rest of the unused air through the damper back to the cooling coil and the process is repeated.


The property of air is controlled by the following methods; volume control, bypass control, reheat control, dual duct system and multizone system.


The all-air conditioning systems are mainly used in schools, hotels, offices, apartments e.t.c


The main advantages of an all-air conditioning system are that their initial cost and running costs are low.


All-water conditioning system.

It uses water to either cool or heat a space.


The cooling or heating function is performed by the chilled water circulated from a central plant to the air terminal unit where the space to be conditioned is, and that is where the heat exchange takes place.


This type of conditioning system is used in areas where large cooling capacities are needed such as the hypermarket, industrial processes and large offices and factories.


This system uses water as its secondary refrigerant. The water is used to distribute the heat within the conditioning system.


A chiller is used to remove heat from the water and circulate it through other components to absorb heat from the space.


Water makes a good secondary refrigerant for this conditioning system because it’s easily available, cheap, non-toxic, and non-corrosive and it has a specific heat value.


The main components of an all-water conditioning system.

Terminal unit/air handling unit; this is the part that is involved in heating or cooling the space.


The terminal unit is usually placed in the space that it’s needed to cool or heat.


Piping/ducts; are used to convey the chilled water through the conditioning system.


Electric chiller; it’s used for heat exchange in the conditioning system (takes heat from the water and takes it to the air handling unit).


Compressor; it’s used to compress the water as it moves around the condenser and evaporator (within the chiller).


Evaporator; heat exchange takes place in this place.


Condenser; It’s used to cool the water in the conditioning system.


The cooling tower; allows the escape of hot air out of the conditioning system.


Working principle of all-water conditioning system.

When the air enters the air handling unit, it comes in contact with the chilled water supply.


The warm air entering the terminal unit from the outdoors partially heats up the water.


The chilled water supply is then supplied to the electric chiller which contains the evaporator, compressor and valve.


The water is heated at the electric chiller evaporator and then supplied to the cooling tower.


The hot water enters the cooling tower and is sprayed through the nozzles in the tower.


The cooling tower has a fan that cools the hot water entering the tower.


The hot air goes out of the tower through the top part of the tower.


The water that is slightly cooled drops to the bottom of the tower. The tower has air openings that allow air to enter thus slightly cooling the water at the bottom of the tower.


The water that is slightly cooled at the bottom of the tower is pumped by the condenser water pump to the electric chiller where it’s further cooled down by the chiller condenser to chilled water.


The chilled water passes through the valve and enters the evaporator (still in the electric chiller) and then it’s pumped by the chilled water pump to the air handling unit.


The air handling unit cools the space with the aid of the fan that is located in the air supply, these fans contain coil units which consist of fins and fans with a large surface area that absorbed heat from the space through the air heat exchange process.


The chilled water is usually piped into these fan coil units to aid the heat exchange and cool the space.


And once the temperature of the chilled water has changed (heated up) it’s then recirculated back to the chilled water supply tank.


The air handling unit has a return fan that extracts the hot air from the space to be conditioned back to the chilled water supply.


This is to ensure that there is a higher cooling efficiency.


The hot air coming from outdoors and the extracted hot air from the space both are used to heat up the chilled water supply then it flows to the chiller where the heat exchange takes place.


And the process is repeated.


The advantages of using an all-water conditioning system are that, it can be used in a very large space, it offers efficient cooling, less space is required for its installation, and you can turn off cooling to any unoccupied areas without messing up the other parts to be conditioned and minimal space for terminal unit is needed.


Disadvantages of using an all-water conditioning system; it needs regular maintenance, the ventilation is from the wall aperture and it’s not easily controlled due to wind and stack effect, the coils in the fan can freeze thus hindering cooling capabilities and the humidity may be very high in the summer.

Related articles to check.

  1. Factors To Consider When Choosing Air Conditioning System
  2. Central Air Conditioning System: Components And Working Principle
  3. Factors Affecting Human Comfort In Air Conditioning System
  4. Refrigeration Evaporators: Functions, Types, Design Characteristics And Maintenance.
  5. Two Stage Refrigeration Cycle Using A Flash Chamber: Working Principle

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