How Does an Air Conditioner Work?

An air conditioner’s fundamental function is to cool or heat a space to increase its comfort for the occupants. Air conditioners also help to reduce humidity levels and generally help homeowners maintain healthier indoor air quality, providing increased comfort in indoor environments. But how does air conditioning work? 



What is an air conditioner?  

They come in a variety of shapes and sizes and are used in all manner of applications around the world but each air conditioner derives from a common premise. They make a space cooler by transferring heat from the inside of a building to the outside, in this case, the building is your home and the types of units are referred to as Residential Air Conditioners.  

In Residential Air Conditioning there are several types, including the instantly recognisable Split system, which is generally characterized by a wall-mounted unit that is connected to an outdoor unit and found in homes in every country. Within this lineup of units, there are other types of air conditioners and an option for everyone home, like multi-split, ducted systems, cassettes type, window type and floor mounted consoles. You can learn more about it here in our Air Conditioner Buying Guide.

For the purpose of this article, we focus on the iconic wall-mounted Split system type of air conditioning and its cooling cycle. 



How does air conditioning work? 


The key to understanding how an air conditioner works is to remember that a unit does not make cool air but that it removes the heat from your home. Air conditioners also remove excessive humidity, further increasing the comfort and health of an indoor environment.   


A standard Split system is essentially in two halves, an indoor unit and an outdoor unit. Between these two units, 5 main components work in harmony together to create the cooling cycle that helps maintain optimal indoor comfort.  

  • Evaporator Coil: This is located in the indoor unit of the Split system and is made of copper piping which is inside a series of aluminium fins, both materials of which are ideal for transferring heat. An evaporator coil is what delivers cool air indoors and it also removes the heat from the air in your home. It works in tandem with the indoor unit's internal blower fan and the refrigerant inside the coil.
  • Compressor: Housed within the outdoor unit, the compressor circulates the refrigerant between the indoor and outdoor unit, transferring heat as it does. This component is often referred to as the heart of the system because it compresses the refrigerant and pumps it to a coil in the form of hot gas. There a couple of different types of compressors that are used in air conditioning units, but in Residential Air Conditioning, it is rotary compressor type. 
  • Condenser: Also located in the outdoor unit, and it works with its own fan that blows the air across the condenser coil to transfer the heat. Sharing a similar structure to the Evaporator Coil, this component is available in different sizes and formats, for example, a double-fan version is used for high-capacity units and offers increased efficiency. In most Residential Air Conditioning applications, a single-fan Condenser is preferred because this means a smaller outdoor unit.  
  • Expansion Valve: Another vital component is the expansion valve, which performs the crucial task of controlling the amount of refrigerant flowing into the evaporator coil, improving user control over the unit’s performance. This component is essential because by controlling the amount of refrigerant flowing back into the evaporator coil, and letting small amounts through, it causes it to expand, causing the pressure to drop and the temperature with it. 
  • Refrigerant: The cooling cycle would be impossible without refrigerant. If the compressor is the heart of the system, then the refrigerant is the blood. Refrigerant is used because of its ability to shift from a liquid (cool state) to a gas (heated state), and helps carry the heat from the indoor unit to the outdoor unit, and then, on its way back, cooling into your home.  


How does an AC cool my home?


What is the cooling cycle? 

Now that you are familiar with the key components, how do they work together to produce the cooling cycle? We explain in these 4 key steps:  


1) Starting with the evaporator coil in the indoor unit, the cool liquid refrigerant that is within the evaporator coil (also called a heat exchanger) absorbs the heat from the air inside your home. The heat enters the indoor unit via vents and the internal blower fan moves the indoor air over the coil. As this happens the heat from the air is transferred to the refrigerant, also known as heat exchanging.  

With the heat removed, the air is blown back out into the room at the desired temperature to create a comfortable environment. 

The air conditioning process in 4 steps

2) The compressor is the refrigerant’s next stop. When absorbing the heat, the liquid refrigerant inside the evaporator coil takes on a gaseous state. This gas then flows through to the outdoor unit and into the compressor, where the gas is pressurised, raising the temperature even further. This is to increase the amount of heat that the refrigerant gas will expel.  


3) The superheated gas enters the condenser where heat exchanging occurs once more, only this time the heat is transferred to the outside air. As this happens the refrigerant returns to its cool liquid state once more and the compressor sends it back into the indoor unit.  

The air conditioning process has 4 fundamental steps 


4) The refrigerant flows to the expansion valve before it passes back into the evaporator coil. The expansion valve calculates the amount of refrigerant required to provide the precise temperature requirements and sends it back to the indoor unit. By regulating the amount of refrigerant entering the evaporator coil, precision cooling can be achieved. Then as the refrigerant passes through the evaporator coil, it absorbs heat from the indoor air, ready to start the cooling cycle again.  



Improving the cooling cycle with Hitachi technology 


Hitachi Cooling & Heating have developed a series of innovative components that are designed to support the cooling cycle performance of our air conditioners. For example:  


Vector DC Inverter Technology 

This technology makes our units smart, allowing them to adjust the controls and send real-time feedback to the operating system while running. With Vector DC Inverter technology, once the indoor temperature is achieved, the compressor will run at a minimum speed to avoid stopping the compressor which in turn avoids the need for a power surge when restarting. This can provide constant cooling or heating, operating at a minimal capacity to maintain the room temperature at a comfortable level, meanwhile minimising power consumption


Innovative Programming System

An essential part of any air conditioner, the Hitachi Cooling & Heating internal programming systems facilitate the communication between hardware and software to improve and maintain the efficiency of an air conditioner’s performance.  

For example, a special microchip that is pre-loaded with the compressor’s data will constantly monitor the compressor’s operation while it is running. This helps the unit to adjust the amount of energy needed by sending accurate instructions to the compressor to achieve the optimal rotation speed and avoid unnecessary power waste. 



Not only do we have sensors that monitor human activity in indoor spaces but we also have sensors that protect our units’ condition. Throughout our range of air conditioners, sensors are integrated into indoor and outdoor units to ensure optimal unit function, for example, sensors are used to monitor the refrigerant inside your unit to help protect the compressor from overheating.  


Air conditioning innovations for local markets

Innovative components for local products 

With climates varying wildly from region to region, Hitachi Cooling & Heating has to adapt and adopt the different user behaviours that come with these climates. Localized teams listen to feedback from our users, looking at the gaps to create a product that suits their needs depending on where they are.  


In some places, air conditioners are used for longer periods of time throughout the day than others, while some regions only have cooling type units due to climate and ambient temperature needs. Or in Europe, where heating is more demanded than cooling and so a different range of products is offered – heat pumps.  


An air conditioner built for use in the UK won’t have the same components as one built for use in India. In North America, they require units that can work in very cold ambient temperatures whereas in the Middle East air conditioners need to be able to offer optimal cooling in extremely hot ambient temperatures.  


To achieve this variety within our product range, our regional teams work closely within their local communities to understand their needs. So, whilst Hitachi Cooling & Heating is a global company we are working with the local markets.  


No matter when you live, there is the perfect Hitachi Cooling & Heating solution for your house and your requirements. If you’re interested to learn more about our Residential Air Conditioning range, click here to see which products are available.


You can also contact your local Hitachi specialist if there are any questions you'd like to discuss.


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