If you’re wondering “what is an air cooled chiller”, look no further. Finding the right chiller presents a key decision for many companies who need this piece of equipment.
From manufacturing processes to district cooling efforts, deciding on the right chiller for each project can have a significant impact on energy efficiency and performance. In fact, choosing a chiller that matches the application’s cooling load is a crucial step for an efficient and reliable cooling performance. Let’s then look at questions such as what is an air cooled chiller and how an air cooled chiller works.
What is an air cooled chiller
An air-cooled chiller is a type of cooling system that is able to remove heat from a space by using ambient air as the heat rejection medium.
In order to do so, air is used to cool water or other fluids, which are then circulated through a system to absorb heat and lower the temperature of the desired area or equipment.
In other words, the chiller is not in charge of generating cold: it dissipates heat, facilitating its transference outside of the allocated space.
There are various applications of air-cooled chillers: they’re used on industrial processes, data center cooling, HVAC and district cooling.
How air cooled chiller works: a comparison between the three types of chillers
1. Air-cooled scroll and air-cooled screw chillers
An air-cooled scroll chiller is a specific type of air-cooled chiller that utilizes scroll compressors as the primary cooling technology. On the other hand, air-cooled screw chillers employ screw compressors as the primary cooling technology.
Both use ambient air as the heat rejection medium to remove heat from a space. They follow a refrigeration cycle that starts with a compressor acting on the refrigerant gas and increasing its temperature. This marks a difference with absorption chillers.
Then comes a condenser, which is in charge of liquefaction. Passing through an expansion valve, pressure and temperature of the refrigerant are reduced, so that it evaporates. It’s now time for the heat absorption in an evaporator. After performing this task, it’s ready to repeat the cycle.
What these two air-cooled chillers have in common is their suitability for smaller process applications, with a simple installation and low water consumption. However, they present a limited cooling capacity and efficiency, so they’re only adequate for small residential projects or medium-sized towers.
2. Water-cooled chillers
A water-cooled chiller represents an alternative to air-cooled chillers. They employ specific cooling towers and can present high efficiencies as liquids offer better heat transfer capabilities.
The working principle of water-cooled chillers follows a logic in which evaporator, to compressor, condenser and expansion valves are employed. Again, through the interchange of the material’s temperatures and pressures, water can act as a cooling agent.
These solutions are suitable for higher cooling loads, such as district heating projects. In fact, they are employed in large and medium-sized structures and buildings. However, its high use of water resources must be considered, both for environmental as well as economic reasons. However, as we’ve mentioned above, their use involves using a large amount of water.
Water-cooled chillers offer several additional advantages over air-cooled solutions. This includes taking up less space and a reduction in maintenance and repair costs.
h3. 3. Magnetic-bearing chiller turbocompressors
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The comparison between air-cooled and water-cooled compressors should take into account this innovative approach. This type of chiller compressors represent a recent solution for high efficiencies compared to screw and scroll chillers.
As such, they’re increasingly incorporated into high-cooling load solutions, such as district cooling initiatives. In fact, the U.S. Department of Navy quantifies there are now 35,000 of these, logging over 55 million run-hours just in the U.S. These include their application in many diverse sectors, from the plastics industries to pharmaceutical and exceedingly efficient cooling initiatives. The key for their outstanding efficiencies lies on several distinctive factors.
On the one hand, it removes oil from the equation. The magnetic bearings allow the compressor to operate without oil for lubrication. This has an enormous impact on facilitating and reducing maintenance costs, but its impact goes beyond that. The lack of oil reduces energy losses and maximizes heat transfer efficiency, as oil doesn’t enter evaporators or condensers.
Additionally, this approach to zero-oil in cooling equipment improves the U-Value inside heat exchangers, as verified by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
All heat transfer rates and bubble size values experiment optimizations in this type of equipment, which then has an impact on costs and maintenance needs. The result is a 49% average power savings achieved, as identified by the U.S. Navy Techval and a 6.4 years average return on investment.
The benefits of this innovative approach to air-cooled chillers continue. They’re able to operate much more efficiently at partial loads as well as quietly. Their light weight allows for a faster installation
All in all, a magnetic-bearing chiller compressor can be a good option both for new and retrofit projects, as well as chillers that run at partial load a majority of the time. They deliver a better energy performance and great savings in energy costs, thus becoming a preferred option for a number of projects.
All things considered, cooling engineers and designers should take into account the options outlined above when making a choice. At ARANER, we work to provide projects with their most suitable cooling solutions. As such, we offer cutting-edge centrifugal and magnetic-bearing compressors to fit our state-of-the-art district cooling solutions.
Get in touch with us and find out more about how we can help you.
In this article we will be looking at how air cooled chillers work. Air cooled chillers are very common, especially in small to medium size commercial and office type buildings. They are usually located externally, either up on the roof or at ground level. This is because Air Cooled Chillers do not use cooling towers, instead they dump their heat into the ambient air and therefore need access to a lot of fresh air, in order to reject the unwanted heat from the building. Scroll to the bottom to watch the tutorial video on this subject.
How Air Cooled Chillers work – animation
The chillers will produce “chilled water” which is pumped out around the building to the Air Handling Units (AHU’s) and Fan Coil Units (FCU’s) Which remove the unwanted heat from the building and transfer it into the chilled water loop. The chilled water will enter the AHU’s/FCU’s at around 6°C (42.8°F) and by the time it leaves the heat exchanger within the AHU/FCU it will have risen to around 12°C (53.6°F) and will then make its way back to the Air Cooled Chiller to dump this heat into the atmosphere before repeating the cycle.
The warm return “chilled water” only enters the evaporator where it passes along the outside surface area of the inner tubes, which contain the refrigerant, it then exits at the opposite end having given up its thermal energy. The refrigerant is the only fluid which moves around each of the components of the chiller. It changes its pressure, temperature, enthalpy and entroy as it moves around the machine and transports the unwanted heat away from the evaporator chilled water.
The Air Cooled Chiller has 5 main components.
- The compressor – typically screw, scroll or reciprocating
- The condenser – a bundle of horizontal pipes which contain the hot refrigerant, these are surrounded by a number of thin sheets of metal in the vertical axis. These help distribute heat away from the tubes and into the air which is blown across the tubes and thin sheets of metal.
- Condenser fans – These suck air across the condenser coils, entering from the sides, and then force this air out the top of the unit upwards into the ambient atmosphere.
- Expansion Valve – This expands the refrigerant before it enters the evaporator
- Evaporator – This is where the chilled water is produced and the heat from the warm return “chilled water” is extracted, to be sent to the condenser.
Main components of an Air Cooled Chiller
How the refrigerant moves around the chiller
How refrigerant changes around an air cooled chiller
The compressor is the driving force of the refrigerant. The refrigerant first leaves the compressor as a high pressure, high temperature, superheated vapour and then enters the condenser.
When the refrigerant enters into the condenser, it will run along the horizontal pipes and transfer its thermal energy into the ambient air stream which is forced by the fans on top.
As the refrigerant transfers its thermal energy, it begins to condense into a liquid. By the time the refrigerant leaves the condenser, it will be a high pressure, medium temperature, saturated liquid.
Next the refrigerant enters the expansion valve. The expansion valve meters the flow of refrigerant around the system. The most basic type is the thermal expansion valve which controls the flow of refrigerant by measuring the pipe temperature at the evaporator outlet and will adjust the flow rate to keep the temperature within a desired setpoint.
The expansion valve holds back the refrigerant and maintains the high pressure of the condenser. Inside the expansion valve, a small orifice allows a restricted amount of refrigerant to continue to flow. As it flows through this restriction it reaches the low pressure side of the valve. This sudden pressure drop allows the refrigerant to expand from a liquid into a liquid/vapour mixture. As this occurs it will drop in pressure and temperature. The same amount of refrigerant flows through, it just has more space so it expands to fill this gap.
The refrigerant then enters the evaporator and will pass through a series of horizontal tubes which are surrounded by the “chilled water” and these will flow in the opposing, counter flow to each other. By the time the refrigerant leaves the evaporator, it will have picked up the unwanted heat from the return chilled water and will leave as a low pressure, low temperature saturated vapour. The chilled water will have given its thermal energy up to the refrigerant and will leave around 6°C (42.8°F).
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