The Differences Between Air-Cooled Chillers and Water Chillers

A chiller system performs the basic function of removing heat from a location. Whether it is from some kind of process in the industry, such as die-casting, machine tooling, along with many others, or as part of a Heating, Ventilation & Air Conditioning (HVAC) system – that is the singular purpose of a chiller. All chillers do the same thing.  At their very core, they have similar configurations as well.  A chiller system generally consists of:

Evaporator – water or air enters the chiller system.  Through the use of refrigerant, it is transformed into a low-pressure gas.

Compressor – takes low-pressure gas and compresses it to a higher pressure, which in turn allows it to flow through to the next step, the condenser.

Condenser – the high-pressure gas is cooled by refrigerant, whereby it converts back to low-pressure liquid form.

Expansion Valve – the liquid returns to the expansion valve and is directed back to the evaporator, and the cycle is repeated.

The Main Difference – Air-Cooled Vs. Water-Cooled Chiller Systems

It’s important to note that, in fact, both air-cooled and water-cooled chillers make use of a common force: An air stream whose job it is to facilitate the heat transfer away from the intended source.  

The main difference is that air-cooled chillers depend on a humid stream of air – i.e. the ambient air; air-cooled chillers do not require an external water source, normally from a cooling tower. Instead, they exclusively use a stream of ambient air driven by fans located outside of the structure or process to be cooled.  Otherwise, the components and the process cycles are quite similar.

The Requirement of a Cooling Tower in a Water Cooled Chiller System

The requirement of a cooling tower is the main visible difference between water-cooled and air-cooled chiller systems.  Both configurations require some procedure for supplying intake air.  The cooling tower needed for a water-cooled chiller is the main visible difference between the two systems.  While air-cooled systems have their own apparatus for supplying air – large fans – their presence is smaller and therefore is both less visible and space consuming.

Differences in Efficiency:  Air-Cooled Vs. Water-Cooled Chiller Systems

There is considerable debate over whether one chiller system is superior to another in terms of overall efficiency.  The general consensus is that water-cooled systems tend to be more efficient than their air-cooled counterparts, mainly due to the fact that the incoming water from the cooling tower is usually at a low enough temperature that it makes the entire cycle less energy-consuming.  For example, air-cooled chiller units in a hot southern US climate will obviously have to work much harder, as the ambient air temperature will be quite high over the hot daytime hours.

One obvious downside to water-cooled chiller systems is their ongoing requirement for water – this may be considered a knock against their overall efficiency, especially in areas where there is scarcity of water supply.  Water-cooled systems also require specific, ongoing maintenance related to their continuous use of water – including corrosion, scale and mineral deposit accumulation in the system.

Differences in Space Requirements and Noise Issues

Space requirements for chiller systems: The requirement of a cooling tower in a water-cooled chiller system means that in general, they will need more space for a setup location – often on the roof of a building, for example.  In this regard, air-cooled chiller systems possess an advantage, in that with no requirement for a cooling tower, there is usually a smaller space requirement.  This is also why air-cooled chillers are also very frequently chosen for temporary or portable installations.

Noise issues with air-cooled chiller systems: One notable difference between the two systems we are comparing is the generation of noise.  Air-cooled chiller systems require large, powerful fans for the continuous supply of incoming air into the system.  These types of installations generate a considerable amount of continuous sound from the ongoing high-speed movement of their fan blades and motors.  This can become a significant issue in locations, for example, near occupied residential or office settings. Designers and specifiers should be cognizant of the potential for issues such as noise well ahead of time.

Other Considerations Regarding Chiller Units and Their Differences

There are some other considerations that also illustrate the differences between air-cooled and water-cooled chiller systems. These include:

Water availability considerations – the local cost of water or its general scarcity in a particular location or region – for example, in arid climate conditions – may negate the option of a water cooled chiller system.  A lack of water means higher water costs, which makes the choice impractical from an economic standpoint.  This factor is present in many parts of the world and should not be overlooked at the evaluation stage.

Night-time dry bulb (ambient) temperatures – in areas where the night-time bulb temperatures are much lower than daytime, an air cooled chiller can capitalize on the night-time plunge in air temperatures, which can result in lower running costs.  This particularly applies to situations requiring 24-hour running applications, where the most benefit can be derived overnight.

Space considerations – a scarcity of space tends to give air cooled chillers the edge over water cooled chillers – the key difference being that water-chilled units, and their associated cooling tower, makes them bulkier in general.  With no need for a cooling tower or mechanical room, air-cooled chillers may be installed in tight quarters, including on the ground.

Air recirculation requirements – obstruction to continuous airflow will have a severely negative impact on the performance of air-cooled chiller units.  This becomes especially important when considering the location of the installation – high walls and other buildings or structures close by could all be an impediment to the airflow required for an air cooled chiller system to work properly.

Is One System the Superior Choice in Selecting a Chiller Unit?

We’ve shown that while there are some significant differences between air-cooled and water-cooled chiller systems, they share the same common goal – the removal of heat from whatever the intended source is.  The need for such systems spans all kinds of processes, from high-heat industrial settings to HVAC systems, both commercial and residential.

Every situation is different; designers, facility managers and owners, and engineers must conduct a thorough assessment, preferably with the chiller system manufacturer, to determine which system represents the best fit.  We’ve outlined some of the differences, along with the advantages and disadvantages of each.

We would be pleased to discuss your specific situation and requirements for heat removal via a chiller system. Contact our team today.