The evolution of the modern chiller

By Ilana Koegelenberg

Although chillers have been around since the 1930s, the technology has come a long way since then, making these HVAC&R ‘stalwarts’ more efficient than ever — what is new?

When it comes to commercial and industrial HVAC&R systems in particular, the chiller has always been a plant room favourite. But this is not exclusively for big projects anymore … “Large developments and buildings have been using chiller systems for many years, and with the benefits that chilled water presents, it is becoming increasingly popular in smaller developments and even residential applications these days,” explains George Thomaides, Gauteng regional manager for Aersa.

Chillers001Carrier’s AquaEdge centrifugal chiller with inverter technology runs on
low GWP R1233zd(E) refrigerant

Image credit: Carrier

However, traditional chillers are facing fierce competition from new technologies, such as variable refrigerant flow (VRF) systems, which are frequently considered to be easier to install and maintain. Manufacturers are pushing back, though, noting that chillers offer exceptional energy efficiency as well as greater design flexibility, better comfort, and lower total life cycle costs — all of which can make them a better choice for high-performance buildings.


Since HVAC systems account for a significant portion of a building’s energy use, chillers can be critical components in improving a building’s overall efficiency. In fact, ASHRAE Standard 90.1-2013 shows water-cooled centrifugal chillers with capacities of 400 tons or more to be more efficient than other mechanical cooling technology, including air-cooled chillers, rooftop units, and self-contained systems.

Since HVAC systems account for a significant portion of a building’s energy use, chillers can be critical components in improving a building’s overall efficiency.

Chillers also have a low total cost of ownership, offering cost savings to the owners of high-performance buildings over the lifetime of the systems. Well-designed chillers work with HVAC systems to deliver the right temperatures, humidity levels, and ventilation for the space, while also prioritising low operating cost and energy efficiency as well as ensuring low sound levels and minimal environmental impact.

Chillers004Following on from VRF technology, Hitachi has developed a modular screw chiller that
will fit into tight or awkward spaces.

Image credit: Hitachi

Another plus is that chillers contribute to the sustainability of high-performance buildings because they operate at lower head pressures, which uses much less energy and reduces greenhouse gas emissions.


Technology is advancing at a rapid pace and the HVAC&R industry is no different. So, how has the chiller changed over the years?

Although the basic components of refrigeration systems and fluid chillers have remained unchanged for decades, improvements in compressor technology, refrigerant gases, manufacturing methods, and electronic controls have developed chillers into high-tech equipment with increasing functions and applications in not only comfort applications, but also in the industrial sector, says Thomaides.

Electronics, building management systems (BMS) communication, and data analytics have become powerful and are used to control chiller systems more efficiently than previously possible. These days, a single chiller control module can have up to 52 inputs/outputs and links via Modbus, BACnet, and other BMS communication protocols.

Chillers002Chillers come in many sizes and are often the preferred choice for large industrial applications.
Image credit: Pictech

Basic chiller controls now include proportional integral derivative (PID) algorithms that read information during the operation of the chiller, monitor system parameters, and then control various functions, such as fans, compressor loading, and expansion valves, to achieve the required set point, and do so without overshoot or cycling on and off, thus saving energy, explains Thomaides.

Smart functions allow low noise operation during night-time periods, as well as floating set points, which can be controlled via ambient temperature probe readings. It even allows free-cooling during low ambient conditions and various methods of heat recovery with multiple set points for either domestic hot water generation or heating water for comfort applications.

One of the biggest areas of development in chillers has occurred in terms of controls. Chillers have become far more suited towards part load conditions, explains Neil Cameron, Johnson Controls area general manager: building efficiency – Africa. “Previously, building managers and owners would assess a chiller on its efficiency. Today, they look at its part load efficiency, as chillers seldom operate at 100%,” he says. In reality, most applications for chillers demand them spending less than 1% of the time operating at full load. “As such, we have seen the emergence of variable speed drives (VSDs), as well as variable speed compressors and fans that have played a big role in the major design change,” explains Cameron.

Chillers003Chillers have come a long way since the technology was first invented and the modern chiller boasts great improvements in terms of energy efficiency.
Image credit: Aersa

In fact, VSDs are on everyone’s list of notable new technology in terms of chillers. “The advantages of the variable speed drive technology applied particularly to four-pipe smart heat pumps, and displays top-level efficiencies especially at partial loads, which are the most common conditions throughout the entire year in a traditional comfort application,” explains Frans Jooste of Intramech, distributor of Climaveneta chillers. A multipurpose unit is actually sized to cover the maximum peak demand which, depending on the country where it is installed, may be in summer or in winter. However, in traditional comfort applications, the HVAC plant usually works at full load for a few hours every year; this implies that for most of the time, the unit works at partial load. The presence of variable speed drive technology allows units to effectively follow each combination of thermal loads required by the system, achieving total efficiency ratio (TER) values (calculated considering the unit’s performance in hot and cold water production) of up to 19% higher compared to traditional fixed-speed units, says Jooste.

Cameron explains that another big development is the move to design the chiller and controls around the entire building. Previously, the chiller would be set to create water at a certain temperature. However, buildings or facilities do not require water to be chilled all day and night. This uses a substantial amount of energy and as such, we have seen the integration of chillers with BMS to dynamically offset the performance based on the conditions of the building. “In the past, the chiller would be self-sustained, but now we are seeing the intelligence reside outside the chiller in BMS,” explains Cameron.

“Another major change we have seen in controls is the ability to connect the chiller to the ‘cloud’,” says Cameron. Information is sent from the chiller to the cloud where it is analysed, which enables reporting to be generated on how the chiller is performing or if there are potential issues or problems. It can even alert the building owner to a problem before the tenant reports it and highlight imminent failures before the chiller actually fails. “We are also seeing machine learning incorporated into the analysis, which can provide the user with suggested ‘fixes’,” explains Cameron. “This makes maintenance and uptime easier and delivers more predictability.” Johnson Controls has approximately 6 000 ‘connected’ chillers that make use of the cloud.

Controllers have become more user-friendly, interactive, and multifunctional, adds Alistair Sansom, director of Service First, authorised distributor of Trane. The interface is now also available in multiple languages.

Many chillers now come equipped with a 10.4-inch, high-resolution, full-colour touch screen, and are able to deliver comprehensive information in a very efficient and secure manner for the smooth running of daily activities and periodic maintenance, explains Jaco Smal, AHI Carrier’s commercial sales director. This is possible due to the intuitive menu, animated component level interface with timely running data, graphic trending, auto pushed alarm mail, and smart password.

Trane has made significant developments in chiller controls, according to Sansom. For example, the next generation microprocessor control system provides improved control capabilities with Adaptive Control technology to keep the unit operating even in adverse conditions. Advanced microelectronics protect both the compressor and the motor from typical electrical fault conditions like thermal overload and phase rotation.

But it is not just about the controls. There has been quite a lot of change in making chillers dynamic as well, Cameron explains. For example, York has a range of mini chillers that is modular and can be assembled in selective ways that the building owner/manager can increase or reduce the actual size of the chiller plant with relative ease. This is really useful for customers who require flexibility with their chillers. They can move the modules to different parts of the building, or even to a different site, and can ‘scale’ as and when required in a speedy manner.

Chillers006The Climaveneta Integra i-FX-Q2: a new air source smart heat pump chiller, complete with variable speed drive technology.
Image credit: Climaveneta

Another fairly new development that pertains to niche environments such as data centres, is fast start-up, explains Cameron. A chiller with bearings that make use of oil will need to have an oil circuit, which requires time to start pumping the oil. The pressure needs to be monitored until it has been stabilised, and only then can the load be applied. With VSD fast start-up technology, the load can be applied immediately, which is critical in a data centre environment where heat can impact the performance and longevity of the data centre equipment and even result in failure.

“We are also seeing a lot of research and development around gas and in all likelihood, new gases will be launched in approximately a year’s time,” says Cameron. “Some suppliers will succeed and others won’t — everyone is waiting with bated breath.”

Sansom agrees that refrigerant gases are one of the key exciting developments in the evolution of the modern chillers. The use of energy efficient and environmentally responsible refrigerants, and incorporating next generation low global warming potential (GWP), is changing the game.

Another significant technological advancement has been the move towards electronic commutation (EC) motor technology, says Sansom. “Motors require approximately four times less energy (watt) than conventional alternating current (AC) motors.”


Heat pump chillers are also becoming more prevalent and some units, like the latest in Climaveneta’s Integra range, boasts incredible efficiencies thanks to a four-pipe full inverter design. This air source smart heat pump further raises the efficiency bar, making the production of hot and cold water absolutely cost-effective. It is able to perfectly and continuously match the real demands of the plant by dynamic adaptation of the rotational speed of compressors and fans, ensuring the maximum exploitation of the absorbed power, in any condition, and therefore minimum energy wastage.

These heat pumps can contain two VSD screw compressors placed in two completely independent circuits. “A special configuration that ensures not only simplified maintenance of the compressors but also greater redundancy of the cooling circuit,” explains Jooste. The inverter technology results in no in-rush currents. This means that there isn’t any electrical and mechanical stress as the units never exceed the nominal current, and do not need additional devices such as soft-starters or star/delta commuters.

The ability of these heat pumps to continuously modulate the rotational speeds of the compressors and fans according to the needs of the system, results in reduced noise emissions when working at partial loads: the higher the partialisation, the lower the sound levels. Just another way that equipment has improved over the years with new technology and advancements.


The Trane series E EcoWise duplex CenTraVac chiller.
Image credit: Trane


So, how have chillers become more energy efficient? A lot of what we have already mentioned speaks to this aspect, but let us look at specifics.

According to Thomaides, some of the improvements that contribute to energy efficiency are the following:

  • Implementation of variable speed fans and compressors: This allows optimal operation during low load and low ambient conditions, reducing on/off cycling of the system, and allowing operation at the minimum required condensing pressure — being the most efficient point of operation for the chillers.
  • Aluminium micro-channel condenser coils: These types of coils not only improve heat rejection and decrease operating costs, but are cheaper to manufacture, corrosion resistant, and require lower refrigerant charges in the chillers than standard copper/aluminium coils.
  • Heat recovery: Heat recovered from chillers optimises the operation of the chiller, while providing free energy to be utilised in other areas of the building.
  • Free-cooling: During low ambient conditions, the fluid in the closed loop can be circulated through additional coils fitted on the chillers to reject heat naturally, without the need for the refrigerant system to be operating.

“Furthermore, we have seen significant technology developments in tubes with ridges that ensure a greater surface area, making them highly efficient,” says Cameron.

Refrigerant gases also influence energy efficiency, explains Sansom. “As the industry evolves through its next refrigerant transition, from HCFCs and HFCs to HFOs, refrigerants play a significant role in chiller efficiency,” he says. The selection of new, near-zero GWP refrigerant enables manufacturers/suppliers to optimise chillers to best-in-class efficiency levels. “Trane boasted the first chiller to employ an HFO refrigerant, which is now a trend we are seeing across the sector,” says Sansom.

Innovation in chiller compressor design to deliver highest efficiency in all operating conditions, under full load or part load, is also making a big difference, explains Sansom. “Integration of direct-drive, specific-speed screw compressors, permanent-magnet motors and things like adaptive frequency drives, have significantly improved chiller efficiency.” Likewise, compressor and heat exchanger technologies continue to evolve and improve efficiency significantly.

We do not believe that chiller systems will be phased out, and the global market also shows a trend towards quite the opposite.

With some units like the new Carrier AquaEdge centrifugal chiller, the compressor’s low-speed, direct-drive, back-to-back design significantly improves efficiency while balancing internal forces, enabling the use of energy-saving ceramic bearings that use the refrigerant — already in the chiller — as the lubricant. This refrigerant lubrication solves potential oil-related failures and cuts down maintenance expenses, explains Smal. “Cutting edge manufacturing technologies ensure that these ceramic bearings are the ideal solution for this kind of lubrication,” says Smal. The bearing uses high-nitrogen steel with excellent toughness, a ceramic rolling element with a very smooth surface, and a glass fibre-reinforced Polyetheretherketone (PEEK) cage. This simple structure incorporates less hardware, meaning a more reliable operation throughout the lifespan of the chiller.

Footprints are getting smaller, too. On the Carrier units for example, the footprint of the R1233zd(E) chillers and the crescent-shape economisers are specifically designed to leverage the space between the evaporator and the condenser, subsequently minimising the plant installation space needed. “Comparing this unit to a conventional R123 chiller, it saves up to 15% of plant installation space that can now be better used for business operations,” explains Smal.

Chillers005Industry believes that chillers will never go out of fashion.
Image credit: York


What does the future look like for chillers? Will they ever be replaced? The answer seems to be a resounding … no!

“We do not believe that chiller systems will be phased out, and the global market also shows a trend towards quite the opposite,” says Thomaides. With the refrigerant laws and restrictions becoming stricter and more heavily enforced, a central refrigerant system with lower volumes of gas is preferable in many installations, he explains. Chillers are pressurised, charged, and tested in a clean environment according to strict regulations. This eliminates contamination of the system on site.

“Chillers will never go out of fashion,” Cameron agrees. They were developed in the 1930s and since then we have seen radical enhancements; yet, there has not been a breakthrough in another groundbreaking form of heating/cooling, such as air-to-air cooling. “We have seen major improvements in efficiency and reliability, but essentially, chillers are still designed on the first iteration from the 1930s,” says Cameron.

“With rapid urbanisation and the boom of new construction, cooling demands at their peaks, so it is fair to say that chillers are here to stay,” say Sansom. “Based on large tonnage requirements, chilled water application is still the most viable option to cool a building today. Moreover, significant improvements have been made in chiller designs, making them more reliable and energy efficient.”

As with all HVAC&R equipment, it’s ‘horses for courses’ and the chiller is not the be all and end all of solutions. But it sure does make for a worthy option in many applications. Not all chillers are built equal though, so always ensure that you buy from a reputable supplier and have a proper maintenance plan in place. Else, you will learn the hard way just how expensive a chiller can be.

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