Screw Chiller vs Centrifugal Chiller – Which is the Best Cooling System for your Facility

Large office spaces, malls, or industrial facilities can be quite suffocating, especially during the summer, when it is sizzling hot.

To keep these fundamental spaces comfortable and cool, facility managers and HVAC engineers explore varying chillers, particularly screw and centrifugal chillers. That is why this article focuses on these two advanced chillers, in the hope of helping you find the right refrigeration system for your space.

What is a Screw Chiller?

A screw chiller is a distinct refrigeration unit often installed in small and medium industrial facilities and commercial spaces to cool these spaces using a compressor whose shape resembles a screw. The chiller comes with identical helical rotors, which rotate continuously while compressing the refrigerant gas in preparation for chilling in the condenser.

What is a Centrifugal Chiller?

A centrifugal chiller is a high-performance refrigeration unit suitable for cooling large industrial facilities and commercial buildings, using rotating impellers to compress the refrigeration gas in readiness for condensation by air or water. These chillers deliver highly pressurized refrigeration vapor to designated condensers, which consequently generate the chilled air to be circulated in your building or industrial facility.

Understanding the Differences Between Centrifugal and Screw Chillers

· Structure

Screw chillers are comparatively smaller in size, and this often translates into a simpler structure. The entire screw chiller system comes with a compressor, an evaporator, and a condenser, amongst other key components. The screw compressor, which is tasked with generating highly pressurized refrigerant gas, features twin screws, one male and the other female.

Centrifugal chillers, in contrast, have relatively more components, giving them a larger footprint. In addition to the centrifugal compressor and the condenser, these chillers also come with a motor, amongst other key components. This gives centrifugal chillers a relatively higher cooling capacity.

· How they Work

Centrifugal chillers deliver steady loads while operating at relatively higher capacities, and this is simply down to their distinct working principles. For one, they come with a rotating impeller whose rotation at a very high speed pressurizes the refrigerant air whilst generating high temperatures. This stream of pressurized and heated air is driven into a condenser before being passed through an evaporator. The condenser dislodges the heat, lowering its temperature and converting it back to water.

Screw chillers, in contrast, generate heated and highly pressurized gas by squeezing the refrigerant gas using male and female helical rotors. The generated hot gas is then driven into a condenser, where the heat is absorbed by air in air chillers or water in water chillers. The resulting air is then passed through expansion valves, which restore its low pressure before it is driven to the evaporators for a new cooling cycle.

· Capacity

Screw chillers thrive in buildings and facilities with relatively lower cooling demands. This is primarily because their cooling capacity ranges between 30RT and 500RT. Centrifugal chillers, in contrast, are more suited to large industrial facilities and buildings, thanks to their significantly higher refrigeration capacity, ranging between 150RT and 30,000RT.

· Energy Consumption

Whereas centrifugal and screw chillers thrive in distinct capacity ranges, they consume varying amounts of power while operating at the same capacity and load. Screw chillers, in particular, demonstrate a higher energy efficiency. While operating under partial loads, they can consume up to 15% less energy compared to centrifugal chillers.

· Efficiency

Screw chillers demonstrate a superior efficiency when deployed in small and medium-sized facilities or buildings, where they operate at part loads. This is because they boast an energy regulation range of between 10% and 100%, which qualifies their use in commercial spaces with varying air conditioning loads.

Centrifugal chiller systems, conversely, exhibit greater efficiency when deployed in large buildings such as shopping malls and industrial facilities. Their energy regulation range is slightly smaller (40%-100%). However, they are likely to experience a surge, which can be quite damaging if run at loads below 40%.

· Maintenance Requirements

Owing to the simple design and structure of screw chiller systems, their maintenance is relatively easier and cheaper. Their structure may include numerous compressors, meaning you will not have to shut down the entire system to undertake maintenance. Centrifuge chillers, in contrast, rely on a single compressor, meaning the entire system must be shut down to undertake maintenance. This can drive up the cost of maintaining these chillers.

· Applications and Suitability

The difference in load suitability and capacity ranges of screw chillers and centrifugal chillers means that they both suit different applications. The table below summarizes and compares the specific applications of these two chillers.

· Pros and Cons

Screw Chillers

Pros

The unique structure of screw chillers makes them ideal for distinct functions. They promise a number of distinct rewards, including;

• Requires low starting current.
• Quieter operation.
• Greater efficiency at part-load conditions.
• Remains stable even under different load demands.
• Compact footprint.
• Cheaper to maintain.
• Higher liquid refrigerant carryover.

Cons

Despite the multitude of rewards that come with screw chillers, they are not immune to challenges. They are prone to limitations such as;

• Higher operational costs at full load.
• Capacity limitations.
• Higher lubricant consumption.

Centrifugal Chillers

Pros

Centrifugal chillers have been and remain the preferred refrigeration system for large industries, facilities, and buildings. This is because they come with numerous rewards, key amongst them being;

• Greater energy efficiency in large-scale operations.
• Higher efficiency at full-load operation.
• Quiet when operating at full capacity.
• Longer service life.
• Smooth, oil-free operation.
• Perfect for large cooling capacities.

Cons

Whilst centrifugal chillers thrive in large-capacity cooling operations, their efficiency when handling partial loads or while operating in smaller capacities shrinks significantly. This is just one of the main limitations of these chillers. Other limitations include;

• Inefficient when operating at part-load conditions.
• Relatively larger footprint.
• Higher starting current.

· Noise

Screw chillers rely on spinning rotors to pressurize refrigerant gas. However, the speed at which these rotors rotate remains comparatively lower, meaning that they generate significantly less noise. Centrifugal chillers, conversely, rely on rotating impellers, whose speed can be as high as 40, 000 rpm. This means that they generate more noise, often surpassing 80 dB (A) compared to the 75dB (A) generated by screw chiller systems.

FAQs

Are screw chillers water-cooled or air-cooled?

Whilst the vast majority of screw chillers come in water-cooled models, some come as air-cooled models. However, the water-cooled versions demonstrate greater efficiency and can be relatively less noisy, making them more popular.

What are screw chillers best for?

Screw chillers demonstrate peak performances when deployed in medium or relatively smaller facilities and buildings such as hotels and pharmaceutical labs. Additionally, they thrive in part-load conditions, making them perfect for spaces prone to fluctuating weather conditions.

What are centrifugal chillers best for?

Centrifugal chillers, thanks to their oil-free operation and greater efficiency when operating at full load conditions, thrive in spaces with greater cooling demands. This includes large manufacturing plants, shopping malls, and airports, amongst others.

Between Centrifugal and screw chillers, which boasts a higher cooling capacity?

Centrifugal chillers are capable of delivering greater refrigeration consistently, hence they are highly revered in spaces with relatively high cooling demands, such as airports and malls. This greater capacity is facilitated by the centrifugal compressors they exploit to generate high-pressure refrigerant gas.

Chillerone; Your No.1 Choice for Chilling Systems

Whether you are looking for screw or centrifugal chillers, Chillerone customizes every chiller to suit your unique cooling requirements. From water-cooled screw chillers, modular chillers, to magnetic chillers,  every chiller design feature unique and optimized features for cooling efficiency and reliability.

Partner with us today, for all your chiller systems – Get our Chillerone product catalogue now.