How Chiller Systems Work & How they Achieve High Cooling Efficiency

The working principle of chiller systems involves series of processes that involve heat absorption and dissipation.

Therefore, before you choose any chiller system for your cooling requirements, it is important to understand how the system works. Although they may have virtually the same working principle, the variation comes in the technological aspect.

But, before we explore how chillers work, let’s start with the basics.

What is a Chiller System?

A chiller system is a distinct refrigeration system that typically provides chilled water to cool buildings and industrial machinery, thus making air conditioning efficient.

It absorbs heat from your home, equipment, hospital, or mall before cooling it down and recirculating it. This keeps your space comfortable and protects your heat-sensitive equipment or processes from damage as a result of extreme heat.

Key Components of Chiller System

Key Cycles in Chiller System Operation

Many machineries and buildings rely on chiller systems, which exploit the thermodynamic cycle to keep the heat levels bearable. The working principle of chillers involve key steps which include:

Step 1: Evaporation

It all starts with hot or warm process fluid, such as water from your machinery or building, hitting the evaporator for heat transfer. As it passes through the evaporator, it is subject to a refrigerant either directly or indirectly, prompting its cooling. This chilled refrigerating fluid absorbs the heat from the heated incoming fluid, subsequently becoming vapor.

Due to the difference in warmth between the incoming water and the refrigerant, heat transfers organically to the refrigerant. This means that you are left with chilled water, ready to be recirculated into your building’s or machinery’s air handling unit to absorb more heat.

For optimal efficiency, constantly calculate your evaporator’s approach temperature using the formula highlighted below;

Leaving Chilled Water Temp – Refrigerant Evaporation Temp = Evaporator Approach Temp

Step 2: Compression

After the heated fluid is introduced to the evaporator, it loses its heat to the refrigerant, causing the latter to vaporize. This vaporized refrigerant is subsequently driven into a compressor, where it is compressed under controlled conditions.

As a result, it becomes pressurized and absorbs the heat generated during compression to the extent that it cannot absorb any more heat. As a matter of fact, it becomes hotter than the outside air, prompting its release from the compressor as a highly pressurized gas.

Step 3: Condensation

The hot, pressurized gas released from the compressor makes its way into the condenser, before a stream of chilled water is also introduced. The chilled water is primarily drawn from a cooling tower, and once it comes into close proximity with the hot refrigerant gas, it removes all the heat.

However, it works differently in air-cooled chiller systems, where the heated refrigerant is cooled by air rather than water. In these distinct chillers, the condenser features fans, which blast chilled air over the coils holding the refrigerant vapor. This cools it, prompting its transformation into liquid. To determine if your chiller system is efficient, pay attention to the approach temperature, which you can calculate using this formula:

Refrigerant Condensing Temp – Leaving Condenser Water Temp = Condenser Approach Temp

Step 4: Expansion

The refrigerant, after being cooled by air or water, depending on the type of chiller system in your hands, is driven into an expansion valve. Despite having been cooled, it flows in as a hot fluid.

However, it is restrained by this valve, causing its pressure to drop significantly. As a result, its temperature decreases, simultaneously transforming it into a cold and low-pressure refrigerant.  It is ultimately reintroduced into the evaporator via the refrigerant circuit, marking the start of yet another chilling cycle.

Comparing the Working Principle of Different Chiller Types

Heat Rejection Technology

· Water-Cooled Chiller Systems

These chillers feature prominently in enormous buildings since they are much more economical.

Water cooled chillers rely on chilled water, which is supplied by an attached cooling tower to significantly lower the temperature of your refrigerant, converting it into a liquid. This liquid is then dispensed into an extension valve, where its pressure is decreased, making it ready for a subsequent cooling cycle.

· Air-Cooled Chiller Systems

These chillers are favored in relatively smaller buildings thanks to their ease of use and maintenance. They get rid of unwanted heat using specialized fans that blast chilled air into the coils holding the hot refrigerant vapor. This results in the generation of liquified refrigerant, which is ultimately driven into the evaporator, albeit through the expansion valve, to kickstart the next chilling cycle.

Compressor Type

· Centrifugal Chiller Systems

These compressors thrive in chiller systems designed to cool enormous buildings and heavy industrial machinery due to their high load profile and efficiency. They boast Variable Frequency Drives, which greatly minimize their power consumption, thus saving you a fortune on energy bills. They pressurize the refrigerant using high-speed impellers before dispensing it to the condenser.

· Reciprocating Chiller Systems

This chiller compressor relies on cylinders equipped with pistons to raise the pressure of your chiller’s refrigerant vapor. The refrigerant gets to the compressor via the bottom of the cylinder once the piston moves upwards. As the piston moves downwards, it compacts the drawn-up refrigerant, prompting its release as high-pressure gas via the respective exit valves.

· Scroll Chiller Systems

These chiller compressors utilize twisted scrolls to quietly compact the refrigerant in your chiller system.  One of these twin scrolls is rotated, and as it orbits, it leaves a series of compartments, holding the refrigerant. The continuous rotation sees these compartments grow smaller and smaller, consequently squeezing the gas until its pressure surges upwards.

· Screw Chiller Systems

Screw chiller compressors squeeze the refrigerant vapor dispensed by the evaporator using helical rotors. These rotors bear compartments, which often house the refrigerant vapor, and as they rotate at increasingly higher speeds, their size decreases. This squeezes the gas, consequently increasing its pressure and temperature.

Conclusion

Keeping the temperature levels in buildings such as homes, hospitals, and industries housing key machinery is essential, and chiller systems can go a long way in helping you achieve this. And now that you have a deeper understanding of how they work, finding a chiller that can handle your load capacity comfortably and integrate seamlessly with your Building Automation System should be a walk in the park.

FAQs

What affects chiller system efficiency?

You may notice that your chiller is experiencing higher approach temperatures after a while. This is a sign that your chiller system is either experiencing some mechanical hitches or suffering from fouling.

Are air chillers efficient?

Yes. Air chillers only necessitate ambient air to chill your refrigerant, meaning that their energy consumption is relatively low. Their primary energy consumer is the fans needed to blast cold air.

Which is the best refrigerant for chillers?

Thankfully, you can choose from a series of proven and accredited refrigerants, including R717, R134A, and R290. However, you should prioritize a refrigerant that best suits your chiller and promises the best efficiency.

What is the coefficient of performance in chillers?

This is a parameter that tells you how efficient or productive your chilling system is. It compares the degree of cooling the system offers to the amount of power it consumes. Chillers that record a high COP, for instance, 5, offer the most efficiency.

What is the difference between variable primary flow and primary-secondary pumping in chillers?

VPF IS greatly favored in most chiller systems thanks to its efficiency in energy use, brought about by its reliance on one pump to distribute water to and from your building and chiller. Primary-secondary pumping, in contrast, features a main loop, which oversees the distribution of water via the chiller system, and a second loop in charge of water circulation through the building.