Chiller energy consumption is a major component of your long-term operational costs. For chiller suppliers, distributors, or system integrators, a more energy-efficient chiller can improve your ROI and system performance. So, what is the most energy-efficient chiller? This article gives you the solution.
Key Metrics to Measure Chiller Efficiency
Energy efficiency reflects not only the chiller performance itself but also the operating conditions, system design, and partial-load performance. Here are some specific metrics that can clearly show you chiller efficiency and load performance. Knowing them helps you better assess your chiller’s efficiency.
COP (Coefficient of Performance)
COP reflects how many units of heat can be transported for every unit of electrical energy consumed by your chiller. The higher the COP value is, the higher your chiller efficiency is and the lower the operating cost is. The COP of an efficient chiller unit is usually between 3.0 and 7.0.
COP = Cooling Capacity (kW) / Input Power (power consumption) (kW)
EER (Energy Efficiency Ratio)
EER represents the cooling efficiency of your chillers under specific rated conditions. It refers to how many British Thermal Units (Btu) of cooling capacity the equipment can generate for every 1 watt (W) of electricity consumed.
The higher the EER value is, the more cooling capacity is generated with the same power consumption, and the more energy-efficient the chiller is. Modern energy-efficient chillers typically have an EER of over 12.0.
EER = Cooling Capacity (Btu/h) / Input Power (power consumption) (W) = COP × 3.412
IPLV (Integrated Part Load Value)
IPLV is used to measure the part-load efficiency over time of the chiller under various loads. In practical applications, the chiller is hard to keep operating at 100% full load, so usually IPLV can more truly reflect the energy-saving effect throughout the year.
The Most Energy Efficient Chiller Type: Air-Cooled vs Water-Cooled
| Comparison Aspect | Air-Cooled Chiller | Water-Cooled Chiller |
| Typical Efficiency Level | Moderate efficiency | High efficiency |
| COP (Coefficient of Performance) | Lower (typically 2.5–3.5) | Higher (typically 4.0–6.5+) |
| IPLV (Part-Load Efficiency) | Moderate | Significantly higher |
| Impact of Ambient Temperature | Strong impact (efficiency drops in hot weather) | Less affected (more stable performance) |
| Energy Consumption (Overall) | Higher energy consumption | Lower energy consumption |
| Part-Load Performance | Less efficient at partial loads | Highly efficient at partial loads |
| Compressor Workload | Higher due to higher condensing temperature | Lower due to better heat rejection |
| Condensing Temperature | Higher → reduces efficiency | Lower → improves efficiency |
| System Efficiency Stability | Fluctuates with the weather | More stable year-round |
| Auxiliary Energy Use | No cooling tower, lower auxiliary energy | Requires pumps & cooling tower (adds energy use) |
| Net System Efficiency | Lower overall system efficiency | Still higher, even with auxiliary equipment |
From the chart, it is clearly for you to find that the water-cooled chiller is generally more energy-efficient than the air-cooled chiller. So, if you want to get the most energy-efficient chiller for your industry and you are not in a water-scarce area, consider the water-cooled type first.
Features of the Most Energy-Efficient Chiller
Many configurations can enhance the efficiency of the industrial water chiller. If you want to upgrade or change chillers, knowing the following features is vital and helpful to identify and pick out the most energy-efficient chillers for your industry.
Core Components
Evaporators
Many advanced chiller evaporator types can enhance the chiller efficiency. One good type is the Flooded Evaporator. Its tubes are completely submerged in the refrigerant, so its heat transfer coefficient is very high, achieving a very small approach temperature (usually approximately 0.5°C – 1°C), which reduces the compressor power consumption.
One of the most efficient evaporators is the Falling Film Evaporator, which has a lower refrigerant charge. The refrigerant is evenly sprayed onto the heat exchange tube bundles and forms a thin liquid film, highly improving evaporation efficiency.
Compressors
Oil-Free Magnetic Bearing Compressor is the most effective one because it eliminates mechanical friction and the contamination of lubricating oil to the heat exchanger, achieving 40% higher part-load efficiency.
Screw Compressors adopt dedicated rotor profiles and hydraulic regulation, suitable for medium to high load applications.
Scroll Compressors employ digital scroll technology to improve small chiller system energy efficiency.
Large centrifugal chillers can apply multi-stage compression combined with economizers to improve efficiency.
Condensers
For air-cooled chillers, you can improve chiller efficiency by employing Microchannel Technology (changing traditional round tubes to flat multi-channel aluminum tubes), which both increases chiller efficiency and reduces the power consumption of the condensing fan.
Improving the flow channels within the tubes and enhancing the heat exchange tubes can reduce the temperature difference and lower the exhaust pressure, thus also lowering energy consumption.
Heat Exchangers
Modern high-efficiency chillers employ high-performance enhanced tubes with precisely machined surfaces, such as internal threads/finned tubes (increase the surface area, prevent turbulence, and break the boundary layer thermal resistance) and micro-porous surfaces (promote the refrigerant to vaporize).
Electronic Expansion Valve (EEV)
Compared to traditional throttle devices, such as thermal expansion valves (TXVs) and orifice plates, the Electronic Expansion Valve can precisely adjust the value based on the sensor data, maintain a very low level of superheat (like 1.5 – 3°C), and prevent liquid from entering the compressor. Besides, EEV is not affected by the change of system pressure, so it can keep precise throttling even under low pressure differences.
Water Pumps
To reduce the water pump power consumption, you can apply a large temperature difference design to reduce water flow.
Evaporators and condensers also make a difference. If your evaporators and condensers have low resistance, then you can choose pumps with a lower head and smaller power.
Advanced Technologies
Variable Frequency Drive (VFD) / Variable Speed Drives (VSDs)
Variable Frequency Drive is the most effective method to improve chiller efficiency. It can control the rotational speed of the compressor, water pump, and fan by changing the power supply frequency. Here are its main functions:
- Reduce rotational speed when the load demand decreases, saving nearly half of the energy. Theoretically, the power consumption of the compressor can be reduced to approximately 12.5% of the rated value.
- Adjust a proper refrigerant flow.
- Achieve a smooth current rise, reducing additional energy loss caused by frequent starting and stopping.
- Increase the power factor of the motor to approximately 0.95 – 0.98, improving the efficiency of power grid utilization.
Oil-Free Magnetic Bearing
Oil-Free Magnetic Bearing has solved two great problems.
First, it eliminates the physical contact in traditional compressors. Through electromagnetic force, the rotor is suspended in the air without any physical contact with the bearings. Such “Zero Mechanical Friction” reduces 3% – 5% mechanical energy consumption and can maintain a high efficiency for over 20 years.
Second, it abandons the lubrication system. Traditional chillers have to use lubricating oil, which will form a thin “oil film” on the heat transfer tubes and produce a high thermal resistance. However, the magnetic bearing system employs no oil, increasing the COP by more than 10%.
Free Cooling
Free Cooling chiller can reduce the energy consumption of the chiller compressor or even completely shut down the compressor. When the outdoor temperature is lower than the required chilled water temperature (usually 3-5°C lower), the free cooling system can dissipate heat by using the outdoor cold air.
If the outdoor temperature is low enough, the system can achieve Total Free Cooling (the compressor is completely shut off), highly reducing chiller energy consumption.
Heat Recovery System
The Heat Recovery System can transfer the waste heat into usable energy, making the chiller a machine that can both provide cooling and heating. Through this system, COP can reach 5.0 to over 7.0.
What’s more, recycling waste heat for your pool heating, space preheating, or industrial processes can reduce the total energy consumption by 20% – 30%.
Thermal Energy Storage (TES)
Thermal Energy Storage transfers the cooling process during the night, which reduces the condensation pressure, increasing the COP by 10% – 15%. When the chiller goes wrong, TES can provide immediate cooling output without the need to start high-energy-consuming generators.
During the thermal energy storage mode, your chiller can still operate with an energy efficiency load point of 70%-90%.
Floating Head Pressure Control
Floating Head Pressure Control can lower the condensing pressure as the ambient temperature drops. Every 1°C decrease in the condensation temperature can reduce approximately 2% – 3% of the compressor’s power consumption.
It should be noted that the floating head pressure control technology should be combined with EEV to achieve a safe operation.
Intelligent Control System
Intelligent Control System makes the chiller system operate smartly and harmoniously through data analysis and algorithm optimization. It has realized multiple functions:
- By monitoring outdoor temperature, humidity, and weather forecasts, the intelligent control system can predict load changes. Combined with VSD, it can adjust the compressor speed to adapt to the load, reducing unnecessary energy consumption.
- The intelligent control system coordinates the relationships among compressors, water pumps, and cooling tower fans. It automatically calculates solutions with the lowest energy consumption and controls the parts.
- The intelligent control system keeps monitoring temperature and vibration and reminds you to maintain your chiller when something goes wrong.
- It can adjust the chilled water outlet temperature automatically.
AI and Digital Twin Optimization
AI can calculate the power balance among the condensing fan, the pump, and the compressor. Before making real adjustments, the digital twin can conduct thousands of simulations and give the best solution in the final.
Closed-Loop System
In a Closed-Loop System, the circulating water does not come into contact with the outside, so it wouldn’t evaporate and produce incrustation. At the same time, the air is eliminated, reducing metal pipe oxidation and corrosion.
The pipes of a closed-loop system are filled and sealed, so the water column pressure in the ascending pipe and the descending pipe achieves a static pressure balance. This reduces the demands of the chiller water pump, so you can use pumps with lower head and lower power.
Optimized Refrigerant
Optimized refrigerants can be beneficial to thermal physical properties, heat transfer efficiency, and compressor power consumption.
Some optimized refrigerants, such as R-1233zd(E) or R-1234ze, require a smaller pressure difference between the inlet and outlet of the compressor, increasing your chiller’s rated COP.
Refrigerants like R-32 or R-454B require less flow rate, which reduces the pressure drop and reduces ineffective energy consumption.
Water Treatment
Advanced water treatment can prevent scales and inhibit microbiological and biofilm growth, keeping a clean pipe and ensuring that the heat exchange always operates effectively.
You can employ micro-sand filters or vortex separators to continuously filter the circulating water volume. This can also reduce the fouling of the heat exchanger.
Renewable Energy Integration
Some renewable energy can also improve your chiller efficiency.
For example, in Solar-Assisted Cooling, the direct current generated by the solar panels can be supplied to the chiller.
In Geothermal Integration, the chiller condenser can release heat into the cool underground, greatly reducing the condenser pressure.
How to Choose the Most Energy-Efficient Chiller for Your Application?
After learning the technologies that can improve your chiller efficiency, here are the practical steps for you to pick out the most energy-efficient chiller for your specific industrial applications.
Determine Your Cooling Load Requirements
For different applications, your load requirements are also different, so you need to consider corresponding chiller components or technologies to improve your chiller efficiency.
- For applications with strong load fluctuations, such as office buildings and shopping malls, you can choose chillers with VSD/VFD technology to greatly enhance the IPLV.
- For some applications with high loads throughout the year, such as data centers, Oil-Free Magnetic Bearing is a good choice to quickly recoup the initial investment.
Choose the Right Chiller Type
We have discussed before that, in comparison, water-cooled chillers are a more energy-efficient type, while the load ranges can decide the most energy-efficient subdivided chiller type for you.
- Usually, for large-scale, high-efficiency applications, such as some large factories, data centers, and district cooling systems, centrifugal chillers are the best choice because they have the highest efficiency at scale.
- For medium loads, such as some manufacturing plants, process cooling, and medium-sized commercial facilities, it’s better for you to choose screw chillers. They have stability under varying load conditions and have a lower initial cost compared to centrifugal chillers.
- For small to medium loads, such as some small facilities, light commercial use, and backup cooling systems, you can choose scroll chillers. Their efficiency is lower, but they have a compact design and lower initial investment, and their installation and maintenance is easier.
Assessing Climate Adaptability
The climate and working environment are also important to consider when choosing your most energy-efficient chiller.
- If your chiller needs to operate for a long time in a cold environment, selecting the one with a free cooling function can highly save your energy for heat dissipation.
- If you have high demand for hot water, a heat recovery function can utilize waste heat and largely enhance the overall energy efficiency.
- If there is a large environmental temperature difference, you can choose chillers with floating head pressure to utilize the low-temperature environment to reduce compressor power consumption.
Calculate the Life Cycle Cost (LCC)
To prevent being mistaken by the initial price, it’s better for you to calculate the LCC in the end.
LCC = Initial cost + (Annual electricity bill * Service life period) + Maintenance cost
Usually, if you can recover the premium of an efficient chiller within 3-5 years, then it can be the choice of your most energy-efficient chiller.
FAQ
Does Chiller Sequencing Influence Chiller Efficiency?
Yes, chiller sequencing can largely influence energy efficiency. Most efficient chillers operate at their highest efficiency between 40% and 70% of the load. You can use the fixed-frequency units to operate at a stable load close to 100% and use variable-frequency units to regulate the remaining load.
Why is Water Quality Critical for Efficiency?
Minerals such as calcium, magnesium, and silicon in the water will form scales on the inner walls of the heat-exchange tubes, increasing thermal resistance. If there are algae, bacteria, and the formation of biofilm, the thermal resistance will be much higher.
In addition, unbalanced water quality can cause pitting or oxidative corrosion on the pipe walls, increasing the fluid resistance.
How to Calculate Chiller Efficiency?
To calculate chiller efficiency, you can calculate COP or EER directly with the formula we have proposed in the above part.
To obtain more accurate and real data, you can calculate IPLV. It calculates the weighted average of the efficiency of your chiller at four different load points: 100%, 75%, 50%, and 25%, which simulates the actual performance of the equipment throughout the operating season.
How to Maintain My Chiller to Keep It Highly Efficient?
To maintain your chiller, the key is to clean heat exchangers regularly. For water-cooled units, you can use mechanical flushing to remove scales, or you can set up a rubber ball cleaning device.
You need to monitor the water quality every day, including checking conductivity, pH value, and corrosion rate of the cooling water.
Regularly conduct leak detection of the refrigerant, especially at joints and valves, and electrical and mechanical components should also be inspected regularly. For traditional chillers, you need to regularly analyze the quality of the lubricating oil.
Is a High-Efficiency Chiller Worth My High Investment?
On most occasions, applying highly efficient chillers is definitely worthwhile. High-efficiency chillers can save up to 30% – 50% of energy compared to standard chillers, which greatly reduces the operating costs.
If your industry does not operate at full capacity throughout the year, it will be more valuable because the partial load energy efficiency maximizes your ROI.
For some conditions, high-efficiency chillers may not be worth it. If your chiller is only used as a backup for a few hundred hours each year, or you only use it for one or two years, the savings may not be enough to cover your high initial investment.
What Are the Signs That My Chiller Is Inefficient?
You can assess the condition of your chillers by inspecting if there are the following conditions: too large an approach temperature, abnormally increased electrical bills, frequent short cyclings, low delta T syndrome (The temperature difference between the inlet and outlet water is much lower than you desire), abnormal noise or vibration, excessive condensing pressure, and refrigerant that is cloudy or has bubbles.
All of these phenomena can reflect that there is something wrong with your chillers.
Retrofit or Replace My Existing Chiller, How to Determine?
To determine whether to retrofit or replace your chiller, first, you can check its age. If your chiller has been used for over 20 years, it’s better to replace it. If the actual operating COP is much higher than the rated COP of the new chiller, and the electricity bill saved can cover the cost of replacing the machine within a short time, you can replace it with a new one.
If your chiller has been used for 15 – 20 years, you can improve its efficiency by installing a VSD, replacing the refrigerant, and upgrading the control system.
Final Thoughts
The most energy-efficient chiller is the one that can bring the greatest profit to your industry. As we discussed, there are multiple factors that can influence chiller efficiency. For different conditions and customer requirements, Chillerone has provided multiple advanced chiller solutions and can customize them for you. Contact us, and get your exclusive high-efficiency cooling solution.
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