Rethinking Chiller Efficiency: Strategies That Work

Energy bills are one of the biggest overheads for industries and commercial buildings. And a large share of this cost comes from chillers. These cooling systems quietly run in the background, but their appetite for energy makes them a prime candidate for efficiency improvements.

This article discusses on key strategies that will help unleash the full potential of chiller systems in cutting energy costs and carbon emissions.

Understanding Chiller Efficiency

Chillers are complex machines that work by balancing different parameters and operating conditions to produce cooling. Energy consumption from chillers is due to following major components:

• Compressor: The cooling process in chiller is done by taking in a low-pressure refrigerant and compressing it to a higher pressure. For this, an appreciable quantity of electrical energy is required.

• Condenser: The condenser rejects the heat absorbed by the refrigerant. It can be air-cooled or water-cooled. The fans or pumps facilitating the heat transfer add to the energy consumed by the chiller.

• Evaporator: The cooling effect of a chiller is imposed on the refrigerant if it absorbs heat from the building or process. The evaporator thus is not directly involved in consuming any energy. However, the energy consumption involved with the pumps and fans that circulate the chilled water or air contribute to energy consumption.

• Ancillary Equipment: Other items like control equipment, valves, and pumps also consume energy in a chiller system, although the amount from each may not be huge.

Understanding the Energy Efficiency Metrics

There are various parameters on which one can measure and assess the efficiency of a chiller:

• Coefficient of Performance (COP): The COP is the cooling output in kilowatts divided by the electrical input in kilowatts. When the COP is high, the efficiency of the chiller is high.

• Energy Efficiency Ratio (EER): The EER is the ratio of cooling output (in BTU/hr) to electrical input (in watts). A higher EER equates to a more efficient chiller.

• Integrated Part Load Value (IPLV) and Non-Standard Part Load Value (NPLV): These ratings assess chiller efficiency at various loads rather than at full loads alone. This becomes pertinent as chillers seldom truly work through a full load during their lifetime.

• Cooling Load (kW/ton): This one measures the heat removal capacity of the chiller, while the actual output of cooling is in kilowatts per ton of refrigeration.

Key Strategies to Improve Chiller Efficiency

Having created a solid background of chiller efficiency concepts, we thus delve into key strategies and techniques to optimize your chiller system performance.

Compressor Retrofit

One of the most significant improvements in compressor efficiencies can come through targeted retrofitting. Businesses can go with variable speed scroll compressors if their technology is quite old. In this way, the biggest energy savings would come by installing a new, more energy-efficient compressor.

Energy savings of almost 9% may be realized if the fixed-speed scroll compressor is replaced by the variable-speed one. The part load operating profile of the chiller becomes the critical factor in deciding the potential savings. If the chiller remains in part-load mode for most of the year, the variable-speed compressor will create more efficiency in savings.

Compressor Variable Frequency Drives (VFDs)

If completely replacing the compressors cannot be done, consider retrofitting the existing compressor with a variable frequency drive. This technology allows the compressor to modulate its speed and capacity to meet the cooling load, rather than operating at a fixed speed.

Retrofitting with VFD for a compressor can achieve an average of about 20% energy savings if chiller operation is under part load. However, before retrofitting with VFDs, the chiller manufacturer or a qualified technician must be consulted to confirm compatibility and install the system correctly.

Chilled Water Reset

Earlier, the chilled water systems operated at a fixed outlet temperature, mostly around 6°C (42.8°F). However, a chilled water reset would allow the temperature to be increased under part-load conditions. This reduces the chillers’ workload and increases efficiency.

Generally, the chiller efficiency increases by 1-2% per °C (1.8-3.6 % per °F) temperature rise in chilled water. It can be determined by monitoring parameters such as outdoor air temperature, cooling load, or average demand on the cooling coils and adjusting the chilled water setpoint accordingly.

Condenser Water Reset

Just like the chilled water reset, optimizing the condenser water temperature can fetch huge efficiency gains. Water-cooled chillers depend on the condenser water system to get rid of heat from the refrigerant. In such cases, lower condenser water temperatures make it easier for the compressor to operate.

Energy savings of around 1-2% per °C can be expected for every degree of reduction in condenser water temperature. It is achieved by reducing the cooling tower fans or opening a bypass line at a condenser water return temperature fixed at around 27°C.

Evaporator and Condenser Cleaning

Chillers attain fouling over time from the accumulation of dirt, dust, and biological growth on their evaporator and condenser coils. It leads to reduced heat transfer efficiency and higher energy consumption. A periodic cleaning and maintenance program for these two critical parts can restore their efficiency and provide further energy savings.

Energy savings as a result of cleaning the evaporator and condenser coils can be 1-10%, depending on the degree of fouling. But one must keep in mind that the actual savings will depend upon the conditions of the chiller system it serves and the frequency of the cleaning.

Expansion Valve Upgrades

The expansion valve controls refrigerant flow into the evaporator to maintain the proper superheat level. Replacing a traditional thermostatic expansion valve with an electronic expansion valve improves efficiency and controls refrigerant flow more precisely.

EEVs can respond very quickly to changes in operating conditions. It provides an optimized superheat control and also reduces compressor work. Depending on the chiller’s part-load performance, EEV upgrades can produce energy savings of up to 14%.

Improved Air-Cooled Condenser Fans

The air-cooled chillers are cooled by condenser fans. These fans could be traditional on-off or multi-stage. However, one option for higher efficiency is EC or electronically commutated fans.

Variable-speed EC fans can change their airflow in relation to cooling demand. Therefore, these fans consume up to 6% less energy than the fixed-speed fans.

Free Cooling or Economizer Strategies

The application of free cooling or economizer strategies might reduce the energy consumption of chillers. These strategies are used when ambient air is used to cool down the chillers with minimal use of compressors if required.

Free cooling is most suitable for data centers or buildings with a fairly constant cooling load. Here, the outdoor air temperatures are sufficiently low for a substantial portion of the year. Thus, the energy savings through free cooling can be evaluated in the range of 20-50% depending on the local climate and operational conditions.

Chiller and Plant Sequencing

Chillers, cooling towers, pumps, and fans have varying performance curves and part-load efficiencies. This gives an option to resort to a chiller and plant sequencing control strategy. This strategy makes sure that the equipment selection employs the most efficient combination for the current cooling load.

This practice can yield energy savings of 20% or more, depending on the existing control strategy and the efficiency of the individual components.

Cooling Tower, Pump, and AHU Fan VFDs

The cooling tower, fans and pumps can also benefit from variable frequency drives (VFDs) along with the chiller compressor. A VFD allows their motor to vary its speed and output in accordance with the actual needs of the system rather than operating at a constant speed. This alone can save about 5-20% energy per motor, as the system can more closely follow the cooling load.

Intelligent Control Systems and Sensors

The optimization of the chiller operation is also done by investing in advanced control systems and high-accuracy sensors. Integrated building management systems (BMS) can coordinate the operation of the chiller with the rest of the HVAC components. These systems rely on predictive maintenance algorithms to warn of any impending failure in advance. It also gives an advantage of analytics and machine learning to evolve the control strategies with respect to shifting operating conditions.

Proper Refrigerant Charge and Leak Detection

Proper refrigerant level is a must for attaining chiller performance. Undercharging or overcharging can bring lower efficiencies and sometimes damage the compressor. In addition to that, leak detection and monitoring programs should be used too. These systems help to maintain the charge and detect any problems in early stages.

Effective Water Treatment Programs

Condenser and evaporator water systems of water-cooled chillers should be treated to prevent scaling, corrosion, and biological growth. These contaminants decrease heat transfer efficiency considerably and cause a rise in energy consumption.

Therefore, one must set up and carry out a good water treatment program. It includes regular testing, chemical dosing, and physical cleaning that maintains the heat exchanger performance of the chiller.

Monitoring Fluid Quality

Any change in fluid quality may adversely affect chiller performance. Hence, one has to set a proper routine maintenance to clean coils of evaporators and condensers. Filtration systems are generally used to remove unnecessary particle from the fluid.

Glycol Based Systems should be monitored regularly and dirty fluids should be replaced for proper functioning of chiller.

Increasing Supply Temperatures

Proper dehumidification is used in most chillers for chilled water supply in building during peak hours. However, it is seen that the system may not reach these peak chilled temperatures every time. Therefore, it is advisable to increase water temperature which results in easy flow of heat to refrigerant without needing high amounts of energy. Just about 2°F increase can increase the efficiency by 3-5% in mild weather conditions.

Let’s Talk Chiller Efficiency Optimization

At AvignaAI, we specialize in bringing IoT intelligence to your chiller systems. By integrating advanced sensors, real-time monitoring, and predictive analytics, we help you track performance, detect inefficiencies, and prevent costly breakdowns before they happen. Our IoT-enabled solutions are designed to reduce energy consumption, lower operational costs and extend equipment lifetime, all while supporting your sustainability goals. If you are ready to make your chillers smarter, reliable, and more efficient, contact us today.