The Ultimate Guide to Chiller Systems. Everything You Need to Know.

Sep. 01, 2025

The Ultimate Guide to Chiller Systems. Everything You Need to Know.

What are Chiller Systems?

Commercial buildings use Heating, Ventilation and Air Conditioning (HVAC) systems to dehumidify and to cool the building. Modern commercial buildings seek efficient HVAC systems and components as part of broader initiatives centered on building performance and sustainability. Building occupants similarly carry great expectations, that the HVAC system will function as intended . . . to create a comfortable interior environment regardless of the conditions external to the building.

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Chillers have become an essential HVAC component of a wide variety of commercial facilities, including hotels, restaurants, hospitals, sporting arenas, industrial and manufacturing plants, etc. The industry has long recognized that chiller systems represent the single largest consumer of electrical usage in most facilities. They can easily consume more than 50% of the total electrical usage during seasonal periods. According to the US Department of Energy (DOE), chillers can combine to use approximately 20% of the total electric power generated in North America. Moreover, the DOE estimates that chillers can expend up to 30% in additional energy usage due to various operational inefficiencies. These acknowledged inefficiencies cost companies and building facilities billions of dollars annually.

In general, a chiller facilitates the transfer of heat from an internal environment to an external environment. This heat-transfer device relies on the physical state of a refrigerant as it circulates through the chiller system. Certainly, chillers can function as the heart of any central HVAC system.

How Does a Chiller Work?

A chiller works on the principle of vapor compression or vapor absorption. Chillers provide a continuous flow of coolant to the cold side of a process water system at a desired temperature of about 50°F (10°C). The coolant is then pumped through the process, extracting heat out of one area of a facility (e.g., machinery, process equipment, etc.) as it flows back to the return side of the process water system.

A chiller uses a vapor compression mechanical refrigeration system that connects to the process water system through a device called an evaporator. Refrigerant circulates through an evaporator, compressor, condenser and expansion device of a chiller. A thermodynamic process occurs in each of above components of a chiller. The evaporator functions as a heat exchanger such that heat captured by the process coolant flow transfers to the refrigerant. As the heat-transfer takes place, the refrigerant evaporates, changing from a low-pressure liquid into vapor, while the temperature of the process coolant reduces.

The refrigerant then flows to a compressor, which performs multiple functions. First, it removes refrigerant from the evaporator and ensures that the pressure in the evaporator remains low enough to absorb heat at the correct rate. Second, it raises the pressure in outgoing refrigerant vapor to ensure that its temperature remains high enough to release heat when it reaches the condenser. The refrigerant returns to a liquid state at the condenser. The latent heat given up as the refrigerant changes from vapor to liquid is carried away from the environment by a cooling medium (air or water).

Types of Chillers:

As described, two different cooling mediums (air or water) can facilitate the transfer of the latent heat given up as the refrigerant changes from vapor to liquid. Thus, chillers can use two different types of condensers, air-cooled and water-cooled.

Air-cooled condensers resemble the “radiators” that cool automobile engines. They use a motorized blower to force air across a grid of refrigerant lines. Unless they are specially designed for high-ambient conditions, air-cooled condensers require ambient temperatures of 95°F (35°C) or below to operate effectively.
Water-cooled condensers perform the same function as air-cooled condensers, but require two steps to complete the heat transfer. First, heat moves from refrigerant vapor into the condenser water. Then, the warm condenser water is pumped to a cooling tower where the process heat is ultimately discharged to the atmosphere.

Water-Cooled Chillers:

Water-cooled chillers feature a water-cooled condenser connected with a cooling tower. They have commonly been used for medium and large installations that have a sufficient water supply. Water-cooled chillers can produce more constant performance for commercial and industrial air conditioning because of the relative independence to fluctuations of the ambient temperature. Water-cooled chillers range in size from small 20-ton capacity models to several thousand-ton models that cool the world’s largest facilities such as airports, shopping malls and other facilities.

A typical water-cooled chiller uses recirculating condenser water from a cooling tower to condense the refrigerant. A water-cooled chiller contains a refrigerant dependent on the entering condenser water temperature (and flow rate), which functions in relation to the ambient wet-bulb temperature. Since the wet-bulb temperature is always lower than the dry-bulb temperature, the refrigerant condensing temperature (and pressure) in a water-cooled chiller can often operate significantly lower than an air-cooled chiller. Thus, water-cooled chillers can operate more efficiently.

Water-cooled chillers typically reside indoors in an environment protected from the elements. Hence, water-cooled chiller can offer a longer lifespan. Water-cooled chillers typically represent the only option for larger installations. The additional cooling tower system will require additional installation expense and maintenance as compared to air-cooled chillers.

Air-Cooled Chillers:

Air-cooled chillers rely on a condenser cooled by the environment air. Thus, air-cooled chillers may find common application in smaller or medium installations where space constraints may exist. An air-cooled chiller can represent the most practical choice in scenarios where water represents a scarce resource.

A typical air-cooled chiller can feature propeller fans or mechanical refrigeration cycles to draw ambient air over a finned coil to condense the refrigerant. The condensation of the refrigerant vapor in the air-cooled condenser enables the transfer of heat to the atmosphere.

Air-cooled chillers offer the significant advantage of lower installation costs. Simpler maintenance also results due to their relative simplicity as compared to water-cooled chillers. Air-cooled chillers will occupy less space, but will mostly reside outside a facility. Thus, the outdoor elements will compromise their functional lifespan.

The all-inclusive nature of air-cooled chillers reduces maintenance costs. Their relative simplicity coupled with reduced space requirements produces great advantages in many types of installations.

Actions to Increase Efficiency of Chiller Systems:

Chiller costs consume a substantial part of your building’s utility bills. What measures should one take to obtain energy savings through maximal efficiency of the chiller system? Let’s examine some possibilities.

Ongoing Maintenance

Chiller systems will operate more efficiently through proper ongoing maintenance. Most organizations recognize this value and have taken steps as part of their day-to-day facility management best practices. Some common best practices for chiller systems include:

Inspect and clean condenser coils. Heat transfer has a large effect on chiller systems and remains fundamental to producing efficient chiller operation. Routine maintenance should inspect condenser coils for clogging and free air passage.
Maintain refrigerant charge. A chiller’s cooling quotient depends on proper refrigerant levels in the system. Maintaining proper refrigerant charge can greatly impact energy efficiency by reducing cooling costs by nearly 5-10%.
Maintain condenser water: Condenser water loops used with cooling towers must maintain proper water flow as designed. Any debris like sand, erosive solids and contamination materials can affect the condenser water loop. Fouling or scaling can inhibit water flow and greatly impact the chiller operating efficiency.

Predictive Maintenance

Artificial Intelligence (AI) continues to advance in everyday practical applications. Machinery such as chiller systems will benefit from AI algorithms that can detect potential failures before they occur. Predictive maintenance leverages the collection and analysis of chiller system operational data to determine when maintenance actions should be taken prior to catastrophic failure. As chillers systems represent the heart of most modern HVAC systems, the prevention of catastrophic failures that produce significant “downtime” will save on emergency repair costs as well as reputation. The critical role played by a chiller system warrants the increased scrutiny. Big Data and AI will minimize downtime and maximize productivity.

The Internet of Things (IoT) provides the data collection tool that can enable AI applications such as predictive maintenance. In fact, the future of HVAC is AI and IoT. IoT enables the collection of real-time data from a chiller to enable continual analysis of its operation. The granular IoT data collected from a chiller will go far beyond that obtained by visual inspection. IoT connects building engineers to real-time visibility of critical HVAC assets, thereby enabling informed monitoring of actual operating conditions.

Optimization

Chillers operate as part of a complex HVAC system. Water-cooled chillers have greater complexity due to the connection to a cooling tower system. Evaluating overall chiller plant performance will therefore involve an analysis of total power consumption of the compressor, pumps, cooling tower fans, etc. to evaluate comprehensive efficiency measures such as kW/ton.

Optimization of the overall chiller plant must be performed holistically. Various adjustments focusing on optimal chilled water set points, chiller sequencing and load balancing, peak demand management, cooling tower water management, etc. can only be performed with operational data. IoT can provide the tools for such optimization by providing real-time monitoring of power consumption from each part of the chiller plant, supply/return temperatures from the chiller and cooling tower, water flow rates from the condenser water loop, etc. IoT has found practical application in HVAC to facilitate true optimization.

Conclusion:

Chiller operational efficiency will greatly impact your building operating costs. Ongoing routine maintenance represents the minimum from the perspective of facility management. Predictive maintenance and optimization of the chiller system requires real-time operational data. IoT has opened the door to new forms of chiller efficiencies.

Editor's Note: This post was originally published in November and has been completely revamped and updated for accuracy and comprehensiveness.

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Chiller Troubleshooting Guide: Common Problems & Solutions

Chiller Troubleshooting Guide: Common Issues & Solutions

Chillers are essential for meeting the temperature requirements of several industrial processes, thus, consuming significant amounts of energy in these facilities. As a result, operators must prioritize the correct operation and maintenance approach to maximize system performance, ensure prolonged lifespan, and minimize energy costs. This article identifies common chiller problems and solutions and highlights relevant troubleshooting guidelines.

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3 Common Causes of Chiller Problems

Incorrect operating practices, negligence to maintenance, and incorrect chiller sizing are three common causes of chiller problems. Therefore, operators must actively consider these factors to mitigate potential threats to the cooling equipment.

1. Improper Operation

Industrial chillers come with manuals containing manufacturer’s guidelines for correctly operating them. Operators must follow these guidelines as poor operating practices adversely affects equipment efficiency and lifespan. While these cooling systems may continue working regardless of improper practices, it is noteworthy that the systems become more susceptible to more severe and expensive problems. Mitigating this threat involves implementing training programs on correct chiller operation and maintenance and efficient chiller maintenance programs.

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2. Maintenance Neglect

Operators may disregard proper maintenance practices, which are detrimental to the overall performance of water cooled and air cooled chillers and lead to excessive energy consumption. Operators must ensure effective maintenance comprising adequate equipment diagnostics using operating logs. Moreover, chiller units require regular inspections to ascertain their conditions and schedule preventive and corrective maintenance.

3. Incorrect Sizing

Proper chiller sizing is crucial for efficient cooling in industrial facilities. An incorrectly sized unit can cause several issues:

Undersized chillers may struggle to provide sufficient cooling, leading to inadequate airflow and system inefficiencies.
Oversized chillers can limit low-load operation, increasing energy consumption and operating costs.

Operators should evaluate the cooling capacity of existing air cooled chillers to ensure they match the facility’s cooling demands.

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Troubleshooting Basics for Water Chillers

Air cooled and water cooled chillers remain vulnerable to damage regardless of proper operation and regular maintenance due to degradation or deterioration over time. Understanding common initial troubleshooting steps can allow operators to identify the potential issue before chiller repairs.

Chiller Won’t Start

Two common factors that can prevent chillers from starting include loose wiring and a blown fuse/circuit breaker. Moreover, a power switch in the off state may prevent the chiller from running. Operators must check the equipment for these common problems to ensure the system runs effectively.

Causes:

Loose Wiring – Connections may have loosened over time, preventing proper electrical flow.
Blown Fuse or Tripped Circuit Breaker – Electrical overloads can cause these safety devices to shut down the system.
Power Switch Off – The chiller may have been inadvertently turned off or not properly restarted after maintenance.
Control System Issues – Faulty relays, sensors, or PLC malfunctions can prevent startup.
Low Refrigerant Pressure – If the pressure is too low, built-in safety controls may prevent operation.

Troubleshooting Steps:

Inspect and tighten any loose electrical connections.
Check for blown fuses or tripped breakers and replace/reset as necessary.
Verify that the power switch is in the “on” position.
Review error codes on the control panel to diagnose potential issues.
Check refrigerant pressure levels and ensure they are within the required range.

If the issue persists, a technician should perform a more detailed electrical and mechanical inspection.

Insufficient Cooling

When a chiller isn’t providing adequate cooling, the issue may stem from temperature regulation failures or system inefficiencies.

Causes:

Iced-Up Evaporator – Excess moisture or low refrigerant can cause ice buildup, reducing heat exchange.
Degraded Coolant Fluid – Old or contaminated coolant loses efficiency and can’t properly absorb heat.
Dirty or Blocked Condenser – Dust and debris can obstruct airflow or water flow, reducing cooling capacity.
Incorrect Setpoints – Temperature settings that don’t align with process requirements can impact performance.

Troubleshooting Steps:

Check the chiller outlet temperature and compare it to the setpoint.
Inspect the evaporator for ice buildup and allow it to thaw if necessary.
Drain and replace degraded coolant fluid with fresh, manufacturer-approved coolant.
Clean condenser coils or ensure proper water circulation for water-cooled units.
Adjust temperature settings to align with operational needs.

If cooling issues persist, a deeper system evaluation may be required.

Insufficient Pumping

Poor coolant flow can be caused by several factors, including low coolant volume, a partially closed valve, pump failure, or restrictions in the process line. Any of these can disrupt the refrigeration cycle and reduce the system’s efficiency. Checking these components can help identify and resolve the issue.

Causes:

Low Coolant Volume – A shortage of coolant in the reservoir prevents proper circulation.
Partially Closed Valves – Restricted flow due to improper valve positioning can reduce pumping efficiency.
Pump Failure – A malfunctioning pump may struggle to circulate coolant through the system.
Process Line Restrictions – Blockages in pipes or heat exchangers can limit flow.

Troubleshooting Steps:

Check the coolant reservoir and refill if necessary.
Inspect and fully open any partially closed valves.
Listen for unusual pump noises that may indicate wear or failure.
Flush process lines to remove potential blockages.

If coolant flow remains inadequate, a detailed inspection of the pump and piping may be needed.

Additional Chiller Problems

Manufacturers equip modern-day chiller systems with fault or error code display capabilities. These features can rapidly notify operators about prevalent conditions affecting system performance. Moreover, operators can rapidly diagnose and identify problems due to the specificity of the error codes and fault displays. Some common conditions or faults chiller systems notify operators about include:

High Temperature

The process temperature may increase above the user-set temperature value of the chiller system. This condition can trigger an alarm from the system and may result from a higher heat load than the chiller capacity. Moreover, a lower setting than standard requirements in the chiller system may also trigger the high-temperature alarm.

Causes:

Excessive Heat Load – The chiller is trying to cool beyond its chiller capacity.
Restricted Heat Dissipation – Dirty condensers, low water flow, or blocked airflow reduce cooling efficiency.
Incorrect Temperature Setpoint – A setpoint too high for the process needs can trigger an alarm.
Refrigerant Issues – Low refrigerant levels or leaks can cause poor heat absorption.
Mechanical Failures – Malfunctioning pumps, fans, or compressors can prevent proper cooling.

Troubleshooting Steps:

Reduce the heat load if it exceeds the chiller’s capacity.
Clean condensers and ensure proper water or air circulation.
Verify temperature setpoints and adjust if needed.
Check refrigerant levels and inspect for leaks.
Ensure pumps and fans are operating correctly.

If the problem persists, professional maintenance may be required.

Low Temperature

A process temperature below the user-set temperature value can also trigger an alarm. This condition is common with insufficient heat load or improper low-temperature alarm settings in the chiller system.

Causes:

Insufficient Heat Load – The chiller is removing more heat than the process generates.
Improper Setpoint Configuration – A temperature setting too low can cause unnecessary alarms.
Faulty Temperature Sensors – Malfunctioning sensors may incorrectly detect low temperatures.
Refrigerant Overcharge – Excess refrigerant can cause the system to overcool.

Troubleshooting Steps:

Increase the heat load or adjust process conditions.
Verify and adjust temperature setpoints as needed.
Inspect and calibrate temperature sensors.
Check refrigerant levels and adjust if necessary.

If freezing occurs, turn off the chiller and let it thaw before restarting.

Low Coolant Level

A low coolant level alarm indicates that the chiller’s coolant has dropped below the acceptable range. This can reduce heat transfer efficiency and lead to system failure if not addressed.

Causes:

Evaporation – Over time, coolant can naturally evaporate, especially in open systems.
Leaks – Cracked hoses, faulty seals, or worn-out fittings can cause fluid loss.
Improper Maintenance – Failing to monitor and refill coolant levels regularly can lead to shortages.

Troubleshooting Steps:

Inspect the system for visible leaks and repair any damaged components.
Check hoses, seals, and fittings for signs of wear or damage.
Refill coolant to the recommended level using the correct type.
Monitor the system for recurring drops in coolant level.

If coolant loss continues, a professional inspection may be needed to identify hidden leaks.

Over-Temperature

An over-temperature alarm occurs when the chiller’s process temperature exceeds the set safety limit. This issue can reduce efficiency, strain components, and lead to system failure if not addressed.

Causes:

Excessive Heat Load – The chiller is cooling more than its rated capacity.
Poor Heat Dissipation – Dirty condensers, low airflow, or inadequate water flow reduce cooling efficiency.
Refrigerant Issues – Low refrigerant levels or contamination can impair performance.
Restricted Coolant Flow – Clogged filters, pump failure, or piping issues can prevent proper heat transfer.
Faulty Sensors or Settings – Incorrect temperature setpoints or malfunctioning sensors can trigger false alarms.

Troubleshooting Steps:

Check if the heat load exceeds the chiller’s capacity.
Inspect condensers for dirt buildup and ensure proper airflow or water flow.
Verify refrigerant levels and check for leaks.
Ensure the coolant system is free of blockages and the pump is operating correctly.
Review temperature setpoints and recalibrate sensors if needed.

Questions? Contact the Experts at Cold Shot Chillers!

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