How Does an Air-Cooled Chiller Work?

Air-cooled chillers are an important part of modern HVAC and process cooling systems. They provide efficient cooling for industrial and commercial applications. Unlike water-cooled chillers, which use a water-based heat exchange system to remove heat, air-cooled chillers rely on ambient air to directly disperse excess heat through fans and condenser coils.

An air-cooled chiller removes heat from a process or building and releases it into the surrounding air using fans and condenser coils. These cooling systems are useful in places with limited water resources. They also perform well in areas where cooling towers cannot be installed or footprint is limited.

In this blog post, we will look at how air-cooled chillers work. We will explain their main parts, how they operate and their efficiency. We will also discuss their lifespan and potential for heat recovery.

Understanding how an air-cooled chiller works is important for optimising performance and efficiency. These systems operate using the vapour compression refrigeration cycle, which consists of four stages:

1. Evaporation
2. Compression
3. Condensation
4. Expansion

Air-cooled chillers are different from water-cooled chillers. They do not use cooling towers or water loops to release heat. Instead, they use fans and the surrounding air to remove extra heat from the system. 

Feature	Air-Cooled Chiller	Water-Cooled Chiller
Cooling method	Uses ambient air and fans to remove heat	Uses water and a cooling tower or air cooled chiller for heat rejection
Installation	Easier to install, requires less infrastructure	Requires additional cooling equipment, piping and water supply
Efficiency	Can be less efficient in high ambient temperatures	Generally, more efficient in large-scale applications
Maintenance	Requires minimal maintenance (no water treatment needed)	Requires regular water treatment
Best for	Smaller to medium applications, locations with limited water resources	Large-scale facilities requiring high cooling capacity

• Ideal for facilities without access to a reliable water source Or in areas that restrict water usage
• Lower installation and maintenance costs because of the absence of a cooling tower.
• Suitable for applications with moderate cooling loads and space constraints.

With this knowledge, businesses can get a better idea of whether this particular type of chiller meets their cooling needs. They can balance efficiency, cost and operational requirements.

To understand how an air-cooled chiller works, we need to look at its main parts. These parts work together to provide efficient cooling. Each part is important in the vapour compression refrigeration cycle. It helps absorb, transfer and release heat effectively.

Evaporator: absorbs heat and cools the water
The evaporator is where the cooling process begins. Warm water from the building or process flows through the evaporator, where it transfers heat to the refrigerant. As the refrigerant absorbs heat, it evaporates into a gas, cooling the water before it recirculates.

Compressor: increases refrigerant pressure and temperature
The compressor is responsible for compressing the refrigerant gas. Common compressor types include centrifugal, screw, reciprocating, and scroll compressors, each suited to different chiller capacities.

Condenser: transfers heat to the air
The condenser is where heat is released from the refrigerant into the atmosphere. Fans blow ambient air over the condenser coils, helping to release the heat. As the refrigerant cools down, it condenses back into a liquid 

Expansion valve: regulates refrigerant flow
The expansion valve plays an important role in controlling the amount of refrigerant entering the evaporator. It reduces the refrigerant’s pressure and temperature, preparing it to absorb heat again. This regulation helps maintain consistent cooling efficiency.

Fans: assist in heat release
Air-cooled chillers use powerful axial or centrifugal fans to force air over the condenser coils. This airflow increases the heat exchange rate, improving cooling efficiency.

When selecting an air-cooled chiller, efficiency and capacity are two key factors to consider. These aspects determine the system’s energy consumption, cooling performance and long-term operating costs.

Knowing how air-cooled chillers work and how to measure their efficiency can help businesses save energy and cut costs.

Air-cooled chiller efficiency refers to how effectively the system converts energy input into cooling output. The following metrics are commonly used:

• Energy efficiency ratio (EER)

  Measures the ratio of cooling output (BTU/hr) to energy input (watts). Higher EER values indicate greater efficiency.

• Coefficient of performance (COP)

  Compares the cooling effect to the energy required to operate the system. A higher COP means the chiller delivers more cooling with less energy consumption.

• Integrated part load value (IPLV)
  Evaluates chiller efficiency across various load conditions rather than just peak operation. Useful for understanding real-world performance.

The cooling capacity of an air-cooled chiller is measured in:

• Tons of refrigeration (TR)
• Kilowatts (kW)
• British Thermal Units per hour (BTU/hr)

Typical capacity ranges:

• Small chillers (10-100 kW/3-30 TR)

  Ideal for small commercial buildings and HVAC applications.

• Medium chillers (100-1000 kW/30-300 TR)

  Used in shopping centres, hospitals and manufacturing plants.

• Large chillers (1000+ kW/300+ TR)
  Found in data centres, industrial facilities and district cooling systems.

• Assess the cooling load: determine the total heat based on building size and usage.
• Consider operating conditions: ensure the chiller can handle seasonal temperature variations.
• Factor in efficiency ratings: higher efficiency models reduce long-term energy costs.
• Evaluate space constraints: air-cooled chillers require sufficient airflow for optimal performance.

Understanding air-cooled chiller efficiency and capacity enables businesses to make smarter choices. This helps them invest in the right cooling system to balance performance, cost and sustainability.

The lifespan of an air-cooled chiller is an important consideration when investing in a cooling system. A well-maintained chiller can operate efficiently for 15 to 25 years, depending on build quality, maintenance frequency, operating conditions, and component reliability.

• Rising energy costs: efficiency drops because of component wear.
  
• Frequent breakdowns: more repairs indicate system ageing.
  
• Inconsistent cooling performance: temperature fluctuations signal system inefficiencies.
  
• Obsolete technology: older chillers may lack energy-saving features and compliance with environmental regulations.
  
• Regulatory compliance (F-gas): a chiller is running on a non-compliant refrigerant and cannot be retrofitted to an alternative. 

Regular air-cooled chiller maintenance can extend the equipment’s lifespan. This helps reduce downtime and ensures long-term cooling efficiency.

Many businesses focus on cooling efficiency. However, few use heat recovery in air-cooled chillers to improve sustainability and reduce overall energy costs. Heat recovery allows a chiller to use waste heat from the cooling process. This heat can be used for space heating, hot water and process heating. This enhances overall system efficiency and reduces reliance on additional heating equipment. 

An air-cooled chiller works by taking heat from a process or HVAC system. It then releases this heat into the air through condenser coils. In a heat recovery air-cooled chiller, heat is not wasted. Instead, it is captured and used for another purpose within the facility.

Through the recovery of heat that would be otherwise lost, businesses can achieve significant energy savings and reduce carbon emissions.

1. Partial heat recovery
   Captures a portion of the rejected heat and repurposes it for applications such as preheating water for domestic use. Ideal for moderate heating requirements without significantly affecting cooling performance.
2. Full heat recovery
   Redirects all the waste heat into a secondary system for full-scale heating. Commonly used in hot water generation, underfloor heating and industrial process heating.

• Reduces energy waste: converts unwanted heat into a useful energy source.
• Low operating costs: less reliance on separate heating systems saves money on fuel and electricity.
• Improves overall efficiency: a chiller that provides both cooling and heating optimises system performance.
• Enhances sustainability: reduces CO2 emissions by making better use of available energy.
• Supports green building certifications: can contribute to achieving certification for energy-efficient buildings.

• Hotels & hospitality: recovered heat can be used for domestic hot water and pool heating.
• Hospitals & healthcare facilities: used for space heating and sterilisation processes.
• Industrial manufacturing: provides hot water for production processes while cooling machinery.
• Commercial buildings: helps improve HVAC efficiency by using waste heat for air conditioning reheat or pre-heated ventilation.

To understand whether heat recovery is beneficial, businesses should evaluate:

• The amount of waste heat generated
• Heating demand
• Cost vs savings
• System compatibility

Adding heat recovery to air-cooled chiller systems can help businesses to boost energy efficiency and cut waste.

Air-cooled chillers are important for HVAC and process cooling systems. They provide efficient, cost-effective and reliable cooling for many uses.

Whether you’re looking to reduce energy costs, extend the lifespan of your chiller or explore heat recovery solutions, a well-maintained air-cooled chiller can deliver long-term value and operational benefits.