Air Cooled Chillers

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Introduction

This article will take an in-depth look at air cooled chillers.

The article will bring more detail on topics such as:

• Principle of Air Cooled Chillers
• How Air Cooled Chillers Work
• Types of Air Cooled Chillers
• Applications and Benefits of Air Cooled Chillers
• And much more…

Chapter 1: Principle of Air Cooled Chillers

This chapter will discuss what air cooled chillers are, their components, and their working principle.

What are Air Cooled Chillers?

Air cooled chillers are refrigeration systems that cool fluids and work in tandem with the air handler system of a facility. These types of chillers rely on fans to reject heat to the atmosphere instead of using cooling towers. The process involves air cooling water and other fluids circulating within the system to absorb and dissipate heat, thereby reducing the temperature of equipment, processes, or areas.

Key components of air cooled chillers include a compressor, evaporator, condenser, and expansion valve. They are suitable for large industrial operations and various structures such as indoor malls, hotels, and hospitals. Thanks to their design, these chillers are also advantageous for facilities with multiple buildings like theme parks. Known for their portability, affordability, and ease of installation, they are ideal for large events or emergency cooling needs. Commonly, air cooled chillers use either screw or scroll compressors.

Air cooled chillers are also referred to as modular chillers due to their ability to be stacked horizontally to enhance cooling capacity, typically ranging from 10 RT to 550 RT. Chillers using scroll compressors can achieve a maximum cooling capacity of about 200 RT, whereas those with screw compressors can go up to 550 RT. These chillers usually have two or more compressors to ensure functionality even if one fails, albeit at reduced capacity. However, their energy efficiency is lower compared to water cooled chillers, with air cooled systems having an efficiency of around 1.00 kW/ton compared to 0.50 kW/ton for water cooled systems.

Components of an Air Cooled Industrial Chiller

The components of an air cooled chiller include:

Air Cooled Industrial Chiller Compressor

The compressor, the driving force of the refrigerant, can vary in type: screw, reciprocating, scroll, rotary, or centrifugal. The centrifugal type is unique as it employs dynamic compression rather than the positive displacement method used by the other types. In positive displacement compressors, a constant amount of gas is compressed, thereby increasing pressure through mechanical action.

Compressors can be hermetic, semi-hermetic, or open. Hermetic compressors have the motor and compressor sealed in a non-openable casing, suitable for low-capacity applications. Semi-hermetic compressors feature a two-piece casing, allowing maintenance access. Open compressors separate the motor from the housing but connect them via a coupling, making them ideal for high-capacity needs.

Air Cooled Industrial Chiller Condenser

The condenser in air cooled chillers is a heat exchanger that transfers heat from the refrigerant to the air. They commonly consist of copper tubes carrying refrigerant and aluminum fins aiding heat transfer. Air cooled condensers utilize air as a cooling agent. Water cooled and evaporative condensers are variants but are less common. The evaporative type uses both air and water for cooling.

Evaporative condensers use water to cool the refrigerant through evaporation. In air cooled chillers, the emphasis is on air as the cooling medium, as it's blown across the condenser fins, facilitating heat dissipation and the transition of refrigerant back to liquid form.

Air Cooled Industrial Chiller Condenser Fans

The condenser fans distinguish air cooled chillers from their water cooled counterparts by moving air across the condenser to expel unwanted heat. This initiates the cooling cycle anew.

Air Cooled Industrial Chiller Expansion Valves

The expansion valve regulates refrigerant flow between the condenser and evaporator, adapting to cooling load variations. It converts high-pressure refrigerant to a low-pressure mixture, enabling it to absorb heat efficiently in the evaporator. Various types exist including thermal, low pressure, high pressure, electronic, and automatic, each maintaining the balance between condenser and evaporator pressures efficiently.

Air Cooled Industrial Chiller Evaporator or Heat Exchanger

The evaporator functions as a heat exchanger, cooling the refrigerant by converting it to gas. The main types are shell and tube, finned, and plate evaporators, each with unique designs to maximize heat transfer and efficiency. These configurations often involve copper or steel tubing, aluminum fins, or grooved metal plates.

The purpose of this component is to cool down the refrigerant. It achieves this by transforming it into gas. The purpose of the cooldown of the refrigerant is for the collection of heat from the water that comes from the fan coil to the evaporator, or air handling units to the evaporator.

The evaporators are classified into three categories based on their structure:

1. Shell and Tube: Often composed of copper or steel tubes, used mainly for cooling liquids.
   
2. Finned Evaporators: Incorporate fins over tubes to enhance heat transfer and cooling efficiency.
3. Plate Evaporators: Feature two metal plates with grooves or tubing in between, improving contact and efficiency using indentation-filled solutions.

This improves the contact between the tube running the refrigerant and the plates.

Air Cooled Industrial Chiller Filter Drier

Filter driers eliminate contaminants and moisture, protecting the chiller system. Regular replacement ensures optimal operation.

Chapter 2: How Air Cooled Industrial Chillers Work

The working principle of air cooled industrial chillers is based on the absorption of heat from processed water. Once the air handler system uses up the water, it becomes warm and is returned to the chiller. The chiller’s evaporator is utilized to transfer heat away from the water. A low-pressure gas is created by the evaporation of liquid refrigerant over the evaporator tube. Next, the refrigerant that has been evaporated travels to the compressor. At the compressor, low-pressure gas is compressed into high-pressure gas.

The gas will then leave and travel to the air cooled condensers. While inside the condenser, heat is removed from the chiller by blowing out the heat to the outside through the fans located on the side of the condenser. It is ideal if the chiller is placed outdoors or in a large indoor location. This is so because the heat is blown outside the chiller, and the excess heat effect is reduced.

The refrigerant turns into a high-pressure liquid soon after the gas leaves the condenser. The high-pressure liquid then flows to the evaporator via the expansion valve. As this process takes place, the refrigerant changes from a high-pressure liquid to a low-pressure liquid. Since an industrial air cooled chiller’s working principle is also based on a continuous cycle, this low-pressure liquid will then be transferred back to the evaporator. At the evaporator, the whole cycle repeats itself.