Chillers

Chapter One – What is a Chiller?

A chiller is a cooling mechanism designed to produce fluids that can lower temperatures by removing heat from the fluid. The type and use of a chiller depends on the required temperature and kind of refrigerant, which can be a liquid or a gas. The cooled fluid is used to cool a room or piece of equipment.

The complete process can be seen in the diagram below from Thermal Care.

Chillers operate on the principle of compression of a vapor or its absorption. They are designed to provide a continuous flow of coolant to maintain a preset temperature. As the diagram demonstrates, it is a continually circulating system of fluid that lowers the temperature.

Chapter Two - What are the Uses of a Chiller?

For many years, industries searched for ways to provide cooling for a variety of manufacturing processes. Though the basic air conditioner has existed since the beginning of the 20th Century, it did not seem capable of providing sufficient cooling for large spaces and production processes. Discoveries at the end of the twentieth century have created chilling equipment capable of creating temperatures for cooling processes for a wide variety of industries

Uses of Chillers

Industrial:

Industrial operations create heat through the use of friction, high powered equipment, and furnaces or ovens. To increase the lifespan of heavy duty equipment, a chiller circulates cooled liquid through equipment in order to maintain efficiency and productivity.

Work Environment:

On the manufacturing floor, temperatures can rise rather rapidly when equipment is in full operation, which creates an unsuitable working environment. To protect employee safety, industrial operations use chillers to keep working conditions at the proper temperature. Chillers cool work areas with chilled air much like an air conditioner. Depending on the building, air cooling chillers can be on the top of the building or inside of the building.

Plastic Manufacturing:

Plastic is a very temperature sensitive material that can be damaged by being too hot and needs to be properly cooled. The correct cooling temperature of a mold determines the quality of the final product. Chillers are used to provide a cooling bath that maintains the quality of plastic products. In the extrusion process, a heat exchanger separates the water from the extrusion process from the cooling water.

Metal Plating:

The metal plating industry uses high temperature electroplating or electroless in the plating process. The bonding a coating on metal produces extreme temperatures requiring heavy duty chillers to remove the heat from the plated metal.

Food Production:

The food industry has strict regulations regarding the storage temperatures of ingredients and products. Chillers send cooling gases through cooling coils to keep food products at an approved temperature.

Power Generation:

Power plants generate a great deal of heat to produce electrical power. Chillers cool components and processes by absorbing the heat they generate.

Medical Industry:

Medical equipment requires precision temperature control. MRI scanners, CT scanners, and LINAC machines produce heat that has to be removed and controlled. Chillers provide a constant source of cool temperatures to ensure the efficient operation of critical equipment.

Pharmaceutical:

Medicines require the use of chilled water in the manufacturing process and need precise temperature control. Chillers have the accuracy and precision for the chilling process and can be central process chillers or compact process chillers. The four basic types of pharmaceutical chillers are reciprocating, screw driven, centrifugal, and absorption.

Laser:

Laser chillers are designed to cool laser equipment or laser processes. For a laser to perform at peak efficiency, it has to maintain an optimal wavelength. CO2, high power exciters, and ion lasers have to be precise and accurate. They depend on a chiller water cooling system.

Temporary Chiller Systems

Nearly half of major construction projects have temporary HVAC systems, which are rented, installed, operated, and maintained to remove temporary heating, ventilation, and cooling systems. Builders and contractors use the flexibility of temporary systems to win contracts for their projects.

There are three common reasons for the use of a temporary HVAC system, which include:

• Heating – new construction during cold weather, when replacing equipment, or when a heating system has failed.
• Ventilation – maintaining negative pressure or circulate air in a smoke filled area
• Air Conditioning – projects being worked in the summer, replacement of present system, or when chiller plant has failed.

The portable chiller below is an example of a temporary chiller that could be used at a project site. This particular model comes air and water cooled and has other features that provide excellent and exceptional performance.

Chapter Three - How Does a Chiller Work?

Though there are a wide variety of chillers, the majority of them work on the same principle of removing heat. The most essential part of the process is the coolant or refrigerant, which holds more heat than water and aids in maintaining an efficient cooling process. Heat is removed from the coolant and released into the air.

The two main circuits of an industrial chiller are the fluid and refrigeration. The four parts of the refrigeration circuit are the compressor, condenser, expansion valve, and evaporator, while the pump, filters, and heat exchanger are parts of the fluid circuit. All of the components of the system can be seen in the diagram below from North Slope Chillers.

How Does a Chiller Work?

Compressor:

The compressor takes low pressure and low temperature refrigerant and compresses it until it becomes a high pressure and temperature gas. Three of the types of compressors are centrifugal, turbocor, and screw.

Condenser:

The compressed gas flows through coils in the condenser, where air or water moves over the coils to remove heat from the refrigerant. Once the refrigerant loses its heat, it condenses into a liquid.

Evaporator:

In the evaporator, the refrigerant returns to being a gas, becomes very cold, and absorbs heat. It is in the evaporator where the refrigerant and fluid interact, where heat is removed from the fluid to be transferred to the refrigerant. Three common types of evaporators are copper coil, shell and tube, and plate.

Expansion Valve:

The expansion valve, which may also be known as a thermostatic or electronic expansion valve, controls the amount of refrigerant that passes between the condenser and evaporator and changes the flow based on the cooling load.

Fluid Circuit

The fluid circuit or cycle carries the processed fluid to the item to be cooled and directly lowers its temperature.

Pump:

The pumping system circulates cool water, or a water/glycol solution, from the chiller to the process to be cooled

Filter:

The filter is designed to capture contaminants, dirt, and particles that may enter the chiller fluid. They are also part of the air intake system.

Heat Exchanger:

Though the condenser acts like a heat exchanger, some systems have a heat exchanger as part of the fluid cycle system, depending on the design of the system.

Chapter Four – Types of Chillers

There are several divisions of chillers based on how the refrigerant dispels the heat it absorbs, the type of compressor, and specialty designed chillers that perform unique and unusual functions. Due to technological developments, there have been improvements and changes to chillers making it impossible to have a complete list of all types of chillers.

Types of Chillers

Water Cooled Chillers:

Water cooled chillers are normally combined with a cooling tower and use a condenser water treatment system to remove mineral deposits. The cooling tower sends water to the chiller to be cooled.

Air Cooled Chillers:

An air cooled chiller absorbs heat from water and transfers it into the air and is used where discharge is not a problem. Heat from circulating chilled water is absorbed in the evaporator. In the condenser, the refrigerant condenses, releasing the heat into the air.

Screw Chillers:

Screw chillers can be water or air cooled and use a helical rotor to move and compress the refrigerant vapors.

Scroll Chillers:

Scroll chillers have a set of scrolls that are used to compress the refrigerant and operate quieter and more efficiently. Since they are environmentally friendly, they are becoming more popular.

Centrifugal Chillers:

Centrifugal chillers use compression to convert kinetic energy into static energy to increase the temperature and pressure of the refrigerant. Impeller blades pull in the refrigerant and compress it.

Absorption Chillers:

In an absorption chiller, a generator uses steam or hot water to change the refrigerant into a vapor, which moves to the condenser where the vapor is sent back to the absorber. The refrigerant vapor is absorbed by a solution, which condenses into a vapor to release heat.

Reciprocating Chillers:

Reciprocating chillers use pistons and a chamber to create pressure in the refrigerant. They can have sealed or open construction with sealed units having all of the components sealed in a single unit. Since reciprocating units function like an automobile engine, they require regular maintenance.

Explosion Proof Chillers:

Explosion proof chillers are designed for heavy duty use and must follow specific National Fire Protection Agency (NFPA) guidelines in their construction. They have a special reinforced structure for protection against flammable materials and have to be specially ordered. The main purpose of explosion proof chillers is for the protection and safety of workers. Explosion proof chillers operate on the same principles as a regular chiller but with added reinforced protection.

Low Temperature Chillers:

Low temperature chillers are for industries that operate below freezing and require chillers that can produce temperatures at – 40o F. They are used for ice rinks and petrochemical cooling. Other industries that use low temp chillers include medical and food processing as well as product testing labs.

Chapter Five – Chiller Maintenance

Though the basic mechanism of a chiller is substantially the same for all of the types, as with any type of industrial equipment, regular maintenance guarantees that it will perform according to its specifications. Manufacturers strongly encourage scheduled monitoring and checking of chiller components and provide guidelines for how it should be performed.

Chiller Maintenance

Condenser:

Heat transfer is a major part of a chiller’s operation. Condenser coils can become clogged or have free air passage.

Refrigerant:

A chiller’s ability to perform properly is highly dependent on the refrigerant. Improperly charged refrigerant can severely impact the chiller’s performance.

Water:

Water used with cooling towers has to meet the parameters for proper water flow. Debris, dirt, solids, and contaminants can interfere with water flow and be detrimental to the chiller.

Reservoir Check:

For the best performance from a chiller, all of its reservoirs should be checked to be sure they have an adequate supply of fluids.

Temperature Check:

Chillers operate at their optimum at 50o F. Unmonitored temperature changes can be harmful to the operation of the chiller. For best results, a regular examination of the glycol inlet and outlet temperatures help in catching possible problems.

Cleaning:

All equipment collects dirt and dust in the manufacturing process. For peak efficiency, the exposed parts of a chiller should be regularly cleaned. Filters should be changed to avoid clogging.

Conclusion

• A chiller is a cooling mechanism designed to produce fluids that can lower temperatures by removing heat from the fluid.
• Discoveries at the end of the twentieth century have created chilling equipment capable of creating temperatures for cooling processes for a wide variety of industries.
• There are several divisions of chillers based on how the refrigerant dispels the heat it absorbs, the type of compressor, and specialty designed chillers that perform unique and unusual functions.
• Though there are a wide variety of chillers, the majority of them work on the same principle of removing heat.
• Though the basic mechanism of a chiller is substantially the same for all of the types, as with any type of industrial equipment, regular maintenance guarantees that it will perform according to its specifications.