Water Cooled Chiller Design Data

Water cooled chiller design data. In this article we are going to be taking a very detailed look at the design data for a centrifugal, water cooled, chiller. This is a pretty advanced chiller video, so if you're new to the topic then I highly recommend you start from the basics first.

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Scroll to the bottom to watch the YouTube tutorial video on chiller design data.

I want to stress that this is simply design data. Every chiller is different and you should speak to your manufacturer for the relevant information. The results will vary from the real world and also with loading.

In the illustration above we have shown the main chiller components. The compressor, which is the driving force of the refrigerant around the system. The condenser which removes the unwanted heat from the system and send this to the cooling tower. The expansion valve which expands the refrigerant and controls the superheat into the compressor and the evaporator which collects the unwanted heat coming from the building and generates the chilled water.

We're going to be looking at all the points on these two charts to see the pressure, temperature, enthalpy and entropy are around this system. The left chart is our Temperature v's Entropy chart and the right chart is our Pressure v's Enthalpy chart.

• Point 1 is just before the compressor, and the exit of the evaporator. That will be a low pressure, low temperature saturated / slightly superheated vapor.
• Point 2 is just after the compressor, before the condenser. That's a high pressure, high temperature superheated vapor.
• Point 3 is just after the condenser, but before the expansion valve. That's going to be a high pressure, medium temperature saturated liquid.
• Point 4 is just after the expansion valve but before the evaporator. This will be a low pressure, low temperature and it's going to be a mix between a liquid and vapor.

Compressor

In this example the compressor is pushing a refrigerant with a flow rate of 16.5 kg/s (36.4 lbm/s). That motor is then consuming 425.9 kilowatts and the compressor is running 100% load. If the chiller runs at part load then the values will be different.

The refrigerant is being sucked in from the evaporator (Point 1) at around 356 kPa (3.56 Bar) and at a temperature of 5.5 ° C (41.9 ° F). The refrigerant enthalpy is 402 kJ/kg (173 BTUs/lbm). The entropy will be 1.73 kJ/kg.K (0.41 BTUs/lbm.F).

The compressor is compacting the refrigerant into a smaller space, and looking at our charts we know that the enthalpy is going to increase, the entropy is going to slightly increase and the pressure and temperature will massively increase.

When the refrigerant leaves (Point 2), it will be 915 kPa (9.15 bar). The temperature reaches 43.6 ° C (110.5 ° F). The enthalpy is now 426 kJ/kg.K (183 Btu/lbm) and the entropy is now 1.74 kJ/kg.K (0.042 Btu/lbm.F).

Remember the temperature of the refrigerant entering into the condenser has to be higher than the incoming condenser water temperature for heat transfer to occur. If they were the same temperature, then no heat transfer would occur and the chiller would do no cooling.

Condenser

The next part we'll look at is the condenser. In this example the condenser water is flowing through the condenser at 116.6 L/s (247 cfm). The condenser water is coming into the condenser, from the cooling tower, at 29 ° C (84.2 ° F). The refrigerant will then transfer the buildings unwanted heat into the condenser water. This will increase the temperature of the condenser water, so when it leaves to go back to the cooling tower it will be around 35 ° C (95 ° F).

Now the reason the flow rate is higher in the condenser compares to the evaporator is because the condenser has to reject more heat. It also has to take the heat away from the compressor and other parts of the machine.

The refrigerant came from the compressor and entered the condenser at a pressure of 915 kPa (9.15 Bar), a temperature of 43.6 ° C (110.5 ° F) with an enthalpy of 426 kJ/kg.K (183 Btu/lbm) and an entropy of 1.74 kJ/kg.K (0.428 Btu/lbm.F).

Once the refrigerant has give away some of its energy to the circulating condenser water, it will now leave as a liquid at 36.1 ° C (97 ° F) but still at the same pressure as it entered. It's entropy will have dropped to 1.17 kJ.kg.K (0.28 BTU/lbm.F) and the enthalpy increases to 250 kJ/kg.K (107.5 BTU/lbm). It then enters into the expansion valve.

Expansion Valve

The expansion valve controls the flow of refrigerant, it measures the superheat on the suction line of the chiller and then reacts to this by allowing or restricting refrigerant flow to maintain a certain value. The refrigerant is entering the expansion valve as a liquid and leaving as a vapour/liquid mixture.

It enters, in this example, at a temperature of 36.1 ° C (97 ° F), a pressure of 915 kPa (9.15 Bar), the entropy is 1.17 kJ.kg.K (0.28 BTU/lbm.F) and the enthalpy is 250 kJ/kg.K (107.5 BTU/lbm).

The refrigerant is expanded through a small orifice which sprays the refrigerant. It expands into a larger volume and decreases in pressure as a result, which allows it to drop in temperature as it's now not packed so tightly. It will leave at a temperature of 5.5 ° C (41.9 ° F), a pressure of 356 kPa (3.56 Bar) and from the charts we know it will maintain the same enthalpy but the entropy will change slightly and it leaves at 1.20 kJ/kg.K (0.29 BTU/lbm.F).

Evaporator

The evaporator generates the cold 'chilled water' which cycles around the building, providing air conditioning and collecting the buildings unwanted heat. This now warm chilled water returns to the evaporator and transfers this heat into the refrigerant, the chilled water then leaves cooler and cycles around the building, meanwhile the refrigerant boils and carry's the thermal energy to the compressor.

In this example, the chilled water is flowing through the evaporator at around 99.5 Litres per second, which is around 210 cubic feet per minute. The chilled water enters the evaporator at around 12 ° C (53.6 ° F). After the chilled water has transferred it's heat over to the refrigerant, it will leave the evaporator at around 6°C (42.8°F).

The refrigerant is picking up thermal energy but the temperature only changes slightly which confuses many people. The reason it doesn't increase dramatically is because it is undergoing a phase change from a liquid to a vapour so the thermal energy is being used to break the bonds between the molecules. The enthalpy and entropy will increase and this is where the energy is going

When the refrigerant leaves it will be a slightly superheated vapour at 5.5 ° C (41.9 ° F), a pressure of 356 kPa (3.56 Bar) an entropy of 402 kJ/kg.K (173 Btu/lbm) and an enthalpy of 1.73 kJ/kg.K (0.41 btu/lbm.F).

The refrigerant then returns to the compressor to start the cycle all over again.

WHAT IS A CHILLER & HOW DOES IT WORK? | INDUSTRIAL CHILLER WORKING PRINCIPLE

If your facility uses process fluids or heavy-duty machinery that generates heat, you'll need an industrial chiller system to cool your processes and internal machine components. Understanding how an industrial chiller works and the various types of chillers available will help you make the right choice for your cooling needs.

What Is a Chiller?

An industrial chiller is a refrigeration system used to lower the temperature of machinery, industrial spaces, and process fluids by removing heat from the system and transferring it elsewhere. Industrial chillers are essential for temperature regulation in several industrial processes, such as injection molding, metal plating, oilfield production, and food processing.

Why Use a Chiller?

Industrial chiller systems are beneficial for applications where strict operational temperatures are required. When integrated with heat-sensitive processes, chillers will prevent thermal damage to process equipment and ensure no alterations to the final products from exposure to unsuitable temperatures.

Working Principles

Industrial chillers work based on the following principles of operation.

1. Phase Change: When heated, a liquid coolant undergoes a phase change into a gas, and when the gaseous coolant is supercooled, it condenses back into a liquid.
2. Heat Flow: Heat energy always flows from an area of high concentration to an area of lower concentration.
3. Boiling Point: Reducing the pressure over a liquid decreases its boiling point, and increasing the pressure increases its boiling point.

How Does a Chiller Work?

An industrial chiller system is driven by one of two operational principles:

• Heat absorption
• Vapor compression

Heat absorption chillers integrate heat exchangers that pull heat away from any associated processes and dissipate them exteriorly. Heat exchangers are typically composed of piping containing coolant fluids (air, water, or a mixture of water and other liquids).

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Vapor compression chillers achieve a cooling effect by circulating coolant in pipes through the processes requiring cooling. This will pull heat from any associated processes into the coolant, which is then circulated to a refrigerant system that cools the chiller fluid and prepares it for a new cycle of process cooling.

Chillers consist of four essential components; an evaporator, a compressor, a condenser, and an expansion unit. In addition, every chiller system contains a refrigerant.

The process starts with a low-pressure refrigerant entering the evaporator. Inside the evaporator, the chiller refrigerant is heated, causing it to undergo a phase change into a gas. Next, the gaseous refrigerant goes into the compressor, which increases its pressure.

The high-pressure refrigerant goes to the condenser, which rejects the heat using cooling water from a cooling tower or air from the surroundings, condensing it into a high-pressure liquid. The condensed refrigerant then goes to the expansion unit, which has a valve that acts as a metering device to limit refrigerant flow. Learn about new chiller refrigerants.

Consequently, this lowers the pressure of the refrigerant and begins the cooling process again. The entire process is known as the refrigeration cycle.

Basic Chiller Components

The central chiller components include the following:

• Condenser
• Compressor
• Evaporator
• Expansion valves
• Power unit
• Control unit
• Water boxes

Condenser

The function of a chiller condenser unit is to eliminate heat from the refrigerant being circulated through the chiller unit. This is achieved by circulating water between a cooling tower and the condenser for water-cooled variants or blowing cool air over condenser piping for air-cooled chiller units.

Compressor

The compressor is the driving unit of any chiller system. It generates the pressure gradient necessary to push refrigerant around the chiller unit to achieve process cooling. Various condensers are available, with the most popular types including centrifugal, screw, and reciprocating compressors.

Evaporators

An evaporator is placed between the expansion valve, and the condenser removes heat from any associated process into circulating refrigerant. This is then channeled to a cooling tower or air-cooled depending on the chiller configuration.

Thermal Expansion Valves

Thermal expansion valves located between the compressor and the evaporator serve to expand refrigerant passing through them. This action diminishes the pressure and improves the heat elimination from the evaporator.

Power Unit

Every chiller incorporates a power unit that controls electrical energy flowing through the system. Power unit components usually include starters, power monitoring panels, and circuit breakers.

Control Panels

Control panels serve to regulate the entire process of cooling operation. They usually integrate sensors, alarms, and display screens that allow operators to adjust system settings for optimal thermal control.

Water Boxes

These devices may be mounted on either the chiller system evaporator or its water-cooled condenser. Their purpose is to conduct water flow effectively.

Types of Industrial Chillers

The three main types of chillers in use today are air-cooled chillers, water-cooled chillers, and absorption chillers. We will also briefly touch on cooling towers (an alternative or supplemental cooling system) and special chillers like glycol and centrifugal.

Selecting the right chiller for your application will help you to save costs, reduce downtime, and improve operational efficiency.

Water-Cooled Chillers

Water-cooled chillers use water from an external cooling tower to reject heat from a gaseous refrigerant in the condenser before it undergoes a phase change into a liquid.

Air-Cooled Chillers

In place of the cooling water, air-cooled chillers use ambient air to reject heat from the refrigerant in the condenser. Learn more about air-cooled vs. water-cooled chillers.

Vapor Compressor Chillers

This type of chiller uses refrigerants to cool process fluids and spaces. A compressor is used as the driving force to pump refrigerant around the system.

Vapor Absorption Chillers

Vapor absorption chillers have no compressor in the unit. Instead, they use a heat source, e.g. solar energy or waste heat to drive the coolant through the system.

How does an absorption chiller work?

The process starts with liquid coolant in an evaporator which turns it into gaseous form. Next, the gaseous coolant is absorbed by a concentrated absorbent such as Lithium Bromide or Ammonia, provided by a generator. Finally, the diluted solution absorbs the coolant while the heat is absorbed by the cooling water.

The diluted solution of coolant and absorbent flows through a heat exchanger to the generator, where it is heated. The coolant vaporizes out of the solution, condenses, and is sent out for cooling again. The now-concentrated absorbent is recycled as well.

Glycol Chillers

Glycol chillers are special types that use propylene glycol, an anti-freeze, in the system. They are widely used in food-grade applications such as in the production of alcohol and for brewery chilling systems.

How does a glycol chiller work?

The mode of operation of glycol chillers is the same as a standard chiller.

Centrifugal chillers

Centrifugal chillers consist of the usual evaporator, compressor, condenser, and expansion device set-up but with additional rotating impellers which compress the refrigerant and transport it around the system.  They are beneficial for medium to large-scale cooling operations (from 150 ' tons of refrigeration).

Uses of Industrial Chillers

Industrial chiller systems can be used for cooling operations in diverse industries. Below are some of the most common applications:

• Food Processing ' Industrial chillers are used extensively in food production and processing operations, which require a high degree of precision in temperature control. For instance, winery chillers are used for temperature control during the fermentation and storage of wine. Likewise, bakery chillers help with mixer cooling, potable water cooling, and cooling jacketed tanks of yeast which are all critical bakery components.
• Metal Finishing ' Temperature control is essential in metal finishing processes such as electroplating or electroless plating to remove the excess heat as they typically require very high temperatures (several hundred degrees) to bond the metals. Some industries use metal-finishing chillersto cool the anodizing liquid in a heat exchanger or use glycol/water as a cooling medium to lower the temperature inside the tank.
• Injection Molding ' Injection molding is a mass-production technique for creating plastic parts using an injection-molding machine, thermoplastic pellets, and a mold. The process and melt must be maintained within precise temperature limits to prevent problems such as cracks, warping, and internal stresses in the final product. An injection molding chillercan supply a stream of supercooled fluid to cool the mold at an ideal rate to ensure optimum product quality.
• Space Cooling ' In manufacturing plants that generate a lot of heat from the heavy-duty machinery they use, a chiller can help prevent temperature extremes in the offices and other working spaces. They also help save costs on purchasing separate HVAC systems for cooling.

Determining the Right Size of Chiller for Your Needs

An adequately sized chiller is critical for efficient and cost-effective processes, machinery, and space cooling. Cold Shot Chillers' easy-to-use sizing tool can help you quickly determine your optimal chiller capacity, tonnage, and size.

Getting The Most Out of Your Chiller

The cost of installing and operating chiller systems can be pretty high. Chiller units must be run as efficiently as possible to avoid additional charges during routine operation. Scheduling and conducting regular maintenance for your system will prevent costly chiller repairs in the long term. Applicable chiller maintenance should include condenser coil inspection and cleaning, condenser water, and refrigerant maintenance. Real-time monitoring apps like Cold Shot Guardian® can be used to monitor equipment, predict system failures and suggest pre-emptive interventions.

Trust Cold Shot Chillers for All Your Chiller Needs!

With over three decades of expertise in manufacturing industrial chiller systems, Cold Shot Chillers provides cooling equipment and expertise for the most challenging process cooling needs.

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