Author: Gerson Mora

Looking for the right capillary tube size for your refrigeration system can be a daunting task, but fear not, the R22 Capillary Tube Chart is here to help!

This chart is a lifesaver for refrigeration technicians, allowing them to choose the perfect diameter and length of capillary tube based on the system’s evaporator temperature and cooling capacity.

When it comes to sizing capillary tubes, there are a few rules to keep in mind.

• The tube’s diameter and length both play a critical role in determining its total restriction. Interestingly, even a slight percentage change in diameter can have a more significant impact on flow than a change in length.
• You can also change the restriction by altering the tube’s length. Longer tubes result in slower flow rates, so going to extreme lengths to increase restriction may not always be the best idea. Once the pipe length decreases, the flow rate gradually increases until it reaches a critical point where the flow rate starts to rise rapidly with each reduction in length.
• However, when the pipe becomes too short, even small changes in length can cause significant increases in flow. At this point, the tube starts acting more like an orifice than a capillary tube.
• As a general rule of thumb, it’s best to keep your capillary tube length between 5 and 16 feet. Of course, there are always exceptions, but staying within this range for day-to-day operations can help eliminate many problems.

When using the R22 Capillary Tube Chart, the evaporator temperature is the first parameter to consider. Take into account:

1 HP = 746W

Cooling Capacity

It is the cooling capacity of a compressor at a given evaporation temperature of refrigerant r22. It represents a base parameter for selection, it is measured in Btu/h, Kcal/h and some models in the international system use W, it should not be confused with electrical power, because in this case we are talking about energy in the form of heat.

Chiller Fault Finding is divided into:

1. Chiller failures in the refrigeration cycle.
2. Chiller failures in the control system.
3. Chiller failures originating in the hydraulic circuit.

Chiller failures in the refrigeration cycle include:

• Low suction pressure in a chiller:
  • Caused by a lower amount of refrigerant in the circuit due to leaks or improper recharge.
  • Insufficient water flow through the cooler or evaporator compared to the chiller’s capacity.
  • Reduced thermal load in the application.
  • Inadequate chiller control strategy with an excessive number of compressors operating.
  • Issues with the expansion valve or temperature sensors.
  • Lack of maintenance and poor cleaning of the evaporator.
  • Chiller not adequately adapted to partial loads due to low IPLV values.
• Compressor with a flooded start:
  • Occurs when refrigerant migrates into the compressor crankcase while it is off.
  • Migration is caused by temperature, concentration, and pressure differences.
  • The presence of liquid refrigerant in the crankcase displaces and dilutes the compressor oil, leading to wear in vital parts.
  • Proper operation of the heating elements in the compressor crankcase and adherence to manufacturer’s design and control strategies are crucial to prevent this failure.
• Refrigerant liquid in the suction of the compressor in operation:
  • Refrigerant should only enter the suction of the chiller compressor in a vapor state.
  • Liquid refrigerant cannot be compressed by the compressor and can cause severe damage.
  • Improper control strategies or issues with the expansion valve can result in liquid refrigerant in the compressor suction.
  • Modern chillers may experience inadequate control strategies due to sensor problems.
  • Proper functioning of the expansion valve is essential to eliminate this problem.
• High discharge temperature:
  • High discharge temperatures degrade the compressor oil and affect vital properties such as viscosity.
  • Potential causes should be investigated and addressed.
• Lubrication-related failures:
  • Check oil traps, the compressor station’s lubrication system, oil separator, and details in new installations such as pipe diameter.

What failure presents the compressor according to the color of the oil?

• Colorless or light yellow:
  • Indicates good performance.
• Black oil:
  • Indicates carbonization caused by air in the system or the presence of wear particles containing iron.
  • Change compressor oil and oil filter.
• Light brown oil:
  • Use an acid test kit to test for acidity in a sample of the compressor oil.
  • Change the compressor oil if the test indicates acidity.
  • Indicates that dissimilar metal surfaces have become coated with copper due to moisture in the system.
• Brown oil:
  • Indicates air in the system or high compressor temperature.
  • Chemicals can cause oxidation, resulting in the oil turning brown.
  • Change compressor oil if the test indicates acidity.
  • Copper plating may occur due to moisture combining with the refrigerant, forming an acidic solution that dissolves copper-containing materials.
  • Inspect and replace worn or damaged components.
• Metallic gray oil:
  • Indicates the presence of wear and particles containing aluminum.
  • Usually caused by bearing wear or piston scoring.
  • Disassemble the compressor and inspect for worn or damaged components.
  • Change the oil and oil filter.
• Green oil:
  • Green compressor oil indicates water in the system, and copper coating may have occurred.
  • Disassemble the compressor and shaft seal.
  • Inspect wheels, gears, and rotors.
  • Replace the oil separator, oil, and oil filter.

What are the breakdowns of a chiller evaporator?

The problems in the evaporator of a chiller are presented by:

• A dirty evaporator with scale buildup that hinders heat exchange between the refrigerant in the refrigeration circuit and the chilled water.
• A low flow of water to be cooled can cause the evaporator to freeze.
• A low refrigerant charge in the chiller’s refrigeration cycle can result in poor cooling quality.
• Inadequate chiller control strategies can lead to excess or insufficient cooling in the chiller evaporator.
• Failure of water or chiller refrigerant temperature sensors can result in inadequate control strategies.

Chiller condenser high-pressure faults:

Depending on the cooling method of the condenser, the following issues may arise:

• For air-cooled condensers, verify the adequate fan speed.
• Check the condition and cleanliness of the condenser for efficient thermal exchange.
• If the condenser is water-cooled, check for the concentration of embedded particles on the condenser walls that may impede heat exchange.
• Insufficient cooling tower performance can hinder proper freshwater conditioning.

Chiller failures in the control system:

Chiller sensor failures:

• Temperature sensor failures:
  • Temperature sensors in chillers are often of the thermoresistance type.
  • Resistance thermometers, such as the PT1000, provide linear temperature signals.
  • Use an acid test kit to check the acidity of the compressor oil sample.
  • Change the compressor oil if the test indicates acidity.
  • Failure of temperature sensors can cause the unit to stop to prevent damage due to insufficient water flow.
  • The compressor discharge temperature sensor informs the controller of the superheated steam temperature at the compressor outlet.
  • Monitor values provided by the temperature sensor to prevent damage to the oil or compressor components.
• Pressure sensor failures:
  • The discharge pressure sensor allows control measures to be taken to prevent chiller problems.
  • The suction pressure sensor recognizes refrigerant overheating at the chiller evaporator outlet.
  • Use a digital multimeter to measure the supply voltage and signal and a pressure gauge to measure exact pressures.
  • Compare the pressure values from the gauge with those transformed by the sensor.
  • If the pressure sensors send out-of-range signals to the controller, the equipment will be stopped.

Ensure proper functioning of sensors and address any faults in the thermistor, engine cooling system solenoid, or wiring.

Hydraulic circuit failures:

Air inside pipes: Air can be introduced into the pipes, affecting heat exchange. The percentage of air dissolved in the water depends on the temperature and pressure. Higher pressure leads to a higher content of dissolved air in the water. With higher temperatures, the dissolved air content decreases. Under conditions of high temperature and low pressure, oxygen is released in greater proportion. Changes in pipe slope cause pressure variations that can release dissolved air, forming air pockets. The air pockets move through the pipeline and accumulate in higher areas. Air pockets also accumulate in exchangers, affecting their performance.

Issues with the expansion vessel: The expansion vessel has a gas-filled membrane that can absorb changes in water volume without affecting the system. To avoid failures, it is necessary to know the manometric height and the minimum and maximum working pressures when calculating an expansion vessel. Having very large or small vessels does not achieve the desired function. The operation of the vessel at different locations (highest point, basement, before or after pumping equipment) differs. A pressure measuring device should be installed in the supply line to the vessel as a standard requirement. The expansion vessel marks the reference pressure value of the closed circuit. Pressure measuring equipment must be installed in the supply line to the vessel.

Failures with pumps in installations with chillers: Installations with chillers require centrifugal pumps to move water through the pipes.

PRIMARY PUMPS: Responsible for sending water to the chiller.

SECONDARY PUMPS: Responsible for sending chilled water to the desired point.

CONDENSER PUMPS: In the case of chillers with a water-cooled condenser, an additional pump system is required to deliver water to the condenser and cooling tower.

Possible pump failures and solutions:

• Pump on but no water supply:
  • Verify that the suction pipe is full and free of air or obstructions.
  • Check the condition of the foot valve and filter for any blockages.
  • If there is no water in the suction pipe, prime the pump by removing the priming plug and adding water until no air comes out and the water overflows. If the pipe doesn’t fill, replace the foot valve.
  • Check the motor’s rotation direction.
• Low water flow:
  • Air ingress in the suction pipe or through the seal.
  • If the pump has gaskets, replace them if excessive fluid leakage is observed.
• Motor overload:
  • Check if the equipment is operating within the correct range.
  • Throttle the discharge valve to decrease pump flow.
  • Inspect impeller blades for damage that may cause imbalance and vibrations affecting motor operation.
  • Check motor bearings, pump shaft, and insulation in motor coils.
  • Ensure proper alignment.
  • Loss of prime in the pump.
  • Defective foot valve and water leakage.
  • Water leaks due to damaged seals or gaskets.
  • Leaks in piping or fittings.
  • Air ingress in the suction pipe or excessive leakage in the discharge area.
  • Premature failure of seals or gaskets.
  • Unbalance or misalignment.
  • Lack of lubrication.
  • Verify that the pump is not running idle.

Water treatment for the chiller system generally includes the following filtration steps.

• Filtration and Ultrafiltration Processes.
• Ion exchange and water softening.
• Addition of chemicals.
• Reverse osmosis systems.

Water Treatments for Chillers

The precise treatment processes fluctuate depending on the cooling tower’s needs, the state of the circulation, and the feed water. Next, we will explain the basic steps mentioned above.

Filtration and Ultrafiltration:

• Filtration is a process required to remove impure substances, such as organic matter and suspended solids, from the feed water.
• It is more effective to use filtration systems at the initial stage, as the eradication of suspended particles upstream can maintain the safety and efficiency of membranes and ion exchange resins against fouling

Ion exchange for water softening:

• If the water contains large amounts of hardness, there are certain treatments available to remove it.
• Water softening systems are effective at removing ions that cause water to increase in hardness.
• Typically, these ions tend to be magnesium, calcium, and iron ions which are selected and removed.
• Ion exchange resins provide a similar function by replacing these hardening ions with non-hardening ions, such as sodium ions.

Addition of chemicals:

• At this stage, chemicals such as anti-acid bicarbonates and other inhibitors are usually added to prevent the build-up of scale deposits.
• Fortunately, pretreatment can decrease the number of chemicals required during this stage, which is preferable since many of these chemicals are expensive.

Reverse Osmosis Systems:

• Reverse osmosis systems remove virtually all unwanted dissolved solids by filtering the feed water using high-quality semi-permeable membranes.
• The reverse osmosis process is incredibly efficient at producing ultrapure water for consumption or use in a variety of applications and is often the backbone of any well-designed water purification system.

Why is it essential to treat chiller water?

• While many problem areas can affect chiller performance, perhaps the biggest culprit is the contamination of its heat transfer surfaces.
• If a chiller’s tubes become covered or clogged with scale, sediment, or biological growth, their ability to transfer heat is significantly reduced.
• The rate at which this fouling occurs is highly dependent on the quality of the water in the system, but even a thin layer of contamination can significantly reduce overall efficiency.
• Chemical water treatment helps prevent this buildup of contaminants on heat transfer surfaces.
• Open systems, such as condenser water systems, that include a cooling tower require an ongoing chemical water treatment program.
• Closed systems generally require only a one-time chemical treatment.
• Concentration levels of water treatment chemicals that are too low, or that do not match the conditions encountered, will be ineffective.
• The wrong chemicals or concentrations that are too high can damage internal components.
• Even with a good water treatment program, the cleaning of chiller condenser tubes will be necessary.
• With a brush, annual cleaning can remove mud buildup, biological growth, and any loose material.
• If there is a buildup of scale on the tubes, it will usually need to be removed by a chemical cleaning process.

Glycol chiller maintenanceis of special importance to maintain the quantity and quality of the chilled water that is supplied and to avoid inconveniences with freezing of the fluid, deterioration of facilities, and heat exchange problems.

Ethylene glycol:

Ethylene glycol is an efficient and generally less expensive antifreeze protectant than propylene, but it is toxic and therefore facilities must adhere to proper safety protocols when applying or discharging it.

Propylene glycol

This is a non-toxic alternative to ethylene glycol, but it is also more expensive. For facilities that process food or those with green or organic initiatives, this is the obvious choice.

Aspects of Glycol Maintenance in Chillers:

• Checking for good glycol pressure is one way to verify that the pump is working and that the chiller is delivering the normal amount of glycol.
• An extreme drop in pressure could mean there is a problem with your process piping or a low glycol level in your reservoir.
• Checking the glycol level in your reservoir is easy to do as there is an external sight tube.
• Low glycol levels can cause major difficulties throughout the cooler.
• Checking the glycol mix is ​​done with a refractometer.
• Keeping the glycol at a 26.5 Brix mix is ​​a must in your cooler. That results in 35% propylene glycol to 65% water.
• Test the freezing point of the mixture.
• Adjust or replace mix as needed. Typically, the range is 20-25% glycol; however, each manufacturer is different, so check their recommendations before making any changes.
• If the glycol levels are too low, or the glycol in your system breaks down, you may be in for some expensive difficulties.
• Calculate the lowest temperature your system can be subjected to, to determine the desired freezing point. Then refer to the freezing point table (for example, the one above) to find the desired concentration.
• Ideally, the pH should be between 8 and 10. If your pH is too low, you may need to add additional inhibitors or flush and refill the system, depending on your lab results.
• Measurement of the alkalinity reserve will help determine whether the liquid can be restored. If the reserve alkalinity is depleted, the useful life of the fluid has expired and the system will need to be flushed and refilled.
• Automotive antifreeze should never be used because it is formulated to cool the engine and can cause difficulties with flow rates with pressures, and reduced heat transfer.
• Uninhibited glycol and water mixtures are highly corrosive. Inhibitors protect against corrosion, scale, and rust and act as pH buffers and biocides.
• Never use less than 25% glycol, this will ensure that an adequate amount of inhibitors is present. Never over mix – use only the concentration of glycol needed to protect equipment.
• DO NOT mix different types of glycol or different brands. Incompatibilities can lead to formulation separation, plugging filters, strainers, and pump suctions, as well as reducing its transfer properties.
• Check local regulations for measures regarding glycol and antifreeze solutions. Soil structure, water table, drainage, and disposal may be things to consider.
• A glycol solution is denser than water and does not offer the same level of heat transfer as water. Therefore, it will produce slightly reduced cooling capacity, exclude pumping power consumption, and highlight fluid temperature differences.
• Most systems use running water from the “tap”. However, the proper application of inhibitors is vitally important to prevent damage to the cooling system.
• Using distilled, demineralized, deionized, or RO water will eliminate all the unpredictability associated with public mains water.
• The chilled water system must be flushed, cleaned, and sanitized before adding a new water-glycol solution.
• The water and glycol solution should be sampled and analyzed periodically to ensure that no problem arises.