A Comprehensive Guide to Charging Your Refrigeration System with Freon Gas

Posted on 24 August 2023 by chiefengineerslog

Refrigeration systems are devices that transfer heat from a lower temperature region to a higher temperature region, using a working fluid called refrigerant. The refrigerant undergoes phase changes from liquid to vapor and back to liquid as it circulates through the system, absorbing and releasing heat. One of the most common refrigerants used in refrigeration systems is freon gas, which is a generic term for a group of chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs).

Example of provision refrigeration system onboard vessel

Maintaining and servicing a refrigeration system requires careful attention to detail, especially when it comes to charging the system with the right amount of Freon gas. The performance and efficiency of a refrigeration system depend largely on the amount and quality of the refrigerant in the system. Too much or too little refrigerant can cause problems such as reduced cooling capacity, increased energy consumption, compressor damage, and environmental pollution. Therefore, it is important to charge the refrigeration system with the correct amount and type of refrigerant, following proper procedures and safety precautions.

In this comprehensive guide, we’ll walk you through the step-by-step process of charging your refrigeration system with Freon gas, including the proper use of a recovery bottle, which is a device that collects and stores the excess or contaminated refrigerant from the system. We’ll also delve into potential problems that might arise during charging and provide troubleshooting tips to help you identify and resolve issues effectively.

Understanding the Importance of Proper Charging

Properly charging a refrigeration system is essential to ensure its efficient cooling capacity and prevent potential problems such as reduced performance, increased energy consumption, and even compressor failure.

Icing evaporator

Overcharging or undercharging the system can lead to serious issues, including decreased cooling efficiency, frost formation on evaporator coils, and potential damage to components due to inadequate lubrication.

Step-by-Step Guide to Charging with Freon Gas

Gather the Necessary Equipment: Before you begin the charging process, ensure you have the required tools and equipment, including a recovery machine, a recovery bottle, a pressure gauge, a charging hose with a manifold gauge set, and the appropriate type and amount of Freon gas. To learn more about EU-regulation related to the type of Freon approved to use, please follow THIS LINK.

Recover Existing Refrigerant (if needed): If you’re working on an existing system, you might need to recover any remaining refrigerant. Use a recovery machine to safely remove the old refrigerant from the system and store it in a recovery bottle according to environmental regulations. To learn more about refrigerant regulations, please follow THIS LINK.

Prepare the System: Ensure that the refrigeration system is turned off and has equalized in pressure. Connect the manifold gauge set to the system’s low and high-pressure ports.

Attach the Charging Hose: Connect the charging hose from the manifold gauge set to the refrigerant supply cylinder, ensuring a secure and leak-free connection.

Purge the Charging Hose: Before connecting the charging hose to the system, carefully purge it to eliminate any air or contaminants. This can be done by briefly opening the hose valves and allowing a small amount of refrigerant to escape before closing them again.

Charge the System: Slowly open the valve on the refrigerant supply cylinder and begin charging the system. Monitor the pressure gauges on the manifold gauge set to ensure that the system’s pressures are within the recommended range for the specific refrigerant type and ambient conditions.

Monitor Superheat and Subcooling: As the system charges, keep an eye on the superheat (for evaporator coil) and subcooling (for condenser coil) temperatures. Adjust the charging process accordingly to achieve the recommended superheat and subcooling values for the specific refrigerant and system.

Seal and Disconnect: Once the system is properly charged and the pressures and temperatures are stable, close the valve on the refrigerant supply cylinder. Disconnect the charging hose from the system’s ports and securely close the manifold gauge valves.

Check for Leaks: It’s crucial to perform a leak check to ensure that there are no refrigerant leaks in the system. Use a refrigerant leak detector or a soap solution to check for any escaping gas.

Liquid Recovery Method

The liquid recovery method is one of the most common and efficient methods of charging a refrigeration system with freon gas. In this method, the refrigerant is transferred while still in the liquid state, which minimizes the loss of refrigerant and reduces the charging time. The liquid recovery method can be used for most types of refrigeration systems, regardless of the metering device (such as TXV, capillary tube, or piston).

Recovery method schematic example. Source and credit: http://www.endocrinologue-agadir.ma

To perform the liquid recovery method, you will need the following tools and equipment:

A manifold gauge set with hoses and valves
A recovery machine with a filter-drier
Example of a recovery machine
A recovery bottle with a float switch
A digital scale
A vacuum pump
A thermometer or a temperature clamp
A pressure-temperature (PT) chart for the type of refrigerant you are using
Personal protective equipment such as gloves and goggles

The steps for the liquid recovery method are as follows:

Turn off the power supply to the refrigeration system and disconnect it from the power source.
Connect the manifold gauge set to the service ports of the system. The high-pressure gauge (red) should be connected to the liquid line service port, and the low-pressure gauge (blue) should be connected to the suction line service port. Make sure that both valves on the manifold are closed.
Connect the recovery machine to the manifold gauge set. The inlet port of the recovery machine should be connected to the center hose of the manifold, and the outlet port of the recovery machine should be connected to another hose.
Connect the recovery bottle to the outlet hose of the recovery machine. The recovery bottle should have a float switch that automatically shuts off the recovery machine when it reaches 80% of its capacity. This prevents overfilling and possible explosion of the bottle.
Connect the digital scale to the recovery bottle and place it on a flat surface. The digital scale will measure the weight of the refrigerant that is transferred from the system to the bottle.
Connect the vacuum pump to another hose and attach it to either one of the service ports on the system. The vacuum pump will remove any air or moisture from the system before charging.
Open both valves on the manifold gauge set and turn on the vacuum pump. Evacuate the system until it reaches a vacuum level of at least 500 microns. This may take several minutes depending on the size and condition of the system.
Close both valves on the manifold gauge set and turn off the vacuum pump. Disconnect it from the service port and cap it with a protective cap.
Turn on the recovery machine and open only the high-pressure valve on the manifold gauge set. This will allow liquid refrigerant to flow from the system to the recovery bottle through the recovery machine.
Monitor the pressure readings on the gauges, the weight reading on the scale, and the temperature reading on the thermometer or the clamp. The pressure readings should decrease as the refrigerant leaves the system, and the weight reading should increase as the refrigerant enters the bottle. The temperature reading should be close to the saturated liquid temperature for the type of refrigerant you are using, which you can find on the PT chart.
Continue the recovery process until you reach the desired amount of refrigerant in the bottle, or until the float switch activates and shuts off the recovery machine. The desired amount of refrigerant depends on the specifications of the system, which you can find on the nameplate or the manual of the system.
Close the high-pressure valve on the manifold gauge set and turn off the recovery machine. Disconnect the outlet hose from the recovery bottle and cap it with a protective cap.
Turn on the power supply to the refrigeration system and reconnect it to the power source.
Start the system and let it run for a few minutes to stabilize.
Check the refrigerant charge level by measuring the subcooling or the superheat of the system, depending on the type of metering device you have. Subcooling is the difference between the actual liquid temperature and the saturated liquid temperature at a given pressure. Superheat is the difference between the actual vapor temperature and the saturated vapor temperature at a given pressure. Both subcooling and superheat can be calculated using the PT chart and the thermometer or the clamp.
Adjust the refrigerant charge level by adding or removing refrigerant as needed, using the same procedure as in steps 9 to 12. The optimal refrigerant charge level depends on the specifications of the system, which you can find on the nameplate or the manual of the system.
Verify that the system is operating properly and efficiently by checking the temperature, pressure, and airflow readings, as well as the performance indicators such as cooling capacity, energy consumption, and noise level.

How to Correctly Use the Recovery Bottle

The recovery bottle is a device that collects and stores the excess or contaminated refrigerant from the system. The recovery bottle has a valve that allows refrigerant to enter or exit, and a float switch that automatically shuts off the recovery machine when it reaches 80% of its capacity. The recovery bottle also has a label that indicates the type and amount of refrigerant it contains.

To correctly use the recovery bottle, you should follow these guidelines:

Use only approved recovery bottles that are compatible with the type of refrigerant you are using. Do not mix different types of refrigerants in the same bottle, as this can cause chemical reactions, pressure changes, and performance issues.
Check the label on the recovery bottle before using it. Make sure that it matches the type of refrigerant you are using, and that it has enough space to accommodate the amount of refrigerant you are transferring. If the label is missing or damaged, do not use the bottle.
Connect the recovery bottle to the digital scale and place it on a flat surface. The digital scale will measure the weight of the refrigerant that is transferred to or from the bottle.
Connect the recovery bottle to the outlet hose of the recovery machine. The recovery machine will pump refrigerant to or from the bottle, depending on whether you are charging or recovering refrigerant from the system.
Open the valve on the recovery bottle and turn on the recovery machine. Monitor the weight reading on the scale and the pressure reading on the gauge. Do not exceed 80% of the capacity of the bottle, as this can cause overfilling and possible explosion of the bottle. The float switch will automatically shut off the recovery machine when it reaches 80% of its capacity, but you should also keep an eye on it as a backup.
Close the valve on the recovery bottle and turn off the recovery machine when you are done transferring refrigerant. Disconnect the outlet hose from the bottle and cap it with a protective cap.
Update or replace the label on the recovery bottle with accurate information about the type and amount of refrigerant it contains. Store or transport the recovery bottle in a safe and secure place, away from heat sources, sparks, flames, or direct sunlight.

Troubleshooting Common Charging Problems

Charging a refrigeration system with freon gas is not a simple task. It requires proper tools, equipment, procedures, and safety precautions. If done incorrectly, it can cause problems such as reduced cooling capacity, increased energy consumption, compressor damage, environmental pollution, and personal injury.

Some of the common problems that can occur during charging are:

System Doesn’t Reach Desired Pressure: If the system pressures are not reaching the desired values, check for restrictions in the refrigerant lines, a faulty expansion valve, or an undercharged system.
Frost on Evaporator Coils: Frost formation on the evaporator coils indicates a potential undercharge. Check the superheat values and consider adding more refrigerant if necessary.
Excessive Pressure: If the system’s pressure becomes too high, it could be due to overcharging, a faulty condenser fan, or a clogged condenser coil. Reduce the refrigerant charge if overcharging is suspected.
Leak Detected: If a refrigerant leak is detected, use a leak detector to identify the source. Repair the leak before proceeding with charging.
Inaccurate Pressure Readings: If pressure readings on the manifold gauge set are inaccurate, check for leaks or faulty gauge components.
Insufficient Cooling: If the system is not cooling adequately after charging, verify that the superheat and subcooling values are correct. Inadequate cooling could be due to incorrect charging or a malfunctioning component.

In conclusion, charging a refrigeration system with Freon gas is a critical process that requires precision and attention to detail. Properly charging the system ensures its efficiency, performance, and longevity. By following the step-by-step guide outlined in this article, you can confidently navigate the charging process and troubleshoot any issues that may arise. Remember to prioritize safety, adhere to environmental regulations, and seek professional assistance if you encounter complex problems. With the right approach, your refrigeration system will provide reliable cooling for years to come.

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Understanding Refrigeration System Thermostatic Valves: Operation, Maintenance, and Troubleshooting

Posted on 15 August 2023 by chiefengineerslog

Refrigeration systems play a vital role in various industries, from food preservation to air conditioning. Among the key components within these systems are thermostatic valves.

A thermostatic expansion valve (TXV) is a device that regulates the amount of refrigerant that enters the evaporator in a refrigeration or air conditioning system. It is designed to maintain a constant superheat, which is the difference between the refrigerant temperature and its saturation temperature at the evaporator outlet.

A TXV schematic

A TXV consists of four main parts:

- diaphragm
- power element
- setting spring
- an orifice.

The power element is a bulb that contains a liquid that has similar thermodynamic properties to the refrigerant. The bulb is attached to the evaporator outlet and senses the temperature of the refrigerant leaving the evaporator. The diaphragm is connected to the power element by a capillary tube and acts as a valve that controls the opening of the orifice. The setting spring provides a counterforce to the diaphragm and can be adjusted to change the superheat setting. The orifice is the opening through which the refrigerant flows from the high-pressure side to the low-pressure side of the system.

Operation of the Thermostatic Valve

The operation of a TXV is based on the balance of three forces: the bulb pressure, the spring pressure, and the evaporator pressure. The bulb pressure is proportional to the temperature of the refrigerant leaving the evaporator and pushes down on the diaphragm. The spring pressure is constant and pushes up on the diaphragm. The evaporator pressure is proportional to the load on the system and pushes up on the diaphragm. When these three forces are in equilibrium, the valve maintains a constant superheat. If the superheat increases, it means that there is not enough refrigerant in the evaporator and the bulb pressure increases. This pushes down on the diaphragm and opens the valve more, allowing more refrigerant to enter the evaporator. If the superheat decreases, it means that there is too much refrigerant in the evaporator and some of it may be in liquid form. This reduces the bulb pressure and allows the spring pressure to push up on the diaphragm and close the valve more, restricting the refrigerant flow.

In conclusion, the operation can be broken down into several key steps:

1. Pressure Differential Sensing: A thermostatic valve relies on the pressure differential between the high-pressure side and the low-pressure side of the refrigeration system. This pressure difference helps regulate the flow of refrigerant.
2. Bulb and Capillary Tube: Most thermostatic valves incorporate a temperature-sensing bulb connected to a capillary tube. The bulb is usually placed at the outlet of the evaporator, and it senses the temperature of the refrigerant returning from the evaporator.
3. Expansion and Contraction: As the temperature in the evaporator changes, the refrigerant in the sensing bulb expands or contracts. This expansion or contraction applies pressure to the diaphragm inside the valve, which, in turn, adjusts the size of the valve’s orifice.
4. Flow Control: By changing the size of the orifice, the valve controls the flow of refrigerant into the evaporator. As the evaporator’s temperature rises, the valve opens further, allowing more refrigerant to enter. Conversely, when the temperature drops, the valve closes slightly to reduce the refrigerant flow.

Maintenance of the Thermostatic Valves

Proper maintenance is essential to ensure the efficient operation of thermostatic valves. The maintenance of a TXV involves checking and adjusting its superheat setting, cleaning its orifice and strainer, and replacing its power element if it is damaged or leaking.

Here are some maintenance tips:

1. Regular Inspection: Inspect the valve and its components for signs of wear, corrosion, or damage. Replace any worn-out parts promptly. The power element can be replaced by disconnecting it from the capillary tube and diaphragm and installing a new one.
2. Cleaning: Keep the valve and surrounding areas clean to prevent debris from affecting its operation. Clean the sensing bulb and capillary tube to maintain accurate temperature sensing. The orifice and strainer can be cleaned by removing them from the valve body and blowing compressed air or nitrogen through them.
3. Calibration: Some valves have adjustable superheat settings. If applicable, ensure that the valve is calibrated correctly according to the manufacturer’s guidelines. The superheat setting can be checked by measuring the temperature and pressure of the refrigerant at the evaporator outlet and using a chart or calculator to find its saturation temperature. The difference between these two temperatures is the superheat. The superheat setting can be adjusted by turning the adjustment stem on top of the valve clockwise to increase it or counterclockwise to decrease it.
4. Refrigerant Quality: Maintain the appropriate refrigerant charge and ensure that the refrigerant is clean and free from contaminants. Contaminated refrigerant can lead to valve malfunctions.

Troubleshooting Thermostatic Valve Issues

The troubleshooting of a TXV involves diagnosing its symptoms and finding their causes. When a thermostatic valve malfunctions, it can lead to inefficient cooling or even system breakdown. Here are some common issues and troubleshooting steps:

1. Insufficient Cooling: If the system isn’t cooling adequately, the valve might be stuck in a closed position, a clogged orifice or strainer, a faulty power element, loose or broken bulb, a low refrigerant charge, a high load in the system. Check for debris or ice buildup around the valve. Cleaning or thawing the valve might resolve the issue. Check and replace the power element as found necessary.
2. Excessive Cooling: If the system is overcooling, the valve might be stuck in an open position. Also this may be caused by: a faulty power element, a loose or broken bulb, an oversized TXV or low load in the system. Verify that the sensing bulb is properly positioned and securely attached to the evaporator outlet. Check and replace the power element as found necessary.
3. Frequent Cycling: Rapid on-off cycling could indicate a misadjusted superheat setting. Also, when the TXV oscillates between opening and closing rapidly, this may be caused by: a faulty power element, a high suction pressure, an oversized TXV or low load in the system. Adjust the superheat setting based on manufacturer recommendations or s described above.
4. Temperature Variations: Inconsistent temperature control could be due to a faulty sensing bulb or a damaged capillary tube. Inspect and replace these components if necessary.

In conclusion, thermostatic valves are crucial components in refrigeration systems, regulating the flow of refrigerant to ensure optimal cooling performance. Proper operation, regular maintenance, and prompt troubleshooting are key to maintaining the efficiency and reliability of these valves. By understanding how thermostatic valves work and following best practices, you can contribute to the smooth operation of refrigeration systems onboard vessels.

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Marine Compressed Air Dryer – Ensuring Efficient Operation and Reliable Maintenance

Posted on 22 July 2023 by chiefengineerslog

Marine compressed air dryers are vital components used aboard ships and offshore platforms to remove moisture and contaminants from compressed air systems. These devices play a crucial role in ensuring the efficient operation of various pneumatic equipment and systems on board. In this article, we will delve into the purpose of a marine compressed air dryer, its correct operation, the significance of regular maintenance, and troubleshooting tips to keep it in optimal working condition.

Example of a control dryer

Purpose of Marine Compressed Air Dryer

The main purpose of a marine compressed air dryer is to eliminate moisture from the compressed air. In a marine environment, humidity is ever-present, and when compressed air is exposed to it, it tends to become saturated with water vapor. When moisture-laden air passes through pneumatic systems and equipment, it can lead to several detrimental consequences:

- - Corrosion of air tools and equipment – moisture in the compressed air can cause rust and corrosion in pneumatic components, pipes, and machinery, leading to premature failure and potential safety hazards.
  - Damage to electrical components – moisture can damage sensitive instruments and controls, causing malfunctions and compromising the overall safety and reliability of the vessel.
  - Reduced efficiency of air tools and equipment – water in the compressed air can hamper the performance of pneumatic tools and systems, leading to decreased productivity and higher operational costs.
  - Increased maintenance costs
  - Health and safety hazards

Correct Operation of Marine Compressed Air Dryer

Control air dryer operating principle is as follow: The humid air flows into the air inlet connection and is pre-cooled in the heat exchanger before it enters the evaporator. As the air passes through the evaporator, which is cooled by the liquid refrigerant, the air temperature drops to 10°C, which is the dew point at which the moisture in the air is condensed. The condensed water is now separated from the air and is purged out of the system through the automatic drain trap. The high pressure liquid refrigerant now passes through the expansion valve and is evaporated in the evaporator, before returning to the compressor to continue the refrigeration cycle.

To operate a marine compressed air dryer correctly, it is important to follow the manufacturer’s instructions. To ensure the marine compressed air dryer operates efficiently and effectively, follow these guidelines:

- - Proper Installation – install the dryer in a clean, well-ventilated area away from potential sources of contamination, such as chemicals or exhaust fumes. Adequate ventilation prevents overheating and prolongs the lifespan of the dryer.
  - Filtration – prioritize the installation of filtration systems upstream of the dryer to remove larger particles, oil, and other contaminants that could clog the dryer and reduce its performance.
  - Adjust Air Pressure – normally dryer is connected to the compressed air supply line. Set the air pressure within the recommended range as per the manufacturer’s guidelines. High pressures can stress the dryer unnecessarily, while low pressures may result in insufficient drying.
  - Drain Moisture Regularly – most marine compressed air dryers are equipped with automatic drains. Ensure these drains are functional and regularly inspect and clean them to prevent blockages and ensure proper moisture removal.
  - Monitor Performance – regularly check the dryer’s output dew point and pressure levels to verify its efficiency. An increase in the dew point may indicate potential issues that need to be addressed promptly.

Maintenance of a Marine Compressed Air Dryer

To ensure the long life and reliable operation of a marine compressed air dryer, it is important to maintain it on a regular basis. Here are some maintenance practices to follow:

- - Cleaning – clean the dryer’s exterior regularly and ensure that the surrounding area is free from dust and debris that could obstruct air intake vents.
  - Filter Replacement – Follow the manufacturer’s guidelines for filter replacement intervals. Clogged or dirty filters can restrict airflow, leading to decreased performance and increased energy consumption.
  - Heat Exchanger Inspection – Regularly inspect and clean the heat exchanger to prevent a build-up of scale or debris, which can reduce the dryer’s efficiency.
  - Check Drains – Routinely inspect and test automatic drains to ensure they are functioning correctly and effectively removing moisture from the system.
  - Lubrication – If the dryer has any moving parts, ensure they are well-lubricated according to the manufacturer’s recommendations.

Troubleshooting Marine Compressed Air Dryer

Despite proper maintenance, issues may still arise. Here are some common problems associated with marine compressed air dryers and possible troubleshooting steps:

- - Insufficient Drying – if the dew point remains high despite correct settings, check for clogged filters, heat exchanger fouling, or malfunctioning drains. Clean or replace components as needed.
  - Excessive Pressure Drop – a significant pressure drop across the dryer can indicate clogged filters or obstructions in the air passages. Inspect and clean the filters and air pathways to restore normal pressure.
  - Unusual Noises or Vibrations – noises or vibrations may indicate loose components or worn-out bearings. Inspect the dryer and address any issues promptly to prevent further damage.
  - Leakage – check for air leaks around fittings, valves, and connections. Repair or replace damaged components to maintain the dryer’s efficiency.
  - If the dryer is not operating at all – it may have a problem with its electrical connections. In this case, you will need to check the dryer’s electrical connections and make sure that they are properly secured.
  - If you are still having trouble with your marine compressed air dryer, you should contact the manufacturer for assistance.

In conclusion, marine compressed air dryers are indispensable in maintaining the reliability and efficiency of pneumatic systems aboard ships and offshore installations. By understanding the purpose, correct operation, and significance of regular maintenance, operators can optimize the performance and prolong the lifespan of these essential devices. Troubleshooting skills further enable swift identification and resolution of issues, ensuring a smooth and safe marine environment with reliable compressed air systems.

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What you need to know about ship’s refrigeration and air conditioning operation, maintenance and fault findings

Posted on 1 May 2023 by chiefengineerslog

Lately, I keep receiving on every social media group that I own and manage, different questions about ship’s refrigeration and air conditioning. The systems themselves are not very complicated, not difficult to understand, but still found a lot of engineers being “scared” when it comes to work on these systems.

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Even though a significant amount of refrigeration and air-conditioning equipment is now designed to function in a fully automatic manner, the engineer is still responsible for being familiar with the device’s operation and being able to observe it in action. If this is not done, or if there is no other method to monitor performance, the plant may run abnormally for some time before a fault is found, at which point significant damage may have already been done.

The very first prerequisite is that all of the machinery must be outfitted with appropriate pressure gauges and other monitoring devices so that it can display an accurate representation of the conditions in which it is operating. During the process of commissioning the plant, it is beneficial to label these with the normal working limits.

The engineers who are in charge of operating the plant need to be aware of the significance of any indicator or warning lights that are installed on the control panels. It is essential that the engineer be aware of the temperature gradients that are to be anticipated with the system in order to be able to compare the actual working circumstances with the figures that were designed for them. Any changes at all ought to be viewed as shifts in either the ambient or load conditions. To the best of one’s ability, a running log ought to be maintained for the purpose of monitoring the working circumstances.

When the switching of plant is done entirely manually, the instructions for the plant should describe the boundaries of control. These should not be left up to the duty engineer, who might not have the necessary level of expertise to make the appropriate choices. It is common practice to install standby plant, and one of the disciplines involved in the operation is to switch machines in order to guarantee that they receive even wear and to keep all sets in operational condition. Every member of the operating crew ought to be familiar with the procedure for activating the backup plant in the event of an unexpected breakdown.

Only members of the staff who are knowledgeable and responsible should be allowed to open or close the valves that control the flow of refrigerant when this is required for the operation of the plant. In order to avoid the probable escape of gas, an open compressor that is going to be turned off for any amount of time should first be pumped down and then valves closed off.

It is reasonable to anticipate that a senior member of the staff will take a close interest in the operation of the system, and that they will not assign all of the duty to individuals with only a moderate level of expertise. This necessitates having a solid understanding of the function, makeup, and features of the system that is being controlled.

In situations in which the engineer is responsible for the day-to-day operations of the plant, which covers the vast majority of situations in which the machinery is totally automatic while it is functioning normally, the engineer is also expected to do the essential maintenance tasks.

When it comes to maintenance, in general, this consists of running the equipment that is not automatic, cleaning the filters and strainers, paying attention to the levels of oil and lubricant, tensioning the belts, performing general cleaning, operating the backup equipment, and verifying that the controls are working properly.

Full flow must always be maintained via the heat exchangers in order for any plant to function in an appropriate and effective manner. Filters for both air and water should be regularly cleaned. Regular cleaning is required for finned coils, particularly those that are found in outdoor condenser coils. As soon as a change in the working conditions indicates that the water side of the heat exchanger coils are getting unclean, any accumulations of scale or algae should be cleaned off of it.

When dirt builds up on air filters, it causes an increase in resistance, which in turn leads to a reduction in air flow. This is by far the most common source of problems with air-conditioning systems, thus addressing this issue is essential.

It is important to have spare filters on hand so that a switch from clean to filthy may be performed in a single operation, and dirty filters should be removed from the conditioned space in sealed bags for subsequent cleaning or disposal. This will avoid the spread of dirt throughout the space. It is helpful for the person who is changing the filters to have a hand vacuum cleaner so that they can clean the filter frames and pick up any dirt that may become dislodged during the process of changing the filters.

The replacement of huge filters will have to wait until the system can be shut down for the amount of time that will be necessary to complete the work. Fans should never be allowed to run without first installing filters, as this may cause dust to settle in areas of the plant that cannot be reached.

The installation of a manometer across the filter to measure the change in pressure will provide a clear indicator of whether or not the filter needs to be cleaned or replaced. These resistances can be approximated using the data provided by the filter manufacturer; they should be recorded when the filter is being commissioned, and they should also be noted on the filter itself.

Water strainers are cleanable, either as a single-mesh basket that must be removed after separating the water flow or as a twin structure that allows cleaning of one while the other is functional.
Strainers should be placed where they can be easily cleaned, while also being accessible and isolated from the water pipe, and where a minimal amount of escaping water may be allowed.
Closed water system strainers will require cleaning shortly after the circuit is turned on, but will require little attention once the pipe dirt has been washed out. In open systems, such as sea water cooling, the frequency of cleaning must be determined by operational conditions, with a preference for doing so frequently rather than infrequently.

The day-to-day operation of many plants is manually regulated, which necessitates knowledge of, and familiarity with, the system, which must be provided by the manufacturer. Untrained engineers can cause a considerable deal of malfunction and inefficiency, as well as numerous errors and a few major accidents.

It is insufficient that only one individual possesses this knowledge. A clear set of operating instructions should be posted nearby machinery or plant, allowing any authorized person to start, run, and shut down the system in a correct, safe, and efficient manner. All personnel who may be required to operate the plant must be trained and practiced.

It is customary to record the grade of lubricant on each item that may require periodic care. Most equipment is meant to run for extended periods of time without lubricant, and the consequences of adding too much should be considered.

The system will have a routine for draining the circuit and replenishing the compressor sump as per vessel’s planned maintenance system. Please follow the link if you want to learn more about oil in refrigeration and air conditioning system.

Drive-belt tensioning and replacement of damaged or worn belts is a standard maintenance procedure that can be overlooked if the equipment is out of sight. These will be discovered during a routine check.

The general cleanliness of the plant reflects the care and interest shown by the engineering crew and serves as an encouragement to anyone working on it. There is no explanation or excuse for dirt and garbage accumulations on or around any system.

Standby plant must be run on a regular basis to ensure that it is in good operating order and to keep components like shaft seals greased and run-in, and therefore gas-tight. Any changeover valves that must be operated in combination with backup plant should be clearly marked with their location and function.

Many malfunctions and potentially dangerous situations result from incorrectly set control and safety instruments. It is expected that these are all established and the correct settings are recorded at the time of commissioning, although such settings may be tampered with later by uninformed or unauthorized individuals. As a matter of routine operation, the correct adjustment of any instruments ordinarily set by the user remains his or her duty.
At least once a year, the operation of safety controls should be verified.

Many systems are shut down for extended periods of the year, either for process closure or because they are not needed in the winter. Pumping down into the receiver or condenser is recommended in refrigerant circuits to decrease leakage losses. If not in use, cooling water should be closed off.

The following should be taken into consideration by the responsible engineers:

- Under no circumstances should refrigerant be added to a leaking circuit without first making a repair. The one exception to this rule may be a continuous process plant, where the cost of a shut-down may override the cost and inherent danger of a small continuous leak.
- Where gas is detected at the shaft gland of an open compressor which is not turning, the compressor should be run for a short time to re-lubricate the gland. The leak may then cease.
- The drier should be changed and the sight glass watched for reversal of the colour to “dry”.
- If the liquid line leaving the drier or strainer (if separate) is colder than the inlet, there is a severe pressure drop within, indicating dirt. A new drier, or cleaning of the strainer, will cure this.
- Heat exchanger surfaces need to be kept clean.
- The checking and readjustment as necessary of all safety controls is an essential part of periodic maintenance – possibly annually.
- It is essential that all major maintenance work and findings are recorded in the plan maintenance system as a guide to the reliability of components, the need for cleaning, and other indicators to future work.

The immediate tragedy of a mechanical breakdown and the gradual decline in performance that can be identified as a malfunction in its early stages but will also lead to a breakdown if it is not remedied are the two general classes that defects in a system fall into. Both of these types of faults are considered to be system faults. The first will be easy to recognize as the one in question. The process of determining what caused a malfunction will become more difficult.

It is common practice to think of fault-tracing as a multi-step process of deduction, the culmination of which is a return to normal operation and a record of the event that may be shared with other operatives. The following is a list of the steps:

1. 1. Detection, i.e. detection of abnormal operation
  2. Knowledge of the system to track down the cause
  3. Observation of exact operating conditions
  4. Identification of the fault
  5. Decision: what to do? how? when? can it be left?
  6. Action to rectify the fault
  7. Test: is it now normal?
  8. Record note in log, for future information

A lot of help in fault-tracing may be had from charts for specific pieces of apparatus, prepared by the manufacturer.
Detailed examination of a sophisticated item may be beyond the skills of the plant operators and require the assistance of a specialist, such as an electronics engineer.

As mentioned at the beginning training courses and apps are available in analytical methods of fault-tracing.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries.

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Vessel domestic refrigeration system explained…

Posted on 29 May 2022 by chiefengineerslog

Every ship has a provision cooling plant, which can range from a refrigeration-cooling combination to 3 to 4 cold storage rooms depending on the ship size and type. Cold storage rooms on passenger ships can include up to 30 – 50 rooms, including dedicated storage rooms for wine, flowers, cigars, and so on.
The purpose of cold storage rooms is to maintain optimal storage conditions in terms of temperature and air humidity. To avoid radiation losses, insulation layers are built on the ceilings, walls, and floors. Windows are not supplied, and special heat-insulated doors are fitted. Antechambers are installed to avoid cold loss during entry and leave.

The layout is determined by the vessel’s trading region and duration of voyage, as well as national and international legislation, classification society regulations, environmental regulations, and so on.

Example of a cold provision room onboard vessel

The refrigeration plant is fully automated, with two compressors (which can be scroll type or semi-hermetic reciprocating piston type), two condensers and each cooling and refrigerating room has an evaporator coil and an air circulation fan.
A direct expansion Freon gas (usually R134a) system provides cooling for the cooling and refrigerating rooms. The expansion valve regulates the amount of liquid flowing to the evaporator in accordance with the current room temperature; if the temperature has risen, more liquid passes to the evaporator. The liquid travels through the expansion valve, converting to gas and absorbing heat from the evaporator.
An electrically powered fan circulates air over the evaporator coil, cooling the provision room. The supply of refrigerant to the expansion valve is controlled by the provision room thermostat via a solenoid valve in the supply line. On some systems a suction line heat exchanger is fitted to protect the compressor from any refrigerant liquid droplets by vaporizing any droplets by the hot refrigerant liquid.

Refrigeration system working principle. Source and credit: Academic Gain Tutorials

The refrigeration unit is controlled by an electronic controller, which performs the following functions:

Setting of thermostat set points
Selection of defrost times
Selection of fan operating options during defrosting
Monitoring plant’s functions, such as room temperatures
System alarm indication and self-check functions
Temperature probe recalibration

Electric defrosting elements are installed in the refrigerating room evaporator. The frequency of defrosting is controlled by a timer that is part of the electronic control system of the refrigerating unit, but defrosting can also be initiated manually.
Compressors function automatically and should not require any configuration changes. The cut-in, cut-out, and pressure differential settings on the controllers can be adjusted, although this should only be done if a new controller is installed. High pressure, low pressure, low lubricating oil pressure, and condenser cooling water failure cut off switches protect the compressors.
Under typical circumstances, one compressor/condenser unit is in use, with the other ready for manual start-up. All valves on the standby unit should be closed until it is required for service. The compressor collects R134a gas from the cooling and refrigerating room evaporator coils and discharges compressed/hot gas to the condenser. Water circulating from the central cooling FW system cools the condenser, which cools the heated gas, which condenses into a cool liquid. The liquid refrigerant is returned to the evaporators in the cooling and refrigerating room via a dryer unit and filter.

Some compressors (scroll type) have additional cooling provided by the economizer which allows a small amount of refrigerant into the middle of the compression process. The refrigerant is allowed into the middle of the compressing scrolls by means of a capillary tube. The cooling effect of this refrigerant improves efficiency.

A thermostat fitted in each room enables the liquid refrigerant solenoid valves to operate independently, this reduces the number of compressor starts and the running time of the compressors. It is important to note that the operation of the compressor plant is not designed for continuous parallel running. When one compressor is running, the standby compressor must be isolated from the system. If the valve in the liquid line is not shut, R134a in the system will accumulate in the standby condenser, which will be at the lowest pressure. This will result in the system to stop working due to the lack of refrigerant. Emptying the system of R134a will also transfer lubricating oil from the running compressor and damage the in-use compressor.

The expansion valves of the evaporators accept the refrigerant as a supercooled vapor and the temperature of the chamber being served by the evaporator determines the opening of the expansion valve. The vapours are then returned to the compressor after being heated by the evaporator.
The room thermostats open and close the solenoid valves on the air coolers (evaporator units), allowing refrigerant gas to flow to the evaporator while open. With the solenoid valves closed, there is no gas flow to the evaporators; thus, there is no gas flow to the compressor suction, and the low pressure switch will shut down the compressor.
The evaporator in the refrigeration room is equipped with electrical defrosting equipment, which comprises of electric heating components attached to the evaporator and drip tray.
Any refrigerant gas escapes from the system will cause the system to become undercharged. Low suction and discharge pressures will indicate an undercharged system, which will eventually become useless. There will be bubbles seen in the liquid gas flow sight glass.
When necessary, more refrigerant can be injected through the charging line after venting the connection between the refrigerant bottle and the charging connection to prevent air from entering the system through the connection pipe.
Before the extra refrigerant enters the system, it is dried. Any trace of moisture in the refrigerant system will result in the thermostatic expansion valve icing over and being obstructed.

Refrigerant R134a is a hydrofluorocarbon (HFC) refrigerant and if gas is lost from the system, only R134a should be used to top the system up. To comply with the Montreal Protocol, the maximum annual leakage of this gas into the atmosphere should be restricted to 10% of the total system charge. To verify this and to monitor the number of times the system has to be recharged, a record has to be made in the Refrigerant Recharge Log. A regular system of leak detection to minimise gas leaks is to be implemented to ensure leaks are detected at an early stage.

The start and stop procedure of the system is similar with the one from the air conditioning system which has been explained on an earlier post which can be found here.

The procedure for defrosting the refrigerating room evaporator is usually as follow:

The evaporator in the refrigeration room is fitted with electrical defrosting equipment, i.e. the evaporator and drip tray are provided with electric heating elements. The frequency of defrosting is chosen by means of a defrosting relay built into the starter panel. The defrosting sequence is automatic and as follows:

The compressor stops and all the solenoid valves in the system are closed.
The fan in the refrigerating room stops working. The fan in the cooling room continues the circulation of the warm air over the coolers, in this way keeping the cooling surfaces free from ice.
The electric heating elements in the refrigerating room are switch on.
As long as the coolers are covered with ice, the melting takes nearly all of the heat supplied and the temperature of the cooler and the refrigerant is constantly kept near zero. When the ice has melted, the refrigerant temperature rises in the refrigerating room. When the temperature reaches the set point (approximately +10°C) of the defrosting thermostat, the heating elements are switched off.
The compressor will now restart and the solenoid valves will be opened according to operating conditions..
When the coil surface temperature has gone below the freezing point, the fan in the refrigerating room starts.

The system is now back on the refrigerating cycle again. If the defrosting is not completed at the expiration of the defrosting period, a new defrosting cycle will commence.

If the plant is to be shut down for maintenance or repair and it involves opening up the compressors or breaking into the refrigerant lines, the refrigerant must first be pumped down to the condenser and isolated in a similar way to that described in my previous post regarding air conditioning system which can be found in here. However, pumping down until the LP cut-out trips the machine will usually not capture all the refrigerant, which may be entrained in the lubrication oil in the compressor sump and around the system. To ensure that the entire refrigerant charge is pumped into the condenser, the system is run until the LP cut-out trips the compressor and the condenser is isolated. The low pressure in the system will allow any refrigerant to evaporate and the process of pumping down until the LP cut-out trips the compressor again. This process is repeated at hourly intervals until there is no rise in system pressure following LP cut-out.

When complete, the inlet and outlet valves must be kept closed until all maintenance work has been completed and the system returned to normal operation.

If more substantial repairs are to be undertaken, it may be necessary to remove all of the refrigerant gas/liquid from the system. Because this operation involves evacuating the condenser and pressurising recovery cylinders, it should only be undertaken by a member of ship’s staff trained in this operation, or by a qualified service engineer. Additionally, for safety reasons, reference should be made to the manufacturer’s operating manuals before undertaking this task.

The first stage in this process is to shut down the refrigeration plant in accordance with the previously described procedure. For full refrigerant evacuation, a designated gas recovery unit must be used together with dedicated gas recovery cylinders. Normally the cylinders used to charge the system cannot be used, as they will typically only have a single non-return valve on the top of the cylinder as opposed to a normal recovery cylinder that has two isolating valves, one for gas and one for liquid, and an internal dropper pipe from the liquid valve.
The liquid valve from the recovery cylinder must first be connected via a flexible hose and isolating valve to the bottom of the condenser, and the gas valve of the cylinder connected in a similar manner to the suction side of the recovery pump. The discharge side of the recovery pump must then be connected to the top/gas side of the condenser. With the valves open to the recovery cylinder and recovery pump, the pump is to be run until all of the liquid refrigerant has been evacuated. The purpose of the pump is to compress gas evaporating from the top of the recovery cylinder, and use it to put a positive pressure inside the condenser on top of the liquid refrigerant.
When all of the liquid has been expelled, the connections to the recovery pump need to be changed. The suction side of the pump now has to be connected to the condenser. The pump’s discharge should be connected to the liquid connection on the recovery cylinder, and the gas valve on the recovery cylinder either left closed or also connected to the inlet side of the recovery pump.
Using this method, all of the gas is then removed from the condenser. The gaseous refrigerant passes through the recovery pump where it is condensed in its own air-cooled condenser and pumped into the liquid connection on the recovery cylinder.
When the unit has been run sufficiently and allowed to pull a small vacuum on the main condenser, all of the refrigerant gas will have been removed.
Switching off the pump and closing all of the valves will allow any necessary maintenance work to be undertaken. During this operation, a set of weighing scales must be used to ensure the recovery cylinders are not overfilled. It is important to ensure that any cylinder used is only filled to 80% capacity. The scales will also allow a record of the amount of gas recovered to be logged.

Example of gas recovering equipment and procedure

Before reintroducing any refrigerant into the system, all repair works must have been completed, and the pipelines and compressors visually checked for integrity. A vacuum pump, not the recovery pump, must then be used to create a vacuum in the system. A vacuum of 10 torr will be sufficient. This will allow leakage checks to be undertaken and also ensure any atmospheric moisture has been removed before refrigerant is introduced.

It is important to note that If there is water in liquid form in the system, rapid evacuation may cause the water to freeze. If this happens, there will be a rise in pressure (loss of vacuum) which could be confused with a pipework leak.

The vacuum is broken by flooding the system with dry nitrogen and again a pressure test, this time with positive pressure carried out. The nitrogen pressure is released to atmosphere until there is a slight positive pressure in the system and the vacuum pump then used to re-evacuate the system. The vacuum needs to be held for sufficient time to confirm that there is no leakage. Obviously the ship may not be carrying sufficient nitrogen for this process to be carried out, but it is the recommended practice.

The system is now ready to introduce refrigerant via a flexible hose into the condenser. The exact charge will be noted in the manufacturer’s handbook, and checked by suspending the refrigerant bottle from a set of scales. With modern refrigerants being gas mixtures, charging is always done via the liquid line as this ensures correct composition.

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Vessel accommodation air conditioning plant explained…

Posted on 22 May 2022 by chiefengineerslog

Air-conditioning and ventilation-related conditions on ships have a considerable impact on the comfort of passengers, the well-being of the crew, and the efficient operation of equipment, systems, and installations, regardless of the type of ship.

Both temperature and humidity must be controlled in order to provide a comfortable environment. Higher temperatures are more tolerable if the air is dryer. The cooling impact on the air as it travels over the evaporator coil removes moisture, but comfort requires a certain level of humidity, thus it is required to humidify the air again by sprinkling water into the circulating air flow.

The air conditioning plant is designed in principle to be self-contained within the fire zones or water tight compartments and to perform the following functions:

Supply cool air to the accommodation and wheelhouse.
Provide heating to the accommodation and wheelhouse air when necessary.
Remove excess moisture from the air or humidify it to a comfortable level if necessary.
Filter the air before it passes to the accommodation and wheelhouse.

The air is supplied to the accommodation by an air handling unit (AHU), which is usually located inside accommodation block, in the air conditioning unit room. The unit consists of an electrically driven fan drawing air through the following sections starting from inlet to the outlet:

One air filter
One steam preheating unit
One enthalpy exchanger of the rotating composite type (Econovent)
One steam reheating unit
Two air cooler evaporator coils

The exhaust section of the air handling unit comprises, from inlet to the outlet:

One return air filter
One exhaust ventilator

Air handling unit working principle. Source and credit: AMJ Engineering

Automatic control for the humidification of the air is installed in the outlet portion of the AHU and the humidistat controller is positioned in the room housing the air handling unit. The humidifier nozzles are supplied with steam from the ship’s steam system. The air is driven through the distribution trunking that supplies the living quarters and wheelhouse. Air may be drawn into the system either from outside or from the accommodation via the recirculation trunking. With heating or cooling coils in use, the unit are generally designed to operate on 70% fresh air supply. The ratio of circulation air may be varied manually using the damper in the inlet trunking. The inlet filters are of the washable mat type and preheating of the air is provided by coils supplied with steam from the ship’s steam system.

This rotary heat exchanger (Econovent) is installed in the accommodation ventilation system for heat recovery purposes, where it exchanges thermal energy from one counter-flow air stream to another over a rotary wheel. The rotary wheel consists of corrugated aluminum/stainless steel foil, which is driven slowly by an electric motor and V-belt/pulley arrangement.

Rotary heat exchanger (econovent) working principle. Source and credit: Energy Recovery Industries

The Freon gas (usually R134a) system with direct expansion provides cooling. The plant is automatic and is comprised of two compressor/condenser units that supply the evaporators housed in the AHU. The expansion valves for the coils are supplied with liquid refrigerant from the air conditioning compressor, which have been compressed in the compressor and condensed in the condenser. The liquid is then delivered to the evaporator coils via dryer units, where it expands under the supervision of expansion valves, before being returned to the compressor as a gas. It removes heat from the air that passes over the evaporator coils.

Refrigeration system working principle. Source and credit: Academic Gain Tutorials

The compressor is usually fitted with an internal oil pressure activated unloading mechanism which affords automatic starting and variable capacity control of 100%, 67% and 33% of full capacity by unloading groups of cylinders. This variable capacity control allows the compressor to remain running even when the load is relatively light and thus avoids the need for frequent stopping and starting. The compressor is protected by high and low pressure cut-out switches, a low lubricating oil pressure trip, a cooling water pressure trip and a high pressure and oil supply pressure differential trip and crankcase heater and cooler are also fitted.

Any refrigerant gas loss from the system will cause the system to become undercharged. Low suction and discharge pressure will indicate an undercharged system, and the system will eventually become useless. Low refrigerant gas charge is accompanied by an obviously low oil level in the sump, as the low charge level will result in the entrapment of extra oil in the circulating refrigerant gas, causing the sump level to decrease. This extra oil will be segregated and returned to the sump when the system is charged to its maximum capacity. The level indicated by the condenser level indicator will fall during operation.

If the system does become undercharged, the whole system pipework should be checked for leakage as the only reason for an undercharge condition after operating previously with a full charge is that refrigerant is leaking from the system. When required, additional gas can be added through the charging line, after first venting the connection between the gas bottle and the charging connection. The added refrigerant is dried before entering the system. Any trace of moisture in the refrigerant will lead to problems with the thermostatic expansion valve icing up and subsequent blockage.

To comply with the Montreal Protocol, the maximum annual leakage of this gas into the atmosphere should be restricted to 10% of the total system charge. To verify this and to monitor the number of times the system has to be recharged, a record has to be made in the Refrigerant Recharge Log. A regular system of leak detection to minimize gas leaks is to be implemented to ensure leaks are detected at an early stage.

As refrigerant R134a is mostly used nowadays and as is a gas mixture, if is lost, it may be one component of the mixture, and a top-up with new refrigerant can result in a slight change in the composition. If a substantial leak has occurred, the system should be evacuated and refilled with a fresh charge.

Air is circulated through ducting to outlets in the cabins and public rooms and the air flow through the outlets can be controlled at the individual outlets. On some vessels the system allows reheating of the air at the outlets from circulating hot water. A valve at the outlet allows hot water to circulate around a heating coil over which the air flows before discharge through the cabin outlet. The reheat water comes from a separate accommodation heating water system. Two water circulation pumps are fitted, one working as the duty pump and the other set as the standby pump. These pumps circulate water through a heater which is heated by steam and the water is then circulated through the accommodation spaces with branches to individual air outlets. A valve at each air outlet vent allows for individual control of reheat.

Air is extracted from various parts of the accommodation by the exhaust fan in the air handling unit. Areas from which air is extracted include toilets, bathrooms and public rooms. The exhaust air passes through the enthalpy heat exchanger unit before discharge to atmosphere. Heat energy in the exhaust air is recovered in the exchange unit and used to warm incoming air.

The air conditioning system is designed to run with the one compressor at a time meeting the full air conditioning load of the accommodation. Capacity control of the compressor is automatic and controlled by the suction pressure, but for borderline temperatures capacity can be controlled manually.

When starting the ventilation system, the following procedure generally apply:

Check that the air filters are clean.
Set the air dampers to the outside position.
Start the AHU supply fan, exhaust fan and enthalpy exchanger.
Check that air is flowing to all parts of the accommodation.

The starting procedure of air conditioning compressor is generally as follow:

All stop valves, except the compressor suction, in the refrigerant line should be opened and fully back seated to prevent the pressure in the valve reaching the valve gland.
The crankcase heater on the compressor to be used should be switched on a least 3 hours prior to starting the compressor.
Check that the crankcase oil level is correct.
Check the quantity of refrigerant charge.
Start the cooling water supply for the condenser cooling. The cooling water comes from the engine room low temperature central cooling FW system and will probably already be running.
Start the compressor.
Slowly open the suction stop valve until it is fully open. If the compressor starts making a knocking noise, close the valve immediately as this indicates that liquid refrigerant has been drawn into the machine. When the noise has stopped open the suction valve again very slowly. Repeat this operation if necessary, until the compressor runs smoothly with the suction valve fully open.

It is important to note that a fully closed suction valve with the compressor running might cause
foaming of the lubricating oil in the crankcase.

If the compressor need to be stopped for short period of time, the following procedure will generally apply:

Close the condenser liquid outlet valve and the outlet from the filter.
Allow the compressor to pump down the system to the condenser so that the low level pressure cut-out operates.
Isolate the compressor motor.
Close the compressor suction valve.
Close the compressor discharge valve.
Close the inlet and outlet valves on the cooling water supply to the condenser.
Switch on the crankcase heater

If the cooling system is to be shut down for a prolonged period, it is essential to pump down the system and isolate the refrigerant gas charge in the condenser. Leaving the system with full refrigerant pressure in the lines increases the tendency to lose charge through the shaft seal.

Shut the liquid outlet valve on the condenser and the outlet from the filter.
Run the compressor until the low pressure cut-out operates. The refrigerant gas will be condensed and will remain in the condenser as the condenser outlet valve is closed.
After a period of time the suction pressure may rise, in which case the compressor should be allowed to pump down again. This procedure should be repeated until the suction pressure remains low and the compressor does not start again automatically.
Shut the compressor suction and discharge valves.
Close the cooling water inlet and outlet valves and drain the condenser of water.
The compressor discharge valve should be marked closed and the compressor motor isolated, in order to prevent possible damage.

In conclusion, the air conditioning system will cool the air if required, will provide heating to the air if needed, will remove excess moisture from the air if necessary, and will humidify the air to the correct level for comfort. A comfortable atmosphere is a combination of temperature and humidity, and both must be controlled. Higher temperatures are more tolerable if the air is drier. The cooling effect on the air as it passes over the evaporator coil removes moisture, and a level of humidity is important for comfort, so it is necessary to humidify the air again by spraying steam into the circulating air flow.

It is also important to note that the moisture removed from the air is collected into a drain pan inside AHU and therefore it is essential that no water should be lying in the air conditioning system as this can become a breeding ground for legionella bacteria, which can have serious, or even fatal, consequences. Drains should be kept clear and areas where water can lie should be sterilized at frequent intervals.

It is most important that the AHUs are kept clean as follows:

AHUs should be regularly cleaned internally.
Air filter material should be replaced at suitable intervals depending on dust concentration in the air.
Damper control mechanism must be lubricated at regular intervals.
Steam heating coil steam traps are to be regularly checked for correct operation.
In the cooling section, ensure that drip pans are kept clean and that drains are clear.

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Chief Engineer's Log

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Category Archives: Refrigeration compressors

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