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:
- Detection, i.e. detection of abnormal operation
- Knowledge of the system to track down the cause
- Observation of exact operating conditions
- Identification of the fault
- Decision: what to do? how? when? can it be left?
- Action to rectify the fault
- Test: is it now normal?
- 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.