Chiller Systems: Routine Maintenance: Chapter 2
Compressor Maintenance
In this module, we will take a look at routine maintenance of the compressor in the chiller system. Skip to quiz!
Introduction
Recall that a compressor’s main job is to increase the pressure of a refrigerant. Compressors are the most energy consuming component in chiller systems. We will look at the routine maintenance of compressor of chiller systems.
Recall that earthing is the process of transferring unwanted electricity to the earth through a wire. We remain safe as all unwanted electricity is transferred to the earth. We give earthing to electrical systems to protect the system and the user from an electric shock.
We can find green and yellow earth wire that is connected to the metal casing of the compressor. The green and yellow wire is the earthing wire. We inspect the earthing of the system using a digital multimeter.
We have to place one of the leads on the copper tubing and the other on earth wire. If the electric system is connected to the earthing, it will show less resistance, or it will show infinite resistance. A good electric system should show a resistance value less than 0.5 ohms.
We have to check the resistance between each of the three terminals of the compressor. As a rule of 3-phase motors, the resistance value between each of the three terminals should be the same.
Compressor oil in chiller systems is very clear and transparent. It keeps its color over a period of chiller system operation. Correctly designed and installed chiller system will operate without any problems. Generally, there is no need to replace the compressor oil even after 2 to 3 years of operation.
Compressor oil will become dark in color if it is exposed to
impurities, or
excessive temperatures on the discharge side of the compressor.
The quality of oil can also be degraded by the presence of moisture in the system.
When the compressor oil has changed color or degraded quality, it must be changed.
For changing compressor oil, we first turn off the power supply and shut off the exhaust and suction valves. We open the needle valve to release gas inside the compressor. We then open the oil discharge outlet screw to remove compressor oil inside the compressor. After removing all the oil, we tighten the oil discharge outlet screw.
By connecting the vacuum pump to the needle valve, we fill the oil from the oil can into the compressor until the oil mirror fills up. We open the exhaust and suction valves. After turning the power back on, we then check compressor working.
Oil analysis is a routine activity for monitoring oil health, oil contamination, and machine wear. The purpose of the oil analysis is to verify that the compressor is working according to the expectations. When an abnormal condition or parameter is identified through the oil analysis, immediate actions are taken to correct it.
Oil analysis is required on chillers to determine the condition of the compressor oil. We can also have an idea of the condition of the compressor from which the oil sample was taken. Through oil analysis, we can know that if any metal objects have contaminated in the chiller system.
Regularly scheduled analysis of the chiller’s compressor oil is a valuable aid in evaluating the internal compressor condition. Compressor oil holds valuable information about the chiller’s condition since it comes in contact with many important internal components.
Laboratory oil analysis can identify potential chiller problems so they can be resolved before creating issues. It can detect the presence of
harmful acids,
corrosion causing elements, and
abnormal metal wear particles.
The oil sent to compressor parts usually passes through the oil filter. This oil filter helps to trap the contaminants in the oil, which could damage the compressor. A clogged oil filter will prevent oil circulation in the compressor and must be changed.
For changing compressor oil, we first turn off the power supply and close the inlet and outlet valves. We then remove the filter housing to remove old filter.
We replace the old filter with new filter and put the housing. We open the inlet and outlet valves. After turning the power back on, we then check compressor working.
As a rule of 3-phase motors, the resistance value between each of the three terminals should be the same. When the compressor oil has changed color or degraded quality, it must be changed. We have to change the clogged oil filter in the compressor.
Air-cooled condenser maintenance
In this module, we will take a look at routine maintenance of the condenser in the air-cooled chiller system. Skip to quiz!
Introduction
Recall that a condenser’s main job is to cool down the refrigerant. Condition of condenser has a significant effect on the overall chiller system efficiency.
Non-maintained condenser may result in:
Compressor cycling on and off frequently,
Reduced cooling tonnage capacity,
Increased electrical power consumption, and
Chiller system has to work harder and run longer for the same set temperatures.
The two types of condensers in air-cooled chiller systems are:
Fin and tube condensers, and
Microchannel condensers.
Recall that fins are made of aluminum, and tubes are made of copper. The cleaning procedure for both the above condensers is the same.
Even a thin layer of dust on the condenser can act as insulation. It creates a barrier for the heat transfer from the condenser to the outdoor air, thereby reducing the efficiency of the condenser. This can result in a higher condenser discharge pressure. So condenser should be inspected periodically and cleaned thoroughly.
Before starting the cleaning, we first turn off the power supply to the chiller. We clean the top of the air-cooled chiller and condenser fans with water hose.
We then clean the condenser coils in the opposite direction to the airflow. We have to make sure that there is no debris on the condenser coils. Lastly, we have to clean the floor and the surroundings of the chiller.
Insufficient air supply over the condenser coils can increase the condenser discharge pressure. Insufficient air supply can be caused by
Damaged condenser fins,
Loose condenser fins, or
Restrictions to the airflow.
We have to straighten the condenser coil fins with a fin comb if they are bent. This process is similar to combing our hair. We should straighten the fins slowly. Else it may damage the coil.
Fins are always tightly attached to the copper tubes. When the fins get loose on the copper tubes, the condenser efficiency decreases substantially. This is because the condenser will not have sufficient surface area to transfer heat from the refrigerant to the outdoor air.
Something on the condenser like leaves and paper would restrict the airflow. This results in inefficiency by not rejecting the heat to the outdoor. Look if anything is blocking airflow through the condenser and remove it.
The two types of condensers in air-cooled chiller systems are:
Fin and tube condensers, and
Microchannel condensers.
Even a thin layer of dust on the condenser can act as insulation. So condenser should be inspected periodically and cleaned thoroughly.
Water cooled condenser maintenance
In this module, we will take a look at routine maintenance of the shell and tube condenser in the water-cooled chiller systems. Skip to quiz!
Introduction
Recall that a condenser’s main job is to cool down the refrigerant. Condition of condenser has a significant effect on the overall chiller system efficiency.
The type of condenser in water-cooled chiller system is:
Shell and tube condenser
Recall that shell and tube condensers consist of a series of copper tubes inside a larger shell. Water flows in the tubes, and hot refrigerant flows in the shell.
Scales form on the copper tubes due to the impurities in the water. We can see an example of scales in our daily life on our kitchen utensils. The whitish layers that form on any utensils are scales. Similar scales are seen on a chiller's condenser tubes.
Scales act as insulation for heat transfer, thereby reducing condenser efficiency. So we have to clean the condenser water tubes periodically.
For cleaning the water-cooled condenser, we first turn off the power supply and shut off the condenser inlet and outlet valves. Then we have to circulate the descaling chemical through the condenser with the help of a pump. Descaling chemical is a liquid used to remove scales from the metal surfaces.
We have to mix the proper amount of descaling chemicals and water in the chemical tank. More amount of chemical mixing can damage the copper tubes, and a low amount of chemical mixing may not be able to descale it properly. So the amount of descaling chemical mixing with water is a very important factor.
The external water pump circulates the descaling chemical through the condenser by increasing the pressure. The water pump circulates the descaling chemical from the chemical tank to the condenser and returns it back to the chemical tank.
The time of descaling chemical circulation through the condenser depends on the amount of scales. A higher quantity of scales requires a higher amount of descaling chemical circulation.
The more foam forms in the chemical can the more scales can be removed. We have to change the descaling chemical and water mixture if it becomes dirty during circulation.
After the circulation descaling chemical, we have to open the front side and back side covers of the condenser. Then we have to check whether the descaling chemical circulated through condenser tubes properly or not.
Due to descaling chemical circulation, the hardness of the scales reduces. We will clean the condenser with a tube cleaning brush attached to a steel rod. This process helps to clean the inside surface of copper tubes and clear all the blockages, scale, and dust properly.
After the brushing process, we have to flush the water from the condenser. Flushing is a very necessary process. This helps in getting out all the loosened scales.
Cooling Tower
Recall that the chiller’s shell and tube condenser is cooled with water from the cooling tower. For cooling the condenser effectively, the water supplied to the condenser should be kept as low as possible. For this, the cooling tower should be in good condition and of sufficient capacity.
Recall that cooling towers reduce water temperature by the evaporation process. As the evaporation process continues, scale forming minerals deposit in the basin. If the cooling tower is not cleaned, thick scales can form on the heat transfer areas and reduce cooling tower efficiency.
The main problems with the cooling tower are:
Corrosion,
Scaling,
Microbiological growth, and
Fouling.
All these problems occur due to solids suspended in the air.
Corrosion reduces the lifespan of the cooling tower and may result in an unexpected breakdown. Scales reduce heat transfer efficiency. Microbiological growth reduces heat transfer, increases corrosion, and causes health problems.
Chemical dosing means adding chemical substances into the water. These chemicals used in the cooling tower can be used as a disinfectant to destroy the microorganisms and prevent recurring growth. These chemicals also reduce corrosion and scaling in the cooling tower.
Without proper chemical dosing, a cooling may lose its efficiency because of corrosion, scales deposition, and biofilm growth. To keep the cooling tower secure and productive, proper chemical dosing in the cooling tower is essential.
Scales buildup on the fills reduces water flow through them. This causes a reduction in the amount of water evaporation, thereby reducing the cooling tower efficiency.
Before starting the inspection, we first disconnect the power supply to the cooling tower. We then add cleaning chemicals to water in the basin of the cooling tower and mix them. We have to clean all components of the cooling tower like basin, nozzles, fills, etc.
Scales form on the copper tubes due to the impurities in the water. Descaling chemical is circulated through the condenser to remove scale from the metal surfaces. We will clean the condenser with a tube cleaning brush attached to a steel rod.
As the evaporation process continues in the cooling tower, scale forming minerals deposit in the basin. Chemical dosing means adding chemical substances into the water. To keep the cooling tower secure and productive, proper chemical dosing in the cooling tower is essential.
Question #1: Which of the following wire transfers all the unwanted electricity to the earth?
Red
Black
Blue and yellow
Green and yellow
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Answer: Green and yellow
The green and yellow wire is the earthing wire. It transfers all the unwanted electricity to the earth.
Question #2: The resistance value between each terminal of the compressor should be ______.
same
different
infinite
zero
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Answer: same
The resistance value between each terminal of the compressor should be the same.
Question #3: We have to change the compressor oil when it becomes ________ in color.
dark
white
green
blue
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Answer: dark
We have to change the compressor oil when it becomes dark in color.
Question #4: Which of the following is monitored by oil analysis?
Oil condition
Oil contamination
Machine wear
All the above
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Answer: All the above
Oil analysis is a routine activity for monitoring
Oil health,
Oil contamination, and
Machine wear.
Question #5: Where is compressor oil analysis performed?
Hospital
Chiller plant
Data center
Laboratory
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Answer: Laboratory
Compressor oil analysis is performed at the laboratory.
Question #6: Which of the following prevents the circulation of oil in the compressor?
Dirty air filter
Clogged oil filter
Worn out impeller
Electric motor
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Answer: Clogged oil filter
A clogged oil filter prevents the circulation of oil in the compressor.
Question #7: Which of the following are the results of the non-maintained condenser? (Select all that apply)
Frequent compressor on and off
Reduced electricity consumption
Reduced cooling tonnage capacity
Increased cooling tonnage capacity
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Answer: Frequent compressor on and off
Reduced cooling tonnage capacity
Non-maintained condenser may result in:
Compressor cycling on and off frequently,
Reduced cooling tonnage capacity,
Increased electrical power consumption, and
Chiller system has to work harder and run longer for the same set temperatures.
Question #8: A thin layer of dust on the condenser _________ the chiller efficiency.
increases
decreases
does not affect
all the above
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Answer: decreases
A thin layer of dust on the condenser decreases the chiller efficiency.
Question #9: Which of the following might be the reasons for the insufficient air supply over condenser coils?
Damaged condenser fins
Loose condenser fins
Restrictions to the airflow
All of the above
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Answer: All of the above
Insufficient air supply over the condenser coils can be another reason for increased condenser discharge pressure. It can be caused by
Damaged condenser fins,
Loose condenser fins, or
Restrictions to the airflow.
Question #10: _________ is a liquid used to remove scales from the metal surfaces.
Descaling chemical
Coil cleaner
Refrigerant
Ammonia
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Answer: Descaling chemical
Descaling chemical is a liquid used to remove scales from the metal surfaces
Question #11: Which of the following reduces the hardness of the scales on the copper tubes in a shell and tube condenser?
Refrigerant
Hot water
Ammonia
Descaling chemical
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Answer: Descaling chemical
Descaling chemical reduces the hardness of the scales on the copper tubes in a shell and tube condenser.
Question #11: At the end of the descaling process, we have to flush the condenser tubes with _________.
Refrigerant
Water
Coil cleaner
Descaling chemical
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Answer: Water
At the end of the descaling process, we have to flush the condenser tubes with water.