ALARMS AND FAULTS
It is of critical importance to the long term health of the
compressor that EVERY time a chiller is visited, or contacted via
remote contact, there is a detailed review of the FAULTS and EVENTS
logs from the chiller controller.
Any ALARMS or FAULTS being displayed must be examined to determine
of the alarm or fault is the result of a routine event (such as a
power failure) or is being generated due to some abnormal operating
condition.
For most of the operating limits of the compressor, there is an ALARM limit and a FAULT limit. Normally, when the compressor exceeds an ALARM limit, the compressor controls will attempt to limit the compressor in some manner as to avoid getting to the FAULT limit and to return compressor operation to the point where it is no longer in ALARM.
Exceeding a FAULT limit will cause the compressor to shut down.
Of particular concern are FRONT RADIAL BEARING DISPLACEMENT FAULTS
that are not associated with a power failure. In the
case where there are repeated FRONT RADIAL BEARING DISPLACEMENT FAULTS
there is a significant probability that these faults were generated
as a result of the compressor entering a ¨surge¨ condition.
Any fault that is occurring repeatedly bears detailed investigation
to determine and eliminate the cause of the fault.
Clients should be routinely advised to report any ALARM or FAULT
condition to a trained Turbocor Service Technician.
Ignoring
ALARM and/or FAULT conditions is opening the door to a potential
compressor failure.
Tuesday, October 1, 2019
DISCHARGE CHECK VALVE OF COMPRESSOR
DISCHARGE CHECK VALVES
The installation of a check valve on the discharge of Turbocor compressor is mandatory to prevent the compressor rotating backwards on shutdown as well as pressure from the condenser flowing backward through the compressor to the evaporator when the compressor is shut down.
While there is little to guide the service technician regarding the maintenance/ replacement of this item, it is the experience/ recommendation of the author that anytime the Turbocor compressor operates in surge for any length of time, or has a failure due to a front radial bearing issue (which probably has been caused by surge), as a minimum, the discharge check valve should be inspected for possible damage and replaced as appropriate.
There are two types of check valves commonly used with the Turbocor compressor. One is a wafer type, swing check valve. The other is a plunger type combination check valve/ isolation valve.
The wafer type, swing check valve uses a ¨flapper¨ type disc with a spring to assist it in closing. It can be mounted with the valve opening horizontally or opening in an ¨up¨ position. This type of valve can´t be mounted such that it opens in a ¨down¨ orientation. Normally, this valve is used in conjunction with a ¨ball¨ valve for isolation purposes.
The swing check valve has advantages in that it takes up less space, is less expensive and is easier to replace when replacement is necessary.
The disadvantage of the swing check valve is that when it closes, it does so rather forcefully and seals with a metal on metal seal. While there is no proof of this, the observation of the author is that when the swing check valve closes, it creates a more abrupt disruption of the gas flow and possibly is more likely to cause a displacement of the compressor shaft which could lead to the shaft coming in contact with the touchdown bearing (and possible failure of the touchdown bearing). Additionally, the author has experienced several instances where the ¨flapper¨ of the swing check valve fractured, causing parts of the ¨flapper¨ to be sucked back into the compressor, damaging the compressor rotors.
The plunger type combination check valve/ isolation valve, there is a substantial Teflon seal that takes the ¨impact¨ of the closing force of the valve, plus the inertia of the plunger is much less than that of the swing check valve. The valve takes up more space in the installation, but does not require a separate isolation valve. However, in order to inspect the valve, the refrigerant charge must be removed from the condenser. There is a rebuild kit available for these valves.
In the opinion of the author, these valves are much less subject to a ¨catastrophic¨ failure that could also lead to compressor failure. On the other hand, damage to the valve could impair its ability to close properly, which would allow reverse refrigerant flow through the compressor and possible compressor damage. However, as with the swing check valve, in the case where the compressor has been subject to repeated episodes of surge or there has been a compressor failure due to front radial bearing issues, this valve should be torn down and inspected, as a minimum.
The installation of a check valve on the discharge of Turbocor compressor is mandatory to prevent the compressor rotating backwards on shutdown as well as pressure from the condenser flowing backward through the compressor to the evaporator when the compressor is shut down.
While there is little to guide the service technician regarding the maintenance/ replacement of this item, it is the experience/ recommendation of the author that anytime the Turbocor compressor operates in surge for any length of time, or has a failure due to a front radial bearing issue (which probably has been caused by surge), as a minimum, the discharge check valve should be inspected for possible damage and replaced as appropriate.
There are two types of check valves commonly used with the Turbocor compressor. One is a wafer type, swing check valve. The other is a plunger type combination check valve/ isolation valve.
The wafer type, swing check valve uses a ¨flapper¨ type disc with a spring to assist it in closing. It can be mounted with the valve opening horizontally or opening in an ¨up¨ position. This type of valve can´t be mounted such that it opens in a ¨down¨ orientation. Normally, this valve is used in conjunction with a ¨ball¨ valve for isolation purposes.
The swing check valve has advantages in that it takes up less space, is less expensive and is easier to replace when replacement is necessary.
The disadvantage of the swing check valve is that when it closes, it does so rather forcefully and seals with a metal on metal seal. While there is no proof of this, the observation of the author is that when the swing check valve closes, it creates a more abrupt disruption of the gas flow and possibly is more likely to cause a displacement of the compressor shaft which could lead to the shaft coming in contact with the touchdown bearing (and possible failure of the touchdown bearing). Additionally, the author has experienced several instances where the ¨flapper¨ of the swing check valve fractured, causing parts of the ¨flapper¨ to be sucked back into the compressor, damaging the compressor rotors.
The plunger type combination check valve/ isolation valve, there is a substantial Teflon seal that takes the ¨impact¨ of the closing force of the valve, plus the inertia of the plunger is much less than that of the swing check valve. The valve takes up more space in the installation, but does not require a separate isolation valve. However, in order to inspect the valve, the refrigerant charge must be removed from the condenser. There is a rebuild kit available for these valves.
In the opinion of the author, these valves are much less subject to a ¨catastrophic¨ failure that could also lead to compressor failure. On the other hand, damage to the valve could impair its ability to close properly, which would allow reverse refrigerant flow through the compressor and possible compressor damage. However, as with the swing check valve, in the case where the compressor has been subject to repeated episodes of surge or there has been a compressor failure due to front radial bearing issues, this valve should be torn down and inspected, as a minimum.
CONDENSATE ON EXTERIOR OF COMPRESSOR/ UNDER SIDE SERVICE COVER
CONDENSATE ON EXTERIOR OF COMPRESSOR/ UNDER SIDE SERVICE COVER
When doing service work on the Turbocor compressor, it is Always good to note the level of condensation near the rear bell housing and in the area of the cooling solenoids and rear bearing power pass through plug.
The amount of condensation experienced will depend to a large extent on the environment surrounding the compressor. In tropical areas where I am accustomed to working, there is always a significant amount of condensation.
I always remove the side service cover of the compressor and examine the area to the left as facing the compressor where the cooling solenoids are located (near the top left) and the rear bearing power pass through plug (near the bottom left).
On older compressor, there is a plug mounted directly on the pins of the Bering pass through plug. On newer versions, the pass through connections at the pass through plug are hermetically sealed and the connection is at the end of a short cable that is attached to the pass through plug.
You should take note if there is any obvious corrosion present in the area of the pass through plug. The compressor manufacturer recommends application of a non-conductive, lanolin based grease as a means of preventing corrosion in this area.
Spend some time with the compressor running, watching the inverter temperature and the motor cavity temprature. The cooling solenoid is activated by relays in the serial card. There is a max inverter temperature setting and a minimum setting. These are fixed in the compressor controls. As the inverter temperature increases, when it gets to the maximum temperature, the cooling solenoid will energize. With the cooling solenoid energized, the inverter temperature will fall to the minimum, at which the cooling solenoid will be de-energized. This cycle will continually repeat.
On the backplane board, near the top, just right of middle are the connection plugs for the cooling solenoids and there is a LED for each solenoid. You can note that the LED lights up whenever the cooling solenoid is activated.
One problem I have seen is that the relay contacts in the Serial Card ¨weld¨ and the cooling solenoid is permanently energized. This will result in the inverter temperature staying low and will result in more extensive condensation in the areas mentioned above.
While this situation is not immediately detrimental to the compressor operation, the problem should be corrected within a reasonable amount of time to prevent the excessive condensation resulting in corrosion.
When doing service work on the Turbocor compressor, it is Always good to note the level of condensation near the rear bell housing and in the area of the cooling solenoids and rear bearing power pass through plug.
The amount of condensation experienced will depend to a large extent on the environment surrounding the compressor. In tropical areas where I am accustomed to working, there is always a significant amount of condensation.
I always remove the side service cover of the compressor and examine the area to the left as facing the compressor where the cooling solenoids are located (near the top left) and the rear bearing power pass through plug (near the bottom left).
On older compressor, there is a plug mounted directly on the pins of the Bering pass through plug. On newer versions, the pass through connections at the pass through plug are hermetically sealed and the connection is at the end of a short cable that is attached to the pass through plug.
You should take note if there is any obvious corrosion present in the area of the pass through plug. The compressor manufacturer recommends application of a non-conductive, lanolin based grease as a means of preventing corrosion in this area.
Spend some time with the compressor running, watching the inverter temperature and the motor cavity temprature. The cooling solenoid is activated by relays in the serial card. There is a max inverter temperature setting and a minimum setting. These are fixed in the compressor controls. As the inverter temperature increases, when it gets to the maximum temperature, the cooling solenoid will energize. With the cooling solenoid energized, the inverter temperature will fall to the minimum, at which the cooling solenoid will be de-energized. This cycle will continually repeat.
On the backplane board, near the top, just right of middle are the connection plugs for the cooling solenoids and there is a LED for each solenoid. You can note that the LED lights up whenever the cooling solenoid is activated.
One problem I have seen is that the relay contacts in the Serial Card ¨weld¨ and the cooling solenoid is permanently energized. This will result in the inverter temperature staying low and will result in more extensive condensation in the areas mentioned above.
While this situation is not immediately detrimental to the compressor operation, the problem should be corrected within a reasonable amount of time to prevent the excessive condensation resulting in corrosion.
HIGH COMPRESSOR INVERTER TEMPERATURE
HIGH INVERTER TEMPERATURE
High inverter temperature alarms/ faults on an air cooled unit is frequently an indicator of low charge.
On an air cooled chiller, the control of the expansion valve attempts to maintain the liquid level in the evaporator in accordance with the liquid level setpoint. In the case where refrigerant charge is lost from the chiller, the liquid refrigerant ¨seal¨ in the liquid line will be lost and the compressor will begin to experience high inverter temperatures due to reduced liquid available in the compressor cooling connection.
In this case, bubbles will be observed in the motor cooling line sightglass.
This can be temporarily resolved by lowering the liquid level setpoint, which will back up liquid in the liquid line, restoring sufficient liquid to the compressor motor cooling line.
Other possible causes could be a problem with the temperature sensor itself, the cooling solenoid on the compressor or the relay in the Serial card that controls the cooling solenoid.
Trouble shooting on this depends a lot on if there are multiple compressor available, or only a single compressor. With multiple compressor, you can change out components to identify where the problem lies.
Under normal circumstances, with the compressor running, watching the reading from the inverter temperature sensor, you will see the temperature rise until the cooling solenoid opens, then the temperature will fall until the cooling solenoid closes. This cycle will repeat continuously.
There are LED´s on the backplane that indicate if the cooling solenoid is energized. These LED´s can give an indication to the service technician if the problem is with the solenoid if they are lighting up but the solenoid is not energizing. On the other hand, if the lights on the backplane are not lighting up, the problem can be with the relay in the Serial Card, or with the inverter temperature sensor itself.
High inverter temperature alarms/ faults on an air cooled unit is frequently an indicator of low charge.
On an air cooled chiller, the control of the expansion valve attempts to maintain the liquid level in the evaporator in accordance with the liquid level setpoint. In the case where refrigerant charge is lost from the chiller, the liquid refrigerant ¨seal¨ in the liquid line will be lost and the compressor will begin to experience high inverter temperatures due to reduced liquid available in the compressor cooling connection.
In this case, bubbles will be observed in the motor cooling line sightglass.
This can be temporarily resolved by lowering the liquid level setpoint, which will back up liquid in the liquid line, restoring sufficient liquid to the compressor motor cooling line.
Other possible causes could be a problem with the temperature sensor itself, the cooling solenoid on the compressor or the relay in the Serial card that controls the cooling solenoid.
Trouble shooting on this depends a lot on if there are multiple compressor available, or only a single compressor. With multiple compressor, you can change out components to identify where the problem lies.
Under normal circumstances, with the compressor running, watching the reading from the inverter temperature sensor, you will see the temperature rise until the cooling solenoid opens, then the temperature will fall until the cooling solenoid closes. This cycle will repeat continuously.
There are LED´s on the backplane that indicate if the cooling solenoid is energized. These LED´s can give an indication to the service technician if the problem is with the solenoid if they are lighting up but the solenoid is not energizing. On the other hand, if the lights on the backplane are not lighting up, the problem can be with the relay in the Serial Card, or with the inverter temperature sensor itself.
CONDENSER APPROACH
CONDENSER APPROACH
On a chiller with water cooled condensing, this is the difference between the saturated temperature of the discharge pressure and the leaving condenser water temperature. On a high efficiency chiller with flooded type condenser, this should normally be no more than 1 to 2 degrees C (1.8 to 3.6 degrees F). Where historical information is available, it is always good to compare previous approach readings with the current Reading.
High condenser approach will cause loss of chiller efficiency and capacity.
The most likely case of increasing condenser approach is fouling of the waterside of the condensing tubes. Looking at the quality of the condenser water itself can give an indication of the probability of condenser tube waterside fouling.
High condenser approach may also be due to ¨drift¨ in the pressure reading of the compressor discharge pressure/ temperature sensor or the reading of the leaving condenser water temperature sensor. These items can be verified by comparing against a refrigerant manifold reading or temperature meter reading, as appropriate.
On a chiller with air cooled condenser, the approach is the difference between the saturated temperature of the discharge pressure and the ambient air temperature. Normally, this will be 10 to 15 degrees C.
Possible causes of high approach on air cooled chillers can be error in the compressor discharge pressure sensor Reading. A likely cause is dirty coils. This can easily be discerned with a visual inspection.
On a chiller with water cooled condensing, this is the difference between the saturated temperature of the discharge pressure and the leaving condenser water temperature. On a high efficiency chiller with flooded type condenser, this should normally be no more than 1 to 2 degrees C (1.8 to 3.6 degrees F). Where historical information is available, it is always good to compare previous approach readings with the current Reading.
High condenser approach will cause loss of chiller efficiency and capacity.
The most likely case of increasing condenser approach is fouling of the waterside of the condensing tubes. Looking at the quality of the condenser water itself can give an indication of the probability of condenser tube waterside fouling.
High condenser approach may also be due to ¨drift¨ in the pressure reading of the compressor discharge pressure/ temperature sensor or the reading of the leaving condenser water temperature sensor. These items can be verified by comparing against a refrigerant manifold reading or temperature meter reading, as appropriate.
On a chiller with air cooled condenser, the approach is the difference between the saturated temperature of the discharge pressure and the ambient air temperature. Normally, this will be 10 to 15 degrees C.
Possible causes of high approach on air cooled chillers can be error in the compressor discharge pressure sensor Reading. A likely cause is dirty coils. This can easily be discerned with a visual inspection.
EVAPORATOR APPROACH
EVAPORATOR APPROACH
Evaporator Approach is the difference between the saturated temperature of the suction pressure and the leaving chilled water temperature.
Normally, in a high efficiency chiller with a flooded type evaporator, the evaporator approach should be less than 2 degrees C. (3.6 degrees F.).
When historical information on a unit is available, it is always a good idea to compare historical evaporator approach readings with the current reading.
High evaporator approach results in a loss of efficiency and capacity in the chiller.
Potential Causes of High Evaporator Approach:
Loss of refrigerant charge in air cooled chiller – if the chiller experiences high inverter temperature alarms or faults and the evaporator approach is higher than normal, there is an excellent chance the chiller has lost charge. In this case, the actual liquid level in the evaporator will be less than the liquid level setpoint.
On a water cooled condenser chiller, condenser level is being controlled to a setpoint. Loss of refrigerant charge will result in lower liquid level in the evaporator. Verify visually the liquid level in the evaporator. If liquid level not visible, try lowering the condenser liquid level setpoint, which should raise the liquid level in the evaporator...... This also should result in some reduction of evaporator approach. Caution must be taken to not lower the condenser liquid level setpoint to the point where there is a loss of liquid ¨seal¨ on the compressor cooling connection. This will result in bubbles in the motor cooling line sightglass and increasing compressor inverter temperatures.
Fouling of the waterside of the evaporator tubes – This is not very likely that the evaporator tube watersides have fouling, but this is Always a possibility that must be considered.
Problem with the compressor suction pressure/temperature sensor – A small ¨drift¨ in the suction pressure sensor reading can dramatically affect the performance of the chiller. This can easily be verified by connecting a pressure manifold to the system and verifying the suction sensor pressure reading. I have actually seen this problem on several different installations.
Problem with the leaving chilled water temperature sensor – This can be verified by measuring chilled water temperature with a meter. If no meter available, turn of chiller and verify that entering and leaving chilled water readings are the same.
Evaporator Approach is the difference between the saturated temperature of the suction pressure and the leaving chilled water temperature.
Normally, in a high efficiency chiller with a flooded type evaporator, the evaporator approach should be less than 2 degrees C. (3.6 degrees F.).
When historical information on a unit is available, it is always a good idea to compare historical evaporator approach readings with the current reading.
High evaporator approach results in a loss of efficiency and capacity in the chiller.
Potential Causes of High Evaporator Approach:
Loss of refrigerant charge in air cooled chiller – if the chiller experiences high inverter temperature alarms or faults and the evaporator approach is higher than normal, there is an excellent chance the chiller has lost charge. In this case, the actual liquid level in the evaporator will be less than the liquid level setpoint.
On a water cooled condenser chiller, condenser level is being controlled to a setpoint. Loss of refrigerant charge will result in lower liquid level in the evaporator. Verify visually the liquid level in the evaporator. If liquid level not visible, try lowering the condenser liquid level setpoint, which should raise the liquid level in the evaporator...... This also should result in some reduction of evaporator approach. Caution must be taken to not lower the condenser liquid level setpoint to the point where there is a loss of liquid ¨seal¨ on the compressor cooling connection. This will result in bubbles in the motor cooling line sightglass and increasing compressor inverter temperatures.
Fouling of the waterside of the evaporator tubes – This is not very likely that the evaporator tube watersides have fouling, but this is Always a possibility that must be considered.
Problem with the compressor suction pressure/temperature sensor – A small ¨drift¨ in the suction pressure sensor reading can dramatically affect the performance of the chiller. This can easily be verified by connecting a pressure manifold to the system and verifying the suction sensor pressure reading. I have actually seen this problem on several different installations.
Problem with the leaving chilled water temperature sensor – This can be verified by measuring chilled water temperature with a meter. If no meter available, turn of chiller and verify that entering and leaving chilled water readings are the same.
CORRECT CHARGE LEVEL IN CHILLER WITH FLOODED EVAPORATOR
DETERMINING CORRECT CHARGE IN A CHILLER
WITH FLOODED EVAPORATOR
Determining when a Turbocor compressor based chiller is very
different as compared to a DX type system.All units should have a nameplate which should include the design charge of the system. On smaller systems, if there is doubt about the charge, system charge can be removed and the correct charge weighed back in.
However on larger systems, this may not be practical. The typical Turbocor compressor based chiller will have something on the order of 1 to 1.5 kilos of charge per TR.
With a DX system, if it is not practical to remove the charge and weigh in the correct charge, charge can be added until suction superheat stabilizes and until the discharge pressure starts to increase (indicating liquid is backing up in the condenser).
However, in a Turbocor compressor based chiller with flooded evaporator, determining correct charge is completely different.
On a water cooled chiller with flooded type evaporator and condenser you must determine the correct charge level in the condenser and the evaporator.
Normally, the water cooled condenser will have a subcooling circuit at the bottom of the condenser tube bundle that designed to be immersed in liquid during normal operation. In most cases, there will be a sightglass mounted low on the condenser such that, when condenser charge is correct, a liquid level will be visible in this sightglass. If there is no sightglass, depending on the size of the chiller, you will need to estimate the height of the sub-cooling circuit. The sub-cooling circuit will be the bottom 6 to 12 rows of tubes (6 on smaller capacity chillers, 12 on larger capacity chillers) with tube spacing about 2/3 of an inch.
In the case of the air cooled condenser, correct level of liquid in the condenser is somewhat more difficult to determine. Normally, the air-cooled coils will have a sub-cooling circuit near the bottom of the coil. This can only be determined through visual inspection of the header end of the coil. If the air cooled coil has a sub-cooling circuit, correct charge of the condenser can be determined by the fact that the liquid header of the air cooled coil will have a lower temperature in the area of the sub-cooling circuit as compared to the area of the liquid header in the area where only hot gas is present
Normally, the evaporator will have a sightglass mounted such that the top row of evaporator tubes is visible through this sightglass. Evaporator charge is correct when during full load operation, the liquid refrigerant in the evaporator is visible just barely covering the top row of evaporator tubes.
To determine correct charge in a chiller with flooded water cooled condenser, adjust the setpoint on the liquid level sensor (which will be measuring the liquid level in the condenser) until the liquid level in the condenser is at the desired level.
Once the liquid level in the condenser is correctly established, with the chiller fully loaded, the liquid level in the evaporator should be just covering the evaporator tubes. If the liquid level in the evaporator is not visible, add charge until the liquid becomes visible.
HINT FROM THE AUTHOR - When I have the correct level in the condenser established, I reduce the condenser liquid level setpoint by 5%. Then when I see the evaporator liquid level come up over the top evaporator tubes, I can make a fine adjustment to the evaporator level by increasing the condenser setpoint slightly.
With the flooded evaporator in an air cooled chiller, the liquid level sensor will be directly in the evaporator. To determine the correct charge in a chiller with air cooled condenser coils, you will need to adjust liquid level setpoint until the liquid level in the evaporator just covers the top tubes in the evaporator. Then, sufficient charge must be added to back liquid refrigerant up into the liquid line and up into the very bottom part of the air cooled coils.
On the Turbocor compressor based air cooled chiller, there is a motor cooling connection on the condenser liquid line and a sightglass on the cooling line going to the compressor. As a minimum, when the chiller is correctly charged, there will be no bubbles in the motor cooling lone sightglass during compressor operation.
Absolute correct charge on the air cooled unit will be when liquid is backed up into the sub-cooling circuit of the air cooled coil during full load operation.
As with air-cooled DX systems, excessive charge in the unit will result in an increase in the discharge pressure of the air cooled chiller.
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