Ammonia Chiller Repair

A plate evaporator with end plate removed during ammonia chiller repair

Ammonia Chiller Repair

An ammonia chiller had been found to need an evaporator repair on a previous call out. The water Inlet and Outlet to the plate evaporator had been valved off and then it had been drained down. This was to stop any further leaking of water into the refrigerant system.

News Article No.30

Equipment

The plant is located on a roof, so the pump out unit and recovery cylinders were lifted into place with a block and tackle. These in place, the extension lead was run out from the adjacent plant room. Having done this, the recovery unit was plugged in and tested.

Ammonia Pump Out during Chiller Repair

The refrigerant recovery operation was started by removing the ammonia liquid. Then, the vapour was removed until the pressure was zero barg. By this time, the refrigerant temperature had risen to near ambient temperature.

Oil Drain Down

The oil used to lubricate the compressor is located in the:
• Oil separator
• Oil cooler
• Economiser pot
• Oil supply pipe.
Therefore, it was drained from the various service ports into drums and then taken away for recycling.

Breaking into the System

Our engineers then decided to break into the refrigerant system. They both donned their breathing apparatus and full ammonia resistant PPE. First, the refrigerant hoses were removed from the pump out unit. They then opened all of the service valves around the chiller.

Leaking Plates

The evaporator on this chiller is a plate heat exchanger. The leak had been identified as coming from in between the plates along the side of the evaporator. An attempt had been made to ‘nip’ the evaporator up by tightening the end plate bolts. This had not made any difference to how fast the leak was occurring.

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All of the plates removed from an ammonia chiller evaporator being repaired
Chiller pipework sealed during repairs

Evaporator Strip Down during Ammonia Chiller Repair

The end plate was unbolted from the rest of the evaporator according to standard industry guidelines. It was then slid to the end of the rail. Having done this, the plates and gaskets were removed and then inspected...

Plates

The plates were found to be in good condition, so they were cleaned using our plate cleaning agent. Then, they were taken to the plant room for storage until the rebuild.

Gaskets

The gaskets were found to have deteriorated over time- causing the leak.

Evaporator Rebuild during Ammonia Chiller Repair

We made the gasket set in our workshop from raw materials suitable for ammonia. Then, we sent them to site for the rebuild. The rebuild was the reverse of the strip down: the plates were collected from the plant room and replaced on the evaporator using the new gaskets.

Torque Wrench

The end plate was lifted into place and the bolts were fitted. Then, the bolts were ‘torqued up’ to the correct value according to standard industry guidelines.

Oil Filter

The oil filter which is fitted to the oil pipe on the compressor was blocked due to the moisture reacting with the ammonia refrigerant and turning into ammonium hydroxide. Our Engineer used his socket set to remove the filter housing, then he slid out the oil filter. Spares are kept on site in the stores- so the oil filter was swapped out.

Pressure Test

Having closed all of the service ports, the entire system was pressure tested, noting the start and the finish readings. These readings were witnessed by the customer and recorded on the Pressure Test Certificate which was then filed by the Facilities Manager.

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Dehydration Process during Ammonia Chiller Repair

The standing and running refrigerant pressures are both higher than the water pressure of the Inlet and Outlet pipes. Therefore, only a small amount of water had entered the refrigerant pipework during the evaporator leak.

Industrial Vacuum Pump

Smaller vacuum pumps need to be repaired, usually each morning, due to the moisture being removed from the system. We at Maximus Chillers have an industrial vacuum pump which speeds up the dehydration process. This unit can cope with a higher amount of moisture removal, therefore removing the need for monitoring during the process.

Set Up

Our engineers used their fittings to connect the vacuum pump, via a hose to the chiller. Then, the dehydration process was started. A Torr gauge was fitted to the appropriate part of the system using a ¼” hose and 2 fittings to get from one thread type to another.

Monitoring

The vacuum pressure was being monitored, at intervals, by the customer. Therefore, the customer let us know when the system pressure had reached the achievable vacuum pump pressure.

Recharge during Ammonia Chiller Repair

The block and tackle was used to winch the refrigerant to the location of the chiller, then the anhydrous ammonia was charged into the system. Having completed the recharge, the service port was valved off and all service ports checked for leaks using an ammonia leak detector.

Start Up Procedure

All readings including superheat, subcooling and economiser subcooling are available on the chiller controller. After the start up checks had been carried out, the start up procedure was commenced including checks to the chiller panel in the plant room and enabling the chiller on the BMS.

Run Testing during Ammonia Chiller Repair

There was available load for the chiller, so this enabled a full run test at 100%. The chiller loaded steadily until it reached full load. As the set point was neared, the controller unloaded the compressor to match the load which was coming from the building. After an hour, the chiller achieved set point, counted through an off cycle timer and then continued to run seamlessly.

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Large air cooled chiller failure showing refrigerant cylinders and vacuum pump

Chiller Failure

Chiller failure can be expensive and even result in buying a new, or refurbished chiller. Read below to have a look at two different scenarios…

News Article No.23

F-gas Chiller Failure

We carry out regular f-gas leak tests at periodic intervals to prevent unnecessary refrigerant leaks to atmosphere. This leak, however, occurred in between tests and was alerted to us by the factory personnel. They had noticed icing up, near to a solenoid coil due to liquid refrigerant leaking and then boiling off.

Leaking Solenoid Valve

The plant had failed due to the stem of a solenoid valve splitting at the base and causing a refrigerant leak. The valve provides a bypass of liquid refrigerant to the economizer. This is used to further subcool the rest of the liquid refrigerant before it enters the expansion valve. This subcooling improves the COP (coefficient of performance) and so reduces electricity costs.

Decant during Chiller Failure

When our engineer attended site, he decanted the remaining refrigerant into recovery cylinders which were weighed, adding the TARE weight into the calculation.

Remove and Replace

The same size solenoid valve was sourced from the suppliers. The area was cleaned up using an emery cloth and a wire brush, then the valve was brazed into position using oxy-acetylene.

Nitrogen Pressure Test

The system was then put on pressure test according to industry guidelines with the customer witnessing the start and the finish. The result was satisfactory, so this was recorded on the pressure test certificate. The certificate was filed with other chiller paperwork which is available for inspection by external auditors.

Dehydration during Chiller Failure

The picture was taken during the refrigerant leak repair in this article. You can see the gauge pulled down to 2 Torr of a vacuum. This was after an overnight dehydration process.

Recharge and Switch On

The refrigerant was recharged into the system until the superheat and subcooling values came to within standard industry guidelines. The plant had sufficient load to run at 100% for an extended period which was a good opportunity to monitor the compressor temperature and the oil return. Eventually, the compressor unloaded to match the demand coming from the process.

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Chiller Failure due to Evaporator Freeze Up

A new customer of ours had not had a maintenance contract for some time. This section emphasises just how important PPM (planned preventative maintenance) is. During these visits we carry out checks and tests to the various components that protect the evaporator.

Flow Switch causing Chiller Failure

This component was found to have failed which allowed the compressor to carry on running when the pump had gone off.

Water Out Sensor

Another safety device on this machine is the Water Out sensor. Because of the way that this chiller had failed, however, this sensor was reading high while the inside of the evaporator was freezing up.

Buckle and Burst

Ice has a larger size than water due to how the atoms form into a crystalline structure when freezing. This caused a catastrophic failure in the evaporator. The copper tubes in the evaporator shell started to bend then buckle. Eventually, a proportion of the pipes bust which caused the refrigerant to leak into the water system.

Low Pressure Switch

The compressor low pressure switch did not activate. This was because the refrigerant had leaked down to the same pressure as in the water system, then the water was sucked into the chiller.

Compressor Smash Up

As a compressor cannot compress a liquid, the water damaged the bearings and then a smash up occurred.

Condenser

While this was happening, the water in the refrigerant system continued to the condenser and so the whole system was ruined.

What a Mess!

As you can see from the above, there couldn’t be a worse thing that could happen to a chiller. Regular maintenance was all that was needed to prevent this. Give our Technical Support Desk a bell to discuss our range of maintenance packages that will keep your chillers running in the best condition.

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Pick up the Pieces after Chiller Failure

After the above failure occurred, it was a big job to pick up the pieces…

Compressor

The compressor needed to be lift and shifted to our remanufacturing facility at Head Office for a full strip down, inspection and clean out. Then, a list of parts was composed for the rebuild. When the parts arrived, the compressor was rebuilt making sure that the clearance of the bearings and the run out of the shaft were within industry guidelines. All of the internal bolts were torqued to the correct value which was recorded on our remanufacturing sheet. A lick of paint was applied and then the compressor was shipped back to site.

Components

All of the components around the system were replaced or dried out, then the compressor was lifted back in with the suction and discharge valves closed. This was to prevent the moisture in the system from ingressing into the newly rebuilt compressor.

Dehydration

An industrial vacuum pump was used which carried a changeable oil filter. Our system dehydrating vacuum pump came on a skid which was located next to the chiller. We used a ¾” refrigerant hose that was fitted to the same size service port on the chiller. This prevented any pressure drop in between the vacuum pump and the refrigerant system.

Oil Filter Changes after Chiller Failure

The moisture being removed from the system went into the oil filter which caused it to block. Therefore, the oil filter needed to be changed daily at the start of the process and then less often towards the end. We also use a special catching device depending on how much water there is in a system that needs to be removed.

Torr Gauge

The Torr gauge dropped quickly at the start of this process until it reached the saturation point of water. At this point it stopped until the water was removed and only vapour was left in the system. Then, the Torr gauge started to slowly drop down to 2 Torr.

All of this article was due to a lack of routine maintenance!

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Troubleshooting of a chiller panel on a system running on ammonia refrigerant

Chiller Troubleshooting

In this article a bespoke chiller with ammonia refrigerant is having troubleshooting carried out to identify the faults. Read below to have a look into the various issues that commonly occur on this machine…

News Article No.19

Chiller Troubleshooting of Low Oil Level

There are times when this machine experiences a low load condition. This is because another chiller is also available as well as free cooling.

Building Management System

The BMS regulates the sequencing of the chillers, the pump sets, the water system valves and the free cooling. We found after troubleshooting that, especially in the winter, the BMS can be slow to react. This causes the chiller to continue running with low load.

Slide Valve at 0%

During a low load condition, the compressor has been designed to run with the slide valve at 0% to prevent too many start ups. These start ups would cause a higher amount of electricity to be used because of the amps being drawn to get the compressor going. Although the compressor uses star/ delta contactors which are a soft start, the repeated starts would still draw a lot more amps. Therefore, the compressor continuing to run at 0% is a lot more efficient.

Oil Pump and Oil Level

When this condition occurs, however, the oil pump continues to suck and then discharge the oil. Eventually, the level in the oil separator drops to below the oil level switch and the alarm is triggered. The photo shows this switch which is a float on a stem. The circuit is completed when the float is at the top of the stem. When the float slides down the stem- this triggers the alarm.

Stainless steel oil level switch removed from the chiller showing the float and the stem
The switch protects the compressor

The Repair

Specialist ammonia resistant personal protective equipment, or PPE is donned by our engineers. Then, ammonia grade oil is pumped in so as to complete the circuit of the switch. After a start up, the same amount of oil has to be taken back out at the other end of the system using the dead man’s valve. This is a valve on the bottom of the economizer which shuts by itself using a spring.

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Chiller Troubleshooting of Oil Filter Differential

When this alarm occurs, you can see the discharge pressure remain at 8 bar and the pressure after the oil filter slowly drop off to less than 6 bar. When interrogating the program, the oil pressure differential trip out is set to 2 bar. After this differential is exceeded, a timer starts to prevent spurious trip outs occurring if the differential pressure is exceeded momentarily. If the differential pressure continues to be exceeded after the timer has timed out- the machine goes into a fault condition which needs a manual reset.

Chiller Troubleshooting Inspection

When removing the cover for the compressor enclosure, the discharge oil pipe can be seen going into the oil filter. An oil pressure transducer can be seen on the far side of the filter.

Contaminants

After the above troubleshooting, it was found that with this kind of system, the oil becomes contaminated with sludge and debris from around the system. Over time this builds up behind the oil filter and so causes the trip out.

The Repair

The repair requires the oil filter to be valved off on either side. Then, full length PPE suitable for the handling of ammonia is required along with beathing apparatus. Each of our engineers carries a portable ammonia alarm and state of the art ammonia handling equipment. We also produce our own ammonia oil filters which we keep on the shelf at Head Office. Give our Technical Support Desk a bell for further assistance.

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Chiller Troubleshooting of Slide Valve Potentiometer

This is a 4-20mA sensor which detects the position of the slide valve. 4mA being shut and 20mA being open. We attended a call out to troubleshoot the alarm message of “slide valve failed to reach the closed position” There is a spring on the end of the slide valve which is used to push it to the closed position when the compressor is off. We decided to activate the drain and fill solenoids which are used to open and close the slide valve. Still the same fault persisted. Having decided that the slide valve was indeed at its closed position, we decided to calibrate the closed and also the open position of the valve.

The Repair

The compressor was valved off and our engineer donned the necessary PPE. The sensor stem was removed from the end of the spring which is attached to the slide valve. A lock nut is available to hold the stem at the required position. This was found to have vibrated loose and so causing the problem. The correct length was set on the stem and the lock nut was re tightened. After rebuilding the end of the compressor, the valves were opened and the compressor checked for leaks. Then, the system was run tested using the manual load and unload buttons on the controller. A good read back was recorded and the machine went into seamless operation.

Chiller Troubleshooting of Ammonia Leak Detection System

This device is stand alone from the chiller and has its own uninterruptable power supply. This UPS is needed so that when there is a power failure to the building, the alarm would still function. There are 2 toxic gas sensors and 2 fire detectors fitted in different locations on the chiller.

Out of Calibration

When we took over the contract 5 years ago, the chiller had been in fault for some time with a leaking shaft seal. After troubleshooting the problem, we found that the small amount of ammonia leaking from the shaft seal and onto the sensor had knocked it out of calibration. This is because the sensor needs to be calibrated to a zero ammonia atmosphere as a reference point.

The Repair

After changing the shaft seal, we decided to change all 4 of the sensors and plug the detection system into our laptop for calibration. The benchmark was set for each sensor, then each sensor was bump tested to the required parts per million of ammonia to ensure that the detector trips when it should. All read backs were found to be okay, so we completed the calibration certificate which the customer keeps in his chiller file.

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Blue ammonia chiller with panel open during chiller controls company visit

Chiller Controls Company

Having an effective chiller controls company saves money! We at Maximus Chillers can repair any fault and upgrade where necessary. Read below to learn more…

Non Condensables

One of the non condensables that is found in a chiller is air. It had got into the system of the chiller in the photo due to a poor repair having been carried out. The end user had tried to save money by using a cheaper company to carry out a change of the suction strainer. They had forgotten to purge the pipework of air, leak test, and then pull a vacuum.

High Subcooling

The ingress of air had caused a ‘high subcooling’ message to appear on the PLC display. The controls work out the subcooling by looking at the pressure transducer reading, in this example it was 14 bar. Then, the onboard comparator understands the pressure/ temperature relationship of the refrigerant which is ammonia. This gave the saturation point temperature of 39°C. Also, the temperature sensor reading on the condenser was 25°C. The 14°C difference between the two temperatures was the subcooling. The parameters in the controls trigger this message if the subcooling is more than 12°C.

Air Purging

Our engineer attended site to carry out air purging according to standard industry guidelines. Our Risk Assessment Method Statement outlined the necessary PPE that was needed when handling this refrigerant. It also outlined the training and certification required by our engineer to handle anhydrous ammonia.

Subcooling Readings

He then ran the system up and checked the subcooling readings again. The condenser pressure was now 11 bar which corresponds to a saturation temperature of 31°C. The condenser temperature was still 25°C, so the subcooling was now 6°C. This was now below the alarm trip out level.

Dalton’s Law of Partial Pressures

This gas law states that all gasses in a pressurised vessel will act as if they are on their own. Therefore, with the air that was in the system, the condenser pressure was 14 bar, then after the air purging it was 11 bar. This means that there was 3 bar of air sat on top of the liquid refrigerant in the condenser. The air was causing a false reading of subcooling and therefore triggering the fault condition.

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Electrical Problems

Another fault message which had occurred during the time we have maintained this machine was oil separator low temperature. The oil separator is the vessel, just visible, to the left of the panel in the photo. This alarm is critical to protect the screw compressor from running with cold oil which will cause an expensive failure.

No Heater Burn Out

The oil separator heater was found to be off despite the cold temperature of the oil. The obvious reason was that it had burned out. The breaker was found to be in the 'on' position and there was no electrical charring visible.

Ohms Checked by Chiller Controls Company

When our engineer checked the ohms readings, they were found to be okay and there was no short to earth.

Run Signal

It was found that the 3 phase contactor was not pulling in to bring the heater on. Therefore, the next thing our engineer checked was weather the controller was sending out the run signal. It was- with 24v coming from the controller and the light being lit on the display. Somewhere in between, there was a problem…

Blown Relay

After consulting the wiring diagram, our engineer traced the fault to a blown relay. This relay provides a step in between from the 24v coming from the controller, to the 240v coil on the oil heater contactor. Rainwater had ingressed through a screw hole in the back of the panel. It had dribbled to the location of the A1 coil terminal on the relay. Here, it had been ‘tracking’ a few volts to earth. This was sufficient to burn out the coil without blowing the fuse. A drying agent suitable for electrical components was used, then the hole was sealed using a compound. There was a spare relay of the same type in the panel, so it was a quick job to swap it out.

Monitoring by Chiller Controls Company

Having done this, the contactor pulled in and the oil heater came on. Balanced amp readings were recorded on all three phases of the heater and the oil started to warm up. The oil separator temperature sensor was monitored for an hour on the controller. When the oil temperature rose to above the trip out level of 46°C, the fault condition automatically reset and the chiller came back on.

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Software Upgrade by Chiller Controls Company 

We had also previously found that the controller software was too finicky- causing a lot of spurious trip outs. Therefore, we decided to design our own software and upload it. This is easy to do because the controller is Bejer Electronics. It is a blank control system which can be used for almost any chiller, or other application. Read below to find out how we did it…

Chiller Controls Company Reliability

We rationalised what the customer needed and developed an upgraded program which was much more reliable. Getting a chiller to settle down and cost the customer less money is what we at Maximus Chillers are all about.

Chiller Controls Company's Test Rig

The controller had been removed from the chiller and wiped of its program. Then, the finished program was uploaded to the controller and a test rig set up. This was to iron out any teething problems before sending it back out into the field.

Laptop Plug In

When our engineer attended site, he fitted the upgraded controller and plugged it into his laptop. All of the program settings can be adjusted on the controller without the need of a laptop by entering the correct passwords for the program level required. However, a laptop has a bigger screen and so multiple readings can simultaneously be monitored. This facilitated the commissioning process.

Chiller Controls Company Testing and Adjustment

The chiller was run tested under various load conditions to check its performance. Also, all the fault conditions were either simulated or tripped out on the chiller. This was so that the program could be put to the test and adjusted accordingly. There were minor problems with fault timers which were adjusted, one at a time, so that no spurious trips would occur.

Completion

After monitoring the chiller for the rest of the day, it was time to talk to the customer about the job and get a signature. This chiller is in South West Wales, so it is a long, but very scenic, drive back for whichever of our engineers attends site. Read more about chiller upgrade.

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Large chiller, refrigerant cylinder, brazing equipment and tools during chiller service company visit

Chiller Service Company Visit

A typical rainy day in the North West, perfect for a chiller service company visit.

News Article No.11

Electrical Faults during Chiller Service Company Visit

This was a return visit to do a refrigerant leak, but the customer alerted our engineer’s attention to an electrical fault. System 2 was found to be locked out in fault on the recent maintenance visit, but now System 1 was being held off too. The fault message on the controller was High Pressure. The controller sends a 240v fault feedback signal, through the high pressure switch which returns to the controller. Our engineer had a look at the wiring diagram to find the number on the terminal strip and checked it out with his multimeter. As he suspected, there were volts going out, but not coming back. He removed the side panel for system 1 and found the switch on the discharge pipe. It was the type that has a red button on the top. When he pressed it, there was a click and volts returned to the controller.

Alarm Reset during Chiller Company Service Visit

He interrogated the Carel controller and followed the reset procedure. The controls went through a timer and then the start sequence was initiated.

Run Testing during Chiller Company Service Visit

After the first scroll compressor started, the head pressure started to build up, but the condenser fans did not start. The on board high pressure gauge carried on rising until the high pressure switch was tripped again.

Head Pressure Control

A transducer on the discharge is used by the controller to sense the pressure in the condenser. When our engineer looked for this in the controller, it was found to be reading wrong by a considerable amount. There is a facility to enter a password and recalibrate the transducer, but this only allows for a small adjustment.

Test Instrument

Our engineers carry various kinds of test instruments which can be used to give a temporary false reading to the controller. This gets the customer up and running and back in production whilst a new transducer is ordered and sent to site.

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Chiller Company Service Low Pressure Visit

Now on with the job to resolve the low pressure issue with the chiller.

Refrigerant Pump Out

Our engineer lifted the liquid line solenoid valve and decanted the remaining refrigerant into a vessel using his recovery unit. He only got out 7kg of a charge of 36kg.

Leak Testing during Chiller Company Service Visit

We use nitrogen for the leak testing as it is an inert gas that will not cause problems with the refrigerant system. There was a sign of the leak in between the steel frame at the middle of the condenser and the condenser tubes. We always strip the chiller down and leak test the entire system though. This is so that the job does not end up going round in circles. At first the leak could not be found, so the pressure was built up in stages, taking into account industry recommended guidelines for a chiller. Sure enough the leak was where it was suspected to be. The occurrence of this kind of leak can be reduced with the use of vibration eliminators.

Brazing during Chiller Company Service Visit

The location of the leak was reported to the maintenance engineer onsite and a hot work permit obtained. The equipment we use is tested at regular intervals to be safe and in good working order. A half hour fire watch was stipulated in the permit, along with the removal of combustible materials from the work location. Correct PPE being donned, he brazed the leak to the required industry standards.

F-gas Pressure Test

A chiller has a different pressure test procedure to other systems, so our engineer built the pressure up according to industry standards, then recorded it on his pressure test certificate. After the required time had elapsed, he rechecked the readings which were found to be satisfactory.

Vac Pump

Each of our engineers carries a state of the art 10 cfm vacuum pump to speed up the dehydration process. We use high quality Torr gauges too, so as to get an accurate pressure reading. A good read back was achieved at the end of the process.

Recharge and Run Test

After the refrigerant recharge was carried out, a satisfactory run test was achieved.

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Refrigerant Economizers

This particular chiller uses an economizer to further subcool the refrigerant. Chiller designers have worked out that the end user can save a considerable amount of money over 10 years if these components are used. After the subcooled liquid refrigerant leaves the condenser, it goes through a plate heat exchanger. Some of this refrigerant, however, is diverted through a thermostatic expansion valve, to the other side of this plate heat exchanger. Further subcooling occurring through the plates.

Expansion Valve

The refrigerant drops in pressure as it goes through the expansion valve. A bulb is fitted to the suction pipe on the outlet of the heat exchanger. The bulb has to be at the correct 'o clock position as oil insulation will affect the operation of the valve. A capillary tube connects the bulb to the valve. Inside the bulb, the same kind of refrigerant that is running in the system is present in its liquid state. As the temperature rises in the suction pipe, this refrigerant boils off, adding pressure into the capillary tube. This added pressure forces the power element down on the valve body and a needle forces the valve open.

Flash Gas

Imagine if the refrigerant was not subcooled at all. It would be around its saturation point with a lot of it flashing off into its vapour phase. Not good when you have warm water coming back from the process. The refrigerant would not absorb very much latent heat into the refrigerant system.

Efficiency

Imagine, on the other hand, the economizer which is fitted to this chiller. Now we have a good proportion of refrigerant in its liquid phase, on the low side of the system, with a minimum amount of flash gas. The warm process water has more chance to cool and the refrigerant absorbs a lot more latent heat. The chiller achieves set point easier and therefore saves a considerable amount of electricity. With this further subcooling monitored for a while, time for a signature from the customer and another job well done!

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Oil return solenoid removed during industrial chiller service

Industrial Chiller Service

On an industrial chiller service visit, the ammonia alarm was found to have been triggered.

News Article No.10

Industrial Chiller Service Faults

The onsite engineer had fault found the chiller and silenced the alarm, the yellow light was still flashing. The red light was lit on the panel and the red LED was illuminated on the ammonia alarm console. He had reported a smell of ammonia to us over the phone. This gave us a priority of getting to site, as many other alarms of this nature are often spurious. Our engineer attended site within an hour and confirmed that the fault finding was correct as described by the onsite engineer. The chiller is containerized in design as it is situated outside. All around the chiller are door panels for access to the various system components.

Breathing Apparatus and PPE

He donned his mask and full length ammonia resistant PPE before opening one of the panel doors. This was to ensure that he did not get overwhelmed by the refrigerant when he opened the door. He started with the door into the storage area of the containerized chiller. A strong blast of ammonia came out in his face- lucky for the PPE!

Localising the Fault

Working his way around the chiller, our engineer found more and more hazardous door openings! Eventually he found the culprit: one of the two flanges were leaking on the oil return solenoid. The refrigerant vapour was coming out in its usual white form. The oil return pipe feeds off the oil pot which is a chamber that the oil sinks into from the refrigerant economizer. This vessel was valved off and the other end of the pipe valved off too.

Pinpointing the Fault

Now that the ammonia refrigerant leak had started to calm down- it was possible to see through the white vapour to exactly which of the flanges was leaking. It was the right one as seen in the picture. It consists of an ‘o’ ring made of ammonia resistant rubber material.

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Industrial Chiller Service in Local

The above mentioned chiller runs in local in a lead/ lag configuration with the adjacent chiller. That is to say- there is no wire or modem to a remote location. A panel is available in between the two chillers to sequence the switch over between the two. When the chiller tripped out due to the fault, the other chiller was supposed to have been enabled. This did not happen, so our engineer investigated the situation. The sequencer panel sends out a 24v fault feedback signal to each chiller. This, in turn, goes through a relay and back to the sequencer panel if all is good. When a fault occurs, the volts drop out to the relay in the chiller and a relay drops out in the sequencer. When the relay drops out in the sequencer, a normally closed contact makes and brings a red light on. This was not happening, so our engineer followed it through with his multimeter. He found a blown 1 Amp control fuse in the chiller, he replaced it and it blew again. After some careful research he found that there was an earth leakage due to the ingress of water into a safety switch. This switch was nothing to do with the above, but it blew the whole control circuit. Having reinstated the fuse, he found that the panel switched over satisfactorily in local.

Advantages

This kind of operation method has an advantage in its simplicity. There are no complicated BMS systems for the chiller to be integrated into. A sequencer panel is easy to construct and maintain- keeping the costs down to the end user.

Disadvantages

The disadvantage of this kind of system is that the first thing the factory usually notices is that they are loosing the process. The water temperature getting too high is the first alarm signal. With this site, however, there is a permanent onsite engineer on hand. He is experienced with the first checks to carry out and can often get the plant running with no problem.

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Standing Pressure during Industrial Chiller Service

The standing pressure was taken into account on the return visit to fit the oil return solenoid valve seal. Because the valve is on the low side of the system, when the chiller is off, the pressure is higher than when it is on. Therefore, so long as the seal pressure tests to this pressure, then all will be good when the system is running. That is assuming that the valve seals work satisfactorily at a lower temperature range. There are issues sometimes when a seal will be okay at ambient temperature but will leak when it becomes brittle at a colder temperature. This happens usually on an old seal and, indeed, this condition can be tested for when run testing the system.

Leak Testing during Industrial Chiller Service

On fitting the seal, our engineer donned full length ammonia resistant PPE and breathing apparatus. A little at a time, he introduced refrigerant into the area of the valve seal. Any residual air being purged through a valve.

Pressure and Temperature

The standing pressure of refrigerant is affected by temperature. That is to say- that the higher the temperature- the higher the pressure. On the day this job was carried out, the ambient temperature was 12°C and using an app on his phone, he calculated that the pressure should be 5.6bar. This is consistent with Charles’ Law of Constant Volume with a coefficient added for this particular refrigerant. If the pressure had been higher than this, it would indicate the presence of air in the system. Daltons’ Law of Partial Pressures states that all gasses in a vessel will act as if they are on their own, therefore, causing a higher pressure.

Run Testing during Industrial Chiller Service

After the pressure was built up to full standing pressure and the seal held satisfactorily, the system was then run tested to ensure, as stated above, that the seal performed well across the full temperature range during the operation of the plant.

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Mass Flow Rate during Industrial Chiller Service

The mass of refrigerant passing, which is measured by the second.

Suction Density

In this case of the oil return valve seal, we are looking at the density of the low side refrigerant as it passes into the suction port of the compressor. This is shown on the LP gauge near to the compressor. The higher the pressure of the refrigerant, the more refrigerant there is- so it has a higher mass flow rate. This system has a refrigerant saturation point of 1°C which corresponds to a pressure 3.4bar. That is a high mass flow rate for this kind of refrigerant. This is because this refrigerant is usually used in low temperature applications where the pressure of the refrigerant is below that of the atmosphere. In that condition, when a leak occurs on the low side of the system- air leaks in. Air bleed valves are available to remove this unwanted air from the system.

Compressor Loading

The bigger the compressor on a chiller- the higher the mass flow rate. Most compressors have loading solenoids, vanes, or a slide valve to regulate this.

Piston Displacement

Reciprocating compressors use loading solenoids to increase piston displacement. Usually, oil from the oil pump holds the piston valves open and so preventing compression on that cylinder. When more flow rate is needed- the loading solenoid de energizes- the piston valves drop and the cylinder comes into action. Therefore, increasing the mass of refrigerant through the compressor.

Vanes

Vanes are used on centrifugal compressors to increase the flow of refrigerant through the compressor. An actuator linked to a chain is used to open the vanes. The controls work out the correct position of the vanes for a given load condition.

Slide Valve

The slide valve offers a seamless amount of loading, anywhere between 0% and 100% A slide valve potentiometer senses the position of the slide so that the controls can regulate the flow through the compressor. The screw compressor in this article uses a slide valve- on full load with the slide at 100% all readings were taken with a good read back. Another job done- another happy customer!

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To read more about chiller fault finding hit the Tag at the top of the page.

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400 kw white chillers with panels open during air cooled chiller maintenance

Air Cooled Chiller Maintenance

A nice day to carry out air cooled chiller maintenance at a new site we have taken over in the South East.

News Article No.6

Our engineer attended site at around 9am with the risk assessment method statement having been sent in advance. A site survey was carried out to see if there were any additional risks. Should there have been any changes- the RAMS have a section for the additional risks and control measures. After gaining a permit to work, our engineer was issued with a security pass to access the chiller compound. Three chillers are located in the compound which feed air handlers for a critical application. Two of the chillers are multiple system, scroll compressor, air cooled chillers. The other is a single system screw chiller.

Program Settings during Air Cooled Chiller Maintenance

A complete download of the program settings is available in our engineer’s phone. This is to cross reference the settings, should one of them be accidentally changed by the maintenance engineers. On site engineers are the first port of call for chiller trip outs, with the responsibility to get the plant up and running. We offer real time assistance, over the phone from our Technical Support Desk and can send user manuals in PDF form, direct to their computer. The settings were found to be nominal, so a detailed analysis of the alarm history was carried out:

Alarm History during Air Cooled Chiller Maintenance

In reverse date order, the alarm history of all the systems was interrogated. There had been several system shut downs to carry out the periodic maintenance by the onsite personnel. The electricity having been shut down, there was a subsequent oil pre heating timer in the history too. On Chiller 2, System 1 however, there had been several low pressure trip outs. Our engineer decided to start the maintenance with this system by carrying out a full diagnosis of the low side of the refrigerant system:

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Superheat during Air Cooled Chiller Maintenance

The system runs on R410a refrigerant. This refrigerant has higher operating pressures in comparison with other HFC refrigerants. It has an efficient temperature range which can be seen on a pressure enthalpy chart. Below or above this range- the refrigerant loses efficiency and so has a lower coefficient of performance. The most common saturation point for this refrigerant is 0°C which corresponds to a 7 bar suction pressure in the evaporator. Above this is the superheat of the refrigerant returning to the compressor. On this occasion there was found to be 26°C of superheat and a suction pressure of 4 bar- close to the low pressure trip out. After careful diagnosis, our engineer decided to focus his attention on the expansion valve:

Thermostatic Expansion Valve

There are 4 forces acting on a TEV:

Liquid line pressure coming from the condenser.
Versus
Suction pressure down the equalising line from the far side of the evaporator. This compensates for the pressure drop across the evaporator and shows the true compressor side pressure.

Spring pressure acting upwards and closing the valve.
Versus
Bulb pressure forcing the valve open.

To reduce the superheat, the bulb should have forced the valve open. The refrigerant charge in the bulb acts upon the bellows to achieve this. The reason for the malfunction, on this occasion, was found to be the failure of the expansion valve orifice. It had become jammed- causing a shortage of refrigerant in the evaporator and high superheat.

Latent Heat

Our engineer was carrying out the above fault finding with one compressor running and the other two being held off. This was to prevent a low pressure trip. Where chillers are left running with a high superheat condition, the reduced amount of latent heat causes a higher cost in electricity relative to refrigeration effect (COP) The refrigerant carries on superheating without absorbing latent heat- pointless and inefficient for a chiller.

Chiller Pump Down

For convenience, this chiller can be pumped down and valved off using the service valves. The evaporator can be worked on after breaking in procedures are carried out. Therefore, we have arranged for this to be carried out before fitting the new expansion valve parts. These chillers also have the ability to pump down the refrigerant on receiving a fault feedback from the electronic leak detector. This is an added measure to lower the environmental impact of refrigerant leaks.

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Subcooling during Air Cooled Chiller Maintenance

This is cooling the refrigerant vapour down, through the latent heat phase and then subcooling the liquid down further. On System 2 of the same chiller, a subcooling issue was identified. 21 bar/ 36°C saturation was normal for that system as defined by the fan speed controller. Now, the system pressure was higher at 28 bar/ 47°C saturation, so our engineer decided to work out the subcooling. A very high reading of subcooling was recorded at 28°C this was diagnosed to be due to non condensables in the refrigerant:

System Non Condensables

Non condensables are gases that will not condense, such as, air and nitrogen. If nitrogen is not vented properly and a deep vacuum then achieved, the gasses will remain in the refrigerant system. When calculating the subcooling, the readings work out incorrectly due the presence of the gasses. This can lead to false diagnosis. The remedy for the issue was to arrange a full refrigerant decant, pressure testing and dehydration, before charging with new refrigerant.

Efficiency

Having good subcooling values on a refrigerant system is critical to efficiency. Where there is no subcooling- the refrigerant has not fully rejected all the latent heat from the condenser. This can be seen when looking at a PH chart and plotting the pressures and temperatures. This heat remains in the refrigerant and adds to the system along with heat added from the compressor and heat from the process. This is another reason the coefficient of performance is reduced and so incurring increasing electricity costs for the plant.

Economizer

These chillers are also fitted with refrigerant economizers- one for each system. They work by diverting some of the refrigerant from the condenser, through a small expansion valve, then through a plate heat exchanger. The rest of the liquid refrigerant passes on the other side of the plate heat exchanger and so is further subcooled.

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To read more about chiller control systems hit the Tag at the top of the page.

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Yellow oil drums, ammonia refrigerant cylinders and flammable flushing agent of chiller supplier

Chiller Parts Supplier

Chiller Parts Supplier of Compressors

Centrifugal

As a chiller parts supplier, all kinds of centrifugal compressors are remanufactured in our workshop. With an overhead gantry crane and specialist equipment to hand- Maximus Chillers completes the picture. We have a lift and shift team who are skilled at getting the compressor out of the most awkward locations. A variety of lifting equipment is used, including 3 phase electric hoists and trollies. Our team do this kind of work all the time, so they are accustomed to overcoming all the difficulties and obstacles.

Screw

Screw compressors are remanufactured on the bench. With compressed air and bearing tools- our skilled technicians are seasoned in high tolerance measurements. The bearing clearance and shaft run out are accurately measured and adjusted. This means that the useful life of the compressor is extended, often to beyond the lifespan of the chiller.

Scroll

We have a range of off the shelf Copeland compressors for a fast lead time on process chiller repairs. These can be sent to site on the day using our fast door to door supply chain. We have all the sizes of compressor available. The pipework and mountings can be adapted too. This means that if your compressor is a different make with a longer lead time- our compressor will be fitted and adapted to your machine- fast!

Chiller Parts Supplier of Condensers

Air Cooled

When the condenser on an air cooled chiller is in poor condition- our site survey team will attend to measure up for a new bespoke condenser. This is done free of charge and ensures that the new condenser will fit easily into the old chiller. The exact subcooling requirement of the old condenser is taken into account which is duplicated on to the new condenser. This means a like for like swap can take place even when the old condenser is obsolete.

Shell and Tube

This type of condenser is used on water cooled chillers. It is protected from contaminants by a strainer on the water system. We have these condensers built to order by our bespoke manufacturer. They are shipped to site on an overnight delivery, so we can get straight down to work in the morning. We therefore minimise downtime in the swap out of this part.

Chiller Parts Supplier of Evaporators

Shell and tube are the most popular type of evaporator for large chillers. The low temperature refrigerant is on the outside of the tubes in liquid form. The water is pumped through the tubes, releasing heat from the process and into the refrigerant. This is latent heat as the liquid refrigerant boils off into a vapour. Where the heat exchange does not greatly improve after cleaning, we recommend replacing this part.

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Vibration Eliminators

We have all of the sizes of anacondas on the shelf in our stores. This saves on the delivery time to site when your process is off due to the chiller. Maximus Chillers will get you up and running- fast! We can also fit flexible vibration hoses which achieve the same result as anacondas. Whereas two anacondas are fitted vertically and horizontally, only one, long vibration hose is needed.

Chiller Parts Supplier of Flushing Agent

When things go wrong, we stock a solvent based flushing agent which is blown through the system using nitrogen. The waste product is caught on the far end in drums that come with the kit. This is then returned to the suppliers for recycling.

Refrigerant Economizers

These are another term for a subcooler. If the refrigerant is further subcooled after the condenser- the system will run more efficiently. This part usually takes the form of a plate heat exchanger with an expansion valve providing the refrigeration effect needed to further subcool the remaining liquid.

Chiller Parts Supplier of Pressure Transducers

We can make temporary repairs to faulty pressure transducers using our test equipment. This will keep your plant running while the part arrives on site. Then we can get your chiller up and running with the correct readings in the controls. This will assist your onsite maintenance engineers in giving us useful readings when we are in communications over the phone.

Chiller Parts Supplier of Ammonia and HFC Refrigerant

A full selection of refrigerants are available including: anhydrous ammonia, R407c, R134a and R410a. These refrigerants come in small 12kg, midi 26kg, large 56kg and bomb 800kg sizes. Our vehicles are equipped with tail lifts and lifting gear to facilitate delivery. We can therefore arrange the delivery and collection of refrigerant at your site, free of charge, anywhere in the UK. For our overseas customers, we arrange the transportation from the local suppliers.

Chiller Parts Supplier of Oil

Low, medium and high viscosity oils in 5ltr cans and 20ltr drums are ready for shipping from our storage area. It is critical to select the correct grade of compressor oil as bearing wear and reduced service life will result. We take regular samples of this oil to see if things are starting to go wrong in the compressor. We can then nip these problems in the bud, giving you dramatic savings.

Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere- The MAXIMUS ADVANTAGE™

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To read more about chiller evaporators hit the Tag at the top of the page.

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Air cooled chiller planned maintenance showing both economizers with solenoid valves and expansion valves

Air Cooled Chiller Planned Maintenance

An air cooled chiller planned maintenance visit for a long standing customer of ours. They have just signed up to another 3 year contract. We know at Maximus Chillers that if we want to keep our customers, we must continue to offer the Maximus Service. Maximus is Latin for the highest and the greatest.

Critical Air Cooled Chiller Planned Maintenance

Planned maintenance is essential for these chillers as they are critical plant. They feed a large conference room which is a major part of the end user’s business. They cannot afford to loose the conference room when there is an event on. There is redundancy in the plant, but the customer always makes sure that the issues highlighted on the maintenance are acted on promptly. Also, the chillers feed a water cooled condenser for a pack which cools £50,000 of products used during the conferences.

Air Cooled Chiller Oil Planned Maintenance

There is 1mw of cooling across the 2 chillers. Our engineer noticed that the oil level was slightly below the sight glass on one of the 250kw Bitzer compressors. The machine had previously been extensively run tested to ensure no oil return issues were present. Therefore, he decided to adjust the level with the oil available onsite.

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Economizer

The economizers, in the picture, were tested to ensure the solenoids were opening when the program sent the run signal. The electronic expansion valves functioned correctly and subcooled the liquid further after the condenser.

Head Pressure Control

The head pressure control was functioning correctly, keeping a steady 8 bar of pressure across all stages of loading and water system temperatures. This is because these chillers use a fan speed controller for each system. The fans cut in at the minimum running speed, which prevents stalling and over heating. Also, all fans running together are more reliable. Fans fail on systems using relays or pressure switches as the higher pressure fans don’t often come on. When they do, moisture has ingressed into them causing them to fail.

To read more about chiller critical plant click the Tag at the top of the page.

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