Monthly Archives: December 2021

Offshore oil rig showing chiller service being carried out in marine environment

Offshore & Marine Chiller Service

North Sea Offshore & Marine Chiller Service

On a previous visit for offshore & marine chiller service on an oil rig, our customer had shown us to a large air cooled chiller. His complaint was that it was tripping out all the time when there was nothing wrong it. Complicated ‘in house’ controls, where a string of PCBs, plugged into each other were found in the panel. We recommended a controls retrofit and received the order to carry out work…

Finicky Controls

All of the finicky control PCBs were removed from the panel and placed in the electrical recycling skip.

Offshore & Marine Chiller Service to Control Wiring 

The control wiring was removed and grouped together according to colour. This was because the same wiring was going to be re used to re wire chiller.

Inverters

Two Danfoss inverters were installed into the panel. These were to provide a VSD (variable speed drive) for two large screw compressors.

Electronic Expansion Valves

Danfoss EEVs were easily brazed into place as both systems could be pumped down and valved off. This part of the fridge system was then nitrogen pressure tested then vacuumed according to standard industry guidelines.

Fan Speed Controllers

Both systems had a Danfoss fan speed controller fitted to the chiller frame to control the condenser fans. Then, the control transducers were wired in to the FSCs. This made them stand alone and capable of independently controlling the head pressure of each system.

Danfoss Chiller Controller

The controller in the photo is capable of running the inverter drives for the compressors and the electronic expansion valves. It was wired in, one wire at a time: first the Inputs, then the Outputs and finally the power supply.

Offshore & Marine Chiller Commissioning Service

We always carry out commissioning in the morning as this is the best time of the day to solve problems. It was time for a cup of coffee and a deep breath. Our engineer had only re wired one panel previously and he was also a long way from the office.

Switch On

When he switched the power supply on, there were no immediate problems, so he waited for the for the timer to count down. System 1 started and after a while System 2 started too. There were a few teething problems with the settings, but then the chiller settled down. No more spurious trip outs.

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Controller used in offshore chiller service
Cheap and very reliable

Offshore & Marine Chiller Service in Liverpool

A bulker had got into difficulties in the Irish Sea and been towed to Liverpool for service. It was discovered that a rope had got wrapped around the propeller. Aside from this, one of two chillers which are used for the cooling of the living quarters had tripped out. The Chief Engineer had therefore decided to kill two birds with one stone. Most of the crew were from around Tanger Med in Morocco and so spoke only a little English. They also have limits as to how far they will go with a fridge system. Not to worry though: all we need is to see the plant and we can take it from there...

Seawater Cooled

The plant had a sea water cooled condenser which was fed via a pump set in an adjoining plant room.

Offshore & Marine Chiller Service to Controller

The controller alarm message stated that there was a low pressure condition in the evaporator. On interrogation of the menu, however, the pressure of the evaporator was found to be 7 bar which was the same as in the condenser.

Reset

Our engineer therefore decided to follow through the reset procedure. The alarm cleared and the machine started up. Then, it pumped down to 1 bar and tripped out on the same fault.

Liquid Line Solenoid Valve

While this was happening, our engineer was quick to notice that the liquid line solenoid valve had not activated. He decided to manually jack it open with his test equipment and the refrigerant rushed through okay.

Liquid Line Solenoid Coil

Having decided that the valve was okay, he then investigated the coil. The connection box and the wiring was found to be in poor condition.

Isolate

He then isolated the power supply and checked that it was dead.

Rewire

The wiring was cut back and he re made the connections onto the solenoid coil without using the connection box. Then, he insulated the area with a special compound.

Test Operation

Now to see if he had got the diagnosis correct. He powered up the chiller and carried out a run test- all readings were found to be nominal and the machine went back into service.

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Planning for Offshore & Marine Chiller Service

The main part of the planning for an offshore visit is done on the previous job. A detailed list of the required parts, materials, refrigerant, tools and equipment is composed on our Offshore Manifest Sheet. The questions and headings have been designed to prompt an engineer into thinking about all aspects of the job in detail.

Preparation for Offshore & Marine Chiller Service 

Having emailed the above mentioned sheet to Head Office, we cross reference the information with the engineer while he is still offshore. All this preparation is to ensure that the upcoming job goes as planned. There would be nothing worse than to have to postpone the job due to a lack of preparation.

Steel Chests

We have several steel chests that we use for shipping to oil rigs. After the parts and materials arrive at Head Office, they are checked off, one at a time into the shipping chests. Then, the necessary tools and equipment is checked off too.

Offshore Stores

Our customers also have their own equipment in their stores. They have things like fittings and fuses too. This is a good backup for when something is unforeseen, or if something breaks.

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Chiller Controls

Chiller Commissioning

Chiller Controls Company

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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!

Related Articles:
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Water Chiller Service of Evaporator

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Read more about how a solenoid valve works on The Engineering Mindset.


Ammonia warning sign and yellow light flashing during chiller call out

Chiller Call Out

Chiller call out is the essence of what a company like Maximus Chillers is all about. It is a time when our engineers come into their own. Read on to see examples of how we do it…

News Article No.22

Chiller Call Out for Ammonia Leak Alarm

At first sight this appears to be a dangerous situation as ammonia is very harmful to human health. This is because of its corrosive and toxic characteristics. Each of our engineers carries breathing apparatus and full length ammonia PPE should it be required.

Location Assessment

The work location in the photo is assessed using an NH3 detector. This is sensitive enough to detect lower than the 35 parts per million short term exposure limit. The detector is fitted to the work wear of our engineers whilst near to the plant. When the alarm does not sound and there is no smell of ammonia- it is safe to proceed.

Electrical Fault

Usually this alarm is due to a controls issue rather than a leak. There are various reasons:

UPS and Alarm System Malfunctions

Chiller panels for this kind of plant have a UPS (uninterruptible power supply) This is a battery which is charged by the mains. When a power failure occurs, the charge in the battery supplies 240v to the ammonia alarm. This means that the chiller continues to be protected. When malfunctions occur to the UPS or the alarm system, the yellow warning light and siren is activated which needs to be manually reset.

Sensor Failure

The sensors have to be calibrated at regular intervals. The base setting of 0 parts per million has to be set and then the trip outs of 35 and 25 parts per million. These sensors can be knocked out of calibration by small leaks over a long period of time, or they can malfunction internally. If you require the service of your leak alarm- email our Technical Support Desk and will arrange a site visit.

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Chiller Call Out for BMS Failure

Chillers can get blamed for everything as the customer can notice a building that is getting warm and then call us out. An example of this is when a new customer of ours signed up to a maintenance contract after a long period of neglect. They did so because the office workers in a large office block had started to leave their desks and walk out of the building.

Investigation

When our engineer attended site, he found various faults with a row of four, 500 kW chillers on the roof. There was found to be N+1 redundancy built in, so he considered there to be sufficient cooling available to satisfy demand.

No Run Signal

Despite there being available load, the chillers were not being given the run signal from the BMS. The toggle switches on the BMS panel did not give the run signal to the chillers when they were put into Hand. This was found to be because of other issues with the poorly maintained panel.

Link Out

Our engineer therefore decided to link out each of the chillers in their respective panels. He consulted the wiring diagram and made the modifications accordingly. He then entered the password for that particular chiller and adjusted the program settings. These changes made the chillers stand alone and not reliant on the BMS run signal.

Chiller Call Out for Pump Sets

The pump sets were also found to be in poor condition. There were found to be failed pumps, blown contactors and defunct controls. The good news was that by changing components in the panel, he managed to get at least one of each pair of pumps going for the various water systems used around the building.

Pressurisation Unit

This is a machine with an internal pump and a pressure switch which is used to maintain the pressure of the water system. Both the run and the standby pumps were found to have failed with other component failure in the unit as well. Our engineer decided to manually fill the water system with mains water to build up the pressure.

Get it Away

Having done all this, our engineer got the chillers away and watched the water temperature come down from 24°C to 6°C. As the chiller systems came down to set point, they unloaded to match the demand from the building.

Return to Work

The office staff started to return into the building and resumed work at their desks.

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Fault Finding during Chiller Call Out

Now that the pressure was off, our engineer carried out the necessary fault finding to the systems that had failed:

 Refrigerant Leaks

Three of the systems were found to be locked out with low pressure alarms. He assessed the quantity of recovery cylinders and refrigerant that was required. Then, he submitted a report to Head Office for a return visit to carry out the repairs.

Blocked Condensers

Some of the systems were found to have blocked condensers. The call out was during the summer when a high pressure condition was more likely to occur. A build up of contaminants had reduced air flow and caused the high pressure switches to be activated. We arranged a site visit with a special cleaning agent to remove the contaminants and restore the air flow through the condenser fins.

Chiller Call Out for Flow Switches

These are a switch used to detect water flow and two of them were found to have had failed. There are various types for different applications. We select a suitable flow switch and then make the necessary adjustments to the internal control screws. This ensures that the switch will function correctly when problems with the water system occur. 

Related Articles:
F-gas Chiller Leak Testing

Chiller Fault Finding & Diagnosis

Air Cooled Chiller Condenser Testing

Chiller Breakdown

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