Preventative Chiller Maintenance

Carel controller showing R134a refrigerant readings during preventative chiller maintenance

Preventative Chiller Maintenance

We at Maximus Chillers will optimise the efficiency and take years off the life of your plant with preventative chiller maintenance.

News Article No.9

Chiller Control Panels

The first thing our engineers check at the start of the maintenance is the chiller control panel. In here he checks:

Programmable Logic Controller

Alarm History

The alarm history is analysed in sequential order to build up a picture of the last maintenance period.

Settings and Timers

The various levels of password accessed menus are checked and adjusted for efficiency and to eliminate any spurious trips on the running of the chiller.

Compressor Run Hours

We make a note of the compressor run hours on our detailed Tick Sheet. Bearings on centrifugal compressors and valve gear on reciprocating compressors are changed at pre prescribed intervals as defined by the manufacturer. This is to prevent an expensive failure and the resulting remanufacturing of the compressor.

Preventative Chiller Maintenance of Electrical Safety Devices

Fuses

Each one of these is popped from its holder and the continuity checked with a multimeter. This is maintenance the right way round, instead of run testing and following the fault back to the fuse.

Circuit Breakers

Each of the breakers is tested to ensure it will function correctly when it needs to.

Residual Current Device

RCD’s work by detecting current leakage to earth. It monitors the difference between the live and neutral poles. As above these are tested on each visit.

Preventative Chiller Maintenance of Refrigerant Safety Switches

High Pressure Switches

The settings and dead band (the difference in pressure between cut out and cut in) are checked and adjusted on each visit. Sometimes due to malfunctioning controls or condenser condition, fans can be manually left off or can be forced on. Not the best running condition, but we will keep you up and running until we send out the new parts. Where this is a bespoke manufactured condenser, we have the best lead time available.

Low Pressure Switches

As above, the low pressure switches are checked and adjusted as need be. The seasonal and varying load conditions affect the saturation point of the refrigerant in the evaporator. This can cause untimely trip outs when the plant is otherwise running in optimum efficiency.

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Coefficient of Performance during Preventative Chiller Maintenance

The coefficient of performance is the cooling effect compared with the electrical energy supplied to the chiller. It is represented in a ratio, for example 6:1. That is six times more cooling effect compared with the electricity supplied. The higher the cooling effect relative to electricity supplied, the lower the cost in electricity. The ratio is often divided by 1 to show as just a number- in this example 6. The cooling effect is measured in kj/kg and the electrical supply is represented in kw/h.

Latent Heat 

A chiller system would have a COP of less than 1 if not for latent heat. Exploiting this hidden heat when both evaporating and condensing the refrigerant is one of the founding principles of the basic refrigeration cycle. It takes a lot of heat added to the system to get the refrigerant to boil, then the same amount of heat is rejected from the condenser in the liquification of the refrigerant.

System Efficiency

A lot of basic things routinely drag down the efficiency of a chiller system. Just with the effect of our engineer attending site to carry out the maintenance- he will keep the COP optimised. Here are some of the system checks and procedures he carries out:

Superheat

When a compressor never goes off due to refrigerant shortage, there is a dramatic increase in electricity consumption. Also, the system will not have very much cooling effect. Continuing like this will cost more money and achieve little.

Subcooling

Basic condenser maintenance will improve the subcooling values. These readings will be taken at various load and ambient conditions at different times of the year. This is so we can build up an understanding of the plant. We carry a wide range of chemicals for the maintenance of your condenser. These chemicals are carefully selected so that they do not damage the condenser causing leaks. Condenser fans also cause a poor COP:

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Preventative Chiller Maintenance and Condenser Fans 

Basic Design

With some basic chiller designs, the chiller condenser fans come on and off forwards and backwards at different pressures. This means that when other fans have failed, or are stuck going backwards- the one on the end comes on with the higher pressure then blows to earth. This is due to the ingress of water in the year it did not run.

Refrigerant Leaks

The above design means that there are fluctuating pressures in the condenser. This causes continuous expanding and contracting of the copper tubes. These copper tubes rub against the steel frame which is holding them in place- causing reoccurring leaks. Another reason for repeated leaks on the condenser is the vibration issue of the fans banging on and off. Add into this equation a cheap, flimsy frame that develops its own resonance- you then have an un ending problem.

Preventative Chiller Maintenance with Fan Speed Controllers 

Part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere is that we can source any fan speed controller from our fast supply chain. This remedies the problem, as fan speed controllers bring all the fans on together at different speeds. Therefore, extending the lifespan of the fan and maintaining an efficient coefficient of performance.

Axial Fans

Most air cooled chillers use axial fans. They suck the air through the condenser and reject it upwards and away from the chiller. Ducts are often fitted to help this process. Scaffolding is erected to provide safe access to engineers.

Radial Fans

Radial fans are also called centrifugal fans or blowers. They are very popular in server rooms where air is blown down into a mezzanine floor and up through the racks. They are also used outside in chillers where they blow out and away from the chiller. They are usually driven by belts which require regular inspection and maintenance.

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Preventative Chiller Maintenance and R134a Refrigerant

In the photo, the controller shows R134a refrigerant and the 8.3° of superheat as calculated by the program. This superheat may look at first to be okay, but when considering the compressor loading and expansion valve- it points towards a system issue. Our engineers diagnose if the issue is related to a component or a refrigerant shortage.

Characteristics

HFC refrigerant which has a chemical name of Tetrafluoroethane or CF3CH2F. It has low toxicity which is good for the health and safety or our engineers. It is not combustible, but other chemicals are made as a result of a fire. It is non corrosive too, which extends the lifespan of the pipework and components around the system.

Centrifugal Drop In

This refrigerant is widely used as a replacement for HCFCs, such as, R22 used in centrifugal chillers. It is only one fluid, where as the other popular HFC refrigerants are blends. These blends fractionalize in a flooded condenser or evaporator. That is to say: one or two of the refrigerants in the blend separate out and do not continue their cycle around the system. The chiller now has the wrong refrigerant circulating around the system for the application temperature. Extreme running faults follow, such as, ice on the compressor, suction pipe and expansion pipe. This is as a result of the refrigerant pressures and temperatures being outside of nominal conditions.

Global Warming Potential

A global warming potential of 1430 is considered to be high. Therefore, the refrigerant is being phased down to 21% by 2030 in line with F-gas guidelines. These guidelines are in accordance with the European Union and the Kyoto Protocol. Because of the regulations for the handling of fluorinated gas, our engineers attend college to learn how to decant the refrigerant safely. We then ship it to the recycling centre for disposal. A waste carrier note being completed each time to track the refrigerant from dispatch to disposal. Finally, F-gas leak tests are carried out and recorded on each visit. Maximus Chillers completes the picture.

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

To watch a video about chiller efficiency and the coefficient of performance | Click Here


Blue recovery unit with a grey recovery cylinder during a chiller breakdown

Chiller Breakdown

A rainy day for a chiller breakdown for our engineer in the North West.

News Article No.8

Electrical Faults during Chiller Breakdown

Our customer called us out because he was having electrical faults with the chiller. The power supply to part of the panel had gone down and he required our assistance. Our engineer found a blown fuse which he replaced and tested operation- it blew again. Using his multimeter, he followed the diagnosis though to an earth fault on the flow switch…

Water System Flow Switches

The flow switch vapour seal had failed allowing rain water to ingress. This caused an earth failure on the 240v control circuit, and so blowing the fuse. The customer raised an order forthwith and so our engineer replaced the flow switch with the stock from his car. Each of our engineers keeps a range of flow switches for a variety of applications…

Stainless Steel

Where water system chemicals are corrosive, we carry corrosion resistant flow switches. This type has a longer working life due to the use of stainless steel. They are more expensive due to the higher manufacturing costs, but they are worth the money as they are less likely to fail, causing a potential loss of production.

Outside Use

This was the type fitted by our engineer on site in this news article. It has been developed and tested across a range of adverse weather conditions including freezing conditions and heavy rain. The electrical and switching compartment is protected by a sealing gland to keep the weather out. A rubber ‘o’ ring provides the seal into this compartment.

Inside Use

Some applications have the flow switch located inside the building in the plant room with the control cable extending out to the chiller controls. Another configuration allows for the flow switch to trip out the building controls and so dropping out the run signal to the chiller. In either case there is no need for weather proofing. This kind of flow switch is cheaper due to the lower construction costs.

High Pressure

Some water systems operate at considerable pressure. Therefore, high pressure flow switches have been developed for this application. They are capable of preventing water ingressing from the water system and into the electrical and switching compartment.

Test and Adjustment

Our engineer carried out testing and adjustments to the flow switch to ensure that it ran reliably. He achieved this by monitoring the water system readings and measurements against the design specifications of the switch. When he got it to settle down, he replaced the fuse and ran tested the chiller...

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Condenser Fans

The condenser fans were not coming on at all at first and later only slowly. They are controlled by a fan speed controller which is sensitive to pressure. A minimum value of volts is supplied to the fans, so as to prevent stalling and over heating of the internal motor windings. The fans were found to be in good working order, so he decided to turn his attention to…

Refrigerant Pressure Temperature Relationship

There was found to be a lower pressure and so a lower temperature in the condenser. After careful fault finding and diagnosis involving putting the pressures and temperatures into a calculator, our engineer decided that the chiller was running short of refrigerant. This is consistent with Charles’s Law of Constant Volume: one of the fundamental scientific principals of how a chiller works- the higher the pressure- the higher the temperature/ the lower the temperature- the lower the pressure.

Refrigerant Recovery Units

After receiving a further order from our customer, we gave the go ahead to our engineer to use his refrigerant recovery unit to decant the gas. The refrigerant is sucked into the unit using a small one cylinder reciprocating compressor. The compressor discharges into the on board condenser which is cooled by a fan. The subcooled refrigerant travels down a refrigerant hose which is connected to the recovery cylinder in the picture. After this process was complete, he started looking for a leak...

Leak Testing and Pressure Testing

The leak was identified on the flange for the expansion valve. This component was removed, cleaned with our in house refrigerant grade solvent, then the joint re made with a compound suitable for the temperature range of the component. After a satisfactory nitrogen pressure test, the evacuation process can begin…

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Refrigerant System Vacuum Pumps

Each of our engineers carry a high capacity vacuum pump of the highest quality. We believe in investing in state of the art equipment as this is part of how we provide the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. Good equipment makes the job go easy.

Vane Pump

The pump works by sucking vapour into the inlet port. A rotary vane system extracts the vapour and discharges it through the top of the pump module. Oil is used to lubricate the vanes that slide around the pump cylinder. The vanes are kept a tight fit against the cylinder with the use of springs. As our pumps are high capacity, an oil filter is fitted to the outlet with a gauze inside to catch any oil droplets.

Electric Motor

This motor fits onto the back of the vane pump module. It comes from the factory set to 240v, but we change the pins for the electrical connections to convert it for use with 110v. This is because customers and engineers demand the use of 110v as if is safer for use in the UK climate. The 110v plugs and extension cable are shrouded and weather resistant. Weather resistant does not mean weatherproof, so we take measures to limit the exposure to adverse weather conditions. The pump motor, however, is not weather resistant at all, so care is taken to locate it somewhere dry. After a long time running, the motor runs hot, so our engineers take readings and carry out adjustments to ensure that it stays within its nominal operating temperature range.

Oil Changes during Chiller Breakdown

The vac pump oil is changed before each use with our specialist grade, high quality oil. Contact our office for prices and delivery times. The manufacturer of the pump recommends these oil changes as moisture and impurities absorb into the oil and so reduce its performance, also the working like of the pump.

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Refrigerant System Evacuation Process

Having set up the vacuum pump, our engineer started the evacuation process.

Torr Gauges used During Chiller Breakdown

We use analogue Torr gauges as they are more reliable than digital ones. Also, they do not need batteries and it does not matter if they get wet. He attached the Torr gauge to a suitable part of the system with a refrigerant hose, ensuring that a good seal was made between the components with a sealing compound.

Fittings used during Chiller Breakdown

Fittings were used to get between the different thread types from the vac pump to the fridge system. Having warmed up the pump for half an hour he was ready to start the process.

Non Condensables Removed during Chiller Breakdown

One purpose of evacuation is to remove the gasses that will not condense such as nitrogen remaining in the system from pressure testing. Another non condensable is air that has entered the system from when the expansion valve was removed. These non condensables affect how a fridge system works according to Dalton’s Law of Partial Pressures: that all gasses in a vessel act as if they are on their own. The non condensables cause a higher head pressure and false readings: when this pressure is added into our calculation- it throws out the sum and so gives a false reading of subcooling.

Dehydration during Chiller Breakdown

The other purpose of evacuation is to dehydrate the system. Water, as we know, has a boiling point of 100°c at sea level, which is 1bar absolute or 760 Torr. As you start to drop the pressure, so correspondingly, the boiling point also drops. For example, water boils at the top of Mount Everest at around 68°c. If we continue vacuuming a refrigerant system, eventually we can remove all moisture by dropping the pressure below the saturation point of water. This works even in the winter in UK ambient conditions. Moisture in the system causes system failures and malfunctions leading to expensive breakdowns.

To read more about flow switches hit the Tag at the top of the page.

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Chilling plant maintenance of grey machines with red warning signs

Chilling Plant Maintenance

We at Maximus Chillers carry out chilling plant maintenance in factories and facilities around the UK and overseas.

HFC Refrigerants

HFC (hydrofluorocarbon) chiller refrigerants were developed to be chlorine free. For a while they were seen to be the great new thing until the GWP (global warming potential) of the refrigerants became more of a concern. The release of these refrigerants from leaking systems dramatically increases the green house effect and so trapping more heat in the atmosphere. For this reason, F-gas regulations are phasing them down to 21% by 2030. Because of the 650kg charge in the chillers in the photo, we carry out leak testing at one month intervals. Where a leak is identified with this refrigerant, the system can be pumped out using the push/ pull method. There are no refrigerant system shut off valves available to allow the systems to be pumped down.

Chilling Plant Maintenance using Leak Detectors

We employ HFC refrigerant leak detectors to identify any leaks around the system. On systems of this size, there may be more than one leak, with a large leak alerting the attention of the engineer and the smaller leaks found subsequently. Our leak detectors are sent off periodically to be calibrated with the internal replaceable components upgraded as necessary.

Static Leak Detectors

Static leak detectors are available for each machine to catch any leaks as soon as they happen- before the one month intervals. This reduces the amount of refrigerant leaking to atmosphere and so adding to global warming. These leak detectors are bump tested on each visit to ensure reliability with replacements available on site, should one of them fail.

Chilling Plant Maintenance for One World

The above measures are essential with this kind of refrigerant in the interests of the environment. Basic checks now, protect the future of the planet. We only have one world, so we need to look after it as best we can. You can rest assured that you are in safe hands with how we handle this range of refrigerants.

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Shell and Tube Chiller Condensers

During the maintenance, we assess the subcooling values under part and full load to diagnose the efficiency of the shell and tube condensers. This kind of condenser is very popular with larger chillers in the UK. They are not sensitive to different weather conditions as the heat rejected into the condenser water system is pumped into the cooling towers outside of the plant room.

Chilling Plant Maintenance of Copper Pipework

The nest of pipes inside the shell are constructed using copper. This is because of the excellent heat transferring properties of this metal. On other sites where the refrigerant is ammonia for example, stainless steel is used as ammonia corrodes copper and most other metals and alloys. Thorough maintenance of the pipework is carried out on each visit.

Water System Maintenance

The water loop is inspected at various test points around the system with our range of test equipment. Where there are readings that are starting to go beyond nominal conditions, we carry out adjustment to bring them back into line. If the water system is behaving abnormally, this will in turn affect the efficiency of the condenser. In extreme circumstances, a system failure can occur causing a potential loss of production. Effective maintenance from Maximus Chillers has evolved over time to prevent this from happening in the first place. Each time we encounter a new issue, a thorough investigative process is carried out, the solution is arrived at and this is added into the routine.

Air Bleed Ports during Chilling Plant Maintenance

Air can be pulled into the condenser from the cooling towers outside. This can sit on top of the water in the condenser and so prevent the heat exchange of latent heat from the refrigerant and into the water. An air lock in the condenser amounts to that portion of the heat exchanger from not being in use. This dramatically affects the efficiency of the plant. We carry out checks to each condenser and bleed any air on each visit to ensure the best running conditions of the plant.

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Refrigerant System Standing Pressure

One of the ways to assess the condition of the refrigerant is the standing pressure. Only during factory shut down are all the chillers off for long enough for the system pressures to stabilize and so have a consistent standing pressure around the system. The pressure readings can be taken and added into our software to determine the composition and purity of the refrigerant and the presence of non condensables. Where the refrigerant is found to be in poor condition, maintenance can be arranged to rectify the issue.

Coefficient of Performance

The coefficient of performance is the cooling effect compared to the amount of electricity used. In an inefficient system, a small amount of cooling is achieved relative to a large amount of electricity used. In this age of environmental concerns, we carry out extensive measures and adjustments to improve the COP. Not only is an efficient plant cheaper to run, it is better for the environment too.

Control Panels

The control panels for the chillers in the photo are defunct. That is to say- the component parts are no longer manufactured. I am sure there is the odd circuit board rolling around on a shelf somewhere, but we fit state of the art controls. Our supplier builds bespoke panels exactly suited to each particular machine. They are plug and play with associated sensors, transducers and vane loading actuators supplied. The panel is fixed next to the chiller, wired in and ready to go. All settings come as default, so just the odd one needs to be modified. The panel can be easily integrated into the existing remote start stop and variable speed drives.

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To read more about shell and tube chiller condensers hit the Tag at the top of the page.

For further reading on Hydrofluorocarbon Refrigerants | Click Here


Large white chiller being inspected to compose a chiller maintenance schedule

Chiller Maintenance Schedule

The chiller maintenance schedule in essence is as follows:

  • What is the plant? According to the asset list for that particular contract.
  • What are we going to do with it? The checks, procedures and diagnosis in the pursuit of the maintenance of the chillers.
  • How Often? The periodic maintenance schedule defining the required interval between visits to ensure seamless operation of the plant.

News Article No.5

Chiller N+1

N+1 is intrinsic in the development of a chiller maintenance schedule. N+1 means the amount of cooling required + the same amount again in parallel. It can also be represented as 2N. Two water system pumps are a good example: where the pipework splits in two- one pipe for each pump. When a pump fails, the redundant pump comes online. Chillers are arranged in parallel, in this way, on the water system. This redundancy allows for a stress free maintenance of the plant. The failed system can be rectified and brought back online while the redundant system takes the load.

Intervals of Chiller Maintenance Schedule

The intervals in the contract are influenced by the redundancy of the chillers on site. The less run hours the compressor does, the less maintenance is required. We at Maximus Chillers can tailor make a maintenance schedule exactly to your needs by looking at how much the chillers are used and how hard they work.

Load affecting Chiller Maintenance Schedule

For some applications, the chiller operates under a high load condition all the time, with a redundant system in standby. On other applications, the chiller works in minimal load conditions. Regardless of the load conditions, the chiller is critical to the cooling of buildings or for an industrial process.

Lead/ Lag of Chiller Maintenance Schedule 

An important thing to remember is to balance compressor run hours and bearing wear by rotating the lead/ lag duty of the chillers. This can usually be done in the in the sequencer (if fitted) by changing a program setting. Otherwise, the switchover controls can be changed on the off/hand/run toggle switches. Where manual changeover is required, the onsite engineers are usually conversant with the procedure concerning the water system pumps, valves and controls. During the maintenance, the stop checks can be carried out on the redundant system, while the run checks are carried out on the system which is online.

Chiller Maintenance Schedule for Reciprocating Compressors

Reciprocating compressors require a log of the compressor run hours. This is because the valves and bearings should be changed at pre prescribed intervals as laid down by the maintenance schedule. Particularly important to reciprocating compressors are regular oil changes and oil sampling- a small change in the result of an oil sample can prevent a serious compressor smash up. A check list including the model number and serial number is completed on each visit and kept in a file on site. This file can be consulted during diagnosis and maintenance to decide on the beast way forward with an on going issue.

Chiller Maintenance Schedule for Air Cooled Chiller Condensers

Air cooled chiller condensers can often be looked after by the onsite engineers in between maintenance visits. Just a quick brush down every few months is usually all it takes. Where the environment lends to a type of contaminant being collected on the condenser coils, an effective chemical is selected from our stores and used on the coil. Where there is an issue with the serviceability of the condenser, we can put together a plan to keep on top of it. We can even retrofit a new condenser- it’s what we at Maximus Chillers call the MAXIMUS ADVANTAGE™

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Shell and Tube Evaporators

The shell is made from a heavy steel sheet rolled into a circle. The seam is welded together to form a cylinder. The tubes are pushed though the tube holders which are made from steel and are welded into the shell of the evaporator. The tubes are copper because of its good thermodynamic properties.

Direct Expansion Evaporators

Direct expansion is achieved in an evaporator with a thermostatic, or electronic expansion valve. The refrigerant enters the valve from the condenser as a high pressure, hot liquid. The pressure drop on the evaporator side of the valve makes the refrigerant flash off into a cold, saturation point liquid and vapour mix. The liquid boils off, absorbing latent heat through the inside of the copper tubes. On the outside of the copper tubes is the return water from the process, or the cooling of buildings.

The parts of the maintenance schedule that relate to DX evaporators are:

Oil Pooling

The inside of the tubes are in the clean environment of the fridge system. This means they do not become fouled. A tube insulating issue can be caused on the inside by oil. If there are issues with the oil return system, the oil can pool in the evaporator. A low refrigerant charge can have the same effect. Written into the maintenance schedule are manual oil return and oil draining visits. During these visits, the monitoring of the refrigerant charge is also carried out.

Sensor Location

If a sensor is not located in its pocket correctly, or without sufficient heat transfer paste- it will read incorrectly back to the electronic expansion valve driver. This will cause the expansion valve to malfunction.

Pressurisation Units

A full maintenance of the pressurisation unit is carried out. This includes the pumps, controls and program adjustments as required. Incorrect pressure in the water system will cause a knock on effect of faults on the chillers.

Pump Sets

As above with chiller lead/ lag change over, water system pumps are manually changed over from lead to lag in the building controls. Carrying out this procedure reduces the chance of pump failure between visits. This is because it balances the pump run hours and so prevents bearing seizure after a long period not running.

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Flooded Evaporators

Flooded evaporators are the reverse of the above DX evaporators. The refrigerant is on the outside of the tubes, with water on the inside of the tubes. Gravity and refrigerant charge determine the refrigerant level in the condenser and evaporator. In between the two is located the liquid pipe with the orifice located in the pipe for the expansion of the refrigerant. The cooling water flows through the condenser tubes and off to the cooling towers. On the low side, the chilled water flows through the evaporator tubes and off to the process, or the cooling of facilities.

The parts of the maintenance schedule that relate to flooded evaporators are:

Tube Fouling

Because the condenser cooling water and chilled water systems are pumped through the pipes, the tubes become dirty over time. This occurs more often on the condenser as the water towers are open to atmosphere. Contaminants from surrounding buildings and factories gets into the water system and thermally insulates the tubes. This thermal insulation reduces the heat exchange through the copper tubes. The knock on effect is higher head pressures and eventually high pressure trip outs.

Specialist Cleaning Equipment

We at Maximus Chillers have in our stores the required equipment to carry out the cleaning of the tubes. Our engineers can attend site and liaise with the onsite engineers as regards the draining, strip down and lift out of the heat exchanger end plates.

Flushing Agents

A water sample is taken from the cooling and chilled water systems. These samples are sent off to our laboratory for analysis. Bacteria can build up in the water system causing slime- this can be rectified with a careful selection of chemical agents. Also, silt can build up- various chemicals are added to positively charge the silt and so carry it around the system to the strainer. Where the issue is caused by rust- an inhibitor can be added to prevent, or slow the oxidization of the steel.

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F-gas Chiller Leak Testing

The frequency of F-gas leak testing is determined by the size of the plant. This will be detailed in your F-gas file which is kept on site. Another record of this is kept by the chiller company at their registered office. The copies of the periodic leak testing sheets are kept by both parties. These detail the result of the test, refrigerant added to the system, refrigerant removed from the system and the required follow up actions. Some methods of leak detection are:

Visual Inspection

On each visit our engineers remove the coverings of the ends of the condensers and panels. This is to inspect the whole machine for a sign of a leak. Any potential leak is marked for future identification of the location. A visual inspection will always be backed up with a further diagnosis such as:

Superheat and Subcooling

These readings are taken during a maintenance visit to determine the refrigerant charge of the chillers. The engineer, however, has to bear in mind that the subcooling and superheat readings can read abnormally due other reasons.

Bubble up Leak Spray

Various makes are available from the suppliers. Each engineer having his own preference. We at Maximus Chillers stock leak sprays and a wide selection of other materials.

Electronic Leak Detectors

Fixed

This type of leak detector is installed in the chiller low down in the panel. This is because HFC refrigerant is heavier than air. The leaking refrigerant will tend to pool in the bottom of the various panels around the chiller.

Portable

Each of our engineers carries a portable sniff tester. It comes with an extended tip to get into the most tight and awkward places. The leak detector has a replaceable element inside the unit. It also comes with replaceable tips which can be swapped out periodically. They come with a portable plug socket and transformer to charge the on board batteries after use in the field.

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Air Cooled Chiller Condenser Maintenance

Glycol Chiller Maintenance

Chiller Maintenance Company

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For further reading on chillers and the chiller maintenance schedule- visit Better Bricks | Click Here


Chiller service company's PLC and relay board in a panel

Chiller Service Company

Chiller Service Company Diagnosis

System Testing

A chiller service company can carry out diagnosis even when a wiring diagram is not available- our engineers can trace the wiring around the chiller.

News Article No.3

This often aids with diagnosis even when there is a wiring diagram, as to have your eyes on a component often makes more sense than a symbol. In any case, our engineers carry out system testing with Fluke multimetes and ammeters. We carry a range of thermocouples and probes to be used in conjunction with our calibrated digital thermometers. We use these along with comparators to carry out leak testing…

F-gas Leak Testing

According to the frequency dictated by the quantity of refrigerant, we use the above test equipment to carry out F-gas leak testing. First, we have a visual look around the chiller for a sign of a gas leak. All parts of the pipework and system components are inspected. Then, we carry out a full refrigerant diagnosis to determine that the refrigerant system is operating with a full charge of refrigerant. The report for each chiller being completed and filed in the onsite F-gas leak register. A history can be built up to assess the serviceability of the plant and the frequency of leaks.

Chiller Service Company Monitoring

Where intermittent faults are concerned, on going system monitoring is required. If the job is not progressed on each visit, there is little point in a call out. We carry out tests during monitoring and ensure that the wiring is tight. Hopefully, waiting for the fault to occur whilst next to the machine. Alongside this, we rely on a report from the end user, as regards, the symptoms and the circumstances of the chiller when the fault occurred. From this we extrapolate the diagnosis and decide the next step to take. This may be to attempt to move the fault to another machine or, at least eliminate one thing each visit.

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Chiller Service Company Evaporators

Shell and Tube Evaporators

These have a rolled steel shell, welded down the seam with and end plate on either end. The water system pipes can be bolted to the sides or the end. The endplate can be removed for access to the waterside of the tubes. A strainer is fitted to the inlet to catch any foreign objects that may have been carried around the water system. Inlet and outlet gauges are fitted for the monitoring of the water system readings during a service visit. On larger chillers the screw or centrifugal compressor is mounted directly on top of the evaporator- sucking directly off the top of a flooded evaporator…

Flooded Evaporators

This kind of evaporator has the refrigerant in liquid form on the outside of the tubes. These are a rack of copper tubes extending through the length of the shell. The warmer process water running through the tubes causes the refrigerant to boil off. A sight glass is usually available to check the state of the refrigerant evaporating on the copper tubes. The suction from the top of the evaporator goes round a baffle so as to prevent the slug back of liquid refrigerant into the compressor. The refrigerant flow into the evaporator is controlled by the expansion valve…

Expansion Valves

This takes the form of a fixed size orifice on the liquid line in between the shell and tube condenser and the flooded evaporator. The size of the orifice previously being calculated to match the mass flow rate of the refrigerant dictated by the compressor. Some newer systems have a variable orifice for the more efficient running of the plant. This is controlled electronically along with the loading of the compressor, relative to the available load condition.

Multiple System N+1

Smaller DX evaporators are usually multi system. This gives an N+1 redundancy of the plant. Indeed, when one side of a 2 system evaporator is having service work carried out, the other side continues to operate normally. Thinking ahead and allowing for additional capacity is essential when the application is critical, such as, a data centre or a hospital. When a redundant system comes online due to a failure- getting the system back up and running is a matter of urgency. For this we offer same day delivery of parts and a fully stocked mobile workshop.

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Chiller Service Company Condensers

Various configurations are employed to ensure good air flow through the chiller condenser fins. The most popular being a ‘v’ condenser as the surface area is increased with this design. Powerful fans are used to reject the air and heat upwards and away from the chiller. Where system location causes the recirculation of air, duct work can be fitted to direct the air away from the chiller.

Pressure Transducers

Johnson Controls

A popular kind of pressure transducer used on condensers is Johnson Controls. These can be bolted onto the refrigerant discharge pipe to sense the system pressure. They have a 5vdc input that comes into the transducer on a red wire, a black wire is the ground and a white wire is the signal back to the fan speed controller. The transducer has a minimum to maximum range, so a chart can be used to determine if the signal is reading back correctly. On chillers where the transducer is wired directly in the controller- calibration can be carried out to offset the readings.

Keller

Another kind of pressure transducer is the 4-20mA type. It sends a mA signal back to the controller or the fan speed controller. 4mA is the minimum position, so this relates to the minimum of the transducer pressure range.

R134a Refrigerant

R134a refrigerant operates at a lower pressure in a condenser than the other commonly used HFC refrigerants. If you were looking for a chilled water set point of 6° in the UK ambient for example, the R134a refrigerant saturation on the high side of the system would be around 36° Latent heat from the water system and heat added into the refrigerant from the compressor are rejected from the condenser. As the refrigerant passes down the condenser tubes, cool air blowing across the outside of the tubes, cools the refrigerant vapour down through the latent heat phase and into a subcooled liquid.

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Chiller Service Company Compressors

Centrifugal Compressors

This kind of compressor has a lower volumetric efficiency compared with the positive displacement compressors below. This is because the refrigerant is compressed using centrifugal force off the tip of the impeller, instead of being mechanically compressed. The advantage of this kind of compressor is a high mass flow rate of refrigerant. These compressors are used in factories where a large amount of chilled water is required to cool the process. They are also used in countries where district cooling is used. The chillers are arranged in rows in a chiller hall and are piped into the district cooling loop.

Screw Compressors

Oil used to lubricate the bearings is also used to create a seal between the rotors. Computer aided design (CAD) software and computer numerical control (CNC) grinding machines are used in the construction of screw rotors. The shape of the rotors is designed to compress the refrigerant along the screw. The length of the screw that is available to compress the refrigerant can be adjusted with a slide valve. Any stage of loading between 0- 100% can be achieved. This is regulated with a slide valve potentiometer. Screw compressors are very reliable and have a long service life. They also have a low vibration reading which ensures a lower instance of refrigerant leaks around the compressor.

Scroll Compressors

A service free compressor. Service free assuming that the rest of the system is functioning correctly. This kind of compressor relies on oil migration around the system. The oil is entrained along the inside of the pipework, around the system and back to the compressor. An oil level sight glass is fitted into the body of the compressor at the required level. Refrigerant shortage can cause the oil to stay in the bottom of the evaporator, causing a low oil level condition in the compressor. Chiller service companies can be scheduled to attend site to drain the oil, then pump new oil into the compressor.

Compressor Failure

When any of the above compressors fail, you are in safe hands with Maximus Chillers. We have the capability to lift and shift the compressor to our remanufacturing facility for a full overhaul. The reason for the failure is diagnosed to ensure the new compressor does not fail for the same reason. Improving the reliability of your plant and extending its life is what we are all about- if we can reduce your service costs- that makes us happy! All temperatures and pressures are recorded to ensure the replacement compressor goes into seamless operation.

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

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Read more about pressure sensors on Wikipedia | Click Here


Large air cooled brown chiller with test equipment during planned preventative chiller maintenance

Planned Preventative Chiller Maintenance

Featuring planned preventative chiller maintenance- in a series of longer, in depth news articles:

News Article No.2

This time concentrating on the checks, adjustments and diagnosis our engineer carries out while on site. We can extend the life of your plant and reduce energy costs- just with the effect of our maintenance. As well as completing a detailed checklist which is sent in to your office in PDF form, our engineer carries out extensive F-gas leak testing.

Planned Preventative Maintenance of Chiller Controls

The first part of the maintenance is carried out to the controls of the redundant systems. This is because all the pressures and temperatures should be reading the same. If not, this is an opportunity for:

Sensor Calibration

Before calibrating a sensor that is reading out, our engineer carries out a diagnosis to assess the serviceability of the sensor. With NTP (negative temperature coefficient) and PTC (positive temperature coefficient) sensors, the resistance is taken at a given temperature, which is then compared with a chart. With pressure transducers the 0-5vdc feedback signal is analysed to see if it is within the allowable tolerance. Once this diagnosis is complete and the sensor is deemed to be in good working order, our engineer will then calibrate the sensor. A password is entered into the PLC (programmable logic controller) to gain access to the service menu. From here, he can select the particular sensor, then offset it by the required amount. A lot of controls are not linear, that is to say, a sensor reading 2° high being reduced by 2° may not calibrate correctly. An amount of trial and error is often required, also the monitoring of the sensor against a digital thermometer at various temperatures.

Program Settings and Timers

Each program setting and timer in the various menu levels is checked against the previous maintenance checklist. Sometimes these are changed accidentally by the onsite engineer when looking for something else- it is easily done.

Planned Preventative Chiller Maintenance of Safety Chain

Each component on the safety chain is manually tripped or the fault condition is replicated to cause the device to trip. This part of the PPM (planned preventative maintenance) is essential to ensure the safety chain protects the chiller during a fault condition. Compressor failure or evaporator freeze up can occur with dramatic cost implications. We routinely prevent small problems, such as a faulty switch, becoming big problems.

Planned Preventative Chiller Maintenance of Wiring

Each wire on the chiller is checked for tightness including the fans (on air cooled chillers) the compressor motor connectors and compressor contactor contacts. Loose line wiring will cause breaker and fuse faults. Loose control wiring will cause error messages and chiller faults. This is a call out in between visits that can be eliminated. With the effect of our maintenance, any chiller becomes more reliable and has lower energy costs.

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After the above stop checks are carried out, system run checks are carried out:

Superheat

Using R134a refrigerant as an example, the refrigerant pressure will be 1.9 bar at 0° This refrigerant is in the HFC (hydrofluorocarbon) family- a commonly used refrigerant. If the refrigerant vapour returning to the compressor is excessively superheated- this is a sign of system issues. Here are some of the causes for a high superheat condition:

Refrigerant Shortage

Not enough latent heat being absorbed by the refrigerant in the evaporator. This allows the refrigerant to carry on superheating with the available heat load. Refrigerant leak testing is required to identify any leaks. The history of maintenance checklists can be consulted to see if the issue had been deteriorating over several maintenance visits.

Expansion Valve Failure

A thermostatic expansion valve operates with a higher superheat value, whereby an electronic expansion valve has a much closer control. In either case, our engineer will be accustomed to the nominal readings.

Thermostatic Expansion Valves

This type of valve is operated with a power element and orifice. A bulb is clamped onto the suction pipe which is connected to the power element via a capillary tube. The power element is pressurised with the same refrigerant as in the chiller. Some of this refrigerant is in its liquid phase, so with an increase in temperature, there is a corresponding increase in pressure. This pressure acts against the diaphragm and so pushes the orifice open. The orifice allows more refrigerant through the valve. When load conditions change and there is a reduction in heat load, the reverse happens- the orifice closes and reduces the amount of refrigerant through the valve. When the power element looses its charge- the orifice shuts down causing a high superheat condition. A low pressure trip out can also occur.

Electronic Expansion Valves

This type of valve uses sensors on the liquid and vapour sides of the evaporator, or a transducer and sensor vapour side of the evaporator. This is so the program can work out the superheat value. If the sensors are faulty, the valve will not operate correctly and a high superheat condition may occur. If the step motor or driver have failed- replacement parts are required.

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Subcooling

This is the measurement of the refrigerant condition in the condenser. Air cooled condensers are particularly popular in the UK as the ambient conditions make them very efficient. Shell and tube condensers are used on lager systems- these are cooled down using a water tower. When there is a refrigerant shortage, the liquid does not stay in the condenser long enough for it to subcool sufficiently. Some of the refrigerant stays in its vapour phase. With not enough latent being rejected in the condenser- the chiller’s COP (coefficient of performance) will be reduced. This means high energy consumption relative to the refrigeration effect of the chiller. This condition can be remedied with a scheduled visit from one of our team.

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For further reading on the subject of  preventive maintenance on Wikipedia | Click Here


Brazing equipment box and vibration eliminators during packaged chiller service

Packaged Chiller Service

Packaged chiller service due to a refrigerant leak, resulting in a trip out. This visit was to identify the leak and get the plant back online.

Leak Testing During Packaged Chiller Service

Nitrogen was added to the system to aid in the identification of the leak. All parts of the system were checked, including the removal of lagging around the couplings onto the evaporator. The leak was found on a poor quality ‘eliminator’ which had rubbed through on the evaporator.

Vibration Eliminators

We decided to fit high quality vibration eliminators- see picture. These are fitted one in the horizontal position and the other in the vertical. They absorb both directions of vibration then they are clamped to the chiller frame.

Brazing During Packaged Chiller Service

The pipework brazing was carried out with all combustible materials being removed from the work location. A permit to work was opened with our engineer as the responsible person. A half hour fire watch was carried out on completion of works.

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Pressure Test During Packaged Chiller Service

The pressure testing was carried out using nitrogen. As nitrogen is an inert gas, it will not cause other potential risks to the chiller and other personnel. The pressure test was a pass, so the next phase of the job could be carried out…

Vacuum Pump

Each engineer carries a 10 cfm vacuum pump. This high capacity ensures a fast vacuum. The Torr gauge was fitted to the system and 2 Torr was pulled.

Refrigerant Saturation

In the cylinder, the saturation of R407c is 7 bar at 11° The refrigerant in the cylinder is in its liquid phase with vapour on top.

Subcooling

On run testing the chiller, the subcooling value was found to be nominal at industry standard level.

Superheat

The superheat was adjusted, little by little, with the charging of the refrigerant until a good value was achieved. This was tested across all loading conditions for the rest of the visit.

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Read more about reducing refrigerant leaks at the Institute of Refrigeration | Click Here


Green Bitzer compressor being vacuumed during HFC chiller service

HFC Chiller Service

The HFC chiller being serviced in the photo is 600kw. It consists of two systems with a large Bitzer compressor for each system. It has a bespoke Micro Control System front end to run the machine and stop it should there be a fault condition. The chiller had been reported by the customer to have tripped out on a low pressure fault.

HFC Chiller Diagnosis Service

The readings of superheat and subcooling are available in the controller. This removes the need to fit instrumentation carried by our engineers. The process of diagnosis was therefore speeded up. The result being that the chiller was found to be running short of refrigerant.

Return Visit to Decant the Refrigerant

A Quote was submitted to the customer for approval. Once the Order was raised, a convenient time was arranged to return to site and carry out the service visit. The remaining charge of refrigerant was decanted into our recovery vessels with one of our fast pump out units which are carried by each of our engineers.

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Looking Around the Pipework for a Leak

Nitrogen, an inert gas, was introduced into the system to assist in the location of the leak. The leak was quickly found on one of the end turns of the condenser.

Brazing and Pressure Testing

Our engineer made good the leak using his brazing torch. Then, the integrity of the system was proven to industry standards with a system pressure test.

The Evacuation Process for HFC Chiller Service

The picture shows a 10 cfm (cubic feet per minute) vacuum pump being used to dehydrate the system during the visit. Each of our engineers carries a vacuum pump of this capacity as it speeds up the process. One refrigerant hose being fitted to the discharge pipe and another, smaller hose being fitted to the suction pipe. The system being vacuumed to a deep vacuum.

Recharge and Run Testing

After the chiller had been recharged with some of the charge of the refrigerant R134a, the remaining refrigerant was charged in its liquid phase, away from the compressor, until the superheat and subcooling values were within industry limits. A large amount of load was available as the chiller feeds an air blown film plastic manufacturing facility.

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Mirror looking for leak during chilled water system eev service

Chilled Water System EEV Service

Chilled water system EEV service was being carried out because the mechanical parts had failed. This particular valve is prone to this fault. It is an OEM electronic expansion valve, so our technician found the voltage for the motor and found a similar part with the same amount of steps.

The EEV driver was found to be functioning satisfactorily. Sometimes, depending on how the mechanical part of the EEV has failed, the driver can be overloaded and burned out.

Electronic Component Refurbishment

Where electronic parts, such as the EEV driver, are found to be burned out- Maximus Chillers has a refurbishment laboratory at head office. We have the capability to strip down the component and fault find where it has blown. Usually it is quite simple: the jammed mechanical part of the electronic expansion valve has burned out the power control on the driver for example. More complex fault finding and component replacement on the circuit board can be carried out also. Another option is to replace the driver with a like for like swap or retrofit to a different driver.

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Pump Down for Chilled Water System EEV Service

The chiller was pumped down and valved off. This saves on the time and recovery vessel to pump the refrigerant out.

Remove and Replace

Once pumped down, our engineer removed and replaced the valve, sealing it on its knife edge seal. The wire was passed up the conduit and into the panel. The wiring colour scheme was different on the new valve, so some time was taken to ensure it was wired up correctly.

Open it up and Switch it on

After leak testing, the refrigerant system valves were opened back up and the plant switched back on. The correct superheat and subcooling values were achieved concluding a successful visit.

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To read the Institute of Refrigeration guide to expansion valves Click Here


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