Chiller Commissioning

Chiller commissioning of a large white chiller with the pipework still disconnected to the buffer tank

Chiller Commissioning

Chiller commissioning is carried out to resolve any issues and get a machine running with optimum efficiency. The first three days are the most important part of a chiller’s life. This is because a chiller will carry along with it any problems that were not resolved at the start.

News Article No.15

New Chiller Commissioning

We at Maximus Chillers are the approved supplier for various manufacturers as their first choice to commission their new chillers. This is because we have earned a reputation within our industry for the capability to do anything- this is just part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere.

Used Chiller Commissioning

Our customers are concerned with lowering their carbon footprint and reducing the environmental impact made by cooling systems. One of the ways they do this is by purchasing used chillers which still have 10 years of life in them. This means that there is a dramatic saving in the carbon emissions that would have been released during the manufacture of new chillers. Used chillers often come from factories that have been re located. They also come with a full service history.

Chiller Commissioning on Site

The chiller in the photo is about to have the commissioning process carried out. All that is left to do is for the onsite engineers to fit the Inlet and Outlet pipes to the evaporator. Then, fit the water system pumps and other water system components.

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Chiller Commissioning Day 1

A cup of coffee and a good look round before staring anything. There were still a few nuts, bolts and washers left lying around by the onsite engineers, so a good opportunity for some house husbandry. This done, our engineer switched the main power supply on to the chiller…

Flow Fail

The machine went immediately into the flow fail fault. Then, he powered up the chiller pump set and the process pumps that feed the factory. The flow fail alarm cleared- so that was the flow switch ticked on our detailed Commissioning Sheet.

Line Voltage

He then checked the 415v power supply to the chiller which gave a good read back and balanced phases. Then, he checked the volts, amps and rotation on the pumps which also gave a good read back.

Buffer Tank Level

The buffer tank auto fill sensors had been positioned incorrectly. He adjusted them to the correct level, the mains water auto fill started and the tank filled to its set level.

Water System Leak

A small leak was found in between the outlet pipe from the buffer tank and the inlet of the process water pump. Our engineer rang one of the onsite engineers who arrived to tighten the connection.

Tighten Wiring

There hadn’t been an opportunity to tighten the wiring for some time as this chiller had been in continuous production in another part of the factory. Each wire around the chiller was tightened including the panel, the fan decks and the motor terminals on the Bitzer screw compressors.

Chiller Commissioning Day 2

The application and set point were different for the process at the new location of the chiller. Therefore, the controller was interrogated using a password to access the parameters. The parameters were modified, one at a time, until they came in line with the customer’s requirements.

Remote Controller

A remote controller had been fitted in the factory near to where the process workers carry out their duties. This was so that they do not have to walk outside to monitor the running of the chiller when they are also monitoring the process. Simultaneous monitoring of chiller loading, faults and water temperature is needed, as well as the monitoring of the process temperatures and production rates. The production rate can be slowed down if the chiller is in a fault condition. This is so as to balance against the process chilled water temperature.

Display Fault

A fault was showing on the remote controller display that was not showing on the chiller controller. After following the diagnosis and consulting the wiring diagram, the fault was traced to three wires that had been connected in the wrong order- an easy fault to rectify.

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Chiller Commissioning Day 3

Having sorted out the above, it was time to run the chiller up in anger…
A time was selected for start up when maximum load was available from the factory. This was to ensure that the machine could cope and to show up any problems.

System 1

This system started at 25% capacity and loaded up through each stage until it reached 100%.

Oil Level

A low oil level was recorded on the oil sight glass. Therefore, our engineer carefully monitored the compressor amps, temperatures and pressures to see if the compressor was starting to leave its nominal operating conditions. Bitzer screws are a high quality and very robust compressor, so the readings stayed good until the oil level returned.

System 2

This system then started and loaded steadily to 100%. All of the chiller readings were taken and were found to be within standard industry guidelines.

Load Matched

As the chiller started to near the set point, both compressors started to unload to match the load. The load can vary according to what the process engineers are doing at the time, so proving the compressor loading was critical to the efficient running of the plant.

Scheduled Maintenance

With the Commissioning Sheet filed in the cabinet, the next scheduled maintenance visit was talked through with the customer. There are 3 minor visits and 1 major visit during the year. The major visit is scheduled to take place during the winter. This is because there is more time available to carry out the periodic oil and filter changes.

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Chiller fault finding & diagnosis tool case and car boot

Chiller Fault Finding & Diagnosis

Accurate chiller fault finding & diagnosis saves money! This is because when the wrong parts are ordered and your machine still does not work- it has been a wasted visit with unneeded parts.

News Article No.12

Expert Training for Chiller Fault Finding & Diagnosis

All of our engineers are time served, attending the Government approved college course. This includes the F-gas HFC and BESA ammonia refrigerant handling certificates. Our engineers also go through rigorous training at The Maximus School of Chillers at Head Office in Droylsden. Here we have various chiller types ranging from small air cooled chillers, to the panels for large water cooled, screw and centrifugal chillers. They have been wired up as test rigs to simulate the various fault conditions. The manager will simulate a fault and the engineer will then have to follow it through to a successful diagnosis. This off site training ensures that when our engineer attends site, he is armed with all the skills he needs to follow through the fault finding easily.

Technical Support Desk

Whilst on site, our engineer is connected to our live stream, real time Technical Support Desk on his laptop and smart phone. He can also face time the support desk on his device. We often find that it is a lot easier to show somebody something than describe it. This service is available to you the customer too- free of charge. It is just one of the many features that help us to achieve The MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. PDF chiller manuals and wiring diagrams can be sent to our engineer’s phone and then printed off on your computer. This means that you have all the technical information you need, in the chiller panel for when our engineer is not in attendance. Just face time our support desk and we will talk you through. This helps to keep your service costs down as it will often save you the cost of a call out.

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Mobile Workshop for Chiller Fault Finding & Diagnosis

Each car boot is a mobile workshop with a blueprint of equipment repeated across each car in our fleet. We have recently opened The Spanish Office with one engineer down there now too. Our fleet of cars in the UK are Peugeot 508 and in Spain our engineer has a Seat Arona. In both countries the equipment is duplicated and standardised. This is so that Head Office knows what each engineer has at his disposal while on site, so he can find out what the problem is- fast!

Fuse Wire

It is the small things that we carry that help- fuse wire for example. This is so that a big box of spare fuses does not have to be carried.

Contactors

We carry 4 medium sized contactors which have 24vac, 24vdc, 110v and 230v coils. Each has NO (normally open) and NC (normally closed) contacts. This means that a blown relay, or a process chiller compressor single phasing- will be repaired while on site. Just another cost saving exercise for you the customer.

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Fluke Multi Meters

Our multi meters are calibrated annually for accuracy. They are equipped with fused leads to protect the engineer when working on high voltages. They have long, thin prongs too for access to the most difficult locations. Electrical plugs which are fixed onto relay boards are a good example. We test:

Resistance Temperature Detectors

RTDs are sensors that are often: NTC (negative temperature coefficient) where the resistance drops when warmed. PTC (positive temperature coefficient) where the resistance goes up when warmed. The sensor reacts to temperature in a predictable way, so a chart can be composed by the manufacturer. This chart shows the resistance reading, which should correspond to a given temperature. When a resistance reading on the multi meter is not where it should be on the chart- the sensor has failed. We carry crocodile clips for our multi meter prongs because sensor wires can be difficult to hold against our standard prongs.

DC Chiller Fault Finding & Diagnosis

We mostly fault find the direct current which is associated with the controls of a chiller. DC is also found in inverter drives before it is re inverted back into AC on the compressor. We usually fault find inverter drives on either end, however, when the volts are AC. PCB electronics usually run on 5vdc as computer components work well with this kind of voltage. That is not to say that there is not 24v and 230v present on a PCB, it may be part of other things that the PCB is doing. We have the function to read DC on our multi meters.

AC Chiller Fault Finding & Diagnosis

The most often used function on our multi meters is AC. This is because most components around a chiller panel are usually AC. The safety chain including the low pressure, high pressure and flow switches are usually fed by a 230v supply. The 415v line volts to fans, pumps compressors etc. are AC too. On large air cooled chillers, the panel is quite big to control all of the components and devices around the chiller. On large screw and centrifugal chillers, it is just a small panel with the compressor starter panel usually being separate.

Fridge System

Our calibrated gauges can be fitted to a HFC or ammonia chiller with a selection of fittings for each machine type. We carry digital thermometers with various probe types to access the different parts of the machine. Usually, however, the pressures and temperatures are available on the chiller controller. We use these pressures and temperatures, along with a comparator app to diagnose the condition of the fridge system. Superheat and subcooling values are worked out which are transmitted, real time, to our technical support desk. This means, along with the data plate of the chiller which is stored in our system, we can provide you with a Quote for the service job while the engineer is still on site.

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6 green Bitzer scroll compressors being maintained in a chiller

Scroll Chiller Compressor Maintenance

Here at Maximus Chillers, we carry out scroll chiller compressor maintenance to extend the lifespan and reduce downtime to your critical plant. This planning ahead is central to how we do things- we resolve small problems before they become big problems. Having the capability to do anything is part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere.

How they Work

The refrigerant vapour passes in between two scrolls (spirals) One of these is fixed, the other orbits backwards and forwards against the fixed scroll using a swing link. This creates a series of crescent shaped gas pockets in between the scrolls. These gas pockets get smaller in size as the refrigerant travels from the suction at the edge, down the spirals to the discharge at the centre. It then leaves downwards through a port. There are check valves to prevent back feeding of refrigerant during off cycles when other compressors on the same system are still running.

Advantages

There are several gas pockets occurring at any one time through the scroll, therefore giving a smooth and continuous compression cycle. Other advantages are low internal friction resulting in a quiet operation and low vibration levels. These low vibration levels help to lower the occurrence of leaks around the compressor.

Oil Level during Scroll Chiller Compressor Maintenance

The correct oil level is noted on our detailed Tick Sheets for all of the compressors. This record helps with the diagnosis when things start to go wrong. We can look for a pattern where the level starts to drop off in the compressors on a particular system, then look at the other readings which may be the cause.

Oil Samples during Scroll Chiller Compressor Maintenance

At periodic intervals, we take oil samples which we analyse in our laboratory at Head Office in Droylsden. We look for white metal, coloured metal, refrigerant composition, acid and sludge. This means that we can notice, then resolve system issues before a costly compressor failure occurs.

Oil Changes during Scroll Chiller Compressor Maintenance

This kind of compressor is fitted with a service port for the draining and filling of oil. The correct procedure is followed due to system pressure being present inside. We then carry out the oil changes using our specialist oil handling tools. Our skilled engineers carry the correct PPE for the work being carried out. We also we provide Risk Assessment Method Statements for each job.

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Crank Case Heaters

In the photo you can see the silver band of the crank case heaters at the bottom of the compressors. They keep the oil at the required temperature so as to not cause compressor wear on start up. The heaters also have the effect of ensuring that the refrigerant cannot condense into liquid during cold weather. As a compressor cannot compress a liquid, compressor failure would occur. A normally closed contact on the delta compressor starter contactor usually runs the heater: it drops out when the compressor starts. The function of all of these heaters is checked on each maintenance visit.

Discharge Temperature

It is critical that the discharge temperature is not too high, as this is the cause of the refrigerant breaking down into acid and sludge as previously mentioned. The acid rots the insulation on the copper windings inside the compressor. When this has occurred, an electrical failure will result in the compressor, causing the fuses to blow and a fault condition on the chiller. Compressor swap out is the cure which is expensive and inconvenient. We take the discharge temperature readings during the maintenance so as to fault find the cause.

Suction Pressure

Adequate suction pressure is needed to ensure good oil return to the compressor and prevent low pressure trips. As the refrigerant entrains the oil around the system, a good mass flow rate is needed, or the oil will just ‘pool’ in the bottom of the evaporator. Poor oil return will result in a seized compressor. Therefore, particular attention is taken to the low pressure gauge by our engineers. System adjustments or recommendations are made to ensure the seamless operation of your plant. If system overhaul is required, a Quote will be submitted at the end of the visit.

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Compressor Holding Down Bolts

There are usually four of these on each compressor. They fit though a steel sleeve which, in turn, fits through a rubber mount. The whole assembly is bolted into the frame of the chiller. The function is to securely hold the compressor in place and to dissipate vibration. We check the tightness is correct with our torque wrenches and change the rubbers periodically. A compressor rattling around uncontrollably, especially during start up and stopping causes catastrophic leaks around the compressor. This usually leads to the whole, or the most part of the refrigerant charge being lost to atmosphere.

Motor Protection Module

A resistance sensor embedded in the compressor windings plugs into this module on the S1 and S2 terminals. The fault feedback to the controls is on the M1 and M2 terminals. The power supply to the module is on the L and N terminals. When the windings start to get hot, the module detects this after a pre determined level of resistance is reached. The M2 terminal opens and volts drop out to the relay board, then a lower volt control signal drops out to the controller. We check the sensor resistance and compare it to a chart to ensure it is within the allowable range on each visit.

Wire Tightening during Scroll Chiller Compressor Maintenance

We waggle the motor connectors and check for any cracking to the wires which may lead to an earth sort out. We tighten the wiring on the compressor starter contactors and check the condition of the contactor contacts. These become ‘splattered’ causing an uneven amount of amps to the compressor. This volt drop causes the contactors to fail and will eventually cause compressor motor failure. We change the contactor contacts from our range of parts at Head Office.

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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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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…

Pressure Temperature Relationship of Refrigerant

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. It is one of the fundamental scientific principals of how a chiller works: the higher the pressure- the higher the temperature/ the lower the pressure- the lower the temperature.

Recovery Units for Refrigerant

After receiving a further order from our customer, we gave the go ahead to our engineer to use his 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 Vac 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

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. Our engineer 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 in the condenser. 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.

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F-gas Chiller Leak Testing

Chiller Commissioning

Air Cooled Chiller Condenser Testing

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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.

For further reading on chilled water visit Wikipedia | Click Here


A pile of completed chiller maintenance checklists on a table

Chiller Maintenance Checklist

Introducing a series of in depth news articles, this time featuring the chiller maintenance checklist:

News Article No.1

This article has been written with you- the customer in mind. Read below for practical advice on how to keep your chillers in the best condition.

Each day when you walk round, you can check to see if your plant is starting to malfunction. Become accustomed with the usual readings to help you diagnose the faults.

Here are the things to check for and how to remedy them:

Water System Pressure

Keep an eye on the pressure in the water system.

Small Chiller Maintenance Checklist

On a small chiller, there will be a water outlet pressure gauge. Make a mark on the gauge where the pressure is when the chiller is in good working order. You can use this mark to notice if the pressure is starting to drop off.

Strainer

The most common cause for low water system pressure is a blocked strainer. It is usually a ‘Y’ type with a bolted fitting. With the chiller off and the water system valves closed, unscrew it and check for debris. If it is blocked, make a note of how long it took to block, then add the cleaning of the strainer into the periodic maintenance schedule.

Pump

Ensure the pump rotation is correct by checking that the cooling fan is sucking into the pump. If it is going backwards: isolate electrically, then swap any 2 of the 3 phase wires. Brush down the inlet to the cooling fan to ensure good air flow and a cool pump motor.

Large Chiller Maintenance Checklist

On a large chiller, the water system pressures may be available in the controller- have a look through the menus. The pressure will be measured in bar. Another popular method on a large chiller is a flow meter. This may be a stand alone device on the chiller panel, or on a control panel nearby. It will read in m3/hr. Check to see if the pressure or flow is lower than usual. If so, ring one of our trained professionals.

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Water System Temperature

The chiller should be:

  • Matching the load and running continuously.
  • Loading and unloading in sequence with other chillers.
  • Going through a cycle and achieving set point.

In any case, you will become accustomed with the usual chilled water temperature according to varying load conditions. If the plant is struggling to achieve set point, or is running higher than usual- this is a sign of system faults.

Walk along the chillers that feed the same water system and make a log of the faults showing on the controllers.

Here are the things to check when you have high water system temperature:

Small Chiller Maintenance Checklist

Low Pressure

If the chiller has a low pressure gauge, look to see if the pressure is lower than usual. If so, this is a sign of refrigerant shortage in the plate evaporator. A scheduled visit from one of our trained engineers to carry out a pressure test can be arranged.

Breakers

Look for any breakers that have tripped in the panel. One reset can be carried out by a qualified onsite electrician. If the fault reoccurs- ring our support team. If the scroll compressor has tripped, check to see if the compressor is hot. If so, isolate and do not attempt a restart.

Condenser

A blocked condenser will inhibit the rejection of heat. Brush it down and give it a rinse with water. A common occurrence onsite with some condenser designs is a panel being left off with the chiller running! This happens when the onsite engineers are fault finding another issue with the chiller. The fans will suck through the opening as this is the easiest path. The gauge will be higher than usual as the condenser builds in pressure. A high pressure trip out will occur.

High Pressure Switch

To locate the switch- first identify the discharge pipe. It is the smaller of the 2 pipes on the compressor. The high pressure switch will either be bolted onto the pipe, or a thin pipe will lead from the discharge to the frame of the chiller. In any case, you are looking for a small box with a button and a wire leading to the panel. Press the button and you should hear it click. If this fault reoccurs- ring our technical support desk.

Large Chiller Maintenance Checklist

Suction

Should there be a refrigerant shortage, the controller will display a pre alarm like 'suction limiting' This is the controller preventing the compressor from loading up, so as to prevent a low pressure trip out. As above, one of our team of engineers can be sent to site to resolve the issue.

Discharge

If the controller is showing 'discharge limiting' this is a sign of a condenser issue. A full strip down and cleaning of the tubes may be required. Ring our technical support desk for further advice.

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Chiller Remote Monitoring

We at maximus chiller can install remote monitoring systems to your chillers so we can fault find and diagnose from a laptop. This means we can give you real time advice over the phone. Now you are accustomed with our chiller maintenance checklist, you can give feedback regarding the plant to assist our engineer.

Parts

For our contract maintenance customers: a range of commonly used parts are kept onsite to reduce downtime. We can give practical, step by step advice on the fitting of parts. We often carry out video calls with our customers, as chiller data plates, parts and components can be easier to show than describe.

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

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Preventative Chiller Maintenance

To read more about air cooled chiller condensers hit the Tag at the top of the page.

Read more about chillers on Wikipedia | Click Here


Controls panel open during chilling plant maintenance

Chilling Plant Controls Maintenance

Prior to this chilling plant controls maintenance visit, another contractor had changed some of the settings and adjustments in the controllers. They did this while they were diagnosing a fault with the water system and the pumps. Therefore, this visit was to recommission the plant and to resolve the issues resulting from the adjustments.

Chilling Plant Flow Controls Maintenance

The flow controls were found to be set wrong. Therefore, our engineer adjusted the pumps, then various valves on the water system, a little at a time, while monitoring the controller. Full load and part load readings were taken until they came to within standard industry limits.

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Compressor Run On Time

A timer had been adjusted which made the compressor wait to stop after reaching 0%. In the meantime, some more heat would build up in the water system and the compressor slide valve would open up a little. The result was that the compressor would run for an hour with the slide valve shut most of the time. The oil pump carried on pumping during this time resulting in a head of oil building up in the discharge pipe- all the way back up to the oil separator. Then, a low oil level fault had occurred. This being confirmed by the sight glass on the oil separator. The compressor had enough oil charged into it to allow a start up. During the start up, a low oil level timer counts down. As soon as the compressor loaded and started pumping, the oil level returned to the correct level on the sight glasses. The timer was adjusted along with the dead band to ensure the chiller off cycled after achieving set point.

Slide Valve Potentiometer

The slide valve potentiometer has a configuration mode button. It can be pressed to set the 4mA or 0% position. This is the usual position of the slide valve as a spring and 2 drain valves return it to the start position. The slide valve can then be manually opened in the program. Then, the potentiometer button can be pressed to set the 20mA or 100% position. “Chattering” can occur on the fully closed position so a setting is available to only close the slide valve to 2%.

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

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