Chiller Types

Example of chiller types: 2 grey containerised ammonia chillers with air cooled condensers on top

Chiller Types

In this article we will be exploring the various chiller types. They can be categorised according to: how the condenser is cooled, weather they use vapour compression or absorption and the required chilled water temperature…

News Article No.17

Air Cooled Chiller Types

This type of chiller uses the ambient air to cool the refrigerant in the condenser. Fans suck the air through the condenser fins and so exchanging heat energy from the refrigerant and into the air. They are particularly popular in the UK due to the low ambient temperatures. They are also used in the Middle East, but the higher ambient means that they run less efficiently. Read more by following this link Click Here

Water Cooled Chiller Types

This type of chiller uses a shell and tube condenser to remove the heat energy from the refrigerant. The refrigerant condenses from a gas and into a liquid on one side of the tubes. On the other side of the tubes, condenser cooling water is being pumped through and so absorbing latent heat from the refrigerant. The water flows up to a cooling tower where it cascades down through trays and into the sump. In the opposite direction, air is blown up through the cooling tower and so creating the required heat exchange. The cooled condenser water is then pumped back to the chiller. This kind of system is more often used with large capacity chillers. Read more by following this link Click Here

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Vapour Compression

Vapour compression is the most popular kind of chiller. An electric motor drives a compressor. The refrigerant is then discharged into the condenser where the heat energy is rejected from the refrigerant as it cools down into a liquid. It goes through an expansion valve where it drops in pressure and temperature. Then, the refrigerant goes into the evaporator where it boils off absorbing latent heat from the water being chilled. The refrigerant is then sucked back into the compressor. This is called The Basic Refrigeration Cycle and you can read about it in detail by following this link Click Here

HFC Chillers

HFC chiller refrigerants, such as, R407c were developed to replace refrigerants which contained chlorine. This is because chlorine was found to have caused a hole in the ozone layer. The downside to HFC refrigerants is that they have a high Global Warming Potential. That is to say that when they find their way into the atmosphere due to refrigerant leaks, their heat trapping qualities add to the greenhouse effect.

Ammonia Chillers

The photo is of two ammonia chillers with air cooled condensers on top. A steel braided refrigerant charging hose can be seen coming into the foreground of the photo. This refrigerant has a zero global warming potential and so is environmentally friendly. The downside to this refrigerant is that it is highly toxic and corrosive. Therefore, special procedures, equipment and training is required to handle it. Read more by following this link Click Here

Propane Chillers

Propane didn’t really catch on in the UK due to the higher initial cost of the chiller. It is, however, popular on the continent in countries such as Italy. The downside to this refrigerant is that it is highly flammable. Intrinsically safe equipment is required to handle the refrigerant and so aiding with a spark free environment. Read more by following this link Click Here

Absorption Chillers

This kind of chiller uses a heat source rather than electricity to drive the cooling process. It employs a chemical reaction between two substances, such as, lithium bromide and water. To read about these chillers in detail Click Here This type of chiller is a lot less efficient than vapour compression systems. The coefficient of performance is usually around 0.5, were as with a HFC chiller it is usually upwards of 4. Therefore, they are most often used where there is a surplus of waste heat being produced by a process, such as, in a power station.

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High Temperature Chiller Types

Laser cutters use a chiller which operates with a high temperature set point of around 25°C. The laser head and the oscillator need to be cooled to a very close deadband of usually around 0.2°C. If there is a problem with the chiller, the controls shut the laser cuter down to prevent expensive failures from occurring. Read more by following this link Click Here

Medium Temperature Chiller Types

Most chillers operate at this temperature which is used for a variety of applications including…

The Cooling of Buildings

The chilled water set point is usually around 6°C. Large capacity chillers are used which supply chilled water to the building. A plant room is located near to the chillers where a pump discharges into the chillers. The water system pressure is maintained using a pressurisation unit. A different pump is used to supply fan coils around the building. The fans blow air across the chilled coils and so cooling the spaces in the building. This heat exchange warms the chilled water which returns back to the chillers.

The Plastics Industry

Two popular ways of forming plastic are by using: plastic extrusion moulding machines and plastic injection moulding machines. Plastic granules or powder is melted down and forced through a die or into a mould. Chilled water is then used to control the cooling of the newly formed plastic to below its freezing point. Small chillers are used next to each of the plastic forming machines. Alternatively, large, centralised chillers are used to provide chilled water to the whole factory.

Low Temperature Chiller Types

Breweries are a good example of the use of low temperature chillers. The setpoint is often around -5°C with glycol being added into the water to prevent it from freezing. The water/ glycol solution is pumped around the jackets of stainless steel vats which are used to brew the beer. The fermentation process created by the yeast is temperature critical and so is controlled by the chilled water. Read more by following this link Click Here

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Nitrogen cylinder and regulator with gauges attached for f-gas chiller leak testing

F-gas Chiller Leak Testing

Regulations

The regulations for F-gas chiller leak testing have been devised to reduce the environmental impact of HFC refrigerants. They are standardised regulations which are implemented across Europe. Now that we have left the EU, we will continue to be aligned with these regulations.

News Article No.14

Leak Test Frequency Required

The frequency of leak tests depends on the type and quantity of the refrigerant. For example, a system which runs on R134a, the frequency is:
• once every 12 months for a charge less than 3.5 kg.
• once every 6 months for a charge less than 35 kg.
• once every 3 months for a charge less than 350 kg.
All of our maintenance schedules far exceed these minimum requirements. This is because our customers require maintenance visits more often to ensure the efficient running of their plant.

Static Leak Detectors

These leak detectors must be fitted to systems with more than 500 tonnes of CO2 equivalent. For the refrigerants most commonly used in chillers this is:
• R410a 239 kg
• R407c 282 kg
• R134a 350 kg

Global Warming Potential

The GWP numbers below represent the amount of greenhouse effect each refrigerant has, by comparison with an equal mass of carbon dioxide:
• R410a 2,088
• R407c 1,732
• R134a 1,300

Now we have had a look at some of the regulations, let’s have a look at a day in the life of our engineers here at Maximus Chillers. Read below for three different examples of leak testing carried out in the field…

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Pressure Testing Following a Leak

In the photo a leak has just been brazed on the condenser. It is recommended in the industry to use a steel braided line with a ¼ turn valve. This is so that if a nitrogen regulator malfunctions, it can be valved off, instead of a system being filled with bottle pressure from the cylinder. For a small system, this could cause a catastrophic explosion. We decided, therefore, to use a small cylinder which would expand into the large volume of the chiller. Should this fault occur, the safe working pressure would not be exceeded. This was taken into account when writing our Risk Assessment Method Statement. The pressure was built up in stages until the test pressure was achieved. This was recorded on our Pressure Test Certificate and witnessed by the customer. The result of the pressure test 4 hrs later was satisfactory and also witnessed by the customer.

Follow up Actions

A return visit was arranged 2 weeks later to leak test the chiller again. Our engineer carried out a visual inspection of all of the parts of the refrigerant pipework. He then used an electronic leak detector to see if it went into alarm. All was okay, so he completed the F-gas Certificate and left it in the customer’s file.

Routine F-gas Chiller Leak Testing during Maintenance

On another site, we look after 6 air cooled MW chillers in a row outside a building at a petrochemical facility. Our engineer ran the systems up, one at a time, to 100% so as to show up any refrigerant shortages. He was looking at the subcooling and superheat values. Two of the systems had poor readings which alerted his attention to a potential leak. On one of the systems, the poor readings were found to be caused by a faulty expansion valve. On the other, he diagnosed that the chiller was running short of refrigerant. He then carried out an inspection and found signs of a leak on a liquid pipe, just after the filter/ drier. The system was locked off with the refrigerant valves closed either side of the leak. This was to prevent the refrigerant from carrying on leaking to atmosphere. Then, he sent a report into Head Office detailing the estimated refrigerant addition needed to replace the refrigerant lost. Refrigerant removal was not needed as the area of the leak had been valved off from the rest of the system. He also detailed the materials required for the job and the necessary labour time that would be needed.

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Looking for a Leak

There are a variety of methods that can be used to identify the location of a refrigerant leak. Here are some examples…

Ultrasonic F-gas Chiller Leak Testing

An ultrasonic leak detector uses a microphone on the end of a wand. This is connected to a battery and processing pack, which is where headphones are plugged into. The sensitivity can be adjusted on the processing pack until a good working level is found. The various components on the chiller can then be inspected to find an audible sound of a leak.

Electronic F-gas Chiller Leak Testing

Otherwise known as a sniff tester, the electronic leak detector is one of the most popular types of leak detectors. The battery can be recharged via the cigar lighter in a car, or can be recharged back at the office with a transformer plugged into the mains. The heated diode sensor and the filter can fail or need to be replaced, so replacement parts are available. The instrument needs to be calibrated to a no refrigerant atmosphere, then it takes samples of the atmosphere being tested. It compares the two atmospheres and looks for a difference. Most electronic leak detectors work with all HFC refrigerants.

Bubble Up F-gas Chiller Leak Testing

There are a variety of bubble up leak detection sprays that are available off the shelf. At Maximus Chillers we make our own leak detection solution in our laboratory at Head Office. We mix two chemicals together in the correct proportions. This solution is carried in sprayer bottles in the boot of each of our company vehicles. When looking for a leak, our engineers use it around the suspected areas of a leak. It is the best form of leak detection that we know, as it can find the smallest of leaks, right up to large leaks which are audible to the ear.

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To read more about the f-gas chiller leak testing procedure hit the Tag at the top of the page.

Read more about checking F-gas equipment for leaks on the Government website | Click Here


Grey centrifugal chiller compressor being maintained

Centrifugal Chiller Compressor Maintenance

Centrifugal chiller compressor maintenance keeps your critical plant up and running and your customers happy. The work can be scheduled to be carried out during factory shutdown, so as not to disrupt your production. We can also carry out this work to your compressors while the factory is in production. This is achieved by isolating the compressor that needs to be worked on when it is in an off cycle. The compressors on remaining machines can carry on running.

Tasks during Centrifugal Chiller Compressor Maintenance

Here are some of the tasks that we carry out…

Oil Changes

The oil becomes dirty over time by picking up contaminants that have formed in the system. Two of these contaminants are…

Acid

Compressor discharge is the hottest part of the refrigerant cycle. Acid can be formed from the refrigerant in this part of the system.

Refrigerant Types

A popular refrigerant for centrifs is R134a. Because it consists only of one kind of refrigerant, it does not fractionalise into different component refrigerants. This would be no good for a flooded system because one or more of the refrigerants would end up in the bottom of the evaporator and condenser. The remaining refrigerant would circulate and the whole plant would not function as it should. Refrigerants popular for other kinds of system are zeotropic HFC refrigerants. This means that the different component refrigerants have different boiling points- R407c is a good example.

Metal

White metal from the compressor and copper from the heat exchangers end up in the oil. They will eventually be caught by the system oil filters…

Oil Filter Change

After completing the above, now is a good time to change the filter as the compressor is valved off and has been broken into. It is also when an oil sample is taken depending on the schedule…

Oil Samples during Centrifugal Chiller Compressor Maintenance

Our oil samples are transported using our specialist kits which include the bottles and labels. This saves mix ups in our laboratory during the analysis.

Leak Rectification

The drawback of carrying out the above are leaks because the pressure has been pumped out of the compressor into another part of the system. The ‘o’ rings and shaft seal can now leak, this kind of failure can be rectified whilst still on site by the knowledge of our engineers.

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Oil Pre Lubrication

When the compressor starts, the oil pressure is built up first using an oil pump. This is so the internal components such as the high and low speed shaft are properly oiled before they start to rotate. They can run at 10,000 RPM and are very expensive to replace. Therefore, we check the oil pressure gauges and the system controls to ensure optimum ‘pre lubing’ of your compressors.

Volumetric Efficiency

The ratio between the volume actually compressed and the theoretical volume derived from compressor design calculations. This kind of compressor has a lower volumetric efficiency than positive displacement compressors. It is because the refrigerant is compressed off the tip of the rotating impellor or impellors. The refrigerant moves outwards in a circular path due to centrifugal force. A centrif more than makes up for this lower volumetric efficiency by the high mass and volume of the refrigerant that it circulates around the system.

Design 

The refrigerant is sucked from the evaporator into the centre of the impellor which is a disc of radial blades positioned to direct the refrigerant outwards. Due to the low differential of pressure, multiple stages of impellors are often arranged in series with the discharge being directed onto the suction of the next impellor. This is simple in design with less moving parts than some other compressor types. Modern centrifs can have magnetic, levitating bearings and so remove the need for oil in the system altogether. The faster the speed, the better the efficiency- so high speed rotation of the impellor is achieved at full load. The compressed refrigerant is discharged into the condenser.

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Electric Drive Centrifugal Chiller Compressor Maintenance

Most modern centrifs are driven by variable speed drives. This is for efficiency as the load can be exactly matched. Another reason for this is to soft start the compressor. 415v and 3.3kv are popular volt inputs, although other voltages can be made available by the onsite transformer.

Open

An open drive electric motor is the most popular design. It has the drawback, however, of needing a shaft seal which needs to be replaced at periodic intervals. This shaft seal is also prone to leaking refrigerant and oil.

Semi Hermetic

The photo is of a semi hermetic design of this compressor type. The motor is contained inside the suction housing and so has the benefit of being cooled by the refrigerant. No shaft seal is needed and therefore it has none of the associated maintenance drawbacks.

Steam Drive Centrifugal Chiller Compressor Maintenance

On oil rigs there can be an abundant supply of steam that can be used to drive the compressor. It is often used on multi stage compressors which are used for the liquefaction of natural gas. The steam goes through a turbine which is connected to a shaft- this drives the impellors. The steam flow and pressure can be tested and adjusted during the visit.

Woops Something Went Wrong

When you suffer a centrifugal compressor failure- don’t worry. You are in safe hands with the team here at Maximus Chillers. We have a team who can get the compressor out and lift it to the workshop on site, or transport it to our Head Office. We have another team who are experts in the remanufacturing of this kind of compressor. A fast supply chain is in place for delivery of the internal moving parts, gaskets and bearings. We are so confident that you will be happy with us- we offer a 12 month warranty on all of our compressor rebuilds.

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Open chiller controls panel showing PLC, relays, contactors and wiring

Chiller Controls

Chiller controls can be remotely operated and monitored, but in this article, we will be looking at chillers operating in local.

Each chiller has a panel where the lead or the lag chiller can be switched from. They have N+1 redundancy built in, so one of two chillers will normally be in standby with the other one running. The chillers in the photo are equipped with kilowatt hour meters because the customer wants to monitor their efficiency. He has targets to meet and wants to gauge the effect that our maintenance has in reducing his energy costs.

Condenser Pressure

The condenser pressure control is external and stand alone from the panel.

Transducer

A transducer is fitted to the discharge pipe near to the compressor. This gives a 0 to 5vdc control signal to the fan speed controller which is bolted to the frame. There is a minimum and a maximum value on the transducer, so the FSC is programmed to work out the pressure from the voltage.

Fan Speed Controller

415v on three phases are the input to the FSC. It uses solid state thyristors to regulate the output to the fans. This is according to the demand received by the transducer. Solid state means that all the parts are electronic with no moving parts. Fan speed controllers are really good at extending the life of the fans. This is because all of the fans operate together- smoothly and reliably.

Chiller Controls Digital Inputs

There are three essential digital inputs to the controls of any chiller. All of them have a volt signal out to them, which returns back to the panel. If there is a fault- the volts drop out.

LP Switch

This protects the chiller from a low pressure condition. Compressor and evaporator failure would result, so this device is set below the running pressure of the system, but high enough to offer protection.

HP Switch

If the head pressure control mentioned above were to fail, this device would save the chiller from damage from excessive pressure in the system. Components or the pressure relief valve can blow causing a catastrophic refrigerant leak.

Flow Switch

This device detects a lack of flow in the water system. Serious system failure would result if this part is not maintained properly. It needs to be periodically tested and adjusted at regular intervals.

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Chiller Controls Analogue Inputs

The essential analogue inputs on a chiller are the Water In and the Water Out sensors. These are usually NTC (negative temperature coefficient) that is to say: if you hold one in between your fingers and warm it up- the resistance will start to drop off. They usually read in kilo ohms which can be read on a standard multi meter. The program looks at these two sensors and using an algorithm, it calculates the loading requirement of the compressor. They can read incorrectly, so a sensor offset function is available in the software for adjustment. This is just one of the many checks and procedures that we carry out during our maintenance visit.

Chiller Controls Relays

In the photo you can see wires from the various devices around the chiller, wired into a row of relays. These, in turn, are wired into the white relay board at the top. This relay board has several expansion boards linked into it which are held together with an electrical ribbon. Next, the relay board is wired into the PLC... 

Chiller Controls PLC

The reason for these steps in between a device and the PLC is for protection. Sensitive electrical components can be blown due to an earth shortage. At each stage there is a volt drop from 240v to 24v and then to 5vdc.The programmable logic controller is the nerve centre of the chiller. This is where all the inputs go to and where all the digital outputs are sent from. The controller on this chiller is Beijer Electronics- it comes blank from the factory. User keys to operate the chiller are positioned below the display. It can be programmed to run most chillers and indeed it is often seen in factories running anything. A laptop plugs into it and the software for the chiller is uploaded. On one visit, we found a fault with this controller. We bubble wrapped it and took it to our electronics laboratory at Head Office. The issue was easy to resolve- it was just dust tracking across the back of the PCB and so corrupting the program.

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Chiller Controls Digital Outputs

The main digital outputs on this chiller are:

Compressor Run Signal

240v is sent to the compressor starter contactors. There are three: Star (lower amps for a soft start) then a timer switches over to Delta (higher amps for a more powerful running of the compressor) On the other end of the compressor windings is the Line contactor. This contactor runs with both the Star and the Delta contactors.

Float Valve

This is a camber where the level of refrigerant which is coming in from the condenser is detected. The level is transmitted to the PLC, where the program sends a signal to the expansion valve. It opens to the correct degree according to the load on the chiller.

Slide Valve

The compressor can run at 0% with the slide valve shut. When load is sensed from the Water In and Water Out sensors by the controller- the slide valve opens up. The position of the slide valve is detected by a potentiometer. This is calibrated from a minimum to a maximum position. The signal is 4-20 mA which the controller translates into the position of the slide valve.

MAXIMUS ADVANTAGE™

Whatever the problem with the controls, we can find a solution to resolve it. With years of industry experience and a fast supply chain, we offer a service that is second to none. Being able to retrofit is part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere.

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

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Green Bitzer screw chiller compressor with oil separator removed on bench in our workshop

Screw Chiller Compressor Maintenance

Open Drive Screw Chiller Compressor Maintenance

Open drive screw chiller compressor maintenance involves changing the shaft seal at intervals, or if it leaks. This kind of compressor is used with ammonia as this refrigerant corrodes the copper windings and the insulation. It is also used with most large HFC (hydrofluorocarbon) and HFO (hydrofluoroolefin) chillers.

Semi Hermetic Screw Chiller Compressor Maintenance

Because all of the components are internal, this kind of compressor needs less maintenance. It is most often used with smaller chillers running on HFC and HFO refrigerants. This is the compressor type featured in the photo.

Matched Helical Rotors

This kind of compressor design uses a matched pair of helical rotors. These are accurately machined so as to trap, then compress the refrigerant as it travels along the screw. Oil injection is used to create a seal between the rotors. The two rotors are different in shape: the male rotor is driven by the motor and usually has 4 lobes. The female rotor meshes with male and usually has 6 interlobe spaces. The cylinder casting around the rotors is equally important as it seals in the vapour along the screw. Both rotors are helixes with the male rotor moving more rapidly. This compressor design provides a continuous pumping action, rather than pulsating as with a reciprocating compressor. Another advantage of this kind of compression is that there is very little vibration. Indeed, you can place a coin, on its side, on top of the compressors we look after and it does not fall over. This lack of vibration helps to prevent refrigerant leaks around the compressor.

Single Screw with Gate Rotors

This kind of compressor design uses one main rotor, meshing with 2 star gate rotors. These are at right angles with the main rotor. The main rotor usually has 6 grooves.

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Screw Chiller Compressor Maintenance and Reliability

Both of these compressor designs are very reliable with a long bearing life. A maintenance free lifespan of 30 years for the bearings is not uncommon. It is quite common that the compressor will outlive the chiller. In the unlikely event of bearing wear, a characteristic is for there to be undue noise from the compressor at part load which goes away at full load. Higher oil temperature and an unsatisfactory oil analysis are also indicators.

Slide Valve

The capacity is seamless as it is regulated with a slide valve. A spring returns the valve to the unloaded position and a gear type oil pump gives above discharge pressure to load it. The oil pump is not for lubrication, it is just to give the valve enough force to slide with the discharge pressure acting against it. A slide valve potentiometer is fitted to a sliding rod on the end of the valve. It translates the movement along this rod into usually 4-20mA. This signal feeds back to the controller which converts it into a percentage loading reading.

Lubrication during Screw Chiller Compressor Maintenance

Pressures and temperatures are taken during the maintenance to ensure seamless operation. The oil sump is usually inside the base of the oil separator which is at discharge pressure. An oil return pipe is available from the oil sump to the suction side of the screw. Because of the pressure difference from discharge to suction, the oil naturally lubricates the compressor without any need of an oil pump. The oil lubricates the bearings and is injected with the refrigerant along the screw. This provides a seal between the rotors or gate rotors, it also lubricates the rotors to prevent excessive wear.

Oil Separator

The oil enters the oil separator after being discharged with the refrigerant from the compressor. This vessel is insulated so as to stop refrigerant condensing inside as it would in the condenser. An oil heater keeps the oil at the optimum temperature for the compressor. This heater also prevents liquid from forming in the oil separator during off cycles. A check valve on the outlet also prevents this from happening by stopping the migration of refrigerant from the condenser. As the oil sump is the oil supply to the compressor, a temperature sensor will make the program lock the compressor out, should the oil be too cold. This is usually because the main power supply to the chiller has been off during maintenance. The larger volume inside the oil separator slows the speed of the refrigerant so as to allow the oil to drop out. A common design is for the discharge to be directed to the top of the vessel, with a spiral going down to the sump. The oil falls out of the refrigerant vapour during this process. For additional oil recovery, the oil goes up through finer and finer layers of mesh. The oil sticks to this mesh and runs down into the sump.

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Oil Return

Small amounts of oil that have escaped the oil separator will end up in various vessels around the system. On smaller HFC systems there is less of a problem as the oil is entrained by the refrigerant, round the system and back to the compressor. In larger, flooded HFC systems, the oil mainly ends up in the bottom of the evaporator. For ammonia systems, the oil does not entrain with the refrigerant, so oil return devices must be used.

Eductor

This is a pot at the bottom of the vessel where the oil collects. At periodic intervals, discharge gas is blown across the top of the oil which has collected. This has the effect of picking it up and carrying it into the suction of the compressor.

Periodic Oil Changes

We at Maximus Chillers have the full range of refrigerant grade oil for all refrigerant types. It is part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. It is critical that the correct oil is selected otherwise compressor failure will result. During each maintenance visit, we make a note of the compressor run hours and carry out oil changes at the correct intervals.

Oil Analysis

We take oil samples which we analyse in our laboratory for signs of compressor wear, oil quality and contaminants. This way, we can prevent untimely compressor failure. If one of your compressors were to fail, however, we have a remanufacturing facility and a lift and shift team to get the job done fast! 

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

Chiller Service Company Visit

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

News Article No.11

Electrical Faults during Chiller Service Company Visit

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

Alarm Reset during Chiller Company Service Visit

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

Run Testing during Chiller Company Service Visit

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

Head Pressure Control

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

Test Instrument

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

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Chiller Company Service Low Pressure Visit

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

Refrigerant Pump Out

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

Leak Testing during Chiller Company Service Visit

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

Brazing during Chiller Company Service Visit

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

F-gas Pressure Test

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

Vac Pump

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

Recharge and Run Test

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

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Refrigerant Economizers

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

Expansion Valve

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

Flash Gas

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

Efficiency

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

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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

Control Panels

The first thing our engineers check at the start of the maintenance is the control panel of the chiller. 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

RCDs 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°C 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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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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PLC and relay board in a panel during chiller service company visit

Chiller Service Company

Electrical Testing

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

News Article No.3

Doing this often aids with the diagnosis even when there is a wiring diagram, as having 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.

F-gas Leak Testing by Chiller Service Company

We also 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. After fitting the probes, we first have a visual look around 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. Reports for each chiller are 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 any leaks.

Chiller Service Company Monitoring

Where intermittent faults are concerned, on site 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 feedback 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

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 visit. 

Flooded

On larger chillers, the screw or centrifugal compressor is mounted directly on top of the flooded evaporator. The refrigerant is in its liquid phase on the outside of the tubes. These are arranged in a rack 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.

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 failed 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 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. The pressure is monitored using a HP gauge.

Pressure Transducers

Johnson Controls

A popular kind of pressure transducer that is 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°C in the UK ambient for example, the R134a refrigerant saturation on the high side of the system would be around 36°C 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. We 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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To read more about chiller diagnosis hit the Tag at the top of the page.

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

Planned Preventative Chiller Maintenance

Featuring planned preventative chiller maintenance, which is part of a series of longer, in depth 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 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°C high being reduced by 2°C may not calibrate correctly. An amount of trial and error is often required. Also, monitoring the sensor against a digital thermometer at various temperatures is carried out.

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) This includes 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°C 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 has been deteriorating over several 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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To read more about chiller control systems hit the Tag at the top of the page.

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°C 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 the 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


Engineer carrying out process chiller service with yellow and black cylinder

Process Chiller Service

Maximus Chillers has just carried out process chiller service to a flooded evaporator. The refrigerant seal on a four bolt, flanged coupling had been found to be leaking liquid refrigerant. There was no possibility to valve off that section of the machine, as the flooded evaporator is the storage vessel for all of the charge of the system in its liquid phase.

Refrigerant Recovery during Process Chiller Service

Our high capacity refrigerant recovery unit was set up next to the machine to carry out the task. 55 kg of refrigerant was recovered in a short time into our recovery cylinder. This refrigerant was collected for recycling after the job was completed.

Stainless Steel

Our unit is made from stainless steel because this metal works well with ammonia.

Condenser for Process Chiller Service

The condenser is made from tubing which is connected to ‘u’ bends on either end. These ‘u’ bends send the condensing refrigerant back along the next tube in the opposite direction. This process, back and forth allows time for the refrigerant to condense into a liquid. Fins are pressed around the tubing to increase the surface area and help to dissipate more heat from the refrigerant. A condenser fan is fitted to suck the air through the fins and so reject the heat.

Reciprocating Compressor

A four cylinder reciprocating compressor is fitted to the unit to provide the pressure difference to pump the refrigerant into the above mentioned condenser. It has an air cooled electric motor fitted which is open drive. This is because ammonia would corrode the windings of the motor if a semi hermetic compressor were to be used. Semi hermetic meaning that the windings, stator and rotor of the motor would be internal to the system. The motor is fitted in the vertical position with the four cylinders opposing each other on the central crank shaft.

Controls for Process Chiller Service

For safety reasons controls are fitted to the unit. These include:

HP Switch

If the recovery cylinder were to become over filled, the pressure would build up to a dangerous level. The TARE and the ullage need to be calculated prior to the job to prevent this from happening. The below mentioned liquid pipes have been designed with pressure issues in mind, but somewhere on the system would be the weakest point. This would burst causing a catastrophic refrigerant leak. The whole charge of the machine and all the refrigerant in the recovery cylinder would leak to atmosphere. The HP switch is set by the engineer on site to the correct level given the ambient conditions. This takes into account the temperature of the refrigerant and the safe operating pressure of the vessel.

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Refrigerant Liquid Pipe

Steel Braided

The refrigerant in its liquid phase is pumped into the above mentioned unit down a steel braided liquid pipe. The steel braiding is to provide additional protection from the pipe being damaged on the outside. Damage like being driven over by a forklift truck, or having sharp objects coming into contact with it. Also, the braiding helps to prevent bursts when pressure builds up on the inside. This can be due to a restriction, malfunction of system components or vessel overfilling.

PTFE

The inner part of the pipe is PTFE. Other types of plastics and compounds corrode due to the toxicity of ammonia. Polytetrafluoroethylene is the chemical name for this compound, it is a fluorocarbon solid and is considered to be non reactive.

Fittings

There are various metric and imperial thread types that can be used. This depends on the fitting size on the machine and the fitting size and type going onto the recovery unit. We carry a wide range of fitting types to step down and step up in size. We can go between male to female types and use male to male and female to female where necessary. We carry adaptors to go from metric to imperial thread types.

Remote Access during Process Chiller Service

We carry an extensive stock of liquid pipes that can be connected end to end to provide remote access. We will always try to get the recovery equipment as near as possible to the plant, but when this cannot be achieved, we can arrange access up cat ladders or the side of a building. We can use our lift and shift team to arrange the hauling of all the required equipment and ancillaries to any location. Just part of what we call the MAXIMUS ADVANTAGEAny Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. Contact our office for prices for the above mentioned pipes.

Process Chiller Leak Service

The flanged coupling was unbolted and the failed refrigerant seal was removed. The new seal was fitted from our full range of sizes that we keep on the shelf in our stores. Our engineer bolted the flanged coupling back up to the correct torque setting.

Pressure Leak Test

A nitrogen pressure leak test was carried out to ensure the integrity of the system with the result being a pass.

Dehydration Process

As the system was open to atmosphere, air had got into the system which carries moisture content. The moisture and non condensables were removed down to a near perfect vacuum using one of our high capacity vacuum pumps.

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Charging of Refrigerant

The photo shows the charging of a cylinder of refrigerant into the system in its liquid phase. The cylinder has a dip tube fitted for ease of handling. Once the pressure in the system and the cylinder equalized, remaining refrigerant was drawn into the system during the operation of the plant.

Run Testing

The sight glasses and level glasses were found to be at the optimum level under the normal running conditions of the plant. As it is a flooded system, there was found to be a low superheat value. A high subcooling value was achieved with the use of a subcooler. Our engineer monitored a full cycle of an hour and a half: compressor temperatures and oil level were found to be within normal operating limits.

Remote Service Monitoring of Process Chiller

The process chiller can be remotely monitored via a data uplink through the internet. Our office continued to monitor the plant for some days as it went into seamless operation.

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Follow this link to purchase BESA pressure testing technical bulletin | Click Here


Chilling plant service showing yellow top recovery cylinder with gauge line and sight glass fitted

Chilling Plant Service

Chilling plant service had been arranged because our customer had been having high pressure problems.

Transducer Required Chilling Plant Service

The 4-20mA transducer needed replacing as it was reading low by a long shot. Therefore, the PLC was not bringing the fans on as it should. The pressure in the high side of the system was getting up to 40 bar. This is because the refrigerant was R410a which has a higher head pressure than other commonly used HFC refrigerants. We ordered the replacement transducer which is fitted with a female fitting.

Chilling Plant Service Leaks

Our engineer concentrated his attention on the high side of the system to start with. Then, he found a leak on a fitting, a leak on the pressure relief valve fitting and a leak on the liquid line near the drier. A sealant was used for leaks on the fittings- they were removed, cleaned and refitted. The leak on the liquid line was re sealed by removing the section of pipe, removing any remaining solder, then the section of pipe was rebrazed.

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Pressure Test

The remaining parts of the system were leak tested then the plant was put on a pressure test to ensure the whole system was leak free. The pressure test was satisfactory and so the evacuation process could be started.

Evacuation Process 

Each of our engineers has a powerful vac pump to speed up the dehydration process. This means that a deep vacuum can often be pulled on the same day, instead of the usual overnight process. The nitrogen and other non condensables were removed quickly and the Torr gauge came down to the pressure where moisture was being removed. At this pressure, any moisture is forced to boil off around the system.

Recharging of the Chilling Plant Being Serviced

In the photo, the plant is being recharged at the end of the work. It is being recharged into the liquid side of the evaporator. All readings were okay when running the system. Further leak tests were then carried out at normal operating pressures.

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Read more about refrigerant reclamation by following this link to Wikipedia | Click Here


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