How Does A Chiller Work

Latent Heat

Latent is the Latin word for hidden. Something less obvious happens when a pan of water gets to its boiling point of 100°C. You continue watching the flame licking up the bottom of the pan, but the temperature stops going up, strange- right? You carry on watching for a good while and the thermometer still does not go up? Then, eventually- the water boils into steam and the thermometer starts going up again. All of the heat energy that was going into the pan while the thermometer was not going up was latent heat. Latent heat was being absorbed into the water to cause it to change its state into steam. All of this hidden heat caused the liquid atoms to shake apart and become a gas.

Example

Now let’s look at the above example again, but this time including latent heat. A different liquid is pumped through the heat exchanger at 0°C which is also its boiling point. The amount of sensible heat, in our example, is still 6°C. Between the outside of the bubble and Step 1, there is 3°C of sensible superheat above the boiling point. Between Step 4 and Expansion, there is 3°C of sensible subcooling below the boiling point. The latent heat is inside of the bubble which, as you can see, has a considerable size. We measure sensible and latent heat energy using kJ/kg.

The Pressure Temperature Relationship

How we produce the above liquid at 0°C is the second scientific principle...

Higher Pressure

If you increase the pressure of a substance- the atoms are pushed together and so they get hot. The higher the pressure- the higher the temperature.

Lower Pressure

If you decrease the pressure of a substance- the atoms spread apart and so they go cool. The lower the pressure- the lower the temperature.

Refrigerant

R134a is a refrigerant that has a pressure of 1.91 barg, relative to a temperature of 0°C.

Refrigerant Saturation Point

The above temperature of 0°C is also the boiling point of R134a. This boiling point can also be called the saturation point because no more heat can be added to the liquid before it boils. The refrigerant liquid is full of heat- or saturated.

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How Does A Chiller Evaporator Work

This is a heat exchanger which is in between two other chiller components: the expansion valve and the compressor. The expansion valve is a restriction in the chiller system and so there is a pressure drop into the evaporator. The compressor sucks from the evaporator and so maintains this pressure drop. This is the pressure temperature relationship: the lower the pressure- the lower the temperature. Liquid refrigerant flows through the evaporator at 1.91 barg and 0°C. It boils off absorbing latent heat, then it superheats, in our example, by 3°C above its saturation point. The evaporator has absorbed heat energy from the water on the other side of the heat exchanger.

How Does A Chiller Compressor Work

A bicycle pump is a compressor- notice how it gets hot when you inflate a tyre. This is the pressure temperature relationship: the higher the pressure- the higher the temperature. Therefore, the compressor also adds heat energy into the system. The refrigerant is sucked into the compressor from the evaporator as a cold, low pressure gas at 1.91 barg. It is then compressed into a hot, high pressure gas which is discharged from the compressor at 8 barg.

How Does A Chiller Condenser Work

The hot, high pressure gas being discharged from the compressor is cooled down with fans which suck air through the fins of this heat exchanger. The gas goes through its latent heat phase again, but this time condensing from a gas and into a liquid. It is then subcooled, in our example, by 3°C below its saturation point into a hot, high pressure liquid. The heat energy absorbed in the evaporator and the heat energy added to the system by the compressor is rejected into the surrounding air.

How Does A Chiller Expansion Valve Work

The hot, high pressure liquid at 8 barg arrives from the condenser at the inlet of the expansion valve. The expansion valve could be seen as being a tap which is partially closed. This restriction causes the refrigerant to back up behind the expansion valve inlet. The refrigerant that gets through the valve and into the evaporator expands into a cold, low pressure liquid/ vapour mix. The vapour is called ‘flash gas’ and is as a result of the refrigerant expanding. Vapour is another word for a gas.

How Does A Chiller Set Point Work

This basic refrigeration cycle continues until the setpoint is achieved and the controller stops the compressor. After some time, the water warms up by a couple of degrees and the controller starts the compressor back up.

Chiller Compressors

Chiller Condensers

Hit the Tags at the top of the page to navigate your way to our extensive library of further reading on this subject.

Read more about vapour compression refrigeration on Wikipedia | Click Here

25/07/2021
Maximus Chillers
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Two large air cooled chillers during condenser testing

Air Cooled Chiller Condenser Testing

Category : Articles

We at Maximus Chillers have recently carried out air cooled chiller condenser testing at a new 3 year maintenance contract in the North West. The last of 4 systems had gone down on the morning that we first attended site. 1.2 MW of cooling had been lost which resulted in the water system temperature rising to 31°C. These chillers are used to cool an office block, so we wanted to get some of the systems up and running as quickly as possible…

News Article No.16

Air Cooled Chiller Condenser 1 Testing

One of the systems was disabled due to a condenser fan failure. 1 of 5 fans was found to be seized and disconnected. Fan speeds have sufficient redundancy built in to allow for a high ambient and a partially blocked condenser. There was a high ambient condition, but the condenser was found to be clean. Therefore, our engineer decided to run test the system and monitor the condenser pressure…

Fan Speed Transformer

3 fan speeds available on this chiller- low, medium and high. The fan speeds are achieved using a transformer which makes a different voltage for each fan speed. This is quite a good way of controlling the condenser pressure, as all of the fans run smoothly together. The program looks at the condenser pressure using a transducer, then selects the required fan speed.

Medium Fan Speed

As expected, the chiller program selected the medium fan speed. This provided the required saturation pressure in the condenser and so adequately subcooling the refrigerant.

Compressor Protection

All of the system pressures and temperatures were nominal, so the compressor was protected. There was a good oil return and sufficient cooling to the suction housing from the refrigerant. This cooling ensured that the internal motor windings did not overheat.

Monitoring

Having got this system away- our engineer monitored the water system temperature which started to come down. More cooling was required, however, to get the water system temperature down to set point…

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Air Cooled Chiller Condenser 2 Testing

Another system had been the only system running for some time.

Blocked Condenser

Grass pollination had caused a covering of organic material to accumulate on the condenser. The increased head pressure had caused the high pressure switch to trip. This type of material was easy for our apprentice to remove, as it clumped together when brushed.

HP Reset

The high pressure switch was reset and the system was run tested. It did not trip again, but a high pressure condition still persisted in the condenser.

Chemical Clean

Therefore, our engineer decided to carry out a chemical clean. After the whole of the ‘v’ type condenser was cleaned- the pressure came down a little.

Non Condensables

This system stayed running, but in the high fan speed. On the upcoming maintenance visit, a refrigerant diagnosis will be carried out to assess whether there are non condensables in the system. If this is the case, a false reading of subcooling will be recorded, as the non condensables throw out the calculation.

Cool Building

With 2 systems now running, the water system got down to set point. Our customer was really happy as the situation had gone from: office workers walking out of the building- to a cool building before 10 o’ clock on the first day of the contract.

Air Cooled Chiller Condenser 3 Testing

The third system had been on pressure test for the past 2 months with the condenser valved off. There was still pressure in the system, but our engineer decided to confirm the pressure test for himself. He did this by leaving it on pressure while having a drive round the suppliers. Several hours later, the pressure had remained constant, so he was able to start the evacuation process. After this was completed, the system was recharged and run tested. Now there were 3 systems up and running.

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Air Cooled Chiller Condenser PRV Testing

The pressure relief valves on the condensers have recently been changed. Industry guidelines state that they should be tested or replaced every 5 years. There is no guarantee that the PRVs will re seal satisfactorily after they have been tested. Therefore, in practice they are usually replaced. We inspected the date of the replacement, the burst pressure, the associated certification and paperwork- all was found to be satisfactory.

Air Cooled Chiller Condenser 4 Testing

The fourth system has a leak on the condenser with some refrigerant remaining in the system. This refrigerant will need to be decanted on a subsequent visit using a pump out unit and a recovery cylinder.

F-gas Leak Testing

The entire system will be pressure leak tested to identify the location of all leaks. Then, the leaks will be repaired using oxy-acetylene. After this, the system will be pressure tested to ensure its integrity.

Dehydration

Then, the dehydration process will be carried out. The achievable pressure of the vacuum pump will be tested and recorded. Evacuation will be carried out until this recorded pressure is achieved. Our engineers are issued with a powerful 10 cfm vacuum pump to speed up this process. This system will then be recharged and its operation tested.

Air Cooled Chiller Condenser Testing and Calibration

One of many tests that we will carry out on the upcoming maintenance visit is condenser transducer calibration. Transducer readings are not linear, so care will be taken to achieve an accurate calibration. A password will be entered into the controller to gain access to the required menu. Then, each of the transducers will be adjusted. The result of this means that accurate diagnosis can be carried out and the correct subcooling readings can be recorded.

The above is just part of the service that we provide to you- the customer! Having the capability to do anything and to extend the life of your chillers is part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere.

Related Articles:
Chilling Plant Service

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Tags : air cooled chiller condensers chiller compressor failure chiller control panels chiller control systems chiller electrical faults chiller pressure transducers chiller refrigerant economizers chiller refrigerant pressure temperature relationship chiller refrigerant saturation chiller refrigerant subcooling chiller refrigerant system non condensables chiller refrigerant system vacuum pumps chiller sensor offset screw chiller compressors

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

Read more about pressure sensors on Wikipedia | Click Here

09/05/2021
Maximus Chillers
-

Chiller Controls Company

Category : Chiller Components

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

Non Condensables

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

High Subcooling

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

Air Purging

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

Subcooling Readings

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

Dalton’s Law of Partial Pressures

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

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Electrical Problems

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

No Heater Burn Out

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

Ohms Checked by Chiller Controls Company

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

Run Signal

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

Blown Relay

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

Monitoring by Chiller Controls Company

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

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Air Cooled Chiller Condenser Maintenance

Software Upgrade by Chiller Controls Company

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

Chiller Controls Company Reliability

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

Chiller Controls Company's Test Rig

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

Laptop Plug In

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

Chiller Controls Company Testing and Adjustment

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

Completion

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

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Scroll Chiller Compressor Maintenance

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Reciprocating Chiller Compressor Maintenance

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

Read more about the controls used for chiller/ heat pump units at the Carel website | Click Here

31/01/2021
Maximus Chillers
-

Chiller Service Company Visit

Tags : air cooled chiller condensers chiller compressor systems chiller condenser high pressure control chiller condenser high pressure faults chiller condenser high pressure switches chiller control systems chiller electrical faults chiller expansion valves chiller liquid line solenoid valves chiller nitrogen pressure tests chiller pipework oxy-acetylene brazing chiller refrigerant discharge pipes chiller refrigerant economizers chiller refrigerant high pressure gauges chiller refrigerant latent heat chiller refrigerant leaks chiller refrigerant saturation chiller refrigerant subcooling chiller refrigerant suction pipes chiller refrigerant superheat chiller refrigerant system vacuum pumps chiller refrigerant system vibration eliminators chiller refrigerant torr gauges f-gas chiller leak testing procedure leaking chiller condensers low refrigerant pressure faults plate chiller evaporators scroll chiller compressors shell and tube chiller evaporators

Category : Articles

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!

Related Articles:
Chilling Plant Service

Air Cooled Chiller Condenser Testing

F-gas Chiller Leak Testing

Chiller Commissioning

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

Read more about F-gas leak checking at Refcom | Click Here

31/12/2020
Maximus Chillers
-

Industrial Chiller Service

Tags : centrifugal chiller compressors chiller compressor loading solenoid coils chiller compressor loading solenoid valves chiller compressor slide valves chiller compressor systems chiller control systems chiller fault finding chiller refrigerant economizers chiller refrigerant low pressure gauges chiller refrigerant mass flow rate chiller refrigerant pressure temperature relationship chiller refrigerant saturation chiller refrigerant standing pressure reciprocating chiller compressors screw chiller compressors screw compressor slide valve potentiometers

Category : Articles

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!

Related Articles:
Chilling Plant Service

Chiller Service Company Visit

Tags : chiller evaporators chiller nitrogen pressure tests chiller pipework oxy-acetylene brazing chiller refrigerant charging chiller refrigerant leaks chiller refrigerant saturation chiller refrigerant subcooling chiller refrigerant superheat chiller refrigerant system pressure testing chiller refrigerant system vacuum pumps chiller refrigerant system vibration eliminators chiller refrigerant torr gauges chiller run testing direct expansion chiller evaporators f-gas chiller leak testing procedure low chiller refrigerant charge

F-gas Chiller Leak Testing

Chiller Commissioning

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

Read more about refrigerant mass flow rate at Science Direct | Click Here

14/06/2020
Maximus Chillers
-

Packaged Chiller Service

Category : Chiller Technology

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.

0161 370 7193

service@maximuschillers.com

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

31/05/2020
Maximus Chillers
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6 large air cooled chiller condensers maintained with 12 fans each

Air Cooled Chiller Condenser Maintenance

Category : Chiller Components

The photo is showing air cooled chiller condenser maintenance being carried out by Maximus Chillers. 6 water cooled chillers are located in the plant room below. They are 750 kw single screw compressors with a control panel located to the side of each. On this visit, the emphasis was to carry out a thorough maintenance of the condensers.

Fan Speed Controllers

The refrigerant for the systems is R134a, so to allow for the saturation of the refrigerant, 8 bar is the head pressure set point. This pressure corresponds to the desired condenser temperature of 36°C. Subcooling of 6°C to 8°C is achieved during the nominal operation of the plant. Each fan speed controller runs the 12 condenser fans together. Other condenser designs where fans bang on forwards and backwards cause vibrations resulting in reoccurring leaks on the condenser. Chiller No. 2 had tripped during a 'discharge override' system message. On inspection of No. 2 condenser- the fans speed inverter had tripped on 'over temperature' alarm. The panel fan, which is the kind to cool computers, was found to be still trying to run but seized. This failure had caused the alarm on the inverter. The panel fan was replaced from the stock of parts in the onsite stores. The chiller was reset and a detailed Tick Sheet was completed noting the occurrence of this fault on arrival.

Air Cooled Chiller Condenser Maintenance Cleaning

Because of the large size of the plant, the customer had installed a fireman’s hose for the cleaning of the condensers. This is located in the free space beneath the condensers. It is fitted to a portable buggy so it can be moved under each condenser. Setting the nozzle to the correct attitude, our engineer moved the buggy sideways, so as to rinse the condenser in the direction of the fins. The condenser was relatively clean as the onsite maintenance engineers carry out this task as part of their monthly schedule.

0161 370 7193

service@maximuschillers.com

Design Considerations for Air Cooled Chiller Condenser Maintenance

The kind of condenser in this article is:

Multiple Row Tubing

3 Rows

It has tubing of ½” diameter which is 3 rows deep. Each pass starts at the discharge header which is at the inlet to the condenser, goes down to the far end, through a condenser end turn, back to the discharge end, through another condenser end turn and back again to the liquid pipe end. The heat removed from the condenser, per kg of refrigerant, is the heat content of the vapour as it leaves the compressor, minus the heat remaining in the liquid at the end of the condenser.

6 Rows

Some condenser designs are up to 6 rows deep. This allows a small footprint of space where there is not much room for the location of the chiller. The downside to this, is that the chiller engineer can often struggle to locate the exact location of a leak when it is deep into the coil. If a condenser is too small, it will cause a higher head pressure and reduce the life of the compressor. We can arrange the lift out and repair of deep row condensers in our workshop.

Finned

This condenser has aluminium fins which are pressed around the copper tubing. This increases the surface area of the condenser heat exchange medium and so increases the dissipation of heat. The same amount of heat delivered to a condenser from the compressor must also be rapidly removed. For this condition to be reached, enough head pressure will need to be built up so that the condenser temperature is at least 15°C above the ambient. This is why the same chiller can be picked up and shipped to the Middle East and still work. It will just run at a higher discharge pressure/ temperature. There will, however, be a loss in the coefficient of performance as the higher pressures will result in more electricity in, versus the same amount of refrigeration effect out.

Forced Convection Type

The fans mounted on the ducting provide this forced convection. The air is sucked through the bottom of the condenser, across the 3 rows of tubes, along the fins and up through the fans. The air flow is stable as it enters the fins so good heat transfer is achieved. As it leaves the fins at the top, there is lower heat transfer as the air is turbulent.

0161 370 7193

service@maximuschillers.com