Category Archives: Chilling Plant

Chilling plant maintenance of grey machines with red warning signs

Chilling Plant Maintenance

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

HFC Refrigerants

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

Chilling Plant Maintenance using Leak Detectors

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

Static Leak Detectors

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

Chilling Plant Maintenance for One World

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

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Shell and Tube Condensers

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

Chilling Plant Maintenance of Copper Pipework

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

Water System Maintenance

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

Air Bleed Ports during Chilling Plant Maintenance

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

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Standing Pressure

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

Coefficient of Performance

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

Control Panels

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

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

For further reading on Hydrofluorocarbon Refrigerants | Click Here


Carel controller and tick sheet during chilling plant maintenance visit

Chilling Plant Maintenance Visit

On this chilling plant maintenance visit, particular attention was made to compressor loading. This was to ensure that the compressors are capable of operating at 100%. With summer now here- we want the plant capable of running at full capacity.

Controller Loading Timer

On start up, the controller goes through a timer, this is to prevent the compressor from loading up too quickly, achieving set point and going off. With available load, the compressor would start back up and go into a short cycling condition. With 5 minute intervals, the controller brings System 1 screw compressor on at 25%. Then System 2 screw compressor on at 25%. In stages, the controller loads up the compressors until it matches the load.

Compressor Loading Solenoid Coils

These are 24vac. The controller sends out a run signal through the solenoid coil which magnetises the lift valve inside.

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Compressor Loading Solenoid Valves

As the valve lifts, discharge pressure oil passes through a channel and pushes the slide valve open a 25% stage. There are 4 valves for the 4 stages.

Chilling Plant Maintenance Visit at 100%

The chilling plant being maintained on this visit was now running at 100% on both systems. The system readings can easily be read by following the menu in the Carrel controller. Superheat and subcooling readings were found to be within normal operating limits. Also, a good read back was recorded on the water system.

Compressor Unloading

At the end of the day, the three way valves on the air handlers closed down according to the BMS schedule. This meant that the water was diverted away from the heat exchangers in the air handlers. This return water had not picked up any heat, so the controller started unloading the compressors. It did this through 75% to 50% then 25% until the water system was down to setpoint.

Off Cycle at Chilling Plant Maintenance Visit

The BMS stops the chiller with the remote start/ stop signal. Should the BMS malfunction, the chiller would stay off most of the night anyway. The water system pump adds heat into the water system. Therefore, every so often enough load would be available to bring one system on at 25% for a short while.

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

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Read all about solenoid valves on Wikipedia | Click Here


Controls panel open during chilling plant maintenance

Chilling Plant Controls Maintenance

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

Chilling Plant Flow Controls Maintenance

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

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Compressor Run On Time

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

Slide Valve Potentiometer

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

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

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Follow this link to read more about potentiometers on Wikipedia Click Here


R134a chilling plant maintenance showing screw compressor and oil separator with tick sheet and digital thermometer on top

R134a Chilling Plant Maintenance

We recently carried out R134a chilling plant maintenance at our customer’s factory in the North West. The chiller is 600kw with 2 single compressor systems. It has an ‘in house’ controller on it with occasional spurious trip outs. We are working with the problem so far, but an option if the problem persists is to fit a reliable, cheap, off the shelf controller. The factory requires a process water temperature of 6°C. The plant is around the middle of the lifespan and has been properly maintained.

Unlock Controller during R134a Chilling Plant Maintenance

The customer had accidentally locked the controller by pressing the wrong buttons. The machine still functioned as it should, but the customer was unable to modify User settings or look at the readings. Our engineers carry a book with an extensive list of information for any controller which has been built up over time. The procedure was followed to unlock the controller, then the settings were checked.

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R134a Chilling Plant Sensor Maintenance

The sensors can be offset to compensate for a sensor reading out slightly. No offsets were saved and the sensors all read to within a degree or two of our digital thermometer. Our engineer then checked the sensor locations to ensure they were fitted correctly and insulation had not deteriorated.

Fan speed Controllers and Subcooling

During the R134a chilling plant maintenance, particular attention was paid to the fan speed controllers and the subcooling of the refrigerant. This is because of occasional spurious high pressure trips. All the wiring was tightened and the plugged connections were checked and tested. The controller sends a variable run signal to the fan speed controllers. This is worked out from the analogue input signal from the high pressure transducer. If the problem persists, we will have to look into fitting more reliable head pressure controls.

Compressor Slide Valve

The oil solenoids which push and pull the compressor slide valve were operating correctly. The controller sends volts to the solenoids to control the position of the valve. A slide valve potentiometer sends feedback so the controller can work out the percentage position of the valve.

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

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Follow this link to read more about pressure sensors on Wikipedia 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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