Air Cooled Screw Chiller Maintenance

Two green screw compressors being maintained in an air cooled chiller

Air Cooled Screw Chiller Maintenance

We recently carried out air cooled screw chiller maintenance at a site we look after in the North West. The plant is described such because it uses two Bitzer screw compressors to create a pressure difference in the R134a refrigerant. The plant has been designed to be remotely operated…

Chiller Remote

This is a way of operating the chiller remotely. Instead of the end user having to walk up to the machine each day to check for faults (chiller local) the plant can be remotely operated and monitored.

Run Signal

The run signal to start the chiller is sent by a relay being energised in the BMS panel (Building Management System) in the plant room. When the chiller receives the run signal, it shows the chiller on message.

Fault Feedback

When the chiller develops a fault, the chiller energises a relay, sending a fault feedback signal to the BMS panel. This fault signal causes the run signal to drop out and a new run signal to be sent to the adjacent redundant system.

BMS Panel

The BMS panel runs contactors which bring the water system pumps on, it also receives analogue signals from temperature sensors on the water system. These inputs and outputs are wired into a PCB which converts them into a data signal. This signal is sent down a CAT 5 plug cable to the supervisor in the facilities management room in the building below.

Remote Monitoring During Air Cooled Screw Chiller Maintenance

A supervisor is a computer which has graphic monitoring of the chillers and the air handlers. The supervisor, is connected down a phone line to the BMS company. Often, the chiller is remotely operated and monitored from a laptop used by a BMS engineer working from home.

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Air Cooled Screw Chiller Maintenance Parts

With a comprehensive range of chiller parts available, off the shelf, for air cooled chillers- look no further than Maximus Chillers for all your chiller parts. We can also supply parts mostly same day. A specialist part on this chiller is the electronic expansion valve driver- this regulates the steps in the expansion valve to ensure correct superheat in the shell and tube evaporator. An electronic expansion valve driver is also available to regulate the expansion valve in the refrigerant economiser. This acts to subcool the refrigerant to ensure optimum system efficiency.

Diagnosis During Air Cooled Screw Chiller Maintenance

Should you need chiller diagnosis- one of our trained professionals onsite during the maintenance will identify the issue with his system test equipment.

To read more about air cooled chiller maintenance click the Tag at the top of the page.

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Read more about remote monitoring and control on Wikipedia | Click Here


Vacuum pump and green compressor during air cooled chiller superheat maintenance

Air Cooled Chiller Superheat Maintenance

Air cooled chiller superheat maintenance at Maximus Chillers. During the visit, we found a high superheat condition with an Italian chiller. The customer had reported a low refrigerant charge trip out. The customer raised the order, so we got straight to work on the leak during the maintenance visit.

Pressure Temperature Relationship

Put simply, the higher the pressure, the higher the temperature of the refrigerant- this is consistent with Charles’s Law of Constant Volume. The refrigerant was found to be at a higher temperature above saturation (or boiling point) than usual- which is a high superheat condition. The chiller runs on R134a, which is a HFC refrigerant.

Air Cooled Chiller Superheat Maintenance with Leak Finding

Our engineer used his leak identification equipment to find the leak. After looking around the chiller he found the leak adjacent to the shell and tube evaporator, where 4 bolts hold the suction pipe on. This coupling is sealed with a gasket.

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Chiller Pump Down

Because of the location of the leak, our engineer decided to pump the chiller down to the condenser and valve the evaporator off. A lot less time consuming than setting up the recovery unit to decant the refrigerant.

Air Cooled Chiller Superheat Maintenance with Leak Repairs

He used his Allen key set to remove the suction pipe from the evaporator. On inspection, the paper gasket had deteriorated then been pushed out by the pressure in the system. All of our engineers carry an extensive range of commonly used parts and materials as standard in their cars. This is to reduce down time for the customer. He made up a new paper gasket, coated it with a special sealing compound, then re fitted the suction pipe to the evaporator. He then used his torque wrench on the Allen key bolts to the correct manufacturer’s recommendations. The system was then pressure tested and dehydrated as per standard industry guidelines.

Screw Compressor

The superheat value at the Bitzer screw compressor was found to be within normal operating values after additional refrigerant was added to the system. A further follow up leak test was carried out at a later date according to F-gas regulations. The paperwork being kept in the F-gas file in the chief engineer’s office.

To read more about air cooled chiller maintenance click the Tag at the top of the page.

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To read more about vapour compression 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 during packaged chiller service with all combustible materials being removed from the work location. A permit to work was opened with our engineer as the responsible person. A half hour fire watch was carried out on completion of works.

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Pressure Test During Packaged Chiller Service

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

Vacuum Pump

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

Refrigerant Saturation

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

Subcooling

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

Superheat

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

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


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 a short cycling condition occur. 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 operating limits and a good read back 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 chilling plant water system had achieved 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 chilling plant maintenance click the Tag at the top of the page.

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Read all about solenoid valves on Wikipedia | Click Here


Green Bitzer compressor being vacuumed during HFC chiller service

HFC Chiller Service

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

HFC Chiller Diagnosis Service

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

Return Visit to Decant the Refrigerant

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

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Looking Around the Pipework for a Leak

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

Brazing and Pressure Testing

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

The Evacuation Process for HFC Chiller Service

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

Recharge and Run Testing

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

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Read more about a film blowing machine on Wikipedia | 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 Decant for Process Chiller Service

Our high capacity pump out unit was set up next to the machine to carry out process chiller service. 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.

Process Chiller Refrigerant 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 cylinder 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 process chiller. 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 service of this 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


Chilled water system repair of condenser to a silver chiller with blue compressors

Chilled Water System Condenser Repair

Chilled Water System Condenser Beyond Repair

Chilled water system repair of condenser was required because the previous company had been chasing leaks round in a circle. Therefore, the customer had decided to buy a new condenser. This was our first job with a new Maintenance Contract, so we wanted to make a good impression.

Condenser Removal on the Chilled Water System

There was no refrigerant in the chilled water system so our engineer cut the discharge and liquid line to the condenser. He then removed the rivets so the frame could be taken apart. Lifting equipment was fitted to the old condenser to aid the removal. Then, slings were fitted and a forklift truck removed the old condenser.

Condenser Replacement on the Chilled Water System

Our engineer supervised the condenser replacement on the chilled water system. He found that the new condenser did not fit correctly. The new condenser was 5mm thicker than the old one. It was decided to lift it back out and angle grind the frame to make more room. Once this was completed, the new condenser fitted correctly and was bolted in place.

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Chilled Water System Pipework Repair

The pipework had to be repaired and brazed in on the chilled water system. Then, the standard practice of a pressure test to ensure the integrity of the system.

The Evacuation Process

Having passed the pressure test, our engineer set up the vac pump and started the evacuation process. This is to dehydrate the system by pulling a vacuum of less than 2 Torr. Any moisture in the system will boil away and leave the system dry.

Recharge and Test Operation

The refrigerant is R410a. Our engineer put around half the charge in, then trimmed the remaining charge according to the superheat and subcooling values. He monitored the chilled water system for the rest of the day. He was looking for leaks as the plant was at operating pressures of 30 Bar. All was well, so the customer signed off the paperwork as he was pleased with the capability of our engineer.

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Read about air cooled condenser installation at the Institute of Refrigeration | Click Here


Mirror looking for leak during chilled water system EEV service

Chilled Water System EEV Service

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

Chilled Water System EEV Service

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

Electronic Component Refurbishment

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

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Pump Down for Chilled Water System EEV Service

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

Remove and Replace

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

Open it up and Switch it on

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

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


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