Monthly Archives: June 2020

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.

Leak Finding for Air Cooled Chiller Superheat Maintenance

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.

Leak Repairs for Air Cooled Chiller Superheat Maintenance 

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.

Related Articles:
Air Cooled Chiller Planned Maintenance

Water Chiller Maintenance

Process Chiller Maintenance Visit

Chilled Water System Maintenance

Air Cooled Chiller Maintenance

Centrifugal Chiller Maintenance

Industrial Chiller Maintenance

Chilling Plant Controls Maintenance

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Chiller Maintenance Checklist

Read all about solenoid valves on Wikipedia | Click Here


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