The chiller maintenance schedule in essence is as follows:
News Article No.5
N+1 is intrinsic in the development of a chiller maintenance schedule. N+1 means the amount of cooling required + the same amount again in parallel. It can also be represented as 2N. Two water system pumps are a good example: where the pipework splits in two- one pipe for each pump. When a pump fails, the redundant pump comes online. Chillers are arranged in parallel, in this way, on the water system. This redundancy allows for a stress free maintenance of the plant. The failed system can be rectified and brought back online while the redundant system takes the load.
The intervals in the contract are influenced by the redundancy of the chillers on site. The less run hours the compressor does, the less maintenance is required. We at Maximus Chillers can tailor make a maintenance schedule exactly to your needs by looking at how much the chillers are used and how hard they work.
For some applications, the chiller operates under a high load condition all the time, with a redundant system in standby. On other applications, the chiller works in minimal load conditions. Regardless of the load conditions, the chiller is critical to the cooling of buildings or for an industrial process.
An important thing to remember is to balance compressor run hours and bearing wear by rotating the lead/ lag duty of the chillers. This can usually be done in the in the sequencer (if fitted) by changing a program setting. Otherwise, the switchover controls can be changed on the off/hand/run toggle switches. Where manual changeover is required, the onsite engineers are usually conversant with the procedure concerning the water system pumps, valves and controls. During the maintenance, the stop checks can be carried out on the redundant system, while the run checks are carried out on the system which is online.
Reciprocating compressors require a log of the compressor run hours. This is because the valves and bearings should be changed at pre prescribed intervals as laid down by the maintenance schedule. Particularly important to reciprocating compressors are regular oil changes and oil sampling- a small change in the result of an oil sample can prevent a serious compressor smash up. A check list including the model number and serial number is completed on each visit and kept in a file on site. This file can be consulted during diagnosis and maintenance to decide on the beast way forward with an on going issue.
Air cooled chiller condensers can often be looked after by the onsite engineers in between maintenance visits. Just a quick brush down every few months is usually all it takes. Where the environment lends to a type of contaminant being collected on the condenser coils, an effective chemical is selected from our stores and used on the coil. Where there is an issue with the serviceability of the condenser, we can put together a plan to keep on top of it. We can even retrofit a new condenser- it’s what we at Maximus Chillers call the MAXIMUS ADVANTAGE™
0161 370 7193
The shell is made from a heavy steel sheet rolled into a circle. The seam is welded together to form a cylinder. The tubes are pushed though the tube holders which are made from steel and are welded into the shell of the evaporator. The tubes are copper because of its good thermodynamic properties.
Direct expansion is achieved in an evaporator with a thermostatic, or electronic expansion valve. The refrigerant enters the valve from the condenser as a high pressure, hot liquid. The pressure drop on the evaporator side of the valve makes the refrigerant flash off into a cold, saturation point liquid and vapour mix. The liquid boils off, absorbing latent heat through the inside of the copper tubes. On the outside of the copper tubes is the return water from the process, or the cooling of buildings.
The parts of the maintenance schedule that relate to DX evaporators are:
The inside of the tubes are in the clean environment of the fridge system. This means they do not become fouled. A tube insulating issue can be caused on the inside by oil. If there are issues with the oil return system, the oil can pool in the evaporator. A low refrigerant charge can have the same effect. Written into the maintenance schedule are manual oil return and oil draining visits. During these visits, the monitoring of the refrigerant charge is also carried out.
If a sensor is not located in its pocket correctly, or without sufficient heat transfer paste- it will read incorrectly back to the electronic expansion valve driver. This will cause the expansion valve to malfunction.
A full maintenance of the pressurisation unit is carried out. This includes the pumps, controls and program adjustments as required. Incorrect pressure in the water system will cause a knock on effect of faults on the chillers.
As above with chiller lead/ lag change over, water system pumps are manually changed over from lead to lag in the building controls. Carrying out this procedure reduces the chance of pump failure between visits. This is because it balances the pump run hours and so prevents bearing seizure after a long period not running.
0161 370 7193
Flooded evaporators are the reverse of the above DX evaporators. The refrigerant is on the outside of the tubes, with water on the inside of the tubes. Gravity and refrigerant charge determine the refrigerant level in the condenser and evaporator. In between the two is located the liquid pipe with the orifice located in the pipe for the expansion of the refrigerant. The cooling water flows through the condenser tubes and off to the cooling towers. On the low side, the chilled water flows through the evaporator tubes and off to the process, or the cooling of facilities.
The parts of the maintenance schedule that relate to flooded evaporators are:
Because the condenser cooling water and chilled water systems are pumped through the pipes, the tubes become dirty over time. This occurs more often on the condenser as the water towers are open to atmosphere. Contaminants from surrounding buildings and factories gets into the water system and thermally insulates the tubes. This thermal insulation reduces the heat exchange through the copper tubes. The knock on effect is higher head pressures and eventually high pressure trip outs.
We at Maximus Chillers have in our stores the required equipment to carry out the cleaning of the tubes. Our engineers can attend site and liaise with the onsite engineers as regards the draining, strip down and lift out of the heat exchanger end plates.
A water sample is taken from the cooling and chilled water systems. These samples are sent off to our laboratory for analysis. Bacteria can build up in the water system causing slime- this can be rectified with a careful selection of chemical agents. Also, silt can build up- various chemicals are added to positively charge the silt and so carry it around the system to the strainer. Where the issue is caused by rust- an inhibitor can be added to prevent, or slow the oxidization of the steel.
0161 370 7193
The frequency of F-gas leak testing is determined by the size of the plant. This will be detailed in your F-gas file which is kept on site. Another record of this is kept by the chiller company at their registered office. The copies of the periodic leak testing sheets are kept by both parties. These detail the result of the test, refrigerant added to the system, refrigerant removed from the system and the required follow up actions. Some methods of leak detection are:
On each visit our engineers remove the coverings of the ends of the condensers and panels. This is to inspect the whole machine for a sign of a leak. Any potential leak is marked for future identification of the location. A visual inspection will always be backed up with a further diagnosis such as:
These readings are taken during a maintenance visit to determine the refrigerant charge of the chillers. The engineer, however, has to bear in mind that the subcooling and superheat readings can read abnormally due other reasons.
Various makes are available from the suppliers. Each engineer having his own preference. We at Maximus Chillers stock leak sprays and a wide selection of other materials.
This type of leak detector is installed in the chiller low down in the panel. This is because HFC refrigerant is heavier than air. The leaking refrigerant will tend to pool in the bottom of the various panels around the chiller.
Each of our engineers carries a portable sniff tester. It comes with an extended tip to get into the most tight and awkward places. The leak detector has a replaceable element inside the unit. It also comes with replaceable tips which can be swapped out periodically. They come with a portable plug socket and transformer to charge the on board batteries after use in the field.
Air Cooled Chiller Planned Maintenance
For further reading on chillers and the chiller maintenance schedule- visit Better Bricks | Click Here
Industrial chiller maintenance including a reciprocating compressor with 8 cylinders. They always have an even number of cylinders so that the compressor is balanced.
Because the refrigerant being used in this article is ammonia, the compressor is open drive. This is because ammonia corrodes the copper windings of the electric motor. An open drive compressor needs a shaft seal to prevent oil and refrigerant escaping from the system. These shaft seals are prone to wearing down and leaking. They have two mating surfaces that have a finish so smooth that it is like glass. Any oil leaking out of the system collects in a pot. This pot is monitored for the rate at which it fills up and so the deterioration of the shaft seal can be monitored. The swap out of the shaft seal can be arranged at a convenient time. This evolves the splitting of the shaft coupling to allow access to the seal.
This means that the electric motor is internal to the compressor. Hermetic meaning sealed and semi meaning that you can bolt components off, such as, the cylinder heads. There is a significant advantage with this type of compressor design as there is no shaft seal. The compressor motor windings are also cooled by the suction vapour returning to the compressor from the refrigerant system. This compressor design is used with HFC, HFO, CO2 and Propane refrigerants. There are some semi hermetic compressors that are suitable for ammonia where the windings have been sealed from the refrigerant.
This kind of compressor has a lot of moving parts that need to be replaced according to the run hours of the compressor. Failure to do so will lead to the compressor going out of balance and an expensive compressor smash up occurring. Usually during a smash up, a connecting rod will fly off causing oil to spurt out from the gallery. This causes a low oil pressure fault which stops the machine. One smash up which I have seen involved all the con rods staying on and flailing round the inside of the compressor. One cylinder was still working, the compressor still running and a sump full of different sized triangle pieces of metal! This highlights the importance of scheduled maintenance.
0161 370 7193
On a recent Major maintenance visit, the scheduled oil change was carried out. The required oil being selected by our oil analysis process to the correct viscosity for a Grasso reciprocating compressor operating at a 1° saturation.
The compressor was valved off from the rest of the system. The standing pressure of the vapour in the vessel was 5.8 bar. On the bottom of the sump is located an oil drain port, this is because it is the lowest part of the system. Using hoses and a valve, the oil was drained into empty oil drums.
Our engineer removed the old oil for recycling, then lifted the new oil to the work location. He used his portable oil pump to pump the oil back in using the same port from which the oil was drained. The oil came to the correct level on the oil sight glass and the vapour was bled from the oil filter so that the compressor was primed with oil. When the system starts, the oil pump pushes the oil through to the cylinders of the compressor.
The oil heater was switched on until the oil was 46°. The chiller was then started and run tested. The Delta P across the oil filter was found to be nominal at 0.5 bar. The oil level remained at the correct level as the three way valve opened to the oil cooler. The oil cooler, in turn being cooled by a cooling loop which uses some of the tubes on the air cooled condenser.
0161 370 7193
We work on all kinds of chillers from the smallest Italian process chillers, through to large air cooled chillers and centrifugal chillers used for industry.
Problems are our bread and butter- that’s what we do best! Whether you require centrifugal compressor remanufacturing, or the system drying out after a burst heat exchanger- it’s all in a day’s work.
We have an excellent supply chain where we pride ourselves on sourcing any part for your chiller. Where a part is no longer manufactured or is not available- we fit a different part. A chiller is just a chiller at the end of the day- we can achieve the same or better design characteristics and efficiency with a different part.
HFC refrigerants are being phased down but are still the most popular variety. They are being superseded by HFO refrigerants which will become more popular over the coming years. We are also adept in the handling of natural refrigerants, such as, ammonia, propane and carbon dioxide.
When you do something as niche as what we do- you cannot expect to just work outside your back door. With blue chip customers around the UK and around the world- nowhere is too far for Maximus Chillers.
Air Cooled Chiller Planned Maintenance
To read more about coefficient of performance hit the Tag at the top of the page.
Follow this link to read about polyolester oil on Wikipedia | Click Here
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.
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.
Our unit is made from stainless steel because this metal works well with ammonia.
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.
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 configuration 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.
For safety reasons controls are fitted to the unit. These include:
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, the temperature of the refrigerant and the safe operating pressure of the vessel.
0161 370 7193
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.
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.
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.
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 is 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 ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. Contact our office for prices for the above mentioned pipes.
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.
A nitrogen pressure leak test was carried out to ensure the integrity of the system with the result being a pass.
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.
0161 370 7193
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.
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.
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.
Chilling Plant Service
Follow this link to purchase BESA pressure testing technical bulletin Click Here
Category : Water Chillers
Maximus chillers provides water chiller maintenance to all kinds of machines. Some of which have kilowatt hour meters fitted. This means we can monitor the reduction in energy consumption, directly as a result of our maintenance being carried out.
Maintenance is carried out to ensure every aspect of your chiller is running efficiently. We believe our maintenance checklist is the best in the industry. It looks in detail at the running conditions of the plant, component adjustments and the parameters in the controls. The checklist is used to assess if there are problems that are starting to occur before a safety shutdown happens. Below are some of the issues that we keep on top of to increase the efficiency of your plant.
The build up of dirt acts as an insulator in shell and tube heat exchangers. These are used for the evaporation and the condensing of the refrigerant.
In the evaporator, should the tubes be fouled, there will be a reduction in latent heat absorbed into the system. This will cause the plant to stay on longer and use considerably more energy. Should the tubes become considerably fouled, the chiller will malfunction and eventually system shutdown will occur.
In a shell and tube condenser, the reverse of the above will occur. Tube fouling, acting as an insulator, will prohibit the rejection of heat from the system. The head pressure control will open the condenser controls to try and assist in heat rejection. Heavy fouling will cause an increase in the consumption of energy. Eventually a safety shutdown will occur causing loss of production.
0161 370 7193
If the loading of the reciprocating compressors is faulty, the plant will not be able to effectively match the load.
Too much loading may occur, causing the water chillers to achieve set point too quickly. The plant will then go through the off cycle. This means that the plant will have to load back up, using more energy than matching the load continuously.
Should the plant be unable to load up to the required level to match the load, this will cause the water temperature to creep up and the lag chillers being called for to match the load. More water chillers running than necessary dramatically increases energy consumption.
R134a Chilling Plant Maintenance
Visit the Refcom site to read about leak checking during water chiller maintenance | Click Here