Monthly Archives: November 2021

Humorous display of various sizes of nails to use as fuses to solve chiller problems

Troubleshooting Chiller Problems

We have a lot of enquiries from our subscribers about troubleshooting chiller problems, so read below for an insight into three commonly occurring issues that are detrimental to the environment…

News Article No.21

Troubleshooting Chiller Problems for Blown Fuses

Although the photograph is funny, not using fuses or using the wrong fuses will result in a fire. When a component burns out and the volts go to earth, the component draws more amps until the fuse blows. Fuses are therefore sized to have a slightly higher amp rating than the running amps of the component. Poorly running chillers with blown fuses and worn out components run inefficiently and so are bad for the environment.

Slow Blow

These fuses are also called motor rated fuses. As the name suggests, they are designed to be used with motors. Motors pull a lot of amps on start up, then settle down to their running amps. The delay before the blow allows for this initial spike of amps. Chillers use motors for:

Condenser Fans

These fans can be radial in design which are driven by a fan belt and motor. They can also be axial with the motor integral at the centre of the impellor.

Water System Pumps

The motor is bolted onto a flange at the back of the pump housing. This means that the replacement is easy as the pump housing remains bolted to the chiller.

Oil Pumps

On centrifugal and screw compressors a motor is often used to drive an oil pump. This sucks oil from the sump and into the compressor bearings to pre lubricate them, therefore preventing untimely bearing wear. Once the compressor is running, the pump motor drops out.

Compressors

Compressors use 2 kinds of electric motor:

Open Drive

An open drive motor can be clamped to a compressor housing. The motor shaft is clamped to the compressor crankshaft using a coupling.

Hermetic and Semi Hermetic

With this design, the motor is located inside of the compressor. An advantage of this is that the motor is cooled by the refrigerant returning back to the compressor.

Refrigerant Pumps

Ammonia systems have all of the liquid refrigerant stored in a low pressure receiver. Motors are used to drive liquid pumps which discharge the refrigerant into the evaporator.

Mobile Workshops

Each of our company cars carries a full complement of cartridge, bottle and centred tag fuses. This means that we can isolate the failed electrical component, replace any fuses and get you up and running whilst on site. We will then arrange the delivery and replacement of the failed component.

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Troubleshooting Chiller Problems for Refrigerant Leaks 

HFC

Because of the high GWP (global warming potential) of HFC (Hydrofluorocarbon) refrigerants, gas leaks are very damaging to the environment. R407c is often used in large air cooled chillers and R134a is often used in centrifugal chillers. The heat trapping qualities of these refrigerants adds significantly to global warming.

Training

Therefore, all of our engineers attend 3 years at college with a refrigerant handling course at the end. The environmental regulations that are studied are…

The Monreal Protocol

This protocol came into force on the 1st January 1989. It was devised to protect the ozone layer by phasing out ozone depleting substances. In chillers, these substances take the form of HCFCs, such as, R22. Most of this refrigerant no longer exists in chillers due to a service ban preventing the repair of the plant. This meant that when problems occurred, the refrigerant had to be decanted and recycled. The chiller was then decommissioned. In some overseas countries there are still systems running on R22. In small systems it still exists too, where no service has been carried out.

Kyoto Protocol

This protocol came into force on the 16th February 2005 and is concerned with the reduction of greenhouse gas emissions that lead to global warming. In our industry, adjustments and procedures to improve chiller efficiency significantly reduce the consumption of electricity.

F-gas Leak Testing

This is a periodic leak test that is carried out to detect a leak that has occurred before the whole charge of refrigerant has been lost to atmosphere. We have written a detailed news article on this subject called F-gas Chiller Leak Testing

Ammonia

This refrigerant has a GWP value of zero: it does not add to global warming. It is highly corrosive and toxic, so specialist equipment and training is required to handle it.

HFO

Hydrofluoro-olefin refrigerants are becoming increasingly popular in newer chillers. They have a very low GWP, but they are still expensive due to the cost of their research and development. The downside is that when they leak, they work their way through the weather system and into the sea where they are harmful to aquatic life.

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Troubleshooting Chiller Controls Problems by Retrofitting

A big chiller problem is when the controls fail and they are found to be obsolete. The manufacture of a new chiller has a massive carbon footprint. Therefore, keeping the current chiller going is the most environmentally friendly option.

Refurbishment

We can refurbish your controller in our electronics laboratory. This is a simple process as we disconnect the controller form the chiller and weatherproof the chiller panel. Once on the bench in the lab, we strip it down for inspection. Often the problem is obvious: dust on the back of the PCB can ‘track’ volts to the wrong part of the board. This can cause component failure to occur. We resolder any failed components and remove the dust from the PCB. On arrival back on site, it is an easy job of just removing the weatherproofing and re connecting the controller.

Controls Upgrade

Alternatively, we can fit a new controller all together. We are on account with MCS for centrifugal controls retrofits, Beijer Electronics for ammonia systems and Carel for most other chillers. This process is more complicated and takes about a week…

Remove and Replace

The old controller and associated wiring is removed from the chiller. Then, the new controller is fitted to the panel and the power supply wires connected.

Inputs

The digital inputs, such as the flow switch are connected. Then, the analogue inputs, such as the pressure transducers are connected.

Outputs

The digital outputs, such as the compressor run signal, are connected.

Commissioning

When the above process is complete, the chiller is switched on and the controller parameters are commissioned. On run testing the chiller, the parameters are further adjusted until the machine goes into seamless operation.

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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 troubleshooting common chiller problems at Process Cooling.


Showing how do chillers work - brass expansion valves inside machine

How do Chillers Work? Expansion Valves

In this article we are going to explore: how do chillers work- expansion valves. They are also referred to as a metering device, as they control the flow of refrigerant into the evaporator. Read below for an insight into the 4 main types that are used on chillers…

How do Chillers Work - Electronic Expansion Valves

This is a refrigerant control which uses a mechanical valve operated by a step motor. A step motor opens the valve according to the number of steps in between the closed and the open positions. This step motor is controlled by a program in the chiller controller…

On Board Comparator

Every engineer has a comparator app on his phone and a set of comparator sliders in his tool case. The controller has sensors fitted to the evaporator and an in built comparator for the refrigerant which runs through the system. The comparator is a scale which compares the pressure of the refrigerant to the corresponding saturation point. Saturation point is another way of describing the boiling point of the liquid refrigerant.

Superheat

The above algorithm is needed to decide the position of the step motor. A pre programmed amount of superheat (the temperature above saturation) is programmed into the controller. This prevents compressor failure due to liquid refrigerant slug back.

Efficiency

Because the above is controlled by a step motor and a microprocessor, the superheat is closely controlled to as low as 1°C. A low superheat value is one of the factors which contributes to a machine running more efficiently.

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How do Chillers Work - Solenoid Expansion Valves

This is a very simple expansion valve. It is just a solenoid valve fitted into the liquid line which is operated by a solenoid coil. The control of this valve is very similar to the above. The difference is that the program works out how long to keep the valve open and how long to keep it shut.

How do high side float expansion valves work when welded into steel ammonia chillers pipework
Refrigerant control on flooded system

How do Chillers Work - High Side Float Expansion Valves

The photo shows this type of valve as used on an ammonia chiller. This kind of chiller is a flooded system where all of the refrigerant is stored in its liquid phase on the low side of the system. As load increases: more refrigerant boils off in the evaporator- it is sucked into the compressor- discharged into the condenser and then arrives as a liquid at the float valve. When the chamber in this valve fills, it lifts a float inside which is made of steel. The float operates a switch which sends volts to the liquid pipe solenoid valve. When this valve opens, it lets the liquid in the float chamber to pass into the evaporator. Having done this, the float drops back down and the valve closes again. The closing of the valve maintains the pressure difference between the high side and the low side of the system.

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How do Chillers Work - Thermostatic Expansion Valves

There are 4 forces acting on a TEV: the power element v spring and liquid line pressure v suction pressure. The expansion valve has been designed to balance these forces.

Power Element

A bulb is fitted to the suction pipe near to the compressor. This bulb is charged with the same refrigerant that is running in the chiller system. It is connected to the power element using a capillary tube (photo at the top of the page) When the temperature rises in the evaporator, liquid refrigerant boils off in the bulb, this forces a diaphragm to open in the power element.

Spring

A needle located on the outside of this diaphragm pushes the spring down. This opens the expansion valve and lets more refrigerant through.

Liquid Line Pressure

The liquid line is the inlet to the expansion valve and carries the refrigerant arriving from the condenser.

Suction Pressure

The pressure drop on the far side of the expansion valve is maintained by the sucking action of the compressor.

Mass Flow Rate

The above allows for a high mass flow rate when the evaporator warms and a lower mass flow rate when the evaporator cools.

Liquid Line Solenoid Valve

To prevent refrigerant passing into the evaporator during off cycles, a liquid line solenoid valve is often used. This type of system usually pumps the evaporator down before the compressor stops. Shortly before the compressor starts back up again, the liquid line solenoid valve opens, the pressure increases in the evaporator and then the compressor starts.

Equalizing Line

This is usually a copper pipe which connects the expansion valve to the far side of the evaporator. It compensates for the pressure drop across the evaporator. It also detects the pressure of the suction pipe at the same location of the sensing bulb. This allows the TEV to accurately adjust the superheat.

Hot Gas Bypass

Some chillers, like laser chillers, require a very close control of setpoint. Sometimes the deadband can be as narrow as 0.2°C. If the compressor were to stop and start all the time to achieve this- it would fail very quickly. Therefore, a hot gas bypass can be used to allow the compressor to carry on running when the chiller achieves setpoint. A solenoid valve opens which allows the discharge hot gas to bypass the expansion valve and return to the suction. It can open and close as many times as needed to achieve a very close control, while at the same time allowing the compressor to run normally.

How do Chillers Work - Expansion Valve Flash Gas

This is the term that describes that portion of the liquid refrigerant which, in any expansion valve, instantly evaporates after it passes through. When this happens, the absorption of latent heat cools the remaining liquid refrigerant in the evaporator to the required saturation temperature.

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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 thermostatic expansion valves at the Danfoss website


Test equipment attached to chiller during chiller maintenance contract visit

Chiller Maintenance Contract

In this article we will be looking into a chiller maintenance contract- how it is composed and examples of how it is put into practice in the field.

News Article No.20

Chiller Maintenance Contract Schedule

This part of the contract details:

Asset list

According to F-gas regulations, each site has to compile an asset list of the plant containing refrigerant. The asset number, model number, serial number, refrigerant type and quantity have to be recorded on this list. It usually takes the form of a file in the facilities manager’s office and is available for inspection by external auditors. Read more about F-gas chiller leak testing

Procedures

Depending on the type of plant onsite, the set of procedures and testing varies. These procedures are used to extend the life of your chillers and improve their efficiency. Read more about chiller efficiency

Tailor Made

These are procedures specific to a particular chiller. They vary from checking the condition of condenser fan belts to changing oil filters. A walk round of the plant is carried out prior to writing the maintenance schedule. This ensures that the individual requirements needed for each chiller are met.

General

These are procedures that apply to all chillers and include the above mentioned F-gas leak testing and refrigerant charge health check. We carry out over 100 checks and procedures to any chiller during the maintenance.

Frequency

Depending on redundant systems being available and how much load there is to the plant, the required frequency of visits varies. Each year we recommend at least 2 visits for small process chillers, 3 visits for large air cooled chillers, 4 visits for ammonia and monthly visits for centrifugal chillers. Read more about chiller maintenance schedules

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Fault Finding

Carrying out the above procedures also highlights the faults. We carry out the fault finding and diagnosis of your chillers whilst on site. This reduces your costs by removing the need for separate call outs.

Mobile Workshops

We also carry an extensive range of materials in our company cars which we use as mobile workshops. This means that we often get a chiller running at no extra cost- just another way we provide you- the customer with a service that is second to none. Read more about fault finding and diagnosis

Tick Sheet

We have spent years developing a Tick Sheet that, we believe, is the best in our industry. It is one sheet for all chillers, so our engineers become accustomed to where each check is listed on the sheet. Checks that are not relevant to a particular machine are crossed out. Read about the maintenance checklist that you can carry out in between visits.

Chiller Maintenance Contract Terms and Conditions

This part of the contract outlines our charges and terms. We are very customer oriented, so we have written our terms and conditions to work well for both parties. At the end of the day, we are on your side and we will bend over backwards to provide you with the best service.

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Chiller Maintenance Contract in Moscow

An example of one of our maintenance contracts is for an overseas customer in Moscow. We have a three year contract because this gives them the assurance that the price will not go up each year. It also gives us the time to plan longer term into the upkeep of the chillers.

Water Cooled Chillers

The main building is cooled by three water cooled chillers. The condenser water system goes up to a row of dry coolers on the roof. The plant is only needed in the summer as Moscow has very cold winters. Therefore, to save the customer from having to drain the water system down each year- glycol is used. We have a specialist test instrument to check the glycol percentage on each visit.

Air Cooled Chillers

There are various air cooled chillers at two sites which are located in plant rooms with ductwork for the condensers. This is so that when the chillers are shut down for the winter, they are protected from the inclement weather. The compressor oil is kept heated with crankcase heaters. This ensures that the compressor bearing life is not reduced during start up after the winter.

Laboratory Chiller Maintenance Contract

The chiller in the photo is used to provide a narrow deadband of temperature to a laboratory in the North West. The fan coils in the building also have the effect of dehumidifying the air. Separate humidifiers are available to control the humidity to 50% RH. A small loss of water occurs from around the building, so a pressurisation unit is available to keep the pressure at a pre determined level. Mains water can be added to the water system to bypass the pressurisation unit for a quicker water system top up.

Retrofit and Rebuild

We have fitted a new condenser which we manufactured bespoke. We also have the capability to retrofit the evaporator and rebuild the compressor. Read more about our compressor remanufacturing facility

Laser Chiller Maintenance Contract

One of our customers has a laser chiller at a site in Cumbria. It is used to cool down an American made laser cutter for the fabrication of sheet metal. They have a high production volume to keep up with, so it is imperative that the chiller is maintained to the highest standard. Non destructive testing is used so as not to disturb the process. As it is a dusty environment, the main issue on every visit is to change the filter media used to protect the condenser. Read more about how we maintain laser chillers

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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 chiller maintenance contracts on the News


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