Chiller Servicing and Efficiency

From a service point of view, strict guidelines now exist to limit direct emissions of refrigerants to atmosphere were they have a powerful warming effect. Leak testing is paramount to limiting these direct emissions and to keep a chiller running at maximum efficiency- more efficient equals, less power, less emission, less costs.

Today’s chillers feature many technologies which enhance efficiency, from ultra efficient inverter driven magnetic bearing compressors, to brazed Aluminium condenser coils with high transfer efficiencies, all have increased efficiencies greatly.

To benefit from these advances it is important to have all chillers properly serviced by professionals that fully understand all of the above. Advanced Cooling and its engineers are fully conversant with all aspects of chiller operation and can apply this experience to keep any chiller in optimum working order. In our experience a good service regime can save considerable costs in terms of energy, material, and downtime costs.

Chiller Repairs

Similarly, it is important to approach any chiller repair works in a practical and cost effective way. Concise fault diagnosis is an important first step, followed by open discussion with the client on the best way to achieve the goal of fully working machine within time and budget constraints.

Advanced Cooling firmly believes in maintaining open and transparent working relationship with our clients.

Chiller Engineering Services Undertaken Amongst Others Include:

• Breakdown fault daignostics- reporting- repair
• Pressure leak testing/ repair/ re-commission
• Major component replacement including compressor, condensors etc
• On-site overhaul of major components or complete machines, including compressor retrofit
• Refrigerant conversion programmes
• Oil and filter replacement programmes
• Laboratory oil testing and condition reporting.
• Electrical testing and repairs
• Fault finding and repair of ascociated plant/ chilled water systems
• Pressure relief valve replacement programmes

Chilled water cooling systems are more critical than ever in modern buildings. Buildings are highly loaded and without any natural ventilation to assist in case of breakdown.

Turbocor Compressor Servicing

Regular Turbocor chiller servicing is critical to maintaining these machines in good running order and to meet the operators statutory obligations in terms of the F-Gas regulations. The principle objective of the regulation is to contain and prevent emissions of F-Gases covered by the Kyoto protocol. The responsibly for compliance lies with the operator of the plant- the person or organisation that has technical control over the machinery.

Whilst the Turbocor compressor contains limited moving parts and by its nature (frictionless bearings) is very reliable from a mechanical point of view, important calibration, electrical and refrigeration system checks are required to maintain the compressor in reliable running order.

Typically, Turbocor compressors are used in high capacity water chillers with flooded evaporators. By their nature these systems hold substantial amounts of refrigerant making good containment practices critical. In refrigeration systems containing oil visual checks are a good primary indicator of leaks, prompting further detailed checks. Obviously this is not possible in systems not containing any and other more detailed and time consuming procedures have to be used.

Indirect emissions are another cause for concern in regards of global warming and financially for the operator. Plant that is running in-efficiently uses more power to do the work, increasing costs and emissions. Regular Turbocor chiller servicing helps maintain the plant in optimum working order as the manufacturer had intended. Advanced Cooling Solutions have developed procedures and systems which can substantially limit the risks of emissions of F-Gases, ensuring that the operator meets their statutory requirements. Our servicing procedures also maximise efficiencies, reducing energy input and costs.

Turbocor Chiller Hire

Advanced Cooling Hire was one of the first companies to offer a Turbocor compressor powered chiller to the rental market in Europe. The Star refrigeration Indigo water chiller is available for long and short period hire periods and offers outstanding reliability and energy cost savings for clients. The Star Refrigeration Indigo chiller features three Turbocor compressors in tandem on a common refrigeration circuit. Please see the specification below.

Chiller servicing and FGas : What does this mean for the operator and their service agents?

High capacity water chillers form the back bone of many large scale cooling systems servicing large offices, data centres, processes and many others. Whilst increasingly VRV/ VRF systems are being utilised in many small to medium sized offices, water chillers are still extensively used in larger systems. Advantages include centralisation of the primary refrigeration system to one accessible place- here leak testing and containment procedures, as well as engineering activities can be carried out more easily with less disruption to business activities.

Planned chiller servicing and FGas compliance systems are critical to maintaining these machines in optimum running order, and for the operator/ owner to meet their regulatory obligations in terms of the FGas regulation No. 842 2006. Regulation has had a defining influence in the refrigeration industry over the last 25 years, not only on working practices, but also greatly influencing the design and development of new technologies.

The Montreal protocol 1987 was the first to set in place a structured phase out of chemical substances (CFC’s) that were shown to deplete the Ozone layer, in the process making much equipment obsolete. The following Kyoto Protocol agreement ratified in 1997 addressed concerns about the potential global warming effects of certain gases including CFC’s extensively used in the refrigeration industry.

In a further tightening of regulations regarding the global warming potential of F-gasses covered by the Kyoto Protocol, the F-gas regulation (EC) No 842/2006 was introduced by the European Union to help meet their obligations as set out in the Protocol- thus, the principal objective of the F-gas regulations is to contain, prevent and thereby reduce emissions, direct and in-direct, of F-gases covered by the Kyoto Protocol.

Indirect emissions of CO2, ie, additional emissions generated by in-efficient machinery, are now an important consideration of all our chiller maintenance programmes. Direct emission (leaks to atmosphere) risks are reduced and controlled by regular leak testing, site refrigerant logging and protocols to be followed if leaks are identified- repaired.

The F-Gas regulations stipulate the following minimum leak testing regimes

• At least once a year for systems containing over 3kg of refrigerant.
• Systems containing over 30 and less than 300kg of refrigerant in any one refrigeration circuit must have a documented leak test twice a year.
• Systems containing over 300kg in any one refrigeration circuit must be tested four times in one year.

The above inspections can be halved by having a maintained refrigerant leak detection system in place. For refrigerant systems containing over 300kg it is a requirement that a leak warning system is fitted, so by default generally these systems only require inspection twice yearly, although it could be argued that generally as a duty of care, equipment holding such large quantities should be serviced quarterly, including leak testing. It should also be remembered that in such systems, loss of refrigerant and/ or running in-efficiencies can lead to large financial losses. In short, good servicing can pay for itself.

So, as can be seen there are important regulatory requirements and financial implications for all operators of air conditioning systems. Customers who take the long view appreciate that good servicing practices can ultimately save considerable energy, material and breakdown costs. That’s not to say that the current financial climate does not have an impact on what could possibly be seen as a burden. This makes it all the more important to employ a technically competent company that has a good understanding of all the issues, which can advise and tailor maintenance programmes to suite the needs of a client.

Advanced Cooling Solutions offer chiller servicing programmes for all makes, including amongst others, Carrier, Trane, McQuay, Climaveneta, Geoclima, Daikin and many more, including chillers fitted with the new Turbocor compressor. We can tailor a chiller servicing and FGas maintenance programme to meet your individual on site technical, financial and regulatory requirements.

We maintain chillers serving all applications including building air conditioning, process cooling, data centre cooling systems and many more.

Chiller maintenance- Improving HVAC Efficiencies

Chiller maintenance regimes are critical for maximising efficiencies from chillers and chilled water systems. Water chillers will probably represent one of the largest electrical loads on a HVAC system in a building. Good maintenance regimes, in many cases, can save substantial amounts of energy, going a good way to, or even surpassing chiller maintenance costs.

Maximise Design Efficiencies

Water flow rates are critical for the correct operation and long term reliability of a water chiller. To little flow and the machine will short cycle, (run for very short periods, frequently) possibly never running to full capacity where the machine can deliver its most efficient duty. Additional stress is also put on the working parts, increasing costs stemming from component failure, and in extreme cases shortening the operational lifetime of the plant. Low flow rates through the machines evaporator can also lead to localised freezing and bursts- mostly a problem in plate heat exchangers where water ways are very narrow.

Conversely, high flow rates can also lead to damage of the evaporator from the effects of vibration. Excessive vibration causes the copper tubes to chafe against baffles and other supports forming holes which let the refrigerant leak out, and then the water in. Refrigerant systems that have had an ingression of water are very expensive and time consuming to repair- not a good position to be in for something that is entirely avoidable.

Component Efficiencies

All chillers work on the basic refrigeration principle- the refrigeration cycle. Essentially moving energy from where you do’nt want it, the load, to another place for disposal, generally atmosphere. The less energy that is expended in the process of moving a given load is what defines efficiency, generally called COP- the relationship between the cooling capacity in RT to the energy consumed by the whole chiller in kW.

To maximise the efficiency of a refrigeration system as the manufacturer had intended it is critical that component parts are maintained in optimum running order. Main components such as the evaporator, condenser, refrigerant and compressor have a great bearing on this.

Condenser efficiency

Condensers should be cleaned regularly to ensure they are clear of blockages and dirt. Any corrosion should be treated and removed. In severe cases a metallised treatment such as Blygold can be used to restore a condensers efficiency. This type of treatment improves thermal transfer between the copper tubes of the condenser that carry the refrigerant, and the aluminium fins over which the air flows.

Evaporator efficiency

Evaporators require the correct levels of refrigerant to maximise efficiency. The level of refrigerant can be determined by calculated superheat and subcooling values, along with visual indicators such as site glasses. Different superheat values are specified for different machines. Those using electronic expansion valves and screw compressors generally run at lower superheat settings- around 3-5degrees at the evaporator outlet. It is important for efficiency and reliability that these settings are checked and adjusted as required.

Refrigerant charge

A shortage of refrigerant in the machine will also lower the refrigerant level in the evaporator (increase superheat) and as such it is critical that the machine is tested regularly for leaks with a view to maintaining a full refrigerant charge at all times. We would generally look for a full column of liquid at the expansion device without flash gas- as a rule of thumb a subcooling value of 12 Degrees is average, although some machines are designed to work with higher. Subcooling is also a good indicator of refrigerant levels inside a refrigeration system and would be calculated and logged as part of a service.

Leak testing regimes are also an important part of the FGas regulations which seek to limit the emissions of refrigerant gases, both direct and in-direct.

Compressor

The compressor is at the heart of the process. It is where the refrigeration cycle starts. Chiller maintenance checks should include operations to ascertain that it is pumping as efficiently as possible. Valve gear should be tested for tightness and that it is not letting-by. Pump down testing and discharge superheat are good indicators of condition. Higher discharge temperatures and superheat readings will be noted if there is let-by from the high to low side of a compressor. Loading mechanisms should also be checked regularly. If the compressor does not load fully, maximum efficiency is unlikely to be achieved.

Staging Multiple Chillers

Systems using multiple chillers on a common chilled water circuit can and should be optimised to ensure efficient operation. It is desirable that in such systems the chillers are staged in individually to meet the load as required. For example, in a system with two chillers, the chiller determined as the lead will stage in first reaching maximum load before the second unit starts. In this way the lead chiller is generally always running in its optimal state- at its most efficient.

Chiller staging as above can generally be achieved by a localised central controller which electronically links the machines for the purposes of control or a building management system, although in our experience neither tend to be applied properly. A good example of a central control system is the Carrier Comfort Network, which we have found to give very good stable control of multiple chillers.

Simple staging of chillers is possible using the local machine set-points and temperature control bands which control sensitivity . The lead chiller can be determined by setting it with a lower set-point and tighter control band. With the lag machine setpoint set outside this, operation only occurs once the lead has reached maximum load. Good results can often be reached with a little application to the task, and even if perfect control isn’t achieved, its at least a more efficient and reliable way of operating the plant.

Summary

So as can be seen there are a number of factors, external and local that have a considerable impact on the efficient and reliable operation of a water chiller. A company that is competent will understand all of these factors and put in place systems and work practices that address all the issues, mechanically, regulatory and environmental.