Although excuses for failing to maintain chiller plant abound – “It’s too expensive… too disruptive… too time-consuming… too difficult… too much effort”, and so on – the case for chiller maintenance really is a no-brainer because the cost of a sound preventive and predictive maintenance programme is absurdly low when compared with the cost of dealing with a catastrophic chiller failure.
On top of this, chillers are responsible for using more than half the energy used on some buildings so, by keeping them working at their optimum efficiency, you will effectively be contributing to your company’s bottom line.
Implementing a solid, well-managed maintenance plan will ensure longer a chiller life and reduce its total cost of ownership dramatically. But how do you go about formulating a plan?
There are essentially two forms of maintenance – predictive and preventive.
Predictive chiller maintenance
Predictive maintenance tools such as vibration analysis, infrared thermography, ultrasonic testing and motor current analysis can be used to diagnose problems in advance.
Many manufacturers also recommend ‘eddy-current inspection’ of heat exchanger tubes, a non-destructive testing method that uses eddy currents which are created through electromagnetic induction. Eddy current testing can help identify pitting, freeze damage, wear, cracks and corrosion in heat exchangers.
Another predictive maintenance technique is oil or refrigerant analysis. Annual analysis of these chemicals can help detect chiller contamination problems before they become serious.
Testing typically involves spectrometric chemical analysis to determine contaminants, including moisture, acids and metals, which impede performance and efficiency. A qualified chemical laboratory specialising in HVAC equipment can be employed to conduct this analysis.
Predictive maintenance helps prevent problems before they occur. However, preventive maintenance should be at the heart of any plan to ensure optimum chiller performance.
Preventative chiller maintenance
Essentially, the preventive maintenance process is in two parts:
- Make certain that the chiller is operating at its highest possible efficiency
- Maintain this performance
The first element involves ensuring the equipment is up to the job. If it is, then make certain it has been well serviced so that it is operating efficiently; if not, consider replacing the chiller – saving capital expense by persevering with ineffective chiller plant is a false economy.
Training personnel in both operating and maintenance practices is the best way to prevent expensive breakdowns. Many chiller suppliers offer training on how to operate and maintain chillers.
The second part of the preventive maintenance process involves a number of steps.
Maintain a daily chiller operating log: Compare the performance you record with design and start-up data.
An accurate log will offer a daily snapshot of the chiller’s operating characteristics making abnormal conditions easier to spot. This means that corrective action can be taken before problems get serious and expensive.
A log will also enable you to put together a history of operating conditions that can be analysed to establish trends and offer advanced warning of potential problems.
You can ask the chiller manufacturer to provide a list of recommended data points specific to its own equipment so that you have a baseline from which to measure performance.
Clean chiller tubes: Chiller performance is dictated by its ability to transfer heat and that starts with clean tubes so clean condenser and evaporator tubes annually to avoid a deterioration of chiller efficiency.
New chillers feature automatic tube-brushing systems and these can be retrofitted to existing chillers. However, if this is not an option, cleaning needs to be done mechanically – ie, scrubbing the tubes – and chemically, using cleaning fluids.
Check for leaks and moisture ingress. It has been estimated that that 1psi of air in a condenser equates to a 3% loss in chiller efficiency.
Moisture in a chiller can create acid that corrodes motor windings and bearings and cause rust to form inside the shell. If this occurs, there is a danger that small rust particles will float in the vessels and get trapped inside heat-exchanger tubes decreasing the unit’s heat-transfer effectiveness and overall efficiency.
Treat water with appropriate chemicals: Chemical treatment will reduce scale and corrosion and prevent biological growth. It pays to work with a chemical treatment vendor familiar with local water supplies who can maintain the water systems.
On top of this, systems strainers should be cleaned every three months. One chiller manufacturer estimates there is a 2% loss in chiller efficiency for every 1% of oil found in the refrigerant, and it is not uncommon to find 10 per cent oil in older chillers’ refrigerant. Based on this estimate, such contamination can lead to a substantial 20%.
Other steps to maximise chiller efficiency:
- Turn off unnecessary chillers or sequence your chillers to save energy as well as wear and tear.
- Scheduled maintenance operations are conducted on a daily, weekly, monthly or annual basis and it pays to draw up a checklist that is signed each time a maintenance operation is completed so that everybody knows the state of the maintenance plan.
- Check for condenser and evaporator tube corrosion and clean. Clues to potential problems include poor water quality and excessive fouling.
- Inspect chilled water and condenser water piping systems annually for evidence of corrosion and erosion.
- Lubricate the compressor, pumps and motors to comply with the manufacturer’s specifications.
- Check refrigerant condition annually and level and top up if necessary. Have the refrigerant analysed to ensure that it has not degraded. Also, check for refrigerant leaks – excessive refrigerant loss indicates a leak, which you need to fix as a matter of urgency.
- Check wiring for overheating and tightness of connections.
- Test the compressor motor and oil pump motor windings with a meg-ohmeter.
Remember, effective maintenance will save a significant sum in the long run because it ensures that the chillers are running at their optimum performance and therefore at their best in terms of energy usage.
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