CHILLERS Maintenance musts


No matter the size of a business or production process, downtime can be incredibly disruptive, incurring large costs and even causing issues when trying to meet customer demand. Alistair Michie, service manager UK at ICS Cool Energy advises on best practice for chiller and system maintenance to help mitigate the risk of downtime, extend the lifetime of equipment, and provide peace of mind that everything possible is being done to keep a process running.


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n the first instance, there are some straight- forward things that end-users can do on a day-to- day basis in the interest of keeping things running. Much like with a car, performing some simple and regular daily checks can go a long way to improving operation and preventing a breakdown. Checking for irregular or unusual sounds and vibrations should form part of a daily routine, as should monitoring temperatures of process fluids. Visual checks should also be undertaken, taking note of and removing debris in the area surrounding the chiller, as well as keeping an eye out for any fluid leaks, excessive condensation, and loose components on the chiller such as thermal insulation. Any issues spotted can quickly turn into serious faults if left unaddressed, so checks should be made daily by more than one person and noted in a log. However, if the chiller performance deteriorates or begins to display fault codes, it is time to call in an expert. Settling for a stop-gap measure to keep production running could at best void the chiller’s warranty and, at worst, result in irreparable damage.


A deeper look


Maintenance certainly doesn’t stop with these daily routine checks – a more thorough examination of equipment will be required, preferably on a weekly basis, and at the very least once a month. Planned downtime is always better than preventable downtime, and as such these checks can be scheduled during quieter periods of the production process. Before starting these checks, the side panels of the unit will need to be removed and the unit will need to be isolated from the electrical supply. Once safe, the fixings and fastenings on the unit can be inspected, ensuring they are tightly secured and adjusted as necessary.


All pipework should then be examined to be certain there is no fluid leaking from the equipment. If any is found, an expert should be contacted immediately. When it comes to any work being undertaken on the refrigeration circuit, this should be conducted


22 August 2018


only by an F-Gas certified engineer. The engineer should look through any existing logs detailing the date of the last check or commissioning, including system design data, and after taking note of the general surroundings they should inspect the four main components (the compressor, the evaporator, the condenser and the expansion devise) and log the circuit(s) during operation.


Compressors


In the main, compressors are positive displacement pumps. Refrigerant is pumped around the circuit, rejecting heat from within the condenser to the atmosphere or fluid, and absorbing heat from the air or fluid in the evaporator. The key things to discuss with an engineer are: ■The suction temperature and saturated pressure ■ The discharge temperature and saturated pressure ■ Oil level and condition (clarity) ■ Measured current, voltage and efficiency.


Evaporators


The evaporator transfers heat from the process or HVAC system into the refrigerant. This effect reduces the chilled water temperature. The flow rate through the evaporator and the system kW capacity determines the outlet temperature compared to the inlet. The engineer will cover the following main points: ■Fluid inlet and outlet temperatures ■Flow rate ■Refrigerant pressure and saturated temperature ■ Compressor suction and evaporator outlet temperature (physical)


■ Refrigerant superheat (a measure of evaporator liquid refrigerant level and system efficiency) of both the evaporator and compressor Insulation condition.


Condensers


The condenser rejects any heat absorbed from the process (evaporator) and from the compression cycle.


Checks will alter slightly depending on whether the chiller is air cooled or water cooled, but will include the following: ■ Dynamic operation


Fluid/air inlet and outlet temperatures Flow rate (water cooled)


Refrigerant pressure and saturated temperature Compressor discharge temperature (physical) Refrigerant superheat


■ Fan motors


Measure current, voltage and motor winding resistance Noise and vibration


■ Condenser coil condition, including brushing off any build-up debris/dirt/dust.


Beyond these checks there are several other important considerations which need to be made. First is checking the equipment’s glycol concentration. The addition of glycol prevents water from freezing, allowing low temperature operation. If the concentration is too low, though, damage to the evaporator can occur, causing irreparable harm and contamination to the refrigerant circuit and its components. It is important that automotive glycol is not used, as this is formulated to protect the engine of a car, not chilled water system components. Ideally the glycol should be inhibited, and a biocide added to protect the system from corrosion and bacteria. Chilled water is frequently overlooked in a planned preventative maintence plan. Oversight and poor control can lead to system failures.


The refrigerant leak test is the most important aspect and a legal requirement for many refrigeration circuits. It is a legal requirement to repair any leak found without undue delay, as loss of refrigerant not only damages the environment but also reduces the efficiency and capacity of equipment.


Using the above information, a detailed action plan can be created which encompasses daily checks and routine planned preventive maintenance. This should include regular chilled water analysis and an ongoing treatment programme.


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