RASTECH Magazine

Fresh Tips: Chiller maintenance tips

July 19, 2021  By From the experts at the Freshwater Institute

Inspecting the heat exchanger with a boroscope

Mechanical chillers are an essential piece of equipment to properly maintain water temperatures for cold water species in RAS. A mechanical chiller is a self-contained unit consisting of a condenser, compressor, heat exchanger, temperature controller, flow switch, and associated electrical components. Depending on the application, the chiller can either be air or water cooled. Both types of chillers require similar upkeep and inspections to maintain efficient operation.

Inspecting heat exchangers
The heat exchanger on most chillers contains a spiral shaped metal tube (i.e., coil) that has cold refrigerant running through it. As process water passes over the coil, it is cooled before exiting the heat exchanger. Heat exchanger coils need to be inspected for mineral buildup and organic matter that can reduce efficiency. An inspection camera or boroscope can be used to view inside the barrel of a heat exchanger (Figures 1 and 2), and coils with fouling or mineral buildup should be cleaned promptly. 

Depending on the operating and water conditions, some heat exchanger coils may need to be cleaned more often. At the Freshwater Institute, chiller heat exchangers are inspected every six months. Always follow your chiller manufacturer’s cleaning and maintenance recommendations for each unit.  


Testing flow and pressure switches
All chillers should be equipped with a flow or pressure switch to shut the compressor off if water fails to flow through the heat exchanger, thereby preventing catastrophic damage to the unit. Safety switches should be tested monthly to ensure that the compressor stops running when the water flow stops. Flow and pressure switches can be tested by manipulating valves to bypass the chiller and confirm that the compressor shuts off when water flow stops. This is also a good time to confirm that minimum water flow rates are being delivered to the chiller. Keep spare switches on hand and repair, replace, or adjust switches that do not shut off the compressor when tested.

Inspecting  temperature controller
All chillers are equipped with a temperature controller to display the temperature set point and inform the chiller when to turn on and off. It is important to check the set point daily against the RAS water temperature to ensure that the controller is reading accurately, cycling as intended, and providing the desired RAS water temperature. Inconsistencies may require temperature calibration or adjustments to hysteresis settings. Datalogging the temperature can provide insight on chiller duty cycle and could indicate if chillers are sized correctly or if performance is beginning to decline.  

Inspecting  condenser
Both air- and water-cooled chillers need their condensers cleaned to maintain proper refrigerant pressures. Air cooled chillers, typically used for light to medium duty applications, have metal cooling fins that cover copper tubing with a fan mounted at the top of the condenser. The fan blows or draws air across the coils to cool the refrigerant and convert it from a gas back to a liquid. These cooling fins can become clogged with dust and debris. Cooling fins can be cleaned out with compressed air but may sometimes need to be washed with a garden hose depending on how much debris has accumulated. 

A water-cooled chiller, typical for medium to heavy duty applications, operates in a similar manner but using cold water to cool the refrigerant gases. Over time, the condensing heat exchanger can become clogged with mineral scale buildup depending on water quality and will need to be de-scaled with a proper non-corrosive cleaning solution. Installing a strainer on the cooling water line can prevent particles from clogging the line and prolong time between cleanings. Inspect condensers monthly and schedule any cleanings during the coolest part of the day to minimize temperature increases in the RAS while the chiller is offline for maintenance.

Leak checks
Check the chillers weekly for leaks. This includes water leaks at all valves, pumps, and fittings, as well as any refrigerant leaks. Look for signs of oil around any of the refrigerant fittings or solder joints. Finding a small leak before large volumes of refrigerant are lost could save time and money and prevent temperatures from rising in the RAS water while an ineffective chiller is repaired by a specialist.   

Maintain instruction manuals and SOPs for the chillers you have on your site. Replacement parts for some systems can take days or weeks to ship and receive. Accordingly, having an inventory of multiple key spare parts for each model of chiller on site will allow for timely repair. 

By performing these few routine tasks, you can extend the life of your chillers, minimize down time, and optimize the growing conditions for your fish.  

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