Chillers often represent the single largest electrical load for a plant. However, operating costs can quickly rise by 8% to 10% when taking into account pipe fouling, refrigerant leaks or countless other factors. Running chillers at optimum performance will save energy and maintenance costs.
Chiller maintenance has made significant progress thanks to new developments in centrifugal chillers with magnetic bearing chillers and new remote monitoring technology. Thanks to remote monitoring, the industry has been moving towards on-demand maintenance schedules rather than pre-determined planned maintenance.
Whichever program you use, here are 6 maintenance tips that apply to most centrifugal chillers to help maintain high efficiency.
A daily log is still the first step in maintaining an efficiently operating chiller. The log allows you to create a history of operating conditions, including temperature, pressure, level and flow rate. Remote monitoring technology allows you to check the machine continuously, rather than monthly or every other month. And, it allows you to easily generate trend reports to help identify maintenance needs before they become a problem.
All condenser water circuits using open cooling sources (e.g. atmospheric cooling towers) require some kind of water treatment to eliminate scaling, corrosion and biological growth. All of these can cause condenser fouling and impede heat transfer, and can reduce the efficiency of pipes and ducts. Check the chilled water circuit once a year or periodically to remotely monitor general water quality and signs of corrosion.
Lowering the condenser inlet water temperature can improve the efficiency of the chiller. In some building systems, operators will lower the chilled water set point to overcome air handler deficiencies such as dirty coils. This can treat the symptoms rather than the cause and make the chiller work harder to achieve the same net cooling effect.
Changing the chilled water flow rate can affect the performance of the chiller. Too low a flow rate will reduce chiller efficiency and eventually lead to laminar flow. The minimum flow rate is usually about 3 feet per second. per second (FPS). High flow rates can cause vibration, noise and pipe corrosion. The recommended maximum flow rate is usually approximately 12 FPS.
The actual amount of cooling provided by the chiller depends on the amount of refrigerant it passes through the compressor. It is important to maintain the right level of refrigerant under the required conditions. Refrigerant leaks, as well as air and moisture introduced into the system, will reduce the efficiency and reliability of the system. A low refrigerant charge will cause the compressor to work harder and thus reduce the cooling effect.
For efficient starter and motor operation, check the safety and sensor calibration on the microprocessor control (see manufacturer's guide). Then, check the electrical connections, wiring and switchgear associated with the chiller for hot spots and worn contacts. To prevent insulation faults, test the motor windings for insulation resistance to ground and winding-to-winding insulation resistance. Check the shaft seal of the open drive motor for possible refrigerant leaks and clean the motor cooling vents to ensure maximum cooling.
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