Here are 15 best practices I would like to share with you to get maximum reliability and efficiency from water-cooled plants. I will discuss each of them in greater detail in the coming issues. For now, here are the pointers.
Maintain an accurate log of the primary indications of system operations. This should include condenser
and evaporator entering and leaving temperatures, chiller load, various pressures (oil, refrigerant, etc.), depending on chiller type, equipment in operation, motor voltage and amperage, weather conditions and any other important factors.
Perform chiller diagnostics and chiller energy diagnostics on at least a weekly or a monthly basis.
Chilled water reset
Reset the chilled water temperature to the maximum that is required to meet the load on the system. This is best accomplished with automated controls and programming to reset on a dynamic basis.
Refrigerant level monitoring
For centrifugal chillers, monitor and log the sight glass levels in the evaporator shell. Check approaches and pressures. If in doubt, weigh out.
Condenser (cooling tower) temperature
Application of VFDs to centrifugal chillers requires a control strategy that understands centrifugal chiller and VFD operation
Maintain the lower condenser temperature recommended by the chiller manufacturer, as per AHRI selections and optimum plant energy consumption.
Maintain chiller condenser tubes in a clean condition
The first line of defense is to follow good water treatment practices. This includes taking steps to control biocides, algae and suspended solids. Filtration will assist in suspended solids control. Mechanical brushing of condenser tubes should be done annually, at the minimum.
Condenser and chilled water flow
Verify the condenser and chilled water flow by measuring it at least annually. A clamp-on or insertion flow meter can
achieve this, if permanent measurement tools are not installed.
When reviewing chiller logs, pay particular attention to the motor amperage as against the voltage to detect increases in amp draw. Check the motor for cooling problems. This should be a part of all annual chiller reviews.
Always consider efficiency versus load when starting and stopping chillers. Various chiller designs have different partial-load and full-load efficiencies. Also, consider the efficiency of the chillers on line as a group. Choose the best combination for the best energy efficiency.
Chiller water flow isolation
Isolate both the chiller evaporator and condenser from the system when the chiller is not in service. Automatic valves are the ideal solution.
Use automatic tube cleaning systems
On condensers in high-fouling applications, automatic tube cleaning systems can save significant energy by maintaining tube heat transfers surfaces in a clean condition.
Cooling tower water filtration
The use of side-stream sand, spring, or disk filters are the most effective ways to remove suspended solids in cooling tower water. Filters designed for this purpose can remove 90-95% of all suspended solids larger than five microns. This level of filtration, which is equal to or better than drinking water, will eliminate the problems associated with dirty cooling tower water. Selection and sizing is site-, equipment- and location-dependent. Owing to the fact that solids are small and airborne (making them low in specific gravity), centrifugal separators are not effective for this application. A filtration system should include a properly designed basin sweeper system to reduce or eliminate the sludge blanket that forms in tower basins.
Hot deck covers
On cooling towers with hot decks, install and maintain hot deck covers. Ensure that procedures require the replacement of the covers following maintenance activities.
Hot deck nozzles
Hot deck nozzles should be inspected on a monthly basis in normal operating conditions. Where frequent problems are encountered with nozzle plugging, install a line strainer on the return line to the tower. The perforations in the strainer should be one-half the size of the smallest opening in the hot deck nozzle. Install a two-inch ball valve in a convenient location for blow down of the strainer, and check it frequently.
Cooling tower cleaning
The cleaning of cooling towers should be done often to prevent any significant buildup of dirt in the tower and tower fill.
Dan Mizesko is Managing Partner, U.S. Chiller Services Int, HVAC & Energy Services. He can be contacted at firstname.lastname@example.org
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