Deciding Whether to Repair or Replace a 20-Year-Old Cooling Tower
A 20-year-old induced-draft cooling tower serves a 500-ton chiller plant. The tower has galvanized steel construction with visible rust on the basin and fan deck, a gearbox that has been rebuilt twice in five years, and a fill media that is partially collapsed. Recent water treatment logs show elevated iron and suspended solids. The tower currently meets the chiller's condenser water temperature at design, but only barely, and the approach has widened from 5 F to 9 F over three years. A new tower is quoted at $310,000 installed with a 20-year life; a rebuild of the existing tower (basin repair, new fill, gearbox replacement, fan repair) is quoted at $145,000 with an expected 8-10 year remaining life. The capital budget is tight this year, and the plant serves a building with no backup tower.
1. Compare repair and replacement on life-cycle and risk grounds, and recommend an option.
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Life-cycle cost. Rebuild: $145,000 for 8-10 years, roughly $14,500-$18,100 per year, plus the risk that the structure continues to corrode. Replacement: $310,000 for 20 years, about $15,500 per year, with a new warranty and modern fill and fan efficiency. On pure annualized cost the two are close, so the decision turns on risk and performance.
Performance risk. The approach has widened from 5 F to 9 F, meaning the tower is losing margin. At design it only barely meets condenser water temperature. A wider approach raises condenser water temperature, which raises compressor head and energy use, and on a hot day it can force the chiller to unload or trip. The collapsed fill and elevated iron suggest the corrosion is active, not cosmetic.
Downtime risk. There is no backup tower. A rebuild is a planned outage of several days; a structural failure or gearbox failure mid-season is an unplanned outage with no fallback. The gearbox has already been rebuilt twice in five years, which is a reliability warning.
Recommendation. Replace the tower. The annualized costs are comparable, but replacement removes the corrosion and reliability risk, restores approach margin, and provides a warranty. If capital is constrained, phase the project: commit to replacement in the next budget cycle, perform targeted basin and fill repairs now to protect the chiller, and secure a rental tower contingency plan for the interim.
2. What interim measures would you put in place if replacement is deferred, and how would you monitor tower condition?
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Interim measures.
- Repair the collapsed fill and clean the basin to restore airflow and reduce solids.
- Rebalance water flow across the tower to improve approach.
- Tighten water treatment: control iron and suspended solids, and add filtration if needed.
- Inspect and repair the fan deck and structural steel; address active corrosion with surface prep and coating.
- Establish a rental tower contingency and pre-qualify a vendor.
Monitoring.
- Log approach temperature weekly and trend it against wet-bulb; set an alarm if approach exceeds 10 F.
- Vibration monitoring on the gearbox and fan, with monthly readings and a baseline.
- Quarterly structural inspections of the basin and fan deck, with photos.
- Water treatment reports monthly, tracking iron and suspended solids.
Decision trigger. If approach exceeds 10 F, if vibration trends upward, or if structural repairs exceed a set threshold (for example, 25% of replacement cost), move replacement to the front of the capital queue.