Until very recently the concept of unplanned shutdowns of HVAC systems and other evaporative cooling equipment in facilities was foreign to most building managers. Shutdowns would usually occur on a wholly scheduled basis, when equipment required planned maintenance, component repair, or replacement.
But, with the occurrence of the global COVID-19 pandemic which saw hundreds of thousands of workers asked to work remotely literally overnight, we have seen thousands of buildings effectively mothballed with no time for planned system shutdown operations to take place.
In this article, we will highlight best practices to follow after an unplanned shutdown of factory-assembled (package) cooling towers as well as inspection and start-up activities. As resources, we recommend following industry best practices as outlined in ASHRAE Standard 188 – 2018 and ASHRAE Guideline 12 – 2020. Additionally, your Water Management Plan, cooling tower user manual, and the advice of your cooling tower manufacturer and water treatment professional are essential resources.
Follow HVAC safety protocols
We have seen thousands of buildings effectively mothballed with no time for planned system shutdown operations to take place
Before beginning inspection and start-up activities, consult with your safety officer and follow all safety protocols. Always shut off electrical power to the tower fan motor prior to performing any maintenance using lockout/tag out procedures.
When planning to start up any cooling loop system after an extended period of shutdown, operators must consider the potential hazards that may exist in the stagnant water within the system. One concern is the potential growth of microorganisms, including legionella bacteria.
Microorganisms, including Legionella bacteria, can grow in water distribution systems containing water that has been stagnant for longer than five days, as cited in ASHRAE Guideline 12-2020. These systems include community water supply pipes, building plumbing, and evaporative cooling equipment.
First steps in starting up a cooling system
The first step to a safe evaporative cooling system restart is to confirm that the quality of the water coming into the system is acceptable. That may mean flushing the facility’s feed lines as well as checking for “dead legs” throughout the distribution system.
Microorganisms can grow in water distribution systems containing water that has been stagnant for longer than five days
For the cooling tower specifically, fully draining and thoroughly cleaning all elements, including the cold and hot water basins and all mechanical equipment, is recommended. More on this later in the article.
After cleaning, the cooling tower must be thoroughly flushed with fresh water and refilled. Your water treatment professional may recommend operating the cooling tower at elevated chemical levels verified via biological test before returning the system to standard chemical levels. Upon verifying acceptable water chemistry and biological activity, and documenting the treatment steps, the cooling tower components are ready for inspection before re-starting.
Inspections and checks to do before restarting your cooling system
Tower casing:
- Inspect the exterior of the tower for leaks and cracks. We recommend walking around the tower twice.
- First, be aware of trip points and focus on the lower portion of the tower.
- The second time look higher for cracks and leaks, signs of vibration and loose hardware, and presence of rust that may have been caused by an overflowing hot water basin.
Louvers, Fill & Drift Eliminators:
- Check louvers for deterioration and excess scale build-up.
- Inspect the fill media for build-up of scale, algae, and other contaminants. Some light scale is typical on fill and can be easily removed with brushing. If the fill is heavily scaled and damaged, tower performance will be adversely affected.
- Drift eliminators should be clean and free of debris. Ensure the seals are in place and in good condition.
Cold water basin:
- It is vital that your cold water basin and anti-vortex screens are clean, free of debris, and properly in place.
- If you have other equipment in your cold-water basin such as basin sweepers that go to side filtration, check nozzle placement to ensure proper water flow.
- Inspect water level probes, whether manual or electronic, for corrosion.
- When the basin is clean and operational condition of components is confirmed, refill the cold water basin to the recommended operating level.
Hot water basin:
- Remove the basin covers to clean the water distribution system basin and nozzles. Then properly secure the covers.
Piping:
- Check all supply and return piping to and from the tower; confirm valves are open and the water treatment system is operational.
Mechanical Equipment – Fan, Motor, Gearbox, Belt Drive and Driveshaft
Fan:
- Check the fan; blades must turn freely with proper tip clearance between the blade and the shroud.
- Verify blade pitch to eliminate vibration.
| Check the fan; blades must turn freely with proper tip clearance between the blade and the shroud. Verify blade pitch to eliminate vibration |
Motor:
- Turn the motor manually and confirm hardware is tight and free of corrosion.
- Moisture and heat are detrimental to motors. Check that open drain holes match motor orientation.
Belt drive:
- Check tension on your belt drive.
- Inspect pulleys for corrosion and loss of metal in the grooves.
Geardrive:
- Check oil level.
- Check oil appearance for cloudiness or particulates, signs of water and other contaminants.
- Check and lubricate bearings.
Driveshaft:
- Check alignment of driveshafts and couplings.
- Inspect for corrosion and damage.
- Check rubber components for cracks and brittleness.
Start-Up Procedure
- Start pumps only with fans off.
- Check water level in hot water distribution basin and avoid overflow.
- Confirm water flow through the cooling tower is clean.
- Check cold water basin. If using a mechanical float valve, ensure that it is functioning correctly.
- Confirm water level sensor is operating correctly and that make-up water flows when required.
- Check below and around basin perimeter to rule out leaks.
- Start the fan motor at low speed – 25-30%. Observe fan operation and listen to confirm free movement with no obstructions.
- If fan operates freely, increase to full speed; Continue listening for unusual noises and monitor vibration levels in the cooling tower and on the fan deck.
This article provides an overview the many considerations necessary to safely restart a factory-assembled cooling tower after an unplanned shutdown. These guidelines are merely a starting point for the process. Always consult the manufacturer and the cooling tower user manual and follow the recommended practices before proceeding.
By Stephen Andrew, Parts & Service Manager - EMEA, SPX Cooling Technologies, Ltd., Worcester, UK and Robert Swafford, Aftermarket Channel Manager, SPX Cooling Technologies, Inc., Overland Park, KS, USA.