Many HVAC evaporative cooling systems are idle or off throughout the winter months, and are often drained to prevent freezing. These extended shutdowns provide excellent conditions for deposits to form and bacteria to grow. When starting up the system for cooling operation, some basic steps should be completed to ensure peak mechanical performance for the duration of the cooling season, and to verify that best practices for Legionella prevention are in place.In addition to the recommendations below, each cooling tower manufacturer may also have seasonal preventative maintenance requirements for mechanical components such as fans and controls. These will be specific to each cooling tower and should be followed in conjunction with your regular start-up procedure.
Here are 5 steps to get the cooling season started properly:
1. Physical Cleaning
Visually inspect all wet areas of the cooling towers. This includes the water basin, water sumps, fill materials, spray nozzles, wet decks, etc. Each of these areas should be physically cleaned where accessible. Physical cleaning may be done by site maintenance staff or contracted out to a specialized company. Whether the physical cleaning is subcontracted or completed in-house, it is important to keep written records of all work performed prior to start-up. At this time, also inspect any permanent filter housings to clean or replace media if required.
2. Fill the System
Fill the cooling water system and initiate pumps for circulation. Ensure the water circulates through all piping and heat exchangers in the system. Place any filtration units online. Re-inspect the spray nozzles and wet decks to remove any debris that may have deposited after initiating circulation. Repeat as necessary over the initial operation period; frequency will vary system to system.
3. Water Quality
Consult your water treatment specialist to ensure the cooling water treatment program is properly commissioned for the season. Water treatment control equipment such as automated pumps, meters, sensors and valves should be inspected, calibrated and functional. Perform a sanitization of the cooling tower(s) utilizing an oxidizing biocide in conjunction with a bio-dispersant. This may be followed in accordance with a written procedure from your building water management plan, or by use of a sanitization kit. Upon completion of the sanitization procedure, system fans can be turned on once water quality has been confirmed within normal operating levels. Completion of this procedure should again be documented in your log books or water management plan.
4. Begin Operation
The system can now be placed into normal operation mode. Ensure that systems utilizing multiple cooling towers, chillers, or heat exchangers are rotated frequently. The frequency of rotation will depend on your system design and should be documented in the building water management plan. This will ensure the active biocide program contacts all wetted areas regularly to minimize biological growth. Depending on local weather patterns, your system may only operate intermittently after initial start-up. Steps should be taken to prevent equipment from sitting idle for long periods of time as stagnation can lead to deposits, fouling, and bacterial growth. Control programming or manual operation of water recirculation pumps may be required to allow the water treatment program to maintain appropriate control parameters.
As part of a best practice approach, both the ASHRAE Standard 188 philosophy and steps outlined in ASHRAE Guideline 12 recommend that a validation should be performed to confirm the efficacy of the actions taken as part of Legionella prevention. A sample of water should be taken from the water basin or flow to the spray nozzles for Legionella culture analysis. Results of the culture testing should be documented in your log books or building water management plan. Throughout the season, detailed records of water quality should be kept. To confirm the system is operating properly, additional Legionella culture samples may be completed depending on the requirements of your building Water Safety Plan, or in accordance with local laws.
Following best practices during your cooling water system start-up will set the tone for a successful season of operation. These five simple steps will give you the best chances to operate safely and efficiently throughout the season. Eldon Water representatives are available to discuss your site specific needs.