This checklist identifies Key Commissioning Test Requirements and Key Preparations and Cautions for cooling towers. When writing a test, use this checklist to help ensure that these key areas have been covered. The buttons following the checklist items link to supporting information within the Functional Testing Guide and the Control System Design Guide.
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Key Commissioning Test Requirements
- ___ 1. During design review, the following items were addressed to avoid issues during functional testing:
- a) Optimum condenser water temperature control strategy should be evaluated. This may include implementing variable flow condenser water, utilizing maximum fill surface area before enabling tower fans, and resetting condenser water temperature setpoint.
- b) Proper clearance around the cooling tower is included to ensure adequate air flow.
- ___ 2. The following "prefunctional" checks were completed and verified prior to performing a functional test (note that this is not a comprehensive list of all prefunctional checks):
- a) Sensor installation and calibration is sufficient to achieve the design control strategies.
- b) All safeties, interlocks, and alarms are programmed (or hard-wired, if applicable) and function correctly.
- c) Condenser water is distributed evenly across the entire fill.
- d) Individual coils and/or distribution piping have been flushed and pressure tested (required in some instances).
- e) Fan vibration switch and alarm are verified.
- a) Sensor installation and calibration is sufficient to achieve the design control strategies.
- ___ 3. Control valves open and close completely, and control valve testing reveals no detectable leakage when valve is commanded closed under normal operating conditions.
- ___ 4. Proper cooling tower staging, water control, and fan control is verified to maintain design condenser water temperature setpoint per the specific sequence of operations.
- ___ 5. For evaporative and “fluid” coolers, proper control of both the spray pump and tower fan is verified to maintain fluid temperature setpoint per the specific sequence of operations.
- ___ 6. Proper condenser water pump staging and VFD control (if applicable) is verified.
- ___ 7. Condenser water temperature setpoint reset schedule is verified per the sequence of operations. The sequence may be revised to optimize system operation relative to atmospheric conditions, chiller energy, and tower fan energy.
- ___ 8. Proper control sequence and integration of all components (such as setpoints and reset strategies, start-up / shut down procedures, and time delays) is verified.
- ___ 9. All cooling tower system components (fans, spray pumps) operate per sequences to maintain condenser water temperature setpoints under varying atmospheric and load conditions.
- ___ 10. All PID control loops achieve stability (i.e., no hunting) within a reasonable amount of time after a significant load change, such as start-up and automatic or manual recovery from shut down.
- ___ 11. Verify cooling tower make-up water control functions correctly.
- ___ 12. Verify water treatment/chemical treatment system functions correctly.
Key Preparations and Cautions
- 1. Prefunctional checklists should be completed throughout construction during normal commissioning site visits as installation of the various components and systems are completed. Sensor and actuator calibration is typically considered to be part of the prefunctional checklist.
- 2. In addition to the prefunctional checklists, all component start-up procedures must be complete in order to conduct functional test procedures. Both the air-side and water-side TAB must also be complete prior to functional testing.
- 3. Valve leakage tests and tests that are targeted at verifying valve stroke, spring range, and sequencing should be conducted with the pumping system operating at its peak differential pressure. The differential pressure across the valve plug can have a significant impact on the close-off rating and shift the operating spring range of the valve. These tests should be performed prior to temporary system operation to ensure that equipment will not be damaged during functional testing.
- 4. Functional performance testing for a cooling tower condenser system can occur during virtually any atmospheric conditions except, perhaps, during extreme cold (unless the system is intended to operate even when outside air temperature is low, such as an HVAC system serving a 24/7 computer room load). However, getting a chiller to operate when conditions typically don’t warrant system operation (for example, the chiller is not intended to run when outdoor air temperature is less than 50°F) may be more difficult. Complete performance verification may require a phased-testing approach to check system operation under various ambient conditions. Care should be taken to ensure that testing conditions will not have an adverse impact on the equipment (for example, low condenser water temperature entering the chiller).
- 5. If testing the cooling tower condenser system during cold weather conditions, be sure that freeze protection controls are functional to prevent adverse impact on equipment.
- 6. If the condenser water system employs a variable flow strategy, or a control strategy in which water flows across all cooling towers before the fans are enabled, ensure that the control sequence does not allow the water flow rate to be lower than the minimum flow specified by the manufacturer for each piece of equipment served (both chiller and cooling tower). Minimum flow through a cooling tower is important to provide even water distribution and full wetting of the fill to prevent scaling. Further, pump speed should not drop below the motor manufacturer’s minimum speed requirement.
- 7. Safety and interlock tests, as well as some test procedures and loop-tuning efforts (for example, high or low refrigerant cut-out setpoints, emergency shut-down procedures, and failure/back-up system operation) could place the system at risk if the sequences do not function as intended. Appropriate precautions and procedures should be in place to protect personnel and machinery, including plans for quickly aborting the test if necessary.
Page last updated: September 11, 2006