This checklist identifies Key Commissioning Test Requirements and Key Preparations and Cautions for testing variable flow pumping systems. 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. The following are considered “prefunctional” checks that should be completed and verified prior to performing a functional test (note that this is not a comprehensive list of all prefunctional checks):
- a) Individual coils and/or distribution piping are flushed and pressure tested (when required).
- b) All safeties, interlocks, and alarms are programmed (or hard-wired, if applicable) and function correctly.
- c) Sensor installation and calibration is sufficient to achieve the design control strategies.
- d) Proper stroke for control valves is verified to ensure that they open and close completely (coil valves, isolation valves, etc.)
- e) Control valve leakage testing reveals no detectable leakage when valve is commanded closed.
- f) Two-position control valves associated with the respective equipment open fully upon start-up and close fully upon shutdown. This is typical for water-source heat pumps and water-cooled process equipment.
- g) Review TAB report, including flow, impeller size, and motor volt/amp measurements.
A pump performance test has been conducted to achieve the following objectives (this test should be performed if the pump appears oversized based on the TAB report and physical inspections, such as the VFD operating at a significantly reduced speed even at a full flow condition):
- ___ 2. The impeller size has been verified.
- ___ 3. The system curve for the pumping system has been established. The system curve should account for minimum system pressure requirements (for example “lift” for a cooling tower, or minimum differential pressure at the most remote coil in the system).
- ___ 4. The operating points of the pump on the system curve have been established:
- a) Discharge valve fully open and the VFD operating at 100% speed.
- b) Discharge valve throttled to design flow and the VFD operating at 100% speed (or the VFD operating at reduced speed with the throttling valve wide open)
- ___ 5. The match between the flow delivered by the pump with the discharge valves fully open and the VFD at 100% speed and the actual head required to deliver design flow requirement have been assessed.
- ___ 6. If the pump capacity with the discharge valve wide open and VFD operating at 100% speed exceeds design flow requirements, opportunities to trim the impeller and allow the VFD to operate near 100% speed in order to meet design flow rate have been evaluated.
- ___ 7. The flow variations produced in the system as valves open and close have been assessed.
The control sequences have been tested to achieve the following objectives:
- ___ 8. Proper distribution pump staging and VFD control (if applicable) is verified per the sequence of operations.
- ___ 9. VFD control loops generate the proper setpoint based on the reset parameters (if applicable). Reset parameters are optimized for the system.
- ___ 10. Differential pressure reset control strategy is verified.
- ___ 11. Proper coordination between individual setpoints and reset strategies is verified.
- ___ 12. Proper control sequence and integration is verified over all components (including proper sequencing of primary and secondary pumps, setpoints and reset strategies, start-up/shut-down procedures, and time delays).
- ___ 13. All control loops achieve stability (i.e. no hunting) within a reasonable amount of time, typically 2 to 5 minutes, after a significant load change (such as start-up, and automatic or manual recovery from shut down).
- ___ 14. For variable primary-only chilled and hot water systems, verify the minimum VFD speed maintains the minimum water flow rate required by the chiller and boiler manufacturers.
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. Ideally, functional performance testing of a variable flow water system should occur during the season in which the system is intended to operate (hot water in winter and chilled water in summer) to observe the entire system under normal operating conditions. If this is not possible due to the construction schedule, system operation and performance must be verified by either creating false loads on the equipment or through manipulation of setpoints to accommodate existing atmospheric conditions. For example, a load can be simulated by adjusting all setpoints to be 10°F higher or lower than the current ambient conditions and allowing the system to respond accordingly.
- 5. Successful execution of the variable flow water system functional performance tests is dependent upon the operation of ancillary equipment (for example, air handling units, terminal units, heat pumps, process loads, chillers, and boilers) At a minimum, the prefunctional checklist should be completed on the components/systems served by the water system and should be capable of safe temporary operation.
- 6. Integration of temperature setpoints must be coordinated between the boiler, chiller, and the equipment they serve. Uncoordinated setpoints can force the distribution pumps to operate at full flow even though there is basically no load on the system, wasting significant pumping energy.
- 7. Reset schedules can also conflict with each other. For example, resetting hot water supply temperature lower, or chilled water supply temperature higher, will tend to cause the respective coil valves to open. This could skew verification of the pump staging and modulation control strategy if the system changes unexpectedly while controlled functional tests are being performed. All resets should be overridden, except for those being tested, to prevent unwanted impact on the system during testing. Individual reset strategies should be disabled and only one control parameter varied at a time so that basic system operation can be verified. Reestablish the resets for other control parameters progressively and verify that system operation remains stable.
- 8. On large systems, heating and/or cooling coil valves may be arranged in a 2/3 and 1/3 configuration in which one valve (or set of valves) will satisfy 1/3 of the load and the remaining valve(s) will handle the remaining 2/3 of the load. The intent is to provide better control over the valve(s) to achieve better turndown characteristics during part load conditions. Proper tuning of a PID control loop may be difficult for a system that was designed to modulate all coil valves simultaneously to satisfy any load condition. Ensure valve control does not create instabilities in the water flow control loop or in the pump staging and discharge air temperature control loops, as well.
- 9. Safety and interlock tests, as well as some test procedures and loop tuning efforts (for example, high/low limit cut-out set points, 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.
- 10. Rapid stroking of valves during a test process can cause water hammer problems in the piping systems. Consider stroking each valve in stages to prevent slamming valves open or closed, giving the system time to respond appropriately. Rapid stroking may be an indication of control loop hunting.
Page last updated: September 11, 2006