Key Commissioning Test Requirements
General
The performance of a variable flow water system being tested is acceptable if it meets the design intent and specified operating sequence.
In some instances, witnessing flushing and pressure testing individual coils and/or distribution piping may be required.
Safeties, Interlocks, and Alarms
Verification that all safeties, interlocks, and alarms are programmed (or hard-wired, if applicable) and function correctly.
Sensors
Verification that sensor installation and calibration is sufficient to achieve the design control strategies.
Actuation and Sequencing
1 Proper stroke for control valves to ensure that they open and close completely (coil valves, isolation valves, etc.)
2 Control valve leakage testing reveals no detectable leakage when valve is commanded closed.
3 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.
4 Verify proper distribution pump staging and VFD control (if applicable) per the sequence of operations. Typically, distribution pumps in variable flow systems utilize a VFD to modulate pump speed in order to deliver water flow that matches system loads. VFD staging and modulation control is normally based on maintaining a constant differential pressure either across the distribution pumps themselves or out in the loop. The differential pressure setpoint is based on the pressure required to provide adequate flow through the worst case load (for example, the load with the highest overall pressure drop piping losses and device requirements) at full load. Often, the setpoint (either specified by the design engineer or estimated by the controls contractor, if not provided) is set artificially high, wasting pumping energy for the life of the building. The actual system pressure setpoint should be determined during the initial system set-up and commissioning to improve system control and minimize pumping energy.
5 Review TAB report, including flow, including flow, impeller size, and motor volt/amp measurements.
Setpoints and Reset Controls
1 The system operates and maintains chilled and hot water supply temperature setpoints and discharge air temperature setpoints in all modes including morning warm-up, occupied mode, and night low limit mode.
2 VFD control loops generate the proper setpoint based on the reset parameters (if applicable). Reset parameters are optimized for the system.
3 Verify differential pressure reset control strategy. Frequently, the discharge pressure setpoint is reset based on dynamic load requirements to reduce pump energy even further. Various indicators can be used to signify reduced load on the system, one example being valve position. In this control strategy, the system pressure setpoint is reset higher or lower in order to maintain one chilled water valve at a pre-set position (95% open, for example).
4 Verify proper coordination between individual setpoints and reset strategies. Resetting the chilled water supply temperature warrants close attention. Without coordination between chilled water temperature reset and discharge air temperature reset, the air handler may be trying to make colder air than is possible with the chilled water supply temperature. This situation will result in distribution pumps operating at full flow even though there is no load on the system, wasting significant pumping energy.
Control Accuracy and Stability
Verify proper control sequence and integration over all components (including proper sequencing of primary and secondary pumps, setpoints and reset strategies, start-up/shut-down procedures, and time delays). Temperature control strategies impact water flow through the system and pump staging, which can cause system instability. Typically, testing entails verifying that the control loop generates the proper signal based on the setpoint. Testing should also verify the setpoints are optimized for the system or recommend modifications, if necessary.
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).
For variable primary-only chilled and hot water systems, verify the minimum VFD speed maintains minimum water flow rate required by the chiller and boiler manufacturers.
Key Preparations and Cautions
Prefunctional Checklists and Start-up
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.
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.
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.
Test Conditions, Considerations, and Cautions
The following points should be noted to avoid testing complications:
1 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.
2 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.
3 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.
4 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.
5 On large systems, heating and/or cooling coil valves may be arranged in a 2/3rd and 1/3rd configuration in which one valve (or set of valves) will satisfy 1/3rd of the load and the remaining valve(s) will handle the remaining 2/3rd 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.
6 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.
7 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.
Instrumentation Required
Instrumentation requirements vary from test to test and typically include, but are not limited to, the following:
Temperature measurement devices (hand-held devices to calibrate existing sensors)
Differential pressure measurement devices (to test installed flow meters or for performing pump impeller tests)
Amperage and voltage measurement devices (to verify that measured values don’t exceed nameplate)
A tachometer (for verifying pump speed)
Flow measurement devices (installed or hand-held devices to measure water flows)
Data loggers (to supplement existing sensors to verify system operation)
Time Required to Test
Overview
The time necessary to execute functional tests on an entire variable flow water system depends greatly on the size and complexity of the installation and specified control sequences. For example, the number of system components (such as coils, unit heaters, radiant baseboards, heat pumps, and water-cooled process loads), as well as the complexity of the sequence of operation (reset strategies, VFD flow controls, staging parameters, safeties/alarms) will significantly impact the time associated with testing the entire system. Therefore, time estimates have been separated out by component on a per unit basis as well as on an overall system level. Component-level tests typically refer to discrete functions of each piece of equipment (for example, start/stop procedures, safeties, operational and failure interlocks, and alarms), whereas system-level tests focus on evaluating proper integration of each component to satisfy the desired control strategy (this includes staging, setpoints, and reset strategies).
The time necessary to develop a specific functional test, or to adapt a generic test procedure to meet the specific needs of the current project, have not been included in the estimates above. A rough estimate is two to four hours for each component type.
The time associated with completing prefunctional checklists has not been included in the estimates above. These checks should be made throughout construction during normal commissioning site visits as installation of the various components and systems are completed. Sensor and actuator calibration, coil/piping flushing and valve stroke tests are typically considered to be part of completing the prefunctional checklists.
Component Level Testing
One to two hours per distribution pump.
One hour or less is needed per control valve (fully modulating and two-position), including individual stroke from full open to full close. Sampling may be appropriate in certain situations (for example in a building that has 100 VAV boxes with reheat coils).
Individual components like cooling or heating coils can require many hours to capacity test. Several team members will be needed to set up and monitor all of the necessary operating points.
System Level Testing
Two to three hours is needed to verify proper reset strategies (for example, discharge air temperature, water temperature, and pressure).
Allow three to twelve hours to verify proper distribution pump staging to satisfy system setpoints.
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