Several years ago our company recognized the need to integrate system commissioning into our construction process in order to consistently meet the owner and design team's needs and expectations. Below is a summary of the process we have developed by trial and error over the last 8 years.
1. Design Review: Review of drawings and specifications to verify the following: Coordination between trades; code compliance; equipment selection and capacities; control sequences for all equipment; and control system component specifications.
2. Submittal Review: Review of HVAC equipment and control system submittals to verify the following: equipment capacities, types and features; control system architecture; and control system component accuracies, ranges, signal types, ratings, and failure modes.
3. Commissioning Plan: Name and telephone number for all participants in commissioning process schedule of activities; HVAC pre-start and start-up checklists; analog device testing and calibration sheets; digital device testing and set point sheets; functional performance test sheets for all DDC control loops; testing and calibration procedures for all devices.
4. Equipment Start-up:
A. Pre-Start Activities: Confirm device wired to the appropriate voltage source; heater elements installed in motor starter devices; shipping restraints removed; device rotates freely; adjust pulleys, belts, couplings; safety devices installed; and disconnect switches installed.
B. Start-Up Activities: Confirm that noise and vibration levels are acceptable; Confirm source voltage is acceptable all phases; record actual and rated amperage; and check device rotation
5. Critical Input Calibration: A. Analog Input Devices
1. Temperature devices without transmitters (Thermistor, resistance type)
a. Disconnect sensing element from loop.
b. Check for failed signal at address.
c. If system shows failed continue to next step. If not, check for shorted wire or a bad software address.
d. Connect decade box or suitable resistance simulation device place of sensing element.
e. Simulate the resistance corresponding to zero, fifty, and one hundred percent of system design rating.
f. Adjust control system software offset or slope and intercept as required to ensure reading with in stated tolerance.
g. Replace sensor element. Make sure the system is receiving the correct signal.
2. Temperature devices with transmitters (RTD type)
a. Assemble required equipment: Decade box, digital VOM, trim screwdriver, and RTD resistance vs. temperature chart specific to the element being tested
b. Adjust the decade box setting so that the transmitter output is 4.00 mA.
c. Record the resistance value and the corresponding temperature.
d. Adjust the decade box setting so that the transmitter output is 20.00 mA.
e. Record the resistance value and the corresponding temperature.
f. Subtract the temperature in step b from the temperature in step c. This is the transmitter span. Adjust the transmitter span potentiometer as required to allow the actual span to match the required span. Repeat steps b and c to confirm.
g. Set the decade box to the resistance corresponding to a 4.00 mA output.
h. Adjust the zero potentiometer as required for the transmitter to produce a 4.00 mA out put signal.
3. Pressure Transmitters:
a. Disconnect the sensing element from the transmitter and replace it with a hand-held calibrated pressure simulation device with an accuracy that exceeds the rating of the transmitter to be calibrated.
b. Install a VOM meter in line with the negative terminal of the transmitter.
c. Determine the following values from the manufacturer's data:
(1) PMIN - Pressure at minimum transmitter output
(2) PMAX - Pressure at maximum transmitter output
(3) TMIN - Minimum transmitter output signal (mA or VDC)
(4) TMAX - Maximum transmitter output signal (mA or VDC)
d. Adjust the pressure until the transmitter output equals TMIN. This value is P1.
e. Adjust the pressure until the transmitter output equals TMAX. This value is P2.
f. Adjust the span potentiometer until the transmitter output signal equals the following:
g. Adjust the pressure to PMIN value.
h. Adjust the zero potentiometer until the transmitter output signal equals TMIN.
i. Adjust the pressure to [PMin - P Max / 2 ] , and confirm that the transmitter output signal is equal to [TMin - T Max /2 ] .
j. Repeat steps d) through i) as required.
4. Relative Humidity
a. Disconnect wire from negative terminal of transmitter.
b. Connect VOM between the sensor and the signal wire to read current (mA) of the device.
c. Using a hand held relative humidity calibration device, compare the output signal of the transmitter to the expected value.
d. Adjust the zero potentiometer of the transmitter as required so that the output matches the expected value.
5. Digital Inputs
a. Remove the control wiring and verify the control system address.
b. Alternatively open and close the control wiring circuit and confirm the corresponding change of state at the control panel.
c. Record the setpoints.
6. Output Calibration:
A. Analog Output Devices
1. Control valve (pump operational during test)
a. Disconnect control signal and record valve position.
b. Command valve to 0%, 25%, 50%, 75%, and 100% position and observe valve response. Adjust the control signal output device(s), including I/P transducer and/or pilot positions, as required.
2. Control Damper (fan operational during testing)
a. Disconnect control signal and record damper position.
b. Command damper to 0%, 25%, 50%, 75%, and 100% position and observe response. Adjust the control signal output device(s), including I/P transducer and/or pilot positions, as required.
3. Fan Speed Control
a. Disconnect control signal and record fan speed.
b. Command VSD to 0%, 25%, 50%, 75%, and 100% maximum speed and observe fan speed response.
B. Digital Output Devices
1. Remove the control wire at the termination of the digital output wiring (relay, E/P, contract, starter, etc.) and verify address.
2. Alternatively command the output opened and closed from the control system, and confirm the appropriate response at the controlled device.
7. Functional Performance Testing:
A. Overview: Functional performance testing is the method by which the control loop logic is tested for proper performance for each controlled system. This is accomplished by revising set points or simulating events and comparing the actual system response to the expected system response.
B. Normal control sequence: Perform a step-by-step test of all the various control logic sequences for each HVAC system by revising setpoints or simulating events (contact closure, etc.) and observing system response.
C. Safety interlocks: Verify that the following interlocks shut down the appropriate equipment when the equipment is operating in either the "hand," "automatic," or "local" control modes: fire alarm, duct detectors, manual safety switches, high or low temperature, and high or low pressure.
D. Overrides: Verify the proper system response to manual override devices, including occupant override switches, life safety override switches, control panel digital switches, and control panel analog output gradual switches.
E. Failure Modes: Remove the control signal and confirm proper position of the analog and digital control devices.
F. Loop Tuning: Upon completion of testing and prior to final acceptance testing, adjust the proportional, integral and derivative gains of each DDC control loop as required to provide stable operation.
8. Acceptance Testing:
A. Upon completion of the functional performance testing, the operation of each control loop shall be demonstrated for the owner's representative(s).
B. The owner's representative(s) shall include the building engineer(s) assigned to operate this facility, as this test is the first step in owner training.
9. Owner Training: Upon completion of the owner's acceptance the owner's representative(s) and building engineer(s) will be trained in the proper operation of the HVAC system. When system commissioning is properly executed, we have found that warranty costs are virtually eliminated. These savings in warranty costs more than pays for the cost of commissioning. Most importantly, thorough system commissioning ensures a working building and adds value for our customers. This added value can differentiate you from your competition.
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