Air System Commissioning Techniques and Airflow Balancing Standards
Air system commissioning is the first step in HVAC system commissioning. Its goal is to ensure that the airflow of each supply air outlet, return air outlet, and exhaust air outlet meets the design requirements and that airflow distribution in each area is uniform. According to Section 11.1 of GB 50243 "Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works," system commissioning must be carried out after the installation of ventilation and air conditioning works is completed. The commissioning content includes airflow measurement and adjustment, as well as verification of the deviation between total system airflow and design airflow. Preparations for air system commissioning: (1) Confirm that all air ducts are installed, air outlets are in place, and damper positions are correct (motorized dampers in the fully open position, manual dampers in the design position). (2) Check whether the fan rotation direction is correct, whether belt tension is appropriate, and whether the fan current is within the rated range. (3) Prepare commissioning instruments: hot-bulb anemometer (accuracy ±3%), air flow hood (accuracy ±5%), micromanometer/digital differential pressure gauge (accuracy ±1Pa), tachometer, sound level meter, etc. Air system commissioning mainly adopts two methods: the proportional method and the base outlet method. Proportional method: First open all outlet dampers fully, measure the actual airflow of each outlet and calculate the deviation ratio from the design airflow, then adjust the opening of each outlet damper proportionally so that the deviations tend to be consistent. This method is suitable for systems with a large number of air outlets. Base outlet method: Select the outlet at the end of the most unfavorable loop as the base outlet, fully open its damper as the reference point, and then sequentially adjust other outlets so that the ratio of their airflow to the base outlet airflow approaches the design ratio. The base outlet method is simpler to operate and is suitable for systems with a small number of air outlets. Technical parameter standards for air system commissioning: (1) The deviation between the measured value and design value of total system airflow shall not exceed ±10%. (2) The deviation between the actual airflow and design airflow of each air outlet shall not exceed ±15%. (3) The deviation between the total supply airflow and design airflow of each air handling unit/fresh air handling unit shall not exceed ±10%. (4) The deviation between the measured fresh air volume and design value of air handling units shall not exceed ±10%. (5) The deviation between the airflow of the exhaust system and the design value shall not exceed ±15%. For five-star hotels, the standards are stricter: the airflow deviation of each air outlet shall be controlled within ±10% (Marriott MIDS standard), and the fresh air volume deviation of each system shall be controlled within ±5%. Common problems in air system commissioning and their solutions: (1) Insufficient airflow at terminal air outlets: Check whether the total system airflow meets the standard, whether the air ducts leak, whether the dampers are fully open, and whether the air duct cross-section is large enough. (2) Excessive system noise: Check whether the air velocity exceeds the design value (main duct air velocity ≤8m/s, branch duct ≤5m/s, air outlet ≤3m/s), whether there is resonance in the air ducts, and whether silencers are installed. (3) Insufficient system static pressure: Check whether the fan speed meets the demand, whether the air duct resistance is too high, and whether the filters and heat exchange coils are blocked. Article 11.1.4 of GB 50243 stipulates that after air system commissioning is completed, a detailed commissioning report shall be produced, including data such as each air outlet number, design airflow, measured airflow, deviation ratio, and final position of the adjusting mechanism, and shall be signed and sealed by the commissioning personnel.
Water System Commissioning Process and Hydraulic Balancing Acceptance
Water system commissioning is the core step in HVAC system commissioning and directly affects the cooling/heating effect of air conditioning terminals and the energy efficiency of system operation. According to Section 11.2 of GB 50243 "Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works," air conditioning water system commissioning shall include four stages: pipeline flushing, water pump trial operation, water system balancing commissioning, and acceptance. Pipeline flushing is a prerequisite for water system commissioning. Its purpose is to remove impurities such as welding slag, rust, and sediment generated during pipeline installation and prevent impurities from blocking terminal equipment valves and heat exchangers. The flushing method adopts the sectional flushing method: divide the system into several sections (generally by riser or zone), with drain valves installed at both ends of each section. The flushing water velocity shall not be less than 1.5m/s, and water pump pressurization is used for flushing. The flushing water shall be discharged to an outdoor drainage ditch or sump and shall not be directly discharged into the indoor drainage system (to avoid blocking drainage pipes). Flushing acceptance criteria: visually, the color and transparency of the water at the discharge outlet are consistent with those at the inlet, and the impurity content in the water is ≤20mg/L. After flushing is completed, drain water at the lowest point of the pipeline and promptly remove and clean the filter screen of the Y-strainer. Water pump trial operation: Before starting the water pump, check the motor insulation resistance (≥0.5MΩ) and rotate the shaft by hand to check whether rotation is flexible. After startup, check that the operating current does not exceed the rated current, the pressure difference between inlet and outlet is within the normal range (the pressure difference for chilled water pumps is generally 20-30mH₂O, and for cooling water pumps 15-25mH₂O), the bearing temperature is ≤75°C, and the vibration value is ≤4.5mm/s. The trial operation time of a single water pump shall not be less than 2 hours. Water system balancing commissioning adopts the proportional method or the resistance coefficient method. The proportional method is suitable for systems with a large number of static balancing valves: first open all terminal balancing valves to the design preset values, adjust the main balancing valve of the riser or zone to the design preset value, and then use an iterative method to gradually fine-tune the opening of each terminal balancing valve so that the deviation between each terminal flow and the design flow is gradually reduced to within ±5%. The resistance coefficient method is suitable for dynamic pressure-independent control valve (PICV) systems: on the premise of confirming that the PICV is working normally, it is only necessary to adjust the static balancing valves of each branch pipeline. Acceptance standards for water system commissioning: Article 11.2.6 of GB 50243 stipulates that the acceptance standard for air conditioning water system commissioning is that the deviation between the actual flow and design flow of each terminal shall not exceed ±10%. The acceptance standard for five-star hotels is stricter: the deviation shall be controlled within ±5% (Marriott MIDS standard). Acceptance method: Randomly inspect no less than 20% of terminal equipment, and use an ultrasonic flowmeter or differential pressure gauge to measure the actual flow. For each sampling point, measure continuously 3 times and take the average to ensure data accuracy. The commissioning records shall include: each balancing valve number, design flow, measured flow, deviation value, final setting scale/preset value of the balancing valve, commissioning personnel, and date.
Control System Commissioning and Interlock Joint Commissioning
Commissioning of the automatic control system is the most complex and technically demanding part of HVAC system commissioning. Its objective is to verify the functional integrity of sensors, controllers, actuators and operating software, and the correctness of system interlocking. According to Section 11.3 of GB 50243 "Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works" and the requirements of GB 50314 "Standard for Design of Intelligent Building", automatic control system commissioning shall be carried out after the commissioning of the air system and water system is completed, and the commissioning content includes three levels: individual unit commissioning, zone commissioning and system integrated commissioning. Sensor calibration is the first step of automatic control commissioning and directly affects control accuracy. The types of sensors requiring calibration include: temperature sensors (accuracy ±0.2°C, calibration points at 0°C, 25°C and 50°C), humidity sensors (accuracy ±3%, calibration points at 30%, 60% and 90%RH), pressure sensors (accuracy ±1%, calibration points at 0% and 100% of range), differential pressure sensors (accuracy ±1Pa), CO₂ sensors (accuracy ±50ppm, calibration points at 400ppm and 1,000ppm), and flow sensors (accuracy ±2%). The calibration method adopts the standard instrument comparison method, and the deviation between the sensor reading and the standard instrument shall be within the specified range. Sensor deviation data found during commissioning: in actual projects, about 5%-10% of temperature and humidity sensors have factory deviations exceeding ±0.5°C/±5%RH and need to be handled by software compensation or replacement. Actuator commissioning: check whether the mechanical action of electric water valves, electric air valves and electric control valves is flexible, confirm that the valve position feedback signal is accurate (the fully closed and fully open position feedback is consistent with the actual position), test the valve action time (full-stroke action time of air valve ≤60 seconds, water valve ≤120 seconds), and verify the power-failure protection mode (the valve shall return to the safe position upon power failure). Controller function test: (1) PID control parameter tuning: determine the proportional band, integral time and derivative time through step response tests. Taking the temperature control loop as an example, under summer design conditions, change the set temperature by 1°C as a step, observe the system response curve, and adjust the PID parameters so that the overshoot is ≤0.3°C and the settling time is ≤15 minutes. (2) Interlock logic test: verify the interlock control of the air and water systems (the water valve opens in linkage after the fan starts, and the water valve closes in linkage after the fan stops), the antifreeze protection logic (start preheating and close the fresh air valve when the ambient temperature is below 5°C), and the filter alarm logic (the differential pressure switch signal triggers the alarm). System integrated commissioning: after individual unit commissioning is completed, carry out system-level integrated commissioning, simulate various operating conditions (such as summer full load, transition season all-fresh-air, winter heat preservation, fire linkage, etc.), and verify the correct response of the system under various operating conditions. The linkage test shall be carried out synchronously with the fire protection system and the BAS system to ensure that after the fire alarm signal is issued, the air conditioning system switches according to the preset program (shutting down the air conditioning, starting the smoke exhaust fans, etc.). Article 11.3.4 of GB 50243 stipulates that after system linkage commissioning, the system shall operate continuously for no less than 24 hours with all functions normal. Commissioning records shall be completely archived.
Completion acceptance procedures and document archiving requirements
Completion acceptance is the final confirmation stage of HVAC system commissioning work and also the point at which construction quality responsibility is handed over to operation management. According to the provisions of GB 50300 "Unified Standard for Constructional Quality Acceptance of Building Engineering" and GB 50243 "Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works", the completion acceptance of HVAC systems shall include four steps: site inspection, performance testing, document review and formal acceptance. Site inspection: the acceptance team (composed of representatives of the construction unit, design unit, supervision unit and construction unit) conducts appearance and installation quality inspections of major equipment (chillers, pumps, cooling towers, air handling units, fresh air handling units, fan coil units, etc.), confirming that the equipment model, specification and quantity are consistent with the design drawings, the installation position is correct, the fixation is firm, the vibration reduction measures are effective, the pipeline connections are tight, the insulation is intact, and the electrical wiring is standard and the grounding is reliable. Performance test re-inspection: conduct sampling re-inspection of key performance indicators, including: (1) Supply air volume of air handling units/fresh air handling units (sampling not less than 30%), with deviation not exceeding ±10%. (2) Air volume of terminal air outlets (sampling not less than 10%), with deviation not exceeding ±15%. (3) Total air volume and total water volume of the system (100% testing), with deviation not exceeding ±10%. (4) Indoor temperature and humidity (sampling not less than 20% of guest rooms and all public areas), meeting the design parameter requirements (summer 24-26°C/50%-65%RH). (5) System noise (sampling typical guest rooms and public areas), meeting the requirements of GB 50118 "Code for Sound Insulation Design of Civil Buildings" (guest rooms at night ≤30dB(A)). Document review: the construction unit shall submit complete completion acceptance documents, including: (1) Construction drawings and design change documents. (2) Equipment factory certificates of conformity, inspection reports and commodity inspection certificates for imported equipment. (3) Acceptance records of concealed works (air ducts, water pipe insulation, pressure tests, etc.). (4) Commissioning reports of the air system and water system (including original test data). (5) Commissioning report of the automatic control system (including sensor calibration records and control logic test records). (6) Individual trial operation records of major equipment. (7) System linkage test records. The documents shall be in triplicate (one copy each for the construction unit, supervision unit and construction unit), and all documents shall be signed and sealed by the responsible persons concerned. Handling of nonconforming items found in acceptance: for nonconforming items found in acceptance (such as excessive air volume deviation, substandard temperature control, excessive noise, etc.), a rectification list shall be prepared and the rectification time limit shall be specified. After rectification is completed, the supervision unit shall organize re-inspection, and only after re-inspection passes can the completion acceptance report be signed. Article 12.1.3 of GB 50243 stipulates that the quality acceptance of ventilation and air conditioning works shall be organized by the supervision unit with the relevant units on the basis of the construction unit's self-inspection and assessment being qualified. The Marriott MIDS standard requires that complete system commissioning reports and functional performance test reports be provided at completion acceptance as one of the necessary conditions before hotel opening.