What are the methods and steps for air system balancing and commissioning of air-conditioning systems? What is the allowable deviation range?
I am an HVAC expert. Air system balancing and commissioning is a key step to ensure that the system achieves its design performance and meets indoor temperature, humidity, and cleanliness requirements. Both GB 50736-2012 "Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings" and GB 50243-2016 "Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works" explicitly require that air volume balancing commissioning be carried out after system installation is completed. Improper commissioning can lead to uneven air volume at terminal outlets, energy waste, and even unit failure, directly affecting the comfort and operating costs of hotel or commercial projects. Below, I will combine the codes and engineering experience to explain in detail the commissioning methods and steps, and clarify the allowable deviation ranges.
I. Methods and Steps for Air System Balancing Commissioning
1. Pre-commissioning Preparation
- Check system integrity: Ensure that the air ducts are tight and leak-free, that outlet control dampers, fire dampers, and motorized control dampers are fully open, and that fans operate normally. According to Article 12.1.3 of GB 50243-2016, before commissioning it should be confirmed that the air duct light-leakage or air-leakage test has passed.
- Preparation work: Calibrate instruments such as anemometers, air flow hoods, and micromanometers, and record the design air volume parameters. For example, the design total air volume of an air handling unit in a hotel lobby is 30,000 m³/h, with a total of 50 terminal outlets, which need to be checked one by one.
- Measure the total air volume of the fan: At the fan outlet or the total measurement section, use the multi-point averaging method (according to Appendix C of GB 50243-2016) to measure wind speed and calculate the actual total air volume. If the deviation exceeds ±10% of the design value, adjust the fan speed or pulley to ensure the total air volume meets the requirement.
- Case: In an office building project, the measured total air volume of the fan was only 85% of the design value. Upon inspection, the fan belt was found to be loose. After adjustment, the total air volume recovered to 98%, meeting the requirement.
- Adopt the "reference outlet method" or "proportional method": First select the outlet of the most unfavorable loop (i.e., the branch with the greatest resistance) as the reference, fully open its control damper, measure its actual air volume, and calculate the ratio to the design air volume. Then adjust the outlets of other branches in sequence so that the air volume ratio of each branch is consistent with the reference.
- Steps: For example, on a hotel guest room floor, there are 4 branches in total. First adjust the outlet of Branch A (the most unfavorable loop) to the design air volume, then use Branch A as the reference to adjust the control dampers of Branches B, C, and D so that the air volume proportion deviation of each branch is within ±5%.
- Point-by-point measurement and fine-tuning: Use an air flow hood or anemometer to measure the actual air volume at each outlet one by one, and fine-tune through control dampers or guide vanes to ensure that the air volume of each outlet is close to the design value. According to Article 6.2.6 of GB 50736-2012, after system commissioning, the air volume deviation of each outlet should be controlled within ±15% of the design value.
- Case: A clean operating room in a hospital required a supply air volume error of ≤±10%. Through point-by-point commissioning, the deviation of all outlets was ultimately controlled within ±8%.
- After completing all adjustments, re-measure the total air volume of the fan and the air volume of key outlets to ensure data stability. Record the measured values of each outlet, branch, and total air volume, and generate a commissioning report. According to Article 12.2.3 of GB 50243-2016, the commissioning report must include the system diagram, measured data, and adjustment measures.
II. Allowable Deviation Ranges
According to Article 12.2.4 of GB 50243-2016 and relevant code requirements:
- System total air volume: The deviation between actual air volume and design air volume shall not exceed ±10%.
- Outlet air volume: The deviation between actual air volume and design air volume at each outlet shall not exceed ±15%.
- Branch air volume: During balancing commissioning, the deviation of the air volume proportion of each branch from the reference branch should preferably be controlled within ±5% to ensure system balance.
- Special locations: For example, cleanrooms (according to GB 50591-2010 "Code for Construction and Acceptance of Cleanrooms"), the outlet air volume deviation shall be ≤±10%; for comfort air conditioning in hotel guest rooms, meeting rooms, etc., it may be relaxed to ±15%.
III. Common Problems and Suggested Solutions
- Excessive air volume deviation: If the air volume at a certain outlet far exceeds the design value, it may be due to uneven air duct resistance or loss of control of the control damper. Check the valve status or add duct silencers.
- Insufficient terminal air volume: This is commonly seen in the most unfavorable loop and can be solved by increasing fan speed, reducing elbows, or installing guide vanes. For example, in a hotel banquet hall, insufficient terminal air volume was caused by excessively long ducts and too many elbows. Later, by installing constant air volume (CAV) valves and adjusting the fan frequency, the air volume returned to normal.
- Noise problems: During commissioning, note that too small a control damper opening will cause airflow noise. It is recommended to combine this with silencer design and avoid damper openings of less than 30%.
Concluding Summary
The core of air system balancing commissioning is to follow the sequence of "total air volume - branches - terminals" and adopt the reference outlet method or proportional method to ensure that the system total air volume deviation is ≤±10% and the outlet air volume deviation is ≤±15%. Through precise commissioning, air conditioning performance can be improved, energy consumption reduced, and equipment life extended. The above are reference opinions. The actual project situation still needs to be further comprehensively evaluated and implemented in combination with specific operating conditions, site conditions, and other factors.