What are the acceptance methods and acceptance criteria for air volume balance and water volume balance in air-conditioning systems?
I am an HVAC expert. The air volume balance and water volume balance of air-conditioning systems are key links in ensuring efficient system operation and meeting indoor temperature and humidity requirements, and are directly related to energy consumption, comfort, and equipment lifespan. In engineering practice, balance commissioning is often overlooked or handled carelessly, leading to later problems such as "large temperature difference with small flow rate" or "uneven cooling and heating." Therefore, acceptance methods and acceptance criteria must strictly follow the standards and be quantitatively verified in combination with actual site conditions.
First, for **air volume balance**, acceptance is mainly based on Article 11.2.5 of the Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works (GB 50243-2016) and Article 6.6.12 of the Design Code for Heating Ventilation and Air Conditioning of Civil Buildings (GB 50736-2012). Acceptance methods include:
- **Air volume testing**: Use an air flow hood or anemometer to measure the actual air volume at each air outlet one by one and compare it with the design value. For variable air volume systems, tests must also be carried out at maximum and minimum air volumes respectively.
- **Total system air volume deviation**: According to Article 11.2.5 of GB 50243, the deviation between the measured total system air volume and the design value shall not exceed -5% to +10%. For example, in an office building project, the total design air volume was 50000m³/h, and the measured value was 48500m³/h, with a deviation of -3%, which is acceptable.
- **Air outlet air volume deviation**: The deviation between the actual air volume at each air outlet and the design air volume shall not exceed ±15% (Article 11.2.5 of GB 50243). If the design air volume of an air outlet is 1000m³/h and the measured value is 850m³/h, the deviation of -15% is a critical value, and the valve needs to be adjusted or the air outlet replaced.
- **Pressure difference testing**: Measure static pressure at key points such as fan outlets and before and after filters to ensure that design conditions are met. For example, an operating room in a hospital required a positive pressure of 15Pa, and the measured value was 12Pa, so the filter or air valve needed to be checked.
- **Acceptance criteria**: The above deviations are within the allowable range, and the system has no obvious noise or vibration. In an actual case, I once handled an air-conditioning system in a shopping mall where the original design air volume deviation reached 20%. By readjusting the air valve opening and installing air volume regulators, the deviation was ultimately controlled within 8%, significantly improving the uniformity of terminal temperature.
Second, for **water volume balance**, acceptance is based on Article 8.4.4 of the Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Works (GB 50242-2002) and Article 8.6 of the Code for Construction of Ventilation and Air Conditioning Works (GB 50738-2011). Acceptance methods include:
- **Water flow testing**: Use an ultrasonic flowmeter or electromagnetic flowmeter to measure flow at the chilled water/cooling water main pipes, branch pipes, and terminal equipment (such as fan coil units and air handling units). For example, in a hotel project, the design water flow of an air handling unit was 50m³/h, and the measured value was 46m³/h, with a deviation of -8%.
- **Pressure difference measurement**: Measure the supply and return water pressure difference through pressure measurement holes on balancing valves or static balancing valves, and calculate the flow using formulas. According to Article 8.6.3 of GB 50738, the deviation between the actual flow and design flow of each loop shall not exceed ±10%.
- **Temperature verification**: Measure the supply and return water temperature difference. The typical design temperature difference is 5℃ (chilled water) or 10℃ (cooling water). If the temperature difference is too large (such as 7℃), the flow may be insufficient; if the temperature difference is too small (such as 3℃), the flow may be too large or the load matching may be incorrect. For example, in a data center project, the return water temperature was only 4℃. After investigation, it was found that the water pump was oversized, resulting in excessive flow.
- **Balancing valve adjustment**: Use intelligent instruments (such as TA balancing instruments) to set valve openings by the proportional method or compensation method to ensure that the flow ratio of each branch is consistent with the design.
- **Acceptance criteria**: The flow deviation of each loop is within ±10%, the total flow deviation is within ±5%, and the temperature difference is within ±1℃ of the design value. In an actual case, because no balancing valves were installed on the horizontal pipes of an office building's air-conditioning system, the cooling capacity in remote rooms was insufficient. By adding static balancing valves and commissioning floor by floor, we reduced the flow deviation from 25% to 5%, and the temperature difference stabilized at 4.5-5.5℃.
In summary, the core of air volume balance acceptance is an air outlet deviation of ±15% and a total air volume deviation of -5% to +10%; the core of water volume balance acceptance is a flow deviation of ±10% for each loop and a temperature difference that meets the design. These standards need to be tested with professional instruments and verified in combination with drawings and operating data. The above are reference opinions. The actual situation of the project still needs to be further comprehensively evaluated and implemented in combination with specific operating conditions, site conditions, and other factors.