How should an HVAC system interlock commissioning plan be prepared? What are the commissioning steps and acceptance criteria?
I am an HVAC expert. Linked commissioning of air-conditioning systems is a key step to ensure that the design intent of the system is realized and that equipment operates cooperatively to achieve the expected results. The quality of the commissioning plan directly affects whether the project can smoothly pass acceptance and enter efficient operation. According to Chapter 11 of GB50243-2016 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works, linked commissioning must be carried out after successful individual equipment trial operation, and must cover the coordinated relationship among cold/heat sources, distribution systems, and terminal equipment.
Key Points for Preparing the Linked Commissioning Plan
When preparing the plan, the following core sections should be included:
1. Basis of Preparation: Cite GB50243-2016, GB50736-2012 Code for Design of Heating Ventilation and Air Conditioning for Civil Buildings, design drawings, and equipment technical documents.
2. Commissioning Scope and Objectives: Clarify the linked logic of chillers, cooling towers, pumps, air handling units, fan coil units, air valves, water valves, and the automatic control system. Objectives such as: total system cooling/heating capacity reaches more than 95% of the design value, and indoor temperature and humidity meet design requirements.
3. Commissioning Preparation: Including personnel organization (HVAC engineers, electrical engineers, control engineers), tools (such as thermal imagers, anemometers, flow meters), and safety measures (such as power-off tagging, emergency plans).
4. Commissioning Steps: To be carried out in stages, for example:
- Stage 1: Individual equipment trial operation (fans and pumps run for more than 2 hours without abnormal vibration or noise).
- Stage 2: System water filling, air venting, and hydraulic balancing commissioning (adjust the flow of each branch through balancing valves, with deviation controlled within ±10%).
- Stage 3: Cold/heat source linkage (for example, after the chiller starts, the cooling water pump and cooling tower fan are put into operation in logical sequence).
- Stage 4: Terminal and automatic control linkage (for example, the air handling unit automatically adjusts the water valve opening according to the return air temperature, and the fan coil unit starts and stops according to the room temperature).
Detailed Explanation of Commissioning Steps
1. Confirmation of Individual Equipment Trial Operation: Check whether the rotation direction, current, and vibration values of chillers, pumps, fans, and other equipment comply with manufacturer specifications. For example, a hotel project once had excessive vibration due to a loose belt on a cooling tower fan, which required retensioning and retesting.
2. System Water Filling and Air Venting: Remove air through the air vent valve at the highest point of the system to prevent air blockage from affecting flow. In actual projects, I once encountered an office building where insufficient air venting caused terminal coils to freeze, which was solved by installing automatic air vent valves.
3. Hydraulic Balancing Commissioning: Use an ultrasonic flow meter to measure the flow of each loop and adjust static balancing valves or dynamic balancing valves. According to Article 6.4.7 of GB50736-2012, balancing devices should be installed in direct-return systems. For example, in a commercial complex project, by installing proportional integral valves, the terminal temperature difference was reduced from 8℃ to 5℃ (design value).
4. Automatic Control System Linkage: Verify the signal response of the DDC controller. For example, after the chiller starts, the cooling water valve should open with a 10-second delay to avoid water hammer impact. A data center project once experienced compressor protection shutdown due to incorrect sequencing, which was solved by adjusting the PLC program.
5. Load Test: Simulate the maximum load condition (such as extreme summer weather) and record system operating data. For example, during commissioning of a hospital project, it was found that the chilled water supply-return temperature difference was only 3℃ (design 6℃). Investigation showed that the pump head was selected too large, and a variable frequency drive was required to reduce speed.
Acceptance Criteria
- Performance Indicators: Total system cooling/heating capacity reaches 95% of the design value (Article 11.2.4 of GB50243-2016). For example, a hotel project measured a cooling capacity deviation of only 2%, meeting the requirement.
- Stability: Continuous operation for 8 hours, with parameter fluctuations not exceeding ±5%. I once witnessed an office building project where clogged cooling tower fill caused condensing pressure fluctuations, which recovered after cleaning.
- Noise and Vibration: Equipment noise does not exceed the design value +3dB(A), and the effective value of vibration velocity is ≤4.5mm/s (GB/T 3785-2010).
- Safety Functions: Emergency shutdown and fire linkage (such as fan shutdown) must respond within 2 seconds.
Actual Project Case
In a five-star hotel project, the air-conditioning system consisted of 2 centrifugal chillers, 4 cooling towers, and 6 air handling units. During commissioning, it was found that the cooling water system temperature difference was only 2℃ (design 5℃). Investigation showed that the cooling tower fan speed did not match, and after installing variable frequency drives, the temperature difference recovered to 4.8℃. In the subsequent linkage test, the automatic control system adjusted the water valve according to the return air temperature, and the indoor temperature remained stable at 24±1℃ with humidity 50±5%, passing acceptance in one go.
Summary
The linked commissioning plan for air-conditioning systems needs systematic design. From individual equipment trial operation to full-system load testing, each step should strictly follow GB50243-2016 and GB50736-2012, and be flexibly adjusted according to actual working conditions. Acceptance criteria should cover performance, stability, and safety to ensure reliable system operation.
The above are reference opinions. The actual project situation still needs further comprehensive evaluation and implementation in combination with specific working conditions, site conditions, and other factors.