Cleaning and flushing of chilled water piping system is very important part of any HVAC project. During installation there are many sources from which debris, dusts and even metallic parts enter the system. Before putting the system in operation cleaning and flushing is must. This ensures protection of involved machines and overall piping system reliability.
This method statement identifies the procedure and responsibilities in cleaning and flushing of the Chilled Water System as mentioned in the project requirements/specifications. This flushing method statement is applicable for the project and provides procedure to identify a specific course of action to be followed for efficiently clean and sterilize the chilled water system. Flushing is carried out methodically from the top to the bottom of the system.
Sensitive equipment shall be bypassed, isolated or completely removed and replaced by a spool piece to ensure system flow continuity. The use of flexible connections on terminal units may provide a easy means of bypassing the terminal coils.
The following preparation checks / works shall be carried out prior to commencement of flushing and cleaning of chilled water system. Check and ensure the system is hydro-statically pressure tested and verify test certificate.
Check the provision of air vents at location as per approved drawings. Check and ensure sufficient quantities of chemicals are available as per requirement. Place warning signs and warning tape as required.
Every effort shall be made for the flushing water velocity to be generated externally and not by the use of system pumps. It is recommended that system pumps be bypassed and isolated from the circuit completely.
All section valves are open including bypass to drain.
Chilled Water Flushing Methodology
- Thoroughly flush the section to be cleaned with fresh water to remove any dirt, dross and debris from pipework.
- Each section is isolated in turn until clean strainers are inspected at regular intervals.
- After the final high-velocity flush, the system shall be filled and a dispersant polymer added; this shall be circulated for 24 hours before draining. No other procedure will remove the magnetic sludge, which adheres to the pipe wall , and keep it in suspension for draining.
- Once the system is clean it should be drained and filled from the bottom up. Filling should be slow, taking care to remove air from extremities and high points. Then circulate for a further 24 hours. At regular intervals during this period strainers are to be isolated and cleaned, drain points opened to remove any debris arising from the cleaning agent.
- Drain and fill the system until all tracers of the cleaning agent and debris are removed and the pH of the water in the system is in the range of 7-8. The water shall be tested to demonstrate compliance with this requirement.
- Drain the system, add sacrificial anodes an flow limiter cores, refill the system with fresh water and add chemical for the treatment.
- On no account should any part of the system be drained and left empty and wet for any significant time after cleaning, as this will promote rapid corrosion and possibly necessitate a re-clean.
- This work shall be carried out before the commissioning engineer or consultant as per the site requirements. The inspection and cleaning reports shall be generated and signed off.
HSE Considerations
In order to ensure that all flushing of chilled water system works to takes place in a safe manner, suitability of the following must be considered:
Drain the system
- To ensure the drain points are away from any electric sources.
- The valves must be open for dumping gently.
- Dumping connection to under ground drainage must be fastened.
Chemical Handling procedures
- Direct touch to the chemicals are disallowed
- If flammable liquid smoke is forbidden
- Wash spills and splashes on away with running water
- always adding acid to water.
Flushing & Cleaning Alternative Procedure Steps
- Fill the system with clean water and drain the water after 30 minutes.
- Refill the system with clean water and run the chilled water pump for 2 hours.
- Open the drain valves in the main lines and drain the water completely. Clean the strainers.
- During the flushing process the drain valves shall be kept open while the pump is running, until the water appears clean.
- Close all the drain valves.
- Refill the system with clean water and add chemicals in required quantities as per Specialist supplier’s instructions (See specialist supplier’s details).
- Samples of solution shall be collected from various parts of the system to ensure the chemical solution has reached all parts of the system.
- Run the pump and circulate the water (with chemicals added) for a minimum period of 24 hours as per specialist supplier’s recommendations.
- After the cleaning process is completed as described above the cleaning solution shall be flushed out.
- The entire system is re-filled with fresh and clean water and treated with corrosion and scale inhibiting treatment chemicals as approved. Specialist contractor shall collect samples and conduct tests until satisfactory results are obtained as required.
- The inspection request shall be raised for Main Contractor and Consultant to witness the flushing and cleaning process. Work Inspection Request (WIR) shall be retained as records.