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.
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.
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.