Chilled water or cooling water system is mostly a closed system that requires strict monitoring and control of certain parameters.
Water during circulation evaporates and it increases the suspended particle concentration, which in result creates scale formation and corrosion etc. Therefore the chemical treatment of any water system is very much necessary on regular basis. Otherwise whole system can be damaged or chocked due to contamination’s.
Before doing the chemical treatment of any water piping system the flushing is must. Flushing removes any solid particles or debris so that cooling water system remains clean.
Below is a brief method statement for doing cleaning, flushing and passivation of closed loop water cooling/chilling system, which is part of HVAC system of a building.
This method statement describes the methodology and procedure for flushing of chilled water system and to ensure that all persons are familiar with the sequence of activities, utilization of resources, and execution of the works in compliance with applicable Safety and Quality Procedures, and Project Documents and Specification.
Scope of Works
This method statement is intended to outline the activities and the methods used in cleaning and flushing of chilled water system and its chemical treatment.
All activities will be carried out in accordance with the contract details and in full compliance to the project specifications.
All work within the rights-of-way of the standards and specifications will be done in compliance with requirements issued by authorities.
This flushing procedure for chilled water system method statement covers all steps that include:
- Cleaning and flushing with fresh water
- Flushing with cleaning chemical
- Addition of Corrosion & Scale Inhibitor
- Addition of Bio-side for biological control
Required Tools/Equipment
- Tool box / Tool kit
- Meters/gauges
- Power Tools
- Temporary pump
- Chemicals
Chilled Water Flushing Method Statement
Preparation: 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.
- Arrangements for draining the flushed water to be made before starting the flushing process. Drain should be connected to main drainage line or as directed by authorities.
Chilled Water Pipes Flushing & Cleaning Steps
Step 1: Cleaning With Fresh Water
- Fill the system with clean water and drain the water after 30 minutes of circulation. The water quality will be as per approved parameters.
- Refill the system with clean water and run the chilled water pump for 2 hours. Take samples to check the quality of water as per applicable requirements in the contract.
- Open the drain valves in the main lines and drain the water completely.
- Clean the strainers
- During the above flushing process the drain valves shall be kept open while the pump is running, until the water appears clean.
- Close all the drain valves
Step 2: Cleaning With Cleaning Chemical
- Desired water quality should be achieved before adding the chemical.
- Refill the system with clean water and add cleaning chemical in required quantities as per Specialist supplier’s instructions i.e. 1 Kg per cubic meter of system volume.
- Once the cleaning process is started, 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.
- Samples to be taken and tested in 3rd party laboratory. The water quality must be achieved as per the requirements agreed in the contract or as applicable
- Specialist contractor shall collect samples and conduct tests until satisfactory results are obtained as required which is a condition when no increase in iron level is observed and a level of iron less than 1ppm is achieved and the water is clear, colorless and odorless.
- After the cleaning process is completed as described above the cleaning solution shall be flushed out.
Step 3: Addition of Corrosion & Scale Inhibitors
The entire chilled water system is re-filled with fresh and clean water and treated with corrosion and scale inhibiting treatment chemical at the rate of 3 Kg per cubic meter of the system volume or as applicable depending upon the chemical concentration.
After 24 hours of circulation samples are taken to ensure the concentration levels i.e. 800-100 ppm as NaNo2
Step 4: Biological Control – Chemical Treatment
Biological control chemical, shall be dosed at the agreed rate per cubic meter using the manual dosing pot.
This is a shock dosing which shall be done after every three months.
Inspection
The inspection request shall be raised for consultant to witness the flushing and cleaning process at different stages and results shall be noted on checklists.
Chemical test reports shall be provided with all other documentations.