Chemical Flushing for Chilled Water System

chemical flushing for chilled water system

Flushing Procedure For Chilled Water System & Chemical Treatment

What is chemical flushing for chilled water system? Chilled water or cooling water system is often a closed system that necessitates strict monitoring and control of a number of parameters.

As water evaporates during circulation, the suspended particle concentration rises, resulting in scale formation and corrosion. As a result, chemical treatment chilled water system is required on a regular basis. Otherwise, contaminants might harm or clog the entire system.

Flushing is required before the chemical treatment of any water piping system. Flushing cleans the cooling water network by removing any suspended solids, jointing compound, welding slag and particles or dirt.

Cleaning, flushing, and passivation of a closed-loop water cooling/chilling system, which is part of a building’s HVAC system, is described in the method statement below.

This method statement outlines the methodology and technique for flushing the system, as well as the sequence of operations, resource utilization, and job execution in accordance with applicable Safety and Quality Procedures, as well as Project Documents and Specifications.

Work Description

This method statement for construction project outlines the actions and procedures utilized in checmical cleaning and flushing, as well as the chemical treatment of the whole system.

All activities shall be carried out in complete compliance with the project requirements and in line with the contract specifics.

All work within the standards and specifications’ rights-of-way will be done in accordance with authorities’ regulations.

HVAC pipeline flushing

This method statement for cleansing chilled water systems comprises all steps, including:

  1. Using fresh water to clean and flush
  2. Using a cleaning chemical to final flush
  3. Addition of corrosion and scale inhibitors
  4. Bio-side has been included for biological control

Tools/Equipment Required

  • Toolkit / Toolbox 
  • Meters/gauges 
  • Power tools
  • Chemicals
  • Temporary Pumps

Method Statement for Chemical Flushing for Chilled Water System

Prior to beginning the flushing and chemical cleaning of the system, the following preparation tests/activities must be completed sucessfully.

  • Verify the test certificate and make sure the system has been hydrostatically pressure tested. Examine the position of air vents in accordance with approved designs.
  • Check to see if enough chemicals are accessible in the quantities required. As needed, post warning signs and use caution tape. Before beginning the flushing procedure, make arrangements to drain the flushed contaminated water.
  • Drain point should be connected to the main drainage line or to the authorities’ specifications. 

Steps for Dynamic Flushing and Cleaning Chilled Water Pipes

Step 1 Cleaning with fresh water

After 30 minutes of circulation, fill the system with clean water and drain the water. The water quality will be within acceptable limits. Fill the system with fresh water and let the chilled water pump operate for two hours.

Take samples to check the water quality in accordance with the contract’s specifications. Drain the water completely by slowly opening the drain valves in the main lines.

Disinfect/clean the strainers. Drain valves must be kept open while the system pumps are running during the aforementioned cleansing operation until the water seems clean. All drain valves should be closed.

Step 2 Clean with a cleaning agent

Prior to introducing the chemical, the desired water quality should be attained. Refill the system with clean water and add the cleaning chemical in the specified amounts as directed by the Specialist supplier, i.e. 1 kg per cubic meter of system volume. To guarantee that the chemical solution has reached all sections of the system, samples of the solution should be obtained from various portions of the system once the cleaning process has begun.

As recommended by the specialist supplier, run the pump and circulate the water (with chemicals added) for a minimum period of 24 hours. Samples will be collected and analyzed by a third-party laboratory.

Water quality must be met in accordance with project specification or as required by law. When no increase in iron level is noticed and a level of iron less than 1ppm is achieved, and the water is clear, colorless, and odorless, the specialist MEP contractor shall collect water sample and conduct tests until satisfactory findings are obtained as necessary.

The cleaning solution must be flushed out after the cleaning process is done as mentioned above.

Step 3 Corrosion and scale inhibitors are added

The entire chilled water network is refilled with fresh, clean water and treated with corrosion and scale inhibiting treatment chemicals at a rate of 3 kilograms per cubic meter of system volume, or as needed depending on chemical concentration.

Samples are taken after 24 hours of circulation to ensure the concentration values, which are 800-100 ppm as NaNo2.

Water sample will be checked by a water treatment specialist to confirm the corrosion inhibitor level is within the correct range after being cycled for two hours.

Step 4 Chemical Treatment – Biological Control

The biological control agent must be dosed using the manual dosing pot at the approved rate per cubic meter.

This is a shock dose that needs to be repeated every three months.


The consultant will be requested to inspect the flushing process and cleaning procedure at various stages and the results will be recorded on checklists.

All other project documents must be accompanied by chemical test reports.

Key Takeaways

System flushing will not eliminate the contaminant, primarily metal oxide, which adheres to the internal surfaces of the pipes. When the system is turned on, the contaminant will be released back into the flowing steam caused by the movement of the pipework due to thermal expansion or contraction. As a result, chemical cleaning’s goal is to remove surface deposits so that they can be flushed away.

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