Water Treatment Specification Guidelines
To avoid problems the installation must be thoroughly flushed before it is filled and commissioned and the services of a water treatment expert must always be used to control and maintain the limiting values highlighted in Table 1.
The natural chemical constituents found in municipal supply water can vary in identity and concentration over a large range of values depending on the source, geographical location or season. The quality of supply water may ultimately have effects on the efficiency and effectiveness of boilers and heating systems. Some constituents may be detrimental and can result in metal corrosion, circulating particulate debris, settled sludge, extraneous noise and interference with moving parts, poor water flow or blockage, degradation of boiler efficiency/system effectiveness and ultimately loss of system integrity.
The key parameters that can have the most detrimental effect on the quality of the heating water are: oxygen content, total hardness, conductivity, suspended solids, total metals, chlorides and pH, which can all be measured. The installation can also play a significant role in the overall performance of the heating system. If non-metallic pipework is used, it must be of the barrier type to prevent oxygen entering the system and initiating corrosion. Oxygen, as well as lime scale minerals, will also enter the heating system every time fresh make up water is introduced. This should be avoided and it is recommended that a water meter should be fitted to monitor any fresh make up to the system. This should not exceed 5% of the total system volume per annum.
Cleaning and Choice of Cleaning Chemical
Primary heating circuits must be thoroughly cleaned and flushed prior to commissioning, re-commissioning following major remedial works or if known or suspected to be affected by corrosion, settled sludge, deposits or build-up of scale on heat transfer surfaces.
The type and extent of debris, dirt and fouling commonly found inside heating circuits largely depend on the age and nature of the system and how well or poorly it has been maintained.
There are many different cleaning chemicals available. These range from mild detergent cleaners, which may be designed for cleaning newly installed systems, through cleaners formulated to penetrate, lift and remove sludge and accretions in older systems to strong acid based cleaners, specifically designed to remove high levels of hardened lime scale deposits and corrosion.
The choice of cleaning agent should be appropriate for the materials of construction of the system, the type of contamination to be removed, the cleaning method employed and any discharge limitations.
Special consideration should be given to systems containing aluminum which is vulnerable to attack at low and high pH. Manufacturers’ recommendations and guidelines regarding the choice / use of chemicals and recommended operating parameters should ALWAYS be followed.
New systems invariably contain contaminants and debris from component manufacture or from the system installation work itself and therefore the entire system, excluding the boiler, should be thoroughly flushed before commissioning the heating system. The cleaning process, normally carried out by a trained professional, can be enhanced by the use of an appropriate cleansing agent.
The system can be filled with softened water but it is recommended that the total hardness is maintained above 10mg/l as CaCO3.
Existing systems, even well maintained installations, may have accumulations of sludge and scale. A thorough system clean not only restores system efficiency and effectiveness, but is critical in preparing interior surfaces for effective corrosion and scale inhibition. Before cleaning, the system should be examined to determine the system size, configuration and complexity, system materials, system age and overall condition of components. Attempts should also be made to determine the nature of the contamination that needs to be cleaned in order to decide the most appropriate cleaning agent and cleaning method.
The choice of cleaner, the cleaning protocol adopted and the clean itself should be carried out by appropriately trained and experienced personnel. The water velocity for flushing and cleaning should be sufficient to help penetrate, dislodge, suspend and transport insoluble debris from the system.
The system must be cleaned and all contaminants and suspended debris flushed from the system before installation of the new boiler and implementation of a suitable water treatment regime. This could also include the installation of a filter located in the return pipe work.
The objectives of water treatment (and pre-treatment) are to minimize the corrosion of system metals and to inhibit the formation of mineral scale. In this way, not only the physical integrity of the system, but its long term efficiency and effectiveness are preserved.
The chosen chemical corrosion inhibitor product must be appropriate for all system metals and should be added during the final fill of the system at a concentration recommended by the inhibitor manufacturer. Always comply strictly with the guidelines and operating instructions provided by the supplier of the water treatment product.
It is important that full circulation and homogenous distribution of the additive is achieved before sampling system water to confirm the correct inhibitor concentration, and subsequent adjustment if necessary.
A log should be kept of all water treatment activities undertaken and retained on site.
The water quality of the heating installation should be checked regularly to ensure the circulating water is always of the appropriate quality – see Table 1.
Parameter Limits Reason Make-up water Conductivity 1,000 µS/cm maximum To ensure system water values can be achieved Suspended Solids 30 mg/l maximum To meet suspended solids limit on system water System water pH range 6.5 – 10.0 unless aluminum in the system, then 6.5 – 8.5 Conductivity 1,000 µS/cm unless treated with appropriate inhibitor, then 3,000 µS/cm max.
Total Hardness (as CaCO3)
Heat output <70kW
10 – 350 mg/l To minimize scale
Total Hardness (as CaCO3)
Heat output 70 - 200 kW
10 – 200 mg/l Higher heat flux increases likelihood of scale formation Chloride (as Cl) 150 mg/l maximum To prevent pitting corrosion Total iron (as Fe) 15 mg/l maximum Indicator of corrosion Soluble iron (as Fe) 3 mg/l maximum Indicator of corrosion control Soluble copper (as Cu) 1 mg/l maximum Indicator of corrosion control. Copper also has the potential to induce pitting corrosion of other metals. Soluble Aluminum (as Al) 1 mg/l maximum Indicator of corrosion control. Suspended Solids 30 mg/l maximum From contamination or corrosion and can lead to system component fouling.
It is recommended that a water meter should be fitted to monitor any fresh make up water to the system and this should not exceed 5% of the total system volume per annum.
Where fresh make up water is added ensure that the chemical additive is replenished to maintain the recommended treatment level.
Side stream filtration is recommended with 10% of recirculating flow passing through the filter.
Before boiler or component replacement or remedial work is undertaken the whole of each heating circuit shall be cleaned with Sentinel (Tel: 877.256.2560) X400 System Restorer (de-sludge) or other equal and approved system cleaner at the correct concentration and in the manner recommended by the chemical manufacturer.
This process shall be undertaken with the boilers isolated and shall take place with the main system pumps running for at least 2 days. The drain valve on the dirt separator shall be opened daily to discharge sludge. Each system shall then be subject to the specified pressure and heat test procedures, before treatment with Sentinel X100 Inhibitor, or other equal and approved corrosion inhibitor at the correct concentration and in the manner recommended by the manufacturer.
After commissioning an entirely new system, or zoning out a new extension to an existing system, clean with Sentinel (Tel: 877.256.2560) X300 Cleaner for New Systems, or other equal and approved pre-commissioning cleaner, at the correct concentration and in the manner recommended by the manufacturer.
Each system shall then be subject to the specified pressure and heat test procedures, before treatment with Sentinel X100 Inhibitor, or other equal and approved corrosion inhibitor at the correct concentration and in the manner recommended by the manufacturer.
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