Periodic testing parameters for closed system circulating cooling water

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Date: 2025-08-04Read: 0

Indirect cooling closed loop cooling water systemAs the name suggests, it is a circulatory system isolated from the external environment, requiring very little supplementary water for its normal operation. A well functioning closed system can supply no more than 5% of water annually. Due to the absence of evaporation concentration effect,The risk of scaling formation is usually much lower than the risk of corrosion.

The recommended weekly regular testing items include

Conductivity/TDS
pH
Iron (dissolved and total)Other metals (tested according to the situation)
Inhibitors (tested according to the situation)
Microbial examination
Turbidity/suspended solids

conductivity

The conductivity of circulating water in a closed system may fluctuate due to differences in initial makeup water conductivity and chemical treatment schemes. By detecting and recording the conductivity at the beginning of system startup and each maintenance, the trend of change can be obtained.

When there is a significant decrease in the conductivity of the cooling water, it indicates that there may be a leak in the system. When there is a significant increase in the conductivity of the cooling water, it indicates that the system may have added additional chemicals after the last maintenance or suffered from some external pollution.

Regularly measuring pH can evaluate whether a closed system is functioning properly. The increase in pH may be due to excessive addition of water treatment agents or contamination of the system. Low pH is usually caused by system contamination or the proliferation of sulfate reducing bacteria producing hydrogen sulfide, which lowers pH. Sulfate reducing bacteria often have serious biofilm problems.

iron ion

The concentration of iron ions is an important indicator of the corrosion rate of cooling water, and corrosion is one of the problems that closed system circulating water usually faces, which is the main cause of system failure. Corrosion problems can often be traced back to the system installation stage, and in most cases, they stem from incomplete pre-treatment procedures before trial operation.

corrosion inhibitor

As one of the crucial testing items in every water quality maintenance, it is necessary to strictly monitor the residual concentration of corrosion inhibitors. The closed system circulating water mainly adopts two types of corrosion inhibition systems, molybdate based corrosion inhibitors and nitrite based corrosion inhibitors. The closed system circulating cooling water has clear corrosion inhibitor control standards, and its detection concentration will be used to calculate the dosage of chemical treatment agents added.

Microorganisms - Total bacteria/NRB/SRB

Multiple microbial parameters can be tested during the maintenance process of closed system circulating water.

For example, using Dipslides agar plates to test the total number of heterotrophic bacteria (TVC);

Use selective agar plates to test Pseudomonas or other special bacterial species such as nitrite reducing bacteria (NRB) and sulfate reducing bacteria (SRB).

It is recommended to increase yeast and mold testing for systems using ethylene glycol as an antifreeze agent.

Total suspended solid particles/turbidity

The clarity of water quality can effectively reflect the operating status of the system. Turbidity can be directly observed by visual inspection. FAU turbidity and suspended solids concentration can be measured using a multi parameter photometer, or more accurate results can be obtained using a turbidity meter.

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