Cooling Towers: Make Blowdown a Measured Decision

EPA’s February 2026 cooling-tower presentation illustrates a conductivity controller opening and closing a bleed valve. It is a practical control mechanism, not evidence that one setpoint suits every installation. [1]

OlbrichCo’s recommendation is to approve a measured operating envelope before reducing blowdown: the deliberate discharge of circulating water. Treat the decision as a joint task for the facility operator, water-treatment specialist and responsible mechanical engineer. The question is not simply whether the valve can remain closed longer, but whether the agreed water-quality, equipment and operational conditions remain satisfied.

This note concerns water discharged from an evaporative cooling-tower circuit, not routine draining of a closed chilled-water loop. Begin with a marked schematic showing make-up supply, basin, circulating circuit, sampling points, bleed valve and discharge destination. Identify which cells share water and which meters serve other equipment. The approved boundary should make every reading attributable to the system being assessed.

For a facility in Iran, establish the actual supply arrangement and the support available at that site. Ask whether supply sources are blended or switched, who maintains the instruments, and whether replacement probes and calibration materials can be obtained. These are project questions, not claims about every Iranian facility. Record responsibility for reviewing water quality after a source change; do not carry yesterday’s assumptions into a different supply.

DOE explains that evaporation leaves dissolved solids behind; concentration must be limited to manage scale and corrosion. Feasible cycles of concentration depend on make-up water quality and the treatment programme. [2]

Commission a representative make-up and circulating-water assessment from the competent treatment specialist. Require the report to identify sampling locations, operating state, test methods and the constituents that constrain the proposed envelope. Ask how tower materials, connected heat exchangers and treatment compatibility affect the recommendation. Conductivity should have a documented interpretation for this water, not become a substitute for its chemical assessment.

Turn the assessment into an approved operating sheet: controlled parameter and units, target range, alarm limits, verification method, review frequency and response owner. Include controller hysteresis or other switching logic, permitted manual overrides and the conditions requiring escalation. The specialist should define settings and chemistry; this article supplies no universal cycles ratio, conductivity limit, pH, temperature target or chemical dose.

Make the contract distinguish supply of equipment from responsibility for continuing performance. Specify who samples, calibrates, reviews trends, replenishes treatment materials and authorizes changes. Require applicable Iranian requirements, discharge permissions, equipment instructions and local engineering review to be resolved for the particular facility. An overseas guidance document is useful evidence, but it does not settle those obligations or demonstrate local compliance.

OlbrichCo proposes a commissioning walk-through that follows the complete signal chain. Confirm meter identities, units, direction and the physical branches included. Record starting totals and the condition of the make-up and blowdown meters. Have the instrument specialist verify the conductivity probe against an appropriate independent reference using the supplier’s procedure. Retain the comparison, instrument identifiers and any correction, not just a tick marked ‘calibrated’.

Test the approved control sequence under a planned, supervised procedure. Demonstrate that the relevant signal produces the expected valve action and that discharge actually starts and stops. Check the response to a failed or implausible signal and loss of communications against the approved design. Do not force an unsafe water condition to test an alarm; use an authorized test method and restore every override.

A useful diagnostic example is a log showing ‘valve closed’ while the blowdown total continues increasing. That discrepancy should trigger verification of timestamps, meter boundaries, valve position and possible bypass paths. It is not proof of a leaking valve on its own. Preserve observations before adjustment, assign a person to investigate and record the evidence that closes the issue; do not silently edit the history.

Keep separate records for measured concentration, water volumes, operating hours and thermal duty. Compare readings over aligned intervals and annotate basin draining, cleaning, supply changes and abnormal operation. Avoid presenting a make-up-to-blowdown volume ratio as an unquestionable chemistry result. Ask the specialist to reconcile the evidence and its assumptions; an unexplained mismatch is a reason to investigate, not to increase the setpoint.

CDC’s cooling-tower guidance addresses Legionella control through a water-management programme, including cleaning and management of scale, corrosion and sediment. It covers both open- and closed-circuit cooling towers. [3]

ASHRAE’s public overview describes Standard 188-2021 as setting minimum Legionellosis risk-management requirements for building water systems, covering responsibilities from design through operation and service. [5]

The editorial implication is clear: passing a conductivity check is not release evidence for the facility’s microbial-risk controls. Require the responsible water-management team to retain its own control limits, monitoring, corrective actions and records. A water-saving trial must not suspend cleaning, alter disinfectant control without authorization, or replace the agreed health-risk response with a lower water-consumption figure.

Before seasonal shutdown, standby or restart, require the facility team to identify the applicable treatment and cleaning procedure and the competent person authorizing return to service. Keep escalation contacts and the current instructions available offline in Persian. Where a control failure or suspected health hazard occurs, follow the approved response and involve qualified specialists; a blog post cannot provide a site-specific disinfection or emergency procedure.

DOE notes that captured air-conditioning condensate is low in minerals but can acquire metals from coils and support bacterial growth in storage. Its guidance also cautions against capturing coil-cleaning water. [4]

Do not approve an alternative make-up source from conductivity alone. Require an assessment of its constituents, contamination pathways, treatment needs and compatibility with the tower programme. Map collection, storage, overflow, isolation and the destination of cleaning water. Ask the responsible designer to establish separation from potable systems and applicable local safeguards; do not copy a foreign plumbing detail without that review.

Compare the proposed source’s availability with the tower’s actual seasonal demand and provide an approved fallback supply arrangement. Include the operator’s workload, cleaning access, sampling, instrument maintenance and ongoing consumables in procurement. Obtain site-specific quotations and assumptions rather than importing foreign water tariffs or generic payback claims. A source that looks inexpensive on a flow diagram may still be unsuitable for the local maintenance arrangement.

For an existing facility, qualify changes in a sequence that preserves a usable baseline: first establish trustworthy measurement and the approved controls, then evaluate a new supply or treatment strategy through formal change review. Do not alter several conditions and attribute the resulting change in water consumption to one intervention. Keep the previous configuration, decision record and specialist-approved recovery plan accessible.

Run a bounded pilot on a clearly identified circuit over operating conditions agreed with the mechanical engineer and treatment specialist. Set the observation period to include the relevant load variation, not an arbitrary calendar week. Before starting, define acceptance evidence: verified instruments, successful control tests, complete records, compliance with the approved water-quality envelope and no unresolved critical defects or unauthorized overrides.

Report make-up and blowdown volumes with the interval, operating hours, supply source and available thermal-duty evidence. Track time outside approved limits, missing readings, valve discrepancies, corrective-action closure and maintenance effort. Compare water use only across meaningfully comparable duty and weather conditions, explaining the limitations. Do not claim savings from a period when the plant ran less or the records cannot support the comparison.

Hand over the schematic, approved settings, test results, sampling plan, instrument and valve identifiers, alarm responses and revision-controlled operating sheet as one package. Demonstrate the routine with the staff who will perform it. A controller display or cloud subscription is not the handover deliverable: the team must be able to recognize a suspect reading, use the approved fallback and retrieve its evidence without relying on continuous connectivity.

Reopen the assessment after a supply-source, treatment, equipment or control-logic change, repeated excursions, or unexplained deterioration in performance. The owner should authorize continued operation within the revised envelope, not merely sign a water-saving target. The cover’s valve wheel and mineral ring are an editorial metaphor for this decision, not an installation detail or a depiction of acceptable deposit on operating equipment.