Water quality and fouling in chillers, heat exchangers and cooling towers

Rated capacity assumes clean surfaces. Write the water conditions into the enquiry so the selection allows for reality.

A heat exchanger's rated capacity assumes heat-transfer surfaces in a stated condition. In service, scale, corrosion products, biofilm and debris build up on the water side and add thermal resistance. The result is lower capacity, higher compressor lift and higher pump energy, unless the selection allowed for it and the plant is maintained.

The fouling factor

A fouling factor is the extra thermal resistance a selection assumes for dirt on a heat-transfer surface. AHRI's Guideline E explains how the industry moved to a lower standard evaporator allowance after ASHRAE-sponsored studies; an ASHRAE interpretation records AHRI 550/590 certification using 0.0001 h·ft²·°F/Btu for evaporators and 0.00025 for condensers. Confirm the value in the current edition that the supplier rated to.

If your water is harder or dirtier than the rating assumes, ask for a selection at a project-specific fouling factor. Comparing one offer rated clean with another rated with a field allowance is not a fair comparison.

Open towers add biological risk

Open cooling towers concentrate minerals as water evaporates and expose the circuit to air. US CDC guidance states that an effective water management programme is the primary strategy to control Legionella, recommends controlling sediment, scale and corrosion, and notes that Legionella can grow in both open- and closed-circuit towers. Our cooling tower selection guide covers the thermal side of the tower.

Where water conditions decide the selection on this site

Plate heat exchangers are compact but have narrow channels; our plate heat exchanger enquiry guide lists the fluid data to send. Serviceable plate packs are described on the Shuangteng plate exchangers, the O-MING OMBR exchangers and the Zhongchuang plate exchangers, while the Jinghai spiral-plate heat exchangers are presented for cleanability and the Jinghai removable plate-exchanger packages discuss materials and service.

Chillers need condenser-water conditions and cleaning access stated: the Sinuo water-cooled screw chiller page asks for exactly that, and our chiller quotation guide explains how fouling affects comparisons. Evaporatively cooled plant such as the Takamura TS-C-UNI chiller and the Jinchuang JCN counterflow towers depends on make-up water quality.

Closed loops have their own fluid rules. The Grand LSS closed pure-water cooling systems are built around controlling the quality of the circulating water, the Envicool SoluKing coolant must be qualified with the circuit's metals and seals, and the Envicool prefabricated secondary loops need site acceptance of the distribution. Ground- and water-source systems need source-water limits, as the Hangli water and ground-source heat pumps page notes, and hot-water exchangers such as the Tegao floating-coil exchangers depend on the supply water as well.

Questions to ask

What fouling factor was each heat exchanger selected with, and under which standard? What water quality limits apply for hardness, chlorides, pH and solids, and which materials suit them? Is a strainer, side-stream filter or water treatment package included? How are tubes or plates cleaned, and what access and isolation does that need? For towers, what water management and drift measures are included?

Common questions

Can a chemical treatment programme replace a fouling allowance? It reduces fouling, but a realistic allowance still protects capacity. Do both.

Is a closed loop free of water-quality problems? No. Closed loops corrode and foul if filled with untreated water or if oxygen enters.

By HVACDeck Editorial · Updated 2026-11-06