High hardness of cooling water on the condenser side of the low-temperature evaporative system, with no water softening

Long-term, hidden loss of heat exchange efficiency (all due to gradual deterioration, which is not normally apparent)

1. A dense layer of scale gradually forms on the condenser heat exchange surface, causing thermal resistance to increase year by year

Excessively high cooling water hardness leads to the thermal decomposition of calcium and magnesium bicarbonates on the condenser heat exchange walls, resulting in the precipitation of calcium carbonate and magnesium carbonate.

As the water temperature on the low-temperature condensing side is not extremely high, thick scale does not form instantly; instead, a thin, uniform and dense layer of scale builds up.

Scale has a thermal conductivity far lower than that of metal, effectively creating an insulating layer on the heat exchange surface;

As thermal resistance continues to rise, condensing capacity gradually and imperceptibly weakens year on year.

2. Insufficient condensing capacity → System pressure build-up, passive decline in vacuum

As heat exchange efficiency in the condenser deteriorates, secondary vapour is not fully condensed, leading to the accumulation of non-condensable gases and uncondensed vapour within the system;

The vacuum in the evaporator cannot be established or maintained, forcing the boiling point to rise; the heat exchange temperature difference narrows, causing the overall evaporation efficiency to decline steadily and energy consumption to rise continuously.

3. Scale induces under-scale corrosion, resulting in thinner tube walls/fins and rougher surfaces

Hard scale adheres tightly to metal surfaces, creating an oxygen-deprived environment beneath the scale where chloride ions accumulate, leading to pitting and crevice corrosion;

simultaneously, the accumulation of corrosion products and scale increases the roughness of the tube walls, raising the flow resistance of the cooling water and slightly reducing flow rate, which further impairs heat exchange, creating a vicious cycle of scaling → corrosion → increased susceptibility to scaling.

4. Narrowing of pipe flow channels, with cooling water circulation flow rate declining year on year

Uniform scale deposition on pipe walls reduces the equivalent pipe diameter and increases friction loss;

At the same pump frequency, the actual cooling water volume gradually decreases, leading to increasingly insufficient cooling capacity. During summer or periods of significant diurnal temperature variation, fluctuations in vacuum and a drop in evaporation rates become particularly pronounced.

5. Combined scale and microbial slime deposits double the rate of latent heat transfer decline

Hard water is inherently prone to scaling and simultaneously provides a substrate for algae, bacteria and slime to attach to;

The resulting composite scale—comprising a scale skeleton covered by a biofilm of slime—is far more insulating than scale alone;

Although thick deposits are not visible to the naked eye, heat transfer efficiency declines gradually month by month, leaving one with the impression that the equipment is becoming increasingly power-hungry and underperforming compared to new units.

6. Problems are more subtle and damaging to equipment under low-temperature winter conditions

In northern regions, cooling water temperatures are low in winter, and with ample cooling capacity to begin with, the impact is not immediately apparent;

However, hard scale continues to accumulate slowly; by the time high-temperature loads return in summer, condensation capacity has been completely stifled by the scale, and the system can never return to its design heat exchange efficiency.

7. Conventional water flushing is ineffective; acid washing is the only option, yet this causes increasing damage to the equipment

The dense scale formed by hard water cannot be completely removed by ordinary backflushing, necessitating frequent acid washing;

Frequent acid washing corrodes the base material and destroys the metal passivation layer, making the equipment more susceptible to subsequent scaling and corrosion, leading to a vicious cycle of ‘scaling – acid washing – increased susceptibility to scaling’.