Definition

A parameter expressing the combined calcium (Ca²⁺) and magnesium (Mg²⁺) ion concentration of water, reported in French degrees (Fr° or °fH) and ppm CaCO₃. 1 Fr° ≈ 10 mg/L CaCO₃ (calcium-carbonate equivalent). Water hardness directly affects scale build-up and the maintenance interval in steam humidifiers; in resistive units the build-up collects in the stainless-steel steam tank and is removed during planned maintenance.

Detailed Explanation

Water hardness is the sum of calcium (Ca²⁺) and magnesium (Mg²⁺) ions, reported as CaCO₃ equivalent. "Temporary hardness" is the part bound to bicarbonates; when heated it loses carbon dioxide and precipitates as calcium carbonate. "Permanent hardness" is the part bound to sulphates and chlorides; it does not precipitate directly on heating, but as it concentrates in a boiling tank it can exceed its solubility limit and form deposits (e.g. calcium sulphate).

Units: 1 °fH (Fr°, FS) = 10 mg/L CaCO₃; 1 °dH = 17.85 mg/L CaCO₃ = 1.78 °fH; 1 °e (English) = 14.25 mg/L CaCO₃ = 1.43 °fH; 1 gpg = 17.1 mg/L CaCO₃. "ppm CaCO₃" is in practice the same as mg/L CaCO₃.

Why It Matters

When water evaporates in a steam humidifier, the hardness ions stay in the tank and build up as scale. For the same amount of steam, the hardness load entering the tank is proportional to hardness. In an electrode humidifier the build-up coats the electrodes in the cylinder, and the cylinder is replaced at intervals. In a resistive humidifier the build-up collects in the stainless-steel steam tank, which is cleaned during planned maintenance; the cleaning interval depends on hardness, operating hours, capacity and drain settings.

Worked Example

14 °fH water = 140 mg/L CaCO₃ = 7.8 °dH. A 50 kg/h humidifier running at full load for 24 hours evaporates about 1,200 L of water, and about 168 g of hardness (as CaCO₃) enters the tank; in continuous operation this is roughly 60 kg a year. Part of it stays in the tank as scale and part leaves with the drain. 28 °fH water brings about twice the hardness load for the same steam output.

Engineering Note

A sodium-resin softener swaps Ca²⁺ and Mg²⁺ for Na⁺; hardness and scale build-up drop, but total dissolved salts and conductivity do not change significantly. Sodium salts do not form scale; they concentrate in the tank and leave with the drain, and because concentrated salts can cause foaming, drain and foam control matter. Removing most dissolved salts requires RO or DI; these waters suit a resistive unit but are too low in conductivity for an electrode unit. Hardness alone does not indicate conductivity: softened water keeps its high conductivity despite its low hardness.

How Nem Kontrol Teknolojileri Applies It

As Neptronic's authorised distributor in Türkiye, Nem Kontrol Teknolojileri asks the customer for a recent water analysis from an accredited laboratory when selecting a steam humidifier and compares the values with Neptronic's feedwater requirements. The resistive Neptronic SKE4 runs on any water, RO and DI included; water quality only affects maintenance frequency. Pre-treatment systems are designed and installed by specialist water-treatment companies.