Humidification load calculator

This online calculator answers question "how to choose humidifier", by calculating humidification requirements given initial and target relative humidity and building parameters.

The calculations were made possible after the creation of Relative humidity to absolute humidity and vice versa calculators.
Now, to use the calculator, it is important to understand the logic behind calculating humidification load.

For home humidifiers manufacturer usually specifies the volume of the air processed by the humidifier per hour as its capacity. Like, 180 cubic meters per hour.

Well, this is quite useless. The true specification of humidifier you should look for is the speed of humidification, i.e., how much water it can add to the air per hour. If you are determined enough, you will find it. At least you can measure it by yourself if you already have a humidifier.

Why is it per hour? Because your apartment isn't in a vacuum, and you have intake and exhaust air. Otherwise, you'd die without the oxygen, wouldn't you? The airflow is characterized by air changes per hour, ACH. For apartments, this value is usually quite low, between 0.1 and 0.5. This calculator uses 0.5, which means that air completely renews for 2 hours. This is quite good value, actually.

So, because air constantly renews, humidifiers should constantly add the water amount enough to close the gap between initial relative humidity and target relative humidity.

And here go the calculations.

1. Volume of air to be humidified
   For this, we need apartment volume and air changes per hour. They give us the volume of air replaced each hour.
2. Water to be added by the humidifier
   For this, we need temperature, initial relative humidity, and target relative humidity. They give us initial absolute humidity and target absolute humidity. The difference is the amount of moisture to be added per cubic meter, then multiplied by air volume to be humidified. This will give us the amount of water to be added to the air each hour. Knowing this, we can compare it with the humidifier's speed and see if it fits our requirements.

The calculator below implements the abovementioned calculations.

Humidification requirements

Building area, square meters

Height, centimeters

Air change rate, 1/hour

Initial relative humidity, percents

Target relative humidity, percents

Temperature, degrees centigrade

Calculation precision

Digits after the decimal point: 3

Calculate

Air volume per hour, cubic meters

 

Initial absolute humidity, kg/cubic meter

 

Target absolute humidity, kg/cubic meter

 

Water to be added each hour, kg/hour

 

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