Humidity control plays a crucial role in many areas of our lives and industry. From preserving our health and protecting our homes from mold to ensuring product quality in manufacturing and storage, moisture measurement is essential.
But why is measuring humidity so important? Moisture affects the materials and products we use every day, as well as the environmental conditions in which we live and work. Too high a moisture content can lead to mold growth, rust formation and a shortening of the shelf life of food. On the other hand, too low humidity can lead to the drying out of materials and products, as well as health problems such as dry mucous membranes and skin.
In this guide article, we explain the most important terms around the topic of humidity.
- Relative humidity (RH): Relative humidity is the ratio of the current water vapor content of the air to the maximum water vapor capacity at a given temperature, expressed as a percentage. A relative humidity of 50% means that the air contains 50% of the maximum amount of water it can hold at the current temperature. In air conditioning and building automation, relative humidity is crucial to control comfort and material properties. In food warehouses, RH control is important to prevent spoilage. The normal humidity outdoors is between 30 and 50 percent. However, these values can vary depending on the climate and weather. Values above and below this range can be perceived as unpleasant.
- Absolute humidity: Absolute humidity indicates the actual amount of water vapor in the air, expressed in grams per cubic meter (g/m³). This unit of measurement is independent of temperature and gives an accurate idea of the amount of water in the air. In industrial drying processes, such as papermaking, precise absolute humidity controls must be carried out to ensure the quality of the final product.
Water vapour content of the air (in g/m³) as a function of temperature
- Dew point: The dew point is the temperature at which the air is saturated and the water vapor condenses into water. This value is important for preventing condensation problems in air conditioning systems and in the storage of industrial goods, as condensation can cause rust and mold. In the oil and gas industry, the dew point is crucial for the dewatering of natural gas.
- Wet bulb temperature: Wet bulb temperature is measured by holding a thermometer with a damp cloth around the sensor in a stream of air. The evaporation of water from the cloth cools the sensor and the difference from the dry temperature indicates the moisture content of the air. This technique is often used in meteorological stations and cold stores.
- Hygrometer: A hygrometer is a device used to measure humidity. There are several types of hygrometers, including mechanical, electrical, and digital versions. In museums, hygrometers are used to ensure stable humidity conditions and protect works of art from moisture damage.
- Capacitive hygrometer: A capacitive hygrometer uses a hygroscopic layer between two electrodes. The moisture changes the capacity of the layer, which is measurable. This type of hygrometer is widely used in HVAC (heating, ventilation, air conditioning) technology and electronics manufacturing, where humidity must be closely monitored to prevent damage to sensitive components.
- Resistive hygrometer: A resistive hygrometer measures the resistance of a hygroscopic material. This resistance changes with moisture. A typical area of application is industrial quality control, such as in food production, where accurate measurement of moisture is crucial for shelf life and quality.
- Electrolytic hygrometer: An electrolytic hygrometer measures humidity by measuring the flow of current through a hygroscopic salt. This method is often used in industrial processes to monitor humidity in drying chambers or in the production of hygroscopic materials.
- Dew Point Hygrometer: A Dew Point Hygrometer determines the dew point by cooling a mirror until condensation occurs. This measurement method is used in gas processing and transportation to ensure that condensation does not occur in pipelines, which could lead to blockages and corrosion.
- Hydrometer: A hydrometer measures the specific gravity of liquids and can also indirectly determine humidity, especially in cooling systems and for battery testing. In the food industry, it is widely used to check the concentrated liquids such as syrup or juice.
- Saturation: Saturation refers to the state in which the air contains the maximum amount of water vapor at a given temperature. This condition is critical for industrial drying processes where humidity must be precisely controlled to ensure effective drying, for example in the textile industry.
- Sorption isotherm: A sorption isotherm shows the relationship between the moisture of a material and the relative humidity of the ambient gases. These curves are important for the storage and packaging of hygroscopic materials, such as pharmaceuticals and grains.
- Water Activity (aw): Water activity is the measure of the availability of water for microbiological activities in a material, expressed as a fraction of the water vapor pressure. In the food industry, water activity is monitored to prevent the growth of microorganisms and increase shelf life.
- Moisture penetration: Moisture penetration describes the process by which moisture enters and spreads through a material. This is crucial in the construction industry to prevent mold growth and in the packaging industry to ensure the integrity of moisture barriers.
