Measuring humidity correctly 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, humidity measurement is essential.
But why is humidity measurement so important? Humidity 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, rusting and a reduction in the shelf life of food. On the other hand, too little moisture can cause materials and products to dry out and lead to health problems such as dry mucous membranes and skin.
In this guide, we explain the most important terms relating to humidity measurement.
- Relative humidity (RH): Relative humidity refers to 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. If the relative humidity is 50% when measuring humidity, this means that the air contains 50% of the maximum amount of water that it can hold at the current temperature. In air conditioning and building automation, relative humidity is crucial for controlling comfort and material properties. In food storage facilities, RH control is important to prevent spoilage. Normal outdoor humidity is between 30 and 50 %. However, these values can vary depending on climate and weather. Values above and below this range can be perceived as unpleasant. In addition to humidity measurement, indoor air quality measurement is also crucial for a healthy working environment.
- Measure 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 paper manufacturing, accurate absolute humidity controls must be carried out as part of the humidity measurement to ensure the quality of the end product. Humidity measurement also plays a central role in indoor climate control. You can find out more about why temperature and humidity are crucial for well-being in our guide.
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 avoiding 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 dehydration of natural gas.
- Wet bulb temperature: The 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 to the dry temperature indicates the moisture content of the air. This technique is often used in meteorological stations and cold stores. For precise humidity measurement, the selection criteria for temperature sensors are also crucial in order to achieve accurate results.
-
Hygrometer: A hygrometer is a device for measuring humidity. There are different types of hygrometers, including mechanical, electrical and digital versions. Hygrometers are used in museums to ensure stable humidity conditions and to protect works of art from moisture damage.
- Capacitive hygrometer: A capacitive hygrometer uses a hygroscopic layer between two electrodes. The humidity changes the capacitance of the layer, which can be measured. This type of hygrometer is widely used in HVAC technology (heating, ventilation, air conditioning) and in electronics manufacturing to measure humidity and thus prevent damage to sensitive components.
- Resistive hygrometer: A resistive hygrometer measures the resistance of a hygroscopic material. This resistance changes with humidity. A typical area of application is industrial quality control, e.g. in food production, where accurate humidity measurement is crucial for shelf life and quality.
- Electrolytic hygrometer: An electrolytic hygrometer is used to measure humidity by measuring the flow of electricity 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 method of humidity measurement 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 often used to check concentrated liquids such as syrup or juice.
- Saturation: Saturation refers to the condition in which the air contains the maximum amount of water vapor at a certain temperature. This condition is critical for industrial drying processes where the 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 content 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 cereals.
- Water activity (aw): Water activity is the measure of the availability of water for microbiological activity 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 penetrates and spreads through a material. This is critical in the construction industry to prevent mold growth and in the packaging industry to ensure the integrity of moisture barriers.
