Chapter 1
What does 50% humidity mean?
This does not mean that 50% of the air is water vapor.
Generally, when we say "50% humidity," it means 50% relative humidity. This does not mean that 50% of the air itself is water vapor.
This shows the current state of water vapor as a percentage, with 100% representing the saturated state of water vapor at that temperature.
Even at the same 50% humidity, the amount of water vapor is not necessarily the same.
Relative humidity is affected by temperature. For example, even if two air samples at different temperatures both have a relative humidity of 50%, the actual amount of water vapor they contain is not necessarily the same.
Therefore, in applications where the actual amount water vapor is important, such as drying process and material management, other humidity indicators may be used in addition to relative humidity.
Chapter 2
Why does humidity change when temperature changes?
The most important aspect of understanding relative humidity is its relationship to temperature.
Relative humidity tends to decrease as the temperature rises.
When the amount of water vapor in the air remains roughly the same while the temperature rises, the saturated water vapor pressure at that temperature increases, resulting in a decrease in relative humidity.
Relative humidity tends to increase as the temperature drops.
Conversely, if the amount water vapor remains roughly the same while the temperature decreases, the relative humidity will increase.
This relationship also explains why warming the outside air indoors during winter can make it feel drier.
What does 100% humidity mean?
A relative humidity of 100% means that water vapor is saturated at that temperature.
When air is cooled while the amount of water vapor remains nearly constant, the temperature at which the relative humidity reaches 100% is called the dew point temperature. If the temperature drops further, some of water vapor will turn into water droplets, leading to dew condensation.
Key point: When looking at relative humidity, it's important to look at the temperature at the same time as the humidity number.
Chapter 3
Differences between relative humidity, absolute humidity, and dew point temperature
There are several ways to express "humidity." In everyday life, relative humidity is the most common, but in industrial applications, other indicators are used depending on the purpose.
| index | What to see | Main Applications |
|---|---|---|
| Relative humidity | This shows the current state of water vapor as a percentage of the saturation state at that temperature. | Weather forecast, indoor environment, air conditioning management |
| Absolute humidity | It is expressed as the mass of water vapor contained in a certain volume of air. | Drying process, quality control, air conditioning design |
| Dew point temperature | The temperature at which the air cools down to 100% relative humidity. | dew condensation control, drying management, compressed air management |
What is relative humidity?
This is the most commonly used humidity level in weather forecasts and for indoor environments. unit is generally %RH.
Since relative humidity changes with temperature, it's important to consider it in conjunction with temperature.
What is absolute humidity?
Absolute humidity is an indicator that shows how much water vapor is actually contained in the air.
One common way to express this is to use g/m³ to represent the mass of water vapor contained in unit volume of gas.
The term "absolute humidity" can refer to different things depending on the field. For technical applications, it is important to check unit and definitions.
What is dew point temperature?
This is the temperature at which condensation begins when air containing water vapor is cooled and its relative humidity reaches 100%.
For dew condensation prevention and managing dry air, dew point temperature may be more suitable than relative humidity.
If you would like to learn more about the meaning of dew point temperature, its relationship to relative humidity, how to calculate it from temperature and humidity, and its relationship to dew condensation, please see "What is Dew Point Temperature? Differences from Humidity and Relationship to dew condensation."
There are even more ways to express humidity in industry.
Humidity can be expressed in various ways, including relative humidity, absolute humidity, dew point temperature, as well as mixing ratio, water vapor pressure, and mole fraction. The choice of indicator depends on the object being measured and the purpose of management.
Chapter 4
What is the difference between humidity and moisture?
"Humidity" and "moisture" are similar terms, but they are treated differently in measurement.
| Item | What it mainly represents | example |
|---|---|---|
| Humidity | State of water vapor in a gas | Indoor air, dry air, constant temperature and humidity chamber |
| moisture | Water contained in materials and products | Food, wood, powder, raw materials |
To check the condition of the air, look at "humidity".
Humidity is used to check the state of water vapor in the air in indoor spaces, factories, warehouses, and other similar environments.
If you want to see the amount of water contained in a product or material, look for "moisture".
When evaluating the water content of solids or materials such as food, powders, and wood, we use the concept of moisture.
Chapter 5
What happens when humidity is high or low?
When humidity is high
Sweat evaporates less easily, making you feel hotter even at the same temperature.
Furthermore, attention should be paid to the occurrence of dew condensation, mold, and dust mites.
When humidity is low
This can lead to dryness of the throat and skin, as well as increased static electricity.
For industrial applications, it is necessary to consider factors such as drying and shrinkage of materials like paper and wood, as well as the impact of static electricity on process.
What is a good percentage for indoor humidity?
The Building Sanitation Act stipulates that if an air conditioning system is installed in a designated building, the relative humidity in the habitable rooms must be kept at approximately 40% to 70%.
This standard does not apply to all ordinary households. When managing humidity in a home, you need to consider factors such as the season, temperature, ventilation, and living environment as well.
Chapter 6
How is humidity measured? How does a hygrometer work?
There are several methods for measuring humidity. The method used depends on factors such as required accuracy, measurement range, environment, and maintainability.
Electronic hygrometer
Measurements are taken using sensors whose electrical characteristic change with humidity. They are widely used, from digital temperature/humidity to industrial sensors.
Polymer Capacitive Type
This method measures humidity by utilizing the change in capacitance caused by the adsorption and release of moisture by a polymer film.
It is used in a wide range of applications, including air conditioning, constant temperature and humidity chambers, and environmental testing.
Wet and dry bulb type
This method calculates humidity from the difference between the dry-bulb temperature and the wet-bulb temperature (which is moistened with water).
Dew point meter
By measuring the dew point temperature, the state of water vapor in a gas is evaluated. This method is used in dry air and low-humidity regions.
Where should I put the hygrometer?
Hygrometer readings can vary depending on the installation location. It's essential to install it in a location that accurately represents the space you want to measure.
- Avoid places exposed to direct sunlight.
- Keep away from heat sources such as heaters.
- Pay attention to localized effects, such as on walls and near windows.
- Be careful of locations where strong winds will directly hit you.
- Check if specifications are suitable for areas prone to dew condensation.
- Regularly check the sensors for dirt and deterioration.
When the hygrometer reading is incorrect or does not match other hygrometers
Even if the hygrometer reading is different from usual, the readings don't match between two hygrometers, or display fluctuates, it doesn't necessarily mean the meter is malfunction. By checking the measurement location, the time it takes for the meter to adapt to the environment, dew condensation, comparison conditions, and sensor status in order, you may be able to pinpoint the cause.
Chapter 7
Simple calculation of absolute humidity and dew point temperature from temperature and relative humidity.
By entering the temperature and relative humidity, you can calculate the approximate absolute humidity and dew point temperature. Let's examine the relationship between temperature and humidity.
*This is a simplified calculation. In environments requiring quality assurance, audit compliance, or compliance with standards, please use measuring instruments and calibrated equipment appropriate for the application.
Chapter 8
Why is humidity control important in factories and research facilities?
In daily life, humidity is controlled for comfort, but in industry, it is a control item related to product quality, process repeatability, and stable operation of equipment.
Quality control
The dimensions, weight, viscosity, adhesion, and shelf life of materials and products may change due to moisture absorption and drying.
process management
In processes such as drying, painting, fermentation, and environmental testing, differences in humidity conditions can lead to variations in process results.
Equipment/environmental conservation
Understanding humidity levels is crucial to prevent dew condensation, corrosion, static electricity, and powder solidification.
Chapter 9
Humidity Management by Field
| Applications | Main risks | Indicators and Information to View |
|---|---|---|
| Factories and research facilities | Quality variations, changes in test conditions | Relative humidity, absolute humidity, temperature, history |
| Warehouse/Storage | dew condensation, mold, moisture absorption, deterioration of packaging materials | Relative humidity, temperature, dew point, fluctuation history |
| Pharmaceuticals and Reagents | Deviation from storage conditions, impact on quality | temperature/humidity history, deviation records, calibration history |
| Food/raw materials | Mold, drying, moisture absorption, process variations | temperature/humidity, changes over time |
| Electronic components and precision equipment | Static electricity, moisture absorption, dew condensation, corrosion | Relative humidity, dew point, temperature change |
| Transportation/Logistics | temperature/humidity fluctuations during transport, deviation from conditions | temperature/humidity history, maximum and minimum values, deviation time |
Factories, research facilities, and environmental testing
Humidity control is necessary for stabilizing process conditions, repeatability test environments, and equipment maintenance. In drying process, painting, environmental testing, and electronic component manufacturing, precise control is often crucial.
Warehouse/storage environment
To prevent dew condensation, mold, deterioration of packaging materials, and moisture absorption of products, it is important to understand not only temperature/humidity levels but also their fluctuation history during long-term storage.
Pharmaceuticals and Reagents
Because deviations from storage conditions can affect quality control, continuous monitoring, recording, and the reliability of measurements are crucial.
Food/raw materials
High humidity can cause moisture absorption and mold growth, while low humidity can cause drying, which can affect the quality of the product.
Electronic components and precision equipment
Humidity control is implemented to address issues such as static electricity caused by low humidity, and dew condensation, corrosion, and moisture absorption caused by high humidity and temperature changes.
Transportation/Logistics
Even if properly managed within the warehouse, temperature/humidity inside the cargo compartment change during transportation due to factors such as outside temperature, door opening and closing, and loading conditions.
Therefore, we record temperature/humidity during transport as needed, so that we can check for changes or deviations over a certain period of time.
Chapter 10
Checkpoints for managing humidity in a factory
| Check items | Confirm |
|---|---|
| Management purpose | What do you want to manage, such as the indoor environment, process, storage, drying, and dew condensation prevention? |
| humidity index | Is relative humidity sufficient, or are absolute humidity and dew point temperature also necessary? |
| Measurement location | Where should we measure the representative value from: the interior, ducts, tanks, storage areas, etc.? |
| environmental conditions | Are there any influences from temperature range, dew condensation, wind, dirt, chemicals, etc.? |
| Recording and monitoring | Is current data sufficient, or do you also need history, alarms, and remote monitoring? |
| Calibration | To what extent should the reliability of measurements be demonstrated in quality assurance and audits? |
Chapter 11
How to choose a hygrometer and humidity control equipment
When choosing a hygrometer, don't just pick one that "measures humidity"; instead, determine the necessary specifications based on your management purpose and usage environment.
- What do you want to measure, such as relative humidity or dew point?
- Required measurement range and accuracy
- Where will it be installed? (Indoors, ducts, tanks, etc.)
- Are there temperature changes or dew condensation?
- How fast does the response time need to be?
- Is just display necessary, or is recording and monitoring also required?
- Is an output signal or communication required?
- Maintainability such as sensor replacement and calibration
Looking for temperature/humidity
Chino offers a lineup of temperature/humidity meters to suit various applications and installation methods.
Chapter 12
Why is calibration necessary for hygrometers?
Humidity sensors are affected by the usage environment and changes over time, so the measured values may change over time with prolonged use.
When reliability of measurement values is required for quality control, research and development, audits, etc., calibration, which involves checking the condition of the measuring instrument by comparing it to a standard, becomes important.
What iscalibration?
We compare the measurement value with a reference value to determine the extent of the difference.
What is the calibration cycle?
Instead of a fixed number of years, we will consider factors such as the usage environment, required accuracy, past results, and the impact of any deviations.
Which calibration method should I choose?
The appropriate calibration method varies depending on the required certification content and intended use.
See the differences between JCSS calibration, general calibration, and Chino calibration.
Chapter 13
Humidity control that Chino can support
Humidity control doesn't end with simply installing a hygrometer. Depending on the application, it may be necessary to record the measured values, monitor for anomalies, and verify the reliability of the measurements through calibration.
Measure
We use temperature/humidity gauges and various sensors to understand the conditions on site.
Record
Record temperature/humidity changes using a recorder or data logger.
Monitor
Monitoring systems and wireless devices are used to understand the status of locations remotely.
Calibration
The measured values are compared to a reference to confirm the reliability of the measurement.
I want to consult about humidity control.
Based on factors such as the items to be managed, installation location, temperature range, need for recording and monitoring, and calibration requirements, you can consider humidity control solutions tailored to your specific site.
I want to consult about humidity control.FAQ
Frequently Asked Questions about Humidity
What exactly is humidity?
This is an indicator that represents the state of water vapor contained in the air. When we simply say "humidity" in everyday life, it generally refers to relative humidity.
What does 50% humidity mean?
This represents the current state of water vapor as a percentage, with the saturation state at that temperature being 100%. It does not mean that 50% of the air is water vapor.
What does 100% humidity mean?
At that temperature, water vapor is saturated. If you continue to cool it while keeping the amount water vapor nearly constant, water vapor may dew condensation.
Why does humidity increase when the temperature drops?
When the amount water vapor is nearly the same, the relative humidity increases as the temperature decreases because the saturated water vapor pressure decreases.
What is the difference between relative humidity and absolute humidity?
Relative humidity is an indicator of the ratio to the saturation point at a given temperature, while absolute humidity is an indicator of the actual amount water vapor contained in the air.
What is the dew point temperature?
This is the temperature at which the relative humidity of air containing water vapor reaches 100% when cooled. It is an important indicator for preventing dew condensation.
Are humidity and moisture the same thing?
They are not the same. Humidity is mainly used to describe the state of water vapor in a gas, while moisture is used to describe the water contained in materials or products.
Where should I place the hygrometer?
The basic principle is to install the device in a location that is representative of the space you want to measure, and to avoid localized influences such as direct sunlight, heat sources, walls, strong winds, and dew condensation.
Is it sufficient to only consider relative humidity in a factory setting?
It depends on the application. Relative humidity is generally convenient for general environmental monitoring, while absolute humidity or dew point temperature may be more suitable for drying process or dew condensation prevention.
Does a hygrometer need to be calibrated?
When the reliability of measurement values is required for quality control or audits, it is important to regularly compare them with standards and check the condition of the measuring instruments.
Summary
Humidity can be understood through the relationship between temperature and water vapor.
The humidity we usually see as "humidity ○%" is generally relative humidity. Since relative humidity changes with temperature, it's important to understand its relationship to temperature rather than just looking at the humidity number alone.
Furthermore, depending on the purpose, not only relative humidity but also absolute humidity and dew point temperature are used. The purposes for managing humidity are also diverse, ranging from comfort in homes to quality, process, storage, transportation, and dew condensation /static electricity control in industry.
In industrial applications, it's crucial to consider not only "what to measure," but also "where to measure," "how to record," "how to monitor," and "how to guarantee the measured values" as a complete system.
References
Reference information
- Japan Meteorological Agency: "Temperature, Humidity"
- Ministry of Health, Labour and Welfare: "Regarding Building Environmental Hygiene Management Standards"
- CHINO Corporation "temperature/humidity Meter"
The information presented is based on publicly available data. Product specifications, calibration scope, and support conditions may change, so please check the latest product and service information before considering implementation.
