Humidity indicates the amount of water or water vapor present in the air. Relative humidity represents the maximum percentage of water vapor that air can contain at a specific temperature. The technical term "dew point" indicates the temperature at which the air is saturated with water vapor, after which the latter condenses into dew. Humidity is one of the climatic aspects that has significant effects on human health and on the objects contained in our homes, but the most important thing is that it determines which species of plants and animals can live in specific environments and when it must rain, snow or let the fog fall. Measuring and calculating the humidity level without having the right equipment is a very difficult process; however, there are different methods to measure relative humidity by building a simple hygrometer with the objects normally present in our homes.
Steps
Method 1 of 3: Measure Humidity with a Hygrometer
Step 1. Choose or build a hygrometer
Decide what type of hygrometer to use, based on the purpose for which you need to measure humidity. For example, if you are simply curious about the percentage of humidity in your home, you can use a simple wet bulb thermometer. If, on the other hand, you need to know precisely the humidity level of a particular environment for conservation or scientific reasons, buying a real hygrometer might be the best thing to do. Ask yourself the following questions:
- Does it have to withstand extreme temperatures (both hot and cold)?
- Does it have to be powered by mains or battery?
- Should it have a notification system to alert you when the humidity percentage rises or falls beyond a certain value?
- Is it simple to calibrate?
- It is expensive? Does it require a lot of maintenance?
- Is it easy to use and understand?
Step 2. Select a representative area to take measurements
After choosing the right hygrometer for your needs, the second step is to choose the ideal place to install it. The measurement of humidity varies according to the ambient temperature, so it is a good idea to choose a place where the temperature is as stable as possible. Install the hygrometer in a place where the temperature is constant and similar to the rest of the house or surroundings.
Avoid installing it near doors, windows, heating or cooling systems, and humidifiers
Step 3. Wait for the hygrometer to adjust to the new environment
In order to make accurate measurements, you must leave the instrument in the new environment for a few hours, so that it can reach the same temperature. By taking a measurement immediately after installing it, you will simply get an inaccurate value.
Step 4. Take moisture measurements regularly
If your goal is to determine if there are fluctuations in humidity in your home, take the measurements every few hours or days. In this way you will have the possibility to graphically represent the trend of the humidity rate over time.
Note that as the air temperature rises, its ability to store moisture also increases. The higher the temperature, the higher the relative humidity
Step 5. If necessary, calibrate the hygrometer
Normally, a hygrometer needs to be recalibrated once a year. The calibration process requires you to read the measured value from the instrument and compare it with correct reference measurements, and then make the appropriate adjustments so that both match perfectly. Calibration is a very important act in the case of a research project or in the scientific field, a situation in which it is good to have the instrument calibrated by an experienced professional.
If you are using a "homemade" hygrometer, you can install it outdoors and compare the humidity value it detects with that reported by the daily weather report
Method 2 of 3: Calculate Relative Humidity
Step 1. Determine the level of water vapor contained in atmospheric air
This datum, expressed as the ratio between the grams of water vapor and the mass of dry air expressed in kilograms, is called the mixing ratio; it can be obtained directly online and is measured using a microwave radiometer.
The measurement of the amount of water vapor present in the air cannot be carried out directly at home with handcrafted tools
Step 2. Determine the amount of water that can be retained by the air
This is where the air becomes saturated with moisture and is called the saturated mix ratio. The amount of water vapor that can be contained in the air depends on the temperature of the air itself. There are tables on the web that indicate the amount of water vapor that can be contained in the air at specific temperatures.
The higher the temperature, the greater the amount of vapor that can be present in the air
Step 3. Divide the mixing ratio by the saturated mixing ratio
With this simple calculation the relative humidity rate is obtained; therefore, if currently the air can store 20 g of water for every kilogram of dry air compared to a maximum of 40 g of water per kilogram of dry air, it means that the relative humidity is equal to 20/40: i.e. 50 %.
Method 3 of 3: Measure the Dew Point Experimentally
Step 1. Fill a metal can with water
You should use a shiny metal or aluminum can so that it can reflect sunlight and heat. For this specific experiment, metal is the best material to use. Fill the can 2/3 of its total capacity, leaving enough space to add ice cubes.
Step 2. Add ice, then continue stirring the mixture until condensation forms on the outside of the can
Gradually add the ice cubes and, as you do this, keep stirring the water mixture using a thermometer. This way, the surface of the can will maintain the same temperature as the water.
Continue adding ice, a few cubes at a time. After each addition, stir carefully until the cubes have dissolved. Continue chilling the mixture with ice until condensation forms on the can
Step 3. Measure the temperature using a thermometer
This is the value that indicates the dew point temperature. The dew point is the temperature at which water vapor completely saturates the air and begins to condense.
The can and cold water represent a simplified form of the condensing hygrometer. The latter is a device equipped with electronic sensors with which meteorologists measure the dew point. The higher the dew point temperature, the greater the sensation of humidity in the air
Warnings
- The higher the humidity level of the external environment, the more difficult it is for the human body to try to lower the internal temperature. Prolonged exposure to an environment with very high humidity can cause increased blood flow to the skin in an attempt to disperse the excessive heat. As a result, the blood supply to the muscles, brain and all internal organs will be reduced. This process strains the body more quickly than in climatic conditions where humidity is lower. Meteorologists always warn of possible health problems caused by the hottest and wettest days, advising the categories most at risk to stay indoors.
- If you have a large number of electronic devices, pay close attention to the specific humidity range in which they can operate correctly and be used without any problems. If the humidity level is excessively low, static electricity discharges could damage the electronic equipment; on the contrary, if the humidity is very high, a short circuit could occur.
