specific humidity vs relative humidity

When understanding the difference between specific humidity Vs relative humidity, it’s crucial that you first understand humidity. Put simply; humidity is the amount of water vapor in the air.

Specific humidity refers to the ratio of water vapor mass to the total mass of air and water vapor.

The relative humidity of air is the amount of moisture it contains compared to the maximum amount of moisture it can have at a specific temperature.

Standard Unit of Measurement

In specific humidity, water vapor mass is measured in grams. The standard volume measurement is in meters cubed. Therefore, specific humidity is expressed in grams per cubic meter (g/m3).

Since relative humidity is a ratio, it’s defined as a percentage. The relative humidity is often described as a percentage (%RH).

In planning tests for humidity, it is essential to choose test conditions that are suitable for the test.

This may not be easy since there are many different standards for testing humidity, and each standard comes with a set of required test conditions.

Fact: Humidity tends to change with temperature because, at lower temperatures, a smaller amount of water vapor leads to higher humidity than at higher temperatures.

Instrument of Measurement

humidity measurement

An instrument called a hygrometer can tell you the humidity of a place. A psychrometer is also used to measure humidity except for the dry and wet bulbs.

Using a psychrometer, the relative humidity of air can be determined by observing the difference in temperature readings taken with a dry-bulb thermometer and a wet-bulb thermometer.

The relative humidity is then calculated from these readings and air temperature. Therefore, the convergence of specific Vs relative humidity is in the measurement since the same instrument can be used to measure both.

How to Measure Humidity Locally

A sling psychrometer—a standard device used by meteorologists to measure relative humidity—is swung around to gauge the amount of water vapor in the air.

In HVAC systems, a humidistat measures the amount of moisture in the air and regulates the temperature to a desirable level to avoid humidity buildup.

It contains a switch, which can be set to power a range of electrical devices, including microwave ovens and humidifiers.

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How to Measure Humidity Globally

Global-scale humidity measurements are possible via remote sensing using satellites.

Sensitive to the concentration of water in the troposphere, between altitudes of 2.5 to 7.5 miles, these satellites are placed over the equator, where their orbits provide a constant observation time of each location on Earth.

global humidity measurement

Radiation-sensitive sensors on satellites measure water vapor. Water vapor absorbs and re-radiates radiation, which sensors on the satellites detect.

These satellites are predominately used in weather forecasts. They can also be used to monitor climatic conditions.

Fact: Humidity moderates the Earth's heat—keeping the planet hospitable to life, and without it, our lives would be much more complicated.

What Measurement Should I Use?

Part of understanding relative humidity Vs specific humidity is to know when to use what. In different contexts, different measurements are used for the humidity of the air.

The relative humidity of the surrounding air is a standard measurement typically used for weather prediction and climate study.

If you are interested in measuring temperature and humidity readings over a long period, specific humidity may be more suitable.

This measurement is used for drying food using airflow and blowers in a spray drying and blower application.

Specific humidity can also be used to prevent your furnace or water heater from icing over in rooms or areas much more relaxed than the typical temperature of the device.

Fact: At different temperatures, the relative humidity of a given air volume can be very different, even while the specific humidity remains nearly constant.

Importance of Specific and Relative Humidity

Now that you understand the basics of specific humidity Vs relative humidity, let’s dive into real-life uses and applications of both.

Applications of Specific Humidity

specific humidity applications

1. Rainfall

The amount of water vapor in the air affects how much rainfall there is. When water droplets in the atmosphere form around small particles, the result is clouded. After the energy balance in the atmosphere changes, clouds release rain.

High humidity means there is a lot of moisture in the air so rain showers will be more frequent and intense.

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Humidity, then, is a critical factor in determining how heavy a rain shower will be and how comfortable it is to walk around on a warm day.

2. Human Health

Because humidity affects thermal comfort, increases in humidity can make us feel colder than we would otherwise; humidity decreases can make us feel warmer than we would otherwise.

If the air is hot and humid, the body has difficulty making the most of its sweat glands because sweat has a more challenging time evaporating into the air.

This is of particular concern during the hot summer months when athletes and spectators need to stay well hydrated and get enough rest.

3. Animal Health

Humidity can affect animals similar to that in which it affects humans. For example, warm, damp conditions can make for dairy and beef cattle uncomfortable environments.

Animals living in such conditions have a more challenging time regulating their body temperatures.

They may eat less than usual, have trouble reproducing, and have higher mortality rates.

4. Water Vapour

Water vapor is the most abundant greenhouse gas in the atmosphere. Water vapor is a gas without which life on Earth would not be possible.

However, water vapor also acts as a greenhouse gas, and less energy is from the Sun.

Much of the Earth’s outgoing energy is trapped by greenhouse gases such as water vapor, which are added to it by the Earth’s oceans and vegetation.

Note: The recommended specific humidity at room temperature is keeping it less than 83 g/m3.

Applications of Relative Humidity

relative humidity applications

1. HVAC Systems

Air conditioners and other building automation systems that focus on human comfort need to be programmed for the correct relative humidity.

Measuring and controlling relative humidity helps maintain a comfortable environment in buildings and helps optimize the efficiency of air conditioning systems.

The relative humidity sensors measure the outside air and adjust the amount of water added to a building’s central heating or cooling system.

2. Pharmaceuticals

When products are too sensitive to moisture, they can be affected by humidity. These include pharmaceuticals, packaging materials, and research equipment.

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Because of this, humidity should be controlled to prevent changes that may render the product useless.

Controlled relative humidity and temperature are critical factors in the storage of many products, including medical pills, grains, and dry powders.

3. Building Materials

Suppose you were building an extension to your home and were laying a concrete subfloor before installing hardwood flooring.

In that case, damp concrete will inevitably cause problems if the flooring is applied before the concrete has dried sufficiently.

When relative humidity is too high, your floor can swell or blister—leaving you with no other choice but to replace it. High humidity can therefore cause damages to items such as building materials, causing costly repairs.

4. Storage Facilities

Monitoring relative humidity helps prevent excess moisture near the final product. This usually means keeping the relative humidity below a certain level.

One example is a chocolate bar. If the relative humidity level in a storage facility rises above a certain point and remains above that point for an extended period, it can cause chocolates to bloom.

This is when a thin, shiny coating of moisture may form on the surface of chocolate during humid weather.

Note: When it comes to how much relative humidity should be in your home, there's a range the American Society of Heating and Air Conditioning Engineers recommends: 30%-50%.

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Final Thought

Understanding specific humidity vs. relative humidity is crucial since humidity plays an essential role in our daily lives.

For example, we say that the humidity bothers us more than the heat.

We’re saying that when there is the higher relative humidity in the air, it feels hotter and thicker and therefore less comfortable.

One of the environmental protection agencies’ concerns is indoor air quality.

Indoor environments that store food, technical equipment like computers or data centers, or your home can be affected negatively by levels of both specific or relative humidity.

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