How to Calculate Humidity and Temperature in a Humidification Plant Using Hygrometers (Step-by-Step Guide)🌡️

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Mastering Humidification: Accurate Calculations, Methods & Devices Explained for All Industries.

Welcome to Insight Control System Blog!
  • Understanding humidity control is essential for HVAC engineers, industrial operators, and even smart homeowners around the world. In this guide, you'll learn how to calculate and measure humidity using both manual and automatic methods. From digital hygrometers to sling psychrometers, we’ll walk you through step-by-step processes and real-world applications.
  • Whether you're working in a textile plant, laboratory, smart home, or industrial setting, this article is crafted to boost your knowledge and confidence. Let’s dive into the world of humidification calculations and discover the tools that make it all possible!

Humidity and Temperature Measuring Instruments
How to Calculate Humidity and Temperature in a Humidification Plant Using Hygrometers

What Is Humidity?

  • Humidity control plays a critical role in HVAC systems, industrial manufacturing, and environmental monitoring. Accurate measurement of temperature and moisture content is essential for maintaining product quality, energy efficiency, and indoor comfort.
  • Humidity in air can be measured using hygrometers and psychrometers, which determine moisture levels based on dry-bulb and wet-bulb temperature differences.
  • Humidity refers to the presence of water vapor in the air, which plays a crucial role in air quality, comfort, and industrial processes.
Three primary measurements of humidity are widely employed:
  1. Absolute humidity 
  2. Relative humidity
  3. Specific humidity
  • Relative Humidity is the amount of water vapor in a given volume and temperature of air compared with the maximum amount of water vapor that volume of air can hold at that temperature (saturation).
  • At a constant air volume, the capacity to hold water vapor increases with rising temperature. This is a key principle in humidity control.
Humidity and Temperature Measuring Instruments
Relative Humidity is the amount of water vapor
  • 1 cubic foot is the most common measurement of volume. 
  • Amount of water vapor is expressed in grains.
  • 1 cubic foot of air at 70ºF holds 8.10 grains of water vapor.
  • 1 cubic foot of air at 0ºF holds 0.48 grains of water vapor.
  • If 1 cubic foot of air at 70ºF is holding 8.10 grains of water vapor, then it is saturated and is at 100% relative humidity.
  • If 1 cubic foot of air at 70ºF is holding 4.05 grains of water vapor, then it is at 50% relative humidity.
  • If 1 cubic foot of air at 0ºF is holding 0.48 grains of water vapor (saturated) and is then heated to 70ºF, the grains of water vapor remain constant and the relative humidity is 6%.

Importance of Humidity in Industrial & Commercial Settings

Proper humidity control ensures:
  • Product quality in textile and paper industries,
  • Comfortable indoor environments,
  • Accurate scientific measurements,
  • Efficiency in HVAC and agricultural operations,
  • Maintaining the correct relative humidity helps avoid mold, damage to materials, and ensures optimal working conditions.

Humidity and Temperature Measuring Instruments:

There are various methods for calculating RH (relative humidity) and temperature in humidification plants. Basically, two types are used. Options include Manual and Automatic modes.

🔻Automatic Mode:

To measure humidity automatically, you need a digital hygrometer or a humidity sensor that provides continuous monitoring without manual operation. 
These devices use electronic sensors to measure humidity and display real-time data.

Digital Hygrometer

  • Mount the digital hygrometer on a wall or place it in your preferred location. 
  • Turn it on whether it’s battery-powered or plug-in and begin real-time monitoring effortlessly.
  • It will automatically measure and display the relative humidity (RH%).
  • Some models store humidity data for trend analysis.
Humidity and Temperature Measuring Instruments
Digital Hygrometer

Use for: Homes, offices, greenhouses, museums, and general indoor monitoring.

Humidity Sensor

  • Install a humidity sensor in the desired area.
  • Connect it to a Programmable Logic Controller (PLC) or Thermostat.
  • The sensor will automatically send humidity and temperature readings to the Programmable Logic Controller.
Humidity and Temperature Measuring Instruments
Humidity Sensor

Use for: Industrial applications, smart homes, HVAC systems, and weather stations.

Smart Humidity Monitoring System

  • Install a smart hygrometer (Wi-Fi or Bluetooth-enabled).
  • Connect it to a mobile app for real-time humidity monitoring.
  • Set automatic alerts when humidity reaches critical levels.
  • Some models integrate with smart home systems (Alexa, Google Home) to control humidity levels.
Humidity and Temperature Measuring Instruments
Smart Humidity Monitoring System

Use for: Remote monitoring of humidity in homes, warehouses, and critical environments.

🔻Manual Mode:

Wall-Mounted Hygrometer

  • A wall-mounted hygrometer is a device used to measure and display the humidity levels in a room or enclosed space. 
  • It is designed to be fixed on a wall for continuous monitoring of humidity without manual operation.
  • There are two thermometers. One thermometer is covered with a tight-fitting muslin sock and is kept wet, preferably with distilled water. 
  • The other is a dry bulb thermometer, which is directly exposed to the atmosphere.
Humidity and Temperature Measuring Instruments
Wall Mounted Hygrometers

✅ Advantages:
Easy to read (digital or dial display).
No manual operation required.
Can provide continuous monitoring of humidity levels indoors.
No need for manual operation like a sling hygrometer.

❌ Disadvantages:
Less portable (fixed in one place).
May require calibration for accurate readings.

👉Use for: Home and office humidity monitoring, Museums and archives, Greenhouses and indoor gardening, Industrial environments, Textile Industry,

Whirling Hygrometer (Sling Psychrometer)

  • A whirling hygrometer, also known as a sling psychrometer is made out of two thermometers mounted on a frame which rotates around a handle, so it can be whirled in the air by hand. 
  • this a device used to measure relative humidity and dew point temperature in the air. 
  • It consists of two thermometers:
  • Dry bulb thermometer (measures air temperature), 
  • Wet bulb thermometer (measures temperature with a water-moistened wick),
  • One thermometer is covered with a tight-fitting muslin sock which is kept wet by preferably with distilled water.
  • This type of thermometer is known as the wet-bulb thermometer. 
  • The other is the dry bulb thermometer and exposed to the atmosphere directly.
Sling Psychrometer
Whirling Hygrometer

✅ Advantages:
More accurate for fieldwork and scientific measurements.
Does not require batteries or electricity.
Portable and easy to use in outdoor environments.

❌ Disadvantages:
Requires manual effort to whirl.
Takes time to get readings.
Needs water to keep the wick moist.

👉Use for: Meteorology Sector, Laboratory experiments, Heating Ventilation and Air Conditioning system, Industrial and agricultural applications, Textile Industries, 

How psychrometer works?

  • The psychrometer is whirled to let air past the bulbs which in turn makes water evaporate from the muslin cloth, This in turn cools down the wet bulb temperature.
  • The amount of cooling that occurs dependent on the amount of relative humidity. With high relative humidity the wet bulb will cool less than in dryer air where the water in the muslin will evaporate faster. 
  • The dry bulb indicates the temperature of the air. 
  • The wet bulb helps determine the relative humidity.
  • With air less than 100 per cent relative humidity, the wet bulb will display a lower temperature than the dry bulb and is known as wet-bulb depression.
  • Use a psychrometric chart or online humidity calculator to convert the wet-bulb depression into relative humidity (%), ensuring precise environmental measurements.
  • The relative humidity can be determined by correlating the readings with those on a simple slide rule, which is supplied with each instrument.

Steps to Use a Whirling Hygrometer

Humidity and Temperature Measuring Instruments
Steps to Use a Whirling Hygrometer

Step by Step Process

  • Ensure both thermometers are clean and intact.
  • Fill the wet-bulb reservoir with distilled water to ensure accurate and contamination-free readings.
  • Check that the wick covers the bulb of the wet thermometer fully and is saturated with water.
  • Hold the handle and whirl the hygrometer in the air for at least 30 seconds to 1 minute.
  • Stop and check the wet bulb temperature. If it is still decreasing, continue whirling until it stabilizes.
  • Once the wet bulb temperature stops changing, quickly record or read the both thermometer readings:
  • Dry bulb temperature (T₁), normal air temperature,
  • Wet bulb temperature (T₂), lower due to evaporation cooling,
  • Find the difference between the dry bulb and wet bulb temperatures (T₁ - T₂).
  • Use a psychrometric chart or humidity table to determine the relative humidity (%) based on T₁ and (T₁ - T₂).
Note:
Use the psychrometric chart to find the dew point (the temperature at which air becomes saturated and condensation begins).

Humidification Formula and Calculation

Formula to Calculate Relative Humidity (%)✏️

Note: This formula is only applicable for using the Fahrenheit (°F) hygrometer.

Step 1: Subtract Wet Bulb from Dry Bulb → (Dry - Wet)
Step 2: Divide the Result by Dry Bulb → (Dry - Wet) ÷ Dry
Step 3: Multiply by 300 → [(Dry - Wet) ÷ Dry] × 300
Step 4: Subtract 98 → Final Result = Step 3 - 98

Example:  
Dry = 98°F, Wet = 88°F  
(98 - 88) ÷ 98 × 300 - 98 = 67% RH
✅ Final Answer: 67% Relative Humidity.
  • This simplified formula provides an approximate relative humidity value. For precise calculations, engineers use psychrometric charts or digital calculators.

Temperature Converting (°C - °F) and (°F - °C)🌡️

Humidification Formula and Calculation
Temperature Converting Formula

Fahrenheit to Celsius Conversion Formula

To convert temperature from Fahrenheit (°F) to Celsius (°C), use the following formula:
Celsius (°C) = (Fahrenheit (°F) - 32) ÷ 1.8

Example:
Let's convert 98°F to Celsius:
Step 1: 98 - 32 = 66  
Step 2: 66 ÷ 1.8 = 36.66°C  
Step 3: Rounded result = 36°C
✅ Final Answer: 98°F = 36°C

Fahrenheit to Celsius Conversion (Alternate Formula)

Convert temperature from Fahrenheit (°F) to Celsius (°C) using this alternate form of the formula:
Celsius (°C) = (5 ÷ 9) × (Fahrenheit - 32)
Or: Celsius (°C) = 0.555 × (Fahrenheit - 32) (approx.)

Example: Convert 98°F to Celsius
Step 1: 5 ÷ 9 = 0.555 (approx.)
Step 2: 98 - 32 = 66
Step 3: 0.555 × 66 = 36.63°C
✅ Final Answer: 98°F = 36.63°C

Celsius to Fahrenheit Conversion Formula

To convert temperature from Celsius (°C) to Fahrenheit (°F), use the following formula:
Fahrenheit (°F) = (Celsius (°C) × 1.8) + 32

Example: Convert 36°C to Fahrenheit
Step 1: 36°C × 1.8 = 64.8
Step 2: 64.8 + 32 = 98.4°F
Step 3: Rounded = 98°F
✅ Final Answer: 36°C = 98°F

Tips for Accurate Readings:

  • Ensure the wick is clean and fully moist.
  • Whirl consistently at a steady pace.
  • Take readings away from direct sunlight or heat sources.
  • Use a psychrometric chart or an online calculator for precise humidity calculations.

Industrial Applications of Humidity Control

  • Textile industry (Prevent fiber breakage)
  • Pharmaceutical industry (Maintain product stability)
  • Food processing (Prevent spoilage)
  • Electronics manufacturing (Reduce static electricity)
  • Museums & archives (Protect artifacts)

Conclusion:

Whether you're an HVAC expert, industrial engineer, or curious student, mastering humidity calculations is vital for environmental control. With tools like digital hygrometers, manual psychrometers, and smart sensors, you can efficiently measure and manage humidity across various settings.

FAQ (Frequently Asked Questions)

1. What is a hygrometer used for?
A hygrometer measures the moisture content (humidity) in the air.

2. What is the difference between dry bulb and wet bulb temperature?
Dry bulb measures normal air temperature, while wet bulb measures temperature after evaporative cooling.

3. Why is humidity important in HVAC systems?
Humidity affects comfort, indoor air quality, and energy efficiency.

About the Author – Insight Control System

Insight Control System provides technical education and practical guidance in the fields of Building Automation Systems (BAS), HVAC controls, PLC programming, sensors, and industrial automation. The content published on this platform is based on field experience, technical documentation analysis, and real-world system applications.
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