How to Calculate Dew Point: Formula and Dew Point Chart

What happens when air cools down and moisture starts to form? This is where the dew point comes in! Understanding the dew point and using a dew point chart is essential for controlling moisture in systems like air compressors. It ensures equipment runs smoothly, prevents corrosion, and improves product quality.What is Dew Point?The dew point is the temperature at which air becomes saturated with moisture, causing water vapor to condense into liquid. It is a critical parameter in many industrial and environmental contexts, especially in air compressor systems, where it is closely monitored to ensure optimal performance and prevent issues caused by excess moisture.Importance of Dew Point in Air Compressor SystemsIn air compressor systems, compressed air is often used in manufacturing processes, pneumatic tools, and other applications requiring dry air. However, as air is compressed, its moisture content becomes more concentrated, potentially leading to condensation. Managing the dew point is crucial for several reasons:1. Preventing Equipment DamageCondensed water can cause corrosion in pipelines and damage sensitive equipment, including valves and actuators.Accumulated moisture in tools can reduce their lifespan and performance.2. Ensuring Product QualityMany industrial processes, such as painting or pharmaceuticals, require extremely dry air. High dew points can lead to defects, such as bubbles in coatings or contamination in medical products.3. Avoiding Freezing in Cold EnvironmentsIn systems exposed to low temperatures, moisture can freeze if the dew point is not adequately controlled, leading to blockages in pipelines.4. Reducing Maintenance CostsControlling the dew point minimizes the need for frequent maintenance and repairs caused by moisture-induced problems.How Dew Point is Controlled in Air CompressorsTo maintain a specific dew point, air compressor systems employ various methods and equipment:DryersRefrigerated Dryers: Suitable for achieving a dew point between 2°C and 7°C. Common in general-purpose applications.Desiccant Dryers: Used for achieving lower dew points (as low as -70°C), essential for processes requiring extremely dry air.Moisture SeparatorsInstalled to remove liquid water from compressed air before it reaches downstream equipment.Filtration SystemsFilters remove fine moisture particles and oil, further drying the air.Dew Point MonitorsSensors continuously measure and display the dew point, allowing for real-time adjustments.How to Calculating the Dew Point1. Measure the Relative Humidity and TemperatureRelative Humidity (RH): Measure the percentage of water vapor in the air relative to the maximum amount the air can hold at a given temperature.Temperature (T): Measure the air temperature in degrees Celsius (°C) or Fahrenheit (°F).2. Use a Dew Point Calculator or FormulaThere are two common approaches:A. Dew Point Approximation FormulaHere is a table showing the calculated dew point temperatures (°C) for air temperatures ranging from -20°C to 30°C and relative humidity levels from 30% to 90%.Air Temp (°C)RH 30%RH 40%RH 50%RH 60%RH 70%RH 80%RH 90%-20-29.4-26.7-24.5-22.7-21.2-19.9-18.7-15-23.0-20.2-18.0-16.2-14.7-13.3-12.1-10-17.5-14.8-12.5-10.7-9.2-7.8-6.5-5-12.8-10.0-7.7-5.9-4.4-2.9-1.60-8.5-5.7-3.4-1.50.01.52.95-4.7-2.00.32.23.85.26.610-1.21.63.95.87.38.810.1152.04.97.18.910.511.913.2205.28.110.312.113.715.216.5258.311.213.415.216.818.319.63011.314.216.518.319.921.422.7In similar way, we can caculate dew point when temperature is measured by Fahrenheit.Here is the dew point chart for temperatures ranging from 20°F to 120°F (in 10°F increments) and relative humidity levels from 30% to 90% (in 5% increments):Relative Humidity20°F30°F40°F50°F60°F70°F80°F90°F100°F110°F120°F90%18°F28°F37°F47°F57°F67°F77°F87°F97°F107°F117°F85%17°F26°F36°F45°F55°F65°F75°F84°F95°F105°F115°F80%16°F25°F34°F44°F54°F63°F73°F82°F93°F102°F110°F75%15°F24°F33°F42°F52°F62°F71°F80°F91°F100°F108°F70%13°F22°F31°F40°F50°F60°F69°F78°F88°F96°F105°F65%12°F20°F29°F38°F47°F57°F66°F76°F85°F93°F103°F60%11°F19°F27°F36°F45°F55°F64°F73°F83°F91°F101°F55%9°F17°F25°F34°F43°F53°F61°F70°F77°F86°F94°F50%6°F15°F23°F31°F40°F49°F58°F67°F77°F86°F94°F45%4°F13°F21°F29°F37°F47°F56°F64°F73°F82°F91°F40%1°F11°F18°F26°F35°F43°F51°F61°F70°F78°F87°F35%-2°F8°F16°F23°F31°F40°F48°F56°F65°F74°F83°F30%-6°F4°F13°F20°F28°F36°F44°F52°F61°F70°F77°FB. Use a Psychrometric ChartLocate the dry bulb temperature (ambient temperature) on the horizontal axis.Find the relative humidity curve that matches the measured RH. 3.Trace down to find the dew point temperature.3. Adjust for Compressed Air ConditionsIn an air compressor system, air is compressed, increasing the dew point due to higher pressure. Use the formula:Where  is the dew point increase due to compression, often provided in system specifications.4. Use Dew Point Sensors (Optional)Advanced systems often include a dew point sensor or hygrometer that measures the dew point directly under specific pressure conditions.5. Correct for System-Specific VariablesIf your system includes a dryer, the dew point will be lower.Use the corrected dew point based on the type of dryer:Refrigerated dryer: Dew point is usually 2°C–10°C (35°F–50°F).Desiccant dryer: Dew point can be as low as -40°C (-40°F).By following these steps or using online calculators, you can calculate or estimate the dew point in your air compressor system for efficient operation and proper maintenance.