Dehumidifier Sizing Calculator

A dehumidifier sizing calculator helps determine the right size of a dehumidifier for a specific space. It calculates how much moisture needs to be removed to achieve the desired humidity level. This guide explains the purpose of a dehumidifier sizing calculator, its workings, and provides an example for clarity.

Purpose and Functionality

The main purpose of a dehumidifier sizing calculator is to ensure that the chosen dehumidifier can effectively remove excess moisture from the air in a given space. By using the calculator, you can find out how much water vapor needs to be removed to maintain a comfortable and healthy humidity level.

Steps to Calculate Dehumidifier Size

To properly size a dehumidifier, follow these steps:

1. Gather Required Inputs:
   • Volume of the Room (V): Measure the total volume of the space in cubic meters (m³).
   • Current Relative Humidity (RH1): Note the current humidity level in the room as a percentage (%).
   • Desired Relative Humidity (RH2): Set the target humidity level as a percentage (%).
   • Temperature (T): Record the room temperature in degrees Celsius (°C).
2. Calculate the Required Dehumidification Capacity:
   • Step 1: Calculate Saturation Vapor Pressure (Pws): Use the Magnus-Tetens formula to find the saturation vapor pressure at the given temperature TTT:rCopy codePws = 0.61094 × e^(17.625 × T / (T + 243.04)) This formula gives the saturation vapor pressure (Pws) in kilopascals (kPa).
   • Step 2: Calculate Actual Vapor Pressure (Pw1 and Pw2): For current and desired humidity levels, calculate the actual vapor pressures:makefileCopy codePw1 = RH1 / 100 × Pws Pw2 = RH2 / 100 × Pws
   • Step 3: Convert Vapor Pressure to Absolute Humidity (AH1 and AH2): Using the ideal gas law, convert the vapor pressures to absolute humidity:makefileCopy codeAH = Pw × 1000 / (R × (T + 273.15)) Here, R is the specific gas constant for water vapor (approximately 461.5 J/kg/K).
   • Step 4: Calculate the Amount of Water to Remove per Hour: Find out how much water needs to be removed per hour:makefileCopy codeWater_to_Remove = (AH1 - AH2) × V This gives the amount of water in kilograms (kg) that needs to be removed per hour.
3. Size the Dehumidifier:
   • Convert the hourly requirement to daily requirement: Since dehumidifiers are rated in liters per day (L/day), convert the hourly water removal rate to a daily rate:bashCopy codeL/day = kg/h × 24 × 1.0 (Assuming the density of water is approximately 1 kg/L).

Example Calculation

Let’s go through an example to make this clearer:

• Volume of the Room (V): 50 m³
• Current Humidity (RH1): 70%
• Desired Humidity (RH2): 50%
• Temperature (T): 22°C

Step-by-Step Calculation:

1. Calculate Pws at 22°C:makefileCopy codePws = 0.61094 × e^(17.625 × 22 / (22 + 243.04)) = 2.64 kPa
2. Calculate Pw1 and Pw2:makefileCopy codePw1 = 70 / 100 × 2.64 = 1.848 kPa Pw2 = 50 / 100 × 2.64 = 1.32 kPa
3. Convert to Absolute Humidity (AH1 and AH2):bashCopy codeAH1 = 1.848 × 1000 / (461.5 × (22 + 273.15)) = 0.0143 kg/m³ AH2 = 1.32 × 1000 / (461.5 × (22 + 273.15)) = 0.0102 kg/m³
4. Calculate Water to Remove per Hour:bashCopy codeWater_to_Remove = (0.0143 - 0.0102) × 50 = 0.205 kg/h
5. Convert to Daily Requirement:bashCopy codeL/day = 0.205 × 24 × 1.0 = 4.92 L/day

Relevant Information Table

Conclusion

Using a dehumidifier sizing calculator helps in selecting the right dehumidifier for your space. By calculating the amount of moisture that needs to be removed, you can ensure that the dehumidifier will effectively maintain the desired humidity level, leading to a more comfortable and healthy environment. This method provides a straightforward way to match your needs with the capabilities of various dehumidifiers.