Guide to Calculating Industrial Dehumidifier Capacity (A-Z) with Real-World Examples

One of the most important questions when investing in a humidity control system is: "What capacity dehumidifier do I need?" Choosing the wrong capacity not only leads to waste but also directly affects product quality and operational efficiency.

The technical process to answer this question is to determine the Total Moisture Load – the total amount of moisture vapor infiltrating and generating within the controlled space. DeAir guides you through the 4 simple yet detailed steps below to accurately determine the capacity of your industrial dehumidifier.

Step 1: Define Design Conditions - The Calculation Foundation

Moisture load calculation begins by clearly defining 3 crucial environmental conditions, using the absolute humidity unit of grs/lb (grains/pound) because it does not change with temperature, ensuring accuracy:

• Space Volume (V): Room dimensions (Length x Width x Height).
• Required Condition (S): The absolute humidity (grs/lb) needed to be maintained inside the room.
• Outside Design Condition: The absolute humidity (grs/lb) of the outdoor air during the most humid time of the year.
• Humidity Difference (G): The difference between the outside humidity and the required humidity. This is the main driver of permeation load.

Step 2: Calculate Permeation Load Through Structure

This is the amount of moisture vapor that "seeps" through the walls, floor, and ceiling. The degree of moisture permeation depends on the quality and type of building materials. The most important factor to consider is the Vapor Barrier.

Important Note: If the humidity control space requires less than 50%RH, a continuous Vapor Barrier is mandatory to optimize dehumidifier capacity and long-term operating costs. Learn more about the role of the Vapor Barrier according to industry standards in reputable HVAC technical documents (ASHRAE).

Step 3: Calculate Internal and Infiltration Moisture Loads

These moisture sources originate internally or penetrate through uncontrolled openings. These are constantly changing moisture loads, making control complex.

Step 4: Convert Total Moisture Load to Machine Capacity

The Total Moisture Load is the sum of all moisture sources calculated in Step 2 and Step 3 (unit Grs/hr). The required dehumidifier capacity is determined based on the principle of Moisture Load Balance:

• Moisture removed by the machine per hour ≥ Total moisture infiltration and generation per hour.

The dehumidifier must have sufficient airflow (CFM) and dehumidification capability to maintain the required condition. You can refer to the Dehumidifier Capacity Calculation Checklist for more detailed guidance.

Real-World Example and Selection Suggestion

Hypothetical Scenario: A functional food production room needs to maintain 75 F/ 35%RH.

• Low Humidity Requirement (35%RH): A Desiccant Rotor technology machine is mandatory to achieve deep dry conditions.
• Permeation Load: Accounts for the highest proportion. A continuous anti-moisture system is needed to reduce the burden on the dehumidifier.

Strategic Selection Suggestion: Instead of choosing a high-capacity condensing unit, investing in a specialized Rotor series like Dezenno will ensure stable performance and achieve the required humidity. The machine chosen must have a certain safety factor (usually 10-20% capacity) to cope with days when outdoor humidity spikes.

Frequently Asked Questions (FAQ)