How to Size Your Dehumidifier
- Summer Neal
- 7 hours ago
- 3 min read
A Technical Guide for Engineers and System Designers
Correctly sizing an industrial dehumidifier is essential to achieving precise environmental control, ensuring process integrity, and protecting sensitive materials or equipment. At Innovative Air Technologies, we specialize in custom desiccant dehumidification systems—so we know that one size definitely does not fit all.
Whether you're specifying a system for pharmaceutical manufacturing, food processing, defense contracting, military storage, or refrigerated/freezer facilities, this guide will walk you through the key engineering considerations to properly size a desiccant dehumidifier for your application.
📏 Step 1: Define the Moisture Load
The foundation of any dehumidification system design is a detailed moisture load analysis—quantifying the total amount of water vapor removal required based on the moisture introduced into the space over time.
Key sources of moisture gain:
Ventilation/infiltration air (outside air introduced through HVAC or envelope leakage)
Internal processes (steam, open water surfaces, or moisture-releasing equipment)
Occupants or product off-gassing
Moisture migration through building materials
The moisture load is typically calculated in grains per pound of dry air (gr/lb) or pounds of water per hour (lb/hr).
Example formula (simplified):
W˙=4.5×CFM×(ωin−ωout)
Where:
W˙ = moisture removal rate (lb/hr)
4.5 = convenience factor (based on air density and minutes per hour)
CFM = airflow rate
ωin and ωout = inlet and outlet humidity ratios (gr/lb / lb dry air)
🌡️ Step 2: Establish Design Conditions
Engineers must define indoor and outdoor psychrometric design points, including:
Inlet air conditions (temperature and RH or dew point)
Desired supply air or space conditions
Airflow (CFM)
Operating hours and cycles
For example:
Outdoor air = 90°F DB / 75°F WB (~130 gr/lb)
Desired process air = 70°F DB / 35% RH (~47 gr/lb)
🔁 Step 3: Determine Airflow and Process Configuration
Sizing a desiccant dehumidifier also involves understanding the air handling strategy:
Recirculation vs. once-through systems
Preconditioning using cooling coils or heat exchangers
Return air mixing (for energy savings)
The airflow rate (CFM) directly impacts sizing and is typically determined by:
Volume of space and desired ACH (air changes per hour)
Process exhaust and makeup requirements
Product drying or environmental stabilization needs
🔄 Step 4: Consider the Desiccant System Configuration
There are several system configurations in desiccant dehumidifiers that affect performance:
Active desiccant systems: Use external heat (electric, gas, steam) to regenerate the desiccant rotor
Passive systems: Use waste heat or ambient air (less effective for deep drying)
Each IAT dehumidifier uses a rotary desiccant wheel with silica gel, engineered for continuous moisture adsorption and regeneration.
When selecting a unit, review:
Process airflow vs. reactivation airflow
Energy source availability (electric, gas, hot water, steam)
Reactivation temperature constraints
Latent load vs. sensible load split
📊 Step 5: Perform Load Matching and Select Equipment
Once you've defined your moisture load and airflows, select a unit based on:
Moisture removal capacity (lb/hr) at your design conditions
Supply air dew point or temperature and RH achievable
CFM range
External static pressure capabilities
Integration with pre/post cooling, heating, or filtration stages
At IAT, our product lines cover a wide range:
Compact Series: 75–600 CFM
Rotor Series: 500–30,000+ CFM
IDP Series: Integrated with cooling coils, electric or gas reactivation
Custom configurations and performance modeling are available based on your specifications.
⚙️ Step 6: Factor in Environmental and Material Considerations
For certain applications, additional factors influence unit selection:
Corrosive environments (choose stainless steel or coated aluminum)
Outdoor installation (weatherized enclosures)
High altitude or low-pressure environments
Cleanroom-rated construction
Why Sizing Matters
Under-sizing leads to:
Inability to reach dew point targets
Excess moisture-related damage or quality control issues
Reduced system lifespan from continuous overload
Over-sizing leads to:
Higher capital and energy costs
Inconsistent control from short-cycling
Potential RH swings if airflow is mismatched
Correct sizing ensures long-term energy efficiency, performance stability, and product/process protection.
📞 Need Help? Let’s Engineer It Together.
Our team of application engineers is available to assist with load calculations, psychrometric modeling, and equipment selection. Whether you need a standalone Compact Series unit or a fully integrated IDP system, Innovative Air Technologies is here to help you engineer moisture out of your critical environment.