Quick answer: Select a commercial dehumidifier in nine steps. (1) Define what you control: RH, dew point, material moisture or a quality outcome. (2) Calculate the moisture load from ventilation, infiltration, people, processes and products. (3) Set the design operating condition, meaning the air temperature and RH entering the unit at the demanding period. (4) Choose refrigerant or desiccant. (5) Choose the format: portable, floor, ceiling or ducted. (6) Set the unit count from capacity and air distribution. (7) Plan installation: power, drainage, ducts, access. (8) Plan controls and monitoring. (9) Agree acceptance tests. Ask suppliers for capacity at your condition, not just the catalogue rating.
Quick answer
- Target → load → design condition → technology → format → count → installation → controls → acceptance.
- Capacity at your inlet condition decides the selection.
- Floor area alone never sizes a commercial unit.
Step 1: define what you control
| Objective | Use when | Example |
|---|---|---|
| RH at a stated temperature | Materials, comfort, storage | Warehouse at 50 % RH, 20 °C |
| Dew point | Condensation on cold surfaces | Electrical cabinet, cold store dock |
| Material moisture | Drying | Water-damaged structure, slab |
| Biological or quality outcome | Mould, disease, shelf life | Greenhouse crops, food storage |
A space can hold 50 % RH and still condense on a chilled surface. Choose the variable that matches the risk; see dehumidifier settings for mould prevention.
Step 2: calculate the moisture load
Worked example (illustrative): a warehouse brings in 2,000 m³/h of outdoor air at 25 °C / 70 % RH (13.9 g/kg); target 20 °C / 60 % RH (8.7 g/kg).
- Excess water per kg of air: 5.2 g.
- Air mass: about 2,400 kg/h → about 12.4 kg/h ≈ 300 kg/day, before internal sources.
Size for the demanding period, not the average, and check pull-down separately. See commercial dehumidifier sizing.
Step 3: set the design operating condition
Capacity depends on inlet temperature and RH. Ratings are at test conditions (for example 30 °C / 80 % RH or 27 °C / 60 % RH, depending on market) that are often warmer and wetter than your space. Request capacity at your condition; see what a daily removal rating means.
Step 4: refrigerant or desiccant
| Condition | Usual route |
|---|---|
| Warm, moderate RH target | Refrigerant |
| Cold space, or dew point below about 5 °C | Desiccant |
| Warm, high load, very low dew point | Refrigerant + desiccant |
Step 5: choose the format
| Format | Suits |
|---|---|
| Portable | Temporary, restoration, small spaces |
| Floor-standing industrial | Warehouses, workshops |
| Ceiling-mounted | Floor space limited; greenhouses, food plants |
| Ducted | Even distribution; plant rooms; pools |
See commercial portable dehumidifiers and ceiling dehumidifiers.
Step 6: unit count from capacity and distribution
N = load ÷ capacity at the design condition, rounded up, then checked for coverage and redundancy. See large commercial dehumidifiers.
Step 7: installation
Power (voltage, phases, kW), drainage (gravity or pump; see condensate pump planning), ducts, mounting, service clearances.
Step 8: controls and monitoring
Sensor location, setpoint and deadband, staging, BMS interface, alarms (high humidity, drain, faults).
Step 9: acceptance and verification
Agree the target, measurement points, period and tolerance; trend for several days in the demanding season; record a baseline for maintenance (see the maintenance checklist).
Information to prepare
Space and use, target, moisture sources, ventilation, temperature range, preferred format, power, drainage, controls, schedule. Send to us via our industrial dehumidifiers page.
FAQ
Frequently asked questions
How do I choose a commercial dehumidifier?
Define the target, calculate the load, set the design condition, choose technology and format, then size the count at that condition.
What size commercial dehumidifier do I need?
Enough capacity at your operating condition to remove the moisture load in the demanding period.
Why does my dehumidifier underperform its rating?
Ratings are at warm, humid test conditions; at cooler or drier inlet conditions, capacity is lower.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics; HVAC Systems and Equipment, Dehumidification.
