In industrial workshops, warehouses, or agricultural greenhouses, humidity control directly impacts product quality, equipment lifespan, and crop growth. Oversizing a unit leads to wasted initial investment and operational energy costs, while undersizing fails to meet process requirements. This article provides an objective, brand-neutral selection method to help you precisely match a humidifier in five steps.

Step 1: Calculate the Room’s Moisture Load—The Data Foundation for Selection

Moisture load is the core basis for selection and must be calculated item by item from four sources:

1. Moisture Evaporation from People

Calculate based on the actual maximum number of workers per shift in the workshop or greenhouse. In light-duty environments, an adult’s hourly moisture evaporation is approximately 50–100 grams; under moderate-intensity labor, it is approximately 100–150 grams per hour. Use the upper limit to allow for a safety margin.

2. Equipment Moisture Emission

Focus on open water tanks, washing equipment, steam vents, etc. The moisture emission of each piece of equipment can be estimated based on its evaporation surface area and water temperature: the evaporation rate of a still water surface at room temperature is approximately 30–50 grams per square meter per hour. For drying process equipment, determine the moisture removal capacity of its exhaust air.

3. Fresh Air Load

Calculated based on the difference in humidity between indoor and outdoor air and the design fresh air volume. The formula is:

Moisture Load (kg/h) = Fresh Air Volume (m³/h) × Air Density (kg/m³) × (Outdoor Humidity – Target Indoor Humidity)

Use meteorological parameters from the wettest month of the local summer as the outdoor conditions.

4. Moisture Diffusion Through Building Envelope

This includes moisture permeation and surface moisture absorption/desorption through walls, floors, and roofs. For general workshops, a value of 0.5–2 g/(m²·h) is typically used; for high-airtightness buildings, the lower limit is applied, while for older factory buildings, the upper limit is used. For greenhouses, soil moisture return must also be considered, which may add an additional 1–3 g/(m²·h).

Sum the above four items to obtain the total moisture load (unit: kg/h). It is recommended to multiply this value by a safety factor of 1.1–1.2 to account for operating condition fluctuations.

Step 2: Determine Humidity Control Accuracy — Determining Control Strategies and Costs

Requirements for relative humidity (RH) accuracy vary significantly across different scenarios:

Step 3: Calculate Airflow Volume and Airflow Distribution—Ensure Uniform Dehumidification

The nominal dehumidification capacity of a dehumidifier is measured under standard conditions (e.g., 27°C/60% RH). In actual use, sufficient airflow must be ensured to deliver the treated dry air to all areas.

Principles for Airflow Estimation:

For every 1 kg/h of moisture load treated, approximately 800–1,200 m³/h of airflow is required (depending on the moisture content of the supply air). For example, if the total moisture load is 15 kg/h, the required airflow is approximately 12,000–18,000 m³/h.

Key Points for Airflow Organization:

For workshops with a ceiling height exceeding 6 meters, it is recommended to use side supply and side return or bottom supply and top return configurations to avoid short-circuiting of airflow caused by overhead supply.

If a greenhouse uses overhead fans, ensure that the recirculated airflow covers all growing beds; auxiliary internal circulation fans may be added in dead zones.

For workshops containing dust or fibers, supply air outlets should avoid facing dust-generating points directly to prevent premature clogging of filters.

Step 4: Select Drainage Method—Direct Drain or Tank

Direct Drain Type (requires installation of drainage pipes)

Suitable for fixed locations with 24-hour continuous operation, adequate drainage facilities, and no need for equipment movement.

Advantages include no need for manual water emptying and no risk of overflow. Ensure drainage pipes have sufficient slope (≥1%); install heat tracing or insulation when indoor temperatures drop below 0°C in winter.

Tank Type (with built-in water storage container)

Suitable for scenarios without drainage outlets, intermittent use, or situations requiring periodic relocation of the equipment.

The tank capacity is generally designed to hold 2–8 hours’ worth of condensate. Note: When the humidity setpoint is below 45% RH, dehumidification water production decreases significantly, allowing for longer intervals between tank emptying.

It is recommended to select models with water level alarms or automatic shutdown functions to prevent overflow incidents.

For large workshops, direct drainage is preferred; for greenhouses, if the cost of installing drainage pipes is too high, a large-capacity water tank combined with a timed water pump can be used.

Step 5: Evaluate Corrosion Resistance and Environmental Compatibility — Extend Equipment Lifespan

In chemical plants, electroplating workshops, salt spray test chambers, or greenhouses using chemical fertilizers, the air often contains acidic (SO₂, Cl₂), alkaline (NH₃), or oxidizing substances. The heat exchangers (copper tubes with aluminum fins) in conventional constant-humidity units will corrode rapidly.

Material Selection Comparison Recommendations: